Study on Grinding and Deformation Fracture Control of Cold Rolled Titanium Strip

Abstract

Surface defects of titanium strip need to be removed by local grinding, but local cracking or band breaking then occurs during subsequent cold rolling. Tensile properties and deformation resistance of 3 mm thick commercially pure titanium strip with grinding pits on the surface were simulated by a finite-element method using a multi-pass cold-rolling deformation process. The stress and strain of grinding pits with depths of 0.25–2 mm were analyzed. During cold-rolling deformation, the stress and strain in the center of a grinding pit were larger than at the edge region. The strip was first subjected to tensile stress in the rolling direction, which then decreased and gradually changed to compressive stress. Partial stress was larger in the rolling direction than in the transverse direction. When the tensile stress and true strain both exceeded the stress and strain limits during second-pass rolling, the strip with a grinding depth of 2 mm cracked, but shallower grinding pits were repaired. The criterion for cracking during rolling after grinding is that the maximum tensile strain at the bottom of the pit must be less than the critical strain of the material: ln ( 1 + h / H ) ≤ ε C r . Results of numerical simulation were verified by the data for cold-rolling tests.