Moo Young Huh

Effect of intermediate annealing on texture, formability and ridging of 17%Cr ferritic stainless steel sheet

Abstract In order to improve the formability of ferritic stainless steel (FSS) sheets, the crystallographic texture of the sheets was modified by way of an intermediate annealing (IA) during the cold rolling. In the as-received hot band pronounced through-thickness texture gradients with a strong rotated cube orientation in the sheet center layer were observed. This strong initial texture has an impact on the texture and the resulting properties, including the undesired appearance of ridging, in the final recrystallized sheet. Instead of forming the {111}//ND γ-fiber texture typical of recrystallized low-carbon steel sheets, the recrystallization texture was notably shifted towards {334}〈4 8 3〉. Introduction of an intermediate anneal during the cold rolling led to a weaker, more typical bcc rolling texture with less pronounced texture gradients. Accordingly, recrystallization gave rise to the characteristic γ-fiber texture. The evolution of the different rolling textures is interpreted by means of texture simulations based on the Taylor deformation theory. The recrystallization textures are explained in terms of a preferred nucleation of recrystallization at the preexisting grain boundaries and a subsequent growth selection. The improvement in sheet formability through the IA is demonstrated by means of analysis of the R-values. Ridging is assessed through surface profile measurements.

Randomization of the annealing texture in aluminum 5182 sheet by cross-rolling

Abstract In order to obtain a randomization of the annealing texture in aluminum AA5182 sheet, the cold-rolling texture is modified through introduction of an additional step of cross-rolling during the deformation. The β-fiber orientations that form during the preceding normal cold-rolling are unstable under cross-rolling conditions. Rather, preferred orientations with {011}//ND (α-fiber) develop. A proper control of the respective reduction degrees before and after the cross-rolling leads to the formation of strong orientation densities along the α-fiber. After recrystallization annealing, the cross-rolled samples depict a very weak, almost random texture. This texture randomization is explained by a suppression of both the nucleation and the subsequent growth of the {001}〈100〉 cube orientation which prevails in normally rolled and recrystallized Al sheets. Because of the resulting homogeneous planar anisotropy (R≈1) of the randomly textured sheets, a better sheet formability was obtained than in conventional sheets with a pronounced cube texture.

Evolution of the cube texture in high purity aluminum capacitor foils by continuous recrystallization and subsequent grain growth

The evolution of the cube-texture in high purity aluminum foils which were produced with a high level of cold reduction and a low finishing temperature is tracked by analysis of microstructure and crystallographic texture. The formation of the cube-texture proceeds in two consecutive steps. (1) During the first stages of annealing, the deformed substructure is transformed into a very fine grained recrystallized microstructure through extended recovery reactions (continuous recrystallization); the rolling texture is retained. (2) Subsequently, the cube-orientation becomes prominent by discontinuous grain growth under consumption of the continuously recrystallized microstructure.

Oxidation of nanophase tin particles

Abstract Tin particles of nanometer size have been synthesized by the gas condensation method using helium as the convection gas. In order to study oxidation behaviors of the nanophase tin powder, the changes in morphology and crystal phases were investigated during heat treatment in air. The as-synthesized powder was oxidized to both the stable tetragonal SnO2 and the non-stable orthorhombic SnO2 which is known to form at extremely high pressure. An intermediate annealing at 225°C for 20 hours gave rise to the oxidation induced amorphization of nano-sized tin particles. The formation of the amorphous tin oxide was explained by suppressed nucleation of crystalline oxides in nano-sized particles. The amorphous tin oxide was transformed into the tetragonal SnO2 through crystallization.

Formation of {111} fibre texture in recrystallised aluminium sheet

Abstract The deep drawability of commercial purity aluminium sheets is improved by introducing a (in fcc materials rather unusual) {111} fibre texture in the sheet surface layers. An additional step of warm rolling after the conventional hot and cold rolling leads to the formation of a pronounced shear texture in the sheet surface layers. During the final recrystallisation annealing, the desired {111} texture prevails at the expense of the other shear texture components. The present paper aims to clarify the mechanisms of the formation of {111}∥ND orientations during both warm rolling and recrystallisation. The effect of the {111} surface texture on the plastic anisotropy of the resulting sheets is discussed.

Effect of lubrication on the evolution of microstructure and texture during rolling and recrystallization of copper

Abstract Two polycrystalline copper specimens were deformed by cold rolling with and without lubrication so as to achieve different deformed microstructures. The effect of the different rolling procedures on the evolution of microstructure and texture during rolling and recrystallization was studied by microstructural observations and X-ray texture analysis. In addition, local orientations in the as-deformed state were determined by selected area diffraction (SAD) in a transmission electron microscope (TEM) and, after recrystallization, by electron backscattering diffraction (EBSD) in a scanning electron microscope (SEM). Whereas the rolling textures of the two differently rolled sheets were surprisingly similar, the microstructures strongly differed in so far as the sample rolled without lubrication contained a much larger amount of shear bands. The present results suggest that the shear component e 13 caused by friction during dry rolling can effectively be dissipated by shear band formation, resulting in a rather homogeneous overall rolling texture. With regard to nucleation of recrystallization, shear bands are known to cut the typical nucleation sites of the cube-orientation, the main recrystallization texture component of rolled copper, but they are also able to act as new nucleation sites. Furthermore, growth of the new recrystallized grains is hindered by the shear bands because of microstructural and orientation discontinuities at the matrix–shear band interfaces. This led to a strong retardation of the recrystallization process and gave rise to a very fine grained microstructure and a weak recrystallization texture in the specimen cold rolled without lubrication.

On the Influence of Cross-Rolling on Shear Band Formation and Texture Evolution in Low Carbon Steel Sheets

In order to understand the influence of the crystallographic texture and the dislocation structure on the deformation mechanism in low carbon steels, the development of the texture and the microstructure in cross-rolled specimens was investigated by employing X-ray texture measurements and TEM observations. The cross-rolled specimens were obtained by rotating the rolling direction by various angles up to 90° after 30% initial straight-rolling of the hot rolled band. Whereas only few shear bands were found in the straight-rolled specimen even after heavy deformation, in the cross-rolled specimen shear bands were often found at reductions in excess of 60%. This observation is discussed in terms of the rotation of the arrangement of dislocations and microbands during cross-rolling. The rolling textures observed in the various samples were interpreted by means of Taylor type deformation models.

Evolution of textures and microstructures in IF-steel sheets during continuous confined strip shearing and subsequent recrystallization annealing

Interstitial free (IF) steel sheets were deformed by continuous confined strip shearing (CCSS) based on the equal channel angular pressing (ECAP). The samples were deformed by CCSS up to three passages and subsequently recrystallized at 700°C for 1 h. The strain history of IF steel sheets in the CCSS die-channel was tackled by finite element method (FEM) simulations. The deformation by CCSS led to the shear deformation and consequently the formation of shear texture components. With increasing number of CCSS passages, the intensity of the deformation texture was hardly increased. The recrystallization texture resembled the deformation texture. The orientation stability was discussed by mean of Taylor deformation model and the formation of recrystallization textures was discussed by occurrence of the discontinuous recrystallization. Observations by transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) revealed the formation of ultra-fine grains in IF sheets deformed by CCSS.

Effect of Initial Textures on Texture Formation in AA 3004 Sheets during Continuous Confined Strip Shearing and Subsequent Annealing

The effect of initial textures on the texture formation during continuous confined strip shearing (CCSS) and subsequent annealing was investigated in AA 3004 sheets. The CCSS tools were designed to provide a constant shear strain of the order of 0.5 per pass while preserving the original sheet shape. During the CCSS deformation, the initial texture disappeared, and shear texture components developed. However, the intensity of the shear texture components did not further develop with an increasing number of CCSS passes. The softer initial sample depicting the cube texture displayed the evolution of {111}//ND fiber orientations. Upon recrystallization annealing, the textures developed during CCSS were randomized through the suppression of oriented nucleation and selected growth which generally dominate the evolution of recrystallization texture in cold rolled aluminum alloy sheets.

Effect of green density on subsequent densification and grain growth of nanophase SnO2 powder during isothermal sintering

Abstract The effect of green density on the subsequent densification and grain growth of nanophase SnO2 powder compacts during isothermal sintering has been investigated. Deagglomeration of the aggregates by applied pressure during compaction was proved to be crucial in subsequent densification and grain growth of nanophase SnO2 powder during sintering. A loose green compact with low coordination number exhibited rapid densification and grain growth in the initial sintering stage, while a dense green compact with high coordination number showed steady densification and very slow grain growth. The fine pores homogeneously dispersed in the dense green compact of the nanophase powder had a strong pinning effect on the grain boundary motion.