Belarusian Steel Works — the management company of the BMC holding, Zhlobin, Belarus

S. A. Savchenko, Leading Engineer-Technologist of the Technical Management of the Rolling Dept., e-mail: gnp.tu@bmz.gomel.by
I. A. Kovaleva, Head of the Research Center`s Research Lab. – the Branch Lab. of Metallurgical and Steel Wire Production Technologies of the Technical Dept., e-mail: nl.icm@bmz.gomel.by

Sukhoi State Technical University of Gomel, Gomel, Belarus
I. V. Astapenko, Dr. Agr., Associate Prof., Dept. of Metallurgy and Materials Processing Technology, e-mail: astapenko@tut.by

Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia
A. B. Sychkov, Dr. Eng., Prof., Dept. of Foundry Processes and Materials Science3, e-mail: absychkov@mail.ru

To ensure quality characteristics of coiled products required by customers after spheroidizing annealing in terms of mechanical properties, microstructure and depth of decarbonized layer (hereinafter referred to as DCL) of ShKh15 steel, production and research technological measures were carried out on rolling mill 370/150 with different conditions of initial temperature and dynamics of cooling of the wire rod. The article contains the results of research and analysis to determine effective initial microstructure of hot-rolled bearing round steel in coils with diameter of 6.5 mm, subjected to subsequent spheroidizing annealing, improving quality of rolled products by improving technological modes of in-line two-stage cooling of wire rod at air cooling stage. Dependence of influence of initial temperature and dynamics of air cooling process on formation of interlamellar distance of pearlite in the primary microstructure of coiled steel has been studied. Influence of austenitization temperature on dispersion of pearlite in bearing steel is described. Effective mode of in-line air cooling of bearing steel wire rod for subsequent spheroidizing annealing has been determined, providing uniform fine pearlite structure along the entire length of the wire rod coil, without presence of quenching structural inclusions. It has been established that initial coarse-lamellar form of pearlite on the surface of coiled steel according to the basic mode of in-line heat treatment in hot-rolling line of wire rod of mill 370/150 (initial cooling with water to temperature of 870-910 °C in the area of coil former and subsequent slow cooling with air on roller conveyor by the first four fans with air supply power of 10%) leads to excessive values of DCL depth and incomplete spheroidization after annealing of coils.

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