Application of eddy current nondestructive method for determination of decarburizing depth in steels

Decarburization has undesirable effects on mechanical properties of steel parts such as hardness، wear and fatigue resistance. At least، one treatment stage at high temperature such as hot forging or heat treatment is predicted in almost any production process of industrial parts. As a result، determination of depth of the decarburized layer is especially important from practical point of view. Traditional destructive methods of determining depth of this layer، include metallographic or hardness test which are time-consuming and costly. Eddy current test is a non-destructive technique which is performed rapidly. Since its response is sensitive to chemical composition and microstructure of the material under consideration of non-destructive method can be used in determining depth of the decarburized layer in steel parts due to difference in the microstructures and as a result in magnetic properties of the decarburized layer with other parts of specimen. In this study Fe–0. 45 wt. % C steel was held in 900°C for different period of time and depth of these layers were determined by using three microscopic observations، hardness test measurements and non-destructive eddy current technique. The results were compared to each other. In present research، the respond of test samples to induction current including primary and secondary voltages، normalized impedance and harmonics are considered and examined. Results show acceptable accuracy in comparison with two other destructive methods.