The concept of cold rolling and hot rolling

1. Hot rolling
Using continuous casting slabs or blooming slabs as raw materials, heating them in a walking furnace, removing phosphorus with high-pressure water, and then entering the rough rolling mill. After the final rolling, it goes through laminar cooling (computer-controlled cooling rate) and coiling by a coiler to become a straight curl. The head and tail of the straight hair curler are often tongue-shaped and fish-tail-shaped, with poor thickness and width accuracy, and the edges often have defects such as wave shape, folded edge, and tower shape. The coil weight is heavier, and the inner diameter of the steel coil is 760mm. (Generally used in the pipe making industry.) After the straight hair roll is processed by cutting head, tail cutting, edge trimming and multi-pass straightening, leveling and other finishing lines, then cutting or re-rolling, it becomes: hot rolling Steel plates, flat hot rolled steel coils, slitting strips and other products. If the hot-rolled finishing coil is pickled to remove the oxide scale and oiled, it becomes a hot-rolled acid-washed coil.

2. Cold rolling
Using hot-rolled steel coil as raw material, after pickling to remove oxide scale, cold continuous rolling is carried out, and the finished product is rolled hard coil. The cold work hardening caused by continuous cold deformation increases the strength, hardness and toughness and plastic index of rolled hard coil. , the stamping performance deteriorates, and it can only be used for parts with simple deformation. Hard-rolled coils can be used as raw materials for hot-dip galvanizing plants, because hot-dip galvanizing units are equipped with annealing lines. The weight of the rolled hard coil is generally 6~13.5 tons, and the inner diameter of the steel coil is 610mm. Generally, cold continuous rolled sheets and coils should be de-annealed by continuous annealing (CAPL unit) or bell furnace to eliminate cold work hardening and rolling stress and achieve the mechanical properties specified in the standard. The surface quality, appearance and dimensional accuracy of cold-rolled steel sheets are better than those of hot-rolled steel sheets.

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Process of hot rolled steel

Advantages and disadvantages of hot rolled steel