Investigation of transformation for ultrahigh strength steel Aermet 100

The heat-stagnation curves of two quenched and cryogenically treated ultrah igh strength AF1410 and Aermet 100 steels during heating and cooling in fur nace have been measured. The results showed that the curve displayed an abn ormal terrace in the course of heating, and within the temperature range co rresponding to the terrace, the formation and growth of both cementite Fe3C and secondary hardening phase M2C in the steel make the carbon content in matrix obviously vary. It is in the region of terrace that the optimum comb ination of tensile strength and fracture toughness is obtained because of s econdary hardening. Based on the measured heat-stagnation curve, several tr ansformation points have been determined and the correctness was also verif ied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Furthermore, the influence of heating rate and tempering temperature on the crystal structure and stability of austenite has been studied.