Some aspects of the determination of retained austenite using the Rietveld refinement

Abstract

Purpose: The aim of the paper is to show the advantage of the application of the Rietveldrefinement for determination of retained austenite amount in multiphase microstructure steels.Design/methodology/approach: The steels used for the investigation were thermomechanicallyrolled and controlled cooled to room temperature. The investigation of themicrostructure was carried out using light microscopy. X-ray diffraction investigations ofanalyzed steel were a major part of the research. The phase identification and quantitativeanalysis of retained austenite were done using the HighScore Plus software that includesthe Rietveld refinement method. The Rietveld analysis takes into account the preferredorientation that occurs during thermo-mechanical processing of steel.Findings: It was found that after the thermo-mechanical processing the microstructureof steel is composed of fine-grained bainitic matrix which includes bainite-austeniteconstituents, martensite blocks and some fraction of retained austenite. The X-ray diffractionshowed that this steel includes phases of Feα (bainite and martensite) and Feγ (retainedaustenite). The Rietveld analysis showed that the volume fraction of retained austenite is14.1%.Research limitations/implications: To confirm that Rietveld refinement methodis a good tool for the quantitative analysis of retained austenite volume fraction EBSDmeasurements should be done for comparison purposes.Practical implications: The obtained results can be used for determination of retainedaustenite fraction in AHSS steels. It is important because the retained austenite content andits mechanical stability decide about a formability level of these steel grades.Originality/value: Some methodological aspects are concerned affecting the finalquantitative results of retained austenite volume fraction is AHSS.