Microstructure and wear resistance of Fe-based hardfacing layer prepared by flux-cored wire feeding MAG welding process

Severe abrasive wear of drill pipe and casing often occurs in exploration drilling operations. To achieve the surface enhancement of the drilling components in terms of abrasive wear resistance, various flux-cored wires (FCWs) containing multiple alloying elements were developed, and the Fe-based hardfacing layers were developed by metal active-gas (MAG) welding process. The macro morphology, microstructure, and phase composition of the alloys were characterized by using OM, SEM, XRD, and EDS methods, while the wear resistance performance was measured by using an abrasion tester. The results showed that the hardfacing layer prepared by Fe-Cr-C FCW is hypoeutectic that mainly consisted of austenite matrix and (Fe,Cr)7C3-type carbides. On this basis, a higher C content in combination with Nb, Ti, and B additives resulted in the microstructure comprised of martensite-based matrix and the precipitations of (Nb,Ti)C and Fe2B hard phases. With the removal of Cr, the further addition of Nb, Ti, and B, the hard phases change from particles to bulk and lath shapes. The hard phases with higher microhardness values than the matrix contributed to an improved Rockwell hardness and a highly decreased wear weight loss of hardfacing layer. Accordingly, the wear mechanism changed from severe plastic fracture to micro-cutting going with a slight brittle micro-peeling. The interlaced distribution of (Nb,Ti)C and Fe2B provided a stable skeleton that enables an further enhanced abrasive wear resistance.