Inconel 625 is widely used in corrosive and high-temperature environments, but welding it introduces a metallurgical challenge: Laves phase formation. These brittle intermetallic compounds (Nb-rich) segregate in the interdendritic regions during solidification, reducing ductility and corrosion resistance.
Per AWS A5.14 and ASME Section IX, controlling heat input and interpass temperature is critical. High heat input promotes segregation because slower cooling rates allow more time for Nb and Mo to partition into the liquid. The result is a continuous network of Laves phase in the fusion zone.
To minimize Laves phase, follow these guidelines:
? Keep heat input below 1.5 kJ/mm.
? Limit interpass temperature to 150?C maximum.
? Use a filler metal with lower Nb content, such as ERNiCrMo-3.
? Apply a post-weld solution anneal at 1095-1150?C when possible.
Auditors and QC engineers should verify that welding parameters are monitored and recorded during production. A simple heat input calculation on the WPS can prevent costly rework.
Source: AWS A5.14
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