Evaluation of post-weld heat treatment behavior in modified 9Cr–1Mo steel weldment by magnetic Barkhausen emission

• Effect of post-welding heat treatment (PWHT) on microstructure, mechanical properties and magnetic properties of 9Cr–1Mo steel.
• Correlation of mechanical and microstructural parameters with magnetic properties.
• An effective tool in evaluation of PWHT parameters in modified 9Cr–1Mo weld joint.

The butt joint of two sight tubes of modified 9Cr–1Mo steel is welded by TIG technique. Subsequently, the post-weld heat treatment (PWHT) of the tubes has been carried out at 650, 700 and 750 °C temperatures for 3 h. Magnetic Barkhausen emission (MBE) measurements are performed in fusion zone, heat affected zone (HAZ) and base metal region of as-welded and all the post-weld heat treated samples. In each weldment, the variation of the MBE signal emanated from fusion zone, HAZ and base metal has been examined. It is found that the RMS voltage of MBE signal increases with PWHT temperature. The conversion of retained austenite to alpha ferrite during PWHT makes the fusion region as a softer zone in the weldment. The variation of magnetic parameters with different PWHT is correlated with hardness and microstructures. This study can be used as an effective tool in evaluation of PWHT parameters in modified 9Cr–1Mo weld joint.