Evaluation of microstructures in 2.25Cr-1Mo and 9Cr-1Mo steel weldments using magnetic Barkhausen noise

Magnetic Barkhausen Noise (MBN) measurements have been used to characterise different microstructural regions such as coarse grain region, fine grain region, intercritical structure (composed of retained austenite and tempered ferrite) within the heat affected zone (HAZ) of 2.25Cr-1Mo steel and 9Cr-1Mo steel weldments using simulated HAZ microstructure samples. It is observed that MBN level decreases with increase in hardness corresponding to different microstructures. This behaviour has been confirmed by the measurements on the actual weldments of 2.25Cr-1Mo steel and 9Cr-1Mo steels. It has been observed that the intercritical region and the base metal region can be distinguished from the peak position of MBN which would be useful for measuring the extent of HAZ non-destructively. This study also shows the possibility of measuring the extent of different microstructural regions using miniature MBN probes with prior calibration.