evolution of stainless_steel-m s rahman

8/3/2019 Evolution of Stainless_steel-M S Rahman

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Technical Note-1Date: 20 Jan 2011

o As molten iron cools down it crystallizes at 1538 °C into its δ allotrope, which has a body-

centered cubic (BCC) crystal structure.o Its crystal structure changes to face-centered cubic (FCC) at 1394 °C, when it is known as γ-

iron, or austenite, as it cools further.o At 912 °C the crystal structure again becomes BCC as α-iron, or ferrite, is formed.

o At 770 °C (the Curie point, Tc) the iron becomes magnetic.

2.0 STEELSSteel: Steel is an alloy of iron, contains up to ~ 2.1% (by weight) of carbon, as a hardening agent.

Besides carbon, there are other elements that form part of steel alloys.

Carbon Steel or Plain Carbon Steel: Carbon steel, (also called plain-carbon steel), is steel wherethe main alloying element is carbon. It constitutes about 90% of structural works [1]. Accordingto AISI (American Iron and Steel Institute) Steel is considered to be carbon steel when nominimum content is specified or required for chromium, cobalt, columbium, molybdenum, nickel,titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desiredalloying effect.

Low Carbon Steels: Contains up to 0.30 percent of Carbon by weight with a Manganese content of

0.40. The largest category of this class of steel is flat-rolled products (sheet or strip) usually inthe cold-rolled and annealed condition.

Medium Carbon Steels: Contains from 0.30 to 0.60 percent of Carbon by weight with a Manganesecontent of 0.60 to 1.65.

High Carbon Steels: Contains from 0.60 to 1.00 percent of Carbon by weight with a Manganesecontent of 0.30 to 0.90.

Cast Iron: Alloys with carbon content higher than 2.1 % are known as cast iron because of their lower melting point and castability.

Wrought Iron: Iron alloy with very low carbon content and has fibrous inclusions known as slag.Wrought iron is tough, malleable, ductile and easily weldable.

2 of 11 M S RAHMAN(M Sc In Welding Engineering)

FIG 2: PART OF IRON-CARBON DIAGRAM

http://maps.thefullwiki.org/Ferrite_(iron)

http://maps.thefullwiki.org/Curie_point

http://maps.thefullwiki.org/Magnetic

http://en.wikipedia.org/wiki/Alloy




http://en.wikipedia.org/wiki/Carbon


http://en.wikipedia.org/wiki/Cast_iron

http://en.wikipedia.org/wiki/Welding

http://maps.thefullwiki.org/Ferrite_(iron)

http://maps.thefullwiki.org/Curie_point

http://maps.thefullwiki.org/Magnetic




http://en.wikipedia.org/wiki/Cast_iron

http://en.wikipedia.org/wiki/Welding




Alloy Steels: Steel is considered to be alloy steel when that exceeds one or more of theseelements: ≥ 1.65% Mn, 0.60% Si, or 0.60% Cu [5]. The total carbon content is up to 1% and thetotal alloying elements content is below 5%. A material is also an alloy steel if a definiteconcentration of alloying elements, such as Ni, Cr, Mo, Ti, etc. is specified, or any other elementadded to obtain an alloying effect. Technically, then, tool and stainless steels are alloy steels.

Stainless Steels: It is a family of corrosion resistant steel of wide variety, with Iron, Carbon,Chromium and Nickel are the primary alloying element. Technically, these are known as stain-resistant steels.

The stainless properties of stainless steels are primarily due to the presence of chromium (Cr) inquantities roughly greater than 12% (by weight). This level of Cr is the minimum level of Cr toensure a continuous stable layer of protective chromium rich oxide films on the surface.

Upon solidification, stainless steel develops a continuous-strong oxide film to protect the steel from theenvironment.

The ability to form chromium oxide in the weld region must be maintained to ensure stainless propertiesof the weld region after welding.

Due to any reason, if the base metal or weld metal contains Cr less than 12% (by weight), the finishedcomponent will rust at normal or ambient temperature.

o In addition to the primary alloying elements, stainless steels are alloyed with some other alloying elements to control microstructure or enhance welding properties by changingthe changing the chromium or nickel equivalents.

3.0 STAINLESS STEEL CLASSIFICATIONS

Stainless steels are generally classified by their microstructures and are identified as ferritic,martensitic, austenitic, or duplex (austenitic and ferritic). The microstructure significantly affectsthe weld properties and the choice of welding procedure used for these stainless steel alloys. Inaddition, a number of precipitation-hardenable (PH) stainless steels exist. Precipitation-hardenable stainless steels have martensitic or austenitic microstructures.

4.0 AUSTENITIC STAINLESS STEEL (THE WORKHORSE)


STAINLESS STEEL –Iron based alloy

containing 12% or more Cr

200 & 300SERIES

400 SERIES

400 & 500SERIES [3]

600 SERIES

2000 & 3000

SERIES [3]

AUSTENITIC

FERRITIC

MARTENSITIC

DUPLEX

(AUSTENITIC +FERRICTIC)

PRECIPITATION

HARDENABLE(PH)




Austenitic Stainless Steel: These steels remain in austenite form (FCC) at normal roomtemperature because of the presence of certain alloying elements, such as manganese, nickel,chromium.

o AISI 200 (chrome-manganese) or 300 (chrome-nickel) series (UNS S20000 or S30000

series)Crystal structures are similar to copper or aluminumNon-magnetic in annealed condition, but may become mildly magnetic after cold work.Not hardenable by heat treatment, but readily strengthen by cold work.Generally require no pre- or post-weld heat treatmentMechanical and physical properties are more similar to those of brass than of plain carbon steel.Fairly weldable by conventional arc welding process.List of common austenitic stainless steels and typical applications [2]:

Sl No Grade UNS No. Typical Applications

1.0 201 S20100 Lower cost, reduced nickel version of Grade 301

2.0 202 S20200 Lower cost, reduced nickel version of Grade 301

3.0 301 S30100 General purpose steel with good corrosion resistance for mostapplications. Employed where its high work-hardening exponent isdesirable. Can be supplied cold worked to give high strength andductility. Used for structural applications such as rail carriages and

wagons4.0 302 S30200 General purpose steel with good corrosion resistance for most

applications. Previously used architecture, food processing,domestic sinks and tubs. Mostly replaced by 304.

5.0 303 S30300 Free machining steel used where extensive machining is required.Corrosion resistance and weldability are inferior to 302.

6.0 304 S30400 Similar corrosion resistance to 302 and now generally replaces 302.Used where higher resistance to weld decay is needed, e.g., inbrewing, etc.

7.0 304L S30403 Lower carbon content version of 304. Used in chemical plant andfood processing industry where freedom from sensitization isrequired.

8.0 305 S30500 Spun sheet parts, cold headed screws.

9.0 253MA S30815 High temperature applications to 1150ºC. Excellent resistance to

scaling, and having high temperature strength.10.0 309 S30900 High temperature oxidation resistant. Furnace parts.

11.0 310 S31000 Furnace parts and equipment. Resistant to temperature 900ºCto1100ºC

12.0 316 S31600 Used where higher corrosion (pitting) resistance is required, i.e.,marine equipment, chemical industry equipment.

13.0 316L S31603 A low carbon modification of 316 where heavy section weldmentsare required without the risk of intergranular corrosion.

14.0 317 S31700 For chemical plant, where a greater corrosion resistance than 316 isrequired, e.g., in contact with brines and halogen salts. More usuallyavailable in the low carbon ‘L’ grade.

15.0 321 S32100 Heavy weldments in chemical and other industries. Suitable for heatresisting applications to 800ºC.

16.0 904L N08904 High resistance to general corrosion in e.g., sulphuric and aceticacids, crevice corrosion, stress corrosion cracking, pitting in chloride

bearing solutions. Good weldability.





Evolution of most widely used Austenitic Stainless Steel Grades:


30923Cr, 13.5Ni,

0.15C

High Cr for high

temp oxidation resistance

31025Cr, 20Ni,

0.12C

S3081521Cr, 11Ni,

1.8Si, 0.16N,0.05Ce

Higher Si, N, Ce for scaling resistance,

creep strength &stable microstructure

31719Cr, 13Ni,

3.25Mo,

0.07C

Higher Mo for greater

pitting resistance

31617Cr, 12Ni,

2.25Mo,0.06C

Mo added for

pitting resistance

316L17Cr, 12Ni,

2.25Mo,0.03C

Low C (upto0.03% for

resistance toSensitization

30518Cr, 12Ni,

0.08C

Higher Ni for lower work

hardening rate

30418.5Cr, 9Ni,

0.06C

Lower C for

improved weldability

304L18.5Cr, 9.5Ni,

0.03C

32118Cr, 10Ni,0.5Ti, 0.06C

Ti added for stabilizing

and for heat resistingapplication

30318Cr, 9Ni,

0.12C, 0.25SAdded S for

free machining

Lower cost

replacement for 302

20218Cr, 5Ni,

9Mn, 0.15N,0.12C

30219Cr, 9Ni

0.08C

Basic Alloy for Austenitic SS

30117Cr, 7Ni,

0.08C

Lower Cr, Ni for

higher workhardening rate

20117Cr, 4.5Ni,

6.5Mn, 0.15N,0.12C

Lower cost

replacement for 301




5.0 FERRITIC STAINLESS STEEL

Ferritic Stainless Steel: These steels remain in ferrite form with body centered cubic (BCC)structure at normal room temperature.

o AISI 400 series (UNS S40000 series)

BCC crystal structures, are similar to mild steelMagnetic at room temperature.Not hardenable by heat treatment.Fairly weldable in thin sheet form, but not suitable for heavy welds requiring large heat inputs, or

multiple pass welding, due to susceptibility to grain growth in the weld zone.List of common ferritic stainless steels and typical applications [2]:


1.0 405 S40500 Welded fabrications for mildly corrosive environments and in heatresistant applications.

2.0 409 S40900 Heat resistant steel, easily formed and welded. Mainly used for automotive exhausts or welded applications where superior performance to galvanized steel is required.

3.0 410S S41008 Used for heat resistant applications up to 650ºC in power plant and

oil refineries, where high strength at elevated temperatures in notrequired.

4.0 430 S43000 Interior architectural component, stove and automotive trim. Weldstend to be brittle.

5.0 444 S44400 Heat exchanger and hot water tanks, and in chloride containingwaters. Not prone to chloride stress corrosion – superior resistanceto pitting, crevice and intergranular corrosion. Possesses excellentdeep drawing properties.

6.0 446 S44600 Used for severe heat resistant applications up to 1200ºC. Inrecuperators, highly resistant to sulphidation and oil ash corrosion

7.0 182 S18200 Free machining bar variant of 444. Superior machinability to 303

Evolution of commonly used Ferritic Stainless Steel Grades:


44418.5Cr, 2Mo,0.02C, Ti (Nb)

40911.5Cr,

0.06C, Ti

410S12.5Cr, 0.06C

Lower Cr for

utility applicationsresistance

40513Cr, 0.06C,

Al

Lower Cr alloy more

weldable than 410S

43017Cr, 0.08C

Basic Alloy for Ferritic SS

Higher Cr, Mo for increased

general and pitting resistance

Lower Cr, lower corrosion

resistance, stabilized for improved weldability




6.0 MARTENSITIC STAINLESS STEEL

Mertensitic Stainless Steel: These steels remain in body centered cubic (BCC) structure atnormal room temperature.

o AISI 400 & 500 series (UNS S40000 & S50000series)

BCC crystal structures, are similar to mild steelMagnetic at room temperature.Hardenable by heat treatment.Difficult to weld due to their susceptibility to hardening in the weld zone.Pre- and post-heating is required.List of common ferritic stainless steels and typical application [2]:


1.0 410 S41000 General purpose grade for use in mildly corrosive environments

2.0 403 S40300 Capable of attaining higher hardness than 410

3.0 416 S41600 Free machining variation of 410

4.0 420 S42000 General engineering uses, such as pump and valve shafts

5.0 420C --- Developed for high hardness after heat treatment. Used for

cutting tools, surgical knives, etc.6.0 431 S43100 Hardenable steel with corrosion resistance approaching302.

Used for pump shafts etc. Should be double tempered after hardening.

7.0 440C S44004 Capable of being hardened to 60 HRC. Hager hardness andabrasion resistance of all the stainless steels. Corrosionresistance similar to 410.

Evolution of commonly used Mertensitic Stainless Steel Grades:


43116Cr, 2Ni,

0.18C

41612.5Cr, 0.1C,

0.2S

40313Cr, 0.15C

Capable of attaining

higher hardness than 410

41012Cr, 0.1C

Basic Alloy for Mertensitic SS

Added Cr for increased

corrosion resistance

Added S

for free machining

42012.5Cr, 0.25C

420C12.5Cr, 0.3C

440C17Cr, 1.1C,

0.4Mo

Higher C for

higher strengthor hardness

Mo added withhigher Cr and C for

High hardness andabrasion resistance




7.0 DUPLEX STAINLESS STEEL

Duplex Stainless Steel: These steels are alloys of iron with higher chromium and lower nickel thanthe austenitic alloys and having two phase microstructure ferrite and austenite:

o UNS S20000 & S30000 series

Two phase microstructure, typically with 45 to 65 % ferrite and 55 to 35 % austenite.Magnetic at room temperature.Have weldability similar to austenitic stainless steel with controlled heat input to the desired

microstructure.o Stronger and more resistant to corrosion cracking and pitting corrosion

List of common duplex and super duplex stainless steel [2][4]:

Sl No Grade UNS No. Typical Application

1.0 329 (First Generation) S32900 Shafting for pumps, boats. Superior corrosionresistance and strength to 316L, poor weldability.

2.0 3RE60*** (FirstGeneration)

S31500 Superior corrosion resistance to 316L, highresistance to stress corrosion. General fabrication inchemical industry equipment. Suitable for welding in

heavy sections without risk of intergranular corrosion

3.0 Uranus50 (FirstGeneration)

S32404

4.0 2304 (SecondGeneration)

S32304 Similar corrosion resistance to 316L. Highresistance to stress corrosion and erosion, highyield strength. Used where high corrosion resistanceis required, i.e., marine, mining, chemical, food,metallurgy and power industries.


S31803 Superior corrosion resistance to 317L. Excellentstress corrosion resistance. Typically used in heatexchangers, scrubbers, calorifiers, fans, in chemicalprocess tanks, oil and gas and refining industrieswhere outstanding corrosion resistance is required.

Suitable for welding heavy sections without risk of intergranular corrosion.


S32205

7.0 DP-3 (SecondGeneration)

S31260

8.0 UR52N+ (SecondGeneration)

S32520

9.0 Ferralium 255 (SecondGeneration)

S32550

10.0 2507(SecondGeneration)

S32750

11.0 Zeron 100 (SecondGeneration)

S32760





Evolution of Duplex Stainless Steel Grades:

Plain Carbon Steel is ferritic – body centered cubic structure with little or no nickel content. Thecrystallographic structure changes from body centered cubic (BCC) to face centered cubic(FCC) by adding nickel (at least 8% by weight is required to change majority of themicrostructures). With intermediate nickel contents (equal to or below 8%), the microstructurewill contain some grains with ferritic and some grains austenitic, resulting in two phase structure.Further addition of nickel, the ferritic structure will turn to austenitic structure (Fig 3).


FIG 3: EVOLUTION OF DUPLEX TO AUSTENITIC STAINLESS STEEL [4].

[Increasing the Nickel content changes the microstructure of stainless steelfrom ferritic (left) to duplex (middle) to austenitic (right)]

UNSS31500

18Cr, 4.9Ni,2.7Mo, 0.03C,

0.07N

32926Cr, 5Ni,

1.5Mo, 0.06C

Basic Alloy for Duplex SS

Duplex structure impartshigh strength and

resistance to stresscorrosion cracking

Lower C and added N

for improved weldability

UNSS31803

22Cr, 5.5Ni,

3Mo, 0.03C,0.14N

Improved general andlocalized corrosion

resistance over 316L

UNSS3230423Cr, 4Ni,

0.03C, 0.1N

Higher Cr and Mo for greater general

corrosion and pitting

resistance than 317L

Higher Cr, without Mofor general corrosion

resistance




8.0 PRECIPITATION HARDENABLE STAINLESS STEEL

Precipitation Hardening (PH) Stainless Steels are iron, chromium and nickel alloys with other additions such as Cu, Al, Nb, Mo or Ti and derive their properties from solid-solutionstrengthening, strain hardening, age hardening and martensitic reaction. They provide anoptimum combination of the properties of martensitic and austenitic grades.

o Like martensitic grades, PH stainless steels are known for their ability to gain high

strength through heat treatment plus they possess the corrosion resistance of austeniticstainless steels. The high tensile strength of PH stainless steels come after a heattreatment process that leads to precipitation hardening of a martensitic or austeniticmatrix. Hardening is achieved through the addition of one or more of the elementscopper, aluminum, titanium, niobium, and molybdenum.

Evolution of Precipitation Hardening Stainless Steel Grades:

The steel is first heated and quenched to permit austenite to transform to martensite. Reheatingpermits precipitates such as Ni3Al to form from the martensite.

o AISI 600 series

Martensitic, Semi-austenitic and austeniticMartensitic and semi-austenitic are readily weldable. Precautions are required to prevent liquation crack

for austenitic gradesList of common ferritic stainless steel [2]:

Sl No UNS No. Name

1.0 S17600 StainlessW

2.0 S17400 17-4PH

3.0 S45000 Custom 450 (xM-25)

4.0 S13800 PH 13-8 Mo (xM-13)

Semi Austenitic

5.0 S17700 17-7PH6.0 S15700 PH 15-7 Mo

7.0 S3500 AM-350

Austenitic

8.0 --- 17-10P

9.0 S66286 A286

9.0 MARKET SHARE OF MOST WIDELY USED STAINLESS STEELS World Stainless Steel demand has been increased beyond the common trend in the last couple of

years. In the world stainless steel market, four grades,304, 430, 409 and 316 account for 80% of the total tonnage used.


Grades % of Market [3]

1.0 2XX 9

2.0 304 53

3.0 430 13

4.0 409 12

5.0 316 7

Total 94

2XX is the entire seriesSource: International Stainless Steel Federation (ISSF)




REFERENCES:

[1] Metallurgy of Welding, 6th Edition, J.F. Lancaster, Abington Publishing, 1999, Page 289.[2] Welding Technology Institute of Australia (WTIA) TN 13-00, Stainless Steels For Corrosive

Environments, 1998 Edition, Page 4[3] marketfriendly, inc. – [email protected][4] Practical Guidelines For The Fabrication Of Duplex Stainless Steels, by Marketing Resources

Inc. of Pittsburgh, Pennsylvania, USA. (www.tmrstainless.com), Consultants to IMOA


mailto:[email protected]



evolution of stainless_steel-m s rahman

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