Effect of cyclic heat treatment on microstructure and mechanical properties of 50CrV4 steel

LI Hong-ying(李红英)¹, HAN Mao-sheng(韩茂盛)¹, LI De-wang(李德望)¹, LI Jun(李俊)², XU De-chao(徐德超)²

(1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
2. Research Institute, Baoshan Iron & Steel Co., Ltd., Shanghai 201900, China)

Abstract:an annealed 50CrV4 steel was subjected to cyclic heat treatment process that consists of repeated short-duration (200 s) held at 840 °C (above A_c3 temperature of 790 °C) and short-duration (100 s) held at 700 °C (below A_c1 temperature of 710 °C). The spheroidization ratio of cementite and the average size of particles increase with increasing the cyclic number of heat treatment. After 5-cycle heat treatment, the spheroidization ratio of cementite is 100%, and the average size of the cementite particles is about 0.53 μm. After cyclic heat treatment, the hardness, ultimate tensile strength and yield strength of the experimental steel gradually decrease with increasing cyclic number of heat treatment. The elongation of the as-received specimens is about 7.4%, the elongation of the 1-cycle specimen is 14.3%, and the elongation of 5-cycle specimen reaches a peak value of 22.5%, thereafter marginally decreases to 18.3% after 6-cycle heat treatment. Accordingly, the fractured surface initially exhibits the regions of wavy lamellar fracture. By increasing the cyclic number of heat treatment cycles, the regions of dimples consume the entire fractured surface gradually. Some large dimples can be found in the fracture surface of the specimen subjected to six heat treatment cycles.

Key words:cyclic heat treatment; accelerated spheroidization; mechanical properties