Improvement of creep strength of TIG welded hastelloy X alloy joint

The creep strength of the TIG welded joints of Hastelloy X is sometimes weaker than that of the parent material. Especially in the internal pressure creep test using cylindrical test pieces, this phenomenon appears conspicuously. This is because in the case of the cylinders having circumferential joints, the rupture time becomes short due to the enhanced creep phenomenon, in which the welded metal is pulled by the parent material having large creep rate, and its creep rate increases. In order to improve this defect, it was attempted to improve the creep strength of the welded metal by adding B, Zr and rare earth elements to the welding rods. As the result, by adding several tens ppm of B, the weldability was not harmed, and the remarkable effect of improvement was observed. Also it was found that rare earth elements were considerably effective. In the cylindrical test pieces having joints, for which these improved welding rods were used, the joints which broke in the parent material were able to be obtained. As for the case of the cylindrical test pieces having circumferential and longitudinal joints, the comparison of creep strength was carried out, but nearly the same strength was shown, and it was proposed to regard the circumferential joints as important similarly to the longitudinal joints. (Kako, I.)