Residual stresses in turning: Part II. Influence of the machined material

The paper presents an experimental study on the influence of turning parameters and of the machined material on surface residual stresses. In the first part of the paper the relationship between the most relevant process parameters and residual stresses was established. This second part is aimed to the assessment of the influence of the machined material. Carbon and alloyed steels were machined varying feed rate and nose radius, and results show that the effect of process parameters can be considered to be additive to the influence of the material. This means that for the investigated steels the increase in residual stresses due to a variation in process parameters remains almost the same, while material characteristics only influence the mean level of residual stresses. Based on this observation, a first empirical predictive model was identified, which is valid only for carbon steels. It was found that for this kind of steels the equivalent carbon content fully characterises the material. A second predictive model was then derived for both alloyed and carbon steels, and it was found that the Rockwell hardness can be directly related to the mean level of residual stresses. The models were then used to build two nomograms that can be useful in the selection of the optimal turning parameters of a generic steel, different from the ones investigated in this work.