Development of nickel-added, iron-based, slag-free, self-shielded metal-cored wire

Previously, an iron-based, slag-free, self-shielded metal-cored wire showing a mechanism of porosity prevention was reported in the Welding Journal (Ref. 1). In this paper, a type of iron-based, slag-free, self-shielded metal-cored wire with various nickel contents was developed to fabricate experimental hardfacing alloys. The influence of nickel addition on the microstructure and wear performance was investigated. The results showed the hardfacing alloy with 0.13 wt-% nickel had a typical hypereutectic microstructure consisting of primary M ₇ (C, B) ₃ carbonitrides with a eutectic of long, bar-like M ₃ (C, B) carbonitrides and martensite. The addition of nickel promoted the formation of austenite dendrites as well as changed the morphology of the eutectic colonies. As the nickel content increased from 2.75 to 3.83 wt-%, and to 4.64 wt-%, the austenite was observed to develop from a scattered structure to a dendritic structure, and, finally, to a networked structure, respectively. The hardness of the hardfacing alloy was found to decrease from 64.2 HRC with 0.13 wt-% nickel to 58.2 HRC with 4.64 wt-% nickel. The morphology of the worn surfaces of the hardfacing alloys showed cracks in the hardfacing alloy with 0.13 wt-% nickel; a smooth texture for the hardfacing alloy with 2.75 wt-% nickel; and extensive plastic deformation and grooving as the nickel content was further increased. The optimum wear resistance and cracking resistance of the 2.75 wt-% nickel hardfacing alloy can be attributed to the presence of a higher fraction of martensite in the matrix, and an optimum amount of retained austenite needed to provide crack resistance.