With the world economy, the corrosion resistance of stainless steel requires a gradual increase, the use of ultra-low carbon stainless steel is becoming increasingly popular; addition, because the scarcity of resources of nickel, nickel prices high, 400 series stainless steel, duplex stainless steel and super fast development, and therefore should be of stainless steel smelting Combination of two-step and three-step process. In the production of ordinary carbon stainless steel to two-step based; in the production of low carbon and nitrogen stainless steel, mainly in three steps, in order to improve the quality of stainless steel smelting.