the schaeffler

8/6/2019 The Schaeffler

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The Schaeffler-de-Long Diagram for estimating weldabilityThe Schaeffler-de-Long diagram

An aid in determining which structural constituents can occur in a weld metal is the

Schaeffler-de-Long diagram. With knowledge of the properties of different phases, it

is possible to judge the extent to which they affect the service life of the weld. The

diagram can be used for rough estimates of the weldability of different steel grades

as well as when welding dissimilar steels to each other.

Click for large Schaeffler-de-Long diagram

Weldability of Martensitic Steels

The quantity of martensite and its hardness are the main causes of the

weldability problems encountered with these steels. The fully martensitic

steels are air hardening. The steels are therefore very susceptible to hydrogen

embrittlement.

By welding at an elevated temperature (= the steel's Ms temperature), the HAZ can

be kept austenitic and tough throughout the welding process. After cooling, the

formed martensite must always be tempered at about 650-850 C, preferably as a

concluding heat treatment. However, the weld must first have been allowed to cool to

below about 150 C.

Martensitic-austenitic steels, such as 13Cr/6Ni and 16Cr/5Ni/2Mo, can often be

welded without preheating and without post-weld annealing. Steels of the 13Cr/4Ni

type with low austenite content must, however, be preheated to a working

temperature of about 100 C.

If optimal strength properties are desired, they can be heat treated at 600 C after

welding. The steels are welded with matching or austenitic filler metals.

Weldability of Ferritic Steels

These steels are generally more difficult to weld than austenitic steels. This is

the main reason they are not used to the same extent as austenitic steels.
http://www.avestapolarit.com/upload/steel_properties/Schaeffler_large.jpg


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The older types, such as AISI 430, had greatly

reduced ductility in the weld. This was mainly

due to strong grain growth in the heat-affected

zone (HAZ), but also due to precipitation of

martensite in the HAZ. They were also

susceptible to intergranular corrosion after

welding. These steels are therefore often welded

with preheating and post-weld annealing.

Today's ferritic steels of type S44400 and

S44635 have considerably better weldability due to low carbon and nitrogen contents

and stabilisation with titanium/niobium. However, there is always a risk of

unfavourable grain enlargement if they are not welded under controlled conditions

using a low heat input. They do not normally have to be annealed after welding.

Weldability of Ferritic-Austenitic Steels

Today's ferritic-austenitic steels have considerably better weldability than

earlier grades. They can be welded more or less as common austenitic steels.

Besides being susceptible to intergranular

corrosion, the old steels were also susceptible

to ferrite grain growth in the heat affected

zone (HAZ) and poor ferrite to austenite

transformation, resulting in reduced ductility.

Today's steels, which have higher nickel

content and are alloyed with nitrogen, exhibit

austenite transformation in the HAZ that is sufficient in most cases. However,

extremely rapid cooling after welding, for example in a tack or in a strike mark, can

lead to unfavorably high ferrite content. Extremely high heat input can also lead to

heavy ferrite grain growth in the HAZ.

When welding UNS S31803 (AvestaPolarit 2205) in a conventional way (0.6-2.0

kJ/mm) and using filler metals at the same time, a satisfactory ferrite-austenite

balance can be obtained. For the super duplex stainless steel (AvestaPolarit SAF

2507) a somewhat different heat input is recommended (0.2-1.5 kJ/mm). The reason

for lowering the minimum value is that this steel has much higher nitrogen content

than 2205. The nitrogen favours a fast reformation of austenite, which is important

when welding with a low heat input. The maximum level is lowered in order to

A typical macroscopic

image of a weld bead.

These steels are welded

with matching or austenitic

super-alloyed filler metal

(such as AvestaPolarit P 5).


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minimize the risk of secondary phases.

The steels are welded with ferritic-austenitic or austenitic filler metals. Welding

without filler metal is not recommended without subsequent quench annealing.

Nitrogen affects not only the microstructure, but also the weld pool penetration.

Increased nitrogen content reduces the penetration into the parent metal. To avoid

porosity in TIG welding it is recommended to produce thin beads. To achieve the

highest possible pitting corrosion resistance at the root side in ordinary 2205 weld

metals, the root gas should be Ar+ N2 or Ar+ N2 + H2. The use of H2 in the shielding

gas is not recommended when welding super duplex steels. When welding 2205 with

plasma, a shielding gas containing Ar+5% H2 is sometimes used in combination with

filler metal and followed by quench annealing.

Weldability of Austenitic SteelsThe steels of type ASTM 304, 316, 304L, and 316L have very good weldability.

The old problem of intergranular corrosion after welding is very seldom

encountered today. The steels suitable for wet corrosion either have carbon

contents below 0.05% or are niobium or titanium stabilised.

They are also very unsusceptible to

hot cracking, mainly because they

solidify with a high ferrite content. The

higher-alloy steels such as 310S and

N08904 solidify with a fully austenitic

structure when welded. They should

therefore be welded using a controlled

heat input. Steel and weld metal with

high chromium and molybdenum

contents may undergo precipitation of

brittle sigma phase in their

microstructure if they are exposed to

high temperatures for a certain length of time. The transformation from ferrite to

sigma or directly from austenite to sigma proceeds most rapidly within thetemperature range 750-850 C. Welding with a high heat input leads to slow cooling,

especially in light-gauge welds. The weld's holding time between 750-850 C then

increases, and along with it the risk of sigma phase formation.

Weldability of Martensitic Steels

The quantity of martensite and its hardness are the main causes of the


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weldability problems encountered with these steels. The fully martensitic

steels are air hardening. The steels are therefore very susceptible to hydrogen

embrittlement.

By welding at an elevated temperature (= the steel's Ms temperature), the HAZ can

be kept austenitic and tough throughout the welding process. After cooling, theformed martensite must always be tempered at about 650-850 C, preferably as a

concluding heat treatment. However, the weld must first have been allowed to cool to

below about 150 C.

Martensitic-austenitic steels, such as 13Cr/6Ni and 16Cr/5Ni/2Mo, can often be

welded without preheating and without post-weld annealing. Steels of the 13Cr/4Ni

type with low austenite content must, however, be preheated to a working

temperature of about 100 C.

If optimal strength properties are desired, they can be heat treated at 600 C after

welding. The steels are welded with matching or austenitic filler metals.

Austenitic Stainless Steels

This type of stainless steel is dominant in the market. The group includes the

very common AISI 304 and AISI 316 steels, but also the higher-alloy AISI

310S and ASTM N08904.

Austenitic steels are characterized by their

high content of austenite-formers, especially

nickel. They are also alloyed with chromium,

molybdenum and sometimes with copper,

titanium, niobium and nitrogen. Alloying with

nitrogen raises the yield strength of the

steels.

Austenitic stainless steels have a very wide

range of applications, e.g. in the chemical

industry and the food processing industry.

The molybdenum-free steels also have very good high-temperature properties and

are therefore used in furnaces and heat exchangers. Their good impact strength at

low temperatures is often exploited in apparatus such as vessels for cryogenic liquids.

Austenitic steels cannot be hardened by heat treatment. They are normally supplied

in the quench-annealed state, which means that they are soft and highly formable.

The image shows the microstructure of an

austenitic stainless steel, type ASTM 304L.


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Cold working increases their hardness and strength. Certain steel grades are

therefore supplied in the cold stretched or hard rolled condition.

Martensitic Stainless Steels

Martensitic steels have the highest strength but also the lowest corrosion

resistance of the stainless steels.

Martensitic steels with high carbon

contents are used for tool steels.

Due to their high strength in

combination with some corrosion

resistance, martensitic steels are

suitable for applications where thematerial is subjected to both corrosion

and wear. An example is in

hydroelectric turbines.

Mechanical Properties of Martensitic SteelsRoom Temperature

Martensitic and ferritic-martensitic steels are characterised by their high strength and

the fact that the strength is strongly affected by heat treatment.

Martensitic steels are usually used in a hardened and tempered condition. In this

condition the strength of the steels increases with the carbon content.

The ductility of martensitic steels is relatively low. Ferritic-martensitic steels have a

high strength in the hardened and tempered condition in spite of their relatively low

carbon contents, and good ductility. They also possess excellent hardenability: even

thick sections can be fully hardened and these steels will thus retain their good

mechanical properties even in applications where thick sections are used.

Elevated Temperatures

Martensitic and martensitic-austenitic steels in the hardened and tempered condition

exhibit high strength at moderately elevated temperatures. However, the useful

upper service temperature is limited by the risk of over-tempering and embrittlement.

The creep strength is low and this type of stainless steel is normally not used above

Microstructure image of a

martensitic stainless steel


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300 C. However, certain martensitic grades are used at higher temperatures. The

wide range of elevated temperature strength is due to the wide range of strength

levels offered by different grades and heat treatments.

Mechanical Properties of Ferritic-Austenitic SteelsRoom Temperature

Ferritic-austenitic steels have a high yield stress which increases with

increasing carbon and nitrogen levels. Increased ferrite content will, within

limits, also increase the strength of duplex steels.

Their ductility is good and they exhibit strong work hardening.


Ferritic-austenitic steels have a high yield stress which increases with

increasing carbon and nitrogen levels. Increased ferrite content will, within

limits, also increase the strength of duplex steels.

Their ductility is good and they exhibit strong work hardening.

Mechanical Properties of Ferritic SteelsRoom Temperature

Ferritic steels have relatively low yield strength and the work hardening of thesesteels is limited. Their strength increases with increasing carbon content, but the

effect of chromium on strength is negligible. However, ductility is lower in steels with

high chromium content and for optimum ductility, the levels of carbon and nitrogen

must be kept to a minimum.


Ferritic steels have relatively high strength up to 500 C. The creep strength, which is

usually the determining factor at temperatures above 500 C, is low. The normal

upper service temperature limit is set by the risk of embrittlement at temperaturesabove 350 C. However, due to the good resistance of chromium steels to high

temperature sulphidation and oxidation, a few high chromium-alloyed grades are

used at higher temperatures.

Mechanical Properties of Austenitic SteelsRoom Temperature


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Austenitic steels generally have a relatively low yield stress and are characterised by

strong work hardening. The strength of austenitic steels increases with increasing

levels of carbon, nitrogen and, to a certain extent, also molybdenum. Austenitic steels

exhibit very high ductility and toughness.


Most austenitic steels have lower strength than other types of stainless steels

when used at temperatures up to about 500 C.

The highest elevated temperature strength among austenitic steels is

exhibited by nitrogen-alloyed steels and those containing titanium or

niobium.

A few high alloyed and nitrogen alloyed austenitic steels have elevated

temperature strengths that are almost as high as those of duplex steels.

In terms of creep strength austenitic stainless steels are superior to all other

types of stainless steel.

Toughness of Stainless Steels

The toughness of the different types of stainless steels shows considerable

variation, ranging from excellent toughness at all temperatures for austenitic

steels to the relatively brittle behaviour of martensitic steels. Toughness is

dependent on temperature and generally improves with increasing

temperatures.


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One measure of toughness is

the impact toughness, i.e. the

toughness measured on rapid

loading. The figure shows

categories of stainless steel at

temperatures from -200C to +

100C.

It is apparent from the diagram

that there is a fundamental

difference at low temperatures

between austenitic steels on

the one hand and martensitic,

ferritic and ferritic-austeniticsteels on the other.

Martensitic, ferritic and ferritic-austenitic steels are characterised by a transition in

toughness, from tough to brittle behaviour, at a certain temperature, the transition

temperature.

For ferritic steel the transition temperature increases with increasing carbon and

nitrogen content, i.e. the steel becomes brittle at successively higher temperatures.

For ferritic-austenitic steels, an increased ferrite content gives a higher transition

temperature, i.e. more brittle behaviour.

Martensitic stainless steels have transition temperatures around or slightly below

room temperature, while those for ferritic and ferritic-austenitic steels are in the

range 0 to - 50C, with ferritic steels in the upper part of this range.

Austenitic steels do not exhibit a toughness transition as do the other steel types, but

have excellent toughness at all temperatures, although the toughness decreases

slightly with decreasing temperature.

Corrosion Resistance of Austenitic Steels

Wet Corrosion

These steels are mainly used in wet environments. With increasing chromium and

molybdenum contents, the steels become increasingly resistant to aggressive

solutions. The higher nickel content reduces the risk of stress corrosion cracking.

The figure shows categories of stainless steel at

temperatures from -200C to + 100C


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Austenitic steels are more or less resistant to general corrosion, crevice corrosion and

pitting, depending on the quantity of alloying elements. Resistance to pitting and

crevice corrosion is very important if the steel is to be used in chloride-containing

environments.

Resistance to pitting and crevice corrosion increases with increasing contents of

chromium, molybdenum and nitrogen.

The rich chloride content of seawater makes it a particularly harsh environment,

which can attack stainless steel by causing pitting and crevice corrosion. However,

two stainless steel grades designed to cope with this environment have been

developed by AvestaPolarit - 254 SMO and 654 SMO.

254 SMO has a long record of successful installations for seawater handling within

offshore, desalination, and coastal located process industries.

Some crevice corrosion has still been reported and for more severe situations, i.e.

severe crevice geometries and elevated temperatures, the natural selection should be

654 SMO.

High Temperature Corrosion

Most molybdenum-free steels can be used at high temperatures in contact with hot

gases.

An adhesive oxide layer then forms on the surface of the steel. It is important that

the oxide is impervious so that further oxidation is prevented and the oxide film

adheres tightly to the steel.

At very high temperatures, the oxide begins to loosen (scaling temperature). This

temperature increases with increasing chromium content.

A common high-temperature steel is 310S. Another steel that has proved to be very

good at high temperatures is AvestaPolarit 253 MA. Due to a balanced composition

and the addition of cerium, among other elements, the steel can be used at

temperatures of up to 1150-1200 C in air.

Corrosion Resistance of Ferritic Steels

Wet Corrosion


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The modern molybdenum-alloyed ferritic steels have largely the same corrosion

resistance as AISI 316 but are superior to most austenitic steels in terms of their

resistance to stress corrosion cracking. A typical application example for these steels

is hot-water heaters.

For chlorine-containing environments, where there is a particular risk of pitting, for

instance in seawater, the high-alloy steel S44635 (25Cr 4Ni 4Mo) can be used.


Ferritic steels with high chromium contents have good high-temperature properties.

As mentioned previously, the steels readily form a brittle sigma phase within the

temperature range 550-950 C, but this is of minor importance as long as the

product, such as a furnace, operates at its service temperature.

AISI446 with 27% chromium has a scaling temperature in air of about 1070 C.

Corrosion Resistance of Austenitic Steels

Wet Corrosion

These steels are mainly used in wet environments. With increasing chromium and

molybdenum contents, the steels become increasingly resistant to aggressive

solutions. The higher nickel content reduces the risk of stress corrosion cracking.

Austenitic steels are more or less resistant to general corrosion, crevice corrosion and

pitting, depending on the quantity of alloying elements. Resistance to pitting and

crevice corrosion is very important if the steel is to be used in chloride-containing

environments.

Resistance to pitting and crevice corrosion increases with increasing contents of

chromium, molybdenum and nitrogen.

The rich chloride content of seawater makes it a particularly harsh environment,

which can attack stainless steel by causing pitting and crevice corrosion. However,

two stainless steel grades designed to cope with this environment have been

developed by AvestaPolarit - 254 SMO and 654 SMO.

254 SMO has a long record of successful installations for seawater handling within

offshore, desalination, and coastal located process industries.


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Some crevice corrosion has still been reported and for more severe situations, i.e.

severe crevice geometries and elevated temperatures, the natural selection should be

654 SMO.


Most molybdenum-free steels can be used at high temperatures in contact with hot

gases.

An adhesive oxide layer then forms on the surface of the steel. It is important that

the oxide is impervious so that further oxidation is prevented and the oxide film

adheres tightly to the steel.

At very high temperatures, the oxide begins to loosen (scaling temperature). This

temperature increases with increasing chromium content.

A common high-temperature steel is 310S. Another steel that has proved to be very

good at high temperatures is AvestaPolarit 253 MA. Due to a balanced composition

and the addition of cerium, among other elements, the steel can be used at

temperatures of up to 1150-1200 C in air.

Considerable Work-Hardening

Work-hardening means that the hardness increases considerably as the

material is deformed, e.g. during the process of producing chips.

It also means that, after a

first pass, the machined

surface has become harder,

changing the working

conditions for the cutting

edge during subsequent

posses, as the edge then

has to work in a hard

surface layer.

Austenitic and ferritic-

austenitic steels have the

greatest tendency to work-

harden, which results in both high cutting forces and a high hardness of the machined

surface, see figure. This means that the cutting edge has to work in a material that is


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much harder than is indicated by the hardness of the base material. This often results

in problems during finishing, as the depth of cut is then often so small that the

cutting edge is working entirely in the work-hardened layer.

It is, of course, not only cutting that causes work-hardening, but also all other types

of cold working. Shot or sand blasting, for example, or a straightening operation can

all produce a hard surface layer that affects machinability. In such cases, the

hardness gradient is similar in principle to that resulting from machining, but the

increase in hardness can extend to a greater depth into the metal. After a substantial

straightening operation the increase in hardness can extend to a depth of 2-4 mm

below the surface.

Low Thermal Conductivity

Stainless steels are poor conductors of heat, and the thermal conductivity ofall types of stainless steel falls off with increasing alloy, see table below.

Austenitic steels have the lowest thermal conductivity, while ferritic and martensitic

steels have better conductivity.

Steel Grade Thermal conductivity at 400 C

(W/m, K)

Carbon steel 35

420 26.5

444 26.5

304 20.0

316L 18.52205 24.0

904L 18.0

The low thermal conductivity means that, for a given machining operation, the cutting

edge temperatures are higher in stainless steel than in carbon steel. This naturally

imposes severe requirements on the high-temperature hardness of the cutting edge

and on its ability to withstand high temperatures.

High ToughnessAustenitic stainless steels in particular have very high toughness which means

that a considerable amount of energy is required to form each chip.

This, in combination with work hardening, results in a high power requirement for

machining stainless steels. This applies particularly for austenitic steels. The high

cutting forces, in combination with the low thermal conductivity, impose very severe

requirements on the strength of the cutting edge.


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Tendency to Stickyness

This tendency is most marked in austenitic stainless steels, although both

ferritic and ferritic-austenitic steels give rise to chip sticking and built-up

edges on the cutting tool.

The formation of a built-up edge results in a poor surface finish on the work piece and

very high stresses on the cutting edge. The formation of a built-up edge can often

result in failure of the cutting edge, resulting in tool failure.

Formation of a built-up edge and chip sticking can also occur when machining

ordinary structural steels and other carbon steels, although in such cases (as opposed

to the stainless steels) it is often sufficient to increase the cutting speed in order to

get out of the built-up edge range. When machining stainless steels it can, in certain

cases, be difficult to find a cutting speed range where built-up edge formation does

not occur.

Low Chip-breaking Characteristics

The high toughness of many stainless steels, and particularly of austenitic

steels, means that it is very difficult to break the chips formed during

machining.

This often causes considerable problems in removing the chips from the tool area, or

when a machining operation is to be automated. In the latter case, tangled chips

around the work piece can mean that, say, portal loaders and/or measuring stations

cannot be operated unmanned.

Some Rules of Thumb for Machining Stainless Steels

There are some general rules of thumb that can be applied when machining

stainless steels, to avoid (to some extent) the problems described, or at least

to minimise them.

These rules are particularly important when machining austenitic and ferritic-

austenitic stainless steels.

Always use rigid machine tools, as the machining of stainless steels

involves high cutting forces. Tools and work pieces must be firmly clamped, and the tool overhang mustbe as small as possible. (Long overhangs, or unstable machining conditions,increase the already substantial risk of vibration when machining stainlesssteels.)

Do not use too great a nose radius, as this can cause vibration.

Use tools with good edge sharpness and high edge strength. (Cemented

carbide tools should have a positive cutting edge, with a protective negative land,although this must not be greater than necessary to ensure that the edge is


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effectively sharp. At the same time, the edge must be strong, which means that itis necessary to find a compromise between strength and sharpness of the edge.)

Use sufficient cutting depths, so that the cutting edge tip reaches below thework-hardened zone from the previous cut.

Replace the insert more frequently than when machining carbon steel, as adull edge produces greater work-hardening than does a sharp edge.

When using cutting fluid, ensure that it is always applied. (If possible use

oils and emulsions with EP additive.)

Defintions of Surface Finish

In considering the concept of surface finish,

we will disregard any sporadic surface

defects, which have mechanical or

metallurgical causes. Instead, we will

concentrate on the minute, evenly

distributed irregularities in the surface layer,

which are characteristic of the different

means of production and finishing of the steel product. In terms of strict definition,

the concept "surface finish" can be said to describe the deviation from the ideal flat

surface. This deviation is normally expressed in terms such as roughness, lay and

waviness, which in turn may be defined as:

Roughness represents the size of the finely distributed surface pattern

deviations from the smooth surface.

Lay represents the dominant direction of the surface pattern, such asgrinding scores.

Waviness represents deviations, which are relatively far apart.

Of these, waviness is the most difficult to detect with the naked eye.

Definition of Surface Roughness

Roughness is measured by special precision instruments that measure the vertical

deviations when traversing the metal surface. The measurement is carried out in the

direction that gives the greatest measured values, that is, at right angles to the ray.

In accordance with the relevant international standard (ISO), the instrument

measures and calculates the mean deviation from the average line over a given

measured distance, the reference length (cut-off length), usually 0.8 or 0.25 mm.

The measured value, abbreviated as Ra or CLA (centre line average), is expressed in

m (thousands of a millimetre).

Y=Roughness, S=Lay, V=Waviness

Definition of the mean deviation


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Surface Finishes

Abbreviation2)Type of process

routeSurface finish Notes

Hot

rolled1U

Hot rolled, not

heat treated, not

descaled

Covered with the

rolling scale

Suitable for products which are to be

further worked e.g. strip for re-rolling

1C

Hotrolled,

heat

treated,

not

descaled

Covered

with the

rolling

scale

Suitable for parts which will

be descaled or machined in

subsequent production or for

certain heat-resisting

applications

1E

Hot rolled, heat

treated,

mechanically

descaled

Free of scale

The type of mechanical descaling, e. g.

coarse grinding or shot blasting,

depends on the steel grade and the

product and is left to the manufacturer's

discretion, unless otherwise agreed

1DHot rolled, heat

treated, pickledFree of scale

Usually standard for most steel types to

ensure good corrosion resistance; also

common finish for further processing.

It is permissible for grinding marks to

be present. Not as smooth as 2D or 2B

Cold

rolled2H Work hardened Bright

Cold worked to obtain higher strength

level

2C

Cold rolled, heat

treated, not

descaled

Smooth with scale

from heat treatment

Suitable for parts which will be

descaled or machined in subsequent

production or for certain heat-resisting

applications

2E

Cold rolled, heat

treated,

mechanically

descaled

Rough and dull

Usually applied to steels with a scale

which is very resistant to pickling

solutions. May be followed by

pickling.

2DCold rolled, heat

treated, pickledSmooth

Finish for good ductility, but not as

smooth as 2B or 2R

2B

Cold rolled, heat

treated, pickled,

skin passed

Smoother than 2D

Most common finish for most steeltypes to ensure good corrosion

resistance, smoothness and flatness.

Also common finish for further

processing. Skin passing may be by

tension levelling

2RCold rolled, bright

annealed2)Smooth, bright,

reflective

Smoother and brighter than 2B. Also

common finish for further processing

2Q

Cold rolled,

hardened and

tempered, scale

free

Free of scale

Either hardened and tempered in a

protective atmosphere or descaled after

heat treatment

Special

finishes

1G

or

2G

Ground4) See footnote 5

Grade of grit or surface roughness can

be specified. Unidirectional texture, not

very reflective

1J

or

2J

Brushed4) or dull

polished4)

Smoother than

ground. See footnote

5

Grade of brush or polishing belt or

surface roughness can be specified.

Undirectional texture, not very

reflective

1K

or

2K

Satin polish4) See footnote 5

Additional specific requirements to a

"J" type finish, in order to achieve

adequate corrosion resistance for

marine and external architectural

applications. Transverse Ra >0,5 m

with clean cut surface finish


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1P

or

2P

Bright polished 4) See footnote 5

Mechanical polishing. Process or

surface roughness can be specified.

Non-directional finish, reflective with

high degree of image clarity

2F

Cold rolled, heat

treated, skin

passed on

roughened rolls

Uniform non-

reflective matt

surface

Heat treatment by bright annealing or

by annealing and pickling

1M PatternedDesign to agreed; 2nd

surface flatChequer plates used for floors

2M PatternedDesign to agreed; 2nd

surface flat

A fine texture finish mainly used for

architectural applications

2W Corrugated Design to be agreedUsed to increase strength and/or for

cosmetic effect

2L Coloured4) Colour to be agreed

1S

or

2SSurface coated4)

Coated with e. g. tin, aluminium,

titanium

4) Not all process routes and surface finishes are available for all steels

4) First digit 1 = hot rolled 2= cold rolled

4) May be skin passed

4) One surface only, unless specifically agreed at the time of enquiry or order

4) Within each finish description the surface characteristics can vary, and more specific requirements may need to be agreed between manufacturer and purchaser (e. g. grade of grit or surface roughness)

Hot Rolled Plate and Sheet

All steel plate and sheet is hot-rolled as a first rolling step, after which it is annealed

in order to attain homogeneous material characteristics. Annealing produces an oxide

coating on the steel, which is removed by shot blasting and by pickling in an acid

bath. As a result of these manufacturing operations, the steel acquires a relatively

coarse, matt grey surface with an Ra value in the order of 2-8 m; the thicker the

plate the coarser the surface, and the higher the Ra value. Localised grinding marksmay appear on the surface, but have no practical implications for the use of the steel.

Hot rolled plate of this finish is mostly used for heavy process equipment and in

thickness from around 5 mm and upward.

Cold Rolled Sheet and Coil

Finishes:

Annealed and pickled finish - 2D

Skinpass rolled finish - 2B Bright annealed finish - BA

Polished

Brushed Patterned

Annealed and pickled finish - 2D

By means of further rolling of the steel in a cold state, both its surface smoothness
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substances do not attach as easily to wet polished surfaces.

The ground or polished surface has more or less clearly visible scoring, which also

makes scratches from daily wear and tear less visible. A polished surface is also easy

to re-create, for example after repairs or welding work, compared with a 2B or 20

surface. Polished sheet is used for purposes where quality of appearance and hygiene

are very important, such as in commercial kitchens (work surfaces, cooking utensils,

dishwashers, freezers) , in house- holds (cooking vessels), and in public places

(sanitary facilities, hospital equipment, kick-plates).Brushed

The use of brushing (with Scotch Brite, for example), usually on a 2B surface,

provides a silky-matt finish without grinding scores. A brushed surface also has the

advantage that it can easily be re-created. Brushed stainless steel sheet is used in

situations where appearance is an important factor, such as in the building industry

(sheet metal cladding and lift interiors), the vehicle industry (car hub caps, wall

panels for express trains) and the home (sink units). The Ra value for brushed sheetcan be around 0.2-0.4 m.

Patterned

Patterned sheet is produced by means of extra rolling of cold-rolled brushed sheet

coils between special imprinted rolls. In this way, a waffle-type pattern can be

obtained on both sides of the sheet. At the same time, the rigidity and strength of the

material is increased by almost 50%. This means that it is possible to use a thinner

sheet, and thus obtain a lower weight.

Cleaning of Stainless Steels

A stainless steel may be discoloured by rust

if it is exposed to a more aggressive environment than that is intended for

a particular grade of steel , e.g. highly polluted air, salt solutions or residues of

cleaning agents containing chlorine

if it has a rough surface finish that provides a foothold for corrosivesubstances and corrosion products from the surroundings

if the design of the structure is inappropriate, with pockets and narrow gaps

if the surface is contaminated by grinding swarf and other iron particles from

tools used in the installation work

if fasteners of ordinary steel are used for securing the material, or if thematerial comes into direct contact with adjacent components made of plain

carbon steel in wet or humid conditions.

The risk of corrosion in the first three situations is highest for the lower-alloy stainless

steel grades and can be reduced substantially right from the start by specifying

molybdenum alloyed stainless grades (such as type 1.4401). In the last two cases,

the surface of the stainless steel will be discoloured by rust from the plain carbon

steel.


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Removal of stains and discolourationsStain Type Cleaning agent and method

FingerprintsWash with alcohol, thinner, thrichlorethylene or acetone, rinse with clean cold water, and

wipe dry.

Oil and greaseWash with organic solvents, such as those mentioned above, then wash with soap or mild

detergent and water, rinse with clean cold water, and wipe dry.

More stubborn stains

and discolourations

Wash with a mild abrasive detergent, rub in the direction of the visible surface structure, rinse

with clean cold water, and wipe dry.

Or:

Wash with a 10% phosphoric acid solution, rinse with ammonia solution, then with clean

cold water, and wipe dry.

Temper colour and

more serious stains

Wash with an abrasive detergent as described above.

Or:

Rub with Scotch Brite sponge in the direction of the visible structure, rinse with clean cold

water, and wipe dry.

Rust stains

Wet the surface with oxalic acid solution, leave it for 15-20 minutes, rinse with clean cold

water, and wipe dry. If necessary, repeat the washing procedure with an abrasive detergent as

described above.

Paint

Wash with paint solvent (use a soft nylon brush), and then rinse with clean cold water, and

wipe dry.

Scratches on a ground

or brushed surface

Polish with a polishing wheel (using an iron-free abrasive) in the direction of the structure,

wash with soap or mild detergent and water, rinse with clean cold water, and wipe dry. N.B.

The method must not be used for material with a 2B or 2D finish, or on patterned or

decorated surfaces.

Preventive Measures in Project Design, Production, andInstallation

All stainless steels are clean and passivated when they are delivered by the

steel manufacturer. In other words, the material has a natural corrosion

resistant film over its entire surface.

The following instructions should be taken into account from the moment of project

design, through to the production and installation stages, particularly for building

components installed outdoors, in order to maintain as much as possible of the

original appearance and corrosion resistance of the stainless material.

Do not use steel brushes or steel tools made of plain carbon steel.

Do not carry out shot blasting using ordinary steel shot or sand that has used for shot blasting plain

carbon steels

Do not use hydrochloric acid to remove residues of cement or mortar on steel. Instead use water to wash

off the mortar before it dries. Hydrochloric acid may not be used for cleaning of stainless steels.

Specify the correct grade of steel, taking into account the occurrence of

deposits and air pollutants such as soot, sulphur dioxide, salt water or road salt

in the immediate surroundings.


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welding due to their speed and reliability. These are employed predominantly in batch

production.

Electrodes - SMAW

Shielded metal-arc welding (SMAW) with covered electrodes is the most common

method of welding stainless steels. It is suited to all weldable grades, in thicknesses of

1 mm and upwards. In principle, there is no upper limit of thickness. However, for

heavier material, the automatic wire processes are often more economical.

When correctly carried out, the heat supply is concentrated and the heat affected zone

(HAZ) on either side of the joint is relatively narrow.


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Gas Metal-Arc Welding - GMAW

In GMAW the arc is struck between the filler wire and the workpieceThe uncovered filler wire is automatically fed through the centre of the gun. The

shielding gas is supplied through the gun and surrounds the arc pool during welding,

thus protecting the weld from the atmosphere. The gas usually consists of argon with

an added 1-2% oxygen or of pure argon.

A distinction is drawn between spray-arc welding and short-arc welding. The latter

method is suitable for welding light-gauge sheet as well as for welding root beads in

heavier material. It is also suitable for position welding. This process takes place at a

lower voltage and current than in the case of spray-arc welding. A thin filler wire (0.8

mm) is used. The arc is short, hence the name, and metal transfer is in the form of big

drops shortcircuiting the arc. This provides rapid alternation between arc heating and

resistance heating.

By contrast, in spray-arc welding, the metal is transferred in the form of a fine mist of

droplets which do not short-circuit the arc. The process, which derives its name from

this feature, is suitable for material thicknesses of 3 mm and upwards.

The GMAW process is either semi-automatic or fully automatic. In many cases, it is

more economical than welding with covered electrodes. However, all gas-shielded


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processes are sensitive to draughts. Thus, they are not suitable for outdoor work or for

welding in open vessels in which a chimney effect may easily occur.

Pickling methods

In most workshops there will typically be the same sequence of operations even if

the type of pickling process may vary:

Pre-cleaning

Pickling

- Brush pickling with paste

- Spray pickling with solution

- Immersion pickling in a bath

Rinsing

Passivation, if necessary

Neutralisation

Drying

Inspection

The choice of pickling method depends on:

The steel grade and type of component to be pickled

The requirements of the specification

The requirements on the visual appearance of the surface

The functional requirements on the surface

The automation potential

The environmental and worker safety aspects

The costs


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the schaeffler

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