Structural characterization of low-carbon multiphase steels merging advanced research methods with light optical microscopy

The paper presents new approach to characterizing low-carbon multiphase steels structure by means of concurrent application of optical and scanning electron microscopy with the emphasis on the latter one. Limitations of optical microscopy in material structure analysis, and the possibilities of information interchange between both methods have been discussed. The microstructure characterization is mostly based on the results obtained by means of scanning electron microscopy with wide application of EBSD method. As part of the work, fundamental constituents of multiphase steels structure with particular focus on consideration of the possibility of influencing their morphological features during thermal treatment have been systematized and described. Referring to the sheets of TRIP 700 and DP 600 steel, a capability of combining the FEG SEM analysis with EBSD method to characterize their structure was presented. EBSD method enables not only distinction of phases of various crystalline structure. Owing to analysis of parameters such as IQ, FIT, CI, KAM and misorientation angle, it is possible to differentiate constituents having different crystal structure. The method of IQ distribution curve deconvolution allows estimation of the fraction of structure constituents representing the same crystal structure. Existence of characteristic ranges of misorientation angles for selected structure constituents was proven.