Hot Rolling Mill And Cold Rolling Mill

The hot rolling process, like the rebirth of steel, heats the billet to a recrystallization temperature (usually above 1100 ° C), at which point the atoms inside the metal gain enough kinetic energy to make the lattice structure soft and plastic. Under the strong pressure of the four-high reversing mill, the red-hot billet stretches and deforms like dough, and the rolling force can reach tens of thousands of cows. This high temperature environment allows the metal to maintain dynamic recrystallization capacity, and the work hardening generated by each rolling process can be immediately eliminated.
The cold rolling process is the frost quenching of metal, and the hot rolled coil is rolled at room temperature after pickling. The metal atoms are frozen in a fixed lattice, and the rolling process causes dislocation proliferation and grain elongation. The precision roll system of the six-high UC mill applies rolling pressure up to 2000MPa, so that the strip thickness accuracy is controlled within ±1μm. The work hardening effect continues to accumulate, forcing the yield strength of the material to increase by 30%-50%.
The temperature difference creates a very different microscopic world: the equiaaxial grain diameter of hot-rolled steel is about 50μm, and the fibrous grain of cold-rolled steel is only 10μm. This difference in microstructure directly leads to the differentiation of mechanical properties, and the elongation of hot-rolled products can reach 25%, while the hardness of cold-rolled materials can be increased to more than HV200.