Ageing behavior study of 5Cr–0.5Mo steel by magnetic Barkhausen emissions and magnetic hysteresis loop techniques

Magnetic hysteresis loop and Barkhausen emissions were recorded and analysed for 5Cr–0.5Mo steel after ageing at 600 °C for various lengths of time. At the initial stage of ageing the interstitial carbon diffuses towards the grain boundary making the matrix magnetically softer. During this stage, extending up to 200 h of ageing, magnetic softness was found to be increasing. This was associated with a decrease in coercivity and increase in Barkhausen voltage. Beyond 200 h of ageing the precipitation of alloy carbides attain subsequent growth, making the material magnetically harder. The evolution of carbides was studied using SEM-EDAX analysis. It was observed that most of the carbides transformed into M23C6 type after ageing for 400 h.