The study of influence of heat treatment procedures on structure and properties of the new high-strength steel with increased cold resistance

The study of influence of different heat treatment procedures on microstructure and mechanical properties of the new high-strength weldable cold-resistant steel 20G2SMRA (20Г2СМРА) is conducted. Morphology of martensite after steel quenching, as well after quenching and consequent tempering, is examined using optical metallography and electron microscopy. Regularities of varying of microstructure parameters, hardness values (HV1) and impact strength KCV were revealed in this work at the temperature –60 °С depending on heating temperature for quenching and consequent tempering. Amount of residual austenite after quenching starting from the temperatures 850, 950 and 1000 °C was determined using X-ray structural phase analysis. The rational procedure of heat treatment was established as a result of the study; it provides combination of guaranteed yield strength σ0,2 ≥ 600 N/mm2 together with low-temperature impact strength KCV–60 ≥ 50 J/sm2 and ductility δ5 ≥ 17%. The obtained results of investigation are aimed for commercial putting into practice in the conditions of heavy plate production at 5000 rolling mill of Magnitogorsk Iron and Steel Works (MMK). The work was done under financial support of the RF Ministry of Education and Science within the framework of execution of the grant of RF President (Agreement No. 075-15-2020-205 dated 17.03.2020 (int. No. MK-1979.2020.8)).