Avaliação da eficácia da técnica de difração de raios-X para caracterizar fases presentes em dois ferros fundidos cinzentos perlíticos com diferentes adições de nióbio

Abstract

The present work aims to present a brief state of the art regarding the characterization techniques currently used to evaluate the effects of manufacturing processes on the structure of gray cast iron, as well as to evaluate the effectiveness of the X-ray diffraction technique ( XRD) to identify and quantify the phases present in two types of gray cast irons: one with low (0.02% by weight) and the other with a high content of niobium (0.21-0.24% by weight). For both samples, the three main phases were identified: graphite-G, ferrite-Fe (α) and cementite-Fe3C. However, not even for the sample with the highest niobium content, niobium carbide (NbC) was identified by this technique, a fact justified by the detection limit of the conventional diffractometer used and the small fraction of this carbide in the analyzed samples. The change in the concentration of niobium was not sufficient to promote significant differences in the diffractograms. The fluorescence of iron excited mainly by Cu Kα radiation resulted in a high level of noise in the measurements and made it impossible to quantify the phases by means of Rietveld refinement. Thus, for the analyzed niobium contents, it is concluded that the XRD technique with Cu tube is not effective for the quantification of phase fractions or for the identification of NbC in gray cast iron.