Stainless steel mainly composed of ferrite in use. The chromium content is between 11% and 30%, and has a body-centered cubic crystal structure. These steels generally do not contain nickel, and sometimes contain a small amount of elements such as Mo, Ti, Nb, etc. These steels are characterized by large thermal conductivity, small expansion coefficient, good oxidation resistance and excellent resistance to stress corrosion. Parts that are corroded by water vapor, water, and oxidizing acids. Such steels have the disadvantages of poor plasticity, post-weld plasticity and corrosion resistance, which limit their application. The application of refining technology (AOD or VOD) can greatly reduce the gap elements such as carbon and nitrogen, thus making this type of steel widely used.