Fracturing in 14MoV6-3 Steel Weld Joints—Including Base Metals—After a Short Time in Service

In order to establish the influence of prolonged exposure to high temperatures on 14MoV6-3 steel, three different weld joints were designed. New-to-new material, new-to-used material, and used-to-used material joints were welded using two welding technologies—GTAW and a combination of GTAW + MMA. The weldments were tested by means of microstructure and tensile testing. The results showed that in all weldments, a fracture occurred in the base metal. Also, in the case of the new-to-used welded sample, the fracture always occurred in the used base metal. Since both materials have the same chemical composition, the difference in microstructure was related to long exposure to high temperatures. New steel has a considerably smaller grain size, while the used material underwent grain growth coupled with carbide coarsening, which decreased its strength. The yield strength (YS) of the new material was higher than the YS of the used material, which exhibited similar values in the used base metal and both weldments. It can be assumed that, since deformation starts in the area with the lowest yield point, the used material is the critical place in a given weldment. Therefore, the accurate extent of strength decrease cannot be evaluated based on the testing of new material, i.e., there is a need to reconsider the traditional qualifications of welding technology.