According to metallurgy textbooks, pressure processing at a processing temperature lower than the "recrystallization temperature" of the steel type under specific deformation conditions is called "cold working." The physical term "recrystallization temperature" is related to the growth form of the inner crystal of the metal during annealing, and will not be explained in detail here. The recrystallization temperature of copper and aluminum is about 200°C, the recrystallization temperature of pure iron is as high as 450°C, and the recrystallization temperature of ordinary "steel " is even higher than 450°C because it contains carbon or other alloying elements or other impurities. ℃ is higher. Therefore, the "recrystallization temperature" limit of the cold rolling process must be slightly higher than 450°C. In 2009, Wuhan University of Science and Technology published an article on studying the recrystallization temperature of cold-rolled sheets through annealing process tests, which verified this temperature limit. The conclusion drawn from the experimental numbers is that the starting temperature of recrystallization is approximately 450°C. As the temperature increases, the hardness of the steel plate drops sharply; when the recrystallization end temperature is 650°C, the hardness reaches the lowest value; after exceeding 650°C, the hardness of the steel plate does not change much; the recrystallization temperature of the experimental steel type is determined according to the "50% platform difference method" About 550℃.
In actual industrial practice, cold rolling is called "a normal temperature rolling process in which the billet is not reheated in advance." However, although the hot-rolled steel coil with a thickness of 1.5mm needs to be cold-rolled into a cold -rolled steel coil with a thickness of 0.25mm to 1mm (the thickness is reduced to 1/6 to 1/1.5 of the original), it seems that the deformation is far less than that of the hot-rolled steel coil. (from a 230mm thick steel billet to a 1.5mm thick steel plate, the thickness is reduced to 1/154 of the original), but rolling deformation in this "cold" state is very difficult.
The cold rolling process itself has many difficulties. It not only requires the subsequent construction of a cold rolling mill with huge rolling power, but also requires the adoption of many special auxiliary process technologies in the early hot rolling process. For example, the amount of deformation in each pass of cold rolling is not large, and it is closely related to the "alloying composition and grain size" of the steel formed in the previous hot rolling process. If the final rolling temperature during hot rolling The higher it is (for example, above 840°C), the lower the deformation strengthening coefficient, the more uniform the grains, and the greater the deformation amount in each pass during cold rolling, which is commonly known as "better rolling".
As the last process of steel production, the cold-rolled sheet production line has become an important basis for measuring the strength of steel companies because of its advanced technology and technology, highest product positioning and broad market prospects. Therefore, after the 1980s, all domestic state-owned or private steel companies have spared no effort to develop cold-rolled steel plates (strips) after having hot-rolled steel plates (strips). Cold-rolled plate and strip steel products are extremely extensive, and representative products include metal -coated plates (tin-plated plates, galvanized plates, etc.), deep-drawn steel plates (automobile plates), electrical steel plates, and stainless steel plates, etc.
