“FOURCRACK”—An investigation of the creep performance of advanced high alloy steel welds

Creep failure by “Type IV” cracking in the weld heat-affected zone (HAZ) is likely to be the life-limiting failure mechanism in high-alloy steel components for advanced power plant. A UK collaborative project, “FOURCRACK”, has therefore been carried out to investigate and compare the cross-weld creep rupture performance of several casts of the advanced steels E911, P92, and P122, and the established steel P91. The experimental matrix included both stress and temperature variations while minimising the testing required to characterise the comparative performance of different welded materials. The results clarify the interplay between weld metal and HAZ failure mechanisms, the relationships between parent material and cross-weld creep strength, and the relative merits of the alternative steels. Finally, problems which arise in the assessment of cross-weld creep test data are discussed, and recommendations put forward to address the risks of biased assessment when failure can take place in different locations within the weldment.