Effect of Mo on microstructure and wear resistance of slag-free self-shielded metal-cored welding overlay

A new type of slag-free self-shielded metal-cored wire with various Mo contents has been developed to fabricate an experimental hardfacing alloy. The developed metal-cored wire exhibits an average Mo transfer coefficient of 90%. All the hardfacing alloys have a hypereutectic microstructure consisting of primary M ₇ C ₃ carbide, and eutectic of M ₃ C carbide plus martensite and residual austenite. The primary carbide fraction is about 38 vol. % in the Mo-free hardfacing alloy; it increases to about 45 vol. % in the alloy when the Mo content increases to 1.35 wt. %. No significant increase in the primary carbide fraction has been observed when the Mo content in the hardfacing alloy is increased further. The wear resistance of Mo-containing hardfacing alloys is better than the Mo-free hardfacing alloy. However, the wear resistance does not increase significantly when the Mo content in the hardfacing alloy is increased beyond 1.35 wt. %. Thermodynamic driving force calculations provide an explanation for the observed primary carbide fraction change in the hardfacing alloys as a function of Mo levels, and the fraction of primary M ₇ C ₃ carbide seems to play a key role in deciding the wear performance of the hardfacing alloys.