Austenitic stainless steel


Austenitic stainless steel is a specific type of stainless steel alloy. Stainless steels may be classified by their crystalline structure into four main types: austenitic, ferritic, martensitic and duplex. Austenitic stainless steels possess austenite as their primary crystalline structure. This austenite crystalline structure is achieved by sufficient additions of the austenite stabilizing elements nickel, manganese and nitrogen. Their crystalline structure prevents austenitic steels from being hardenable by heat treatment and makes them essentially non-magnetic.

200 and 300 series

There are two subgroups of austenitic stainless steel. 300 series stainless steels achieve their austenitic structure primarily by a nickel addition while 200 series stainless steels substitute manganese and nitrogen for nickel, though there is still a small nickel content.
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 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.
Euronorm numberEN designationAISI gradeCCrMoNiOthersRemark
1.4310X10CrNi18-83010.1017.58For springs
1.4301X5CrNi18-10304< 0.0718.59A very common austenitic stainless steel grade
1.4307X2CrNi18-9304L< 0.03018.59Same as above but not susceptible to intergranular corrosion thanks to a lower C content.
1.4305X8CrNiS18-9 e303< 0.101890.3Sulphur is added to improve machinability.
1.4541X6CrNiTi18-10321< 0.081810.5Ti: 5×C ≤ 0.70Same as grade 1.4301 but not susceptible to intergranular corrosion thanks to Ti which "traps" C.
1.4401X5CrNiMo17-12-2316< 0.0717.52.211.5Second best known austenitic grade. Mo increases the corrosion resistance.
1.4404X2CrNiMo17-12-2316L< 0.03017.52.2511.5Same as above but not susceptible to intergranular corrosion thanks to a lower C content.
1.4571X6CrNiMoTi17-12-2316Ti< 0.0817.52.2512Ti: 5×C ≤ 0.70

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

Heat resisting austenitic stainless steels

Heat resisting grades can be used at elevated temperatures, usually above 600 °C.
They must resist corrosion and retain mechanical properties, mostly strength and creep resistance
Corrosion resistance is mostly provided by chromium, with additions of silicon and/or 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.
EN №AISI/ASTMUNSCCrNiSiMnOthers
1.4878321HS32109< 0.11810.5--Ti: ≤ 5×C
1.4818-S304150.061910--N: 0.16; Ce: 0.05.
1.4828--< 0.220122.0--
1.4833309SS30908< 0.082313< 0.75--
1.4872--0.25257-9-
1.4845310S31008< 0.12520---
1.4841314S31400< 0.1525201.8--
1.4876"Alloy 800"N08800< 0.122132--Al: 0.4; Ti: 0.4
1.4854"Alloy 353MA"S353150.062535--N: 0.15; Ce: 0.06.
1.4886330N08330< 0.1518.535--

Type309 and 310, are utilized in high temperature applications greater than 800°C.
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.

Precipitation Hardening grade EN1.4980

Grade EN1.4980 is not considered strictly as a heat resisting steel in standards, but this is popular grade for its combination of strength and corrosion resistance.
EN №AISI/ASTMUNSCCrNiMoOthers
1.4980660S662860.0515251.25V: 0.3; Ti: 2.0; B: 0.006.

ConditionYield stress, min. Ultimate tensile strength, min. Elongation, min.
Solution treated and aged59090013

It is used for service temperatures up to 700°C in applications such as: