what is sponge? in rolled steel plates?

The surface looks like sponge in places on some of the steel plates that we are buying. These are about 80 inches wide and about 0.5- 0.7 inch thick plates. The grades are X60 and X80 type with Columbium and Vanadium for microalloying. Any ideas or references on this surface quality issue?

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"Spongy surface - A porous and cracked surface caused by oxidized subcutaneous blowholes." Definition from "surface Defects in Ingots and Their Products (Recommended Definitions),Special Report No. 63, The Iron and Steel Institute, London, 2nd edition, 1958
Subcutaneous is a fancy word for 'beneath the skin' and blowholes are holes caused by gas entrapped during solidification.
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It would be helpful to know the composition specificallly carbon, manganese aluminum, silicon, columbium, vanadium and copper
Jim M

This kind of problem was very common in semi-killed steels, but this kind of steel is no more produced, since practically all steel slabs are continuously cast nowadays. Perhaps this problem can be due to hot shorteness caused, for example, by the presence of a excessive residual Cu content.
All the best,
Antonio A. Gorni www.gorni.eng.br

Forgive my ignorance. What is residual Cu? Is it the copper content of the steel? or is it the residual after the dissolution limit?
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rolling process of manufacturing of the steel plates.
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