Residual stresses in tool steel due to hard-turning

Residual stresses induced by hard-turning are the result of a combination of mechanical and thermal effects, leading to a compressive or tensile stress state at the surface, depending on the machining parameters and the tool wear state. In this work, the residual stress depth profiles generated on steel grade F-521 (AISI D2) by hard-turning with tools of different wear states were measured by X-ray diffraction. An integral method was applied to determine the full stress tensor and the stress gradient tensors in the tangential, radial and depth directions. Both macroscopic and microscopic residual stresses were investigated. Compressive residual stresses were measured below the surface in all machined specimens. The magnitude of the compressive stress was much lower and the depth was much shallower when using new cutting tools than when using worn tools. However, the sample that has been hard-turned with a worn tool suffered strong microstructural changes in a layer more than 150 µm thick, especially at the surface, where the presence of a hard and very brittle layer of untempered martensite was evidenced.