Structural analysis of austempered ductile iron obtained by Mossbauer spectroscopy

Abstract

Purpose: The composition of metallic matrix in ductile iron as-cast and after austempering at temperatures of 280, 330 and 380oC (ADI) was examined. Design/methodology/approach: The study presents the results of these examinations obtained by Mössbauer spectroscopy. Findings: Using calculated values of the parameters of hyperfine interactions (isomeric shift IS, quadrupole splitting QS and hyperfine effective magnetic field H), isolated by deconvolution of the experimental spectrum, the constituents of the metallic matrix were identified in terms of both quantity and quality. Research limitations/implications: The measured values as well as the data compiled in literature indicate that component Z1 (the, so called, Zeeman spectrum sextet) is related with 57Fe atoms present in the structure of ferrite α1 (I stage of γo→α1 + st transformation), component Z2 is typical of ferrite α2 (II stage of st→α2 + carbides transformation), while component Z3 has its origin in 57Fe atoms seated in the structure of carbides (Fe3C, Fe2C or Fe2,4C). Practical implications: analysis of the parameters of hyperfine interactions describing the non-magnetic components (L and Q) it has been proved that they are typical of austenite. Originality/value: In the case of ADI, the determination of the composition of metallic matrix by Mössbauer spectroscopy is much more precise (the limit is the resolution power), because the experimental spectrum describes an overall volume of the examined specimen, and not only its surfaces, as does the traditional quantitative metallography.