GAめっき鋼板の合金化度分析法

抄録

One of the advantages of galvannealed (GA) steel sheet over electroplated one is that the thick coating is realized in lower cost. The increase of the alloying degree, the iron concentration in GA coating is favorable for coating adhesion and corrosion resistance after painting, whereas accelerates powdering in the press forming process. Therefore, it is important to control the alloying degree in the production of GA steel sheet.
The accuracy σ_d of the alloying degree analytical methcd applicable to on-line analysis is reported as 0.6 mass% using the analytical curve, i.e., the relationship between the alloying degree and the X-ray diffraction (XRD) intensity ratio of (633) plane of Γ alloy phase in the coating to the background. However, the accuracy is not good enough and little is known about the influence of GA steel sheet production condition, e.g., temperature and Al concentration in galvanizing bath, oxidizing degree and temperature of steel sheet before galvanizing and the galvanizing time on the alloying degree analysis. Moreover, few reports deal with the comparison of correlation between the alloying degree and several XRD intensity ratios.
We found out that the XRD intensity ratio most correlated was Γ(633)/ζ(160) and that the analytical curve using Γ(633)/ζ(160) intensity ratio shifted according to the production condition due to the change of the thickness ratio Γ/ζ. Therefore, we introduced the standard analytical curve that predicts the alloying degree from the corrected XRD intensity ratio; corrected according to the production condition. By using this curve and the corrected XRD intensity ratio Γ(633)/ζ(160) for the unknowns, the alloying degree was analyzed with the accuracy ad of 0.46 mass%.