Influence of Electrosmelting Conditions on Rail Quality and Production Costs

Abstract

Analysis of literature and production data shows that, despite significant gains in rail quality made possible in the past decade by the reequipment of Russian rail plants, the rejection rate of rails due to surface defects is still high. Research on the composition of rail steel shows that increase in copper content in the range 0.07–0.15% and in sulfur content in the range 0.006–0.011% in Э76XФ electrosteel at AO EVRAZ ZSMK significantly increases the rejection rate of rails due to surface defects. The mechanism by which the copper and sulfur concentration in the steel affects the rail quality is established. The ratio of iron and scrap in the metal batch is found to determine the copper and sulfur content in the rail steel: increase in the hotmetal content from 20 to 50% decreases the copper concentration and increases the sulfur content. To establish the optimal composition of the metal batch in the electrosmelting of rail steel, taking account of the relation between rail quality and the production economics, the influence of the ratio of iron (in liquid and solid forms) and scrap in the metal batch on electrofurnace performance is assessed. It is found that increasing the content of hot metal and pig iron in the metal batch results in linear decrease in power consumption, parabolic increase in oxygen consumption, and linear decrease in manganese content of the steel discharged from the furnace. The dependence of the smelting time on the proportion of batch components includes a minimum when the hot-metal content is 35–40% and the pig-iron content is 30–35%. On the basis of regression equations, we formulate a statistical model describing how the composition of the metal batch affects the overall performance of the electrosmelting shop in rail-steel production. Optimization is based on two factors: the total costs corresponding to the composition of the metal batch; and the productivity of the shop in terms of continuous-cast billet. This model permits recommendations regarding the optimal iron content in the metal batch at current prices of the batch materials and power, taking account of the change in shop productivity.