PSA., leader in the fabrication of Diesel engines, aims at increasing its productivity for the manufacture of forged steel crankshafts and controlling perfectly their quality. All industrial partners of PSA are contributing to the achievement of this goal. Detailed metallurgical studies and numerical simulation have been used internally to describe the microstructural transformations involved. It has been shown that numerical simulation allows to identify trends for the effect of the modification of various parameters without the need for expensive and time-consuming prototype studies.