The Use of Strain-Induced Martensitic Transformation Phenomena to Estimate the Surface Plastic Strain Produced by Grit Blasting on Overaged 18Ni Maraging Steel

In the present study, strain-induced martensitic transformation has been used to estimate plastic strain resulting from grit-blasting in 18Ni(300) maraging steel. Overaged samples having high volume fraction of γ-austenite phase were blasted at two different blasting angles (at 45° and 75°), keeping constant all the other process variables. The kinetics of martensitic transformation induced by grit-blasting was treated as a function of the strain, according to the Ludwigson–Berger model, and the K_p value was adopted as an indicator of the mechanical stability of γ-austenite. The model was parametrized through the stretching of tensile testing specimens, at specific deformation levels. The increase on the dislocation density (ρ) resulting from blasting could also be determined by the Williamson–Hall method. The volume fraction of γ-austenite (V_γ) was quantified in both blasted and stretched samples by ex situ XRD analyses. It was found that γ-austenite to α′-martensite phase transformation occurred in blasted and stretched samples, after certain stress levels, despite their strain rate differences. For the process parameters employed, the resulting plastic true strain on the steel surface was in the order of 0.031 and 0.047 for blasting angles of 45° and 75°, respectively.