Mechanical properties of 11Cr-0.4Mo-2W-CuVNb steel welded joints at elevated temperatures

High Cr ferritic heat resisting steels are now recognized to be the most potential materials for thermal power plants. In view of such trend, the present paper investigates the creep properties of a W strengthened 11Cr-0.4Mo-2W-CuVNb steel welded joints. Joints were prepared by using gas tungsten arc (GTA) welding and electron beam (EB) welding. In order to simulate the microstructure of heat affected zone (HAZ), a technique of furnace heating was adopted with varying peak-temperature. Specimens of the welded joints and simulated HAZ were subjected to creep tests at 923 K. Most of the joint specimens were ruptured at their HAZ, and inevitably resulted in certainly shorter creep lives of welded joints than those of the base metals. The comparison of creep properties of simulated HAZ specimens showed that fine grains produced by heating to around Ac3 were obviously responsible for such degradation of creep strength in welded joints. The creep lives were longer for EB welded joints by about 2 times than for GTA welded joints. For GTA welded joints creep rupture was always located on the higher bevel angle sides. From these results, it is considered that narrower HAZ width with lower bevel angles surely produce higher creep strength of joints. The EB welded joints, however, showed relatively brittle fracture in the fine-grained HAZ after long-term creep tests. (orig.)