NRC “Kurchatov Institute” – “Prometey” Central Scientific Research Institute of Structural Materials, St. Petersburg, Russia

D. V. Tsukanov, 1st Category Engineer, e-mail: tsumami@mail.ru
D. L. Smirnova, Leading Engineer, e-mail: tsumami@mail.ru

Empress Catherine II Saint Petersburg Mining University, St. Petersburg, Russia
A. P. Petkova, Dr. Eng., Prof., Dept. of Materials Science and Technology of Art Products, e-mail: apetkova@inbox.ru
V. V. Shtertser, Postgraduate Student, Dept. of Materials Science and Technology of Art Products, e-mail: st.valeriaa@yandex.ru

Processes associated with phase transformations during hardening of large-sized forgings made of alloy steels are considered. The basic transformation processes and their possible influence together with cooling modes on the characteristics of the properties are analyzed. The first part of the article studies the issues of phase transformations in the area of pearlite and bainitic transformations determined by standard thermokinetic diagrams and simulated modes. The calculated values of cooling rates for a forging with a maximum cross-section of 1000 mm in three zones (surface, center and ½ radius of the blank) during quenching in oil are presented, the microstructure and kinetics of pearlite and bainitic transformations are determined. The results of dilatometric studies in three different temperature zones along the cross-section of the heattreated blank during cooling at the corresponding calculated rates are presented. The second part of the article analyzes the cooling curves, microstructure and hardness of the samples after quenching in oil, as well as the temperatures of the beginning and end of the austenite transformation in three zones of the blank. Conclusions are made on the importance of taking into account the width of the range of critical points for assessing the nature of the austenite transformation in the area of the pearlite transformation. It is shown that the cooling rates during quenching are not constant over the entire temperature range, which must be taken into account when constructing thermokinetic diagrams of austenite transformation during continuous cooling. The nature of the austenite transformation during modeling of the cooling mode is most indicative and corresponds to real cooling modes during quenching.

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