DOI: 10.18503/1995-2732-2025-23-1-62-72
Abstract
To obtain the structure of granular pearlite, spheroidizing annealing of steel is used. Spheroidization of cementite plates occurs in two stages: division of carbide components into parts and spheroidization itself. Transformation of lamellar perlite occurs during long-term exposure (from 2-4 hours and more) at spheroidization temperatures (A1 ≈ 727°C). First of all, this is caused by the two-stage process. The spheroidization process affects not only the shape, but also the size of the carbides. To obtain the required size of cementite globules, the heating and cooling rate is controlled, and to complete the transformation process, the exposure time at certain isothermal temperatures is controlled. The article presents the study results of the influence of the holding time duration during cyclic (pendulum) spheroidizing annealing of rolled products in coils made of ShH15 bearing steel on the degree of transformation completeness of lamellar pearlite into granular one. The studies were carried out on wire rod with a diameter of 6.5 mm, rolled according to an improved mode, which makes it possible to obtain an initial fine pearlite structure with an interplate distance of 0.126-0.235 μm and a cementite plate size of no more than 0.08 μm. The purpose of the work was to determine the effect of isothermal holding time during cyclic spheroidizing annealing on the completeness and quality of carbide plates into granular pearlite transformation. In this case, four experimental modes were used with isothermal cyclic exposure times 10, 25, 50 and 75% (modes No. 1–4, respectively) less than the current mode. It has been established that modes No. 1-3 make it possible to obtain 100% spheroidization of wire rod lamellar pearlite. In mode No. 4, the effect of forming a structure of 100% granular pearlite was not achieved, however, crushing of cementite plates was not detected, which indicates a one-stage spheroidization process.
Keywords
bearing steel, spheroidizing annealing, initial structure, lamellar pearlite, pendulum (cyclic) annealing, time of cyclic isothermal exposures, decarburized layer, cementite plates and globules
For citation
Savchenko S.A., Kovaliova I.A., Astapenko I.V., Sychkov A.B. Enhancing Spheroidizing Annealing Technology of Rolled Products in Coils from Bearing Steel. Vestnik Magnitogorskogo Gosudarstvennogo Tekhnicheskogo Universiteta im. G.I. Nosova [Vestnik of Nosov Magnitogorsk State Technical University]. 2025, vol. 23, no. 1, pp. 62-72. https://doi.org/10.18503/1995-2732-2025-23-1-62-72
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