Development of Nondestructive Inspection Instrument of Effective Case Depth

This paper describes a magnetic nondestructive inspection instrument which is used to measure effective case depth of steel hardened by induction heating process. The theory of correlation between the coercive force and actual depth of hardened layer was proposed by several papers, and is applied to the instrument developed here. The main features of the instrument developed are as follows; (1) Rapid and high precision measuring. (a) Measuring time: about 8 second. (b) Accuracy: ≤±10% (2) Probe detecting the coercive force is desinged by magnetic field analysis.