Comparison of mechanical properties of 2Cr-Mo and O.5Cr-Mo-V simulated heataffected zones

Reheat cracking during the stress relief of 0.5Cr-Mo-V weldments can occur in the coarse-grained region of the HAZ and necessitates expensive, time-consuming repairs. An HAZ thermal-simulation technique has been used to produce coarsegrained material similar to that obtained in welds of commercial 2Cr-Mo and 0.5Cr-Mo-V material. The mechanical properties of the two material HAZs, measured by slow strain-rate tensile testing, have been compared to establish whether the 2Cr-Mo composition, an alternative low-alloy creep-resistant, steam pipe material, offers any significant advantages in terms of its resistance to reheat cracking. Some practically relevant effects of thermal-cycle and welded-joint restraint variables on the structure and the hot-tensile properties of HAZ material have also been investigated. The results indicate that 2Cr-Mo material has the greater inherent resistance to reheat cracking. However, a change in steam pipe composition should not be necessary as substantial improvements in the resistance of 0.5Cr-Mo-V should be achieved when a high proportion offine-grained material is produced in the HAZ using an appropriate welding technique.