Assessment of the temperature distribution in deep rolling of hardened AISI 4140 steel

Deep rolling consists of plastic deformation of the workpiece surface layer without material removal. Although deep rolling has been systematically investigated over the last decades, the role played by the temperature developed during the process has not been fully understood yet, especially owing to the presence of a white layer seldom found beneath the deep rolled surface. In this work, the workpiece temperature is measured when deep rolling hardened AISI 4140 steel employing two different approaches, both based on the implanted thermocouple method and wireless communication. The influence of deep rolling pressure, speed and feed and workpiece hardness (39 and 50 HRC) on the workpiece temperature is assessed and the temperature in the contact zone between ball and workpiece is determined. The findings indicate that the rolling parameters and workpiece hardness do not significantly affect the temperature beneath the surface. However, a thin white layer is observed when deep rolling using the highest pressure value (300 bar), thus suggesting that severe plastic deformation is the only phenomenon associated with its formation.