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. (c) 2005 Springer Science + Business Media, Inc.