Examination of surface hardness measurement of hardened steel using mutual induction type eddy current testing

摘要

The induction hardening method is used for an extensive manufacturing line of automobile parts, etc. The surface hardness of these steel materials must be inspected to determine the strength. The electric conductivity and permeability of hardening steel materials decrease in proportion to hardness. Therefore, a surface hardness evaluation is believed to be possible by determining differences in these material characteristics using the eddy current testing method. This method is not usually applicable to surface hardness inspection of hardening steel materials, because such materials have a large heterogeneity of initial permeability in proportion to hardness compared with normal steel materials. Since the usual eddy current examining method has a large noise, hardness inspection is difficult. In this research, the alternating magnetic field of a mutual induction type eddy current testing probe was used to test the surface hardness of hardened materials, and examination reduction of the heterogeneity of permeability in hardened materials was examined. This technique can be used to inspect the surface hardness of hardened materials simply on a manufacturing line. Usefulness of this inspection technique was confirmed by a verification experiment.