17-4 is a martensitic precipitation hardened stainless steel. The name comes from the chemical makeup which is approximately 17% chromium and 4% nickel. SAE Type 630 or Alloy 630 stainless steel is the same as 17-4PH, and they both refer to the same grade. 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. (UNS S17400)
Element | Min | Max |
---|---|---|
Carbon, C | – | 0.07 |
Manganese, Mn | – | 1 |
Silicon, Si | – | 1 |
Sulfur, S | – | 0.03 |
Phosphorus, P | – | 0.04 |
Chromium, Cr | 15 | 17.5 |
Molybdenum, Mo | - | 0.5 |
Nickel, Ni | 3 | 5 |
Columbium (Niobium), Nb | 5xC | 0.45 |
Copper, Cu | 3 | 5 |