Microstructure formation and properties of heat treated 25Kh2N4MA steel

Formation of microstructures in 25Kh2N4MA high-strength steel during heat treatment was investigated. Using the dilatometric method, the temperature ranges for the formation of bainite and martensite during continuous cooling at rates from 0.1 to 30 °C/s were determined, and the corresponding continuous cooling transformation (CCT) diagram for the transformation of undercooled austenite was constructed. The mechanical properties were found to vary depending on quenching intensity and tempering temperature. The kinetics of isothermal bainite transformation were analyzed, and the level of properties achievable through bainite formation in different temperature ranges was determined. The presence of bainite in 25Kh2N4MA steel was shown to result in a 20–25% increase in impact toughness compared to the martensitic structure formed by oil quenching and low-temperature tempering. A quantitative assessment of the structural components in the steel after various heat treatments was performed.