Effect of processing temperature on warm shot peening of spring steel

Effects of processing temperature on the residual stress and hardness in the warm shot peening process of springs were investigated to determine the optimum shot peening conditions. Springs made of hard spring steel were heated to facilitate a shot peening operation by the decrease in flow stress. In a model experiment using shots of a large size, the shot peening apparatus was covered to keep the processing temperature constant, and the distributions of residual stress and hardness in the peened workpieces were measured. Although the flow stress of the workpiece is decreased by the increase in the processing temperature, the decrease of hardness and residual stress in the workpiece increases. The compressive residual stress and the hardness in the peened workpiece were the highest at a temperature of 200 °C. The optimum temperature was also evaluated in an experiment using an actual shot peening apparatus with shots of an average size.