Effect of Aqua Blasting, Sandblasting and Laser Engraving on the Corrosion Resistance of Type 316 Stainless Steel

The goal of this paper is to advance our understanding about the influence of com-mercial surface finishing treatments on microstructure development and corrosion resistance of a type 316L stainless steel. Aqua blasting, sand blasting, and application of a laser bar-code engraving treatment were investigated using X-ray phase analysis, X-ray residual stress measurements and surface roughness measurements. All surface microstructures were then assessed with atmospheric corrosion tests at 50°C and 30% relative humidity. Aqua-blasting resulted in compressive surface residual stresses of -500 to -600 MPa, with no evidence of strain-induced martensite. Sand blasting led to compressive surface residual stresses of -700 MPa, with no evidence of strain-induced martensite. The samples subjected to laser engraving exhibited a recrystallized near-surface microstructure, with tensile surface residual stresses in the order of +500 MPa.Atmospheric corrosion tests were carried out using MgCl2 concentrations of 38-772 µg/cm2, with optical and laser confocal microscopy applied to quantify the development of corrosion products over time. The latter was correlated with the maximum depth of attack after exposure for 370 days of exposure. Atmospheric corrosion tests with deposition densities exceeding 38µg/cm2 MgCl2 led to the formation of corrosion products within the first 24 hours of exposure, with the development of corrosion products following parabolic growth laws. It is further shown that higher deposition densities led to fewer localised corrosion sites, but with larger dimensions in size. Laser engraving resulted in a higher number corrosion sites compared to the aqua blasted surfaces, with MgCl2 deposited over the interface between both finishing treatments indicating preferential attack on the laser engraved microstructure.