DEVELOPMENT OF NEW STAINLESS STEELMAKING PROCESSES

For melting alloy steel scraps, a conventional 20 tonne arc furnace wa s revamped to a air-tight structure based on experience with air induc tion and ladle furnaces. A considerable decrease in oxidation loss due to less air infiltration into the furnace chamber has led to greater recovery of alloying elements, and less slag and dust formation. Gas b ubbling through a furnace bottom tuyere and chromite ore addition thro ugh a hollow electrode are essential tools to successful operation of the air-tight furnace. The same concept was also applied to the AOD in which mother metal from the air-tight arc furnace was refined. A 20 t onne AOD vessel was revamped to a vacuum-tight structure and connected to vacuum pumps in the final stage of the decarburisation stage. In t his process, named AOD-VCR or simply VCR, ultra low carbon stainless s teel containing less than 50 ppm carbon could be produced easily, savi ng a considerable amount of argon, ferrosilicon and time.