17-4 stainless steel

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SAE type 630 stainless steel (more commonly known as 17-4; also known as UNS 17400[1]) 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.[2]


17-4 can be heat treated to high levels of strength and hardness, and features corrosion resistance[2] and machinability[3] 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.[2]

Overaging (aging beyond the peak strength condition) improves resistance to stress corrosion cracking.[4]


Uses for 17-4 include components which require high hardness and/or corrosion resistance at temperatures of up to 600 °F (316 °C).[3] Specific applications for 17-4 include the petroleum and chemical industries, as well as use in aircraft parts.[2]


Proportion by mass (%)[2][3]
C a Mn P S Si Cr Ni Cu Nb, Ta
0.07 max. 1.2 max. 0.040 max. 0.030 max. 1.0 max. 15.0-17.5 3.0-5.0 3.0-5.0 0.15-0.45