Influence of welding process on Type IV cracking behavior of P91 steel

Influence of laser welding (LW) and shielded metal arc welding (SMAW) processes on Type IV cracking behavior of modified 9Cr-1Mo (P91) steel has been investigated in this paper. The study involved comparison of stress rupture lives of modified 9Cr-1Mo steel weldments prepared by SMAW and continuous wave CO2 laser welding processes. Width of the heat affected zone (HAZ) in laser weldment was found to be 1.0 mm, whereas it was ~2.5 mm in SMAW weldment. The rupture lives of laser weldment were found to be higher than SMAW weldment at higher stress level and comparable at lower stress level. Under similar stress levels, the creep rupture lives of 875 °C heat treated specimens were found to be lower than that of the base metal and cross weld specimen. These results clearly suggest that the instability of microstructure in the intercritical heat affected zone (ICHAZ) is responsible for lower creep rupture lives of P91 steel weldment than the base metal. The experimentally observed variations in creep cavitation have been corroborated with the results of finite element (FE) analysis.