CHARACTERIZATION OF MICROSTRUCTURES IN 17-4-PH STAINLESS-STEEL BY MAGNETIC BARKHAUSEN NOISE-ANALYSIS

Magnetic Barkhausen noise (MBN) signals have been used to characterize the microstructures in quench-aged precipitation hardening 17-4-PH st ainless steel. The MBN data have been compared with hardness and coerc ivity. Microstructures were evaluated by optical, scanning electron an d transmission electron microscopy. It was found that MBN signals corr elate well with the microstructures manifested by the presence of intr a-lath spherical and inter-lath copper-rich non-magnetic precipitates. The presence of coherency strains at the peak hardness regions of the aged specimens could be inferred from the MBN data. MBN signals were found to provide a better criterion for the detection of the maximum i n coherency strains than the usual hardness data.