630 / 17-4PH

630 (UNS S17400) is a precipitation-hardening austenitic-ferritic stainless steel, mainly composed of chromium, nickel, copper, and niobium. It is renowned for excellent high strength (achieved via precipitation hardening heat treatment), good corrosion resistance, and stable mechanical properties at medium temperatures (up to 315 °C). It balances high tensile strength (over 1000 MPa after aging) and moderate ductility, making it ideal for applications requiring both high structural strength and corrosion resistance.​.

Behaviour that matters in service

• High Mechanical Strength — After precipitation hardening (aging treatment), it exhibits ultra-high tensile strength (1000 – 1300 MPa) and yield strength (800 – 1100 MPa), far exceeding conventional austenitic stainless steels (e.g., 304, 316).​.
• Corrosion Resistance — Good resistance to atmospheric corrosion, fresh water, and weak corrosive media (e.g., dilute acids, alkalis); performance is between 304 stainless steel and martensitic stainless steel, suitable for non-severe corrosion environments.​.
• Medium-Temperature Stability — Maintains stable strength and toughness at temperatures up to 315 °C; no significant creep deformation under long-term medium-temperature service, suitable for medium-temperature structural components.​.
• Controllable Formability — In the solution-annealed state (soft state), it has good cold/hot working performance (e.g., stamping, bending, forging); after aging treatment, hardness increases significantly, limiting secondary processing.​.
• Weldability — Weldable via standard methods (e.g., TIG welding, MIG welding); however, heat input must be controlled to avoid grain coarsening and reduced corrosion resistance; post-weld aging treatment is recommended to restore mechanical properties.​.

Typical applications

• Aerospace & Aviation — Used in aircraft structural components (e.g., brackets, fasteners), engine parts, and missile components; high strength and light weight meet aerospace load requirements.​.
• Petrochemical Industry — Applied to high-pressure valves, pump shafts, pipeline flanges, and wellhead equipment; resists corrosion from oilfield media and maintains strength under high pressure.​.
• Medical Equipment — Employed in surgical instruments (e.g., scissors, forceps), orthopedic implants (e.g., artificial joints), and dental tools; good biocompatibility and corrosion resistance meet medical hygiene standards.​.
• Mechanical Manufacturing — Used in high-strength gears, shafts, bearings, and mold cores; suitable for mechanical parts requiring wear resistance and high load-bearing capacity.​.
• Food & Pharmaceutical Equipment — Applied to high-strength components of food processing machinery (e.g., pressure vessels) and pharmaceutical sterile equipment; corrosion resistance meets food-grade and pharmaceutical-grade requirements.