Microstructural characterization of MIG brazing ERCuAl cladding on API 5L X70 steel

In this study, Cu cladding was applied in pipeline sections of API 5L X70 carbon steel under room-temperature conditions, employing the metal inert gas (MIG) brazing welding process, using an ERCuAl-A2 wire. Microstructural characterization was conducted using optical microscopy (OM) and scanning electron microscopy (SEM). The results showed the formation of a Fe–Cu-rich intermetallic zone (IMZ), where two solidification modes on the Cu cladding were observed, the formation of steel peninsulas and Cu-rich beaches. On the other hand, micro-cracking was observed near the heat-affected zone of the API 5L X70 steel which was produced in the IMZ due to the diffusion of the molten copper along the grain. Pre-heat treatment and a Ni-buttering layer of ~ 2 µm in thickness were used to mitigate the cracking; however, only Ni buttering mitigates the crack generation in the API 5L X70 carbon steel.