Grade 440C stainless steel is a high carbon martensitic stainless steel. It has high strength, moderate corrosion resistance, and good hardness and wear resistance. Grade 440C is capable of attaining, after heat treatment, the highest strength, hardness and wear resistance of all the stainless alloys. Its very high carbon content is responsible for these characteristics, which make 440C particularly suited to such applications as ball bearings and valve parts.
| Country | USA | BS & DIN | Japan |
| Standard | ASTM A276 | EN 10088 | JIS G4303 |
| Grades | S44004/440C | X105CrMo17/1.4125 | SUS440C |
| Standard | Grade | C | Mn | P | S | Si | Cr | Mo |
| ASTM A276 | S44004/440C | 0.95-1.20 | ≦1.00 | ≦0.04 | ≦0.03 | ≦1.00 | 16.0-18.0 | ≦0.75 |
| EN10088 | X105CrMo17/1.4125 | 0.95-1.20 | ≦1.00 | ≦0.04 | ≦0.03 | ≦1.00 | 16.0-18.0 | 0.40-0.80 |
| JIS G4303 | SUS 440C | 0.95-1.20 | ≦1.00 | ≦0.04 | ≦0.03 | ≦1.00 | 16.0-18.0 | ≦0.75 |
| Grade | Density (kg/m3) | Elastic Modulus (GPa) | Mean Coefficient of Thermal Expansion (mm/m/°C) | Thermal Conductivity(W/m.K) | Specific Heat | Electrical Resistivity (nW.m) | |||
| 0-100°C | 0-200°C | 0-600°C | at 100°C | at 500°C | 0-100°C (J/kg.K) | ||||
| 440 C | 7650 | 200 | 10.1 | 10.3 | 11.7 | 24.2 | – | 460 | 600 |
A martensitic stainless steel. It's composed of these major alloy elements (I don't list the minor elements since they don't play a major role) :
Carbon: 1.00-1.25% This increases hardenability and wear resistance, but decreases toughness in higher amounts.
Manganese: .45% This is added to reduce brittleness and improve forgeability, hardenability, and reducing deformation.
Silicon: .30% This is a deoxidizer and improves hot-forming properties.
Chromium: 17.00-18.00% Added in high amounts only to high alloy tool steels: this improves hardenability, high wear resistance, toughness, and corrosion resistance.
Molybdenum: .50% Improves deep hardening and toughness, along with wear resistance.
These basic elements (along with iron) are a simple combination that works well together, and has for many decades.
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