Detection of Iron Oxide Layer in Quenched and Tempered Gear Steel Using Magnetic Barkhausen Noise

This paper deals with the non-destructive evaluation of surface oxidation of gear steel using magnetic Barkhausen noise profiles analysis. Martensitic specimens are subjected to tempering at various temperatures in a muffle furnace. Tempering induced changes result in Barkhausen profile height increase and peak centers shift to lower fields. Single peak profiles are associated with specimens tempered up to 500 °C. Double peak profiles are seen with specimens tempered at 600 °C and 700 °C. Single peak profiles are observed after removing the oxide layer. The utilization of MBN method for this purpose is based on the difference in the inherent magnetic properties between the degraded surface layer and the sub-surface unaffected bulk. The observations are discussed in the light of established models of Barkhausen noise.