Identification and characterization of the grinding burns by eddy current method

Abstract

This work presents an attempt to identify local changes in materials caused by local grinding burnings by using the eddy current (EC) method. The locally heat-treated AISI 9310 steel specimen was prepared by using a laser surfacing process to imitate three different grinding burns. These burn marks were characterized in terms of changes in microstructure and hardness on the surface and cross-section of the specimen. On such a basis, the depth of the heat-affected zone caused by the grinding tool was examined. Subsequently, the specimen was subjected to the EC measurements for the quantitative description of the signal from each of the defects by using a commercial NORTEC 600D flaw detector working in specimen scanning mode and with a pencil probe. The changes in the amplitude and the phase angle of the signal from three defects indicate the possibility to identify burns along with their quantitative description and subsequent estimation of their depth. The differences in the phase angle value, related to the local changes in the stress state, serve as an effective indicator of the specimen overheating degree in the area of the EC induction.

Keywords

• eddy current
• non-destructive testing
• hardness
• heat-treatment