Continuous-cooling-transformation Diagrams for Boron-low Carbon Micro Alloy Hot Rolled Enamel Steel

Abstract

The addition of Element B to micro-alloyed low-carbon steels helps to improve the scale burst resistance of the enameled steel while being able to improve the strength properties of the base steel. It is known that the differences in alloy content change the phase transition temperature and CCT diagram. To test the phase transformation temperature and CCT diagram of B-micro-alloys low carbon steel, this paper uses the thermal expansion method to determine the transformation temperatures Ac1, Ac3, Ar1, and Ar3 with a Gleeble-1500 thermal simulator, and conducts hot compression experiments at 950 °C with a true strain of 0.3 and strain rate of 10 s−1, followed by cooling to room temperature at 0.1, 0.5, 1, 5, 10, and 25 °C/s rates of cooling to room temperature. Based on the expansion diagrams, metallography and hardness are combined to determine the microstructure composition at the corresponding cooling rates. Therefore, the CCT diagrams are plotted. The results show that when the cooling rate is less than 5 °C/s, the phase transformation consists of ferrite and a very small amount of pearlite; when the cooling rate is greater than 5 °C/s, it consists of ferrite, a small amount of pearlite, and bainite, and when the cooling rate is from 5 °C/s to 25 °C/s, it consists of ferrite and bainite.