Anisotropic plastic flow in ferritic stainless steels and the “roping” phenomenon

Abstract

The recent papers of Chao and Takechi, Kato, Sunami and Nakayama are discussed relative to the “roping” morphology and the textures commonly observed in ferritic stainless steels prone to “roping”. The anisotropic plastic flow associated with textures having [110] and [112J rolling directions is reviewed and a transverse plastic buckling mechanism is proposed as being consistent with “roping” morphology and texture combinations. It is proposed that longitudinal bands with a strong (001) [110] (or similar) texture surrounded by material with a (111) [11άcr2] (or similar) texture will undergo plastic buckling under transverse compressive stresses that result from the texture mix and elongation in the rolling direction. The mechanism predicts amaximum ratio of sheet thickness to corrugation width of about 0.43 for buckling with “clamped ends” and about 0.86 for buckling with “hinged ends”. Profile measurements of 430 and 434 stainless steel sheets pulled to 15 pct in the rolling direction show ratios generally under 0.4. Furthermore, the mechanism predicts that aminimum plastic elongation of 0.4 pct is required in the rolling direction to initiate buckling or “roping”. Profile measurements are presented showing that the “roping” corrugations do not develop until 1.5 to 2.0 pct plastic elongation in the rolling direction.