Austenitic stainless steel

 ( Stainless Steel ) 

Austenitic stainless steel is one of the five families of stainless steel (along with ferritic, martensitic, duplex and precipitation hardened). Its primary crystalline structure is austenite (face-centered cubic). Such steels are not hardenable by heat treatment and are essentially non-magnetic. This structure is achieved by adding enough austenite-stabilizing elements such as nickel, manganese and nitrogen. The Incoloy family of alloys belong to the category of super austenitic stainless steels.

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History During World War II, the Schaeffler diagram was invented by Anton Schaeffler, who was then a budding metallurgist in the employ of two American welding electrode manufacturers, Harnischfeger Company and A.O. Smith Corporation.

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AISI 200 and 300 series Austenitic stainless steels are divided into 300-series and 200-series subgroups. In 300 series stainless steels, the austenitic structure is obtained primarily by adding nickel. In 200 series stainless steels, the structure is obtained by adding manganese and nitrogen, with a small amount of nickel content, making 200 series a cost-effective nickel-chromium austenitic type stainless steel.

300 series stainless steels are the larger subgroup. The most common austenitic stainless steel and most common of all stainless steel is Type 304, also known as 18/8 or A2. Type 304 is extensively used in such items as cookware, cutlery, and kitchen equipment. Type 316, also known as A4, is the next most common austenitic stainless steel. Some 300 series, such as Type 316, also contain some molybdenum to promote resistance to acids and increase resistance to localized attack (e.g. pitting and crevice corrosion).

+ Average content by weight (%) of the major alloying elements of most common Cr-Ni austenitic stainless steel grades
1.4310	X10CrNi18-8	301	0.10	17.5		8		1420	For springs
1.4301	X5CrNi18-10	304	< 0.07	18.5		9		1450	A very common austenitic stainless steel grade
1.4307	X2CrNi18-9	304L	< 0.030	18.5		9		1450	Similar to the above but not susceptible to intergranular corrosion thanks to a lower C content.
1.4305	X8CrNiS18-9 e	303	< 0.10	18		9	0.3	1420	Sulphur is added to improve machinability.
1.4541	X6CrNiTi18-10	321	< 0.08	18		10.5	Ti: 5×C ≤ 0.70	1425	Same as grade 1.4301 but not susceptible to intergranular corrosion thanks to Ti which "traps" C.
1.4401	X5CrNiMo17-12-2	316	< 0.07	17.5	2.2	11.5		1400	Second best known austenitic grade. Mo increases the corrosion resistance.
1.4404	X2CrNiMo17-12-2	316L	< 0.030	17.5	2.25	11.5		1400	Same as above but not susceptible to intergranular corrosion thanks to a lower C content.
1.4571	X6CrNiMoTi17-12-2	316Ti	< 0.08	17.5	2.25	12	Ti: 5×C ≤ 0.70

The higher nitrogen addition in 200 series gives them higher mechanical strength than 300 series.

Alloy 20 (Carpenter 20) is an austenitic stainless steel possessing excellent resistance to hot sulfuric acid and many other aggressive environments which would readily attack type 316 stainless. This alloy exhibits superior resistance to stress-corrosion cracking in boiling 20–40% sulfuric acid. Alloy 20 has excellent mechanical properties and the presence of niobium in the alloy minimizes the precipitation of carbides during welding.

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Heat resisting austenitic stainless steels Heat resisting grades can be used at elevated temperatures, usually above .

Rouby (1990). 9782868831422, Les Editions de Physique. ISBN 9782868831422

They must resist corrosion (usually oxidation) and retain mechanical properties, mostly strength (yield stress) and creep resistance.

Corrosion resistance is mostly provided by chromium, with additions of silicon and aluminium. Nickel does not resist well in sulphur containing environments. This is usually taken care of by adding more Si and Al which form very stable oxides. Rare earth elements such as cerium increase the stability of the oxide film.

+ Typical composition of the major grades
1.4878	X8CrNiTi18-10	321H	S32109	< 0.1	18	10.5	-	-	Ti: ≤ 5×C
1.4818	X6CrNiSiNCe19-10	-	S30415	0.06	19	10	-	-	N: 0.16; Ce: 0.05.
1.4828	X15CrNiSi20-12	309	-	< 0.2	20	12	2.0	-	-
1.4833	X12CrNi23-13	309S	S30908	< 0.08	23	13	< 0.75	-	-
1.4872	X25CrMnNiN25-9-7	-	-	0.25	25	7	-	9	-
1.4845	X15CrNi25-21	310S	S31008	< 0.1	25	20	-	-	-
1.4841	X15CrNiSi25-21	314	S31400	< 0.15	25	20	1.8	-	-
1.4876	X10NiCrAITi32-20	"Alloy 800"	N08800	< 0.12	21	32	-	-	Al: 0.4; Ti: 0.4
1.4854	X6NiCrSiNCe35-25	"Alloy 353MA"	S35315	0.06	25	35	-	-	N: 0.15; Ce: 0.06.
1.4886	X12NiCrSi35-16	330	N08330	< 0.15	18.5	35	-		-

Type309 and 310 are used in high temperature applications greater than .

Note: ferritic stainless steels do not retain strength at elevated temperatures and are not used when strength is required.

Austenitic stainless steel can be tested by nondestructive testing using the dye penetrant inspection method but not the magnetic particle inspection method. Eddy-current testing may also be used.

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Precipitation Hardening grade EN1.4980 Grade EN1.4980 (also known as A286) is not considered strictly as a heat resisting steel in standards, but this is popular grade for its combination of strength and corrosion resistance.

+ Typical composition
1.4980	X6NiCrTiMoVB25-15-2	660	S66286	0.05	15	25	1.25	V: 0.3; Ti: 2.0; B: 0.006.

+ Minimum mechanical properties
Solution treated and aged			13

It is used for service temperatures up to in applications such as:

• Aerospace (standardized in AMS5731, AMS5732, AMS5737 and AMS5525 standards),
• Industrial gas turbines,
• Automotive (turbo parts), etc.

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See also

• Stainless steel

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External links

• Austenitic stainless steels Jean H. Decroix et al.

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