Effects of Pulse Current on Residual Stress and Microstructure of S355 Steel Subjected to Laser Surface Treatment
L-Q. Gao, H. Zhou, B-P. Gu, G-H. Xu and J-S. Wang
This research aims to investigate the effects and mechanisms of high energy electric pulse treatment (EPT) on residual stress by applying the EPT on S355 steel after laser surface treatment. The laser surface treatment process was used to simulate residual stress on S355 steel imparted during laser beam welding (LBW) and then the EPT was conducted on the S355 steel specimens under different pulse current recurrence frequencies and electropulsing stress relieving times. The effects of electric pulse on the residual stress and microstructure of the S355 steel samples were analysed and Ansoft Maxwell finite element (FE) software was used to study the influence of skin effect on electric pulse effect. The results show that an electric pulse can directly affect the internal microparticles of the S355 steel, effectively eliminating the residual stress. The effectiveness of eliminating residual stress is improved by increasing the pulse current recurrence frequency and electropulsing stress relieving times. The microstructural morphology of S355 steel specimens does not show significant changes before and after the EPT. The activation and movement of dislocations within the metal material under an electric pulse are the fundamental causes of residual stress release; moreover, the presence of the skin effect is a key factor in enhancing the electric pulse effect on the surface of the metal material. This results in a more effective release of residual stress after the EPT.
Keywords: Nd:YAG laser, electric pulse treatment (EPT), S355 steel, pulse recurrence frequency, skin effect, residual stress, microstructure