17-4 stainless steel 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, 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. Uses
Marine grade stainless the stainless surface can be rinsed by rainfall, which will reduce the tendency for surface chlorides to concentrate by evaporation. Thus, the underside of overhangs will be more susceptible to corrosion due to lack of rinsing, also desert locations near the seashore will typically be more corrosive than seashores in locations with high rainfall. Visible evidence of corrosive attack in a marine environment is known as “tea staining”. Marine grade stainless Marine grade stainless steel is a misunderstood description. There is no industry recognized definition for a marine grade stainless steel though it is routinely used by many end-users. In