SUS440C Stainless Steel Detailed Information
SUS440C is a high-carbon martensitic stainless steel, known for its excellent hardness, wear resistance, and moderate corrosion resistance. It is part of the JIS G4403 standard and is equivalent to AISI 440C and DIN 1.4125. SUS440C is commonly used in cutting tools, bearings, knives, and high-wear components.
Key Features
High Hardness & Wear Resistance
- One of the hardest stainless steels, achieving 56 – 60 HRC after heat treatment.
Moderate Corrosion Resistance
- Better than carbon steels, but lower than austenitic stainless steels.
- Performs well in mildly corrosive environments.
Good Machinability (in annealed condition)
- Can be machined and ground easily before heat treatment.
High Strength & Edge Retention
- Used in knife blades, bearings, and precision tools.
Magnetic
- Unlike austenitic stainless steels (SUS304, SUS316), SUS440C is magnetic.
Chemical Composition
| Element | Composition (%) |
| Carbon (C) | 0.95 – 1.20 |
| Silicon (Si) | ≤ 1.00 |
| Manganese (Mn) | ≤ 1.00 |
| Phosphorus (P) | ≤ 0.040 |
| Sulfur (S) | ≤ 0.030 |
| Chromium (Cr) | 16.0 – 18.0 |
| Molybdenum (Mo) | ≤ 0.75 |
- High Carbon (C) Content → Provides high hardness and wear resistance.
- High Chromium (Cr) Content → Offers moderate corrosion resistance.
Mechanical Properties
| Property | Value |
| Density | 7.7 – 7.8 g/cm³ |
| Tensile Strength | 760 – 2,070 MPa |
| Yield Strength | 450 – 1,700 MPa |
| Elongation | ≥ 10% |
| Hardness (Annealed) | ≤ 250 HB |
| Hardness (Hardened) | 56 – 60 HRC |
| Thermal Conductivity | 24.2 W/m·K |
| Melting Point | 1,400 – 1,460°C |
- Extremely high hardness, making it ideal for cutting tools and wear-resistant applications.
- Moderate corrosion resistance, lower than austenitic stainless steels (e.g., SUS304, SUS316).
SUS440C vs. Other Stainless Steels
| Property | SUS440C (AISI 440C) | SUS420J2 | SUS304 | SUS316 |
| Hardness (HRC) | 56 – 60 | 48 – 52 | ≤ 20 | ≤ 20 |
| Wear Resistance | Excellent | Good | Low | Low |
| Corrosion Resistance | Moderate | Lower | Excellent | Best |
| Strength | High | Medium | Lower | Lower |
| Weldability | Poor | Better | Excellent | Excellent |
Why Choose SUS440C?
- Harder and more wear-resistant than SUS420J2.
- Stronger than SUS304 and SUS316, but with lower corrosion resistance.
- Best choice for high-wear applications like bearings and cutting tools
Applications
Cutting Tools & Knives
- Surgical instruments, industrial blades, and high-end knives.
Bearings & Ball Screws
- High-load bearings, roller bearings, and ball screws.
Molds & Dies
- Plastic injection molds, stamping dies, and wear-resistant mold parts.
Automotive & Aerospace Components
- Engine parts, precision gears, and high-strength mechanical parts.
High-Wear Machine Parts
- Valve seats, pump components, and shaft sleeves.
Heat Treatment Process
Higher tempering temperatures (above 400°C) reduce hardness significantly.
Annealing
- Heat to 850 – 900°C, then slow cool in a furnace.
- Improves machinability and softens the material.
Hardening (Quenching)
- Heat to 1,000 – 1,080°C, then oil or air quenching.
- Achieves maximum hardness (56 – 60 HRC).
Tempering
- Heat to 150 – 300°C, then air cool.
- Adjusts hardness and toughness.
Alternative Materials
- SUS420J2 → Lower hardness but better toughness and weldability.
- SUS304 → Better corrosion resistance but much softer.
- D2 Steel (SKD11) → Better wear resistance but not stainless.
Conclusion
SUS440C stainless steel is a high-hardness, wear-resistant material widely used in bearings, knives, tools, and high-strength mechanical parts.
Best for: Cutting tools, high-load bearings, and precision machinery.
Why Choose SUS440C? It offers the highest hardness among stainless steels with moderate corrosion resistance.
