Characterization of the substructure of retained austenite by X-ray diffraction

The determination of the amount of retained austenite in heat treated steel structures is important in the analysis and control of as-manufactured components as well as in the analysis of structures subjected to testing and service. X-ray diffraction is often used to accurately measure the amount of retained austenite in martensite/austenite structures, but other x-ray diffraction techniques can also be used to characterize the substructure of both the retained austenite and martensite phases as well. In particular, the diffracting particle size of the martensite and austenite can be determined by the line broadening of the appropriate diffraction peaks. This parameter, which is related to the thermal/mechanical history of both austenite and martensite can be used to characterize the phases with respect to thermal and service history, carbon content, and fraction of transformation to martensite. All of these factors influence the diffracting particle size of the retained austenite as well as the martensite phase in steels. This present work was directed at measurement of the diffracting particle size of the retained austenite in case carburized steels and the interpretation of those measurements.