631 stainless steel, also known as SUS 631 or 17-7PH, is a type of stainless steel that is hardened through precipitation. It was developed from 18-8CrNi, an austenitic stainless steel, and has an unstable eat austenite structure after undergoing a solution . This makes it ductile and easy to process. After adjusting the components through precipitation and carbonization, it undergoes martensite transformation treatment to achieve a low-carbon tempered martensite structure with improved toughness. temperatures. Additionally, it has better corrosion resistance than most martensitic stainless steels.

631 stainless steel is commonly used in the manufacturing of high-strength springs, bearings, high-pressure gas cylinders, aircraft parts, and spacecraft parts, among others.