Papers by Keyword: Ridging

Abstract: Experimental and numerical investigations of the ridging in ferritic stainless steels were presented in this paper. Two kinds of ferritic stainless steels exhibiting different levels of ridging were selected as model materials. The measured roughness of the uniaxially elongated specimens up to 15% in rolling direction (RD) was compared to the prediction using a rate-dependent crystal plasticity FEM (CPFEM). Initial textures of the two materials on 5 equi-spaced sequential RD planes were obtained by EBSD measurement. The initial textures were utilized as input data for the constitutive parameters of the crystal plasticity. Measured respective single planar textures were collected all together so that the 5-layer textures complete 3-dimensional structure and they were mapped onto the FE mesh. Ridging profiles predicted by the CPFEM using both every single layer texture and multilayer texture were compared to the experimental results. Predicted ridging profile of a material exhibiting weak ridging by using 5-layer EBSD mapping was in good agreement with the experimental result. On the other hand, prediction by using only single layer texture was efficient to estimate the ridging in a material exhibiting severe ridging due to the elongated cluster of analogous orientations along RD.

Abstract: Equal-channel angular pressing (ECAP) was applied to 16mass%Cr steel sheets for one pass prior to cold rolling in order to improve formability and alleviate ridging of the sheets. Effect of channel angle of ECAP (90° and 120°) on the deformation microstructure and the subsequent recrystallization was focused. One-pass ECAP indeed modified the cold-rolled microstructures, texture and subsequent recrystallization as compared with that in cold rolling alone. In particular, grain-scale shear bands were introduced during ECAP in otherwise hard-to-recrystallize <001>//ND grains by ECAP, and they facilitated the recrystallization. However, the effect of reducing the channel angle from 120°to 90°on the recrystallization and the formability was limited in spite of higher shear strain imposed on the sheets.

Abstract: Aluminium alloys for car body manufacturing often show a specific type of band-shaped surface roughening upon stretching, called “ridging” or “roping”. Experimental research as well as modelling attempts have indicated that the evolving surface roughness profiles cannot be understood based on banding of individual surface texture components, like cube or Goss, only. Therefore, it is proposed to study banding on the “mesoscopic” level of texture banding rather than on the “microscopic” one of orientation banding. In mechanical terms, such patterning in the texture would lead to patterning in, for instance, the Lankford coefficient (r-value), so that the mechanical response can be calculated on an intermediate length scale. The present contribution presents a method for calculating r-value patterning from Electron Backscatter diffraction (EBSD) orientation maps. In a first test case of a strongly ridging AA6xxx sheet, indeed patterning in the r-value is found which corresponds to reported patterning of the surface roughness.

Abstract: The influence of the texture on ridging and forming properties of transformable 16mass-%Cr steel was studied for two different specific processing routes. In the first route (HACA), hot strips were annealed prior to cold rolling, whereas in the second route (HCA), un-annealed hot strips were directly subjected to cold rolling. Results indicate that compared to HACA, HCA results in an improved surface smoothness, i.e. reduced roping, but a lower mean r-value, as a result of strengthening of the α-fiber texture components. Differences in the roping and forming properties could also be achieved by compositional differences resulting in differences in the fraction of austenite at hot rolling temperatures.

Abstract: With prices for metal resources such as nickel and molybdenum soaring, there is a heightened sense of crisis concerning resource scarcity. While Type304, the most common stainless steel, offers excellent corrosion resistance, its price is affected significantly by the cost of nickel because of its 8% nickel content. The stainless steel that has the same corrosion resistance as that of Type304 and does not contain nickel and molybdenum has been required. JFE Steel Corporation has developed a new 21%Cr-0.4%Cu stainless steel, the world’s first ferritic stainless steel, which offers equivalent corrosion resistance to Type304 while containing absolutely no nickel or molybdenum, two rare metals. The newly developed steel contains 21% chromium with the addition of 0.4% copper. The development of the steel is based on a new discovery that the passive films of stainless steels could be strengthened by the synergy effect of high chromium content and copper addition. Copper addition enriches the chromium content in passive films after field exposure. Newly developed 21%Cr-0.4%Cu stainless steel is adopted for many applications as a substitution for Type304, including commercial kitchenware, building materials and industrial machinery. The steel is expected to be a new standard of a ferritic stainless steel as a substitution for Type304.

Abstract: Al-Mg-Si alloy is the suitable material for the automotive body application. However, it is found that a rope-like profile (ridging) develops when the Al-Mg-Si alloy sheet is stretched along the transverse direction. In this study, in order to clarify the formation process of ridging developed in Al-Mg-Si alloy, the relation between ridging and texture components of the sheet was investigated by 3D profile microscope and SEM/EBSD method. It was found that the ridging developed remarkably in the hot-rolled (at higher temperature) and annealed sheets. In ridging sample, there was the band of cube oriented grains (cube band). It was also found that the region of cube band corresponded to the ridges and valleys which caused a rope-like profile in the sheets. It could be thought that the difference of plastic deformability between cube-oriented grains and other oriented grains led to the development of ridging. This assumption is supported by the lower Taylor factor of cube oriented grains than other oriented grains. From these results, it was concluded that the development of ridging was strongly affected by the distribution of cube oriented grains.

Abstract: In this work we present deformation experiments of polymer-coated polycrystalline aluminium sheets. We observe that the straining is accompanied by the development of microstructural defects at the sample surface as well as in the interface between the metal and the different polymers. These defects are due to a variety of dynamical mechanisms which are essentially induced by bulk plasticity of the metal substrate. They micromechanically interact with the polymer coating and transfer some of the metallic roughness to the coating and to the surface.

Abstract: In the present work the characterisation of both the microstructure and the microtexture of two ferritic stainless steel sheets - AISI 430 (Fe17% Cr) and AISI 434 (17% Cr, 1% Mo) - known to display different ridging behaviours, was carried out by optical metallography, EBSD and OIM techniques. It was concluded that severe ridging is a consequence of: (a) presence of {111} and {001} colonies of grains alternating throughout the sheet plane; (b) through thickness texture inhomogeneity with layers of {001}<110> oriented large grains of low Rvalues sandwiched between layers of higher R-value textured material.

Abstract: In order to optimize the recrystallization texture of ferritic stainless steel sheets, the crystallographic texture was modified by means of cross rolling. The as-received hot band displayed pronounced through-thickness texture gradients with a strong rotated cube orientation in the sheet center layer. After the conventional normal rolling, the strong initial texture was retained. Pronounced{001}<110> in the rolling textures led to the formation of {334}<483> in the final recrystallization texture. Cross rolling in the present work was performed by a 45° rotation of RD around ND. Cross-rolling led to a weakening of {001}<110> orienations. After recrystallization annealing the cross-rolled samples displayed stronger {111}//ND orientations. The orientation stability during the rolling deformation was tackled by means of Taylor deformation model.