Continuous cooling transformation of undercooling austenite for low-carbon microalloyed pipeline steel

The different dilatometric curves of continuous cooling transformation were measured on Gleeble-1500 thermal mechanical simulator with methods of dilatometric change and differential thermal analysis. Referencing microscopic test and hardness measurement, the critical points and phase transformation points were determined, and the continuous cooling transformation curves (CCT diagram) of a low-carbon microalloyed pipeline steel were obtained. Transformation of austenite in the course of continuous cooling was investigated. The results show that adding 0.21% Mo can inhibit the formation of ferrite and pearlite, and promote the formation of acicular ferrite. Acicular ferrite can be obtained within a wider cooling rate range of 5.0-20.0°C/s, which shows that the microstructure needed for engineering application can be obtained in the low-carbon Mn-Nb-Mo microalloyed pipeline steel.