Experimental–numerical investigation of solid–liquid jet erosion in AISI 304 stainless steel: effect of impingement angle and strain hardening

Solid–liquid jet erosion of AISI 304 austenitic stainless steel was investigated at impingement angles of 30° and 45° using a coupled experimental–numerical framework. One-hour slurry jet tests (2 wt% SiO₂, mean particle size 230 μm, velocity 1 m·s⁻¹) were combined with transient Eulerian–Lagrangian computational fluid dynamics (CFD) simulations employing the Oka erosion model. The novelty of this work lies in directly linking CFD-predicted erosion fields to the dynamic evolution of surface hardness and microstructure. Both experimental and numerical results confirmed that erosion severity increased with impingement angle, from 30° to 45°. However, the CFD model overestimated the measured mass-loss flux by factors of 6.2 and 6.4 at 30° and 45°, respectively. This discrepancy is primarily attributed to the constant-hardness assumption (149 HV) embedded in the Oka model, as well as to the trap-wall boundary condition and the one-way coupling approach. Post-erosion Vickers microhardness measurements and microstructural analyses revealed an inverse relationship between erosion severity and residual surface hardening. Despite exhibiting the lowest mass-loss flux (6.84 × 10⁻⁷ kg·m⁻²·s⁻¹), the 30° condition produced the highest surface hardening, with hardness increasing from 149 to 162 HV (+ 8.5%), accompanied by pronounced shear-induced deformation. In contrast, the 45° condition, which generated the highest mass-loss flux (8.76 × 10⁻⁷ kg·m⁻²·s⁻¹), exhibited the lowest hardening, with hardness increasing only from 149 to 157 HV (+ 5.4%), together with evidence of indentation-assisted material removal. This inverse trend suggests that higher erosion rates continuously remove the work-hardened surface layer before it can fully develop and stabilize. Consequently, the more severe the erosion, the lower the hardness retained at the eroded surface. These findings establish a direct relationship between erosion severity, hardness evolution, microstructural response, and impact angle, while highlighting the need for erosion models that account for strain-hardening-dependent material evolution to improve predictive accuracy under slurry-jet erosion conditions.