Thermal crack resistance
Generally, the main requirements for rough rolls are strength and thermal crack resistance; the work rolls of small 20-high rolling mills weigh only about 100 grams, while the weight of backup rolls of wide and heavy plate rolling mills has exceeded 200 tons. When selecting a roll, first select the main material (various grades of cast iron, cast steel or forged steel, etc.) that can safely bear the roll according to the basic strength requirements of the rolling mill.
However, the speed of the finishing roll is high, and the final rolling product must have a certain surface quality. The main requirements for it are hardness and wear resistance. Then consider the wear resistance that the roll should have when it is used. Due to the complex wear mechanism of rolls, including mechanical stress, thermal action during rolling, cooling, chemical action of lubricating medium and other actions, there is no unified index for comprehensive evaluation of roll wear resistance. Since the hardness is easy to measure and can reflect the wear resistance under certain conditions, the radial hardness curve is generally used to approximate the wear resistance of the roll.
In addition, there are some special requirements for the rolls. For example, when the reduction is large, the rolls are required to have strong biting ability and impact resistance;
When rolling thin-gauge products, the rigidity, uniformity of structure and properties, processing accuracy and surface finish of the rolls are strictly required;
When rolling profiles with complex sections, the machinability of the working layer of the roll body should also be considered.
When selecting rolls, some performance requirements of the rolls are often opposed to each other, and the purchase and maintenance costs of the rolls are very expensive. Therefore, the technical and economic advantages and disadvantages should be fully weighed to decide whether to use cast or forged, alloy or non-alloy. Yes, single material or composite material.