Magnetic Barkhausen emissions and microstructural degradation study in 1.25 Cr–0.50 Mo steel during high temperature exposure

Low alloy steel such as 1.25Cr–0.50 Mo steel is widely used in thermal power plants, petro-chemical industries and fertiliser plants. In recent years considerable attention has been paid to estimate the remaining life of a service-exposed component for effective utilising such components beyond the design life. Although these steels are heat treated to obtain a stable microstructure, microstructural changes such as carbide coarsening, increasing inter lamella spacing, formation of more stable carbides, dissolution of carbides, etc. take place due to prolong service exposure at elevated temperatures. This paper describes the systematic investigation on microstructural changes, changes of composition on carbides and their effect on the magnetic Barkhausen emission parameters. The materials were heat-treated at different temperatures (500–700 °C) for various duration of time (0–1000 h) to get wide variation in microstructure. RMS voltage and pulse height distributions of Barkhausen emissions signal were calculated. A good correlation between MBE parameters and microstructural changes has been found. The study will be useful for the non-destructive evaluation of microstructural degradation of in-service 1.25Cr–0.5Mo steel structure.