Analysis of microstructural changes during high temperature exposure by means of non-destructive micro-magnetic methods

Microstructural changes during thermal ageing of ferromagnetic materials can be detected in a rapid and nondestructive way by means of micro-magnetic methods. The Fraunhofer Institute for Nondestructive Testing(IZFP, Saarbrücken, Germany) prove the suitability of the technique for the characterization of microstructural changes caused by both mechanical pre-treatment and thermal ageing (at different times and temperatures) of the ferritic steel Crofer 22® H. The testing scheme was based on four magnetic methods: Barkhausen noise, incremental permeability, upper harmonics and eddy current analysis.