Micro-mechanism of central damage formation during cross wedge rolling

Central damage is a serious defect in the solid products of cross wedge rolling. A combined experimental and modelling approach was used to study the micro-mechanism of central damage. The evolution process of the micro-voids initiation, growth and coalescence during cross wedge rolling of steel was observed, and the micro-damage morphology was linked to the stress-strain state to reveal the mechanism of central damage. The influences of process parameters on the central damage were investigated on the basis of analyzing the characteristics of stress and strain in the center of the workpiece. It is found that the micro-voids in the center of the workpiece initiate around non-metallic inclusions and develop into macroscopic damage in the directions of shear stress and tensile stress by growth and coalescence; the shear stress and tensile stress cause significant alternating shear and tensile deformation with the rotation of the workpiece, leading to the central damage. The larger the shear deformation and tensile deformation coefficient, the more the cyclic numbers, the greater the degree of damage; among the process parameters of cross wedge rolling, the forming angle has the greatest influence on the central damage.