Controlled rolling is a rolling process which is carried out in the austenite phase zone or in the austenite and ferrite two-phase zone under the condition of purposefully controlling the process parameters, and then air cooling or controlling the cooling rate to get the ideal structure.

Controlled cooling is to control the cooling rate of rolled steel to improve the structure and properties of steel. Due to the effect of hot rolling deformation, the transformation temperature of deformed austenite to ferrite is increased, and the ferrite particles are easy to grow after the phase transformation, resulting in the mechanical properties are reduced. In order to refine the ferrite particles, reduce the perlite lamellae spacing, prevent carbide precipitation at high temperature, and improve the precipitation strengthening effect, controlled cooling technology is used.

The final rolling temperature determines the internal microstructure and mechanical properties of rolled steel to a large extent. In order to obtain fine and uniform ferrite particles, the final rolling temperature should be slightly higher than the Ar3 phase transition point, and the steel particles are single-phase austenitic particles with uniform structure, and the strip steel has good mechanical properties after rolling. If the final rolling temperature is below the Ar3 phase transition point, not only the rolling metal in the two-phase zone is not plastic, but also the banded structure will be produced, coupled with the annealing effect after coiling, the result will be uneven mixed particle structure, which will have a certain impact on mechanical properties: the final rolling temperature is too high, will lead to excessive growth of austenite grains after rolling, reducing the mechanical properties of steel. At the same time, a large amount of secondary oxide sheet will be produced, which will affect the surface quality of the steel strip, so controlling the final rolling temperature is the key.

From the hot strip rolling, from the slab out to the end of the strip rolling, there are two major links in the middle: transportation and rolling. The final rolling temperature of the strip depends on the heating temperature, the thickness of the slab, the transportation time and the pressing system, the speed system, as well as the number and temperature of the cooling water and a series of factors, among which the slab thickness, the transportation time and the pressing system. Under the condition that the specification of raw material and finished strip is determined, it is some stable factors, and the heating temperature, the amount of cooling water between the rack and the speed system can be used as a means to control the final rolling temperature. In the actual production process, the heating temperature is used to control the final rolling temperature. For some specifications of products, there are heating defects such as increased heat consumption, reduced heating furnace capacity, overheating, overburning, etc. The speed system is limited by the equipment capacity and other factors, so the full use of inter-rack cooling water to strengthen the control ability of the final rolling temperature is the best means of control. According to the temperature control situation in the production process of our factory steel, there is a phenomenon of low final rolling temperature. We adjust the heating temperature and improve the acceleration and the speed of threading, but the effect of final rolling temperature control is not good. At present, we are starting to experiment to control the cooling water between the racks to ensure the control of final rolling temperature.