Numerical analysis to evaluate surface hardness measurement of hardened steel using magneto static-field magnetization eddy current testing

摘要

Since the induction hardening method can be used to perform surface hardening processing in a short time, it is used extensively in the manufacturing of automobile parts and other products. Hardened steel materials need to be inspected for strength and both the depth and surface hardness of the hardened layered checked. The electric conductivity and permeability of hardened steel materials decreases in proportion to hardness. Therefore, it is possible to evaluate surface hardness by detecting differences in the characteristics of a material when it is subjected to eddy current examination. This research studied the application of the eddy current examining method to the technique of simple inspection of surface hardness on a manufacturing line. Hardened steel materials have a large heterogeneity of initial permeability in proportion to hardness when compared with normal steel materials. However, since the usual eddy current examining technique generates a large amount of noise, hardness inspection is difficult. This paper shows how the surface of the hardened steel material was magnetized with a permanent magnet, thus suppressing the heterogeneity of permeability. Numerical analysis and a verification experiment were used to examine the process of inspecting surface hardness by the eddy current examining method employing this magneto static field magnetization technique.