Hot rolled coils are produced by heating large metal workpieces like slabs, blooms, or billets to high temperatures in soaking pits or via induction heating. The heated metal is then passed through rolling mills to reduce the thickness. Approximately 96% of steel is continuously cast and hot rolled in an integrated process to reduce energy usage. Hot rolling is followed by controlled cooling to prevent residual stresses from uneven shrinkage. Mill scale, an oxide layer formed on the surface during high temperature exposure, is removed via pickling in hydrochloric acid. Common grades and finishes of hot rolled coils are also defined.