New Aspects Regarding the Structure of Spheroidal Cast Iron Carbon Inclusions Revealed by WAXD Investigations

Abstract

The paper addresses mainly the atomic structure of the spheroidal carbon inclusions (CIs) from a magnesium treated cast iron. The qualitative phase analysis based on diffraction patterns shows that the CI by-products contain carbon, ferrite and iron oxides. Based on peak angular positions and their half-width at half-intensity, the distances between graphenes and the average height of the graphene stack were calculated. To comply with EN 13005 standard, the calculated results include the extended uncertainties U(95%). The Wide Angle X-ray Diffraction (WAXD) data proves clearly that the CI from the spheroidal cast iron do not have a polycrystalline graphite structure, but rather a turbostratic graphite-like structure with the d(002) surprisingly close to the graphite structure, e.g. to 3.34 Å. If this conclusion is accepted, a new approach of the nucleation and growth mechanisms of the CIs in spheroidal cast irons as turbostratic graphite-like structures should be explored, while the mechanisms based on crystallographic considerations should be revised.