Optimizing austempering for lower bainite formation in DC53 steel: mechanisms for enhanced strength and toughness

This study aims to enhance the strength-toughness properties of DC53 cold work die steel by optimizing the austempering process. Compared to high-temperature tempering, the optimal austempering process increases unnotched impact toughness from 32.8 J/cm 2 to 41.3 J/cm 2 while maintaining a hardness of 61.9 HRC. The simultaneous reduction of the coefficient of friction from 0.674 to 0.621 and the decrease of the volume wear rate from 5.52 × 10 −8 to 3.80 × 10 −8 mm 3 ·N −1 ·m −1 suggest an enhancement in wear resistance. It was attributed to the formation of lower bainite, which exhibited in an acicular morphology and partitioned the prior austenite grains. It can disperse stress concentration similar to the prior austenite grain boundary, thereby reducing the formation of secondary cracks. The film-like retained austenite, distributs along the sides of lower bainite, exhibits high thermodynamic stability. The microstructural features exhibit a synergistic interaction resulting in superior comprehensive performance.