Liquid Phases Tailored for Introducing Oxidation-Sensitive Elements through the Master Alloy Route

Abstract

Introducing alloying elements through Master Alloy (MA) additions provides the unique opportunity of designing their composition to enhance sintering by forming a liquid phase. However, working with liquid phases poses important challenges like maintaining a proper dimensional control and minimizing the effect of secondary porosity on the final performance of the steel. The critical parameters for designing low melting point compositions are analyzed in this work by combining the use of thermodynamic software tools, wetting angle/infiltration experiments, and advanced thermal analysis techniques. Due to their low ability to dissolve iron, Cu-based liquids present remarkable infiltration properties that provide homogeneous distribution of the alloying elements. Dissolutive liquids, on the other hand, tend to render more heterogeneous microstructures, rapidly solidifying in contact with the matrix. As a consequence of their lower infiltration capacity, dimensional changes upon liquid formation are significantly lowered. When using master alloys with high content in oxidation-sensitive alloying elements, the differences in oxygen affinity cause an oxygen transfer from the surface of the iron base particles to the surface of the master alloys. The change in the surface chemistry modifies the wetting capability of the liquid, and the dimensional stability becomes increasingly sensitive to the processing atmosphere.