In the hot-rolling process, steel was subjected to high temperatures which results in the formation of an oxide layer called scale. The oxide scale can be affected to the surface characteristic of the hot-rolled steel product. The scale must be completely removed from the surface of the steel before further processing. This research aimed to examine the adhesion behavior of scale on hot-rolled steel with different silicon contents (0.01, 0.12, 0.18, and 0.29 wt%) using a tensile testing machine with an observation setup. The results showed that the scale thickness decreased with increasing silicon content in the range of 9 µm to 12 µm. The scales were composed of hematite and magnetite. The results of the tensile test showed that the strain initiating the first spallation and the mechanical adhesion energy tend to increase with increasing silicon content. However, it decreased by 0.29 wt% Si hot-rolled steel. This result indicates that scale was difficult to remove after the hot rolling process for higher Si-containing steel.

This article addresses applying a tensile test with a CCD camera to assess scale adhesion on hot-rolled steel as a function of hot-rolled coil position. The scale adhesion in this study was shown in the value of the strain initiating the first scale spallation. The result of strain initiating the first scale spallation was confirmed with an acoustic emission (AE) method. The as-received hot-rolled coil was studied at the head, middle, and tail positions. A scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to examine the scale morphology and phase identification respectively. The results show that the oxide scale comprises hematite and magnetite layers. It was found that the higher strain initiating the first scale spallation was revealed on the scale formed on the hot-rolled coil at the head and middle positions. This indicates that the oxide scale was more difficult to remove than at the tail position of the coil. The scale growth and cooling affects the stresses on the oxide layer and the steel substrate. A thin oxide layer on tail position of the hot-rolled coil will easily first crack and then buckle and followed by spallation, while a thick scale on head and middle positions of the hot-rolled coil was harder than that thin scale.