Cold-rolled strip steel

SMG GROUP’s technical personnel master a complete set of mature cold-rolling technologies, enabling them to independently design small and medium-sized cold-rolling production lines and ensure that the rolling mills maintain high performance over the long term.

Cold rolling typically employs longitudinal rolling. The typical process flow includes raw material preparation, pickling, rolling, degreasing, annealing (heat treatment), and finishing. Cold rolling uses hot-rolled products as raw materials; prior to cold rolling, the material must undergo dephosphorization to ensure a clean surface for the final product. Rolling is the primary operation that causes plastic deformation. Degreasing aims to remove lubricating oils and greases adhering to the rolled strip during processing, preventing contamination of the steel surface during annealing—especially in stainless steel, where it also helps avoid carbon pickup. Annealing comprises intermediate annealing and final heat treatment. Intermediate annealing eliminates work hardening caused by cold deformation through recrystallization, restoring ductility and reducing the metal’s resistance to deformation. Final heat treatment not only relieves hardening via recrystallization but also tailors the microstructure (such as various textures) and desired properties (e.g., deep-drawing characteristics, electromagnetic performance) according to product specifications. Finishing operations include inspection, shearing, straightening (flattening), marking, sorting, and packaging. Cold-rolled products have stringent packaging requirements to prevent surface scratches during transportation.

Since cold-rolled sheet is produced from hot-rolled sheet through the cold-rolling process, and because cold rolling often includes additional surface finishing steps, cold-rolled sheet generally exhibits superior surface quality—such as lower surface roughness—compared to hot-rolled sheet. Therefore, when high-quality coating or painting is required for downstream applications, cold-rolled sheet is usually preferred. Hot-rolled sheet, in turn, is divided into pickled and un-pickled grades: pickled sheet displays a natural metallic color due to acid treatment, yet its surface still falls short of the smooth finish achieved by cold rolling; un-pickled sheet typically bears an oxide layer that appears darkened or even develops a black iron oxide scale—commonly described as having been “fire‑treated.” Moreover, if stored under unfavorable conditions, such sheets may develop some rust.