Naberezhnye Chelny Institute, Kazan (Privolzhkiy) Federal University, Naberezhnye Chelny, Russia
V. I. Astashchenko, Cand. Eng., Prof., Dept. of Materials, Technologies and Quality
G. F. Mukhametzyanova, Cand. Eng., Associate Prof., Dept. of Materials, Technologies and Quality, e-mail: gulnara-ineka@mail.ru
I. R. Mukhametzyanov, Postgraduate Student, Dept. of Materials, Technologies and Quality

KAMAZ PTC, Naberezhnye Chelny, Russia:

T. V. Shveeva, Leading Engineer

The application of computer technologies for determination of the resistance of hardened steels against tempering, for evaluation of the fracture force of articles with a surface-hardened layer, and for a comparative quantitative assessment of the hardenability of medium-carbon tempered steels is considered. The stability of hardened 45, 40G2 and 40KhFA steels against tempering at different temperatures has been studied. Mathematical dependences of the change in the hardness of hardened steels after tempering in the temperature range of 300–680 °C are established. A new criterion for evaluating the tempering resistance of hardened steels is proposed, based on the area under the curve of hardness versus tempering temperature. It is shown that 40KhFA steel has 1.36 times, and 40G2 steel - 1.22 times greater resistance against tempering than 45 steel. A method has been developed to determine the force that causes the destruction of surface-hardened steel articles. The method takes into account the total contribution to the strength properties of the part - the hardened layer and the base metal of the article. Based on the results of metallographic studies of the hardened layer and mathematical analysis using integral calculus, the contribution of the surface hardened zone in terms of article strength is estimated. According to the change in hardness over the cross section of the hardened layer, a functional dependence is established. In the future, this dependence is integrable, and the thickness of the hardened layer of articles acts as an integrating value. Using the equation, determine the force that causes the destruction of case-hardened parts. Comparative studies on the hardenability of improved carbon and alloy steels have been carried out. Information on the contribution of chromium, nickel and vanadium to the hardenability of steel is presented. It is noted that alloying steel with nickel has a noticeable advantage.

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