Cold rolling and hot rolling are two different rolling technologies. Cold rolling is to tie steel at room temperature. This kind of steel has high hardness. Hot rolling is roll steel at high temperatures.

Hot rolling: Continuous casting slab or blooming slab is used as raw material, heated by stepping furnace, descaling by high pressure water and entering rough rolling mill. Rough rolling material is cut and tailed, and then entered into finishing mill. Computer controlled rolling is carried out. After finishing rolling, laminar flow cooling and coiler coiling are carried out to form delivery coil. The head and tail of straight delivery coils are usually tongue-like and fish-tail-like, and the accuracy of thickness and width is poor. The edges of delivery coils are often corrugated, folded and tower-shaped. The coil weight is heavy and the inner diameter of the coil is 760 mm which pipe industry likes to use generally. After the delivery coil is treated by cutting head, tail, edge cutting, multi-pass straightening and leveling, and then cut or rewinding, it becomes hot rolled steel plate, flat hot rolled steel coil, longitudinal cut strip and other products. Hot-rolled finish coil will be hot-rolled pickled coil if the oxide scale is removed by pickling and oiled. The product has the tendency of partial substitution for cold rolled sheet, and the price is moderate, which is popular with the majority of users.

Cold rolling: The hot rolled coil is used as raw material, and the oxide scale is removed by pickling. The product is rolled coil. The cold work hardening caused by continuous cold deformation makes the strength, hardness and toughness and plasticity of the rolled coil increase, so the stamping performance will deteriorate and can only be used for parts with simple deformation. Rolled coil can be used as raw material for hot galvanizing plant because annealing lines are set up in hot galvanizing units. The weight of rolled coil is generally no more than 15 tons, and the inner diameter of coil is no more than 700 mm. Generally, cold continuous rolling plate and coil should be annealed by continuous annealing or bell furnace annealing to eliminate cold work hardening and rolling stress, so as to achieve the mechanical properties specified in the corresponding standards.

The surface quality, appearance and dimension accuracy of cold rolled steel sheet are better than those of hot rolled steel sheet, and the thickness of cold rolled steel sheet is about 0.18mm, so it is favored by users. The cold rolled coil is used as the base plate for the deep processing of the products and becomes a high value-added product. Such as galvanizing, hot-dipping, fingerprint-resistant galvanizing, color-coated steel coil and vibration-absorbing composite steel plate, PVC clad steel plate.

There are two differences between hot rolling and cold rolling. Firstly, the surface of cold rolled sheet has a certain gloss. it feels smoother, similar to the very common steel cup used for drinking water. Secondly, hot-rolled sheets without pickling treatment are similar to the surface of many ordinary steel plates on the market. The rusted surface is red, and the non-rusted surface is purple-black.

The advantages of cold-rolled and Hot-rolled sheets are as follows:

(1) The accuracy is higher, and the thickness difference of cold rolled strip does not exceed 0.01-0.03 mm.

(2) The thinnest cold-rolled strip can be rolled 0.001 mm, hot-rolled strip can now reach 0.78 mm.

(3) Surface quality is better, cold-rolled steel plate can even produce mirror surface, while hot-rolled steel plate has defects such as oxide scale, pitting and so on.

(4) Cold-rolled sheet can adjust its mechanical performance such as tensile strength and technological performance such as stamping performance according to user's requirements.