ANALYSIS OF PROCESSES FORMATION OF METALLURGICAL QUALITY OF RAILWAY RAILS FROM ELECTRIC STEEL

Based on comprehensive studies conducted using optical and electron microscopy methods, X-ray phase analysis, the nature of characteristic metallurgical defects of railway rails manufactured by JSC EVRAZ ZSMK has been determined. These defects, which are the cause of rejection of railway rails during ultrasonic quality control, are mainly stratifications with accumulations of non-metallic inclusions in the form of silicon and aluminum oxides, aluminosilicates and manganese sulfides. Such bundles are localized in the neck of the rail profiles, elongated in the direction of rolling and have a length of up to 2 mm. Based on statistical studies conducted using the multiple regression analysis technique for a sample of 200 melts of E76XF grade rail steel, it was found that an increase in the duration and intensity of purging the melt of rail steel with an inert gas during processing on the ladle furnace unit, a decrease in the oxidation of steel at the outlet of an electric arc furnace, a decrease in sulfur, phosphorus, copper and tin in the finished steel cause a reduction in the rejection of rails for internal defects. The analysis of the relative degree of influence and the mechanisms of influence of each of the listed parameters on the probability of the formation of internal defects of rails allowed us to establish that the main influence on the amount of rejection of rails for defects of metallurgical origin is the oxidation of steel at the outlet from the furnace and the parameters of its purging with inert gas in the bucket (duration and intensity of purging with inert gas). Metallographic studies of melt samples of the specified rail steel after out-of-furnace processing and samples taken from continuously cast billets of this steel confirmed that a decrease in the oxygen content in the steel at the outlet from the furnace, together with an increase in the duration and intensity of purging the melt with inert gas in the steel ladle significantly reduce the contamination of liquid steel and continuously cast billets with oxide, silicate and sulfide non-metallic inclusions, that is, potentially reduce the intensity of the formation of internal defects of the rails.

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