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.[6] 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.[7]
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):[9]
Up to about 0.4%C they are used mostly for their mechanical properties in applications such as pumps, valves, and shafts.
Above 0.4%C they are used mostly for their wear resistance, such as in cutlery surgical blades, plastic injection molds, and 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, and good weldability. 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. This is used 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 (887 °F).
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%
There are many proprietary grades not listed in the standards, particularly for cutlery.
Mechanical Properties
Martensitic stainless alloys are hardenable by heat treatment, specifically by quenching and stress relieving, or by quenching and tempering (referred to as QT).[10][11] 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 seen below, and is largely used for medical surgical instruments, such as scalpels, razors, and internal clamps.[12]
Mechanical properties of a few common martensitic stainless steel grades according to EN 10088-3 Standard
EN
Mininmum Yield stress
Tensile strength
Minimum Elongation, %
Heat treatment
1.4006
450 MPa (65 ksi)
650–850 MPa (94–123 ksi)
15
QT650
1.4021
600 MPa (87 ksi)
650–850 MPa (94–123 ksi)
12
QT800
1.4122
550 MPa (80 ksi)
750–950 MPa (109–138 ksi)
12
QT750
1.4057
700 MPa (100 ksi)
900–1,050 MPa (131–152 ksi)
12
QT900
1.4418
700 MPa (100 ksi)
840–1,100 MPa (122–160 ksi)
16
QT900
1.4542
790 MPa (115 ksi)
960–1,160 MPa (139–168 ksi)
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 (68 °F),
Gpa
Mean coefficient of thermal expansion between 20 and 100 °C (68 and 212 °F)
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 GPa (31.2×10^6 psi)
10.5
30
460
0.60
X20Cr13
1.4021
420
215 GPa (31.2×10^6 psi)
10.5
30
460
0.65
X50CrMoV15
1.4116
420MoV
215 GPa (31.2×10^6 psi)
10.5
30
460
0.65
X39CrMo17-1
1.4122
215 GPa (31.2×10^6 psi)
10.4
15
430
0.80
X105CrMo17
1.4125
440C
215 GPa (31.2×10^6 psi)
10.4
15
430
0.80
X17CrNi16-2
1.4057
431
215 GPa (31.2×10^6 psi)
10.0
25
460
0.70
X3CrNiMo13-4
1.4313
200 GPa (29×10^6 psi)
10.5
25
430
0.60
X4CrNiMo16-5-1
1.4418
195 GPa (28.3×10^6 psi)
10.3
30
430
0.80
X5CrNiCuNb16-4
1.4542
630
200 GPa (29×10^6 psi)
10.9
30
500
0.71
Processing
When formability, softness, etc. are required in fabrication, steel having 0.12% 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 MPa (87 to 131 ksi), 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 1,600 MPa (230 ksi) may be developed with lowered ductility.
A common example of a Martensitic stainless steel is X46Cr13.
Martensitic stainless steels, depending upon their carbon content are often used for their corrosion resistance and high strength in pumps, valves, and boat shafts.[4]
They are also used for their wear resistance in, cutlery, medical tools (scalpels, razors and internal clamps),[12] ball bearings, razor blades, injection molds for polymers, and brake disks for bicycles and motorbikes.
^Budynas, Richard G. and Nisbett, J. Keith (2008). Shigley's Mechanical Engineering Design, Eight Edition. New York, NY: McGraw-Hill Higher Education. ISBN978-0-07-312193-2.