Development of steelmaking process for stainless steel by top and bottom blowing with coke addition in converter.

At Muroran Works, Nippon Steel Corporation, stainless steel has been produced by the LD-RH•OB process since 1972. This process has recently been improved by introducing the hot metal dephosphorization treatment and the top and bottom combination blowing of a LD converter. This paper shows the results when stainless steel scrap is used for the stainless steelmaking process by the addition of carbonaceous materials as an auxiliary heat source in the top and bottom blowing converter.The results obtained are as follows:(1) No significant difference in the heat efficiency is observed between the bottom injection of coke breeze and the top feeding of lump coke in the converter.(2) The most effective way to high Cr yield is the additions of SUS scrap first separately before of HC-FeCr.(3) The bottom gas injection acceralates the reactions to the thermodynamic equilibrium. For example, the (Cr2O3) content in the slag at the turn down is significantly lower than that in the conventional converter.(4) The contents of [S] and [N] in molten steel at the turn down in the LD refining process increase with the addition of coke through the nitrogen bottom blowing. These impurity contents can be reduced to the normal level in the succesive RH refining.