The Application of Quantitative X-Ray Diffraction (Rietveld Refinement) in Characterizing the Microstructure and Precipitates in Microalloyed Steels

Quantitative X-ray diffraction (the Rietveld Method) was used to quantify both the crystallite size (diffracting length) and precipitate size in several grades of microalloyed steels. The crystallite size calculated from diffraction profiles obtained from the rolling faces of X80 and X100 was found to decrease with decreasing coiling temperature. Quantitative X-ray diffraction analysis was also conducted on precipitate residues extracted (by matrix dissolution) from a Grade 100 microalloyed steel. A mean precipitate size of 4.8 nm was calculated for the fine (Nb, Mo, Ti, V) carbides observed in this steel. This value compares favourably with precipitate size measured using TEM and SANS analysis.