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,
Stainless steel Hydrochloric acid will damage any kind of stainless steel, and should be avoided. All types of stainless steel resist attack from phosphoric acid and nitric acid at room temperature. At high concentration and elevated temperature attack will occur and higher alloy stainless steels are required. In general, organic acids are less corrosive than mineral acids such as hydrochloric and sulfuric acid. As the molecular weight of organic acids increase their corrosivity decreases. Formic acid has the lowest molecular weight and is a strong acid. Type 304 can be used with formic acid though it will tend to discolor the solution.