Effect of shot peening treatment on residual stress and magnetic Bakhausen noise of AISI 201LN and AISI 304L stainless steels

This work evaluates microstructural changes and residual stresses on surface samples of AISI 201LN and 304L subjected to shot peening. The residual stresses were measured by Xray diffraction and magnetic Barkhausen noise (MBN) in different shot-peened conditions. The results showed that the 201LN steel presented more martensite than the 304L steel in the initial condition, but with lower δferrite contents. These ferromagnetic phases were present in a low amount with high tensile residual stresses due to brush cleaning and light cold rolling in the final stage of the fabrication process. The shot peening process promoted compressive residual stresses mainly in the δferrite. However, some 'fresh' martensite exhibited tensile residual stress represented by higher and thinner peaks, which together with the low-intensity amplitude in the neighborhood, represented all formed martensite. Thus, small microstructural changes provoked high residual stresses behavior, which can be detected in ferromagnetic phases by MBN. (author)