Interrelation between macroscopic, microscopic and chemical dilution in hardfacing alloys

A common way to extend service life of steel tools under heavy duty service conditions is the use of hardfacing coatings. Coating an economically feasible basematerial like carbon steelwith a hardfacing alloy by any processes based on welding, casting or cladding improves significantly its wear resistance. All these processes involve high heat inputs in order to partially melt the substrate material to create a sound bonding between the substrate and the wear resistant alloy. The intermixing and the elemental diffusion from the hardfacing material into the substrate and vice versa cause a change in microstructure, hardness and wear properties of the diluted alloy. It is not trivial to categorize the amount of dilution and its effects on material properties since composition and microstructure change discontinuously, especially in casting processes, due to different diffusion rates of elements and due to phase transitions. This paper presents a simplified model to correlate the amount of dilution in hardfacing alloys after a casting process considering several reference parameters. Three coefficients are derived to describe the degree of dilution based on crucible casting experiments and are numerically correlated by linear regressions. They specify distinct issues about macroscopic and microscopic dilution, aswell as changes in chemical composition. Themodel is then applied to a spin casting case studywhich can be taken as a reference example for industrial hardfacing processes where dilution effects are clearly observable.