Theory and Technology of Metallurgical Production

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Sychkov A.B., Savchenko S.A., Tulupov O.N., Moller A.B. ENSURING QUALITY INDICATORS OF STRUCTURE FORMATION ON THE STELMOR LINE IN BEARING ROLLED PRODUCTS MADE OF ШХ15 STEEL

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Abstract

The relevance of this work lies in the high scientific and practical significance of developing a technology for producing bearing grade ШХ15 steel and improving its structure formation on a modern 370/150 small-section wire rod mill using continuously cast billets (CCB) with a cross-section of 250×300 mm, featuring a high rolling speed of 100 m/s or more, a 10-stand wire rod unit, and a 4-stand reduction and calibration unit, which significantly influence the structure formation of the rolled product. The aim of this work is to study and form a homogeneous microstructure and properties of rolled steel by developing modes of preliminary heat treatment (PHT - homogenizing annealing (HA) of the cast structure of CCB) and final heat treatment (FHT) - sorbitization of lamellar pearlite and its spheroidization - SO), ensuring maximum technological efficiency of processing rolled steel at consumers. Quality characteristics were analyzed using the following parameters: macrostructure (CCB) with a cross-section of 250x300 mm on macrotemplates, microstructure and mechanical properties of rolled products with a diameter of 5.5–18.5 mm – in accordance with methodological standards. For the first time, it has been established that the level of carbide segregation is achieved through a significant degree of drawing and partial homogenization of the macrostructure of the casting and rolled products during processing on the 370/150 mill line. Casting products for the production of coiled products with a diameter greater than 8.5 mm must undergo preliminary heat treatment (HT) (temperature - 1200°C for at least 6 hours). An efficient two-stage cooling system for ШХ15 steel coils was developed and implemented on a Stelmor line (coiling temperature: 860-870°C, air cooling rate: 18-20°C/s). This process yields at least 95% sorbitol-like pearlite with an interlamellar distance of 0.07-0.14 μm, a cementite plate thickness of no more than 0.08 μm, and minor (less than 5%) areas of thin-lamellar and medium-lamellar pearlite, without tempering. The research results made it possible to achieve the objective set forth in this article.

Keywords:

microstructure, Stelmor two-stage cooling lines, rolled products, bearing steel, continuously cast billets, set of quality indicators, sorbitol, granular pearlite, light microscope, energy-dispersive microanalyzer.

Sychkov Alexander B. – Doctor of Technical Sciences, Professor, Professor of the Department of Foundry Processes and Materials Science of the Institute of Metallurgy, Mechanical Engineering and Materials Processing, Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.;

Savchenko Sergey A. – candidate for the degree of candidate of technical sciences in specialty 2.6.1 - Metallurgy and heat treatment of metals and alloys at the Institute of Metallurgy, Mechanical Engineering and Materials Processing, Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia.

Tulupov Oleg N. – Doctor of Technical Sciences, Professor, Professor of the Department of Materials Pressure Processing named after M.I. Boyarshinov of the Institute of Metallurgy, Mechanical Engineering and Materials Processing, Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia.

Moller Alexander B. – Doctor of Technical Sciences, Professor, Professor of the Boyarshinov Department of Materials Pressure Processing of the Institute of Metallurgy, Mechanical Engineering and Materials Processing, Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia.

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