The Effect of Forging Conditions on the Flow Behavior and Microstructure of a Medium Carbon Microalloyed Forging Steel 940787

Forging simulations with a 1522 steel microalloyed by additions of 0.25% Mo, 0.13% V and 0.01% Ti were performed on a laboratory thermomechanical processing simulator. The forging conditions included a strain rate of 22s^-1, 50% strain, and temperatures in the range from 1200°C to 950°C. The true stress was found to increase with decreasing deformation temperature for all values of instantaneous true strain. The maximum flow stress increased two-fold as deformation temperature decreased from 1200°C to 950°C, and the recrystallized austenite grain size decreased by a factor of two for this same decrease in temperature. Microstructures evolve from bainitic/ferritic at a cooling rate of 1.4°C/s, to fully martensitic at 16.8°C/s, independent of deformation temperature. Room temperature hardnesses depended primarily on cooling rate and were essentially independent of deformation temperature. Hardness ranged from 27 HRC to 48 HRC for the bainitic/ferritic and martensitic microstructures, respectively.