Stainless steel mainly composed of ferrite structure in use. The chromium content ranges from 11% to 30% and has a body centered cubic crystal structure. This type of steel generally does not contain nickel, and sometimes contains small amounts of elements such as Mo, Ti, Nb, etc. This type of steel has characteristics such as high thermal conductivity, low expansion coefficient, good oxidation resistance, and excellent stress corrosion resistance. It is often used to manufacture components that are resistant to atmospheric, steam, water, and oxidative acid corrosion. This type of steel has drawbacks such as poor plasticity, significantly reduced plasticity and corrosion resistance after welding, which limits its application. The application of outside furnace refining technology (AOD or VOD) can greatly reduce interstitial elements such as carbon and nitrogen, making stainless steel standard parts widely used.