Енергозберігаюча термічна обробка легованих сталей зі змішаною структурою

Abstract

The purpose of the work was to research ways to reduce the duration of the intermediate heat treatment mode of alloy steels while ensuring the required level of properties and reducing energy costs. For further mechanical processing of alloy rolled metal, it is necessary to obtain the original rolled product with a structure that has high plasticity and low hardness. In order to achieve the required mechanical properties, a special softening heat treatment is carried out - annealing at subcritical temperatures (A1 - 25...40 °С) with a long exposure. Thanks to annealing, structural transformations take place and the resulting structure has a granular morphology. Research has established that in steels with a mixed structure during annealing, structural transformations begin with thermodynamically less stable structures. For medium-carbon steels alloyed with such elements as chromium, molybdenum, vanadium, increasing the cooling rate after hot rolling by ~1.5 times makes it possible to obtain a structure that is more susceptible to annealing. Thus, for chrome-molybdenum steel, the structure consists of at least 80% bainite, ~15% ferrite and 5% pearlite. For chromium molybdenum vanadium steel, the basis of the structure is bainite (~90%), martensite (~5%) and ferrite (up to 5%). In the resulting structures, upon subsequent annealing, structural transformations occur at reduced temperatures and require a shorter exposure time. The values of hardness and strength of the studied steels processed under the reduced regime decrease by 15-30%, and the plasticity indicators increase by ~50%. Obtaining such a structure after rolling makes it possible to speed up the intermediate thermal softening treatment, thereby reducing energy costs, and ensuring high plasticity of steel before mechanical processing (stamping, forging, etc.)