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

This work aims to present a brief state of the art regarding the characterization techniques currently used to evaluate the effects of fabrication 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 iron: one with low (0.02% by weight) and the other with high niobium content (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 modification in the niobium concentration was not enough 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 and limitations of the instrumental conditions used in this work to minimize these iron fluorescence effects in the samples (but usual operating conditions of copper tube equipment in routine operation), it is concluded that the Cu tube XRD technique is not effective for quantifying phase fractions nor for identifying NbC in gray cast iron.