Abstract: The phase transformation temperature of 07MnNiMoDR steel was measured by means of thermal dilatometer. The optimization process of sub-temperature quenching and tempering and the controlled rolling and cooling were used to conduct heat treatment experiments on the tested steel, thus the influences of different heat treatment processes on microstructure, texture and impact properties of the tested steel were analyzed. The results show that the phase transformation temperature of the tested steel is Ac₁=686.6 ℃, Ac₃=886.4 ℃. By using the process of sub-critical quenching and tempering, the impact absorbed energy of the tested steel with the thickness of 1/4 and 1/2 can be both increased to above 200 J at -50 ℃, and both the microstructure and the randomization of texture contribute to the increase of the impact absorbed energy. After the controlled rolling and cooling, the specimens retain a lot of deformation and phase transition textures, such as {332}<113>, {554}<225>, {223}<110>, etc. Most of the textures are formed in the rolling process of the γ phase non-recrystallized region and the γ/α two-phase region. After heat treatment by the sub-critical quenching and tempering, the strong textures of the α-orientation line and γ-orientation line are weakened, and the texture orientation becomes randomly distributed, thus the preferred crystallographic orientation is not evident.

Key words: transformation point, subcritical quenching, low temperature toughness, texture