The invention relates to the technical field for repairing an ultra-large type
backup roll, in particular to a repair process of a
forging steel
backup roll with Phi2100* 3400mm. Firstly,
welding is carried out on the rib of the
backup roll: the roll body of the
backup roll which needs to be welded is preheated to 250 DEG C, and the temperature is preserved for 10 hours; then the door of a furnace is opened, rib
welding is carried out, zigzag
welding is carried out every 100mm, and the length of the weld pass is 50-60mm;
oxygen is used on the welded part immediately, and ethyne is used for warming the welded part until the welded part becomes blue. After the rib welding is finished, preheating treatment, temperature preservation treatment and destressing treatment are carried out respectively according to a heat treatment curve when the roll body of the
backup roll is overlaid for making a bottom layer, a
transition layer and a working layer. Compared with the prior art, in the technology of the invention, the influence on the service performance caused by the temperature circulation and change of a heat influencing region during the overlaying is considered, uniformity and penetration of preheating workpieces and uniformity of temperature between
layers are guaranteed in the repair process, the blank in the repair rebirth field of the domestic ultra-large type
backup roll is filled in. The time for repair is short, the service life is prolonged, and the cost is saved.