Development of a New Stainless Steel Melting and Refining Process (LD-RH Oxygen Blowing Process)

Muroran Works, Nippon Steel Corporation, started the researches to produce stainless steel by LD converter in 1965. After various difficulties were encountered and overcome in the course of these researches a new process to melt and refine stainless steel (LD-RHOB process) was successfully developed. Since 1972 all the stainless steels have been produced favorably by the LD-RHOB process, and the products were more than 90000t in 1976. The LD-RHOB process consists of the following five steps. (1) Desulphurization treatment : Desulphurization of hot metal by KR treatment. (2) Base metal refining period : Dephosphrization in LD converter. (3) Separation of slag from metal : Tapping and slagging off and then charging into the LD converter again. (4) Chromium melting period : High carbon ferro-chromium melting into base metal. (5) RHOB treatment : Decarburization under reduced pressure. The special features of LD-RHOB process include the following: (1) Chromium yield and productivity are better than of the same as other processes (AOD, VOD process). (2) Chemical composition can be freely controlled and tramp elements are lower than those in electric furnace steels. It is remarkable that high pure stainless steels such as ultra low carbon nitrogen stainless steels can be easily produced. (3) The products are very soft and ensure good workability.