Abstract
A new method for thermo-mechanical treatment of steel 40H2N2MA concerned mixed martensite-bainite transformation of austenite is developed. The thermo-mechanical processing includes hot deformation and rapid cooling down to the temperature in the range between the beginning and finishing of martensitic transformation accompanying with 40% martensite formation. The final stage of heat treatment is to heat up to the temperature of bainite transformation in which the remaining austenite transforms into the structure of bainite and previously formed martensite tempers. The superfine steel structure consists of 60 % bainite and 40% the tempered martensite is obtained. In comparison with well known techniques of thermal treatment, the developed thermo-mechanical treatment increases the impact toughness of the steel 40H2N2MA up to 1.3 - 2 times and fatigue crack resistance up to 1.5 - 3 times (at equal values of strength parameters). The technological process of high-temperature thermo-mechanical treatment with mixed martensitic-bainitic transformation of austenite is recommended for treatment of rolling billets, drilling tools or small parts of stamping impact machines.
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