Effect of cooling path on the phase transformation of boron steel 22MnB5 in hot stamping process

Abstract

Boron steels have phase transformation in hot stamping process, and the mechanical properties of hot stamped parts are determined by the microstructure generated by phase transformation. Cooling path has a significant effect on phase transformation and microstructure of the deformed parts; in order to obtain the tailored-customized mechanical properties, the relationship among cooling path, the phase transformation, and the corresponding microstructure must be investigated. In this paper, the dilatometric experiment with the cooling rate of 2, 10, and 50 °C/s and various dwell temperatures was conducted to explore the influence of cooling path on the start and finish temperatures of phase transformations from austenite to ferrite, bainite, and martensite; lasting times of transformations; and final microstructures in hot stamping process. The controllable factors which influence the mechanical properties of hot stamped boron steel component were also determined. In addition, the metallographic and Vickers hardness experiments were conducted as well to confirm the analysis result of dilatometric experiment. The knowledge about the relationship of cooling path, phase transformation, microstructure, and mechanical property of the hot stamped parts helps the design of hot stamping process of the stamped parts with tailored-customized mechanical properties.