what is sponge? in rolled steel plates?

"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

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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