Using stainless steel based on ferrite organizations under the State. Chromium content in 11~30, with a body - centered crystal structure. This type of steel without nickel, sometimes contains small amounts of Mo, Ti, Nb elements, this type of steel with thermal conductivity coefficient, small expansion coefficient, excellent oxidation resistance, resistance to stress corrosion characteristics, used in the manufacture of air, steam, water and oxidation resistance of acid corrosion of parts. After this type of steel - plastic, welding plastic and significantly reduced the corrosion resistance of shortcomings, which limits its application. External refining technology ( AOD or VOD ) allows the application of gap element such as carbon, nitrogen greatly reduced, thus enabling this type of steel used.