Microstructural control of cavitation erosion in 316L stainless steel: Roles of grain size and grain boundary character

This work investigates the effect of grain size, orientation, and boundary misorientation angle on the ultrasonic cavitation erosion of 316L stainless steel. Grain growth was achieved through heat treatment at temperatures between 900 °C and 1300 °C for durations ranging from 0.5 to 24 h. Grain size, hardness, and tensile strength were characterized. Cavitation erosion tests were performed on as-received (cold-worked) and heat-treated samples, with SEM image analysis used to examine surface damage and erosion mechanisms. Heat treatment increased the average grain size from ≈46 μm to ≈558 μm, while reducing hardness by up to 16%. The cold-worked material showed lower mass loss than heat-treated samples of similar grain size, confirming the positive effect of strain hardening. Notably, although lower hardness is generally associated with higher cavitation erosion, samples with grain sizes of ≈220 μm demonstrated ≈75% lower mass loss than the heat-treated sample with a grain size of ≈46 μm after 5 h of cavitation. This behavior is mainly attributed to the lower grain boundary density of larger grains, as confirmed by SEM observations showing that grain boundaries and slip lines act as primary sites for material removal. However, the high ductility of 316L with grain sizes approaching ≈558 μm promotes greater damage within grain interiors through progressive plastic deformation than at boundaries, leading to slightly higher erosion than that observed in the ≈220 μm grain-sized material after the incubation period. Grains with orientations near <101> and <111> and high-angle boundaries (>55°) were particularly susceptible to erosion, emphasizing the role of crystallographic orientation and boundary character.