Modeling of rolling texture development in a ferritic chromium steel
- PDF / 602,633 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 28 Downloads / 235 Views
I.
INTRODUCTION
MODELING of texture development has great technological importance, as plastic deformation usually induces strong anisotropies in polycrystalline metals, leading to directional dependencies of the physical properties. The behavior of an individual crystal, however, depends on its interaction with its surroundings, which is difficult to account for. Early models (Sachs[1] and Taylor[2]) assumed stress and strain homogeneity, respectively. However, these idealized conditions were not perfectly verified by measurements or simulation results. It was recognized that grainshape effects can be important, and were first taken into account by the relaxation of some stress components (relaxed-constraints model[3–6]). These relaxations, however, can only be justified when the grain shapes are far from equiaxed, i.e., are normally at very large strains (except when they are elongated already at the beginning of deformation, a case that will be studied in the present work). An important step was taken with the introduction of the self-consistent models,[7–10] which consider a grain as an inclusion embedded in the polycrystal. A grain’s surroundings is a homogeneous equivalent medium (HEM) in these models, which is defined by the average physical properties of all grains. This approach can naturally account for the shape and its evolution during deformation. It introduces an interaction law between a grain and the polycrystal, for which several approaches were proposed, namely, secant,[8] tangent,[9] and finite-element-tuned[10] models. Among these, the one that has been calibrated with the help of some finite-element calculations will be employed in the present study.[10] This modified self-consistent model has already been successfully tested for torsion and rolling.[11,12] For completeness and in order to estimate the performance of ´ TH and A. MOLINARI, Professors, are with the Laboratoire L.S. TO de Me´canique et Physique des Mate´riaux, Universite´ de Metz, 57045 Metz, France. D. RAABE, Private Dozent, is with the Institute fu¨r Metallkunde und Metallphysik, 52056 Aachen, Germany. Manuscript submitted January 8, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
the self-consistent model, the classical Taylor and relaxed-constraint approaches will also be considered. All models employed in the present work use the well-known viscoplastic power law for crystallographic slip, incorporating microscopic strain hardening of the slip systems. The cold-rolling textures of a ferritic chromium sheet steel containing 11 pct Cr are studied in the present work. Before cold rolling, it contained already very elongated grains in its middle section, where the textures were measured and also simulated. Important effects of grain shape and hardening were found, which have been studied by the Taylor, the relaxed-constraints pancake, and the self-consistent viscoplastic models. II.
EXPERIMENTAL
A. Material and Rolling Conditions Table I shows the chemical composition of the ferritic stainless steel under investigation. The
Data Loading...
