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An experimental study of two warm and hot forged 0.30% carbon ferrite/pearlite microalloyed steels demonstrates that the optimal combination of strength and toughness is achieved in a warm forged, fan cooled condition. The properties of the warm forged microalloyed steel approached the combination of strength and toughness achieved in a heat treated 1037 steel, tested at an equivalent hardness level of 20 to 28 HRC. These warm forged microalloyed steels were successfully substituted for heat treated 1037/1040 steels in two automotive transmission hub applications. The benefits of implementing the warm forged microalloyed steel hubs include the elimination of the heat treatment, and the associated costs and problems.

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.