Martensitic stainless steels are one of the four main types of stainless steels (Austenitic, Ferritic, Duplex, Martensitic).
Because of its chemical compositions, martensitic steel, a form of stainless steel, can be strengthened and toughened by heat and age processes. These techniques increase the strength of martensitic steel relative to other varieties, making it an excellent material for the manufacture of mechanical instruments, turbine parts, medical devices, and other varied uses.
In order to attain particular qualities, different grades of nickel, selenium, phosphorus, vanadium, and sulfur are added to martensitic stainless steels, which typically include 11.5 to 18% chromium and up to 1% carbon. At high temperatures, these steels have a face-centered cubic (FCC) structure, but during heat treatment, quenching causes the austenite to change into martensite, which has a body-centered cubic (BCC) structure.
Martensitic stainless steels can be quenched and tempered to acquire increased mechanical qualities, such as higher hardness and tensile strength, making them particularly receptive to heat treatment. Additionally, they belong to the class of stainless steels that can be precipitation-hardened to meet specific mechanical property requirements. Even though martensitic stainless steels can be hot worked, they have poor formability and weldability. However, adding sulfur can increase their machinability. These steels are rather simple to cold work when the carbon concentration is low.
| AISI 410 | AISI 420 | AISI 431 | AISI 440A | AISI 440B | AISI 440C | |
|---|---|---|---|---|---|---|
| Yield strength at 20 °C | 540 MPa | 760 MPa | 1070 MPa | 1650 MPa | 1860 MPa | 1900 MP |
| Poisson ratio at 20 °C | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 |
| Elong. at 20 °C | 16% | 12% | 15% | 5% | 3% | 2% |
| Tensile str. at 20 °C | 740 MPa | 980 MPa | 1390 MPa | 1790 MPa | 1930 MPa | 1970 MPa |
| Elec. cond. at 20 °C | 1.68*107 S/m | 1.68*107 S/m | 1.45*107 S/m | 1.57*107 S/m | 1.28*107 S/m | 1.28*107 S/m |
| CTE at 20 °C | 1.1*10-5 1/K | 1*10-5 1/K | 1.2*10-5 1/K | 1*10-5 1/K | 1*10-5 1/K | 1*10-5 1/K |
| Thermal cond. at 20 °C | 30 W/(m.K) | 30 W/(m·K) | 25 W/(m·K) | 30 W/(m·K) | 15 W/(m·K) | 15 W/(m·K) |
| Melting point at 20 °C | 1480°C | 1450°C |
1450°C |
1370°C |
1370°C |
1370°C |
| Specific heat capacity at 20 °C | 460 J/(Kg.K) | 460 J/(kg·K) | 460 J/(kg·K) | 460 J/(kg·K) | 430 J/(kg·K) | 430 J/(kg·K) |
Due to their excellent thermal conductivity, martensitic stainless steels are suitable for heat exchangers and other applications that call for efficient heat transfer. Additionally, they are more likely to maintain their shape at high temperatures due to their low coefficient of thermal expansion (CTE). Due of their high Young's modulus, they are also utilized in aerospace applications where a high level of stiffness is required.
410: martensitic steel for all purposes. used in settings with minor corrosion. Applications include gas and steam turbine blades, bushings, and flatware.
416: contains more phosphorus and sulfur to make it easier to machine. In its version 416Se, selenium is used in place of sulfur. Among the applications are screws and gears.
420: higher carbon content for better mechanical characteristics. Applications include surgical and dental equipment.
431: higher chromium content for improved corrosion resistance. Applications consist of pumps and valves.
414: nickel has been added to the mixture to improve corrosion resistance. Spring applications are one example.
440: greater hardness and corrosion resistance due to higher carbon and chromium content. Measurement devices, ball bearings, gauge blocks, moulds, and dies, etc. are examples of applications. It comes in three subgrades, 440A, 440B, and 440C, with different carbon content to alter its hardness and toughness.