For roughing rolls, strength and thermal cracking resistance are the primary requirements. The working rolls of a small 20-roll mill weigh only about 100 grams, while the support rolls of a heavy plate mill weigh over 200 tons. When selecting rolls, the first step is to choose the main load-bearing material (various grades of cast iron, cast steel, or forged steel, etc.) based on the mill's basic strength requirements.
Hardness
For finishing rolls, the speed is higher, and the final rolled product must have a certain surface quality. Therefore, hardness and wear resistance are the primary requirements. Then, the wear resistance required for roll use is considered. Because the wear mechanism of rolls is very complex, including mechanical stress, the heat during rolling, cooling, the chemical action of lubricating media, and other factors, there is no unified index for comprehensively evaluating roll wear resistance. Since hardness is easy to measure and can reflect wear resistance under certain conditions, a radial hardness curve is generally used to approximate the roll's wear resistance index.
Impact Resistance
In addition, there are some special requirements for rolls. For example, when the reduction is large, the rolls need to have strong biting ability and high impact resistance.
Surface Finish
When rolling thin-gauge products, the requirements for roll rigidity, uniformity of microstructure, machining accuracy, and surface finish are more stringent.
Machining Performance
When rolling structural steel with complex cross-sections, the machinability of the working layer of the roll body must also be considered.
When selecting rolls, some performance requirements are often contradictory. Roll purchase and maintenance costs are very high. Therefore, the technical and economic advantages and disadvantages should be carefully weighed to determine whether to use cast or forged rolls, alloy or non-alloy rolls, and single-material or composite materials.
