Characterization of Graded Subsurface Zones in Industrial Case-Hardening Using a Non-Destructive Testing System

Abstract

For process monitoring and quality assurance of case-hardened components, the determination of the case-hardening depth in the manufacturing process after hardening of the subsurface layer is a quality verification that is often required in industry. Currently, these quality assurance tests can only be realized with destructive measures. During case-hardening, the essential microstructural formation, and thus the key component properties are developed during the heat treatment in the cooling section. The testing technique used in the present study is based on the analysis of harmonic signals of eddy current testing. The aim of this project was to achieve an early identification of incorrect cooling processes in the case of a known transformation behaviour of the components during cooling. The data collected in the industrial hardening process show that an evaluation of the carburizing process on the basis of the case-hardening depth can be carried out non-destructively during component cooling and in the cooled state with the use of eddy current technology.