Synopsis: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. (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.
Synopsis: customarily the phenomenon of iron escaping is explained as the result of build-up of viscous slag bearing reduced titanium compound and Salamander in the hearth. However,it seems that the quantity of iron escaping from cinder notch in case of a certain blast furnace is rather related to the low permeability of furnace column rather than to titanium content in burden.Thereupon,we examined the cause of the phenomenon by measuring slag viscosity and analyzing permeability of column. As the result,the phenomenon is found to result not from the elevation of slag viscosity by titanium compound, but from the reduction of raceway by low permeability of column. This is thought due to the irregularity of slag temperature around the core and a narrowing of space between the inner wall and the core by reduction of raceway.
At }\lJurorall "Vorks, Nippon S teel CO/poration , a research has been started to produce stainless steel by LD cOllverter ill 1965. After various difficulties were overcome in th e COU TSe of the research, a new process to melt and refill e stainless steel (LD-RHO B process) was successfully developed. Since 1972 aLL the stainless s teel has been fa vorably p roduced by the LD-RHOB p rocess and the p roducts were more than 90000 t in 1976. The LD-RHOB process consists of the f oLLowing five steps. 1) D esulpll1lrizatiol1 treatment: D esulphuri z atiol! qj•hot metal by KR treatment 2) B ase metal refining period: D e/Jlwsphoriza tion in LD converter 3) S e/Jara tion of slag from metal : T apping aud slagging off and then cha rging into the LD converter again 4) Ch ro mium melting period: H igh carbon ferro chromium melting into base metal 5) RHOB treatment: D ecarburiz ation under reduced IJ ressure The special f eatures of LD-RHO B p rocess in elude the follo wings : (1) Chromium. yield and /Jrodu ctivity are equal to or better than those qf other /Jrocesses (A OD, VOD process). (2) Chemical com/Jositioll can be freely controlled and tra m/J elements are lower than those ill electric jilT/wce s teels. It is remarkable that high pure stainless steels such as ultra-Iow-carbon-nitrogen stainless steel call be easily produced. (3) Th e /Jroducts are very soft and ensure good workability.
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