A question about hot rolled coils
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Our company received a batch of hot-rolled coil Q235-B with a thickness of 3.75 mm, which is used to make spiral plate heat exchangers. When cutting, there were a large number of small pits on the outside of the plate, some with a depth of 0.1-0.2 mm, and a high density. Observe the outside of the rolled plate when it is not unfolded. The surface is smooth and flat. Some people say that the oxide layer is peeling off ； Some people say that it is because it is too heavy and is squeezed by the uneven ground when cutting materials. Explain: The floor is cement and has good flatness. I can't figure out why. Please explain it to me. Thank you in advance.
I don't understand what the tense "when unloading" means. Was the problem discovered when the rolled plate was unrolled or was it discovered after other processing? 1. The steel plate is relatively thin, and the surface quality of the rollers during the hot rolling process may cause damage to the steel plate. However, generally steel mills rarely allow products with obviously poor surface quality to leave the factory. What's more, the smooth and flat surface of the outside of the coil before unrolling indicates that it is not a product problem. 2. It is caused by squeezing the uneven ground when cutting. It depends on the weight of a roll of steel plate to judge whether the pressure on a narrow strip in contact with the ground will cause damage. 3. Considering the thickness tolerance of the steel plate (the surface quality is not evaluated), as long as the defects do not exceed 12.5% of the nominal thickness, it is within the acceptable range.