440C Steel (UNS S44004)
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440C Steel (ASTM A276, ASTM A314, EN 1.4125)
440C is a high-carbon martensitic stainless steel known for its exceptional hardness, wear resistance, and moderate corrosion resistance. It is capable of attaining the highest hardness among stainless steels (up to ~60 HRC) after heat treatment. Commonly used in bearings, knives, molds, and surgical tools, 440C offers a good balance between mechanical strength and corrosion performance in hardened form.
Chemical Composition:
| Element | Content (%) |
|---|---|
| Carbon (C) | 0.95 – 1.20 |
| Chromium (Cr) | 16.0 – 18.0 |
| Manganese (Mn) | ≤ 1.00 |
| Silicon (Si) | ≤ 1.00 |
| Molybdenum (Mo) | ≤ 0.75 |
| Phosphorus (P) | ≤ 0.040 |
| Sulfur (S) | ≤ 0.030 |
| Iron (Fe) | Balance |
Mechanical Properties:
| Property | Value |
|---|---|
| Tensile Strength | Up to 1900 MPa (hardened) |
| Yield Strength (0.2%) | ~1280 MPa (typical) |
| Elongation (50 mm) | ~4% (hardened) |
| Charpy Impact Strength | ~10–15 J (hardened) |
| Hardness (Rockwell C) | 56 – 60 HRC (hardened) |
Physical Properties:
| Property | Value |
|---|---|
| Density | 7.75 g/cm³ |
| Modulus of Elasticity | ~200 GPa |
| Thermal Conductivity | ~24.2 W/m·K (at 100°C) |
| Specific Heat Capacity | ~460 J/kg·K |
| Melting Point | ~1480 – 1530 °C |
| Thermal Expansion | ~10.2 µm/m·°C (20–100°C) |
| Electrical Resistivity | ~600 nΩ·m |
Heat Treatment:
- Annealing: 840 – 900°C, slow furnace cooling
- Hardening: Austenitize at 1010 – 1065°C, then oil or air quench
- Tempering: 150 – 370°C (avoid 425 – 565°C range to prevent embrittlement)
- Optional cryogenic treatment: may be used after quenching to minimize retained austenite
Applications:
- High-quality ball bearings
- Knife blades and cutting tools
- Molds and dies
- Valve components and pumps
- Surgical and dental instruments
- Aerospace actuator parts
Corrosion Resistance
Good in air and mild environments when hardened and passivated.
Not recommended for use in marine or highly acidic/alkaline conditions. Best corrosion performance when polished.
Not recommended for use in marine or highly acidic/alkaline conditions. Best corrosion performance when polished.