Martensitic stainless steel

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Stainless steels may be classified by their crystalline structure into four main types: austenitic, ferritic, martensitic, and duplex.

Martensitic stainless steel is a specific type of stainless steel alloy.[1][2][3]

Martensitic stainless steels can be high- or low-carbon steels built around the composition of iron, 12% up to 17% chromium, carbon from 0.10% (Type 410) up to 1.2% (Type 440C).[4].

- Up to about 0.4%C they are used mostly for their mechanical properties ( pumps, valves, shafts ..).

- Above, 0.4% they are used mostly for their wear resistance (cutlery surgical blades, plastic injection molds, nozzles...).

They may contain some Ni (Type 431) which allows a higher Cr and/or Mo content, thereby improving corrosion resistance and as the Carbon content is also lower, the toughness is improved. Grade EN 1.4313 (CA6NM) with a low C, 13%Cr and 4%Ni offers good mechanical properties, good castability, good weldability and good resistance to cavitation. It is used for nearly all the hydroelectric turbines in the world (including those of the huge "Three gorges " dam in China).

Additions of B, Co, Nb, Ti improve the high temperature properties, particularly creep resistance (for heat exchangers in steam turbines).

A specific grade is Type 630 (also called 17/4 PH) which is martensitic and hardens by precipitation at 475°C.

They are hardenable by heat treatment (specifically by quenching and stress relieving, or by quenching and tempering).[5] The alloy composition, and the high cooling rate of quenching enable the formation of martensite. Tempered martensite gives steel good hardness and high toughness; used largely for medical tools (scalpels, razors and internal clamps).[6] Untempered martensite is low in toughness and therefore brittle.

The characteristic body-centered tetragonal martensite microstructure was first observed by German microscopist Adolf Martens around 1890. In 1912, Elwood Haynes applied for a U.S. patent on a martensitic stainless steel alloy. This patent was not granted until 1919.[7]

Martensitic stainless steel can be nondestructively tested using the magnetic particle inspection method, unlike austenitic stainless steel.

Also in 1912, Harry Brearley of the Brown-Firth research laboratory in Sheffield, England, while seeking a corrosion-resistant alloy for gun barrels, discovered and subsequently industrialized a martensitic stainless steel alloy. The discovery was announced two years later in a January 1915 newspaper article in The New York Times.[8] Brearly applied for a U.S. patent during 1915. This was later marketed under the "Staybrite" brand by Firth Vickers in England and was used for the new entrance canopy for the Savoy Hotel in 1929 in London.[9]

When formability, softness, etc. are required in fabrication, steel having 0.12 per cent maximum carbon
is often used in soft condition. With increasing carbon, it is possible by hardening and tempering to obtain tensile strength in the range of 600 to 900 N/mm2, combined with reasonable toughness and ductility. In this condition, these steels find many useful general applications where mild corrosion resistance is required. Also, with the higher carbon range in the hardened and lightly tempered condition, tensile strength of about 1600 N/mm2 may be developed with lowered ductility

A common example of a Martensitic stainless steel is X46Cr13.

See also[edit]

References[edit]

  1. ^ "Classifications of Stainless Steel". aws.org. American Welding Society. Retrieved 2019-04-02.
  2. ^ D. Peckner and I.M. Berstein (1977). Handbook of stainless steels. Mc Graw Hill. pp. Chapter 6. ISBN 978-0070491472.
  3. ^ "Martensitic Stainless Steels". International Stainless Steel Forum. 2018.
  4. ^ http://metals.about.com/od/properties/a/Steel-Types-And-Properties.htm, http://www.totalmateria.com/page.aspx?ID=CheckArticle&site=kts&NM=199.
  5. ^ Budynas, Richard G. and Nisbett, J. Keith (2008). Shigley's Mechanical Engineering Design, Eight Edition. New York, NY: McGraw-Hill Higher Education. ISBN 978-0-07-312193-2.
  6. ^ Akhavan Tabatabae, Behnam; et al. (2009). "Influence of Retained Austenite on the Mechanical Properties of Low Carbon Martensitic Stainless Steel Castings". ISIJ International. 51 (3): 471–475. doi:10.2355/isijinternational.51.471.
  7. ^ Rodney Carlisle; Scientific American (2005-01-28). Scientific American Inventions and Discoveries: All the Milestones in Ingenuity – From the Discovery of Fire to the Invention of the Microwave Oven. John Wiley & Sons. p. 380. ISBN 978-0-471-66024-8.
  8. ^ "A non-rusting steel". New York Times. 31 January 1915.
  9. ^ Sheffield Steel, ISBN 0-7509-2856-5.