Hot Processing Maps and Workability Characteristics of As-Cast 42CrMo Steel during Hot Compression

Abstract

In order to investigate the thermal forming behavior of as-cast 42CrMo steel, the isothermal compression tests were performed on a Gleeble-1500D thermal mechanical simulator in the deformation temperature ranging from 850 to 1150°C with an interval of 100°C, the strain rate ranging from 0.05 to 5s-1 and the height reduction of 60%. On the basis of the flow stress data, dynamic materials model (DMM) and Prasad's instability criterion, the processing maps for as-cast 42CrMo steel were constructed at the strains of 0.4 and 0.6. The safe and unsafe areas and the corresponding deformation regimes were predicted during hot working, which are verified through the microstructure observation. The results indicate that the safe zones in the temperature range of 850~1150°C and strain rate of 0.05~0.35s-1, which exhibit the dynamic recovery and recrystallization. However, the flow instability domains are in the domain of deformation temperatures 850~1150°C and strain rate higher than 0.35s-1. Typical microstructure of instability is cracking, which should be avoided so as to obtain desired mechanical properties in hot processing. Finally, the forging parameters were predicted and optimized accurately by the processing maps, the temperature range of 1050~1150°C and strain rate of 0.05~0.1s-1 were recommended as the optimum deformation conditions for hot processing of as-cast 42CrMo steel.