Effect of chromium on dynamic continuous transformation of overcooled austenite for Q345 steel

In order to make use of chromium originated from the low-cost ore, the contents of C and Mn were reduced and Cr was added based on the chemical composition of Q345 steel. The dynamic continuous cooling transformation (CCT) curves of four low-alloy structural steels with different contents of Cr were obtained by DSC analysis and dilatometric method combining with metallographic test and hardness measurement. The results show that with the increase of Cr content, the hardness of the steel greatly increases. Chromium may retard the pro-eutectoid ferrite formation of super-cooled austenite and broaden the transformation region of bainite. Compared to the original Q345 steel, the steel with the adjusted composition (C and Mn reduced and Cr added) may have a higher critical cooling velocity (0.5°C/s) of F+P, the two-phase structure formation. Therefore, a higher cooling rate may be applied in the actual process of steel making to improve productivity.