Investigation on Microstructure, Hardness and Fracture Energy of AISI H13 Hot Work Tool Steel by Cyclic Heat Treatment

This research aims to present the best conditions for cyclic heat treatment of AISI H13 hot work tool steel to improve its mechanical properties and achieve a microstructure with fine grains. To accomplish this, 27 experiments were designed using the full factorial design approach. The austenitizing, intermediate salt bath and quenching salt bath temperatures were kept constant, while the austenitizing times of 5, 10 and 15 min, holding in the intermediate bath of 5, 10 and 15 min and the number of cycles of 2, 3 and 4 were varied. The best mechanical properties were obtained with 5 min of austenitizing, 15 min of intermediate bath and 4 cycles, resulting in a 41% reduction in grain size and a significant increase in toughness compared to the control sample. EDX analysis revealed that higher austenitizing temperatures led to greater carbon dissolution in austenite, which in turn resulted in the formation of carbides and their penetration into grain boundaries, leading to grain boundary fracture.