Accurate Online Measurement of Iron Concentration in Galvannealed Coating Layers by Shift of X-ray Diffraction Peak

The authors have developed a new online measurement system for the Fe concentration in galvannealed (GA) coatings based on the proportionality between the peak angle of X-rays diffracted by the delta(1) phase and the Fe concentration. The online system was realized by high-speed measurement of the peak angle of diffracted X-rays using a one-dimensional detector in conjunction with correction algorithm for the angular error caused by the displacement of the GA steel strip surface from the measurement position. The performance of the developed online system was demonstrated in a continuous galvanizing line with GA strips of Si-added and Si-free base steels. The developed system showed higher accuracy even with the Si-added base steel, with which enough accuracy could not be obtained with conventional online systems based on the diffraction intensity of the Gamma phase. Since the delta(1) phase is the major phase of GA coatings, the main advantage of the developed system is that its accuracy is less sensitive to the composition of the base steel.