SAE type 630 stainless steel (more commonly known as 17-4; also known as UNS 17400) is a grade of martensitic precipitation hardened stainless steel. It contains approximately 15-17.5% (17) chromium and 3-5% (4) nickel, as well as 3-5% copper.
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Properties
17-4 can be heat treated to high levels of strength and hardness, and features corrosion resistance and machinability comparable to austenitic 304 stainless. Being martensitic, 17-4 is magnetic.
17-4 is capable of being hardened up to approximately 44 Rc when heat treated to condition H900.
Overaging (aging beyond the peak strength condition) improves resistance to stress corrosion cracking.
Applications
Uses for 17-4 include components which require high hardness and/or corrosion resistance at temperatures of up to 600 °F (316 °C). Specific applications for 17-4 include the petroleum and chemical industries, as well as use in aircraft parts.