Effects of grit blasting on surface properties of steel substrates

Low carbon steel substrates have been grit blasted using alumina grits of various sizes under varying pressure, time, angle and standoff distances and the corresponding effect on surface roughness and surface residual stress has been studied. The mechanism of material removal in grit blasting has been analyzed. The effect of blasting process parameters on substrate surface residual stress has been studied using a statistically designed experiment. For this purpose the Barkhausen noise analysis (BNA) of the blasted surface has been undertaken. Then the BNA results have been calibrated against and complemented using the residual stress values measured using X-ray diffraction. The correlation between BN signal and the measured residual stress has been studied. The material removal in blasting takes place by microcutting, indentation or by a mixed mode depending on the blasting angle. During blasting the alumina grits themselves also undergo erosion. The analysis of the experimental results shows that the surface roughness increases with grit size, blasting pressure and to an extent with blasting time and blasting angle as well. The compressive residual stress of the surface and subsurface hardness increases with blasting pressure and blasting angle. The Barkhausen noise signal has a strong correlation with the magnitude of the compressive residual stress on the blasted surface.