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Technical Information Sheets Our technical knowledge is something we are proud to share with you. The Technical Information sheets are presently available in English, German and Russian. Problems opening the documents? Please contact your local Elkem representative or our Headquarters. English German Russian Title

01 Oxidation of Ferrosilicon Alloys During Storage 02 Inoculation of Cast Iron 03 Inoculant Alloy Composition 04 Inoculation Practices 05 Inoculation Mechanisms 06 Fading of Inoculation 07 Magnesium Contents in Ductile Iron 08 Sampling of Liquid Cast Iron 09 Magnesium Treatment Processes 10 Tundish Cover Ladle Nodularization 11The "Sandwich Pocket Process" 12 Effects of Minor and Trace Elements in Cast Iron 13 Compacted Graphite Iron 14 Ferroalloy Storage Hopper Design 15 Selection of Inoculants for Grey Cast Iron 16 Selection of Inoculants for Ductile Cast Iron 17 Recommended Target Analysis for Grey Cast Iron 18 Recommended Target Analysis for Ductile Cast Iron 19 Aluminium in Cast Iron 20 Selection of Nodularizers 21 Heat Conservation in Liquid Iron Revised! 22 Late Metal Stream Inoculation

23 Factors Influencing the Recovery and Addition of Magnesium in Ductile Iron Ladle Treatment Processes

24 Partition of Slag Phases in the Treatment and Pouring of Ductile Iron 25 Poor Nodularity in Ductile Iron 26 Fading Nodularity in Ductile Iron 27 Alternative Tundish Ladle Design 28 Magnesium versus Sulphur in Ductile Iron 29 Nitrogen Blowholes 30 Hydrogen Pinholes 31 Carbon Monoxide Blowholes in Grey Iron

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32 Magnesium Slag Defects in Ductile Iron 33 Slag Defects in Grey Iron 34 Internal Shrinkage Porosity 35 In-the-Mould Nodularisation 36 Inoculation of Heavy Section Castings 37 Characterisation of Molybdenum Containing Phases in SiMo Ductile Iron

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Technical information sheets Elkem’s Technical information sheets (TIS) are used by foundry people all over the world and act as both a reference and a reminder. Each TIS is a one or two page summary on an important foundry topic. The Technical information sheets are available in English, German, Russian and Turkish. Copies are available on request. Please contact your local Elkem sales organization for more information. 1. Oxidation of Ferrosilicon Alloys During Storage

Ferrosilicon alloys, such as those used for inoculation or the production of nodular graphite irons, are subject to surface oxidation if exposed to moisture or high levels of humidity during transport and storage. The oxidation can become a serious problem particularly with the more finely divided, crushed and graded materials, leading to loss of efficiency when added to liquid iron. This may lead to the use of larger additions and, consequently, increased costs and possible slag problems. This technical information sheet gives important precautions for storage of ferrosilicon alloys, to avoid the stated problems with oxidation and increased costs.

2. Inoculation of Cast Iron Inoculation is a means of controlling the structure and properties of cast irons by increasing the number of nucleation sites available for the growth of graphite flakes in grey irons or graphite nodules in ductile irons. This reduces undercooling during eutectic solidification thereby minimizing the risk of forming hard iron carbides or "chill" in the structure, particularly in thin sections. This technical information sheet demonstrates the benefits of inoculation and its influence on mechanical properties and microstructure of cast irons.

3. Inoculant Alloy Composition

Ferrosilicon alloys for use, as inoculants for cast irons must contain small amounts of one or more “active” elements in order to obtain the required effects in the iron. Generally, inoculants may contain controlled amounts of several alloying elements in order to improve their effects. This Technical information sheet states the commonly used alloying elements in commercial inoculants, as well as important factors regarding inoculant composition.

4. Inoculation Practices

Inoculants are generally added to cast irons at one or more of three stages during the casting procedure: 1. To the pouring ladle during filling. 2. To the stream of metal as it enters the mould. 3. Using an insert placed strategically in the mould runner system. This Technical information sheet discusses the factors influencing the choice of inoculating method, and states the benefits and details of the alternative methods.

5. Inoculation Mechanisms

Several theories have been developed in the past to explain the mechanisms of graphite nucleation during solidification of cast iron. Most theories are based on the assumption that graphite is formed as a result of heterogeneous nucleation from non-metallic substrates during solidification and that minor elements such as Ca, Ba and Sr play an important role in the nucleation process. This technical information sheet states the latest theories of inoculant mechanisms in ductile and grey irons.

6. Fading of Inoculation Inoculants for cast irons produce their effects by creating a marked increase in the number of nucleation sites suitable for graphite growth during solidification of the eutectic. These become apparent as an increase in the number of eutectic cells in grey irons and in the number of graphite nodules in ductile irons. The effects of inoculation are at a maximum immediately after making the addition and thereafter fade with time. This technical information sheet states the main factors that influences on inoculants fading, the principal results of fading, as well as some well-established facts concerning inoculant fade.

7. Magnesium Contents in Ductile Iron

Magnesium is usually introduced into cast iron melts by the addition of a magnesium ferrosilicon alloy (MgFeSi). When magnesium is added its first effect is to combine with any sulphur and oxygen present in the iron to form sulphides and oxides. No "free" magnesium can occur in solution in the iron to promote the formation of spheroidal graphite until all the sulphur and oxygen have been consumed. In order to cope with variations in the oxygen and sulphur contents of the base iron, a higher addition of magnesium is normally made than is strictly needed. This technical information sheet is concerning how the added magnesium is present in the iron, the fading of the various types of magnesium content, and important characteristics of magnesium analysis and magnesium fading on holding in a ladle.

8. Sampling of Liquid Cast Iron When taking a sample from liquid cast iron it is common to use a sampling spoon from which the metal is poured into a chill mould, which ensures a uniform sample for subsequent analysis. Obtaining a representative sample from the iron is not so simple, since the bulk liquid from which it is taken is not homogeneous with respect to minor and alloying element concentrations. This technical information sheet reveals how segregation of various compounds in the iron will influence on the chemical analysis of liquid cast iron, states the segregation effects of the common elements and provides important considerations for proper sampling of liquid cast iron.

9. Magnesium Treatment Processes The choice of magnesium treatment process for ductile iron may to great extent govern the economy, the consistency and recovery of the process, as well as the nucleation state of the liquid iron. This Technical information sheet gives a comparison of the various magnesium treatment processes in common use in iron foundries. The important characteristics of the different processes are given for various treatment agents such as Ni/Mg alloy, MgFeSi alloys, Mg metal and Mg/Fe briquettes. The various treatment processes considered are: overpour or sandwich, tundish cover, in the mould, flow through, plunging, converter and cored wire.

10. Tundish Cover Ladle Nodularization

Magnesium treatment for nodularization of ductile iron can be made by several different treatment processes. The tundish cover ladle process will under most conditions, be a convenient, effective and reliable process with good economy. The process provides good consistency and high recoveries of magnesium over a wide range of treatment sizes. This technical information sheet demonstrates that a well-operated system will give between 60 – 80 % recovery of magnesium while the operating and maintenance costs normally fall well below most other commercial processes. It provides calculation of filling hole dimensions, as well as guidelines to sulphur contents of the base iron, as well as magnesium alloy and cover material selection.

11. The "Sandwich Pocket Process" The widely used "Sandwich" process for the production of Ductile Cast Iron requires the use of magnesium ferrosilicon alloy that is carefully graded to match the size of the treatment. Even then, variations in magnesium yield can occur due to sporadic, explosive ejection of alloy from the reaction chamber early in the filling cycle thus leading to excessively large additions of alloy being required to compensate for these variations. The "Sandwich Pocket" process, developed by Elkem, has been subjected to extensive foundry trials and found to minimize many of the problems associated with the normal "sandwich" process. At the same time the economics are improved by the use of slightly smaller amounts of finely divided magnesium ferrosilicon alloy over a wide range of treatment sizes. This technical information sheets gives the details of the method, including appropriate dimensions of the alloy chamber.

12. Effects of Minor and Trace Elements in Cast Iron Small quantities of many elements can occur in cast irons and have a marked influence on the structure and properties of the castings. Some are present as deliberate additions while others arise from trace impurities in the raw materials. Several of these elements have beneficial effects, particularly in grey irons, while others are very damaging and must be avoided as far as possible. In two technical information sheets, 12A for Grey Iron and 12B for Ductile Iron, common sources of these elements, the levels at which they are likely to occur and their principle effects are given.

13. Compacted Graphite Iron Compacted graphite irons (CG-irons) are a range of cast irons having mechanical and physical properties intermediate between those of flake graphite and nodular graphite cast irons. They are of interest to engineers because of their useful combination of strength, thermal conductivity and thermal stability. Compacted graphite irons may be produced from many different treatment methods. The production requires controls similar to those applied in the manufacture of ductile iron castings. This technical information sheet summarises a successful production route for CG-iron that has been developed by Elkem, as well as examples of structures and properties for such materials. Treatment is based on a high rare earth containing magnesium-ferrosilicon alloy designed especially for compacted graphite iron production. No introduction of such elements as titanium or nitrogen is necessary with the present alloying concept.

14. Ferroalloy Storage Hopper Design

This technical information sheet describes a ferroalloy storage bin designed to minimise segregation effects of alloys during processing in the foundry. Segregation may cause erratic variations in alloy performances and recoveries when used in cast iron production. By the use of the specially adopted storage bin, such variations can be minimised.

15. Selection of Inoculants for Grey Cast Iron An inoculant must serve several purposes in grey irons:

to eliminate iron carbides or “chill”

to modify the graphite morphology to a uniform “A” type structure

to reduce the section sensitivity between thin and thick sections within the same casting

to be effective over the length of the ladle pouring cycle by minimize the effect of fade

All commercially available inoculants are based either on a ferrosilicon alloy, a blend of graphite and ferrosilicon or a mixture of ferroalloys. Increased demand by the casting end-users for consistency has led most foundries to abandon blends in favour of quality controllable specialist ferrosilicon based alloys. This technical information sheet gives the details of FeSi-based inoculants and describes the effects of common effective alloyed elements in inoculants. It states the main factors to consider for the selection of inoculant for grey iron, as well as giving directions with regards to addition methods.

16. Selection of Inoculants for Ductile Cast Iron Careful selection of inoculants is essential for the final ductile iron performance. Inevitably, inoculation of ductile iron requires greater amounts of treatment agent than grey iron, principally due to the carbide stabilizing properties of the magnesium used during nodularisation. Whereas the graphite flakes govern the properties of grey iron, ductile iron characteristics are dominated by the matrix. Formation of even, rounded nodules is therefore essential to obtain the best properties. This technical information sheet gives the details of FeSi-based inoculants and describes the effects of common effective alloyed elements in inoculants. It states the points that should be taken into account in the consideration of inoculant for ductile iron.

17. Recommended Target Analysis for Grey Cast Iron This technical information sheet suggests target analysis for the common ISO standard grades of grey cast iron. Recommended composition ranges for carbon, silicon, manganese and sulphur, maximum level of phosphorus are given, as well as the calculated carbon equivalents (CEV) for the various grey iron. It demonstrates the effects of carbon content and section thickness on tensile strength.

18. Recommended Target Analysis for Ductile Cast Iron This technical information sheet suggests target analysis for production of common ISO standard grades of ductile cast iron. Recommended composition ranges for carbon, silicon and manganese are given, as well as recommendations to maximum levels of some minor elements. It gives guidelines on other important parameters in order to achieved the required mechanical properties according to the standard.

19. Aluminium in Cast Iron

Aluminium is normally found in cast irons as a mainly harmless residual element. The major sources for aluminium are as residual element in charge sources and as added element through preconditioning, FSM treatment or inoculation. This technical information sheet describes the benefits of Al in cast iron, and the mechanisms of Al and inoculants in grey iron, as well as the mechanisms of Al, nodulariser and inoculant in ductile iron.

20. Selection of Nodularizers Careful nodulariser selection is essential for the final ductile iron performance. This technical information sheet shows some variables that will affect the selection of magnesium ferrosilicon alloy, and may help you to find the right alloy composition for your process and equipment. Additionally, recommendations to alloy composition for special processes like in the mould, flow through, and sandwich pocket processes are given.

21. Heat Conservation in Liquid Iron When processing liquid iron in ladles and holders there will be a continuous loss of temperature from radiation and heat conduction through refractories. Such energy losses can be minimised by using insulating materials and covered vessels for holding and transportation of metal. This technical information sheet gives some examples of how temperature can be conserved in a ladle. Some of the important consequences of heat conservation are also stated.

22. Late Metal Stream Inoculation The main advantages of late metal stream inoculation are:

Reduced addition rates compared to ladle inoculation provide an economic benefit.

Reduced addition rates mean lower calcium and aluminium additions thus leading to less tendency towards slag and pinholes.

Avoiding the promotion of high eutectic cell counts that may lead to shrinkage porosity, again because of the lower addition rates of inoculant.

Operator error is eliminated.

Only the metal entering the mould is inoculated, thus avoiding wasteful treatment of ladle “heels”.

This technical information sheet is a guide to late stream inoculation and applicable inoculants for grey and ductile irons.

23. Factors Influencing the Recovery and Addition of Magnesium in Ductile Iron Ladle Treatment Processes Residual magnesium and magnesium recovery have always been subjects for discussion amongst foundry people. This technical information sheet summarises the most important factors that will influence the recovery of magnesium in ductile iron production.

24. Partition of Slag Phases in the Treatment and Pouring of Ductile Iron One problem encountered in automatic pouring systems incorporating a stopper rod is the build up of slag in the pouring unit, especially on and around the stopper rod, that leads to:

Costly cleaning and maintenance of the holding unit.

The stopper rod not seating properly and metal dripping from the launder.

Inconsistent pouring rates which can interfere with consistent inoculation from dispensing units.

Slag entering the mould.

This technical information sheet gives the results from an investigation of different slag phases that have been found to precipitate in various parts of the system and how barium can be used to alter the slag composition and by that obtain a more favourable deposition of the slag and reducing the need for replacing stopper rods and cleaning out of pouring units.

25. Poor Nodularity in Ductile Iron This technical information sheet summarises some important considerations affecting nodularity in ductile iron production. Factors causing different types of poor nodularity are described and important criteria distinguishing between the different types of poor nodularity given.

26. Fading Nodularity in Ductile Iron When properly treated and inoculated ductile iron is held for prolonged times, it is common to observe deterioration in the nodule shape of the graphite. This is often referred to as fading of nodularity. Fading of nodularity is typically related to one of two possible phenomena, either fading of magnesium or fading of inoculation. It is important that the correct type of fading is pinpointed, as possible cures to avoid poor nodularity during time will differ greatly between the two fading phenomena. This technical information sheet demonstrates the differences between magnesium fading and inoculants fading, and gives possible cures for both types of problems in ductile irons.

27. Alternative Tundish Ladle Design The tundish cover process gives relatively high inoculation effect and Mg-recovery. Low levels of fume and smoke will escape from the tundish vessel, giving a good foundry environment. The process may be designed to suit a range of different foundry conditions. Examples are fixed lid, automatic lifting or manual removable lids. This technical information sheet gives some alternative ways of designing tundish cover ladles with fixed and removable lids.

28. Magnesium versus Sulphur in Ductile Iron Magnesium is added to liquid iron through the nodularizing operation to desulphurize and deoxidize the base iron. When the base iron is properly desulphurized, graphite will grow as spheres instead of flakes resulting in good ductile iron. This technical information sheet gives the details of Mg and S reactions and the formation of slag and nucleation sites for graphite.

29. Nitrogen Blowholes Nitrogen gas porosity defects are predominately a problem in grey iron, but can also occur in ductile irons at higher nitrogen contents. Generally nitrogen fissures are found in medium to heavy sections adjacent to resin bonded mould or core materials. This technical information sheet shows the typical appearance of nitrogen induced defects, gives possible causes and provides cures to the problem.

30. Hydrogen Pinholes Hydrogen pinholes can be found in both grey and ductile irons. They usually appear as small spherical holes just beneath the casting surface and normally will have a smooth and shiny inner surface coated with a dense graphite lining. A graphite flake or nodule depleted zone is typically observed adjacent to the hydrogen pinholes. This technical information sheet shows the typical appearance of hydrogen induced defects, gives possible causes and provides cures to the problem.

31. Carbon Monoxide Blowholes in Grey Iron

Slag related gas porosity in grey iron often occur as rounded or irregular shaped cavities either inside the casting or open to the surface. Typically, clusters of slag or dross are found in conjunction to the cavities. The blowhole itself is a result from gas formation (typically CO gas evolution), from reactions between the slag and the carbon content in the iron. This technical information sheet shows the typical appearance of slag/gas related defects in grey iron, gives possible causes and provides cures to the problem.

32. Magnesium Slag Defects in Ductile Iron Magnesium containing reaction products from ductile iron treatment is a severe potential source for inclusion defects in ductile iron. Slag inclusions are typically found just beneath or at the cope surface as a result of improper separation during liquid metal processing. Magnesium slag defects may also arise from turbulent mold filling, and are often found as dross like stringers in areas of the casting where metal is deadlocked. This technical information sheet shows the typical appearance of slag related defects in ductile iron, gives possible causes and provides cures to the problem.

33. Slag Defects in Grey Iron Slag defects in grey iron is typically found in the cope side or dispersed due to turbulent mold filling. Grey iron slag inclusions are typically a result of improper separation of base metal slag or oxidation of the metal during processing. Defects can also occur as a result of reactions between metal and mold materials. This technical information sheet shows the typical appearance of slag related defects in grey iron, gives possible causes and provides cures to the problem.

34. Internal Shrinkage Porosity Shrinkage porosity in grey and ductile irons are typically present as internal cavities of varying size and shape- from large isolated holes to more scattered and smaller porosity only visible under the microscope. Very often a characteristic dendritic sub-structure is revealed inside the porosities. This technical information sheet shows the typical appearance of shrinkage porosity in cast irons, gives possible causes and provides cures to the problem.

35. In-the-Mould Nodularisation The objective with in-the-mould nodularising processes is to pour untreated base iron into the mould and do the nodularising treatment inside the mould, thus producing ductile iron castings in a one-step operation. A reaction chamber containing the nodularising MgFeSi alloy is incorporated into the runner system inside the mould. The treatment takes place continuously while the iron flows through the reaction chamber before entering the cavity that forms the casting. This technical information sheet states important advantages and disadvantages of the in-the-mould ductile iron treatment process, and provides the details for the design of proper runner systems for in-the-mould treatment, as well recommendations to MgFeSi alloys for the process.

36. Inoculation of Heavy Section Castings The important benefits of inoculation are to eliminate the formation of hard, brittle iron carbides (cementite) in the structure and promote the formation of graphite during eutectic solidification. In grey irons benefits include improvements in machinability and mechanical properties, and also a reduction in the variability of properties caused by differences in casting section.

In ductile iron, an increase in the number of graphite nodules produces more uniform structures over a range of section thicknesses. Such structures promote improved mechanical properties, a reduction in the segregation tendency of some alloying or trace elements in the iron and give better machinability. This technical information sheet provides inoculation practices of heavy section castings, including ladle inoculation and inoculation in the mould.

37. Characterization of Molybdenum Containing Phases in SiMo Ductile Iron In SiMo ductile iron most specifications and standards typically allow for a maximum of 10%

pearlite in the structure. Visual and automatic image analysis of the structure often indicates a

pearlite content in the range of 10 to 15% although all process control measures have been

taken in order to keep the pearlite content at a minimum. Closer investigation of the grain

boundary area in SiMo reveals that several phases in addition to pearlite and Mo-carbides can

be found and that the true pearlite content of SiMo ductile iron is in most cases significantly

lower than initially measured or observed under low magnification.

This technical information sheet provides microstructures of precipitate phases in Si-Mo iron.

Technical Information 1

Elkem ASA, Foundry Products © Copyright Elkem ASAPostal address Office address Telephone Web Revision

+47 22 45 01 00 www.foundry.elkem.com No. 2.1Telefax Org. no. 20.03.2004

P.O.Box 5211 MajorstuenNO-0302 OsloNorway

Hoffsveien 65BOsloNorway +47 22 45 01 52 NO 911 382 008 MVA

Oxidation of Ferrosilicon Alloys During StorageFerrosilicon alloys, such as those used for inoculation or the production of nodular graphi-te irons, are subject to surface oxidation if exposed to moisture or high levels of humidityduring transport and storage. The oxidation can become a serious problem particularlywith the more finely divided, crushed and graded materials, leading to loss of efficiencywhen added to liquid iron. This may mean the use of larger additions and, consequently,increased costs and possible slag problems.

The level of oxidation can be related to the oxygen content of the alloy. The oxygen con-tents of inoculants and MgFeSi-alloys have been determined as a function of storage timewhen stored under dry conditions and under high humidity. The figure below is typical ofthe results obtained. Very small changes in the oxygen content occurred with alloys storedunder dry conditions while alloys subject to wet storage showed severe tendencies tooxidation.

Degree of oxidation for ferrosilicon stored in dry and humid storage.

Important Precautions for Storage of Ferrosilicon Alloys:1. Transportation of ferroalloys should always be carried out in sealed containers or

other watertight units such as big bags or steel drums. Loads should be wellsheeted to protect the units from rain and spray.

2. If ferroalloys have to be stored outside they should be kept in closed, watertightdrums or bags to avoid exposure to water or rain. Large changes in temperature(e.g. exposure to sunlight) should be avoided in order to minimize the risk ofcondensation.

3. The best way to avoid the oxidation of ferrosilicon alloys is to store them in a drywarehouse having constant temperature.






Inoculation of Cast IronInoculation is a means of controlling the structure and properties of cast irons by increa-sing the number of nucleation sites available for the growth of graphite flakes in grey ironsor graphite nodules in ductile irons. This reduces undercooling during eutectic solidificationthereby minimizing the risk of forming hard iron carbides or "chill" in the structure, parti-cularly in thin sections.

An inoculant is a material added to the liquid iron just before casting that provides suitablesites for the nucleation of graphite. The most effective inoculants are ferrosilicon alloyscontaining small amounts of one or more of the elements Ca, Ba, Sr, Zr and/or Ce.

The micrographs and table below show examples of structures and properties obtained ingrey and ductile iron with and without the addition of an inoculant. As seen from the micro-graphs, the uninoculated castings (left) contain large quantities of hard, brittle ironcarbides (cementite, Fe3C) and very poor graphite structures. The inoculated castings(right) contain uniform structures of small, random oriented flakes (grey iron) and a largenumber of small graphite nodules in a ferrite/pearlite matrix (ductile iron).

Graphite structure of uninoculatedgrey cast iron (100X).

Graphite structure of inoculated greycast iron (100X).

Microstructure of uninoculatedductile cast iron (100X).

Microstructure of inoculated ductilecast iron (100X).

Technical Information 2 2

Typical properties of uninoculated compared to inoculated ductile iron.

Property Uninoculated InoculatedProof Strength Rp0.2 Not detected 200 - 400 MPaTensile Strength Rm < 300 MPa 350 - 800 MPaElongation A5 Not detected 3 - 30 %Brinell Hardness HB > 600 140 - 300Nodule Count 10 mm section < 50 per mm2 > 150 per mm2

Microstructure ASTM Classification Carbidic Ferritic and/or Pearlitic

Important Benefits of Inoculation:1. Eliminate the formation of hard, brittle iron carbides (cementite) often referred to as

"chill" in the structure and promote the formation of graphite during eutectic solidifi-cation.

2. Improve machinability and mechanical properties and reduce variations due tochanges in section size.

3. Increase the number of graphite nodules in ductile irons thereby producing finer,more uniform structures over a range of section thicknesses. Such structurespromote improved mechanical properties, a reduction in the segregation tendencyof some alloying or trace elements in the iron and give better machinability.

Note that certain iron conditions, for example initial sulphur content (grey iron), tempera-ture and total “fade” time will affect the selection of a proprietary inoculant. Referenceshould be made to Elkem Technical Information Sheets No. 15 and 16 before selecting aninoculant for use.

For more detailed information on inoculation and proprietary inoculants see ElkemBrochures:

"Cast Iron Inoculation","Foundrisil® Inoculant", and"Superseed® Inoculant".






Inoculant Alloy CompositionFerrosilicon alloys for use, as inoculants for cast irons must contain small amounts of oneor more elements in order to obtain the required effects in the iron. Generally, inoculantsmay contain controlled amounts of several alloying elements in order to improve theireffects but the most important elements in commercial inoculants are:

Primary elements Beneficial elementsCalciumBariumStrontium

ZirconiumCerium (Rare Earth’s)AluminiumSulphurOxygen

Strontium differs from the other elements in that it is only fully effective in the absence ofcalcium and aluminium, whereas the other alloys can benefit from being in combination.

No FeSi-based inoculant will be effective without balanced additions of one or more ofthese elements. The figure below shows a schematic example of inoculation effect as afunction of total reactive element content in the inoculant (i.e. Ca, Ba, Sr, etc.), and showsthat optimum effect is obtained at concentrations above 0.5 per cent.

Inoculation effect (e.g. nodule count or chill reduction) as a functionoftotal reactive element content in a ferrosilicon inoculant.


Important Factors Regarding Inoculant Composition:1. Contents of strontium, calcium or barium between 0.6 to 1.5 per cent normally give

the required level of inoculation in cast irons under most foundry conditions.2. When the strontium content or the sum of calcium plus barium content falls below

about 0.5 per cent the inoculating effect will be significantly reduced and carbidesor chill may occur.

3. Alloy contents above about 1.5 per cent may give improved inoculation under someconditions but may also give a greater tendency to produce slag or dross.

4. Grey irons with sulphur contents below about 0.05 per cent may only respond tocertain specialised inoculants (e.g. strontium plus zirconium containing).

5. Inoculants alloyed with strontium are extremely effective for treating most grey ironsbut may be less effective in ductile irons containing high levels of rare earth’s aspart of their nodularizing treatment.

For more detailed information on inoculant composition please refer to Elkem Brochures :"Cast Iron Inoculation","Foundrisil® Inoculant", and"Superseed® Inoculant".






Inoculation PracticesInoculants are generally added to cast irons at one or more of three stages during thecasting procedure:

1. To the pouring ladle during filling.2. To the stream of metal as it enters the mould.3. Using an insert placed strategically in the mould runner system.

Factors influencing the choice of inoculating method are:1. The time from filling the ladle to pouring the last casting, commonly known as the

fade time.2. Metal temperature.3. Ability to add the inoculant at a particular point in the process.4. Suitability of the casting system to late stream inoculation.

Inoculation to the Ladle

Due to the unavoidable lengths of time involved in handling ladles, it is necessary to addrelatively large amounts of inoculant to offset the fading losses which occur. Addition ratesvary from 0.2% for the majority of grey irons to 0.75% for the most critical ductile irons.Inoculant alloys should be selected according to ladle size and be dust free thus avoidinglosses due to oxidation or thermal air currents. Generally, ladles up to 300 kgs can use a0.5-3 mm grading, and for ladle sizes above this a 1-6 mm material is recommended.

In order to obtain the highest efficiency from the inoculant, simple addition rules should befollowed:

1. Add the inoculant to the stream of metal entering the ladle, not as an addition priorto filling.

2. Trickle the inoculant into the metal stream as the ladle is between 25% and 75%full. This ensures good mixing and solution.

3. Ensure that the metal is slag free before tapping into the ladle. Inoculant trappedwithin the slag is wasted.

4. When several transfers of metal between ladles are involved, add the inoculantduring the last transfer before pouring to minimise fade.

NOTE; Inoculant should never be added to the bottom of the ladle prior to tapping, parti-cularly if the ladle is red hot or if there is a small amount of metal remaining from a pre-vious cast.


When inoculating ductile irons, it is essential to add inoculant only when the magnesiumreaction is finished. Adding inoculant with the nodularising agent or during the reaction willsignificantly reduce the effectiveness of the inoculant and may result in increased carbidesin the castings. In cases where it is necessary to add nodulariser and inoculant in thesame ladle, the tap should be halted when about 2/3 of the iron has been poured onto thenodulariser. Then wait until the reaction has finished and then add the inoculant to thestream of remaining metal as described above.

Inoculation in the Casting Stream

Late metal stream inoculation, addition of inoculant to the stream of metal entering themould, virtually eliminates fade. As such, the addition rates are greatly reduced comparedto conventional ladle treatment, 0.02-0.05% for grey irons, 0.05-0.2% for ductile beingcommon. The inoculant has to be specially graded in 0.2-0.7 mm normally to ensure rapidsolution in the iron and good flowability through the application machine. Specialistapplication machines are commercially available, however many foundries have designedand built screw feed mechanisms to give consistent addition rates during pouring.

Late stream inoculation is most easily applied to static pouring stations or ladletransporters, application to a moving ladle is not readily achieved.

Inoculation in the Mould

Use of an insert made from pressed or cast inoculant can be used as insurance, rarely isthis type of treatment used as the primary source of inoculation. Different size andcomposition tablets are available and prove particularly valuable when the fade time islong, acting as a secondary inoculation, or when late metal stream treatment is notpossible. The possibility of human error in failing to add the tablet to a mould doesnecessitate a high degree of post casting inspection, usually in the few cases wheretablets are used as the only inoculant.

Reference should also be made to Elkem Technical Information Sheets;No 2, “Inoculation of Cast Irons”.No 5, “Inoculation Mechanisms”.No 6, “Fading of Inoculation”.






Inoculation MechanismsSeveral theories have been developed in the past to explain the mechanisms of graphitenucleation during solidification of cast iron. Most theories are based on the assumptionthat graphite is formed as a result of heterogeneous nucleation from non-metallic sub-strates during solidification and that minor elements such as Ca, Ba and Sr play an impor-tant role in the nucleation process.

Ductile Iron

In magnesium treated cast irons, micro-inclusions after treatment contain mainly magne-sium, calcium, sulphur, silicon, and oxygen. These are primary reaction products of themagnesium treatment. The inclusions are composed of a sulphide core and a facetedouter silicate shell. The sulphide core contains both MgS and CaS, while the outer shellconsists of complex magnesium silicates (e.g. MgSiO3, Mg2SiO4). These phases will notact as potent nucleation sites for graphite during solidification because of a largenucleus/graphite interfacial energy barrier.

After inoculation with a Ca-containing ferrosilicon, hexagonal silicate phases of the CaSiO3and the CaAl2Si2O8 type will form at the surface of the existing sulphide/oxide inclusionsproduced during nodularization. These calcium silicates will then act as very favourablesites for graphite nucleation during solidification, due to their hexagonal crystal structurethat matches the graphite crystal lattice very well (i.e. low energy interface). The figurebelow to the left shows a typical micro-inclusion in ductile cast iron that is formed afternodularization, while the figure to the right gives a schematic representation of the inclu-sion composition after inoculation with ferrosilicon containing either Ca, Ba or Sr.

MgO SiO22MgO 2SiO2

Core: MgS CaS

Shell:

Major constituent phases:

XO SiO2 orXO Al2O3 2SiO2

Where X = Ca, Sr or Ba

Duplex sulphide/oxide micro-inclusion in ductilecast iron

Schematic representation of an inclusion afterinoculation with a X-containing ferrosilicon

inoculant (X denotes Ca, Ba or Sr).

The surface shell contains hexagonal calcium silicates formed during inoculant addition,while the bulk particle is a product of the nodularization treatment. Hence, the inoculationdoes not increase the total number of nuclei particles in the melt, but rather modifies thesurface of the already existing products from nodularization.

This explains the important link between magnesium treatment and inoculation, and thatthe basis for effective ductile iron inoculation is laid during nodularization. The resultingnodule number density will also differ greatly due to the inclusion surface modification.


When inoculation is carried out with a strontium or barium containing ferrosilicon inoculant,hexagonal silicates equivalent to the calcium silicates will be formed (i.e. SrSiO3,SrAl2Si2O8, BaSiO3, BaAl2Si2O8).

Grey Iron

In grey iron the nucleation mechanisms differ somewhat from the situation in ductile iron,primarily due to the fact that magnesium is not added prior to inoculation. Consequently,other substrates will play the important role as sites for the Ca, Ba or Sr silicates formedduring inoculation. In principal, the same types of inoculants can be used for both greyand ductile irons, and the inoculation mechanisms from hexagonal silicate phases at thesurface of primary inclusions are equal for all types of irons.

However, in grey cast iron the lack of primary magnesium sulphides and silicates meansthat other particles have to take the primary role. It is assumed that the presence of a highnumber of manganese sulphides (MnS) replaces the magnesium containing particlesfound in ductile iron. The relation between manganese and sulphur in grey cast ironshould be as follows:

%Mn = 1.7 x %S + 0.3

When this balance is correct, the optimum conditions for the formation of small MnS par-ticles is obtained. Furthermore, to have a highest possible number density of MnS partic-les as a basis for effective inoculation, the sulphur content of grey irons should be signifi-cantly higher than for ductile irons. Normally, a sulphur content between 0.05 and 0.15%is recommended.

Some Important Considerations• Pure ferrosilicon has no inoculation effect whatsoever.

• Inoculation does not increase the number of potential nucleation sites in grey andductile iron but modifies existing sites to a beneficial form.

• The important consideration in effective inoculation is the formation of a highnumber of non-metallic micro-particles (sulphides and oxides) during magnesiumtreatment of ductile iron and the formation of numerous manganese sulphideparticles in grey iron.

• Minor elements such as Ca, Ba and Sr as well as silicon in inoculants are critical forpowerful effectiveness of an inoculant material.

• The base metal oxygen content is also critical in the formation of effective oxidesubstrates for graphite nucleation.






Fading of InoculationInoculants for cast irons produce their effects by creating a marked increase in the numberof nucleation sites suitable for graphite growth during solidification of the eutectic. Thesebecome apparent as an increase in the number of eutectic cells in grey irons and in thenumber of graphite nodules in ductile irons. This results in a reduction in undercoolingthus minimizing the risk of forming iron carbides or "chill" particularly in thin, rapidly cooledsections.

The effects of inoculation are at a maximum immediately after making the addition andthey fade with time. The rate of fading depends on:

• The inoculant composition;

• The type of iron to which it is added;

• Temperature;

• Surface energies;

• Diffusion rates.

Fading may be very rapid with much of the effect lost within the first few minutes afteraddition. Fading of inoculation can be explained by the coalescing and re-solution of thenuclei population which causes the total number of potential nucleation sites to bereduced (i.e. growth or coarsening of nuclei particles according to the so-called OstwaldRipening effect). This behaviour is in close agreement with experimental observations offading as illustrated in the following figures.

Reduction in nuclei population (micro-inclusions)with time

Fading characteristics of inoculation.


Principal Results of Fading:1. To cause greater undercooling to take place during eutectic solidification thus

leading to an increased tendency to chilling in grey and ductile irons particularly inthin section.

2. To reduce the numbers of eutectic cells or graphite nodules in the structure and tocause deterioration in graphite form. Severe fading can promote the formation ofundercooled graphite with associated ferrite in grey irons and significant amounts ofnon-nodular graphite in ductile irons, both of which can adversely affect theproperties of the iron.

Some Well Established Facts Concerning Inoculant Fade:• The effects of all inoculants fade with time.

• There is no period after inoculation during which zero fading occurs. To obtainmaximum effect the metal must be cast as soon as possible after inoculation, theultimate being addition of the inoculant to the pouring stream.

• The effects of some inoculants fade more slowly than others depending on theircomposition and conditions of use.

• An inoculant which gives a high eutectic cell number is not necessarily the mosteffective in reducing chill. In grey iron, Strontium-based inoculants are recognisedto give the best combination of a coarse cell structure, low shrinkage tendency, andvery low chill level.

• Under any particular set of conditions it is not possible to predict the fadingcharacteristics of an inoculant from its composition. Foundries therefore shouldcarry out tests to determine which is the most suitable inoculant for their purpose.These tests should be made under careful control to avoid the spurious effects offactors such as metal temperature, inoculant storage, etc.






Magnesium Contents in Ductile IronMagnesium is usually introduced into cast iron melts by the addition of a magnesiumferrosilicon alloy (MgFeSi or FeSiMg). When magnesium is added its first effect is tocombine with any sulphur and oxygen present in the iron to form sulphides and oxides. No"free" magnesium can occur in solution in the iron to promote the formation of spheroidalgraphite until all the sulphur and oxygen have been consumed. In order to cope withvariations in the oxygen and sulphur contents of the base iron, a higher addition ofmagnesium is normally made than is strictly needed. This is in addition to that made tocompensate for losses by evaporation during addition. Only a fraction of the magnesium isdissolved in the iron after the nodularizing reaction is complete.

The total analytical or residual magnesium content of liquid iron immediately after treat-ment is comprised of:

• Dissolved magnesium;

• Micro-inclusions of magnesium compounds (oxides and sulphides)

• Larger, magnesium containing slag particles

These contributions to total magnesium will react in different ways during subsequentholding of the iron. A schematic example of the fading characteristics of the magnesiumcontent on holding is given in the figure below. It is not possible to separate betweenthese three contributions to the residual magnesium by conventional analytical methodsthat will only give the total magnesium content of the iron.

Figure 1: Fading of magnesium during holding of treated ductile iron (left), and schematic represen-tation of magnesium losses from a treatment ladle (right).


Important Characteristics of Magnesium Analysis and Magnesium Fading on Holding:• The total residual magnesium content of ductile iron as analyzed is not the same as

the dissolved magnesium content.

• Fading of the magnesium content on holding treated iron may be the result of slagseparation, inclusion flotation and evaporation loss of dissolved magnesium. Insome instances magnesium fading can make a positive contribution to the metalcleanliness and freedom from slag entrapment since harmful slag particles will floatto the bath surface with holding time and can hence be removed.

• Only the total magnesium content (slags + micro-particles + dissolved) in a samplecan be analyzed by ordinary analytical methods.

• It has been shown that losses of dissolved magnesium on holding generally aresmall and that the degeneration of the spheroidal graphite structure often attributedto magnesium fade, is actually the result of fading of inoculation. Fully spheroidalgraphite structures can often be regained by a small, late addition of inoculant.

Figure 2: Schematic representation of fading of graphitenodularity on holding. A second addition of inocu-lant can regain fully spheroidal graphite structureseven though the analytical magnesium content isfalling continuously.






Sampling of Liquid Cast IronWhen taking a sample from liquid cast iron it is common to use a sampling spoon fromwhich the metal is poured into a chill mould, which ensures a uniform sample forsubsequent analysis. Obtaining a representative sample from the iron is not so simple,since the bulk liquid from which it is taken is not homogeneous with respect to minor andalloying element concentrations.

Reactive elements in cast iron will be present both dissolved in the iron and combined withother elements to form particles such as oxides, sulphides, nitrides, etc. Such non-metallicparticles will normally be lighter than the liquid iron, which means that there will beconstant movement upwards of inclusions as the lighter particles float to the surface.

Dissolved elements will also segregate in the liquid due to the difference in atomic weightwith iron. Lighter elements and gas forming elements have a tendency to move upwards,while heavier elements may accumulate further down. For instance, Carbon (light) has atendency to segregate upwards (even at temperatures well above the liquidus), while Lead(heavy) will be accumulated in the lower part of a vessel.

The schematic figure below shows a container (e.g. furnace, ladle, holding furnace,pouring vessel, etc.) with a segregated liquid metal composition. Two sampling positionswith examples of accompanying analyses are indicated. There will be a significant diffe-rence in composition at the top and bottom of the container due to the flotation andsegregation phenomena.

3.7 %C2.6% Si0.02% P0.015% S0.050% Mg0.020% Al

3.6 %C2.5% Si0.02% P0.010% S0.030% Mg0.010% Al

..

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ParticleFlotationAccordingto Stoke’sLaw

Schematic example of sampling from two different positions in a containerwith liquid iron. Some elements vary due to segregation with time.


Segregation effects of the common elements:

Element Segregation effectsCarbonC

Present mainly as dissolved element above the liquidus temperature. Some graphite, carbidesor supersaturated CO gas may however contribute to the analysis.A relatively strong segregation (flotation) effect occurs, especially in induction furnaces and incold iron where free graphite particles form (below the liquidus temperature).

SiliconSi

Also present mainly as dissolved element in liquid iron. A significant part may however beoxides and silicates that segregate due to flotation. In ductile iron magnesium silicates willfloat and cause some silicon segregation

SulphurS

In grey iron, Sulphur is present mainly dissolved and as manganese sulphides. In ductile iron,there will be no dissolved sulphur, and all is present as magnesium sulphides or calcium andrare earth sulphides. All sulphides segregate due to flotation

MagnesiumMg

In ductile iron Magnesium is present both as dissolved element and as sulphides and oxides/silicates. Dissolved magnesium will segregate somewhat due to a low vapour pressure andlosses to the air. Combined magnesium as sulphides and oxides will segregate due toflotation.

AluminiumAl

Will be present both as dissolved element and combined as oxides. In both grey and ductileiron various complex oxides and aluminates will all segregate due to flotation.

Flotation according to Stoke’s Law

Typical non-metallic particles or inclusions in cast iron have a specific density between 2and 4 g/cm3. Iron has a density close to 8 g/cm3, which means that most particles are lessthan half the density of iron. This will force them to float, and the main driving force deter-mining the velocity is the size of the particles. Stoke’s law can be expressed as follows:

vd gm s=

−2

18( )ρ ρ

µ

where v is the flotation speed (m/s), dm is the diameter of the particle (m), ρs is the specificdensity of the liquid (iron) and ρ is the specific density of the particle phase (both in kg/m3),g is the gravity constant (9.81 m/s2), and µ is the viscosity of the liquid iron (Ns/m2 orkg/ms). A typical viscosity for liquid iron is about 0.007 kg/ms

Important Consideration for Sampling• The sample should always be taken in the same position and at the same time.

• Stirring in induction furnaces or from pouring will equalise segregation. Samplesshould be taken during or soon after mixing actions.

• Chemical analysis can be used to calibrate structure and properties, but cannot becompared to other foundries due to the sampling and segregation variables.

• Analyses should be used with care and not trusted blindly. Variations from sampleto sample must be accepted not only as a process variable, but also as a samplingvariable.

• During pouring of furnaces, lip-ladles, tea-pot ladles and bottom poured holdersthere will be analytical variations due to segregation. There exists no absoluteanalysis for a given volume of liquid metal.

• Due to the flotation and segregation effects, bottom poured vessels as tea-potladles and some autopours will show an inverse fading effect for elements thataccumulate in the upper, last part of the vessel to be poured.






Magnesium Treatment ProcessesThis information sheet gives a comparison of the various magnesium treatment processes incommon use in iron foundries. The important characteristics of the different processes arelisted below for various treatment agents such as Ni/Mg alloy, MgFeSi alloys, Mg metal andMg/Fe briquettes. The various treatment processes considered are: overpour or sandwich,tundish cover, in the mould, flow through, plunging, converter and cored wire.

Overpour orSandwich

TundishCover

In theMould

FlowThrough Plunging Con-

verterCoredWire

Treatment agentsuited to process

Ni basealloy

MgFeSialloy

MgFeSialloy

MgFeSialloy

MgFeSialloy

MgFeSior Mg/Si

Mg/Febriquette Mg Mg/Si

or MgMg-content (%) 4 - 15 3 - 10 3 - 10 3 - 10 3 - 5 10 - 45 15 + 100 20 - 100Mg-recovery (%) 45 - 90 35 - 70 50 - 80 70 - 80 30 - 50 30 - 60 30 - 50 30 - 50 30 - 50Cost of plant Nil Nil Low Nil1) Low Medium Medium High MediumGeneral processflexibility (6=best) 6 6 5 2 3 3 2 1 2

Fume emitted Medium Med/high Low Nil Medium High High High HighFume-collectionrequired Yes Yes No2) No2) No3) Yes Yes Yes Yes

Restrictions on basemetal sulphur (%) 0.04 0.03 0.03 0.01 0.03 0.04 0.1 No No

Treatment locationpoint Furnace Furnace Furnace Mould To suit To suit To suit To suit To suit

Treatment weightrestrictions None None None < 500 kg None > 500 kg > 500 kg > 500 kg > 500 kg

Inoculation effectfrom treatment Nil Low/med Med/high Very

high Med/high Low Nil Nil Nil/low

Violence of reaction Low/med Med/high Low/med Very low Medium Med/high Med/high Very high HighPossible risk ofexcessive silicon No Yes Yes Yes, but

unlikely Yes Yes No No No

Size of productionunit suited to process

Small(alloyed)

Small tolarge

Small tolarge

Mediumto large

Small tomedium

Mediumto large

Mediumto large Large Medium

to largeLicence/royalty No No No No Yes4) No No Yes No1) In the mould process requires specially designed running systems for each pattern.2) Tundish cover and in the mould are the two processes least likely to require the installation of fume

extraction.3) General fume extraction in the treatment area recommended.4) Royalties for the process, not for the MgFeSi-alloy.

The table is designed to help foundries starting production of ductile iron to select the mostsuitable process and treatment alloy for their specific foundry conditions.

For many applications the tundish cover ladle process is likely to be the simplest to operateand to give the best consistency and highest magnesium recoveries combined with the lowestoperating and maintenance costs and should therefore be a good choice for many small andlarge foundries. However, under certain conditions such as large plants dedicated to specificproducts, one of the other processes may be more suitable. Hence, each individual foundrymust select carefully a process that will give the best overall consistency, economy and envi-ronmental control for their situation.


The figure below shows a schematic representation of how the most common treatment pro-cesses affect parameters as reaction violence, magnesium recovery, fume and slag formation,and inoculation effectiveness. There is a clear correlation between these four parameters, andall commercial treatment processes will be located along the shaded line-area of the figure.

At the upper left end of the range, processes applying high magnesium containing materialssuch as the converter and cored wire process will be located, while at the lower right endhighly efficient processes as the tundish cover and in mould process can be found.

Typically, processes having a high degree of violence show a low magnesium recovery, highfume and slag formation and an iron that is difficult to inoculate. On the contrary, processeshaving a low degree of violence show a high magnesium recovery, low fume and slagformation and conditions of very good inoculation performance. No process will be located inthe upper right or lower left corner of the diagram.

HIGH Fume and slag formation LOW

HIGH

Violenceof reaction

LOW

LOW Inoculation effect HIGH

LOW

Magnesiumrecovery

HIGH

*

*

High/pure Mg Low Mg alloys

Converter

Cored Wire

Overpour/Sandwich

Tundish

In mould

Flow through

Plunging

Schematic representation of the important correlation between “violence ofreaction”, “magnesium recovery”, “fume and slag formation”, and “inoculation

effect” for a range of commercial ductile iron treatment processes.






Tundish Cover Ladle NodularizingMagnesium treatment for nodularization of ductile iron can be made by several differenttreatment processes. The tundish cover ladle process will under most conditions, be aconvenient, effective and reliable process with good economy. The process provides goodconsistency and high recoveries of magnesium over a wide range of treatment sizes. Awell-operated system will give between 60 – 80 % recovery of magnesium while the opera-ting and maintenance costs normally fall well below most other commercial processes.Tundish ladle treatments also offer virtually no flare, about 90 % fume reduction, no metalsplashing and minimum carbon and temperature losses. The figure below shows anexample of a tundish cover ladle.

Figure 1: Schematic representation of a tundishcover ladle with dual alloy pockets.

Calculation of Filling Hole Dimensions

The following formula can be used to calculate the diameter of the tundish lid filling hole:

htWd⋅

= 07.0

where d is the filling hole diameter in centimetres (cm), W is the liquid iron batch weight ingrams (g), t is the pouring time in seconds (s), and h is the ferrostatic height of metal in thetundish basin in centimetres (cm). Note: h is the height of metal, not the height of the basinitself.

Base metal sulphur contents should preferably not exceed 0.02% before treatment toensure maximum efficiency of the tundish ladle. If sulphur levels are higher, a desulphuri-zing step is recommended prior to nodularization.


Magnesium Alloy Selection and Addition

The tundish cover process may be used with most magnesium ferrosilicon alloys contai-ning between 3 to 12 % magnesium but generally alloys containing 4 – 6% Mg are used.

Typically an alloy with the composition given in the table would beused to treat base iron composed of a mixture of steel scrap, pig ironand returns. Alloy size grading of about 1 – 10 mm is most suitablefor small treatments while sizes up to 4 – 35 mm are preferable forlarger treatments. See Elkem Technical Information Sheet No. 20 formore details on selection of nodularizers in ductile iron.

The amount of alloy added usually lies between 1.2 and 1.8 weight %depending on the base sulphur content, the metal temperature, themagnesium content of the alloy and the consistency with which theprocess is carried out.

Cover Material Selection

It is recommended to use a cover material over the magnesium alloy in the reactionchamber in order to obtain maximum treatment economy. The cover should retain the alloyin the chamber for as long as possible before the reaction starts. Covers commonly consistof clean steel plate or clippings of a grade similar to that used in the melt charges. Castiron cover plates can be cast from the spare metal left at the end of a cast thus avoidingthe carbon dilution due to the steel cover. However, the best results are obtained using aferrosilicon alloy as a cover material.

Example of Recovery Improvements

Figure 2: Schematic representation of recovery improvements as afunction of sulphur content, treatment temperature, and ladledesign modifications. The initial case of 2.0 wt% addition rate

represents a situation with 0.03% S and 1520°C treatmenttemperature.

Element ContentsSi 45%Mg 6%Ca 1%RE 1%Al max. 1%Fe Balance






The “Sandwich Pocket Process”The widely used "Sandwich" process for the production of Ductile Cast Iron requires theuse of magnesium ferrosilicon alloy that is carefully graded to match the size of the treat-ment. Even then, variations in magnesium yield can occur due to sporadic, explosive ejec-tion of alloy from the reaction chamber early in the filling cycle thus leading to excessivelylarge additions of alloy being required to compensate for these variations.

The "Sandwich Pocket" process, developed by Elkem, has been subjected to extensivefoundry trials and found to minimize many of the problems associated with the normal"sandwich" process. At the same time the economics are improved by the use of slightlysmaller amounts of finely divided magnesium ferrosilicon alloy over a wide range of treat-ment sizes.

Figure 1: Schematic example of the Ladle design; (a) Pocket located in the centreof the ladle bottom, (b) Tea-Pot ladle alternative, (c) Charging funnel.

The advantages of the process arise principally from the use of the specially designed,cylindrical pocket in which the magnesium alloy and its cover material are placed. Thepocket may be formed in the bottom of the ladle as shown in Figure 1(a) or, more frequent-ly, it may be built at the periphery of the bottom as in Figure 1(b). The latter is essentialwhen using the process in conjunction with a tundish cover (see information sheet No. 10).The cylindrical pocket must have a height to diameter ratio of at least 1:1 and must belarge enough to contain the entire magnesium alloy and the cover material. No materialmust lie above the level of the ladle bottom after loading. Figure 1 indicates a method offilling the pocket through a steel tube (funnel) to avoid spilling the alloy on the ladle bottom.A thick layer of refractory material surrounds the pocket in order to avoid rapid heatpenetration to the bottom of the pocket as the ladle is filled.


The magnesium alloy preferably has a relatively fine size grading. Optimum results are ob-tained with alloy sizes ranging from about 0.1 to 10 mm. Regular alloy qualities containing3 to 7 per cent magnesium and normal levels of calcium, aluminium and rare earth’s maybe used with this process. Figure 2 shows the alloy pocket and the table suggested pocketdimensions (diameter and height) for various treatment sizes and alloy addition rates.Typical alloy sizings suited to the process are 0.1-1 mm, 0.1-5 mm, 0.4-4 mm, 0.5-5 mm.1.0-10 mm. All these sizings will have a bulk density of about 2 kg/dm3.

The unique feature of using finely graded alloy is that it has a high packing density in thepocket. As the intense heat from the metal above the pocket penetrates the cover, thealloy tends to sinter into a briquette so that, when the reaction commences, it proceedsslowly and gently downwards through the sintered alloy. This leads to very good processconsistency, high magnesium yields and minimum fume and smoke emission, particularlywhen used in conjunction with a tundish cover.

Suggested pocket dimensions for various treatmentsizes and alloy addition rates. Diameter (d) and hight (h)

dimensions in centimetres (cm), respectively.

Addition rate, wt%Treatmentsize, kg 0.9 1.0 1.1 1.2 1.3 1.4

100 9/10 10/10 9/12 10/12 10/13 10/13300 13/15 13/15 13/18 14/18 14/18 15/18500 14/20 15/20 16/20 16/20 17/20 18/20800 18/20 19/20 20/20 20/22 21/22 21/22

1000 18/25 20/25 20/25 21/25 22/25 22/25Figure 2: Sandwich pocket with alloy andcover material. 1500 22/25 23/25 24/25 25/25 26/25 27/25

The maximum process yields are obtained by using regular ferrosilicon alloy as the covermaterial. 45 or 75 per cent alloy with size gradings of 1 - 10 mm or 5 - 12 mm produce aneffective cover for the fine magnesium alloy below. The ideal amount of cover depends onthe temperature of the metal being treated but will normally be about 10 to 15 per cent byvolume of the magnesium alloy. If the use of ferrosilicon as the cover material leads toexcessive silicon pick-up, satisfactory results can also be obtained from the use of clean,high quality steel punchings as the cover.

When using the "Sandwich Pocket" process it is important to keep the ladle in the invertedposition when empty in order to avoid slag and metal beads draining into the pocket andreducing its capacity.






Effects of Minor and Trace Elements in Cast IronSmall quantities of many elements can occur in cast irons and have a marked influence on thestructure and properties of the castings. Some are present as deliberate additions while othersarise from trace impurities in the raw materials. Several of these elements have beneficial effects,particularly in grey irons, while others are very damaging and must be avoided as far as possible.The following table lists the common sources of these elements, the levels at which they are likelyto occur and their principle effects. The use of some of these elements (e.g. chromium) as majoralloying elements is not included in the table.

Element Common SourcesNormal

Levels (%) Effects in Cast Irons

AluminiumAl

Al-killed steel scrap,inoculants, ferro-alloys, lightalloy components, additionsof aluminium.

Up to0.03

Promotes hydrogen pinholes in light sectionsabove about 0.005 %Al. Neutralizes nitrogen.Promotes dross formation. Detrimental to nodulargraphite above approx. 0.08%. May be neutralizedby cerium. Strong graphite stabilizer.

AntimonySb

Steel scrap, vitreousenamel scrap, bearingshells, deliberate additions

Up to0.02

Strong pearlite and carbide promoter.Inhibits nodularity in absence of rare earth’s.

ArsenicAs Pig iron, steel scrap. Up to

0.05Strong pearlite and carbide promoter.Improves nodular graphite shape.

BariumBa

Barium containinginoculants.

Up to 0.003

Improves graphite nucleation and reduces fading.Reduces chilling tendency and promotes graphite

BismuthBi

Deliberate additions, mouldcoatings containing Bi.

Rarelyabove0.01

Promotes chill and undesirable graphite forms.Increases nodule number in ductile ironscontaining rare earth’s (cerium). Excessive nodulecounts may cause shrinkage problems.

BoronB

Vitreous enamel scrap,deliberate additions as FeB.

Up to0.01

Above 5 ppm promotes ferrite. Above 10 ppm pro-motes carbides particularly in ductile irons. 20 ppmimproves annealing of malleable irons.

CalciumCa

Ferro-alloys, nodularizers,inoculants.

Up to0.01

Improves spheroidization of graphite nodules.Improves graphite nucleation.Reduces chilling tendency and promotes graphite.

CeriumCe

Most magnesium alloys oradded as mishmetall orother rare earth sources.

Up to0.02

Normally not used in grey irons.Suppresses deleterious elements in ductile irons.Improves spheroidization of graphite. Carbidestabilizing due to segregation.

ChromiumCr

Alloy steel, chromium plate,some pig irons, ferro-chromium.

Up to0.3

Promotes chill and pearlite. Increases strength.Form carbide segregates in ductile irons above0.05%.

CobaltCo Tool steel Up to

0.02 No significant effects in cast irons.

CopperCu

Copper wire, copper-basedalloys, steel scrap,deliberate additions of Cu.

Up to0.5

Promotes pearlite. Improves strength.Impairs ferritization in ductile irons.No harmful effects.

HydrogenH

Damp refractories, mouldmaterials and humidadditions.

Produces sub-surface pinholes. Has a mild chill-promoting action. Promotes "inverse chill" whenthere is insufficient manganese present toneutralize sulphur. Promotes coarse graphite.


Element Common SourcesNormal

Levels (%) Effects in Cast Irons

LeadPb

Old paints, some vitreousenamel, free-cutting steel,terne plate, solder, petrolengine deposits.

Up to0.005

Causes spiky and undesirable graphite structuresin grey irons and severely reduces strength atlevels above 0.004 %. Promotes pearlite andcarbides.Cause degenerated nodular graphite forms.Effects on graphite in ductile irons are neutralizedby rare earth’s (cerium).

MagnesiumMg

Additions of magnesiumalloys (nodularizers). 0.03 - 0.08

Promotes nodular graphite in ductile irons.Carbide stabilizing effect in ductile irons.Not used in grey irons.

ManganeseMn

Most pig irons, steel scrap,additions of ferromanganese lump orbriquettes.

0.2 - 1.0

Neutralizes sulphur by forming MnS.Promotes pearlite formation. Forms carbidesegregates in ductile irons. Promotes gas holes athigh levels in conjunction with high sulphur levels.

MolybdeniumMo

Refined pig irons, alloysteels, ferro-molybdenumadditions.

Up to 0.1

Mild pearlite promoter.Increases strength.Can promote shrinkage and carbides.

NickelNi

Nickel plate, steel scrap,refined irons, NiMg alloy.

Up to0.5

Small amounts have little effects.Graphitizing effect in larger quantities.

NitrogenN

Coke, carburizers, corebinders, steel scrap,additions of nitrided ferro-manganese.

Up to0.015

Compacts flake graphite. Promotes pearlite.Increases strength. High levels causes fissuredefects in heavier sections. Can be neutralized byAl, Ti and Zr. Has little effect in ductile irons.

PhosphorousP

Phosphoric pig iron andscrap, additions of FeP.

Up to 0.1

Increases CEV. Increases fluidity. Formsphosphide eutectic. Damaging in ductile ironsabove 0.05 %. At levels above 0.04%, can causemetal penetration.

SiliconSi

Ferro-silicon alloys, steelscrap, pig iron. 0.8-4.0 Promotes graphitization, reduces chill, stabilizes

ferrite, improves castability.

SulphurS

Coke, carburizers, pig iron,scrap iron, additions of ironsulphide.

Up to 0.15(greyirons)

Very damaging to structure and properties unlessbalanced by manganese. Improves grey ironsresponse to most inoculants. Increases Mgrequirements in ductile irons.Should be below 0.03 % in ductile irons.

StrontiumSr

Strontium containinginoculants.

Up to0.003

Improves graphite nucleation in grey and ductile.Strongly reduces chilling tendency in grey irons.

TelluriumTe

Free-cutting copper, mouldcoatings, cooling curvecarbon samples.

Up to0.003

Strongly promotes carbides. Causes manyundesirable forms of graphite. Effects observed aslow as 0.0003 %. Effects reduced by combinationwith Mg and Ce in ductile irons.

TinSn

Solder, tin plated steelscrap, bronze components,tin additions.

Up to0.15

Strongly promotes pearlite. Improves strength.Embrittles ductile irons above 0.08 %.No other harmful effects.

TitaniumTi

Some pig irons, somepaints and vitreousenamels, CG-iron returns,additions of titanium orferro-titanium

Up to0.10

Neutralizes nitrogen in grey irons. Promoteshydrogen pinholing due to aluminium. Promotesundercooled graphite in grey iron. Suppressesnodular graphite in CG-irons.

TungstenW High speed tool steel Up to

0.05Rarely found in significant amounts.Mild pearlite promoter.

VanadiumV

Steel scrap, tool steel,some pig irons, ferro-vanadium additions.

Up to0.10

Promotes chill formation. Refines flake graphite.Markedly increases strength.


Elkem ASA, Foundry Products © Copyright Elkem ASATelephone Web Revision+47 22 45 01 00 www.foundry.elkem.com No. 2.1Telefax Org. no. 02.08.2004

Postal addressP.O.Box 5211 MajorstuenNO-0302 OsloNorway

Office addressHoffsveien 65BOslo

+47 22 45 01 52 NO 911 382 008 MVA

Compacted Graphite IronCompacted graphite irons (CG-irons) are a range of cast irons having mechanical andphysical properties intermediate between those of flake graphite and nodular graphite castirons. They are of interest to engineers because of their useful combination of strength,thermal conductivity and thermal stability.

Compacted graphite irons may be produced from many different treatment methods. Theproduction requires controls similar to those applied in the manufacture of ductile ironcastings.This Information Sheet summarises a successful production route for CG-iron that hasbeen developed by Elkem, as well as examples of structures and properties for suchmaterials. Treatment is based on a high rare earth containing magnesium-ferrosilicon alloydesigned specially for compacted graphite iron production. No introduction of suchelements as titanium or nitrogen is necessary with the present alloying concept.Recommended composition of treatment alloy; CompactMagTM:

% Si % Mg % Ca % RE % Al % Fe44 - 48 5.0 – 6.0 1.8 – 2.3 5.0 – 6.5 max. 1.0 balance

Recommendations for Compacted Graphite Iron Production

Base Iron CompositionBase iron composition should preferentially be hypereutectic with a carbon equivalent(CE) of about 4.3 - 4.5. Suggested base iron composition:

% C % Si % S3.5 – 3.8 1.5 – 1.9 0.007 – 0.012

Other elements are less important, but should not be higher than for ductile ironproduction. Generally a higher level of pearlite and carbide promoting elements may betolerated, as long as the sulphur level is kept low and constant.

Alloy AdditionThe addition rate of the alloy described above has to be adjusted according to base metalcomposition, treatment process and casting requirements for each individual foundry.Base metal sulphur level is the main factor strongly affecting the required alloy additionrate. Experiences with the base iron composition given above have shown best results foraddition rates between:

0.30 – 0.45 wt% addition of alloy specified above.

The addition method may be an ordinary ladle treatment process as for ductile ironproduction (sandwich or tundish ladle).


Inoculant Sandwich CoverIt is recommended to add a moderately powerful inoculant as sandwich cover. Bariumcontaining ferrosilicon inoculants are found to give good results e.g. Foundrisil® inoculant.The inoculant cover has been found to decrease the tendency to chill formation and togive a more homogeneous graphite structure over different casting sections. In manycases subsequent inoculation is not needed, but for chill prone sections adequate postinoculant should also be used. Addition rate of the sandwich cover should be fixed and inthe range 0.2 to 0.3 wt%.

MicrostructuresThe Figures below show examples of microstructures and final iron composition obtainedfor a CG-iron casting produced from a high RE-containing MgFeSi-alloy. Structures in boththin (5 mm) and thick (35 mm) section sizes are given to show the limited sectionsensitivity obtained. Homogeneous CG-structures throughout all section sizes are acharacteristic feature obtained by the high RE-containing alloy in comparison to ordinarylower RE-containing MgFeSi-alloys.

Microstructure of compacted graphite iron produced from a high RE-containing MgFeSi-alloy, 5 mm section size (left), 35 mm section size (right) (100X).

Final CG-Iron CompositionAfter treatment the final iron composition should be in the following range:

% C % Si % S % Mg % Ce3.3 – 3.6 2.0 – 2.5 0.005 – 0.012 0.005 – 0.015 0.005 – 0.015

Fade time and treatment temperatureFrom laboratory and field testing, fade times up to 20 minutes were found not to have anegative influence on the microstructure control.

Treatment temperatures in the range 1400 – 1520°C have been tested without any nega-tive effect on the microstructure. Choice of post inoculant has to be adjusted according totreatment temperature used.

Pearlitic grades of CGIPearlite promoting elements (Mn, Cu, etc) may have to be applied to produce pearliticgrades of CGI.

For more information, see the Elkem Product Data Sheet “CompactMag”.


Elkem ASA, Foundry Products © Copyright Elkem ASATelephone Web Revision+47 22 45 01 00 www.foundry.elkem.com No. 2.11Telefax Org. no. 20.01.2005


Office addressHoffsveien 65BOslo

+47 22 45 01 52 NO 911 382 008 MVA

Ferroalloy Storage Bin Design

This Technical information sheet describes a ferroalloy storage bin designed to minimise segrega-tion effects of alloys during processing in the foundry. Segregation may cause erratic variations inalloy performances and recoveries when used in cast iron production.

How Do Alloys Segregate?

Ferroalloys are often shipped in big-bag packaging. These are provided in a variety of styles andsizes. When alloy is filled into bags, segregation tend to occur which causes more coarse particlesto concentrate along the periphery of the bag and fine particles in the centre. This phenomenon isshown schematically in Figure 1. As alloys are subject to the motions involved with transportation,the finer sizes may also tend to segregate to the bottom of the bag. This effect can be magnifiedwhen alloy is removed from the top of the big-bag, with the last material being rich in finer sizes.This is shown schematically in Figure 2.

When alloy is discharged from the bottom of the bag using a discharge spout built into the bag, orfrom a hopper knife located in the centre of the bag, it is possible that further segregation of sizesmay occur. This is illustrated in Figure 3. In this case the finer sizes tend to discharge first and thecoarser sizes later. If alloy is discharged into another container, such as a bottom dischargehopper, the same effect shown in Figure 1 will be repeated, only the effect will be magnified.

Red bands indicate coarser alloy and blue bands indicate finer sizes in Figures 1 through 3.

Figure 1: Segregation phenomenaoccurring during filling of big-baggiving coarser particles along theperiphery of the big-bag and finerparticles in the centre.

Figure 2: Finer sizes may segregateto the bottom of the package. Thiseffect can be magnified when alloy isremoved from the top, and the lastmaterial will be rich in finer sizes.

Figure 3: Bottom discharge causingfiner material to discharge first and thecoarser material last.

Alloy handling to minimise segregation

It is recommended that bottom discharge steel bins be used to store and dispense MgFeSi alloys.Figure 4, side view, shows the re-blending effect during big-bag discharge that can be gained byusing multiple knives in the top of the bin. These are placed midway between the centre and theside of the bag, in both side and end view directions. This makes 5 knives in total, which open 5discharge holes in the bottom of the big-bag when lowered onto the knives by a crane or a forklifttruck. Figure 4, front view, shows how alloy can be further re-blended by using a rake to pull alloyout across the full length of the discharge trough. The re-blended material falls into a container,which sits on a scale below the trough. This requires considerably less effort than shovelling alloyfrom a bin discharge trough, whilst minimising spillage and segregation.


Figure 4: Re-blending bin discharge. Side view (left), front view (right).

Figures 5 and 6 shows photos of a ferroalloy bin designed to minimize segregation effects.

Figure 5: Upper picture shows example of bin designfor minimised segregation. Dimensions are approx.1250mm wide and 2000mm high. Capacity isapproximately 1500 kg MgFeSi.Lower picture shows knives for cutting open the bottomof the big-bags.

Figure 6: Upper picture showing discharge opening. Lowerleft picture showing a big-bag being lowered into the hopper.Note that knives will open the bag and eliminate the need forthe operator to open bottom discharge spout while the bag issuspended.Lower right picture shows operator raking alloy out of thetrough. Each stroke should be the full length of the trough.






Selection of Inoculants for Grey Cast IronAn inoculant must serve several purposes in grey irons:

• to eliminate iron carbides or “chill”;

• to modify the graphite morphology to a uniform “A” type structure;

• to reduce the section sensitivity between thin and thick sections within the samecasting;

• to be effective over the length of the ladle pouring cycle.

All commercially available inoculants are based either on a ferrosilicon alloy, a blend ofgraphite and ferrosilicon or a mixture of ferroalloys. Increased demand by the casting end-users for consistency has led most foundries to abandon blends in favour of quality con-trollable specialist ferrosilicon based alloys.

These alloys invariably contain either 45-50% silicon or 60-75% silicon, both with additionsof property enhancing elements and a balance of iron.

The most common effective added elements are:

Element ConsiderationsAluminiumAl

Normally present in ferrosilicon alloys, but has little inoculating effect. High aluminium contentstypically found in cheap uncontrolled alloys can cause hydrogen pinhole problems in greensandmoulding systems and a maximum of 1.5% is advised. Some in-the-mould alloys have highaluminium (>4%) and it is claimed that this is effective in this niche application.

BariumBa

A powerful graphite promoting element which also provides good fade resistance. Up to about3% can be used beneficially, however excess can create slag defects. Care should be taken incertain castings containing sharp radii or where the sand is slightly soft as the high eutectic cellnumber generally found with barium containing materials may cause inter-cell shrinkage.

CalciumCa

A medium potency inoculating element, often added in conjunction with other alloyed elements.A combination of barium and calcium can be particularly effective in irons of lower sulphur con-tent (0.03-0.05%).

StrontiumSr

The most powerful inoculants for grey irons of medium/ high sulphur level contain about 1%strontium. Both in terms of chill control, particularly in thin casting sections, and modification ofstructure, strontium containing alloys are found to be very effective. Good fade resistance isfound with these alloys.Peculiar to strontium containing ferrosilicons is the property of powerful chill reduction whilstmaintaining a much lower eutectic cell number than found with other proprietary inoculants.

ZirconiumZr

A medium potency, all-purpose element that gives good chill reduction and, in particular, willcontrol the graphite morphology in high carbon equivalent irons. Zirconium has the added advan-tage of controlling nitrogen in heavily cored or shell systems, creating a harmless ZrN2 inclusion.


Several factors have to be taken into consideration in the selection of an inoculant for greyiron:

• the sulphur content of the base iron;

• the fade time, i.e. the total time taken from adding the inoculant to pouring the finalcasting from the ladle;

• the carbon equivalent of the iron.

The carbon equivalent (CE), given in weight percent, relates the combined effects of diffe-rent alloying elements used in the making of cast irons to an equivalent amount of carbon.This value can be calculated using a mathematical equation, and the following formula iscommonly applied for cast iron:

3%P%Si%C +

+=CE

Addition Methods

Consideration should also be given to the method of adding the inoculant. In-streammethods eliminate much of the inoculant fade and reduce the addition rates encounteredwith conventional ladle treatments. In these cases, attention must be given to theinoculant particle size, a 0.2 – 0.7 mm grading being suited to most in-stream applications.

For ladle inoculation, a 0.5 – 2 mm grade is deal for small ladles, up to 250 kgs capacityand 2 – 6 mm material should be used for ladles above this. Inoculants containing exces-sive fines should be avoided as these contain higher levels of oxides and create dustduring addition.

Elkem is happy to provide further information to help in the correct selection of inoculantsand inoculating practises.






Selection of Inoculants for Ductile Cast IronCareful selection of charge materials and nodularisers is often negated by the use of theincorrect inoculant. Due consideration should be given to this essential part of the processand the following points should be taken into account:

• Which kind of nodulariser and treatment process has been used.

• The fade time of the metal, that is the time from adding the inoculant to pouring thelast metal from the ladle.

• The Rare Earth content of the nodulariser (or otherwise added RE).

Pure Mg processes, such as plunging, cored wires or converters, reduce the number density of inherentnuclei in the iron making the iron difficult to inoculate. MgFeSi processes have a net effect of adding nuclei tothe iron. Typically, a higher inoculant addition will be required when pure Mg processes are employed.

Rare Earth's serve to neutralise the effects of some subversive elements found in steel scrap used in thefurnace charge, however, they can have the same effect on certain elements added as integral parts of theinoculant.

Inevitably, inoculation of ductile iron requires greater amounts of treatment agent thangrey iron, principally due to the carbide stabilizing properties of the magnesium usedduring nodularisation. Whereas the graphite flakes govern the properties of grey iron,ductile iron characteristics are dominated by the matrix. Formation of even, roundednodules is therefore essential to obtain the best properties.

Four main groups of inoculants are commonly available, all based on ferrosilicon plusdeliberately added property enhancing elements.

Element ConsiderationsCalciumCa

Foundry Grade ferrosilicons (FG FeSi) containing balanced amounts of calcium and aluminium.Care should be taken in the selection of these materials as many are supplied with very highlevels of aluminium (>3%) which can cause severe pinholing problems in the casting. Good FGFeSi will give satisfactory nodule counts and iron properties in many medium section castings.

BariumBa

Barium containing inoculants are especially useful where the fade time of the iron is long orwhere the solidification of the casting is slow (e.g., heavy sections). Total barium contents in theinoculant above 3% are unnecessary and serve no purpose but may cause slag generation.

StrontiumSr

Strontium containing inoculants may only be used under certain conditions in ductile iron. Stron-tium will give an excellent chill removal and nodule count in iron treated with pure Mg, RE freeprocesses or in many MgFeSi situations where the RE content of the nodulariser is less than1%. High RE contents will neutralise the effects of Strontium.

ZirconiumZr

Zirconium containing inoculants are excellent medium potency and fade resistant materials. Zir-conium has the added advantage of tying up any N2 from the melting process or cores.

Other inoculants are commercially available, containing a variety of elements, rare earth’s,bismuth and manganese for example and details of the properties of these can beobtained from the manufacturers.

All of the types noted above are available in both ladle and stream gradings, details canbe obtained from your local Elkem sales representative.






Recommended Target Analysis for Grey IronThe table shows suggested target analysis for the six ISO standard grades of grey castiron. Recommended composition ranges for carbon, silicon, manganese and sulphur, aswell as maximum level of phosphorus are given in the table. Also, the calculated carbonequivalents (CE) are shown in the table.

Recommended target composition for grey cast iron according to the ISO standard grades.

ISO GradeElementcontents 100 150 200 250 300 350

% C 3.5 – 3.8 3.4 – 3.7 3.2 – 3.5 3.1 – 3.4 3.0 – 3.2 2.9 – 3.1% Si 2.3 – 2.8 2.1 – 2.6 1.8 – 2.3 1.6 – 2.1 1.3 – 1.9 1.1 – 1.5% Mn 0.4 – 0.8 0.5 – 0.8 0.6 – 0.8 0.6 – 0.8 0.7 – 0.9 0.8 – 1.0% P max. 0.20 Max. 0.20 max. 0.20 Max. 0.15 max. 0.10 max. 0.10% S 0.06 – 0.15 0.06 – 0.15 0.06 – 0.15 0.06 – 0.12 0.06 – 0.12 0.06 – 0.12CE 4.2 – 4.6 4.0 – 4.3 3.8 – 4.1 3.6 – 3.9 3.4 – 3.7 3.2 – 3.5

It is important to note that following the recommended composition ranges given abovewill provide a good basis for obtaining the respective ISO grade properties. However, cor-rect properties are not guaranteed unless several other important parameters are handledproperly. Among these are:

• Correct choice of inoculant material and proper addition procedures (see ElkemTechnical Information Sheets No. 4 and 15).

• Avoidance of superheating and prolonged holding times.

• Careful choice of raw materials in order to avoid excessive concentrations of minor andalloying elements that may interfere with the mechanical properties. (see ElkemTechnical Information Sheet No. 12).

• Proper slag removal to avoid inclusion defects.

• Consideration to the effect of moulding medium on cooling rate and solidificationstructure.

It should also be noted that for special purpose grey irons it may be advantageous todeviate from the recommended analysis in order to improve specific properties (e.g. betterthermal conductivity, lower shrinkage tendency, improved damping capacity, etc.)


The effect of carbon content and carbon equivalent (CE) value on tensile strength can beillustrated in simple diagrams. The figures below show the connection between theseparameters in grey iron.

Effect of increasing carbon content on thetensile strength in grey irons

Tensile strength as a function of carbonequivalent value (CE value) in grey irons






Recommended Target Analysis for Ductile IronThe table shows suggested target analysis for production of the ISO standard grades ofductile cast iron. Recommended composition ranges for carbon, silicon and manganeseare given in the table. Also, recommendations to maximum levels of some minor elementsare given as footnotes to the table.

Recommended target composition for ductile cast iron according to the ISO standard grades.

ISO grade(s)800/2, 700/2, 600/3 500/7 450/10, 400/15, 400/18 350/22

Averagecastingsection[mm] %C %Si %Mn %C %Si %Mn %C %Si %Mn %C %Si1) %Mn

13 3.6-3.8 2.6-2.8 <0.5 3.6-3.8 2.6-2.8 <0.3 3.6-3.8 2.6-2.8 <0.2 3.6-3.8 2.0-2.5 <0.113-25 3.5-3.6 2.2-2.5 <0.6 3.5-3.6 2.2-2.5 <0.35 3.5-3.6 2.2-2.5 <0.25 3.5-3.6 2.0-2.5 <0.1525-50 3.5-3.6 2.1-2.3 <0.7 3.5-3.6 2.2-2.4 <0.4 3.5-3.6 2.2-2.4 <0.3 3.5-3.6 2.0-2.4 <0.1550-100 3.4-3.5 1.9-2.1 <0.8 3.4-3.5 2.0-2.2 <0.5 3.4-3.5 2.0-2.2 <0.35 3.4-3.5 1.8-2.0 <0.2

100 3.4-3.5 1.8-2.0 <0.8 3.4-3.5 1.8-2.0 <0.6 3.4-3.5 1.8-2.0 <0.4 3.4-3.5 1.8-2.0 <0.251) Maximum 2.5% Silicon when impact properties are required.

Important notes:• For Grades 800/2, 700/2 and 600/3 additions of 0.5% Cu or 0.1% Sn may be made.

• Base metal Sulphur content should be restricted to maximum 0.020%.

• Final ductile iron Sulphur content should be maximum 0.015%.

• Phosphorus, in all grades of ductile iron, should be maintained below 0.03%.

• Chromium levels should be maintained below 0.05%.

• Residual Magnesium levels should be in the range of 0.03-0.06%.

It should be noted that following the recommended composition ranges given above provi-des a good basis for obtaining the respective ISO grade properties. However, correct pro-perties are not guaranteed unless several other important parameters are handled pro-perly. Among these are:

• Correct choice of inoculant material and proper addition procedures (see ElkemTechnical Information Sheets No. 4 and 16).

• Avoidance of superheating and prolonged holding times.

• Careful choice of raw materials and ferroalloys in order to avoid excessiveconcentrations of minor and alloying elements that may interfere with themechanical properties (see Elkem Technical Information Sheet No. 12).

• Correct choice of magnesium treatment process and nodularizing agent for theactual purpose and conditions.

• Proper slag removal to avoid inclusion defects.


• Consideration to the effect of moulding medium on cooling rate and solidificationstructure.

Finally, it should also be noted that for special purpose ductile irons it may be advanta-geous to deviate somewhat from the recommended analysis in order to alter specific pro-perties (e.g. improved strength or ductility, reduced graphite flotation, special alloyedgrades, etc.)






Aluminium in Cast IronAluminium is normally found in cast irons as a mainly harmless residual element. Themajor sources for aluminium are steel scrap, contaminated cast scrap (engine blocks etcwith pistons included), the ferroalloys consumed and inclusions of non-ferrous metals inthe charge materials.

A common occurrence in foundries is the pinhole problem from hydrogen gas evolution,which often can be attributed to excessive aluminium contents. It is accepted that alumi-nium has an influence on the surface tension of the liquid iron, a consequence of whichcould be susceptibility to pinholing defects. The figure below shows the relationship bet-ween aluminium in the iron and the tendency to pinholing. It is shown that grey iron ismore sensitive to pinholing than ductile iron due to the overall lower surface tension forgrey iron. Above a certain level (approximately 0.2% Al), the susceptibility for pinholing isreduced as the surface tension again increases. The most critical range is 0.05 – 0.2% forductile iron and 0.008 – 0.2% for grey iron. Consequently, the contents of aluminiumshould always be kept low, preferably below this range where the risk will be highest.

Influence of Aluminium Content on Surface Tension and PinholeSusceptibility of Grey and Ductile Irons

It should also be noted that iron temperature will influence the surface tension and thuswell insulated ladles are of importance (refer to Elkem Technical Information Sheet No. 21for more data). Aluminium will also add to the slag formation, resulting in poor furnace per-formance, more ladle and holder maintenance, and increased risk for slag inclusions incastings.

Aluminium has virtually no inoculating effect as such, but it may add to the hardness of theiron, and it can also be harmful to the nodularity of ductile iron. It is also important to notethat titanium will play the same role as aluminium to a certain extent, although normallypresent in smaller amounts than aluminium. Furthermore, the two elements will have anaggregated effect, and both elements should be monitored and controlled at all times.


It is also well known that many elements can interact with aluminium to affect the iron pro-perties, either by enhanced inoculation potency or by detrimental effects such as the com-bination of aluminium and titanium. The presence of even minor traces of titanium meansthat the tolerable aluminium levels will be dramatically reduced. The figure below showsthe combined effects of aluminium and titanium on the hydrogen pinholing tendency inductile iron. Above the curve there will be a significant risk for such defects to occur.

Combined effects of aluminium and titanium onhydrogen pinholing tendency in ductile iron.

Example of pinhole defect in grey iron.

For ductile iron the permissible aluminium is roughly 5 – 10 times that of grey iron. No datais available concerning the combined effects of aluminium and titanium in grey iron, butthere are reasons to believe the interaction is about as for ductile iron and both elementsshould therefore be closely watched.

Since both nodularizers (magnesium-ferrosilicon) and inoculants will contain variousamounts of aluminium and titanium, it is important that choice of alloys is being made withfull awareness of its total chemical composition. At higher aluminium contents, ferrosilicon-based alloys will tend to improve solubility, but the increased slag formation and pinholingtendency should call for caution. High aluminium containing alloys should hence only beused where low addition rates are applicable (i.e. stream inoculation). Special attentionshould be paid to large amounts of ferrosilicon used as a furnace charge material.

It is worth noting that hydrogen pinhole defects often will have similar characteristics asother type of gas defects, such as nitrogen porosity. A characteristic feature for pinholes isthe graphite lining covering the inner pore surfaces. An example of such a hydrogenpinhole defect is shown in the figure above. This defect characteristic can also occur fornitrogen defects, and it is therefore often difficult to separate between such gas defects. Athorough investigation into nitrogen, aluminium and titanium levels will be necessary todetermine the type of gas involved, since a high Aluminium and Titanium level maypromote hydrogen pinholes but at the same time effectively neutralize nitrogen by formingTiN and AlN inclusions.

Choice of core binder system and green sand humidity level is also vital for the avoidanceof hydrogen and nitrogen pinhole defects.






Selection of NodularizersAmong foundries there is always a debate about the selection of nodulizer for theirparticular process. The two diagrams below show some variables that will affect the selec-tion of magnesium ferrosilicon alloy. The diagrams can help you to find the right alloy com-position for a given process and equipment. On the next page, recommendations to alloycomposition for special processes like in the mould, flow through, and sandwich pocketprocesses are also given.

Effects of Process Variables on Magnesium Ferrosilicon Alloy Selection:

Lower Mg-recovery and increasedviolence. Use high Ca in alloy.

Better Mg-recovery. Low Ca in alloycan be used.

Violent reaction and low Mg-recovery.Use medium Ca in alloy.

Less violent reaction and betterMg-recovery. Low Ca possible.

Fume and flare. Use low Mg and increasedCa in alloy. Normally, use 4-32 mm sizing.

Very little fume and flare. Better Mg-yield. Higher Mgand lower Ca in alloy possible. All sizes possible.

Use more fine sized nodularizer.Less than 12 mm sizing recommended.

Use coarser nodularizer.Typically 4-32 mm or 1-20 mm.

Temperature

Ladledimensions

Tundishcover

Treatmentweight

> 1480oC

< 1480oC

1:1 H:D

2:1 H:D

No

Yes

< 500 kg

> 500 kg

ProcessVariables

Effects of Iron Composition on Magnesium Ferrosilcon Alloy Selection:

MgFeSi/low Si nodularizer mixtureor 10% Mg-FeSi alloy

Low Si nodularizer

All type of nodularizers can be used.

Desulphurization before Mg-treatment

Use nodularizer with low RE-content or lowMg with increased RE.

Requires increased RE-content to balance subversivetramp elements.

Not generally significant in product selection, butMg-recovery slightly lower at high carbon contents.

Siliconcontent

Sulphurcontent

ChargeMaterials

CarbonContent

1.5-1.8%

> 1.8%

0.025-0.04%

> 0.04%

High puritysteel scrap

Low qualitysteel scrap

3.2-4.0%

Base IronComposition

Use a 5% Mg-FeSi alloy0.5-1.5%

< 0.025%

High Mg/RE alloys recommended. Increased slagformation. Desulphurization recommended.


Nodularizers for Continuous Treatment:

The following are typical specifications for MgFeSi alloys for different treatment processes:

Treatment processSpecification In the mould Flow throughSilicon 44-48% 44-48% 44-48%Magnesium 5.0-6.0% 2.8-3.5% 3.5-4.0%Calcium 0.4-0.6% 1.1-1.6% 1.3-1.8%Aluminium 0.8-1.2% 0.5-1.0% 0.5-1.0%Lanthanum 0.25-0.40%Rare earth’s 1.1-1.4% 1.1-1.4%Sizing 1-4 mm 2-12 mm 2-12 mm

Important notes:• Calcium is included to reduce reactivity and give optimum Mg-recovery.

• Low aluminium decreases the tendency to give slag related defects.

• These are typical analyses, and other alloy compositions are also available to meetindividual requirements.

• For details on the sandwich pocket process, see Elkem Technical InformationSheet No. 11.


Elkem ASA, Foundry Products © Copyright Elkem ASPostal address Office address Telephone Web Revision




Heat Conservation in Liquid IronWhen processing liquid iron in ladles and holders there will be a continuous loss of tempe-rature from radiation and heat conduction through refractories. Such energy losses can beminimised by using insulating materials and covered vessels for holding and transportationof metal. This sheet gives some examples of how temperature can be conserved in aladle. Some of the important consequences of heat conservation are also listed in the end.

Heat transfer - refractory linings:

LTT

kL

TTk

dxdTkQ

)()( 2112 −=

−−=−=& (1)

where Q& is heat transfer per unit area (W/m2), k is thermal conduc-tivity (W/m·K), T1 is temperature of the hot face (K), T2 is temperatu-re of the cold face (K), and L is refractory thickness (m). The equa-tion is negative because heat transfer is contrary to the direction ofthe temperature gradient.

Refractory conduction, single component:

Example: k = 1 W/m·K for high alumina liningT1 = 1480°C (1753 K), T2 = 38°C (311 K)L = 0.051 m (51 mm)Q& = 1 (1753 - 311)/0.051 = 28.3 kW/m2

For each square meter of single component alumina refractory, the rate of heat loss isapprox. 28 kW.

Heat transfer, multiple layers:

3

3

2

2

1

1

31 )(

kL

kL

kL

TTQ

++

−=& (2)

where k1 is the conductivity and L1 is the thickness of mate-rial 1, etc.

Refractory conduction, multiple components:

Example: T1 = 1480°C (1753 K), T3 = 38°C (311 K)High alumina: L1 = 25 mm, k1 = 1 W/m2·KInsulating brick: L2 = 25 mm, k2 = 0.5 W/m2·KCeramic paper: L3 = 6 mm, k3 = 0.05 W/m2·KQ& = (1753-311) / (0.025+0.050+0.12) = 7.4 kW/m2

For each square meter of multiple component refractory, the rate of heat loss is about 7kW.


Refractory conduction, savings from multiple components:

Refractory consept Heat lossesSingle component 28.3 kWMultiple components 7.4 kWEnergy savings 20.9 kW

About 75% of the heat loss from a single component refractory can be saved by using amultiple component alternative including insulating bricks and ceramic paper (fibre).

Heat radiation:

)( 42

41 TTQ −= εσ& (3)

where Q& is heat radiation per area (W/m2), ε is emissivity (number between 0 and 1), σ isthe Stefan-Boltzmann constant (5.67·10-8 W/m2·K4), T1 is temperature of the radiating ma-terial (K), and T2 is temperature of the receiving media (K), the latter usually room tempe-rature (25 °C).

Some common emissivity values:

Surface Temperature EmissivitySheet steel 25 - 50 °C 0.81-0.83Molten iron 1400-1600 °C 0.25-0.40

high Al2O3 1000-1500 °C 0.45-0.60Al2O3-SiO2refractories low Al2O3 1000-1500 °C 0.65-0.80

Radiation from metal surface:

Q& = 5.67*10-8 x 0.33 x (17534-2984) = 176.6 kW/m2 @ 1480 °C

Radiation from empty ladle refractory between fills:

Q& = 5.67*10-8 x 0.45 x (17534-2984) = 240.8 kW/m2 @ 1480 °C

Hence, for a 0.17 m2 metal bath surface the heat loss will be about 30kW, while for a 1 m2 refractory area in an empty ladle the loss will beapprox. 240 kW.

Important effects of heat conservation:• Less melting energy required. Thus, lower tapping temperature.• Reduced temperature losses during pouring.• Extended furnace-lining life.• Less formation and accumulation of slag in ladles.• Less magnesium alloy required in ductile iron.• Less maintenance of ladle refractories.• Better environment (especially ductile iron) due to less smoke and fume.






Late Metal Stream InoculationWith increasing demands from end-users for higher quality castings and increasingnumbers of foundries investing in highly mechanised moulding and pouring lines, therequirements for effective inoculation are becoming more difficult to meet.

Non-uniform inoculation from conventional ladle treatments can arise, caused byvariations in metal temperature, human error in addition and the accepted deterioration ofinoculating effect with time (fade). Further, particular difficulties can arise in some pouringunits where satisfactory addition of inoculant is not possible.

Automatic high production moulding lines linked to either a heated or unheated stopperrod controlled pouring unit have proved to be both highly economic and efficient,particularly in the repetition section of the industry where high volumes of castings ofconsistent metal quality are required.

A method of inoculating this iron between the stopper rod and the downsprue is thereforeessential. The system must be automatic, linked to activation of the stopper rod (or insome cases activated by light emitted by the metal flow) and be highly reliable. Severaltypes of inoculating unit are available commercially at variable quality and cost. WhilstElkem does not supply such machinery, it is strongly recommended that a system withadequate safety systems be installed to eliminate the possible requirement for 100%inspection of castings. Specialist advice on the selection of inoculating units andrecommendations on installation can be obtained through local Elkem representatives.

With high investment in moulding lines, pouring units and inoculating systems, it is logicalto control accurately the quality of the inoculant. This must have:

• Good consistent flowability to ensure that particles of inoculant reach the metalstream, even at low flow rates through a small orifice in the injection unit.

• A clean cut on the bottom sieve fraction to avoid excessive fines. Undersizematerial can contain oxides and the heat from the metal stream tends to blow finematerial into the atmosphere. Variations in the undersize fraction can also lead toinconsistency in flow rate and possible blockage of the dispensing unit.

• No oversize particles which can block the injection unit.

• Good solubility in the iron to give maximum inoculation effect without leaving hard,unmachinable inoculant particles which have not dissolved, even at low castingtemperatures.

• Less tendency to give slag inclusions in the iron.


With conventional ladle inoculation, the effects of the inoculant begin to fade instanta-neously and it has been shown that the number of sites available for nucleation deterio-rates.

Coarsening behaviour of nuclei particles in cast iron during holding.

From this, it can be seen that some 5x105 sites per cubic millimetre of metal are availableimmediately after addition of the inoculant, fading to 1x105 after about 10 minutes. Withlate metal stream inoculation, fade is virtually eliminated and the addition rate to providesatisfactory inoculation (chill removal, graphite morphology) is dramatically reduced. Seealso Elkem Technical Information Sheet No. 6 on “Fading of Inoculation” for more details.

Typical addition rates:

Cast Iron Ladle Inoculation Late Stream Inoculation Grey Iron 0.1-0.3% 0.03-0.2%, typical 0.1% Ductile Iron 0.3-0.6% 0.06-0.3%, typical 0.2%

Elkem provides a complete range of materials suitable for late stream inoculation andreference should be made to the Data Sheets for Superseed® 50/75, Superseed® Extra,Zircinoc®, Foundrisil®, Reseed® and Vaxon® 75. These materials are available world-widein a 0.2-0.7 mm grading for maximum flowability and solution into the iron. See also ElkemTechnical Information Sheet No. 15 and 16 on “Selection of Inoculants” for more details.In certain applications a wider grading is acceptable and details are available on request.

The main advantages of late metal stream inoculation are:

• Reduced addition rates compared to ladle inoculation provide an economic benefit.

• Reduced addition rates mean lower calcium and aluminium additions thus leadingto less tendency towards slag and pinholes.

• Avoiding the promotion of high eutectic cell counts that may lead to shrinkageporosity, again because of the lower addition rates of inoculant.

• Operator error is eliminated.

• Only the metal entering the mould is inoculated, thus avoiding wasteful treatment ofladle “heels”.






Factors Influencing the Recovery and Addition of Magnesiumin Ductile Iron Ladle Treatment Processes

Residual magnesium and magnesium recovery have always been subjects for discussionamongst foundry people. This sheet summarises the most important factors that willinfluence the recovery of magnesium in ductile iron production.

1) Sulphur content in base iron.Sulphur has to be neutralised in order to increase the surface tension of the iron. Highsulphur in the base metal means increased Mg addition.

2) Oxygen content in base iron.Oxygen has to be neutralised in order to increase the surface tension of the iron. As withsulphur, increased oxygen content requires higher Mg addition.

3) Slag from the melting or holding furnace.Slag that is transferred from the furnace will react with magnesium and reduce therecovery. Proper separation procedures to minimise slag carry over need to be in place.

4) Tapping temperature.Tapping (treatment) temperature should be kept as low as possible in order to avoidexcessive reaction violence. The higher the temperature, the more vaporization and lowerrecovery of magnesium.

5) Time between MgFeSi addition to the ladle and tapping.Time between magnesium addition and tapping should be minimised to prevent preheatingand oxidation of the alloy. At the same time, there should be no liquid metal residual fromprevious treatments in the ladle as this may start to react with the alloy.

6) Slag in ladle and pocket.Slag building up in the ladle and reaction pocket leads to reduced magnesium recovery,probably due to reactions between the slag and the magnesium and also as the pocketdepth is reduced changing the reaction conditions. Overspill of alloy will occur if thepocket is allowed to fill with slag. Ladles should be kept tilted when empty to avoid slagclogging the pockets.

7) Alloy cover.An alloy cover in the ladle, for example fine sized FeSi or steel plates, will delay thereaction start and give better absorption of magnesium into the liquid metal.

8) Filling time.Filling rate should be high in order to achieve a high ferrostatic head in the ladle before thereaction starts.

9) Fading/Pouring time.Long holding times after treatment and long pouring times require higher initial Mgcontents to compensate for fading effects. Pouring times should be minimised toovercome these effects.


10) Inoculation.With a good inoculation, less residual magnesium is required to give good nodularity. Thisagain means less alloy addition and better magnesium recovery.

11) Ladle design.The ratio of internal Height: Diameter should be at least 2:1 and the pocket should havespace enough to carry the alloy addition and covering material (see TI sheet No.10). Theladle should also be properly insulated to minimise heat losses and consequently therequired treatment temperature (see TI sheet No. 21). A tundish cover lid is also highlyrecommended for alloy and temperature recovery reasons.

12) Chemical composition of nodulariser.High magnesium content in the alloy will give a violent reaction and reduced recovery.High Ca will reduce the reactivity and increase the recovery, but also increase thetendency to slag formation. Rare earth’s (cerium) will assist in giving better recoverybecause it allows for working at lower magnesium in the alloy and lower residualmagnesium in the iron (see TI sheet No. 20).

13) Alloy sizing.A wide alloy sizing gives dense bulk packing in the pocket. The alloy will then fuse andreact (dissolve) slowly in a controlled manner with a minimum of pieces floating. Lumpsfloating and burning on the surface are a waste (see TI sheet No. 20).

14) Storage of foundry alloys.All foundry alloys will oxidise if exposed to moisture. Oxidised alloys will give a lowerrecovery than fresh materials. Containers of alloy should be stored in a dry place and notopened until required at the treatment station (see TI sheet No. 1).

R e q u ire d M g F e S ia d d it io n w t %

1 4 8 0 °C

1 4 6 0 °C

1 5 2 0 °C

5 m in

2 m in

3 0 s c le a nfu rn a c e

s o m e

lo t o f 1 :1

1 :1 ,5

1 :3 f re s h

s o m e

g o o d

C a = 0 ,5 , R e = 0 ,5

C a = 0 ,5

C a = 2 ,5

C a = 1 ,0

C a = 2 ,5 R e = 1 ,5

S = 0 .0 0 6

S = 0 .0 1

S = 0 .0 1 6

S u lp h u r-c o n t.

T a p p in gte m p . T im e b e tw e e n

M g F e S i a d d .a n d ta p p in g

L a d le d e s ig nd ia m e te r : h e ig h t

S la g infu rn a c e .

A llo yC o v e r

C h e m ic a lc o m p o s it io no f M g F e S i

1 .5

1 .6

1 .4

1 .8

1 .7

1 .3

1 .2

1 .9O x id is e dM g -a llo y .

h e a v y

s o m e

n o n e

Factors that can influence the MgFeSi addition to a ductile iron ladle treatment process.

Appendix: Checklist Recovery and Addition of Mg in Ductile Iron Ladle Treatment Processes.

Technical Information 23 - Appendix





CChheecckklliisstt -- RReeccoovveerryy aanndd AAddddiittiioonn ooff MMggiinn DDuuccttiillee IIrroonn LLaaddllee TTrreeaattmmeenntt PPrroocceesssseess

For process improvements fill in information in the white fields.

To help you detect possible causes for sudden changes in Mg-recovery and needed Mg-addition, fill in both white and grey fields.

1 S-Content in Base Iron max. 0.020 wt%Before Now

Final S-Content max. 0.015 wt%Before Now

Residual Mg-Content in the range 0.03 – 0.06 wt%Before Now

2 O Content in Base Iron:Before Now

if measured

3 Remember to remove slag!Any process disturbances reported?

4 Tapping Temperature 1450 – 1500°CBefore Now

Treatment Size Before kgNow kg

5 Keep time between addition to ladle and treatment short!Any process disturbances reported?

6 Slag in ladle or pocket ?

Technical Information 23 - Appendix 2

7 Cover Material % additionBeforeTypeNowType

8 Keep the filling rate into the ladle high!Any process disturbances reported?

9 Keep holding and pouring time short!Any process disturbances reported?

10 Inoculation Before NowNodule count nodules/mm2

Chill wedge mm

11 H : D – Ratio Lower 2 : 1 HigherBeforeNow

12 Alloy Composition Before Now SpecMg-Content wt%Ce-Content wt%Ca-Content wt%Al-content wt%

New lot?

13 Alloy Sizing min max % undersizeBeforeNow

14 Correct storage of foundry alloysIn houseOutdoor

Weather changes? Yes No






Partition of Slag Phases in the Treatment and Pouring of Ductile Iron

One problem encountered in automatic pouring systems incorporating a stopper rod is thebuild up of slag in the pouring unit, especially on and around the stopper rod, that leads to:

• Costly cleaning and maintenance of the holding unit.

• The stopper rod not seating properly and metal dripping from the launder.

• Inconsistent pouring rates which can interfere with consistent inoculation fromdispensing units.

• Slag entering the mould.

An investigation has been carried out into the composition of slag phases contained in atundish ladle/unheated automatic pouring unit system. Different slag phases have beenfound to precipitate in various parts of the system and these are shown schematicallybelow.

Slag constituents:MagnesiumCalciumSulphideIronAluminium

Figure 1: Partition of slag phases in the sandwich treatment ladle (surface, wall and pocket)and in the autopour (inlet, surface, bottom, stopper and nozzle).

Ductile iron slag phases can be categorised into five principle types:1. Magnesium containing slags: MgO (Periclase), MgO•Al2O3 (Spinel), 2MgO•SiO2

(Forsterite) and MgO•SiO2 (Enstatite).These phases tend to be distributed throughout the system, both treatment vesseland pouring unit. The very hard aluminium containing spinel is found to beconcentrated around the stopper rod and pouring nozzle.

2. Calcium containing slags: complex oxides, sulphides and aluminates.Calcium phases can be found in most locations in the system, but arepredominantly concentrated around the stopper rod.

3. Sulphide phases; magnesium and calcium sulphides.Sulphide phases tend to be concentrated around the stopper rod, but can be foundin small quantities elsewhere in the system. Proper control of sulphur in the basemetal and good deslagging practise minimises the harmful effects of this phase.

4. Iron containing slags: Fe,Al (Hercynite), Fe,Mg (Ringwoodite and Magnesoferrite).These are mostly found in the upper parts of the pouring unit and may be regardedas oxidation products generated by contact between the iron and atmosphere.


5. Aluminium phases: Al,Si (Mullite), Al,Mg (Sapphrinite)As with other harmful aluminium containing slags, these tend to be concentratedaround the stopper rod.

In general terms, aluminium and calcium phases have the most tendency to concentrateon the stopper rod. It is possible to alter the slag phase composition and hold the moreharmful phases back in the treatment ladle.

Barium

This is done with the addition of barium, either as an integral part of the MgFeSi alloy or,more commonly, as part of a ferroalloy sandwich cover (e.g. by the use of a bariumcontaining inoculant in the cover material).

The competition between barium, calcium and magnesium to combine with the aluminiumphases seems to be dominated by barium. Barium phases tend to settle in the treatmentladle and only a minimum of slag is transferred into the pouring unit, as shown schemati-cally below.

Slag constituents:Barium

Figure 2: Distribution of barium containing slag phases.

The effect of barium additions is that the stopper rod and the insides of the pouring unitremain cleaner and will have a longer working life. As the barium containing slags settlemainly in the treatment ladle, it appears that more slag is being generated. This is notnecessarily true as the reaction slags are being accumulated in the ladle rather than beingtransferred into the pouring unit. Ladles will therefore require better skimming and cleaningof linings, however most foundries will find this a better, cleaner and cheaper option thanreplacing stopper rods and cleaning out pouring units.

Without doubt, the best way of minimising harmful calcium and aluminium bearing slagsfrom contaminating the pouring unit is to prevent the introduction of such elements into theiron. As this is not possible in many cases, the best alternative is to make a deliberateaddition of a barium-containing alloy to the treatment ladle to control the slag partition andminimise slag fouling the pouring units.






Poor Nodularity in Ductile IronThis sheet summarises some important considerations affecting nodularity in ductile ironproduction. Factors causing different types of poor nodularity are described, and importantcriteria distinguishing between the different types of poor nodularity given.

Compacted graphite:• Low residual magnesium and/or rare

earth’s from poor nodularising practice,high temperature or long holding times.

• Excess sulphur in the base iron notbalanced by sufficient magnesium.

• Excess titanium in iron fromcompacted graphite iron returns.

Exploded graphite:• Excess rare earth additions,

particularly when high purity chargesare used. Normally found in thicksection castings or at higher carbonequivalents.

• Sudden drop in base iron sulphurcontent from change of raw materiallots (steel scrap, pig iron, recarburiser).

Chunky graphite:• Excess rare earth additions when high

purity charges are used.• Low Sulphur to RE ratio.• Promoted by poor inoculation

(pronounced segregation effects).• Similar causes as exploded graphite.


Spiky graphite:• Very small amounts of lead (Pb),

bismuth (Bi), or antimony (Sb) thathave not been neutralized by rareearth’s. This has a catastrophic effecton mechanical properties.

• Insufficient addition of rare earth’s to acontaminated charge.

Irregular graphite shape:• Poor inoculation or excessive fading of

inoculation. Often combined with lownodule counts.

• High holding temperatures or longholding times resulting in “dead” irons.

• Excessive addition of nodulariser.• Can be improved by late addition of a

powerful specialty inoculant.

Nodule alignment:• Low carbon equivalent.• Poor inoculation causing hypo-eutectic

solidification and coarse dendritestructures. Nodule alignment atdendrite arms.

• High pouring temperatures.

Flake graphite surface:• Excess sulphur built-up in moulding

sand. Reversion to flakes asmagnesium in the iron reacts withsulphur.

• Can be overcome by using highermagnesium or rare earth’s innodulariser, or a cerium containinginoculant.

• Mould coating may also be useful.






Fading of Nodularity in Ductile IronWhen properly treated and inoculated ductile iron is held for prolonged times, it is com-mon to observe deterioration in the nodule shape of the graphite. This is often referred toas fading of nodularity. Fading of nodularity is typically related to one of two possible phe-nomena, either fading of magnesium or fading of inoculation. It is important that thecorrect type of fading is pinpointed, as possible cures to avoid poor nodularity during timewill differ greatly between the two fading phenomena. The micrograph below shows agood ductile iron microstructure immediately after magnesium treatment and post inocu-lation. The two lower micrographs show examples of microstructures for the two principalfading mechanisms.

Magnesium fading Inoculant fading

Compacted graphite from magnesium fading Irregular shaped graphite from inoculant fading


Magnesium fading effects:

When magnesium is lost to the liquid metal surroundings (e.g. slag, refractory, evapora-tion) it may cause a loss in nodularizing power over time. This is typically related to a lossof residual magnesium content in the iron, or even a pick-up of sulphur or oxygen from thesurroundings, causing a gradual consumption of the residual magnesium. When residualmagnesium becomes insufficient, poor nodules referred to as compacted graphite or ver-micular graphite will occur. An example of this is given in the left micrograph.

Residual magnesium and effects of Mg-fading is described in more detail in Elkem Techni-cal Information Sheet 7.

Inoculant fading effects:

When the metal is held for prolonged times after addition of post inoculant, the effects ofthe inoculant will gradually fade. Depending on the type of inoculant and the addition rate,the ductile iron will gradually lose its nodule count and the nodules will also lose theirspherical shape. Typically irregular shaped nodules are resulting, associated with a gene-ral drop in nodule count. An example of this is given in the right micrograph.

Fading of inoculation is described in more detail in Elkem Technical Information Sheet 6.

When discovering a poor nodularity condition, it is important for the trained foundryoperator to clearly distinguish between the two types described. Cures for the two types ofpoor nodularity may in some instances actually be converse to each other.

Possible cures for Mg-fading:

Magnesium fading causing compacted graphite shapes can be cured by the followingactions:

• Increase residual magnesium and/or rare earth’s by adding more nodulariser.

• Avoid high metal temperatures and long holding times.

• Reduce base iron sulphur content by using purer charge materials and additives.

• Improve slag skimming operations to avoid resulphurising of the iron.

• Avoid metal exposure to air causing oxidation of residual magnesium.

• Using a RE-containing post inoculant to compensate for Mg-losses.

Possible cures for inoculant fading:

Inoculant fading causing irregular shaped graphite and a low nodule count can be curedby the following actions:

• Use a more powerful, fade resistant post-inoculant or add more inoculant

• Avoid high holding temperatures and long holding times

• Use a second, late addition of a powerful specialty post-inoculant material

• Sometimes irregular shaped nodules and low nodule counts may be a result ofexcessive magnesium or nodulariser addition, – i.e. reduced Mg-addition mayimprove the nodularity.






Alternative Tundish Ladle DesignThe tundish cover process may be designed to suit a range of different foundry conditions.Examples are fixed lid, automatic lifting or manual removable lids. Low levels of fume andsmoke will escape from the tundish vessel, giving a good foundry environment.

The figures below shows some alternative ways of designing tundish cover ladles withfixed and removable lids. A fixed lid requires an alloy charging port for introduction ofMgFeSi-alloy. Ladles with fixed lid can generally not be deslagged, and therefore slag ac-cumulation may be a problem. Hence, low slag forming alloys (low Ca and Al) are recom-mended for such ladles.

The tea pot ladles offers an advantage in that liquid iron can be filled through the tea potspout. This means that the tundish cover basin is eliminated. Both fixed and removablelids can be applied for teapot ladles. Teapot ladles will generally supply cleaner metal intopouring ladles and autopours due to the slag skimming effect of the spout.

The lifting or removable tundish cover design is probably the most flexible and easiest tomaintain. Lifting covers can be either integrated to the ladle with a separate lifting lug or


constructed as a fully removable lid by using for instance a fork lift truck. The lid can alsobe mounted onto the furnace spout. The major advantages with removable lids are easyaccess to deslagging and cleaning of the ladles and also that the same lid can be used forseveral ladles. Charging of MgFeSi-alloy is also easier when the lid is removed from theladle top.

For more information about tundish ladle treatments, please refer to Elkem Technical In-formation sheets 9, 10, and 11, and also 20 and 21 for selection of alloys and heat con-servation.






Magnesium versus Sulphur in Ductile IronMagnesium is added to liquid iron through the nodularizing operation mainly todesulphurize and deoxidize the base iron. When the base iron is properly desulphurized,graphite will grow as spheres instead of flakes resulting in good ductile iron. The principaldesulphurizing reaction of magnesium in liquid iron is as follows:

Mg + S = MgS

This directly implies that lower base iron sulphur content will minimize the requirement formagnesium addition to make good ductile iron. The curves below show a schematicrelationship between the base iron sulphur content and required residual magnesium toproduce ductile iron.

Figure 1. Schematic representation of the relation between base ironsulphur content and required residual magnesium to produce ductile iron.

The curves in Figure 1 can be explained as follows. The lower straight line indicates theminimum theoretical Mg required to give a 1:1 ratio between Mg and S. However, Mg alsogoes into solution in the iron and evaporates (fades) during time, and the upper threecurves shows recommended Mg addition to account for such dissolution and fadingeffects. When iron of a base sulphur of 0.02%S is faded for about 12-15 minutes, a resi-dual initial Mg of about 0.05% may be required.


O

S

Mg Large MgO, MgS andMg-Si-oxide particles

SlagSlag

Small MgO, MgS andMg-Si-oxide particles

Nucleation SitesNucleation Sites

DesulphurisingDesulphurising DeoxidisingDeoxidising+=Figure 2. Principal effects of magnesium in tying up sulphur and oxygen

to produce slag and nucleation sites.

Figure 2 above shows a schematic representation of the principal reactions between Mg,S and O forming potential slag and nucleation sites for graphite. Figure 3 below shows anexample of the effects of two base iron sulphur levels and a low and constant MgFeSiaddition. The higher S of 0.018% is excess for the low Mg causing poor nodularity.

Base S = 0.018 %1.0 wt% MgFeSiFinal Mg = 0.033 %Final S = 0.016 %Nodularity ∼ 50 %

Base S = 0.010 %1.0 wt% MgFeSiFinal Mg = 0.030 %Final S = 0.010 %Nodularity ∼ 90 %

Figure 3. Example of the effects of base iron sulphur at 0.018% and 0.010%respectively, for a constant addition of magnesium at 1 wt% MgFeSi alloy

giving a constant residual Mg around 0.03% in the treated iron.

For more information about residual magnesium in ductile iron, please refer to ElkemTechnical Information sheet 7.






Nitrogen FissuresNitrogen gas porosity defects are predominately a problem in grey iron, but can also occurin ductile irons at higher nitrogen contents. Generally nitrogen fissures are found in medi-um to heavy sections adjacent to resin bonded mould or core materials.

The nitrogen fissures are typically smooth faced surface or sub-surface irregular shapedcavities perpendicular to the surface stretching a few millimetres into the casting. Theinsides of the cavities are mostly black and shiny with dendrites penetrating into the cavity.Nitrogen pinholes are normally surface or sub-surface rounded cavities also with blackand shiny inner surfaces. A graphite flake depleted zone normally surrounds the holes.

Example of Nitrogen porosity defect in grey ironrevealed on machining.

Close-up of defect showing inner graphite liningand flake depleted rim.

Possible causes:• Use of high steel scrap content in cupola

melted iron with high coke charges.• Use of high nitrogen containing raw

materials in electric melting.• Use of high nitrogen containing resins or

build-up of nitrogen in the sand.• Low carbon equivalent.• Insufficient Ti- or Zr-contents to neutralize

free nitrogen.• Use of recarburiser with high nitrogen

content.

Possible cures:• Reduce nitrogen content to below 85 ppm

in heavier sections and 120 ppm inthinner sections.

• Limit the use of high nitrogen containingmaterials in the charge.

• Avoid high nitrogen containingrecarburiser.

• Increase the carbon equivalent.• Add Ti or Zr to tie up excessive nitrogen.• Increase pouring temperature.• Use a lower nitrogen containing resin

binder system for cores (<3%N).• Improve venting of mold cavity and cores.






Hydrogen PinholesHydrogen pinholes can be found in both grey and ductile irons. They usually appear assmall spherical holes just beneath the casting surface and normally will have a smoothand shiny inner surface coated with a dense graphite lining. A graphite flake or noduledepleted zone is typically observed adjacent to the hydrogen pinholes.

Example of hydrogen porosity revealed onmachining.

Close-up of hydrogen pinhole revealing innergraphite lining.

Possible causes:• High moisture content in charge or alloy

materials.• Rusty charge materials containing

hydroxide.• Oil and emulsion residues in charge

material.• Low carbon equivalent.• High content of Aluminium or Titanium

(see Elkem TI sheet No. 19).• High moisture content in moulding sand.• Build-up of clay in greensand.• Wet mould or core coatings.• Use of damp refractories or repair linings.• Incorrect proportion of binder

components in cores.• Cores have become old and have picked

up moisture.

Possible cures:• Limit the use of moist or rusty charge

materials and avoid wet alloy materials.• Reduce Al-content below 200 ppm.• Reduce Ti-content and avoid adding Ti-

bearing alloys.• Increase carbon equivalent.• Adjust Mn-content to below 0.4 x %Si

(grey irons only).• Avoid excess use of ferroalloys with high

Al-content.• Use dry launders and ladles.• Increase pouring temperature.• Check mould and core systems for clay

balls or excess moisture in sand.• Ensure proper drying of coatings and

glue.• Improve venting of moulds and cores.






Carbon Monoxide Blowholes in Grey IronSlag related gas porosity in grey iron often occur as rounded or irregular shaped cavitieseither inside the casting or open to the surface. Typically, clusters of slag or dross arefound in conjunction to the cavities. The blowhole itself is a result from gas formation (typi-cally CO gas evolution), from reactions between the slag and the carbon content in theiron.

Example of surface slag blowhole in grey iron. Close-up of defect showing slag cluster.

Possible causes:• Manganese sulphide or oxide separation

aggravated by high sulphur and manga-nese contents and low pouring tempera-ture.

• Improper slag separation.• High sulphur content.• Slag contaminated ladles and improper

draining leaving a cold metal heel in theladle that oxidized, causing Mn-oxideformation.

• High contents of Ca, Al or Ti.

Possible cures:• Use clean ladles and ensure that ladles

are properly drained between fills.• Reduce sulphur content to below 0.12%.• Avoid excessive manganese content,

maximum 0.7%.• Improve slag skimming and removal

procedures.• Increase pouring temperature.• Check gating system and secure that no

slag enters the mould, and avoid turbu-lent filling.

• Use filters in the gating system.






Magnesium Slag Defects in Ductile IronMagnesium containing reaction products from ductile iron treatment is a severe potentialsource for inclusion defects in ductile iron. Slag inclusions are typically found just beneathor at the cope surface as a result of improper separation during liquid metal processing.Magnesium slag defects may also arise from turbulent mold filling, and are often found asdross like stringers in areas of the casting where metal is deadlocked.

Example of magnesium slag inclusions. Example of magnesium dross stringers.

Possible causes:• Inadequate slag separation from

treatment vessel, metal processing andpouring systems.

• Insufficient time between treatment andpouring to let slags separate to thesurface.

• Lack of slag traps or filter in the gatingsystem.

• Low pouring temperature.• High treatment temperature causing the

need for elevated magnesium additions.• Excessive base sulphur content causing

the need for high magnesium additions.• Excess addition of slag forming elements

with alloys, such as Ca and Al.• Turbulent mould filling.

Possible cures:• Improve slag removal practice by the use

of T-pots or proper surface slag skimming.• Extend hold times between treatment and

skimming to allow for proper slag separa-tion.

• Review gating system and avoid highvelocities and turbulence.

• Use filters in the gating system.• Avoid high treatment temperatures and

excess magnesium alloy additions.• Restrict base metal sulphur content.• Avoid using high Ca and Al containing

alloys.• Improve thermal efficiency and minimize

the treatment temperature.






Slag Defects in Grey IronSlag defects in grey iron is typically found in the cope side or dispersed due to turbulentmold filling. Grey iron slag inclusions are typically a result of improper separation of basemetal slag or oxidation of the metal during processing. Defects can also occur as a resultof reactions between metal and mold materials.

Grey iron slag inclusions are typically high in manganese, silicon and iron, and sometimesother slag forming constituents such as Ca and Al from alloy additions can be found. Slaginclusions common also coexist with sand grains from reactions with the mould.

Example of grey iron slag inclusion cluster. Close-up of slag cluster showing various phases.

Possible causes:• Inadequate slag separation from melting

and pouring systems.• Cold metal heels in ladles and receivers.• Lack of slag traps or filters.• Low pouring temperature.• Excess addition of slag forming

materials.• Turbulent mould filling.

Possible cures:• Improve slag removal procedures.• Proper draining of ladles and received to

avoid cold metal heels.• Review gating system and avoid

turbulent mould filling.• Use filters in the gating system.• Increase pouring temperature.• Use an inoculant with low contents of

slag forming elements such as Ca andAl.

• Use inoculants with fast dissolutioncharacteristics and the correct sizing.

• Avoid adding silicon carbide at a latestage of processing.






Internal Shrinkage PorosityShrinkage porosity in grey and ductile irons are typically present as internal cavities ofvarying size and shape- from large isolated holes to more scattered and smaller porosityonly visible under the microscope. Very often a characteristic dendritic sub-structure isrevealed inside the porosities. The defect normally occurs due to contraction in the lastliquid metal to solidify and is thus often associated with heavier sections, changes insection thickness or hot-spots in a complex casting geometry. These same locations arealso prone to release certain gas related porosity and thus it is often difficult to distinguishbetween gas and shrinkage related defects.

Overview of a sample with internal shrinkage. Close-up of typical shrinkage porosity in greyiron.

Possible causes:• Soft moulds or not properly cured binder.• Insufficient clamping or weighing.• Excessive pouring temperature.• Excessive inoculation giving pronounced

graphite expansion early in solidificationand thus mould wall dilatation.

• No inoculation or under-inoculation.• Insufficient or excessive (>3.8%) carbon

content or inadequate carbon equivalent.• Hot spots resulting from poorly designed

gates and risering systems.• Poor casting design causing unnecessary

changes in casting section sizes.• High percentage of steel scrap in charge

or excessive alloying or trace elements.

Possible cures:• Improve mould rigidity.• Clamp or weight the moulds adequately.• Avoid unnecessarily high pouring temperatures.• Avoid over-inoculation.• Adjust carbon content or carbon equivalent.• Provide adequate feed metal by proper gating

and risering. Use solidification simulation ifnecessary.

• Minimise hotspots by improving casting andgating design. Avoid sharp radii.

• Use internal or external chills to avoid hot-spots.• Use inoculant designed to minimise shrinkage

effects.• Reduce concentration of alloying or trace

elements.






In-the-Mould NodularisingThe objective with in-the-mould nodularising processes is to pour untreated base iron intothe mould and do the nodularising treatment inside the mould, thus producing ductile ironcastings in a one-step operation. A reaction chamber containing the nodularising MgFeSialloy is incorporated into the runner system inside the mould. The treatment takes placecontinuously while the iron flows through the reaction chamber before entering the cavitythat forms the casting.

Some important advantages and disadvantages of the in-the-mould ductile iron treatment process:

Process advantages Process disadvantages

• Reduced number of production steps.• Low capital investment.• Low variable cost.• Reduced temperature loss.• High Mg-recovery gives low addition rate of nodulariser alloy.• No treatment fading.• No post inoculation needed.• Late treatment discourages undercooling and carbide formation.• Excellent interfacing with autopouring operations.• No holding of treated iron reduces slag problems in holding and

pouring furnaces.• Easy recovery after downtime.• Minimal environmental impact.• No treatment slag for disposal.

• Reduced space on the pattern.• Reduced casting yield.• Potential formation of dross in the

mould.• Consistent pouring rate required.• Low base sulphur level needed,

max 0.015%.• Possible variation in Magnesium

analyses in different parts of thecasting.

• 100% quality inspection normallyrequired.

Example of typical in-the-mould magnesium treatment process layout.Common design rules are: A = system choke, B = A+10%, C = A+12%, D = E = A+30%.


Calculating size of in-the-mould reaction chamber using Alloy Solution Factor (ASF):

Factor SolutionAlloy Rate Pouring AreaChamber =

Design of reaction chamber, common rules: Factors affecting Alloy Solution Factor:

• Inlet in drag.• Outlet in cope.• Depth of chamber:

Height needed for nodulariser + 25 mm

• % Mg in MgFeSi.• % RE in MgFeSi.• Pouring temperature.• Sulphur level in base iron.• Flow pattern in reaction chamber.

Typical ASF values range from 0.045 kg/cm2sec to 0.060 kg/cm2sec.Typical addition rate of nodularising alloy range from 0.8% to 1.2%.

Reaction chamber area at different ASF values and different pouring rates.

ASF ASF Pouring rate, W / t [kg/sec][lb/in2sec] [kg/cm2sec] 2 4 6 8 10 12 14 16 18 20

1 0.070 28 57 85 114 142 171 199 228 256 2840.95 0.067 30 60 90 120 150 180 210 240 269 2990.9 0.063 32 63 95 126 158 190 221 253 284 3160.85 0.060 33 67 100 134 167 201 234 268 301 3350.8 0.056 36 71 107 142 178 213 249 284 320 3560.75 0.053 38 76 114 152 190 228 266 303 341 3790.7 0.049 41 81 122 163 203 244 284 325 366 4060.65 0.046 44 88 131 175 219 263 306 350 394 4380.6 0.042 47 95 142 190 237 284 332 379 427 4740.55 0.039 52 103 155 207 259 310 362 414 465 5170.5 0.035 57 114 171 228 284 341 398 455 512 5690.45 0.032

Cha

mbe

r Are

a [c

m2 ]

63 126 190 253 316 379 443 506 569 632

Recommended MgFeSi alloys for in-the-mould ductile iron treatment:

LametTM nodulariser Elmag® MF-6113 nodulariserSi 44 – 48% Si 43 – 47%Mg 5.0 – 6.0% Mg 5.75 – 6.5%La 0.25 – 0.4% RE 0.35 – 0.7%Ca 0.4 – 0.6% Ca 0.35 – 0.6%Al 0.8 – 1.2% Al 0.4 – 0.75%

Conventional MgFeSi alloys when used as in-the-mould nodularising agents can haveseveral disadvantages. Promotion of shrinkage porosity and formation of inclusion defectsare known problems. Recommended in-the-mould MgFeSi alloy sizing is 1 – 4 mm.

The use of LametTM nodulariser, which is very low in slag forming elements, is an effectiveway of making clean ductile iron castings. By using pure lanthanum in the alloy in place ofthe traditional rare earth mixture of elements, LametTM nodulariser promotes a lowershrinkage tendency than traditional alloys used for in-the-mould applications. For furtherinformation, please refer to the Elkem LametTM nodulariser brochure.LametTM nodularizer is a trademark and Elmag® nodularizer is a registered trademark owned by Elkem ASA.


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Inoculation of Heavy Section Castings1. GeneralThe important benefits of inoculation are to eliminate the formation of hard, brittle iron car-bides (cementite) in the structure and promote the formation of graphite during eutecticsolidification. In grey irons benefits include improvements in machinability and mechanicalproperties, and also a reduction in the variability of properties caused by differences incasting section. In ductile iron, an increase in the number of graphite nodules produces more uniformstructures over a range of section thicknesses. Such structures promote improved mecha-nical properties, a reduction in the segregation tendency of some alloying or trace ele-ments in the iron and give better machinability.Note that certain base iron conditions, such as the initial sulphur content (grey iron), tem-perature and total “fade” time will affect the selection of a proprietary inoculant. Referenceshould be made to Elkem Technical Information Sheets Nos. 15 and 16 to optimise theselection of an inoculant.

2. Inoculation practices, heavy sectionsInoculants should generally be added to cast iron in at least two of three stages during thecasting procedure:

• To the pouring ladle during filling from the furnace or holder (ladle inoculation)• To the stream of metal as it enters the mould (late-stream inoculation)• Using an inoculant insert placed strategically in the mould runner system.

A two-step inoculation has shown great benefits.As it may be difficult to inoculate in the stream when casting heavy section castings, steptwo in the inoculation system could then be to place an insert of correct size in the mould.For two step inoculation of heavy section castings, it would be preferable to use a bariumcontaining inoculant, such as Barinoc® inoculant in step 1 and an Al-Ca rich insert,Elcast® insert in step 2.

3. Inoculation to the ladleDue to the unavoidable lengths of time involved in handling ladles, it is necessary to addrelatively large amounts of inoculant to offset the fading losses that occur. Addition ratesvary from 0.2% for the majority of grey irons to 0.75% for the most critical ductile irons.The size grading of the inoculant should be based on the ladle size.In order to obtain the highest efficiency from the inoculant, simple addition rules should befollowed:

• Add the inoculant to the stream of metal entering the ladle.• Trickle the inoculant into the metal stream as the ladle is 25% to 75% full.• Ensure that the metal is slag free before tapping into the ladle.• When several transfers of metal between ladles are involved, add the inoculant

during the last transfer before pouring to minimise fade.


4. Inoculation in the mouldWhen late metal stream inoculation is not possible, an insert of cast inoculant should beused in the mould / casting system as the secondary inoculant in order to give the maxi-mum possible inoculation effect.The inserts are made with defined dimensions as cast-to-shape inoculant pieces that maybe added either inside the mould runner system, or in certain cases as an integral part ofthe pouring basin. Optimum performances are obtained by an addition of only 0.05 – 0.15wt%.Reference should also be made to Elkem Technical Information Sheets No 5 and 6.

5. Insert dimensionsAvailable insert dimensions are as follows (mm).

Insert L W H l wD2kg 164 74 76 134 42D5kg 222 100 110 172 52D10kg 266 130 132 220 80D20kg 312 170 166 260 116

6. Inserts placed in pouring basinMedium and large sized mould castings are ino-culated with the Elcast® inserts in the pouringbasin. The pouring basin should have acapacity of at least 20% of the total melted ironrequired and should always be kept full in orderto avoid turbulence or splashing during rapidpouring. The size of the pouring basin is alsoimportant in order to have a successful mouldinoculation. A combination of several insertscan be made when pouring larger castings.

7. Inserts placed in gating system Placing of the inserts in the gating system formedium-sized castings. The inserts are placedin a reaction chamber in the gating systembelow the sprue. The design of the runners istrapezoidal whilst the ingates are rectangular.The distance between the reaction chamberand the first ingate should be at least 120 mm.The dimensions of the reaction chamber are that of the insert, but multiplied by 1.5 for theheight and with a factor of 2 for the other measurements.

8. Dissolution time

Inserts are required to dissolve within a specific time, governed by the pouring time of thecasting and influenced by the temperature of the cast iron. As an example, for a D2kg thedissolution time will be 40 s at a temperature of 1370 ± 40 °C.


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Characterisation of Molybdenum Containing Phases in SiMo Ductile Iron

In SiMo ductile iron most specifications and standards typically allow for a maximum of 10% pearlite in the structure. Visual and automatic image analysis of the structure often indicates a pearlite content in the range of 10 to 15% although all process control measures have been taken in order to keep the pearlite content at a minimum. Closer investigation of the grain boundary area in SiMo reveals that several phases in addition to pearlite and Mo-carbides can be found and that the true pearlite content of SiMo ductile iron is in most cases significantly lower than initially measured or observed under low magnification.

An SAE paper describes “The presence of a precipitate phase identified as Fe2MoC-typephase in Si-Mo iron may offer an inherent microstructure advantage with respect to dimensional stability at elevated temperatures relative to alternative ductile iron materials containing a pearlitic microstructure” 1

Typical structure in SiMo ductile iron. Overview of the grain boundary area displaying different phases. (Backscatter Image)

Overview of the grain boundary area indicating where EDX analysis was conducted.


Spectrum Si Mn Fe Mo Phase

3.5 1.1 86.7 8.7 Fe – Mo (-Si)

Inter-metallic phase of Fe and Mo and most likely also Si. Dominating phase probably accounting for 50% of the

“pearlite” content.

4.1 0.6 94.1 1.2 Mo-rich ferrite

Iron with 4% silicon and 1,2 % molybdenum. The higher Mo-content

is most likely due to the close proximity to Mo-rich phases causing an enrichment of Mo in the ferrite.

0.6 0.9 20.2 78.3 Mo-carbide

Classical Mo-carbide found along the grain boundary. This phase is hard to detect using an optical microscope, but clearly visible in the scanning

electron microscope. Mo-content in the carbide is around 80%.

4.3 0.9 93.1 1.7 Mo-pearlite

Classical pearlite appearance with a Mo-content of around 1,7% due to either an elevated Mo level in the

ferrite part of the pearlite or in the iron carbide part.

4.3 0.4 94.6 0.7 Ferrite

Ferrite phase further away from the grain boundary showing a

composition in line with the expectedchemistry in SiMo ductile iron with 4%

Si and 0,7% Mo.

1. Brent Black et al, Microstructure and Dimensional Stability in Si-Mo Ductile Irons for Elevated Temperature Applications

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