Welding Nickel AlloysThe solid solution alloys, such as Inconel 625, are readily welded using similar precautions to those for austenitic stainless steel. They are ductile and at high temperatures can be susceptible to hot cracking. This is due to the formation of low melting point sulphur compounds at the grain boundaries. The alloys also have low ductility at about 700°C and cracking can occur where the weldment is heavily restrained preventing cooling contraction. Distortion can be a problem, best solved by a combination of tacking and sequenced short weld runs, about 100mm. Generally, however, given clean surfaces and good gas shielding high quality welds can be produced with no pre or post weld heat treatment. The precipitation hardened alloys, such as Nimonic 80A and Monel k- 500 are not so readily welded as they require heat treatment to give the specified mechanical properties. These alloys should only be welded after consultation, as the full mechanical strength can sometimes not be achieved after welding even after heat treatment.
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