Martensitic stainless steel
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 that can be hardened and tempered through multiple ways of aging/heat treatment.
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. 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.
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.
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):
- 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.
|Chemical composition (main alloying elements) in wt%|
|X12Cr13||1.4006||410||0.12||12.5||—||—||Base grade, used as stainless engineering steel|
|X20Cr13||1.4021||420||0.20||13.0||—||—||Base grade, used as stainless engineering steel|
|X50CrMoV15||1.4116||-||0.50||14.5||0.65||V: 0.15||Used chiefly for professional knives|
|X14CrMoS17||1.4104||430F||0.14||16.5||0.40||S: 0.25||Sulphur improves machinability|
|X39CrMo17-1||1.4122||-||0.40||16.5||1.10||—||Used chiefly for professional knives|
|X105CrMo17||1.4125||440C||1.10||17.0||0.60||—||Tool steel grade (440C), high wear resistance|
|X17CrNi16-2||1.4057||431||0.17||16.0||—||Ni: 2.00||Ni replaces some C for higher ductility & toughness|
|X4CrNiMo16-5-1||1.4418||-||≤ 0.06||16.0||1.10||Ni: 2.00||Highest corrosion resistance of martensitics|
|X5CrNiCuNb16-4||1.4542||630 (17/4PH)||≤ 0.07||16.0||-||Ni: 4.00
Nb: 5xC to 0.45
|Precipitation hardening grade
High strength. Used in aerospace
There are many proprietary grades not listed in the standards, particularly for cutlery.
They are hardenable by heat treatment (specifically by quenching and stress relieving, or by quenching and tempering (referred to as QT). The alloy composition, and the high cooling rate of quenching enable the formation of martensite. Untempered martensite is low in toughness and therefore brittle.Tempered martensite gives steel good hardness and high toughness as can be see below; used largely for medical tools (scalpels, razors and internal clamps).
|Mininmum Yield stress, MPa||Tensile strength, MPa||Minimum Elongation, %||Heat treatment|
|1.4006||450||650 - 850||15||QT650|
|1.4021||600||650 - 850||12||QT800|
|1.4122||550||750 - 950||12||QT750|
|1.4057||700||900 - 1050||12||QT900|
|1.4418||700||840 - 1100||16||QT900|
|1.4542||790||960 - 1160||12||P960|
IN the heat treatment column, QT refers to Quenched and Tempered, P refers to Precipitation hardened
|EN Designation||EN||AISI||Young’s Modulus at 20 °C,
|Mean coefficient of thermal expansion between 20 and 100 °C
|Thermal Conductivity at 20 °C
|Specific Thermal capacity at 20 °C
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.
Martensitic stainless steels, depending upon their carbon content can be seen as
- corrosion resistant engineering steels (see above table on mechanical properties) used in a variety of mechanical engineering applications
-wear resistant and corrosion resistant applications
medical tools (scalpels, razors and internal clamps)
bearings (ball bearings)
injection molds for polymers
brake disks for bikes & motorbikes
- "Premium Alloys 17-4 Stainless Steel". Retrieved 2019-11-26.
- "Classifications of Stainless Steel". aws.org. American Welding Society. Retrieved 2019-04-02.
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- "Martensitic Stainless Steels". International Stainless Steel Forum. 2018.
- "A non-rusting steel". New York Times. 31 January 1915.
- Sheffield Steel, ISBN 0-7509-2856-5.
- 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.
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- Dossett, Jon L; Totten, George E., eds. (2014). Heat treating of irons and steels. ASM International. pp. 382–396. ISBN 978-1-62708-168-9.
- 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.
- 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.