Method for Melting Manufacture of High Purity Stainless Steel

摘要

This report first summarizes the principles of refining for removal of such impurity inclusions as C, N, P, S and tramp elements (as Pb, Bi) that affect the quality of stainless steel and the conventional manufacturing method by melting. The report then introduces a novel technique in respect to a method for solving the hitherto unsolved problem of simultaneously attaining ultra-low carbon and nitrogen contents and a method for dephosphorization. In the melting manufacture of ultra-low nitrogen steel and low nitrogen steel, steel of the kind to be mass-produced can be processed to have C + N < 100 ppm (19 percent Cr steel) by an improved VOD method while the kind to be produced in small quantity with high purity can be processed to have C + N < 50 ppm (25% Cr steel) by a combination of a denitrification process and a vacuum melting process. As for dephosphorization in a stainless steel manufacturing process, the report discloses various possibilities. Particularly, it shows a prospect of attaining a dephosphorization rate between 50 and 70 percent by a reduction refining method using a CaC2 - CaF2 flux even for a mass-production process. The results of the reported studies open a way toward adequately meeting requirements for high purification of stainless steel.