Study on the mechanism of medium-temperature brittleness in deposited metal of high-temperature resistant nitrogen-containing nickel-based flux-cored wire

This article has developed a nitrogen-containing nickel-based flux-cored wire to replace Inconel 625 flux-cored wire for welding operations in boiler applications in thermal power plants. The high-temperature tensile properties of the deposited metal from this wire, ranging from room temperature to 900°C, were tested. The results indicate that the high-temperature tensile properties of this alloy are strongly dependent on temperature. Its tensile strength gradually decreases with increasing temperature, and its formability slightly improves, but medium-temperature brittleness occurs at 700°C. The reason for this phenomenon is twofold: on one hand, the decomposition of M23C6 carbides at grain boundaries weakens the pinning effect; on the other hand, the generation of continuous stacking faults leads to local stress concentration, ultimately resulting in material failure and fracture.