Causes of Common Surface Defects in Cold-Rolled Strip Steel
Release Date:
2022-06-23
Author:
Hengyuan Industry and Trade
The types and causes of surface defects in cold‑rolled strip steel are highly complex; such defects can arise at every stage, from steelmaking and hot rolling through cold rolling to end‑user application. Consequently, controlling surface defects is of paramount importance. Next, Huoluo Steel Strip Co., Ltd., a leading manufacturer of cold‑rolled steel strip, will provide a brief analysis.
1. Hole
Cause: Material tearing leads to the formation of holes. During rolling, certain regions of the strip’s cross-section exhibit porosity, and the applied stress exceeds the material’s yield strength. This phenomenon becomes more pronounced as the strip thickness decreases. Additionally, due to inclusions, gas bubbles, shrinkage cavities, and other defects, localized cracking may occur during subsequent rolling stages as the strip thickness is reduced.
2. Crack
Causes: During rolling, the strip experiences uneven elongation; pre-existing surface defects are not completely removed; and non-metallic inclusions or subsurface bubbles remain on the strip. Additionally, improper roll adjustments or inadequate roll‑profile design during cold rolling can also lead to cracking, as can excessive tension or an unsuitable chemical composition.
3. Pit
Cause: Roll surface defects or foreign matter formed when material is entrapped and subsequently spalled from the strip surface, resulting in one edge of the thin strip being concave while the other is convex.
4. Roller imprint
Cause: Insufficient hardness of the roll surface allows hard contaminants, such as metal chips, to adhere easily. Alternatively, if the strip steel has high strength and is handled improperly, the roll surface may spall, resulting in roll marks. This defect is readily identifiable and can be promptly addressed.
5. Scratch
Cause: The mill guide plates are rough and uneven, or during the winding process, the strip steel rubs against foreign objects.
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