17-4 stainless steel

SAE Type 630 stainless steel (more commonly known as 17-4 PH, or simply 17-4; also known as UNS 17400) is a grade of martensitic precipitation hardened stainless steel. It contains approximately 15–17.5% chromium and 3–5% nickel, as well as 3–5% copper.[1] The name comes from the chemical makeup which is approximately 17% chromium and 4% nickel.

Properties

17-4 can be heat treated to high levels of strength and hardness, and features corrosion resistance[1] and machinability[2] 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.[1]

Overaging (aging beyond the peak strength condition) improves resistance to stress corrosion cracking.[3]

Applications

Uses for 17-4 stainless steel include components which require high hardness and/or corrosion resistance at temperatures of up to 600 °F (316 °C).[2] Specific applications for 17-4 include the petroleum and chemical industries, as well as use in aircraft parts.[1]

Composition
Proportion by mass (%)[1][2]
CMnPSSiCrNiCuNb, Ta
0.07 max.1.0 max.0.04 max.0.03 max.1.0 max.15.0–17.53.0–5.03.0–5.00.15–0.45

References
  1. "Type 630; 17 Cr-4 Ni; UNS 17400" (PDF). Outokumpu.com. Archived from the original (PDF) on December 23, 2015. Retrieved June 5, 2016.
  2. "North American Stainless – Long Products Stainless Steel Grade Sheet" (PDF). North American Stainless. Retrieved June 5, 2016.
  3. "Stress Corrosion Properties of High-Strength Precipitation Hardening Stainless Steels in 3.5% Aqueous Sodium Chloride Solution" (PDF). Retrieved September 6, 2016.


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