Структуроутворення та властивості листових конструкційних сталей при режимах ординарної та комбінованої термічної обробки з витримкою в міжкритичному інтервалі температур

Abstract

The features of the structure, the nature of the distribution of alloying elements and impurities between the structural components of sheet low-alloy steels that have undergone heat treatment with exposure in the intercritical temperature interval (ICTI), the structure formation and mechanical properties of these steels after the combined regimes of heat treatment with exposure in the ICIT were investigated. The analysis of the distribution of elements among the structural components of the studied low-alloy steels allowed us to establish that during heat treatment with direct exposure in the ICTI, such elements as manganese, chromium, aluminum, vanadium, sulfur, and phosphorus are concentrated mainly in the strengthening martensitic-bainite phase, while nickel, silicon and titanium are evenly distributed between the strengthening phase and ferrite. The conducted research on the example of sheet low-alloy steel 14G2 shows that the effects of grinding of ferritic grain, peаrlitic and martensitіс (bainite) components during combined processing with exposure in ICTI can be caused by implementation at low (450-550ºС) temperatures of isothermal decomposition the mechanism of multiple nucleation of ferrite microcrystals. It was established that the combined regimes with exposure in ICTI allow, without the application of hardening and tempering operations, to achieve in sheet low-alloy steel 14G2 mechanical properties at the level of strength class 390 according to DSTU 8541:2015 with yield strength values of 422-425 МPа and with high plasticity and impact viscosity Therefore, the use of these modes in a modified form can be recommended for the creation of end-to-end energy-saving technologies of heat treatment with exposure in the ICTI of low-alloyed steel sheet in the flow of thick-sheet mills equipped with normalization units. Keywords: structure formation, intercritical temperature interval, isothermal decomposition, martensitic-bainite phase, combined regime.