SUS630 is a martensitic precipitation-hardening stainless steel under the Japanese JIS standard, corresponding to the American grade 17-4PH and the Chinese grade 05Cr17Ni4Cu4Nb. Its core advantage lies in the ability to precisely control strength and hardness through heat treatment, while maintaining moderate corrosion resistance, making it a common material for high-strength industrial applications.
1. Core basic properties
Chemical composition: Mainly contains 15–17.5% chromium, 3–5% nickel, 3–5% copper, with 0.15–0.45% niobium, and carbon ≤0.07%. Copper and niobium are key for precipitation hardening, while chromium and nickel ensure basic corrosion resistance.
Microstructure: Martensitic at room temperature. Solution treatment forms a supersaturated solid solution, and aging treatment precipitates fine copper-based phases to achieve performance strengthening.
Key characteristics: Magnetic (more noticeable in the aged state), weldable (post-weld aging required), good machinability in the solution-treated state, and surface properties can be enhanced through polishing and passivation.

2. Core performance
Mechanical properties: After aging, tensile strength is 1000–1400 MPa, yield strength 800–1200 MPa, hardness 30–45 HRC. In the solution-treated state, strength is lower (tensile strength ~620 MPa) but with excellent ductility (elongation ≥30%), facilitating machining.
Corrosion resistance: Resistant to atmospheric, freshwater, and neutral salt corrosion, with moderate resistance to chloride pitting, superior to ordinary martensitic steel, suitable for high-strength applications without strong corrosive exposure.
Temperature adaptability: Stable performance at long-term service temperatures ≤300°C, good toughness at low temperatures (-50°C), and should avoid prolonged heating in the 400–450°C range to prevent “475°C embrittlement.”

3. Typical applications
Mechanical manufacturing: High-strength bolts, gears, shafts, and components for steam turbines.
Aerospace: Aircraft landing gear parts, engine components, and other parts requiring high strength.
Petrochemical industry: High-pressure valves, flanges, pump bodies, and other corrosion-resistant load-bearing equipment components.
Medical devices: Surgical instruments and some implants requiring biocompatibility.
Other fields: Injection molds, high-strength structural components in marine environments.

4. Core machining and heat treatment
Heat treatment process: Core process is solution treatment (1040–1060°C heating + rapid cooling) followed by aging treatment (480–620°C hold for 4 hours + air cooling). Different aging temperatures correspond to different levels of strength and hardness.
Machining characteristics: Preferably performed in the solution-treated state for cutting, stamping, etc. After aging, hardness is high and machining requires specialized tools. Preheating to 80–150°C is recommended before welding, and post-weld aging restores the material's performance.