THE INFLUENCE OF CONTROLLED ROLLING ON THE PULSE-HEIGHT DISTRIBUTION OF MAGNETIC BARKHAUSEN NOISE IN STEEL

Magnetic Barkhausen noise (MBN) refers to the discontinuous changes in magnetization due to domain walls becoming pinned on, and subsequently overcoming, obstacles to their motion. Barriers to domain wall motion may be microstructural in nature, such as precipitates, grain boundaries and regions of localized strain; for this reason techniques based on MBN detection have the potential to characterize and to evaluate non-destructively ferromagnetic materials. The present study investigates the influence of furnace cooling, normalizing and controlled rolling on the MBN pulse height distribution of relatively low carbon steel. In general, randomly oriented undeformed grains result in a narrow symmetrical pulse height distribution which shifts to lower values as grain size is reduced. Controlled rolling to low finish rolling temperatures results in an asymmetrical pulse height distribution when the applied magnetic excitation field lies parallel to the steel rolling direction; this is attributed to domain walls "jumping" beyond individual grains as a result of the influence of texture and/or microstructural strain.