Analysis of ridging in ferritic stainless steel and aluminum alloy sheets

Abstract

The columnar grains in ferritic stainless steel (FSS) slabs containing 11-17%Cr have the texture of 〈100〉//column axis. The columnar grains in FSS develop the rotated cube texture after plane strain rolling and are not easily recrystallized. In addition, the slab does not undergo α to γ or γ to α phase transformation during all processes. Therefore, long grain colonies with similar orientations develop from the columnar grains in the slab during cold rolling and survive even after annealing. These colonies and matrix are likely to show different plastic anisotropies, resulting in undesirable surface corrugations with peaks on one side of the sheet coinciding with valleys on the other side without change in the thickness, known as ridging, when pulled in the rolling direction (RD). The ridges have a depth in the range of 20-50 μm. In ridging, or roping, observed in AA6xxx AI alloys pulled in the transverse direction (TD), the distribution of ridges and valleys is irregular. The roping phenomenon is associated with in-plane banded clusters of the cube {001}〈100〉 and Goss {110}〈001〉 oriented grains. When pulled in TD, the Goss oriented grains are much harder than the cube oriented grains, and hence retains a higher surface level than the cube oriented grains. Thus, ridging is promoted by the presence of grain clusters of the cube and Goss components. The joint occurrence of soft and hard clusters stimulates the surface-strain heterogeneity, entailing ridging. The roping phenomena in FSS and AA6022 Al alloy sheets are analyzed by the crystal plasticity finite element method (CPFEM).