In the carburizing process, it is necessary to control the surface carbon content in order to obtain desirable materials properties. Although quantometry is the most common method for determination of surface carbon content, being destructive, costly and time consuming are some disadvantages of this method. Eddy current testing has long been used as a technique for investigation of defects. However, determination of surface carbon content in carburized steels is a new application for this method which has been studied in this research. Sixteen AISI 4118 steel samples have been carburized in an enriched carbon gas carburizing furnace. Carbon potentials in the furnace were different for each sample; therefore, samples with various surface carbon contents were produced. Subsequently, the carbon content of all samples was measured using quantometry. Finally, determining the optimal frequency, eddy current testing was applied for all samples and the relationship between surface carbon content and various parameters such as normalized impedance and phase angle has been established. The study shows a good relationship between the carbon percent and phase angle can be established (R2=0.91) using phase angle. Besides, the effect of temperature on the relationship was also investigated using three levels in 0, 30 and 80 °C. The formulas presented, shows improvement in corresponding corrections in experimental data.

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