Measurement of decarburisation of steel rods with an electromagnetic sensor using an analytical model

This paper presents the measurement of decarburization of steel rods with an electromagnetic sensor using an analytical model. Loss of carbon (decarburization) at the steel surface can have a significantly detrimental effect on mechanical properties of products, since hardness, fatigue, strength, and wear properties are strongly dependent on carbon content. Currently, measurement of decarburization is by destructive methods, such as metallographic observation or hardness tests on a sample cross section after processing. A nondestructive EM method is proposed in this paper. An analytical solution for the inductance of a circular air-cored coil encircling a steel rod is deduced and further a simplified model is obtained which shows that with certain setups the thickness of the decarburisation layer is proportional to the inductance difference with and without the sample´ presence. Using this simplified model, decarburisation thickness can be easily obtained. The results have been verified by both Finite Element Models and metallographic observations.