Effect of PWHT Larson–Miller Parameter on Mechanical Properties and Microstructure of Line Pipe Microalloyed Steel Joints

In this article, the effects of the postweld heat treatment (PWHT) on grain size and mechanical properties of X52 microalloyed steel joints have been investigated. The joints were welded by high-frequency induction welding (HFIW), and heat-treated at various temperatures and times. Then, the mechanical and microstructural evaluations were done on the heat-treated samples. To study the cumulative effects of PWHT time and temperature, the Larson–Miller parameter (LMP) of all the heat treatment cycles was calculated. Finally, the effects of LMP on the grain size and mechanical properties of the samples were studied. According to the findings, the grain size, toughness, strength and hardness show completely meaningful relationships with the LMP of PWHT for the HFIW welded joints. To achieve high impact energies and ductile fracturing, there was an optimum time and temperature condition for the PWHT, and it was obtained for the LMP range of 23,300 to 25,300.