17-4 stainless steel for 17-4 include components which require high hardness and/or corrosion resistance at temperatures of up to . Specific applications for 17-4 include the petroleum and chemical industries, as well as use in aircraft parts. 17-4 stainless steel 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. 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,
SAE 304 stainless steel cracking above about 60 °C. It is considered resistant to pitting corrosion in water with up to about 400 mg/L chlorides at ambient temperatures, reducing to about 150 mg/L at 60 °C. 304 stainless steel is also very sensitive at room temperature to the thiosulfate anions released by the oxidation of pyrite (as encountered in acid mine drainage) and can undergo severe pitting corrosion problems when in close contact with pyrite- or sulfide-rich clay materials exposed to oxidation. For more severe corrosion conditions, when 304 stainless steel is too sensitive to pitting or crevice corrosion by chlorides or general corrosion