Effect of B Content on Microstructure and Wear Resistance of Fe-3Ti-4C Hardfacing Alloys Produced by Plasma-Transferred Arc Welding

Abstract

The Fe-3Ti-xB-4C (x = 1.71, 3.42, 5.10, 6.85 wt. %) hardfacing alloys are deposited on the surface of a low-carbon steel by plasma transferred arc (PTA) weld-surfacing process. Microstructure, hardness and wear resistance have been investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), Rockwell hardness tester and abrasive wear testing machine, respectively. The results show that the microstructure in all alloys is composed of austenite, martensite, Fe23(C,B)6, Ti(C,B) and Fe2B. The volume fraction of eutectic borides and Ti(C,B) carbides increases with increasing B content. Many brittle bulk Fe2B phase arises when the boron content increases to 6.85%, which causes the formation of microcracks in the hardfacing layer. The microhardness of the hardfacing alloys is significantly improved with the B addition, however, the wear resistance of hardfacing alloys increases firstly and then decreases with increasing of B content. The hardfacing alloy with the 5.10% B content has the best wear resistance, which is attributed to high volume fraction of eutectic borides and fine Ti(C,B) particles distributed in the austenite and lath martensite matrix with high hardness and toughness. The formation of brittle bulk Fe2B particles in the hardfacing alloy with the 6.85% B leads to the fracture and spalling of hard phases during wear, thus, reducing the wear resistance.