Quantitative determination of retained austenite in the continuous annealing production line of cold-rolled steel

An X-ray diffraction method has been developed for quantitative determination of retained austenite in the continuous annealing production line, CAL, of cold rolled steel sheets. A new unit of diffractometer(Cr-Kα source with two proportional counters) was specially designed for the CAL. Intensities of {220} austenite reflection, Iγ, and background, IBG, are measured separately by the two detectors. From Iγ and IBG, real-time calculation of normalized intensity of austenite, IS, is executed by the following equation ; IS = (Iγ-IBG)/IBG. IS was little affected by the fluctuation of the distance between the diffractometer and travelling material. Normalized intensity is well correlated both with the tensile strength and with volume fraction of martensite, of high strength ''dual-phase'' steel sheets. From this findings, the presently developed X-ray diffractometer unit is proved to be successfully employable in the CAL as an effectual method for control of material properties in the high strength ''dual-phase'' steel sheet by monitoring the normalized intensity of austenite. (author)