Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia

D. O. Pustovoytov, Cand. Eng., Associate Prof., Dept. of Materials Processing Technologies, Senior Researcher, A. P. Zhilyaev Laboratory of Gradient Nanomaterials Mechanics1, e-mail: pustovoitov_den@mail.ru

In sheet metal production, grain refinement is one of the few strengthening mechanisms that can simultaneously increase both the strength and toughness of steel. Low carbon steels strengthened by ferritic grain refinement have great potential to replace some microalloyed and low alloyed high strength steels. Modern industrial technologies such as thermomechanical rolling, controlled rolling, normalizing rolling, as well as various types of heat treatments make it possible to obtain sheet metal with a fine-grained structure exclusively in the range from 10 μm to 5 μm. Industrial production of sheet metal products from steels with grain sizes in the range from 4 μm to 1 μm (grain number 13-17 according to GOST 5639-82) remains an unsolved problem. The aim of this work was an experimental study of the technological possibility of forming a fine-grained structure with an average ferrite grain diameter in the range from 4 μm to 1 μm during asymmetric hot rolling of low-carbon steel sheets. The paper experimentally shows that with asymmetric hot rolling with a large (single) relative thickness reduction of 50 % ≤ ε ≤ 60 % and ratio of roll speeds of 1.5 ≤ ku ≤ 1.7, a homogeneous dispersed ferrite-pearlite-bainite microstructure with an average ferrite grain diameter of ≈3 μm (center) and ≈2 μm (surface) can be formed through sheet thickness (≈2.2 mm), which corresponds to grain number 14-15 according to GOST 5639-82. The fundamental possibility of forming a microstructure with an average ferrite grain diameter of less than 2 μm in sheet metal has been demonstrated experimentally (grain number 16). However, to obtain such a microstructure across the entire thickness of the sheet, further research and optimization of temperature, deformation and speed conditions of asymmetric rol ling are necessary.
The research was supported by a grant from the Russian Science Foundation (agreement No. 22-49-02041).

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