De phosphorus removal casting stainless steel has become a common technology of stainless steel production, it is widely used in production of stainless base metal such as austenitic and duplex. The main task for de phosphorization is eliminate phosphorus to make sure that the phosphorus content of stainless steel is less than 0.030%. A low phosphorus steel is produced by de phosphorizing in a ladle which is apply in SS production.
De phosphorus is made by adding industrial oxygen, argon or ferro-alloy deoxidization to stainless steel. Helium shielding gas or slag is usually used as covering outside the bath in order to protect molten steel with high content of oxygen and nitrogen. By adding these protective materials, production proceeded safely in certain conditions in the purpose to solve oxidation and reaction during de phosphorus.
The reduction of phosphorus in stainless steel is achieve thanks to reaction of Al2O3, FeO and silica with phosphorus when it is heated in the ladle. De phosphorus process must be conducted one time in a operational cycle of stainless steel. Generally de phosphorization is the process that require for a long time, its time depending on the concentration of phosphorus and melting condition of stainless steel. If the de phosphorus process is conditioned improperly, the molten steel cooled quickly and phosphorus content dropped too fast, many complex elements such as Sb, As, Sn, Ni, Cr and Mo will emit from stainless steel bath when the cooling is not enough.
The design of ladle should be based on the capacity of the vessel, the lining materials which can tolerate the high temperatures, and the dimensional constraints. The de phosphorus process is typically conducted in highly basic slag, the reaction time is around 60-90 minutes and its interval time should be no less than 2 hours. The slag is added to molten steel in order to adjust the chemical composition, the slag scale is usually 0.06-0.15%. The production cycle are comprised of several processes such as argon-oxygen blowing, maintenance of temperature, stirring of the steel, temperature management of the slag, addition of slag and evaluation of phosphorus concentration.
The operation parameters are adjusted based on phosphorus content in the steel, the chemical analysis results and the analysis of the slag. The temperature range for de phosphorus process is 1540-1560℃, the amount of deoxidization agent must be strictly controlled. The flow of raw material, the power of stirring of the steel and the flux must also be managed well in order to guarantee the phosphorus concentration in the steel is controlled to achieve the best result.
The controllability of the process is an important factor of the quality of stainless steel. During production, the operators need to analyze periodically the phosphorus concentration of the stainless steel and react quickly when out of controlled range. The percentage of phosphorus in the stainless steel should lower than 0.030%, the oxygen content should lower than 30ppm, the nitrogen content should lower than 100ppm, the impurity content should lower than 150ppm and the surface appearance should be clean and free of defect.
The success of de phosphorization is result of collaberation of team work, and the quality of stainless steel produced should be guarantee by preventing operation inconsistencies and systematic errors. The efficient operation of de phosphorus facillity is beneficial for production and the quality of stainless steel.
