Microstructure and Properties of Fe-2Cr-Mo-0.12C (Wt Pct)-Tempered Steel Plate at Different Normalizing Temperature After Hot Rolling

The microstructure and properties of a Fe-2Cr-Mo-0.12C (wt pct)-tempered steel plate at different normalization temperatures after hot rolling were investigated to enhance its comprehensive mechanical properties. The microstructure of the steel was mainly composed of a ferrite-bainite-tempered martensite mixture after the normalization-tempering process. The tensile properties and the ductile-brittle transition temperature values indicated that the best comprehensive mechanical properties can be obtained by normalizing at 930 °C and tempering at 700 °C. When the normalization temperature was 880 °C to 930 °C, the yield strength increased as the bainite and tempered martensite hard phase volume fractions increased. However, when the normalization temperature surpassed 980 °C, the precipitation strength behavior compensated for the adverse influence of the effective grain size growth, and yield strength was nearly unchanged. Total elongation reached a peak value when normalized at 930 °C, due to the optimal volume fraction ratio of the soft to hard phase. The Charpy impact fracture changed from a ductile to a brittle fracture with an increase in the normalization temperature. When the normalization temperature was 930 °C, the existence of a certain volume fraction of nano-precipitates and soft ferrite in the microstructure contributed to excellent ductile properties.