Desulphurization of Ferritic Stainless Steel by Hydrogen-Argon

Plasma Jet Using Calcium Bearing Fluxes

Abstract

Desulphurization of molten ferritic stainless steel (25%Cr-Fe alloy) was studied by using plasma jet of hydrogen-argon gas mixture to which powders of various calcium bearing fluxes were supplied.
The fluxes used were (6-17) wt%CaC₂-CaF₂, 20wt%CaO-CaF₂ and 12wt%CaC₂-(18-35) wt%CaO-CaF₂, the diameters of powder particles were smaller than 149μm, and the powder feeding rates were 0.1 to 0.9g/min. The results were summarized as follows: 1) the desulphurization efficiency of CaC₂ in CaC₂-CaF₂ was 30-40%, and the minimum sulphur concentrations attained were as low as 0.0007% by CaO-CaF₂ and 0.0013% by CaC₂-CaF₂, 2) hydrogen in the plasma, which reacted with CaC₂ to form hydro-carbon gases, effectively enhanced desulphurization, preventing the carburization from CaC₂, but retarded the desulphurization above pH₂=0.5atm by forming gaseous calcium, 3) the present results together with those in the previous work indicated the possibility of the refining of ferritic stainless steel with very low levels of carbon, nitrogen and sulphur by hydrogenargon plasma jet using CaC₂-CaF₂ or CaO-CaF₂ flux.