What is Stainless Steel?

                   

In metallurgy, stainless steel, also known as inox steel or inox, is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass. Stainless steel does not stain, corrode, or rust as easily as ordinary steel (it stainsless, but it is not stain-proof). It is also called corrosion-resistant steel or CRES when the alloy type and grade are not detailed, particularly in the aviation industry. There are different grades and surface finishes of stainless steel to suit the environment to which the material will be subjected in its lifetime. Common uses of stainless steel are cutlery and watch cases and bands.

Stainless steel differs from carbon steel by the amount of chromium present. Carbon steel rusts when exposed to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide. Stainless steel have sufficient amounts of chromium present so that a passive film of chromium oxide forms which prevents further surface corrosion and blocks corrosion from spreading into the metal’s internal structure.

Many types of stainless steel have been developed to resist different corrosion environments and working conditions ensuring that factories are safe, structures last longer and our food is hygienic. Stainless steel is even used for in systems to clean up the exhaust gases from cars and power stations.

Stainless steel is also recyclable: when scrapped, it can be re-melted to make something new.

Effect of Chromium:

Stainless steel are chromium containing steel alloys. The minimum chromium content of the standardised stainless steels is 10.5%. Chromium makes the steel ‘stainless’  this means improved corrosion resistance, as can be seen in the chart. The better corrosion resistance is due to a chromium oxide film that is formed on the steel surface. This extremely thin layer, under the right conditions, is also self-repairing.Besides chromium, typical alloying elements are molybdenum, nickel and nitrogen. Nickel is mostly alloyed to improve the formability and ductility of stainless steel. Alloying these elements brings out different crystal structures to enable different properties in machining, forming, welding etc.

The four major types of stainless steel tube are:

Austenitic Stainless Steel is the most widely used type of stainless steel. It has a nickel content of at least of 7%, which makes the steel structure fully austenitic and gives it ductility, a large scale of service temperature, non-magnetic properties and good weldability. The range of applications of austenitic stainless steel includes housewares, containers, industrial piping and vessels, architectural facades and constructional structures.

Ferritic Stainless Steel pipe has properties similar to mild steel but with the better corrosion resistance. The most common of these steels are 12% and 17% chromium containing steels, with 12% used mostly in structural applications and 17% in housewares, boilers, washing machines and indoor architecture.

Type 430The basic ferritic grade, with a little less corrosion resistance than Type 304. This type combines high resistance to such corrosives as nitric acid, sulfur gases, and many organic and food acids.
Type 405Has lower chromium and added aluminum to prevent hardening when cooled from high temperatures. Typical applications include heat exchangers.
Type 409Contains the lowest chromium content of all stainless steels and is also the least expensive. Originally designed for muffler stock and also used for exterior parts in non-critical corrosive environments.
Type 434Has molybdenum added for improved corrosion resistance. Typical applications include automotive trim and fasteners.
Type 436Type 436 has columbium added for corrosion and heat resistance. Typical applications include deep-drawn parts.
Type 442Has increased chromium to improve scaling resistance. Typical applications include furnace and heater parts.
Type 446Contains even more chromium added to further improve corrosion and scaling resistance at high temperatures. Especially good for oxidation resistance in sulfuric atmospheres.

Austenitic-Ferritic Duplex Stainless Steel has a ferritic and austenitic lattice structure – hence common name: duplex stainless steel. This steel has some nickel content for a partially austenitic lattice structure. The duplex structure delivers both strength and ductility. Duplex steels are mostly used in petrochemical, paper, pulp and shipbuilding industries.

China GBISO Unified Digital CodeASTM / ASMEUNS codeEN CodeCompany Commercial Grade
022Cr23Ni4MoCuNS23043S32304S323041.4362SAF2304 (Sandvik)
022Cr22Ni5Mo3NS22253S31803S318031.4462
022Cr23Ni5Mo3NS22053S32205S322051.4462SAF2205 (Sandvik)
022Cr25Ni7Mo4NS25073S32750S327501.4410SAF2507(Sandvik)
022Cr25Ni7Mo3WCuNS22583S31260S31260
03Cr25Ni6Mo3Cu2NS25554S32550S325501.4507UR52+
022Cr25Ni7Mo4WCuNS27603S32760S327601.4501Zeron100
00Cr27Ni7Mo5NS32707S32707SAF2707(Sandvik)

Martensitic Stainless Steel contains mostly 11 to 13% chromium and is both strong and hard with moderate corrosion resistance. This steel is mostly used in turbine blades and in knives.

Type 410Basic martensitic grade, containing the lowest alloy content of the three basic stainless steels (304, 430, and 410). Low cost, general purpose, heat treatable stainless steel. Used widely where corrosion is not severe (air, water, some chemicals, and food acids. Typical applications include highly stressed parts needing the combination of strength and corrosion resistance such as fasteners.
Type 410SContains lower carbon than Type 410, offers improved weldability but lower hardenability. Type 410S is a general purpose corrosion and heat resisting chromium steel recommended for corrosion resisting applications.
Type 414Has nickel added (2%) for improved corrosion resistance. Typical applications include springs and cutlery.
Type 416Contains added phosphorus and sulfur for improved machinability. Typical applications include screw machine parts.
Type 420Contains increased carbon to improve mechanical properties. Typical applications include surgical instruments.
Type 431Contains increased chromium for greater corrosion resistance and good mechanical properties. Typical applications include high strength parts such as valves and pumps.
Type 440Further increases chromium and carbon to improve toughness and corrosion resistance. Typical applications include instruments.



Precipitation-Hardening –   These alloys generally contain Cr and less than 8% Ni, with other elements in small amounts. As the name implies, they are hardenable by heat treatment.

Duplex –   This is a stainless steel alloy group, or family, with two distinct microstructure phases — ferrite and austenite. The Duplex alloys have greater resistance to chloride stress corrosion cracking and higher strength than the other austenitic or ferritic grades.

Cast –   The cast stainless steels, in general, are similar to the equivalent wrought alloys. Most of the cast alloys are direct derivatives of one of the wrought grades, as C-8 is the cast equivalent of wrought type 304. The C preceding a designation means that the alloy is primarily used for resistance to liquid corrosion. An H designation indicates high temperature applications.

Austenitic Stainless Steel

Corrosion Resistance Stainless Steel

ASMEAISI UNSENJISCmaxCrNiMoCuOthers
TP 304S304001.4301SUS 3040.08018.08.0   
TP 304 LS304031.4307SUS 304L0.03518.08.0   
TP 304HS304031.4948SUS 304H0.04-0.118.08.0   
TP 321S321001.4541SUS 3210.08017.09.0  5(C+N)<Ti< 0.7
TP 321HS321001.4878SUS 3210.04-0.117.09.0  4(C+N)<Ti< 0.7
TP 347S34701.4550SUS 3470.08017.09.0  10×C<Nb<1
TP 347HS34709 SUS 3470.04-0.117.09.0  8×C<Nb<1.10
TP 316S316001.4401SUS 3160.06016.010.02.0  
TP 316LS316031.4404SUS 316L0.03016.010.02.0  
TP 316HS31609SUS 316H0.04-0.116.010.02.0  
TP 316 TiS316351.4571SUS 316Ti0.03016.010.02.0 N0.015(C+N)<Ti< 0.7
TP 317S317001.4438SUS 317L0.08018.011.03.0  
TP 317L317031.4438SUS 317L0.03018.011.03.0  
TP 309SS309081.4833SUS 309S0.8022.012.0   
TP 310S310001.4841SUS 3100.08024.019.0   
TP 310SS310081.4845SUS 310S0.1024.019.0   
TP 310HS310091.4845SUS 310H0.08024.019.0   
TP 904LN089041.4539SUS 904L0.02019.0>23.04.01.0-2.0 

High Temperature Stainless Steel/Heat Resistant Stainless Steel

TP 304HS304031.4948SUS 304H0.04-0.118.08.0 
TP 321HS321001.4878SUS 3210.04-0.117.09.04(C+N)<Ti< 0.7
TP 347HS34709 SUS 3470.04-0.117.09.08×C<Nb<1.10
TP 309SS309081.4833SUS 310S0.08022.012.0
TP 310SS310081.4845SUS 310S0.08024.019.0
TP 310HS310091.4845SUS 310H0.08024.019.0 

*All figures in weight percentage. In case of order, the limits of the order specification will apply.

Duplex Stainless Steel Austenitic Ferritic

DesignationUNSENJISCmaxCrNiMoCuOthers
2101S321011.4162DP20.04021.01.350.100.10N 0.20
2205S322051.4462DP20.03022.04.503.0N 0.14
S31803S318031.4462DP20.03021.04.502.5N 0.08
2304S323041.4362DP20.03021.53.0<0.05-0.60.60N 0.2
2507S327501.4410DP20.03024.06.0>3.00.50N 0.32
S327601.4501DP20.03024.06.03.00.50N 0.20

*All figures in weight percentage. In case of order, the limits of the order specification will apply.

NameASTMUNSENDINSSBSCCrNiMoOther
301S301000.11.43101.43102331301S210.04177
302S302000.071.43191.43192332302S310.06178-–
303S303000.061.43051.43052346303S310.0917.58.1S
304S304000.041.43011.43012333304S310.0618.28.1
304LS304030.021.43061.43062352304S110.0618.28.2
304LNS304530.021.43111.43112371304S610.1418.28.5
304NS304510.041.69071.6907304S710.1418.58.5
305S305000.021.43031.4303305S190.021811.5
308LS308830.021.43161.4316308S920.052011-–
316S316000.041.44011.44012347316S310.0416.810.72
316S316000.041.44361.44362343316S330.0617112.8
316LS316030.021.44041.44042348316S110.0616.210.22
316LS316030.021.44321.44322353316S130.0616.210.22.8
316LNS316530.021.44061.4406316S610.1416.210.22
316TiS316350.041.45711.45712350320S310.0117112Ti
317LS317030.021.44381.44382367317S120.0818.311.53
317LMS317250.021.44391.44390.0819.313.74.3
317LMNS317260.021.44391.44390.1419.313.74.3
321S321000.041.45411.45412337321S310.0117.39.2Ti
347S347000.041.4552338347S310.0417.39.1Cb
20N08020N080202.46600.010.0620332
904LN089040.011.45391.45392562904S130.0620254.5Cu
254 SMoS31254S312541.454723780.010.220186.1
654 SMoS32654S326541.46520.010.524227.3
LDX 2101S32101S321011.41620.030.2221.51.50.3
23042304S323041.43621.436223270.020.1234.80.3
2205S32205/S318030.021.44621.44622377318S130.17225.53
25072507S327501.44123280.020.272574
329S329000.021.4461.44623242209,0.062551.5
405S405000.061.40021.400211.5Al
409S40900 1.45121.4512  10.5
410S410000.121.40061.40062302410S2111.5
410SS410080.061.41.42301403S1712
416S416000.121.40051.40052380416S2112S
430S430000.041.40161.40162320430S1716
434S434000.061.4113 171
439S430350.071.451 17.0Ti
630S174000.041.45421.454215.34.8Cu,
631S177000.051.45681.4568238816.37Al
304HS304090.051.49481.49482333304S510.0618.28.1
321HS321090.051.48781.48782337321S510.0117.39.2Ti
309SS309080.061.48331.4833309S160.0822.212.2
310SS310080.051.48451.48452361310S160.0625.219.2
153 MAS304150.0523722530.1518.59.51.4818
253 MAS308150.0923682530.1721111.4835
353 MAS353150.053530.1625351.4854

Chemical Composition

GradeC (Max)Mn (Max)P (Max)S (Max)Si (Max)CrNiMoAzoto (Max)Cu/Outro
3010.152.000.0450.0301.0016.00 – 18.006.00 – 8.000.10
3040.082.000.0450.0300.7518.00 – 20.008.00- 10.500.10
304L0.0302.000.0450.0300.7518.00 – 20.008.00- 12.000.10
310S0.082.000.0450.0301.5024.00- 26.0019.00 – 22.00
3160.082.000.0450.0300.7516.00 – 18.0010.00 – 14.002.00 – 3.000.10
316L0.0302.000.0450.0300.7516.00 – 18.0010.00 – 14.002.00 – 3.000.10
3170.082.000.0450.0300.7518.00 – 20.0011.00 – 14.003.00 – 4.000.10
317L0.0302.000.0450.0300.7518.00 – 20.0011.00 – 15.003.00 – 4.000.10
3210.082.000.0450.0300.7517.00 – 19.009.00 – 12.000.10Ti5 ( C + N ) Min or 0.70 max
3470.082.000.0450.0300.7517.00 – 19.009.00 – 13.00Cb= 10x ( C Min ) or 1.00 Max
4090.081.000.0400.0101.0010.50 – 11.750.50Ti= 6x (C+ N ) Min or 0.70 Max
409M0.030.81.20.0300.0300.40.7511.00- 12.001.5 max.Ti= 6x (C) Min or 0.70 Max
410S0.081.000.0400.0301.0011.50- 13.500.60
4100.151.000.0400.0301.0011.50- 13.500.75
4200.350.500.0350.0150.5012.00 – 13.000.20.3
4300.121.000.0400.0301.0016.00 – 18.000.75
JSL AUS0.087.08.00.0700.0300.7515.50 – 16.504.25 – 4.750.9 – 1.10
JS- 2030.089.2510.250.0700.0300.7514.25 – 15.252.25 – 2.751.60- 2.0
301M0.104.55.50.0600.0300.7514.50 – 15.506.0 – 7.01.70- 1.90

Details Chemical Composition(GB,JIS,ASTM/ASME/AISI,DIN,EN)
Details Chemical Composition(GB,JIS,ASTM/ASME/AISI,DIN)

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