Correlation between microstructural and SIMS analyses of cast irons inoculated with CG alloy

Abstract

A microstructural and SIMS (secondary ion mass spectrometry) characterization has been performed on cast iron castings, inoculated with the CG alloy and with different titanium and calcium contents. The influence of the above elements on the graphite morphology has been studied. Regarding titanium, its effect results to be the combination of two concomitant mechanisms: the reaction with oxygen and sulphur, and the subsequent reduction of their amount in the matrix; and the reaction with carbon to form carbides, which act as inoculating of the austenite during the solidification. Titanium content has to be optimized in order to avoid the formation of undesirable forms of graphite and the excessive precipitation of carbides (or carbonitrides), which induce brittleness in the material. The main effect of calcium, besides the well known inoculating action for graphite, is to reduce the oxygen and sulphur amounts in the solidifying liquid.

The microanalytical characterization has been performed by SIMS, which appears to be very helpful in studying the segregations in the metallic materials and in particular in the cast irons, where the chemical segregations have a strong influence even on the technological properties.