The distribution of cracks on the surface of SS400 steel plate is basically the same as that of cracks on the surface of continuous casting slabs, especially the distribution of longitudinal cracks. The cracks on the surface of continuous casting slabs are all generated when molten steel solidifies in the continuous casting mold. After the secondary cooling zone, the previously formed cracks will be extended and extended again.
During the heating process of SS400 steel plate, oxidation and decarburization are carried out at the same time. If there are surface cracks in the continuous casting slab during heating, it is easy to produce oxides and decarburization around the cracks. If the crack is generated when the SS400 steel plate is rolled, the crack can only be slightly oxidized, and it is impossible to produce decarburization and oxide inclusions.
From the perspective of the macroscopic appearance of the crack, the crack shape is mainly distributed in the longitudinal direction, but there are also some small transverse cracks. It can be seen that it is not caused by rolling. When scratch cracks are generated during rolling, the cracks are usually distributed along the rolling direction. The directionality is very obvious, and the existence of cracks in the transverse direction can further explain that the cracks are caused by the slab. According to metallographic examination and energy spectrum analysis, decarburization and oxidation have occurred near the surface and on both sides of the crack in SS400 steel plate. The slab was oxidized and decarburized during the heating process, and the cracks at the edge of the SS400 steel plate originated from the cracks at the edge or corner of the continuous casting slab.
The cracks were not welded during the subsequent rolling process of the continuous casting slab, and further expanded along the rolling direction of the SS400 steel plate to form longitudinal cracks. The presence of decarburization layers and oxide inclusions around the cracks further aggravated the rolling process. Therefore, some small transverse cracks appear on the surface of SS400 steel plate.
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