Microstructural characterization of tempered and deformed ferritic steels using magnetic Barkhausen emission technique

In this study, a micro-magnetic non-destructive technique, namely magnetic Barkhausen emission (MBE) has been explored for on-line evaluation of metallurgical quality of as fabricated and service exposed ferromagnetic materials through finer microstructural characterization By carefully optimizing the experimental parameters, we have shown in carbon steel and 2.25Cr-1Mo steel that the MBE signal rms profile systematically changes from a single peak to two peaks. To explain this, a two-stage magnetization process has been proposed, considering rain boundaries and precipitates as the two major obstacles to domain wall movement. We have shown that the variations in the height and position of the two MBE peaks can be used, not only to identify microstructural changes at different stages of tempering/ageing, but also to quantify the microstructural features. The study on the effect of tensile deformation, has confirmed the proposed two-stage magnetization process. It has also revealed the potential of MBE technique for accurately detecting the different stages of deformation