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.[1][2][3][4]

Tweezers made of 410 martensitic stainless steel

History

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.[5] 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.[6]

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]

Overview

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):[8]

  • 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 compositions
Chemical composition of a few common martensitic stainless steel grades from EN 10088-1 (2005) standard
Chemical composition (main alloying elements) in wt%
EN

Steel designation

 EN

Number

 AISI

Number
Number C Cr Mo Others Remarks
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

Cu: 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.

Mechanical Properties

They are hardenable by heat treatment (specifically by quenching and stress relieving, or by quenching and tempering (referred to as QT).[9][10] 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).[11]

Mechanical properties of a few common martensitic stainless steel grades according to EN 10088-3 Standard
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

Physical properties
Physical properties of a few common martensitic stainless steels from EN 10088-1 (2005) standard
EN Designation EN AISI Young’s Modulus at 20 °C,

Gpa

 Mean coefficient of thermal expansion between 20 and 100 °C

10−6K−1.

 Thermal Conductivity at 20 °C

W.m−1K−1

 Specific Thermal capacity at 20 °C

J.Kg−1.K−1

 Electrical resitivity

10−6Ω.m

X12Cr13 1.4006 410 215 10.5 30 460 0.60
X20Cr13 1.4021 420 215 10.5 30 460 0.65
X50CrMoV15 1.4116 215 10.5 30 460 0.65
X39CrMo17-1 1.4122 215 10.4 15 430 0.80
X105CrMo17 1.4125 440C 215 10.4 15 430 0.80
X17CrNi16-2 1.4057 431 215 10.0 25 460 0.70
X3CrNiMo13-4 1.4313 200 10.5 25 430 0.60
X4CrNiMo16-5-1 1.4418 195 10.3 30 430 0.80
X5CrNiCuNb16-4 1.4542 630 200 10.9 30 500 0.71

Processing

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

Applications [4]

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

pumps

valves

boat shafts

-wear resistant and corrosion resistant applications

cutlery

medical tools (scalpels, razors and internal clamps)[11]

bearings (ball bearings)

razor blades

injection molds for polymers

brake disks for bikes & motorbikes

References
  1. "Premium Alloys 17-4 Stainless Steel". Retrieved 2019-11-26.
  2. "Classifications of Stainless Steel". aws.org. American Welding Society. Retrieved 2019-04-02.
  3. D. Peckner and I.M. Berstein (1977). Handbook of stainless steels. Mc Graw Hill. pp. Chapter 6. ISBN 978-0070491472.
  4. "Martensitic Stainless Steels". International Stainless Steel Forum. 2018.
  5. "A non-rusting steel". New York Times. 31 January 1915.
  6. Sheffield Steel, ISBN 0-7509-2856-5.
  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. http://metals.about.com/od/properties/a/Steel-Types-And-Properties.htm, http://www.totalmateria.com/page.aspx?ID=CheckArticle&site=kts&NM=199.
  9. 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.
  10. 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.
  11. 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.
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