At present, more and more production lines of hot rolling and steel heat treatment in metallurgical industry use roller hearth furnace to reheat the billet. The main structure of roller hearth furnace is the furnace roll transverse to the rolling direction, while the material of processing furnace roll is mostly high alloy material. Through intelligent alloying and microstructure adjustment of these alloy materials, the functional characteristics of the casting furnace roll are greatly improved. Therefore, the alloy produced by centrifugal casting process can be used as the material of furnace roll, which can make the furnace roll with roller bottom have good high temperature mechanical strength and oxidation resistance.
With the development of metallurgical industry, the functional characteristics of casting furnace roll are greatly improved by intelligent alloying and microstructure adjustment. The aluminum containing heat-resistant casting alloy has the best anti-oxidation and anti creep effect, which provides a guarantee for the use of water-free cooling furnace roll, replaces the water cooling furnace roll, and creates an excellent opportunity for the steel plant to further improve equipment reliability and save energy cost.
As the key equipment of direct connection of continuous casting and rolling process, roller hearth furnace can increase the output of products, save energy and reduce the cost of flat products in steel industry. In general, the inlet side of heating furnace is connected with the first-class or two streams of continuous caster, and the outlet side is connected with rolling mill, so as to separate casting process and rolling process. The steel industry calls this kind of furnace roller hearth furnace, soaking pit furnace or tunnel furnace. Generally, the heating furnace can be divided into heating zone, soaking zone and buffer zone. Its function is to reheat the billet before rolling, to make the temperature of the billet in the length direction and cross section uniform, and to maintain the status of the billet, so as to meet the rolling conditions of the rolling mill. In addition, the roller hearth furnace is also used for heat treatment of long materials, namely, quenching, solution annealing and normalizing processes. At present, there are many kinds of steel products produced by iron and steel enterprises, including low-carbon steel, high-strength low-alloy steel, pipeline steel, spring steel, tool steel, wear-resistant steel, electrical steel, stainless steel, etc. all adopt thin slab continuous casting and rolling process.
Because the chemical composition and physical properties of each steel are different, each steel has its own process requirements. For example, microalloyed steel contains niobium, vanadium and titanium. To keep niobium in the solid mixture, in the process of thermo mechanical rolling, the strength of alloy steel can be greatly improved by precipitation strengthening. The nitrogen content of steel has certain effect on Nb (C, n) precipitation Therefore, for Nb bearing billets, the start temperature of hot rolling should be 1200 ℃, while for vanadium bearing steel grades, the temperature is relatively low, 1150 ℃. This case shows that the soaking temperature of the heating furnace must be very high, and the residence time of the billet in the furnace should be fully utilized to prevent the premature precipitation of microalloyed elements and lead to excessive grain growth. It is very important to optimize the performance during the subsequent thermal mechanical treatment, so as to obtain the microstructure and mechanical properties required by the user.
Among the many key components of the roller hearth furnace, the furnace roller is the most important one in terms of functionality, because the trouble free performance of the furnace roller directly affects the operability and reliability of the heating furnace, as well as the output and operating efficiency of the hot rolled coil. The roller used in roller hearth furnace is driven by motor, whether it is water-cooled or water-free cooled. Generally, water cooling furnace roller is used in the heating section, while anhydrous cooling furnace roller is used in the soaking section and buffer zone. The furnace temperature here is higher than that in the inlet section of the heating furnace. The heating chamber of roller hearth furnace is heated by natural gas, and the furnace temperature range is 1120-1250 ℃. Heat resistant materials are required. The furnace roll must work continuously under such high temperature without any effect on the raw material of the slab, so as to avoid damage / pollution to the raw material, and prevent the impact on the product quality and the surface of the furnace roll. Whether it is water cooling furnace roll or water-free cooling furnace roll, the furnace roll material is heat-resistant alloy. The adoption of the advanced casting technology, i.e. the centrifugal casting technology, is conducive to the processing of the rotary symmetric component furnace roller. In the design of furnace roll, the innovative metallurgical process of heat-resistant alloy should be considered. Only by correctly understanding the relationship between microstructure, performance and processing, can a new type of alloy with improved performance be produced and the benefit of users can be maximized.
