Forged steel rolls undergo different heat treatments according to their materials and uses.
(1) Medium carbon steel (0.35%~0.65%C) rolls are generally used as hot rolling blooming rolls, rough rolling rolls, and backup rolls after normalizing and tempering or quenching and tempering. The tensile strength is 500-800MPa in the normalized and tempered state, 800-1100MPa in the quenched and tempered state, and the hardness is about 255-325HB. Ferrite is not wear-resistant, and the higher its content, the greater the degree of roll blocking during rolling. Therefore, the carbon content of the hot roll is not less than 0.45%. The content of alloying elements should be determined according to the diameter of the roll and the strength requirements, so as to ensure sufficient strength and toughness. The backup roll with a large diameter can also use differential temperature heat treatment (backup roll heat treatment), and the hardness of the roll body after treatment can reach HS80.
(2) High carbon steel (0.7%～1.0%C) rolls can be used as backup rolls after normalizing and tempering treatment or quenching and tempering treatment. When the hardness of the backup roll body is very high, it needs to be quenched and tempered. The hardness after quenching and tempering can reach 70~80HS, and the depth of the hardened layer is less than 50mm. Forged steel rolls quenched to high hardness are used as work rolls, intermediate rolls, temper rolls, and cold rolling rolls for non-ferrous metals (aluminum, copper, zinc) in strip cold rolling.
The roughing of the machined rolls is done on a roll lathe. In order to ensure dimensional accuracy, ultrasonic flaw detection is also carried out before the final heat treatment of CNC machine tools is widely used. Whether the center hole of the roll is processed or not depends on a series of factors such as rolling mill design, quenching requirements, and inspection results. After final heat treatment, the blank is finished into finished rolls of specified size, surface accuracy, and roughness. Finishing includes turning, drilling, milling, grinding, and other processes. The finished rolls are provided for use after a series of inspections such as hardness, size, structure, and performance.
