Detecting Method of Hardened Depth in Surface-Hardened Steel by Magnetic Field on Steel

The inspection of the surface-hardened depth of the mechanical part in a large-sized heavy industrial machine is important in the intensity or the guarantee of quality of these parts. When the size of its hardened steel parts is large, the destructive testing using the Vickers hardness tester is made difficult. Therefore, the non-destructive inspection method is needed for the evaluation of the hardened depth. The electromagnetic characteristic inside the hardened domain is lower than the non-hardening domain. Then, the non-destructive inspection of the hardened depth is possible by detecting the difference of these electromagnetic characteristics. In this paper, the high-sensitivity inspection method for detecting the surface-hardened depth is investigated by a 3-D nonlinear electromagnetic finite-element method using the evolution strategy method.