Abstract
Purpose. Conduct a study on the kinetics of austenite decomposition and determine the extent of influence of hot plastic deformation and interrupted cooling regimes on the structure formation of boron-containing steel. Methods. The investigation of phase transformations was conducted using differential thermal analysis on samples of boron-containing steel, accompanied by studies of microstructure and hardness. Results. The kinetics of transformations were studied, and a thermokinetic diagram of the decomposition of hot-deformed austenite in boron-containing steel was constructed, based on austenitization tempetatures ranging from 1050 to 11000С, followed by interrupted cooling and further cooling at a rate of 0,09 to 0,120 С/s, comparable to the cooling rate of the external coils of rolled bundles. It was established that the temperature-deformation regimes of rolling and the cooling conditions applied in real production technologies of underlayers (especially in bundled forms) are the cause of the appearance of a range of structural components in the treated steel. The heterogeneity of the structure causes an uneven distribution of properties along the length and cross-section of the underlayer, disrupts the thermodynamic conditions for the spheroidization of cementite, and significantly complicates the process of cold plastic deformation during upsetting. Scientific novelty. The study investigated the impact of hot plastic deformation and interrupted cooling regimes on the kinetics of phase transformations in round bar rolling of boron-containing steel. The patterns of steel structure formation during cooling at various rates from the rolling temperature were established. Practical significance. It has been discovered that for boron-containing steel, hot plastic deformation and interrupted cooling significantly influence the decomposition of austenite. Simultaneously, it has been demonstrated that their separate and individual effects on the kinetics of austenite decomposition differ substantially from the process of phase transformations. The obtained results can be utilized in the development of industrial technology for the production of thermally treated coiled rolled products made from boron-containing steel for cold upsetting with a relatively uniform spheroidized structure.
Published Version
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