ANALYSIS AND THERMODYNAMIC STABILITY OF NUCLEI IN SPHEROIDAL GRAPHITE IN Fe–C–Si ALLOYS

The paper describes the graphite nuclei constitution for spheroidal graphite cast iron melted in a cupola furnace, which is treated by the addition of magnesium and inoculated with a barium-based inoculant. Two samples of spheroidal cast iron were analysed, differing only in tin content. Field-emission scanning electron microscopy (FE -SEM) with energy-dispersive X-ray spectroscopy (EDS) was used to analyse the nuclei. The thermodynamic calculation of the phase equilibria and the associated free formation energies of the alloys were calculated and compared with metallographic observations. It was found that the nuclei in the spheroidal graphite are different in shape and composition. Spherical and rectangular ones were found, and in many cases the porosity was present at the nuclei. The nuclei consisted of different compounds such as (Mg,Ca)S, MgO, (Mg,Al,Si)N. The amount of Sn only affected the pearlite content, and there were no Ba and rare earths present in the nuclei.

Effect of Active Screen Plasma Nitriding on Mechanical Properties of Spheroidal Graphite Cast Iron

Spheroidal graphite cast iron is a material with a wide range of uses such as in automobile parts. By applying active screen plasma nitriding (ASPN) treatment, the use of spheroidal graphite cast iron is expanded, and it can be expected to be used under special load conditions. In this study, we evaluated the effect of ASPN treatment on the mechanical properties of spheroidal graphite cast iron. With ASPN treatment, a nitride layer was formed on the sample surface and a diffusion layer was formed further inside the nitride layer. The thickness of nitride layer increased as the treatment temperature increased. The hardness was improved by ASPN treatment. The abrasion resistance was improved by ASPN treatment, and longer treatment time resulted in higher abrasion resistance. The fatigue strength was improved by ASPN treatment, and longer treatment time resulted in higher fatigue strength. ASPN treatment also improved the corrosion resistance.