The difference between hot rolling and cold rolling?


The difference between hot rolling and cold rolling?

1. The surface of cold-rolled plate has a certain gloss and feels smooth, similar to the very common steel cup used for drinking water.

2. If the hot rolled plate is not pickled, it is similar to the surface of many ordinary steel plates on the market. The rusted surface is red, and the surface without rust is purple-black (iron oxide).

The performance advantages of cold rolled plate and hot rolled plate are:

1, higher accuracy, cold rolled strip thickness difference is not more than 0.01~0.03mm.

2, thinner size, the thinnest cold rolling can roll 0.001mm steel strip; Hot rolling now reaches a minimum thickness of 0.78mm.

3, the surface quality is superior, cold rolled steel plate can even produce mirror surface; The surface of hot - rolled plate has defects such as iron oxide and pitting.

4, cold rolled sheet can be adjusted according to user requirements of its running performance such as tensile strength and process performance such as stamping performance.

Cold rolling and hot rolling are two different steel rolling technology, as the name implies, cold rolling is to tie steel at room temperature, the hardness of this steel is large. Hot rolling is when steel is tied together at high temperature.

1. Hot rolled

The continuous casting slab or primary rolled slab is used as raw material, heated by stepping heating furnace, descaled by high pressure water and then entered the roughing mill. The roughing material enters the finishing mill after cutting head and tail, and then carried out computer controlled rolling. After the final rolling, it goes through laminar cooling (computer controlled cooling rate) and coiler to become straight hair coil. The head and tail of straight hair coil are often tongue and fishtail, and the accuracy of thickness and width is poor. The side part often has defects such as wave shape, folding edge and tower shape. The coil is heavy and the inner diameter of the steel coil is 760mm. (The general pipe industry likes to use.) After cutting head, cutting tail, cutting edge, straightening, leveling and other finishing line treatment, cutting plate or rewinding, it becomes: hot rolled steel plate, flat hot rolled steel coil, longitudinal cutting tape and other products. Hot rolled finish roll is hot rolled pickling plate roll after pickling removing the oxide scale and oiling. The product has a partial alternative to the trend of cold rolled sheet, moderate price, loved by the majority of users. 

2. The cold rolling

The hot rolled steel coil is used as raw material, after removing the oxide scale by pickling, the finished product is rolled hard coil. Due to the cold working hardening caused by continuous cold deformation, the strength and hardness of rolled hard coil increase, and the toughness and plastic index decrease, so the stamping performance will deteriorate, and can only be used for simple deformation parts. Hard roll can be used as raw material for hot-dip galvanizing plant, because hot-dip galvanizing unit is set with quenching line. The weight of rolled hard coil is generally 6~13.5 tons, and the inner diameter of steel coil is 610mm.

Generally, continuous annealing (CAPL unit) or cover furnace annealing should be used 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 dimensional accuracy of cold-rolled steel plate are better than that of hot-rolled steel plate, and the thickness of cold-rolled steel plate is about 0.18mm, so it is favored by the majority of users. Cold-rolled steel coil is used as base plate for deep processing of products, and it has become a high value-added product. Such as galvanized, hot dip galvanized, fingerprint galvanized, color coated steel coil and vibration absorption composite steel plate, PVC coated steel plate.

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