1. Requirements for working rolls in continuous cold rolling
Continuous cold rolling places high demands on the performance of the rolls, especially when the mill is fully integrated with a pickling line and/or continuous annealing line, and high productivity places even higher demands on the work rolls, especially those that maintain a suitable roughness during rolling ability. Therefore, the deterioration of the surface of the work roll is one of the main issues to be considered in cold rolling. The roll must have the ability to maintain roughness while having the best wear resistance because the lowest level of roughness is essential for ensuring rolling. The required friction is essential.
In recent years, the output of cold-rolled work rolls has increased strongly, and rolling technology and roll materials have greatly promoted this. This is a process of continuous development. First, semi-high-speed steel rolls are used in hot rolling, then in cold rolling, and now high-speed steel rolls (HSS) are introduced into cold rolling. These high-alloy cast materials will become valid substitutes for forged steel rolls.
Generally, in order to expand the range of use of forged steel rolls, the surface of forged steel rolls needs to be chrome-plated in many cases. The high-speed steel casting roll has good wear resistance so that it can achieve a similar rolling effect without chrome plating, and there is no additional cost or impact on the environment. In addition to these properties, high-speed steel rolls have many characteristics in the grinding process.
2. Basic situation of high-speed steel rolls in cold rolling trials
The surface structure of the high-speed steel roll produced by the centrifugal casting process is a large number of high-hardness carbides, which are dispersed on the high-toughness ferrite matrix. This steel grade contains a variety of strong carbide-forming alloying elements such as Cr, Mo, and V. Different microstructures and properties are achieved through the relative balance of these alloying elements and C and can be tailored to the specific needs of the rolling mill.
3. Evaluation of high-speed steel roll materials
When a new type of roll is introduced, some aspects are confirmed even before rolling. The systematic evaluation of work rolls in tandem cold rolling mills is based on the following points, in order of importance:
(1) Safety and accident resistance; (2) Grindability; (3) Roughness retention ability; (4) Strip cleanliness; (5) Wear resistance.
The test results of the centrifugally cast high-speed steel roll on the cold tandem mill show that its performance has reached twice that of the forged steel roll without problems in safety and accident resistance. The roughness of the high-speed steel roll can reach Ra0.6-0.8m by using a CBN grinding wheel. Strip cleanliness is slightly lower than with chrome-plated rolls but within acceptable limits.