Investigation of as-quenched and tempered commercial steels by Magnetic Barkhausen Noise method

This study aims to characterise as-quenched and tempered steels by the Magnetic Barkhausen Noise method, and to contribute to optimisation of heat treatment processes. Identical austenitisation and quenching procedures were applied to SAE 1040 and SAE 4140 specimens to eliminate the effect of grain size. Samples were tempered at 200°C and 600°C for 2 hours. Microstructures were characterised by metallographic examinations and hardness measurements. Amplitude, position and frequency spectrum of signals were evaluated using a commercial system. As the tempering temperature increases, in contrast to the reduction in hardness, magnetic response increases due to the enhancement of domain wall displacement