Martensitic Stainless Steel
The composition is such that the austenite in these steels is able to transform into martensite. This allows greater control of the mechanical properties.
The martensite is generall formed by rapid cooling (quenching) of austenite which traps carbon atoms that do not have time to diffuse out of the crystal structure. This martensitic reaction begins during cooling when the austenite reaches the martensite start temperature (Ms) and the parent austenite becomes mechanically unstable.
The martensite can also be formed by stressing the steel.
Typical compositions cover 12 to 18 Cr and 0.1 to 1.2 C wt%
Chemical Composition of Martensitic Stainless Steels
Grade | C | Mn | Si | Cr | Ni | Mo | P | S | Comments/Applications |
410 | 0.15 | 1.0 | 0.5 | 11.5-13.0 | - | - | 0.04 | 0.03 | The basic composition. Used for cutlery, steam and gas turbine blades and buckets, bushings... |
416 | 0.15 | 1.25 | 1.0 | 12.0-14.0 | - | 0.60 | 0.04 | 0.15 | Addition of sulphur for machinability, used for screws, gears etc. 416 Se replaces suplhur by selenium. |
420 | 0.15-0.40 | 1.0 | 1.0 | 12.0-14.0 | - | - | 0.04 | 0.03 | Dental and surgical instruments, cutlery.... |
431 | 0.20 | 1.0 | 1.0 | 15.0-17.0 | - | 1.25-2.0 | 0.04 | 0.03 | Enhanced corrosion resistance, high strength. |
440A | 0.60-0.75 | 1.0 | 1.0 | 16.0-18.0 | - | 0.75 | 0.04 | 0.03 | Ball bearings and races, gauge blocks, molds and dies, cutlery. |
440B | 0.75-0.95 | 1.0 | 1.0 | 16.0-18.0 | - | 0.75 | 0.04 | 0.03 | As 440A, higher hardness |
440C | 0.95-1.20 | 1.0 | 1.0 | 16.0-18.0 | - | 0.75 | 0.04 | 0.03 | As 440B, higher hardness |
In applications where high strength, hardness, wear resistance is desirable and toughness/ductility are of little concern these steels are particularly suitable. They are frequently used for surgical and other instruments, cutlery and springs.
Generally low (414 has 2% nickel) or no nickel content these steels are less expensive than others.
Type 410S
Stainless Steel Type 410S
Contains lower carbon than Type 410, offers improved weldability but lower hardenability. Type 410S is a general purpose corrosion and heat resisting chromium steel recommended for corrosion resisting applications.
Type 414
Stainless Steel Type 414
Has nickel added (2%) for improved corrosion resistance. Typical applications include springs and cutlery.
Type 416
Stainless Steel Type 416
Contains increased carbon to improve mechanical properties. Typical applications include surgical instruments.
Type 420
Stainless Steel Type 420
Contains increased carbon to improve mechanical properties. Typical applications include surgical instruments.
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