METHOD FOR NONDESTRUCTIVE ASSESSMENT OF STEEL

摘要

This invention highly accurately evaluates the surface treatment state of an object of inspection by identifying the cause of magnetic permeability variation in the object of inspection. The method for nondestructive assessment of steel according to an embodiment of this invention comprises a preparation step (S1), mounting step (S3), eddy current generation step (S4), frequency variation step (S5), impedance calculation step (S6), and evaluation step (S7). In the preparation step (S1), a nondestructive inspection device is prepared. In the mounting step (S3), an object of inspection is mounted. In the eddy current generation step (S4), eddy current is generated in the object of inspection. In the frequency variation step (S5), the penetration depth of AC magnetism into the object of inspection is continuously varied. In the impedance calculation step (S6), the impedance values for each penetration depth into the object of inspection are calculated. In the evaluation step (S7), the ratios between the impedance values for each penetration depth into the object of inspection and the impedance values for each penetration depth into steel before surface treatment are calculated and the surface treatment state of the object of inspection is evaluated through the use of the ratio calculation results to identify the cause of the variation in the magnetic permeability of the object of inspection.