EVALUATION OF SURFACE MODIFICATIONS IN HIGH STRENGTH STEEL

Abstract This paper reports on the application of micromagnetic inspection techniques to the evaluation of the surface condition of shot peened, high strength HP9430 steel. It is shown from the results that the modification of the surface condition resulting from different shot peening intensities can be detected from the amplitude of the micromagnetic signals emitted from the surface under alternating magnetic field excitation. It is further demonstrated that the production of residual stresses in the surface of a steel, as a result of shot peening, causes a broadening of the range of critical field strengths for domain wall activation. Consequently the spectrum of activation fields obtained on a plot of micromagnetic activity versus magnetic field strength can be used as an indication of the shot peened condition of the material.