Austenitic stainless steel

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Convergent beam electron diffraction (CBED) transmission electron micrograph of a [111] zone axis of austenitic stainless steel Deus Ex Ferro.tif
Convergent beam electron diffraction (CBED) transmission electron micrograph of a [111] zone axis of austenitic stainless steel

Austenitic stainless steel is one of the five classes of stainless steel as defined by crystalline structure (along with ferritic , martensitic, duplex and precipitation hardened). [1] Its primary crystalline structure is austenite (face-centered cubic). Such steels are not hardenable by heat treatment and are essentially non-magnetic. [2] This structure is achieved by adding enough austenite-stabilizing elements such as nickel, manganese and nitrogen.[ citation needed ] The Incoloy family of alloys belong to the category of super austenitic stainless steels. [3]

Contents

History

Schaeffler diagram Diagramme inox Schaeffler.svg
Schaeffler diagram

During World War 2 the Schaeffler diagram was invented by Anton, who was then a budding metallurgist in the employ of two American welding electrode manufacturers, Harnischfeger Company and A.O. Smith Corporation. [4]

AISI 200 and 300 series

ASSs are divided into 300-series and 200-series subgroups. In 300 series stainless steels the austenitic structure 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 [5]
Euronorm (EN) number [6] EN designation AISI grade [7] CCrMoNiOthersMelts at [8] Remark
1.4310X10CrNi18-83010.1017.5NS8NS1420For springs
1.4301X5CrNi18-10304< 0.0718.5NS9NS1450A very common austenitic stainless steel grade
1.4307X2CrNi18-9304L< 0.03018.5NS9NS1450Similar to the above but not susceptible to intergranular corrosion thanks to a lower C content.
1.4305X8CrNiS18-9 e303< 0.1018NS90.31420Sulphur is added to improve machinability.
1.4541X6CrNiTi18-10321< 0.0818NS10.5Ti: 5×C ≤ 0.701425Same as grade 1.4301 but not susceptible to intergranular corrosion thanks to Ti which "traps" C.
1.4401X5CrNiMo17-12-2316< 0.0717.52.211.5NS1400Second best known austenitic grade. Mo increases the corrosion resistance.
1.4404X2CrNiMo17-12-2316L< 0.03017.52.2511.5NS1400Same 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. [9]

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.

Heat resisting austenitic stainless steels

Heat resisting grades can be used at elevated temperatures, usually above 600 °C (1,100 °F). [10] [11]

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
ENEN designationAISI/ASTMUNSCCrNiSiMnOthers
1.4878X8CrNiTi18-10321HS32109< 0.11810.5--Ti: ≤ 5×C
1.4818X6CrNiSiNCe19-10-S304150.061910--N: 0.16; Ce: 0.05.
1.4828X15CrNiSi20-12309-< 0.220122.0--
1.4833X12CrNi23-13309SS30908< 0.082313< 0.75--
1.4872X25CrMnNiN25-9-7--0.25257-9-
1.4845X15CrNi25-21310SS31008< 0.12520---
1.4841X15CrNiSi25-21314S31400< 0.1525201.8--
1.4876X10NiCrAITi32-20"Alloy 800"N08800< 0.122132--Al: 0.4; Ti: 0.4
1.4854X6NiCrSiNCe35-25"Alloy 353MA"S353150.062535--N: 0.15; Ce: 0.06.
1.4886X12NiCrSi35-16330N08330< 0.1518.535--

Type 309 and 310 [12] are used in high temperature applications greater than 800 °C (1,500 °F).

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 EN 1.4980

Grade EN 1.4980 (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. [13] [14] [15]

Typical composition
EN No.EN designationAISI/ASTMUNSCCrNiMoOthers
1.4980X6NiCrTiMoVB25-15-2660S662860.0515251.25V: 0.3; Ti: 2.0; B: 0.006.
Minimum mechanical properties
ConditionYield stress, minUltimate tensile strength, minElongation, min (%)
Solution treated and aged590 MPa (86 ksi)900 MPa (130 ksi)13

It is used for service temperatures up to 700 °C (1,300 °F) in applications such as:

See also

Related Research Articles

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<span class="mw-page-title-main">Martensitic stainless steel</span> One of the 5 crystalline structures of stainless steel

Martensitic stainless steel is a type of stainless steel alloy that has a martensite crystal structure. It can be hardened and tempered through aging and heat treatment. The other main types of stainless steel are austenitic, ferritic, duplex, and precipitation hardened.

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AL-6XN is a type of weldable stainless steel that consist of an alloy of nickel (24%), chromium (22%) and molybdenum (6.3%) with other trace elements such as nitrogen.

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<span class="mw-page-title-main">Intergranular corrosion</span> When crystallite boundaries are more corrosive than their interiors

In materials science, intergranular corrosion (IGC), also known as intergranular attack (IGA), is a form of corrosion where the boundaries of crystallites of the material are more susceptible to corrosion than their insides.

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<span class="mw-page-title-main">Alloy steel</span> Steel alloyed with a variety of elements

Alloy steel is steel that is alloyed with a variety of elements in amounts between 1.0% and 50% by weight, typically to improve its mechanical properties.

Zeron 100 is a super duplex stainless steel developed by Rolled Alloys. The alloy has excellent corrosion resistance combined with high strength. It typically contains 25% chromium and 7% nickel and 3.6% molybdenum along with copper and tungsten additions. Zeron 100 has a 50–50 austenitic–ferritic structure. It also has greater resistance to chloride pitting, crevice corrosion and stress corrosion cracking than exhibited by the standard 300 series stainless steels.

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<span class="mw-page-title-main">Duplex stainless steel</span> Stainless steel that has both austenitic and ferritic phases

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<span class="mw-page-title-main">Ferritic stainless steel</span> High chromium, low carbon stainless steel type

Ferritic stainless steel forms one of the five stainless steel families, the other four being austenitic, martensitic, duplex stainless steels, and precipitation hardened. For example, many of AISI 400-series of stainless steels are ferritic steels. By comparison with austenitic types, these are less hardenable by cold working, less weldable, and should not be used at cryogenic temperatures. Some types, like the 430, have excellent corrosion resistance and are very heat tolerant.

<span class="mw-page-title-main">475 °C embrittlement</span> Loss of plasticity in ferritic stainless steel

Duplex stainless steels are a family of alloys with a two-phase microstructure consisting of both austenitic and ferritic phases. They offer excellent mechanical properties, corrosion resistance, and toughness compared to other types of stainless steel. However, duplex stainless steel can be susceptible to a phenomenon known as 475 °C (887 °F) embrittlement or duplex stainless steel age hardening, which is a type of aging process that causes loss of plasticity in duplex stainless steel when it is heated in the range of 250 to 550 °C. At this temperature range, spontaneous phase separation of the ferrite phase into iron-rich and chromium-rich nanophases occurs, with no change in the mechanical properties of the austenite phase. This type of embrittlement is due to precipitation hardening, which makes the material become brittle and prone to cracking.

References

  1. ↑ The International Nickel Company (1974). "Standard Wrought Austenitic Stainless Steels". Nickel Institute. Archived from the original on 2018-01-09. Retrieved 2018-01-09.
  2. ↑ "Stainless Steel". Encyclopaedia Britannica. 21 June 2024.
  3. ↑ "Super Alloy INCOLOY Alloy 800 (UNS N08800)". AZoNetwork. 3 July 2013.
  4. ↑ Guiraldenq, Pierre; Hardouin Duparc, Olivier (2017). "The genesis of the Schaeffler diagram in the history of stainless steel". Metallurgical Research & Technology. 114 (6): 613. Bibcode:2017MetRT.114..613G. doi:10.1051/metal/2017059.
  5. ↑ "Loading..." knowledge.bsigroup.com.
  6. ↑ European Committee for Standardization -. "Materials".
  7. ↑ "The Voice of the American Steel Industry". American Iron and Steel Institute.
  8. ↑ "Stainless steel melting points". Thyssenkrupp Materials (UK) Ltd. Retrieved 28 May 2022.
  9. ↑ American Iron and Steel Institute. "Design Guidelines for the Selection and Use of Stainless Steels". Nickel Institute. Retrieved 2018-01-09.
  10. ↑ M, Rouby (1990). Lacombe, P (ed.). Les aciers inoxydables. Les Editions de Physique. pp. Chapter 26. ISBN   2-86883-142-7.
  11. ↑ "EN 10088-1 Standard : Stainless steels Part1: List of stainless steels".
  12. ↑ "310 310S Stainless Steel". TubingChina.com Stainless Steel Directory. Retrieved 2015-09-18.
  13. ↑ "MatWeb - The Online Materials Information Resource". www.matweb.com.
  14. ↑ "Aubert&Duval Datasheet" (PDF).
  15. ↑ "Alloy A286 (AMS 5731/ AMS 5732 / AMS 5737 / AMS 5525)". www.aircraftmaterials.com.
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