Rolls are mainly divided into cast iron rolls, cast steel rolls and forged steel rolls by material. The carbon content of cast iron rolls is about 2.50 / 0 ~ 3.5%. According to the main materials, it can be divided into four categories: chilled cast iron rolls, infinite chilled cast iron rolls, high chromium cast iron rolls and ductile iron rolls. The common structures in cast iron rolls can be divided into three categories: matrix, cementite, and graphite. The matrix structure mainly includes austenite, ferrite, pearlite, bainite, and martensite. The shape of graphite in cast iron generally Flaky and spherical.
Cast steel rolls can be divided into two categories: steel rolls (carbon content 0.4% ~ 114%) and semi-steel rolls (carbon content 1.4% ~ 2.40 / 0). Steel rolls have low carbon content and therefore low hardness. Its structure is generally composed of ferrite and pearlite. As the carbon content increases, the amount of ferrite decreases and the amount of pearlite increases. To increase the hardness, alloy elements such as chromium, nickel, manganese, molybdenum, and vanadium can be added, or special heat treatment can be performed. Because steel rolls have high tensile strength and toughness, they are suitable for use in open-rolling mills or preliminary rolling mills with high rolling temperatures and large rolling loads, and can also be used as backup rolls. If special heat treatment is performed, high hardness above HS90 can be obtained, and it can also be used as a cold rolling work roll.
The carbon content of the semi-steel roll is between the cast steel roll and the cast iron roll, and its hardness is higher than that of the general cast steel roll and lower than that of the cast iron roll. The main feature of semi-steel rolls is that the internal hardness drop is small, so it is especially suitable for manufacturing deep-hole rolls. If the silicon content is increased in the semi-steel roll material, through graphitization treatment, it has high thermal crack resistance and toughness. Vertical rolls can achieve good rolling effects.
Forging steel rolls are made by smelting, forging and heat treatment, so that the working layer of the roll body has high hardness, high wear resistance and excellent accident resistance. At the same time, the roll neck and core of the roll body have certain strength and high toughness. This unique property of forged steel rolls makes it an irreplaceable advantage of cast rolls in cold rolling and non-ferrous rolling.