Material development of cold rolling work rolls

Cold-rolled thin sheets (including galvanized, tin-plated, coated and enamel thin steel sheets) are widely used in the chemical industry, Light industry, automobiles, machinery, construction, hydropower, petroleum, coal and railways are an important and indispensable steel variety in the national economy. Rolls are necessary and very important equipment components for cold-rolled sheet production. The increase in demand for cold-rolled sheets has also led to a significant increase in roll production companies. With the gradual improvement of numerical control, modernization, automation, and continuity of rolling mills, the demand for rolls has increased. Quality also puts forward increasingly higher requirements.

 

cold rolling work roll

 

Material development trends of cold rolling work rolls

1) High chromium cold roll

By increasing the content of the Cr element, the hardenability of the cold rolling work roll material can be improved. Mitsubishi Steel has developed a new type of high-chromium forged steel cold roll material. Test results prove that the wear resistance of a cold roll with a Cr content of 10% is twice as high as that of a cold roll with a Cr content of 3%. When the Cr element content is further increased to 18%, the wear resistance of the cold rolling roll will also be improved. By adjusting the balance of carbon and chromium, not only can higher hardness be obtained at a lower quenching temperature, but the susceptibility to breakage of the roll material can also be reduced, reducing the occurrence of roll breakage accidents. Cold rolling rolls have strong resistance to roll breakage and good roughness retention and can be adapted to rolling under harsh working conditions such as large rolling force and high product precision requirements.

2) Highly alloyed improved cold roll

In order to improve the mechanical properties and performance of the new cold-rolled work roll, improvements were made based on the 5% Cr cold-rolled work roll material, changing the percentage content of elements such as Mo and V or adding an appropriate amount of strong carbide-forming elements such as Ti, Nb, etc. can form new materials for Cr5 series rolls. The wear resistance and thermal shock strength of the new Cr5 series material cold rolls can be significantly improved.

Nitrogen can strengthen the mechanical properties of the roll. It has a strong affinity with alloy elements such as chromium, vanadium, titanium, and niobium in steel, and can generate stable nitrides that exist in steel in different forms. Nitride is more likely to form fine and dispersed second phases, inhibit the growth of austenite grains, and has a significant effect on refining grains, significantly improving the strength, hardness and other mechanical properties of the roll material. Therefore, by controlling the nitrogen content in the cold rolling roll material, we can improve the overall performance of the cold rolling work roll, which also provides an important direction for the development of roll materials.

3) Forged semi-high-speed steel cold rolls

During the actual use of cold-rolled work rolls, production accidents such as steel jamming, steel sticking, and belt breakage may occur, which will cause the local structure and hardness of the cold-rolled work roll body made of Cr3 and Cr5 series materials to change, resulting in roll surface Microcracks or massive spalling may occur locally, thereby reducing the accident resistance of the cold rolling roll. The material of forged semi-high speed steel cold rolling rolls is developed based on the material of 5% Cr cold rolling work rolls. Due to the large addition of strong carbide-forming elements Cr, Mo, and V, the type of carbide obtained after quenching is mainly M7C3 type. (HV2500) and MC-type (HV3000) carbides are mainly used. The existence of high-hardness carbides ensures that the forged semi-high-speed steel rolls have good wear resistance and high accident resistance.

4) High-speed steel cold roll

High-speed steel rolls were first put into practical production and application in Japan in 1988, and then the United States also began to adopt high-speed steel rolls in the early 1990s. At present, high-speed steel cold rolls have been used in dozens of steel companies such as Inland Steel Company in the United States, Dofasco Company in Canada, Akers Company in Sweden, and Nippon Steel Company, and the use results are good.

The material of high-speed steel rolls contains a large number of carbide-forming elements. The carbide types are mainly MC and M2C types, which will greatly improve the strength, surface roughness and wear resistance of cold rolling rolls. Therefore, the use of high-speed steel rolls can significantly reduce roll consumption and reduce the number of roll changes, which helps reduce rolling costs and improve plate quality. Due to the high carbon and alloy content of high-speed steel cold rolling rolls, its production process is more complicated. Currently, there are no reliable smelting, forging, and heat treatment methods. Therefore, its processing technology is poor and the yield rate is also low. This is also a key technology that needs to be solved in the future.

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