Cast high-speed steel rolls are used in many fields including the finishing rolling section and rough rolling section of hot strip hot strip rolling mills, the pre-finishing rolling section of steel pipe rolling mills and high-speed wire rod rolling mills, and their advantages are quite obvious. From the perspective of the development of steel rolling technology, improving the quality of rolled materials, improving the progress of steel rolling, and reducing steel rolling costs are the most mainstream development directions.
Keywords: Hss rolls, high-speed steel roll technology
Analysis of the main advantages of high-speed steel rolls
Compared with steel rolls in the traditional sense, high-speed steel rolls have very outstanding advantages in terms of wear resistance at room temperature and high temperature. At the same time, it has high hardness and good red hardness characteristics, and its thermal crack resistance and accident resistance are very outstanding.
From the perspective of microstructure, it is mainly formed by MC and M6C alloy carbides embedded in the austenite matrix. MC and M6C have very outstanding hardness advantages. In addition, the austenite matrix has high thermal stability, and a large number of alloying elements participate in the reaction during the mosaic process, and a certain amount of dispersed carbides can be precipitated during tempering. The hardening phenomenon after secondary tempering occurs, which promotes the increase of martensite decomposition temperature and shows more precise hardness advantages.
High-speed steel rolls are very adaptable and can improve the quality of rolled products while extending their service life. They can be widely used in hot strip continuous rolling finishing stands and unregulated rolling of strips of various materials. , to promote further development of its advantages.
Hss rolls process improvement analysis
Improvement of the problem of decrease in roller core strength during heat treatment
In order to effectively enhance and improve the wear resistance of the outer layer material of high-speed steel rolls, the key is to increase the quenching temperature during the manufacturing process of high-speed steel rolls. Under the current technical conditions, for composite high-speed steel rolls, the core material of the roll is mainly high-strength alloy ductile iron. Affected by the restrictive factors of the material, if the quenching temperature of the high-speed steel roll is selected above 1250°C, the roll core structure will be significantly coarser and even local melting will occur, which will significantly reduce the strength of the roll core and easily cause roll breakage during use. phenomenon, affecting the normal operation of rolling mill equipment. Many countries have successfully developed sub-temperature heat treatment processes for high-speed steel rolls, but have not made detailed reports on the process. Develop a heat treatment process for high-speed steel rolls. The new process should eliminate high-temperature quenching and ensure high strength of the roll core. It should be simple and easy to implement, with low energy consumption and less pollution. The surface induction quenching process is easy to operate and has little impact on the strength of the roll core. It will be feasible to apply it in casting high-speed steel composite rolls. In order to ensure the depth of the hardened layer, it is recommended to use a double-inductor quenching process.
Improvement of the bonding strength between roller core and outer layer
In the process of manufacturing composite high-speed steel rolls using the traditional centrifugal method, ductile iron is mostly chosen as the core material of high-speed steel rolls, which often has the characteristics of precipitated graphite. Since the outer material, high-speed steel, contains certain special elements, these elements may cause the cast iron to whiten. Therefore, the problem of graphitization deterioration is very serious in the areas where the outer layer is in direct contact with the core of the high-speed steel roll. Under the condition of continuous precipitation of carbides, the brittleness level of the joint part increases significantly, which may cause the outer layer of the composite high-speed steel roll to peel off during use. In addition, under the condition of using cast steel as the core material of high-speed steel roll. Due to its high speed and elongation characteristics, its melting point is higher than that of high-speed steel. During the pouring process, it is easy to have a fusion reaction with the inner surface of the solidified outer high-speed steel, resulting in casting defects and affecting the strength of the joint. To address this problem, during the implementation of the manufacturing process of high-speed steel rollers, an intermediate layer can be added between the roller core material and the high-speed steel material (graphite steel is preferred as the intermediate layer) to improve the bonding state of the roller core interface and the high-speed steel interface. , and achieve the purpose of improving the bonding strength of composite high-speed steel rolls.
Improvement of casting crack problem
During the casting process of high-speed steel rolls, due to the large content and many types of alloy elements, the thermal conductivity of high-speed steel may be affected. Uneven problems occur during the casting cooling process and increase the residual stress level of the high-speed steel roll to a certain extent. In addition, alloying elements are prone to segregation problems during the solidification process of high-speed steel rolls. The phase transition in high-speed steel materials is more obvious and the phase transformation stress has a significant increase trend. Under the influence of the above factors, high-speed steel rolls have a relatively obvious tendency to crack during manufacturing. In order to avoid the formation of cracks from adversely affecting the overall performance of high-speed steel rolls, it is necessary to promptly modify the molten steel during the manufacturing process. For example, you can choose a double-layer coating that combines a heat insulation layer with a refractory layer, or you can reasonably adjust the rotation speed of the centrifuge during pouring to minimize and eliminate casting cracks in high-speed steel rolls.
In order to adapt to the strict requirements of modern rolling mills and the production of high-quality steel on rolling processes, metallurgical workers have made the development and improvement of high-speed steel roll process technology one of their most important tasks. Starting from this perspective, the article analyzes the main advantages of high-speed steel rolls, studies the main current manufacturing process plans of high-speed steel rolls, and finally explains the problems found in the manufacturing process and the main means of process improvement. Hope it attracts attention.
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