Rolls crack resistance increase by reducing welding stresses and heat input

Abstract

The rolling mills working and backup rolls operate under high specific pressures, abrasion and corrosion wear, thermal cycling conditions and they are produced of high carbon steel, prone to hot and cold cracks formation. Therefore, crack resistance and wear resistance increase is an important scientific-technical problem. It has been established that the deposited metal crack resistance is largely determined by welding stresses, which are formed as a result of heat input and thermal deformation cycle, imbalance, at which the energy is zero, and energy increase. According to the superposition law in multilayer electric arc welding, welding stresses are summed up during surfacing of each metal layer, which leads to welding stresses increase and deposited metal scaling. The welding stresses and heat input influence on the deposited metal crack resistance has been established. With increasing the deposited metal thickness, the deformations and welding stresses increase, which leads to cracks formation and weld metal scalings. It has been established by calculation and experiment that the optimum the deposited metal thickness per the rolls radius is 25 mm. With increasing the weld metal thickness up to 40 mm, welding stresses sharply increase, under the action of which cold cracks form and the deposited metal scaling. The welding stresses main role in crack formation has been confirmed. Minimum energy result in maximum quality, weld metal crack resistance and wear resistance. The high-speed surfacing at low heat input process, which provides welding stresses reduction, fine-grained microstructure, the absence of deposited metal scalings, and the rolls crack and wear resistance increase, has been developed