Development of a Non-Invasive Technique Based on Infra-red Thermography to Detect and Estimate Iron in Galvannealed Coatings

Abstract

When the galvannealing process is carried out in an optimum manner, the coating contains about 10-12% Fe. Higher Fe content (around 12%) in the coating leads to an unfavorable deformation behavior of the steel strip and increased powdering occurs during the later stage. To have a desired mechanical and chemical property, the iron content within the zinc iron alloy in galvannealed coating should be in the range of 9% to 12%. The basic problem associated with the determination of iron content in galvannealed coating is that- Iron is contained both in the coatings and substrate so it is very difficult to distinguish them because substrate chemistry affects the alloying reaction.  Non-uniform distribution of iron throughout the alloy coating. The Fe content depends on the Fe-Zn phases present in the galvannealed coatings. Through XRD, the different Fe-Zn phases can be identified but the exact amount of Fe present in the coatings cannot be determined. This project aimed to estimate the Fe content on the surface of galvannealed IF steel sheets by observing the surface temperature and temperature decay rate of the heated sheets through IR thermography. Further exploration and implementation of this technique in the steel plant will help in online estimation of Fe content in the Galvannealed sheets.