ANALYSIS OF PLASTIC FLOW OF METAL DURING MULTI-PASS ROLLING

Abstract

The paper analyzes the features of plastic flow of metal during multi-pass rolling, taking into account the evolution of anisotropy that occurs after each deformation cycle. Traditionally, the isotropic Mises flow criterion is used to describe the stress-strain state, but it does not take into account texture formation, which significantly changes the mechanical behavior of the metal after the first pass. The article substantiates the feasibility of using the Hill criterion, which allows for more adequate modeling of plastic flow for materials with manifestations of anisotropy. The kinematic model of flat rolling is considered, the deformation rates, the mass conservation condition, and the shear components of plastic flow are determined. Based on the equilibrium equations and the Hill criterion, simplified dependences for stresses characteristic of multi-pass deformation are obtained.

The paper presents the associated Hill flow rule and shows the mechanism of the relationship between the main strains and stresses under anisotropic flow conditions. A modified approach to determining the contact pressure is proposed based on the generalized Sim formula adapted to the anisotropic flow criterion. The relationship between the contact pressure and the anisotropy coefficient is established, which increases with the number of passes.

The proposed model of plastic flow velocity is based on the modified Oyen formula, in which the flow stiffness parameter increases in accordance with the accumulation of anisotropy. To assess the state of the material, the stress state indicator and the Cockcroft-Latem damage criterion are introduced, which allows determining the degree of accumulated defects in the process of multi-pass deformation. The obtained dependencies provide a qualitatively more accurate description of the processes occurring in the deformation zone and can be used to optimize rolling modes, increase metal plasticity and prevent the occurrence of defects in finished products.