National University of Science and Technology “MISiS” (Moscow, Russia):

Yu. B. Sazonov, Cand. Eng., Head of the Laboratory, E-mail: u-sazonov@yandex.ru
A. A. Komissarov, Cand. Eng., Head of the Laboratory, E-mail: komissarov@misis.ru
D. Yu. Ozherelkov, Cand. Eng., Engineer, E-mail: d.ozherelkov@gmail.com
D. V. Ten, Postgraduate Student, E-mail: teden92@yandex.ru

The results of the influence of different variants of thermomechanical treatment (TMT) using holding in the subcritical temperature range — SCT = Ac₁ – (5 ÷ 10) °C on the formation of a submicrocrystalline grain structure in structural steel 35KhGSA, prone to manifestation of the negative effect of reversible temper brittleness are presented. The structural transformations at each stage of TMT are described in detail, images of microstructures and the results obtained using the method of scanning electron microscopy — the electron backscattered diffraction (EBSD) are presented. Methods for suppressing reversible temper brittleness, increasing toughness and lowering the cold brittleness threshold temperature of 35KhGSA steel are shown based on the results of serial impact tests. The main effect of improving the properties of the steel under study is achieved due to the formation of a subgrain structure in the steel by the polygonization mechanism during holding in the subcritical temperature range. During the subsequent austenitization, the substructure, by the mechanism of structural inheritance, transforms into the austenite grain with the retention of its fineness. The final grain size was about 2 ÷ 5 microns, which had a positive effect on the complex of mechanical properties of 35KhGSA steel. Recommendations for the optimal TMT mode with preliminary cold plastic deformation with a degree of 10% are given.

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