Evaluation of the surface of alloy tool steel treated by cavitation shotless peening using an eddy current method

Cavitation shotless peening (CSP) of hot forging die made of alloy tool steel is an effective peening method because it increases the fatigue strength of the material, and both introduces compressive residual stress into the material and also work hardens it. In order to evaluate the peening intensity of the die, a quick non destructive method is needed. In this paper, the dependence of the electromagnetic properties of an alloy tool steel, Japanese Industrial Standard (JIS) SKD61, on CSP processing time was investigated using an eddy current method. The induced stress and changes in the microstructure depend on CSP processing time, and these affect the electromagnetic properties of the material, such as the electrical conductivity and the permeability. The peening intensity was evaluated by measuring these electromagnetic properties using the eddy current method.