Influence of grinding and shot-peening on the near-surface microstructure of a maraging stainless steel

The near-surface properties of maraging steels are key to controlling their mechanical properties. They can be tailored by surface treatments such as shot peening and can also be influenced by prior machining. This study aims at determining the respective roles of grinding and shot peening processes on the near-surface microstructure of Custom 465 maraging stainless steel. A combination of experimental techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), and atom probe tomography (APT) provides an in-depth characterization of the initial microstructure and its modifications. The results show that grinding results in a very shallow nano-crystalline region less than 1 µm thick, which contains a high fraction of retained austenite and where most Ni3Ti precipitates initially present, have been dissolved. Shot peening, on the other hand, results in a moderate localized strain close to the surface, and in a deeper destabilization of the retained austenite initially present, which decreases from ∼5% to ∼2% in the first 100 µm below the surface. It has no visible effect on the precipitate microstructures. The different mechanisms that may cause these modifications are discussed.