Measurement of microstructure changes in 9Cr–1Mo and 2.25Cr–1Mo steels using an electromagnetic sensor

This paper presents results from a multi-frequency electromagnetic sensor used to characterize the microstructural changes in 9Cr–1Mo and 2.25Cr–1Mo power generation steels after tempering and elevated temperature service exposure. The electromagnetic sensor can detect the microstructural changes in both steels due to the corresponding relative permeability and resistivity changes. The low-frequency inductance value is particularly sensitive to the different relative permeability values of both steels.