Non-destructive evaluation of decarburization of spring steel using electromagnetic measurement

Surface decarburization in the process of spring steel making often leads to deteriorated fatigue behavior of the finished components in service. Steel industry has a strong interest to replace time consuming and expensive destructive mechanical tests by non-destructive methods, which can be even integrated in-situ within the production process. In the present work, the decarburization profiles in 51CrV4 steel have been investigated based on light microscopic inspection and hardness testing. The latter quantity is also investigated using an electromagnetic measuring and evaluation device. The analysis procedure of this device utilizes the KEMAG method, which is based on the analysis of a combination of various electromagnetic properties. For the first time, the present method is applied to the analysis of non-uniform properties varying with the distance from the surface into the specimen volume. Good agreement between non-destructive and classic destructive methods is achieved.