Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia:

N. V. Koptseva, Dr. Eng., Prof.
Yu. Yu. Efimova, Cand. Eng., Associate Professor, e-mail: jefimova78@mail.ru
A. M. Pesin, Dr. Eng., Prof.
M. V. Chukin, Dr. Eng., Prof.

A study of the 08Yu steel structure during cold rolling at a new rolling mill in the Zhilyaev Laboratory of Mechanics of Gradient Nanomaterials of the Nosov Magnitogorsk State Technical University. It has been found that asymmetric rolling in rollers with speeds that differ 5 times and all other things being equal, resulted in the formation of a gradient structure. In the upper part of the strip section on the side where the rolling speed was lower, a uniform structure is observed, which is formed at more than half the strip thickness and consists of ultra-fine practically equiaxial grains of less than 1000 nm in size. The formation of the ultrafine structure is explained by the dynamic recrystallization under the conditions of heating the strip to a temperature of 250–300 ºC during rolling. In the lower part, on the side where the rolling speed was higher, a fibrous structure with smaller fragments up to 200 nm in size within individual fibers is clearly revealed. The hardness after asymmetric rolling compared to symmetrical rolling increased slightly and turned out to be more evenly distributed over the section. The difference in its values of different sections was not more than 15 % compared to symmetrical rolling, where the hardness in the central and perephyrian sections of the strip section differed by about 35 %. It has been found that these asymmetric rolling conditions lead to a simultaneous increase in reduction from 50 to 80 % and a decrease in force of almost 3 times per pass compared to symmetrical rolling, which can be explained by grinding the structure.
The study was carried out within the framework of grants from the Russian Science Foundation (No. 20-69-46042 dated May 20, 2020), RFBR (No. 20-38-90097 dated September 3, 2020) and Megagrant (No. 075-15-2021-627 dated June 8, 2021).

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