Actual Problems in Machine Building 2018 Vol. 5 No. 1-2

Актуальные проблемы в машиностроении. Том 5. № 1-2. 2018 Материаловедение в машиностроении ____________________________________________________________________ 99 A STUDY OF THERMOCYCLING EFFECT ON STRUCTURE AND PROPERTIES OF EUTECTOID STEEL AFTER THERMOCHEMICAL TREATMENT Butukhanov V.A. 1 , Engineer, e-mail: butuhanov_vyacheslav@mail.ru Lygdenov B.D. 1 , D.Sc. (Engineering), Associate Professor, e-mail: lygdenov59@mail.ru Guryev A.M. 2 , D.Sc. (Engineering), Professor, e-mail: gurievam@mail.ru Tsydypov B.S. 1 , Ph.D. student, e-mail: bulvin@rambler.ru 1 East Siberia State University of Technology and Management, 40V Klyuchevskaya st., Ulan-Ude, 670013, Russian Federation 2 I.I. Polzunov Altai State Technical University, 46 Lenina avenue, Barnaul, Altai region, 656038, Russian Federation Abstract The coarse-grained structure is formed on steel by traditional thermochemical treatment with long duration at high temperatures. This disadvantage leads to decreasing of steel plasticity. Achieving of high plasticity is possible by formation of small grains by using thermocycling after thermochemical treatment. The work investigated the effect of thermocycling and other types of heat treatment on grain size for improving impact of eutectoid steel. The heating during thermocycling was provided by putting steel samples in a furnace preheated to 900 ° C. Heating rate was 3 °C / sec. Thermocycling treatment consists of steel heating to a temperature of 900°C, cooling in air to a temperature of 600–650°C, then - cooling in water. It was carried 3 cycles of "heating - cooling". Thermocycling mode in the final stage includes quenching. It is shown that thermocycling with 3 cycles and isothermal annealing at 650°C leads to a refinement of austenite grain from 18–26 microns (after the thermochemical treatment) to 6–8 microns. It is found that grain refinement by thermocycling leads to a significant increase in impact toughness of steel. The use of thermochemical treatment and thermocycling causes simultaneous increase in the surface hardness and the impact toughness of the eutectoid steel and can be applied on dies for cold deformation. Keywords thermocycling, thermochemical treatment, grain size, impact toughness