The influence of hot rolling parameters on the microstructure and mechanical properties of an ultra-high strength steel

The influence of reheat temperature, percentage deformation, interpass time and finish rolling temperatures on the microstructure and mechanical properties of AISI 4130 steel were studied. Reheat temperatures of 900, 950, 980, 1050, 1100 and 1200 degrees C were used and reductions per pass of 15, 30, 40, 50 and 60% were employed. Finally, finish rolling temperatures from 500 to 850 degrees C were used. The samples were air cooled after the final. pass and the variations of their hardness, tensile and impact properties as a function of thermomechanical treatment parameters were measured and their microstructure studied using both optical and scanning electron microscopy. By a judicious control of thermomechanical treatment it was possible to determine the rolling conditions leading to the optimum combination of strength and toughness. The possible mechanisms responsible for the observed behavior are presented and the results are discussed within the existing models. (C) 2000 Elsevier Science S.A. All rights reserved.