Nosov Magnitigorsk State Technical University (Magnitogorsk, Russia)

D. A. Gorlenko, Cand. Eng., Associate Prof., Dept. of Foundry Production and Material Science, e-mail: d.gorlenko@magtu.ru
O. A. Kupriyanova, Cand. Eng., Associate Prof., Dept. of Material Processing Technologies, e-mail: o.nikitenko@magtu.ru
K. G. Pivovarova, Dr. Eng., Associate Prof., Dept. of Material Processing Technologies, e-mail: k.pivovarova@magtu.ru
M. A. Polyakova, Dr. Eng., Associate Prof., Dept. of Material Processing Technologies, e-mail: m.polyakova@magtu.ru

The article is devoted to the development of the heat treatment mode for TRIP steel with a new chemical composition. Aluminum was chosen as an additional alloying element, since by the nature of its effect on the stabilization of overcooled austenite in the temperature range of diffusion transformation, aluminium is similar to silicon, the main alloying element for steels containing metastable austenite in the structure. For the correct development of the heat treatment mode of modified TRIP steel, the critical points were determined by differential scanning calo-rimetry. After determining the temperature limits of the two-phase area, the cast samples were subjected to heat treatment. For all the studied samples, the exposure temperature in the bainite area was 400 °C, and the annealing temperature in the two-phase area was changed from minimum to maximum. The exposure time for both intervals was 20 min and was the same for all samples. As a result, the dependence of the amount of metastable austenite in the structure of modified TRIP steel on the annealing temperature was determined in the intercritical interval (area between the points Ac1 and Ac3). This dependence is of an extreme nature. The article also provides a comparison of the microstructure of modified steel in the cast state and after heat treatment. The analysis of the microstructure allowed us to conclude that continuous monotonous cooling of aluminium-modified TRIP steel made it impossible to obtain a structure containing metastable austenite. In addition, the modified chemical composition of TRIP steel contributes to sufficient stabilization of overcooled austenite in the temperature range of pearlite transformation. The data obtained in this work made it possible to develop a mode of heat treatment of TRIP steel modified with aluminium.
The research was carried out under contract No. 13.2251.21.0107 (№ SIIS "Electronic budget" 075-15-2021-1031) on the topic "Investigation on 3D-printing of Advanced High Strength Steels with TRIP effect for realization of self-adapting aerospace structural elements", funded by the Ministry of Science and Education of the Russian Federation within the joint program for science and technology cooperation and implementation of joint call for Russian-Italian projects for 2021-2023.

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