INVESTIGATION OF THE PATTERNS OF STRUCTURE FORMATION AND MECHANICAL PROPERTIES OF STEELS DURING HEAT TREATMENT

The relevance of the work. The use of economically alloyed boron-containing steels significantly expands the production volumes of high-strength products obtained by cold bulk stamping methods. Existing methods for preparing metal for cold plastic deformation include the operation of spheroidizing annealing, which is characterized by high energy and time expenditures. Additionally, traditional methods of preparing low-carbon steels for cold deformation have several drawbacks: high consumption of electricity and gas during annealing in furnaces, low productivity, difficulty in ensuring uniform heating and cooling of metal blanks, and environmental pollution. A promising direction is the electrothermal treatment of steel blanks, distinguished by high metal heating rates. To develop high-speed spheroidizing annealing regimes for low-carbon steels, it is necessary to understand the laws governing the formation of structure and properties during heating and cooling. Purpose. To investigate critical points and identify the peculiarities of the influence of cooling rates of undeformed austenite on the volumetric fraction of structural components of 20Mn2B steel. Methodology. In studying the regularities of structure formation, the differential thermal method was used, followed by the investigation of the microstructure and hardness of steel samples. The results. A quantitative and qualitative picture of structure formation during heating and cooling of boron-containing steels was obtained. The possibility of developing high-speed spheroidizing annealing regimes for low-carbon steels with the achievement of a uniform distribution of cementite globules in the ferritic matrix was experimentally confirmed. Conducted research and analysis of the obtained data allowed for graphical analysis of the structure formation of the studied steels of the specified chemical composition and to obtain the quantitative content of structural components during cooling at different speeds of undeformed austenite of the steel. The results of experimental studies of structure formation can be used to develop various regimes of thermal treatment with separate heating of boron-containing steels.