Energy-Dependent Surface Integrity of Stainless Steel AISI 304 After Robot-Based Machine Hammer Peening

Machine hammer peening (MHP) is a high-frequency, incremental surface treatment with a spherical plunger which enables reproducible local plastic forming of metallic surface layers. The elasto-plastic deformation leads to a targeted smoothing or structuring of the surface as well as to the induction of compressive residual stresses and strain hardening. However, since MHP is still a relatively new process, there are still considerably knowledge deficits with regard to the cause–effect relationships of the energy inputs set by the MHP process parameters and the resulting surface integrity of technically relevant alloys. Therefore, the objective of this work is to investigate the influence of the peening strategies and the resulting contact energies on the surface roughness, the surface hardness, the residual stresses, and the microstructure of AISI 304. The results show that MHP leads to smoother and harder surfaces resulting from deformation-induced martensite formation accompanied by high compressive residual stresses and subgrain refinement resulting from higher dislocation densities.