Bright Flat Bar Manufacturer Analyzes the Difference Between Hot-Rolling and Cold-Rolling Processes

Hot Rolling

Using billets or hot-rolled slabs as raw materials, they are heated in a step-down furnace, descaled with high-pressure water, and then fed into the roughing mill. The roughing material is trimmed at both ends before entering the finishing mill, where computer-controlled rolling takes place. After finishing rolling, the steel is cooled in a laminar flow cooler (computer-controlled cooling rate) and then coiled into a direct strip. The ends of the direct strip often have a tongue-like or fish-tail shape, with poor thickness and width accuracy, and are prone to defects like wave, edge crimp, and tower shape. These strips are heavier and have a steel coil inner diameter of 760mm. (Preferred in the general tube-making industry.) After trimming the ends, edges, and undergoing multiple straightening and leveling processes on a finishing line, the strips are then cut or re-rolled to become hot-rolled steel plates, level hot-rolled steel coils, and longitudinal strips, among other products. If the hot-rolled finished coils are pickled to remove scale and oiled, they become hot-rolled pickled steel coils.

2. Cold Rolling

Using hot-rolled steel coils as raw material, after acid pickling to remove scale, they undergo cold rolling in a continuous process. The finished product is a cold-rolled hard strip. Due to cold working hardening caused by continuous cold deformation, the strength and hardness of the cold-rolled hard strip increase, while the toughness and plasticity indices decrease, leading to deterioration in stamping properties, suitable only for parts requiring simple deformation. Cold-rolled hard strips can be used as raw material for galvanized steel plants, as all hot-dip galvanizing lines are equipped with annealing lines. The weight of cold-rolled hard strips is generally between 6 to 13.5 tons, with a steel coil inner diameter of 610mm. Cold-rolled plates and coils should typically undergo continuous annealing (CAPL unit) or be heat-treated in a hood furnace to eliminate cold working hardening and rolling stresses, achieving the mechanical property indicators specified by standards. The surface quality, appearance, and dimensional accuracy of cold-rolled steel plates are superior to those of hot-rolled plates.