420 is a martensitic stainless steel alloy known for its high strength and hardness and good wear resistance. It contains 12-14% chromium, which contributes to its lower corrosion resistance compared to other grades of stainless steel. Its corrosion resistance can be maximized by hardening and polishing.
In the annealed condition, the machinability of grade 420 is good, but it declines as hardness rises. If machinability is a priority, 416 stainless performs better, but has lower strength and hardness. Weldability is also poor, and if done, requires close attention to both pre-heating and post-weld tempering. 420 stainless steel is not suitable for cold working.
420 stainless steel is used for molds because of its resistance to corrosion, and has the capability for being highly polished in the optical grade to a mirror-like finish. Other uses are pump components, bushings, fasteners, knives, and other cutting instruments because it holds a durable edge. Additional applications include hand tools and components like needle valves, ball check valves, and cams and pivots, where hardness and wear resistance are beneficial.
| Property | Value | Notes |
|---|---|---|
| Material Type | Martensitic stainless steel | UNS S42000 |
| Density | 7.8g/cm3 | 0.282 lb/in3 |
| Melting Point | ~ 1,455 – 1,510 °C | ~ 2,651 – 2,750 °F |
| Hardness (Brinell) | ~ 48-56 | When hardened and tempered |
| Tensile Strength | ~ 655-1,620 MPa | ~ 95,000-235,000 psi |
| Yield Strength | ~ 345-1,420 MPa | ~ 50,000-205,954 psi |
| Elongation at Break | ~ 10-25% | Depends on tempering temperature |
| Modulus of Elasticity | ~ 200 GPa | ~ 29.01 x 106 psi |
| Corrosion Resistance | Moderate | Resists fresh water, alkalis, foods, mild acids. Best when polished. |
| Magnetism | Yes | |
| Heat Treatment | Can be hardened, tempered, and annealed | |
| Machinability | Good in annealed condition, difficult when hardened. | |
| Weldability | Poor | Requires both pre-heat and post-weld tempering |
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