CALCULATION OF HARDENING STRESSES IN STEEL MEMBERS TAKING INTO ACCOUNT VISCOELASTOPLASTIC PROPERTIES AND THE CHANGE IN THE PHASE COMPOSITION

As a rule, large-sized monoblock backing-up and working rolls are subjected to induction hardening by commercial frequency currents (CFC) to provide the desired hardness for their contact surfaces. In this case, significant hardening stresses are formed in the rolls, which can lead to the fracture even before the beginning of the operation during the thermal treatment, transportation, and storage. The experimental methods for determining thermal stresses are extremely labor-consuming and expensive because they require cutting of the roll. In the present paper, we develop an approach and a software for the calculation of the stress-strain state in large-sized rolls subjected to CFC induction hardening. The software allows one to choose reasonable modes of hardening by a numerical experiment. The controlled parameters of these modes include the power and speed of motion of the inductor and the intensity of sprayer cooling that facilitates the formation of the prescribed phase composition in the roll material. The hardening conditions must provide the required hardness for the working surface of the roll and, at the same time, must not lead to the fracture due to high thermal stresses. The stresses during the induction hardening arise because of nonuniformity of the temperature field and phase transformations accompanied by a change in the volume. Therefore, the method of calculation of thermal stresses must include the solution of the three problems-thermal, structural, and force ones.