Influences of turning parameters in surface residual stresses in AISI 4340 steel

The study of the residual stresses of parts that work under extreme conditions is of great interest, as they will influence the mechanical behavior of the components. 

This has a huge importance in the automotive and aeronautics sectors, in components such as power shafts or aircraft landing gears. Machining processes produce thermal and mechanical loads causing residual stresses in the surface of the finished component. The influence of the cutting parameters on the surface residual stresses generated during turning of AISI 4340 (40NiCrMo7) treated steel was analyzed. Surface residual stresses were measured using the X-ray diffraction technique and the sin2 ψ method. Both magnitude and direction of the residual stresses were assessed in order to understand how the cutting parameters affect the principal stresses directions and the homogeneity of the distribution of stresses. The ANOVA analysis has been used, obtaining the process window to reduce the tensile residual stresses affecting the component behavior against fatigue loads. When feed is increased, more heat is generated during the cutting process, leading to more tensile residual stresses. An increase in cutting speed results in a more adiabatic process (less heating of the part because heat is dissipated through the chip) that also leads to less tensile stresses. It has been observed that the maximum stress is localized around 30° from the cutting direction.