2020 Volume 19 Issue 4 Pages 327-331
Galvannealed iron-zinc Alloy sheet is one of the main steel products for automotive. In surface inspection of GA steel strip by camera system with image processing, detection of low contrast defects due to metal oxide inclusions that are beneath the surface layer is an important issue. In case a highly sensitive inspection, slight oil adhesion causes error detection, because both the defect portion and the oil portion have comparable reflective intensities in a normal optical system. However, originally, the reflectance of oil is sufficiently smaller than that of GA, and the reason is unknown that the reflective intensity of oil portion is so high as to obstruct inspection. In this report, we analyzed the microstructure of the oil portion and its reflective characteristics, and clarified the reason why it becomes an obstacle to the inspection with comparable contrast to that of defects.
