CONICET | Buscador de Institutos y Recursos Humanos

The laser shock peening (LSP) and shot peening (SP) surface treatments are used to improve the mechanical properties or corrosion resistance of metals and alloys [1]. The magnitude of these beneficial effects depend on the microstructural changes, the roughness, the hardness and the com-pressive residual stresses caused by these treatments on the surface [2,3]. The purpose of this work is compare the influence of the LSP and SP treatments on the fatigue behavior in the austenitic stainless steel 253 MA (UNS S30815).The laser source used was a Q-switch Nd:YAG, the maximum pulse energy was 1 J/pulse, operating at 10 Hz, without protective coating. The pulse density used was 5000 pulses/cm2. The SP was performed using S-460 spheres (diameter: 1 mm) with an intensity that produced an arc height of 1.1 mm, measured using an A Almen strip (thickness: 1.295 mm). Low cycle fatigue (LCF) tests were carried out under fully reversed plastic strain control, Δεp = 0.2 %, at room temperature. The microstructural features, with and without surface treatments, were analyzed with optic (OM) and transmission electron microscopy (TEM). The microhardness profile was obtained. Residual stresses were measured by the hole drilling method. Furthermore, the surface roughness was determined. Microstructural studies from the surface to a depth of 1 mm show that the LSP and the SP generated a high dislocation density and many mechanical twins in which intersections deformation induced martensite is found. At depths, greater than 1 mm from the surface, the microstructure, with and without surface treatments, is similar. These results are coincident with the microhardness values obtained. Although LSP and SP induce compressive residual stresses on the surface, the fatigue life is not improved. However, it is important to note that only the LSP increases the stress level considerably.