Surface decarburisation of steel detected by magnetic barkhausen emission

The effect of decarburisation of the surface layer on magnetic Barkhausen noise (MBN) emission was investigated in quenched and tempered steel containing 0.67% carbon. The MBN profile of intensity versus energising current from the un-decarburised material showed a single peak typifying the martensite structure. After decarburisation, a profile with a double peak was obtained. The presence of the decarburised layer produced a second, overlapping peak at a lower field value. The height of the second peak increased with increasing depth of decarburisation and its position moved to increasingly lower field values.