Laser-Assisted Surface Modification of TRIP Steels: Chemical and Microstructural Evolution, Residual Stresses, and Micromechanical Properties

The use of new lightweight design strategies is implemented in the automotive industry, for applications where high friction forces are present and lubrication systems need to be implemented. Micro-topography modification through laser texturing is an advantageous manufacturing technique that is currently being used by the industry. Combining both ideas, this manuscript aims to analyze the effect of surface modification laser-texturing process on a TRansformation-Induced Plasticity steel. Residual stresses, superficial chemistry, microstructure, and mechanical properties at the submicrometric length scale are investigated. Results show that the intensity and the number of pulses strongly modify the pattern geometry. Also, the pattern distance affects the residual stress state, changing from tensile to compressive stresses for distances higher than 20 mu m. Chemical and microstructural changes at the vicinity of the laser may be associated to the fast cooling of the sublimated material around the pattern induced during the laser-assisted surface modification thermal process. Furthermore, the hardness remains stable, and no changes are evident in the bulk material. However, a hardness reduction of around 95 pct in the austenitic value is evident in the pile-up zone around the laser pattern due to (1) the microporosity and defects confined inside the pile-up region and (2) due to the residual chemical composition created during the solidification process, which is rich in iron, chromium, nickel, and manganese and poor in oxygen.