The stress and strain changes in the center of the multi-pass rolling process are shown in Figure 6 6for a grinding pit of 0.25 mm depth. The center point of the pit was fifirst subjected to tensile stress in the x-direction (TD) and then the tensile stress gradually changed to compressive stress when entering the rolling zone; in the y-direction (RD), compressive stress was applied and, as the rolling process progressed, compressive stress was converted into tensile stress. The tensile stress at the

grinding center exceeded the tensile strength, but its strain was only 0.38, which did not exceed the ultimate strain.

The stress and strain changes in the center of the multi-pass rolling process are shown in Figure 6 6for a grinding pit of 0.25 mm depth. The center point of the pit was fifirst subjected to tensile stress in the x-direction (TD) and then the tensile stress gradually changed to compressive stress when entering the rolling zone; in the y-direction (RD), compressive stress was applied and, as the rolling process progressed, compressive stress was converted into tensile stress. The tensile stress at the

grinding center exceeded the tensile strength, but its strain was only 0.38, which did not exceed the ultimate strain.