A phase quantification method based on EBSD data for a continuously cooled microalloyed steel

• Published in: Materials characterization 2017-01, Vol.123, p.339-348
• Main Authors: Zhao, H., Wynne, B.P., Palmiere, E.J.
• Format: Article
• Language: English
• Subjects: Acicular ferrite; ASPECT RATIO; BACKSCATTERING; Bainitic ferrite; COMPARATIVE EVALUATIONS; COOLING; Electron backscatter diffraction; ELECTRON DIFFRACTION; FERRITE; GRAIN BOUNDARIES; GRAIN SIZE; LOW ALLOY STEELS; MATERIALS SCIENCE; MECHANICAL PROPERTIES; Microalloyed steel; MORPHOLOGY; Phase quantification; SCANNING ELECTRON MICROSCOPY
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2016.11.024

Mechanical properties of steels depend on the phase constitutions of the final microstructures which can be related to the processing parameters. Therefore, accurate quantification of different phases is necessary to investigate the relationships between processing parameters, final microstructures and mechanical properties. Point counting on micrographs observed by optical or scanning electron microscopy is widely used as a phase quantification method, and different phases are discriminated according to their morphological characteristics. However, it is difficult to differentiate some of the phase constituents with similar morphology. Differently, for EBSD based phase quantification methods, besides morphological characteristics, other parameters derived from the orientation information can also be used for discrimination. In this research, a phase quantification method based on EBSD data in the unit of grains was proposed to identify and quantify the complex phase constitutions of a microalloyed steel subjected to accelerated coolings. Characteristics of polygonal ferrite/quasi-polygonal ferrite, acicular ferrite and bainitic ferrite on grain averaged misorientation angles, aspect ratios, high angle grain boundary fractions and grain sizes were analysed and used to develop the identification criteria for each phase. Comparing the results obtained by this EBSD based method and point counting, it was found that this EBSD based method can provide accurate and reliable phase quantification results for microstructures with relatively slow cooling rates. •A phase quantification method based on EBSD data in the unit of grains was proposed.•The critical grain area above which GAM angles are valid parameters was obtained.•Grain size and grain boundary misorientation were used to identify acicular ferrite.•High cooling rates deteriorate the accuracy of this EBSD based method.