Design of Nondestructive System for Hardness of Carbonitrided Steel Parts ‎Using Eddy Current Testing Method: Case study on the Tappet Parts

In this paper, a non-destructive eddy current test system was designed to evaluate the surface hardness of the carbonitrided steel parts. For this purpose, various samples of the tappet were used after the surface hardening and grinding operations as control samples and, if necessary, were subjected to destructive and non-destructive tests. Microstructural studies were performed with a microscope equipped with an image processing and micro and microprocessor based on the Vickers method as destructive tests. Statistical methods were used to identify the critical point for eddy current test position. Then, using a non-destructive eddy current test device, the microstructure and hardness of the good and bad part were evaluated at different frequencies at the critical point. The apparent resistance of the coil (impedance) was used as the eddy current response. Using regression analysis (R2), the frequency was chosen to evaluate the components. The results of this study showed that, using the eddy current method, carbonitrided parts can be identified and separated on the basis of the microstructure and the thickness of the hardened layer in a non-destructive manner. It was also found that the best separation of these samples is obtained at a frequency of 80 kHz.