Integrated influence of melting parameters of rail steel on rail products quality and technical and economic indicators of the production

Abstract

Analysis of literature and production data has shown that despite the significant improvement in quality of domestic rail products, achieved in the last decade due to fundamental technical re-equipment of rail production, there is a problem of increased rejection of rails for surface defects. Based on studies of influence of rail steel chemical composition on quality of rails produced by «EVRAZ ZSMK», there was established a significant effect of increasing copper content in the range of 0.07 - 0.15 % and of sulfur - in the range of 0.006 - 0.011 % in E76KhF steel to increase rejection caused by rail surface defects. Mechanism of the influence of these elements concentration in rail steel on finished rails quality was revealed. Decisive influence of ratio of pig iron and scrap in metal charge on copper and sulfur content in rail steel was evidenced - higher rate of cast iron in metal charge within 20 - 50 % contributes to decrease of copper concentration and increase of sulfur content. To justify optimal composition of the charge for rail steel melting in regard to rail products quality and technical and economic indicators of production, study of the effect of cast iron (liquid and solid) to scrap ratio in metal charge on basic parameters of furnaces’ operation was conducted. As a result, it was found that with an increase in share of both liquid and solid iron in metal charge, there are linear decrease in specific electricity consumption, increase in specific oxygen consumption according to parabolic law and a linear decrease in manganese content in furnace output. The obtained dependences of melting duration on ratio of charge components in metal charge indicates presence of prominent minimum, when using liquid iron in the range of 35 - 40 %, and when using solid iron - in the range of 30 - 35 %. Based on the regression equations, statistical model was constructed for the influence of metal charge composition on technical and economic performance of the melt charge in rail steel smelting, in which optimization parameters are: total cost, depending on the metal stock composition and performance of the shop for suitable billets produced by continuous casting. Application of the obtained model allows to develop reasonable recommendations on the optimal proportion of iron in the metal for current level of prices for materials and energy used in electric smelting, taking into account changes in the shop productivity.