IMPROVEMENT OF THE SURFACING TECHNOLOGY FOR LARGE-SIZED BACKUP ROLLS OF HOT ROLLING MILLS

摘要

It is shown that when surfacing large-sized backup rolls of hot rolling mills made of 90KhF steel, the limited weld-ability of steel leads to the need to select the thermal mode of surfacing that ensures the required performance of the deposited layer. The choice of materials and technology of deposition of the transition zone from the base metal to the working layer determines appearance of hardness dips and formation of a "soft interlayer", which leads to occurrence of spalling. Elimination of such dips depends on the choice of the deposition mode of each of the layers, in accordance with the composition and size of the electrodes used. It is shown that application of 1.0 mm thick 08kp, 30KhGSA, 25Kh5FMS strip electrode for surfacing makes it possible to obtain a smooth (without dips and bursts) change in hardness by the height of the multilayer composition, which contributes to an increase in spalling resistance when the height of the deposited layer decreases during the operation of the roll. The high efficiency of the surfaced backup rolls was confirmed during industrial development of the surfacing technology of the rolls and their long-term operation in the hot rolling mill. The developed and implemented route scheme for movement of the deposited and new backup rolls (the share of deposited rolls reached 30%) in the roughing group of stands of mill 2000 of the Cherepovets Metallurgical Plant made it possible to ensure the operating time of surfaced rolls commensurate with that of new rolls as to the tonnage of rolled products.