EFFECT OF THE BLANK SURFACE CONDITIONS ON THE QUENCHING BEHAVIOR OF A HIGH THICKNESS 22MNB5 STEEL IN PRESSHARDENING PROCESS

Weight reduction in commercial vehicles is increasingly gaining importance, following an already well established trend in the modern car structures. However, the production of high thickness structural components using 22MnB5 steel requires a more profound knowledge of the effect of increased heat and cycle time on the quality of the final martensitic microstructure. The identification of new process parameters offers additional possibilities to control and stabilize the manufacturing process. In this study, the influence of the surface condition of 22MnB5 steel samples with 8.0 mm thickness on the mechanisms that characterize heat transfer by contact is discussed, as is the correlation of this parameter in the characterization of the martensitic transformation and hardness profile. For this, the test specimens with three different surface conditions (natural, ground and polished) were heated to austenitization temperature, and subsequently processed in an experimental tool provided with cooling channels. Through the results of the metallographic analysis and hardness profile, it was verified that the cooling rate is affected by the superficial condition of the specimens, as well as the resulting martensitic microstructure. Higher austenitization temperatures promote austenite grain growth and, thus, deteriorate properties such as toughness and crack propagation resistance.