Hot-rolled coils are produced using slabs (primarily continuously cast slabs) as raw material; after being heated in a reheating furnace (or homogenized in a soaking pit), the material is rolled into steel strip by a roughing mill train and a finishing mill train. As the hot steel strip exits the final stand of the finishing mill, it undergoes laminar cooling to a predetermined temperature before being coiled into a hot-rolled coil by a downcoiler.
Currently, there are two primary types of hot-rolled "endless rolling" technologies. The first involves conventional hot continuous rolling lines, where the intermediate slabs-having just passed through the roughing mill-are rapidly joined together between the roughing and finishing stages to achieve endless rolling during the finishing process. The second type enables the direct rolling of continuously cast slabs; this encompasses the ESP (Endless Strip Production) continuous casting and rolling process, as well as thin-strip casting and rolling technologies. Compared to traditional thin-slab continuous casting and rolling processes, the ESP endless strip production line significantly reduces energy and water consumption; depending on the final product specifications, energy consumption can be reduced by 50% to 70%, while water consumption can be cut by 60% to 80%.
Thin-strip casting and rolling technology represents a frontier technology in the fields of metallurgy and materials research in the 21st century. It integrates processes such as continuous casting, rolling, and even heat treatment into a single unified operation, thereby eliminating the reheating step typically required between the continuous casting and hot rolling stages. The Castrip process, for instance, utilizes two counter-rotating casting rolls; molten steel poured between the rolls solidifies against their surfaces, forming two separate solid shells which are then pressed together by the rolls to form a continuously solidified steel strip. Compared to traditional processes, the Castrip method achieves energy savings of 80% to 90% while simultaneously reducing greenhouse gas emissions by 70% to 80%.