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 sheet and hot rolled sheet are :
(1) higher accuracy, thickness difference of cold rolled strip 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) Superior surface quality, 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 properties such as tensile strength and process properties such as stamping properties.
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. Hot rolled sheet has low hardness, easy processing and good ductility. Cold rolled sheet hardness is high, processing is relatively difficult, but not easy to deformation, high strength. Hot rolled plate strength is relatively low, surface quality almost (oxidation, low finish), but good plasticity, generally medium thick plate, cold rolled plate: high strength, high hardness, high surface finish, generally thin plate, can be used as a stamping plate. Hot rolled steel plate, mechanical properties are far inferior to cold processing, also inferior to forging processing, but has better toughness and ductility. Cold rolled steel plate due to a certain degree of work hardening, low toughness, but can achieve a good flexural ratio, used for cold bending spring pieces and other parts, at the same time because the yield point is closer to the tensile strength, so the use of danger is not predictive, when the load exceeds the allowable load is prone to accidents. By definition, steel ingot or billet is difficult to deform and process at room temperature. It is generally heated to 1100 ~ 1250℃ for rolling. This rolling process is called hot rolling. Most steel is rolled by hot rolling. However, because the surface of steel is easy to generate oxide sheet at high temperature, the surface of hot rolled steel is rough and the size fluctuates greatly, so the steel with smooth surface, accurate size and good mechanical properties is required, and the hot rolled semi-finished products or finished products are used as raw materials and then produced by cold rolling method. Rolling at room temperature is generally understood as cold rolling. From the point of view of metal science, the boundary between cold rolling and hot rolling should be distinguished by recrystallization temperature. That is, the rolling below the recrystallization temperature is cold rolling, and the rolling above the recrystallization temperature is hot rolling. The recrystallization temperature of steel is 450 ~ 600℃. Hot rolling, as the name implies, rolling parts of high temperature, so the deformation resistance is small, can achieve large deformation. Taking steel plate rolling as an example, the thickness of continuous casting billet is about 230mm, and after rough rolling and finishing rolling, the final thickness is 1~20mm. At the same time, because the thickness ratio of the steel plate is small, the dimensional accuracy is relatively low, it is not easy to appear the shape problem, mainly to control the crown. The microstructure and mechanical properties of strip steel can be controlled by controlling rolling temperature, rolling temperature and crimping temperature. Cold rolling, generally there is no heating process before rolling. However, because the strip thickness is small, it is easy to appear the shape problem. Moreover, after cold rolling is finished product, therefore, in order to control the dimensional accuracy and surface quality of strip steel, a lot of very tedious process is used. Cold rolling production line is long, more equipment, complex process. With the improvement of users’ requirements on dimension accuracy, shape and surface quality of strip steel, there are more control models, L1 and L2 systems and shape control methods in cold rolling mill than in hot rolling mill. Moreover, the temperature of roller and strip is also an important control index. Cold rolled products and hot rolled product sheet line, is the difference between the previous process and the next process, hot rolled products are the raw materials of cold rolled products, cold rolled after pickling hot rolled steel coil machine using roller mill, rolling, are cold processing molding, mainly rolling thick hot rolled plate into thin specifications of cold rolled plate, Usually such as 3.0mm hot rolled plate on the machine rolling can produce 0.3-0.7mm cold rolled coil, the main principle is to use the principle of extrusion forced deformation.
Post time: Oct-09-2021