EBSD Investigation on Oriented Nucleation in IF Steels

The mechanism responsible for the formation of recrystallization texture in cold-rolled Ti bearing interstitial free （IF） steel sheets was investigated using electron back-scatter diffraction （EBSD）. In addition, the origin of nuclei with specific orientations was studied. The formation of recrystallization texture was explained by oriented nucleation. Most nuclei have a high misorientation angle of 25-55° with the surrounding deformed matrices, but no specific orientation of misorientation axis between the nucleus and the surrounding deformed matrix is observed. The stored energy of deformed grains is in the decreasing order of the {111}〈112〉,{111}〈110〉, {112}〈110〉 and {001}〈110〉 orientations. New {111}〈110〉 grains are nucleated within deformed {111}〈112〉 grains and new {111}〈112〉 grains originate in the deformed {111}〈110〉 grains.     

深冲IF钢再结晶{111}纤维织构形成机制探讨

为了探讨深冲IF钢再结晶织构与退火温度之间的关系及{111}再结晶织构形成机制,采用X射线衍射三维取向(ODF)和背散射电子衍射(EBSD)分析技术并结合金相组织观察,利用Gibbs-Thom son方程对冷轧IF钢在不同退火温度下的再结晶织构演变规律及形成机制进行研究.实验结果表明:随着退火温度的增加,再结晶量逐渐增多,γ纤维织构强度亦相应增强,同时,α纤维织构强度则逐渐降低;冷轧IF钢再结晶初期的织构转变主要发生在γ纤维织构之间.研究表明,再结晶核心的形成主要以"显微择优形核"为主,晶核的长大则主要以择优生长为主,而Σ重位点阵晶界在再结晶γ纤维织构形成过程中起着重要作用.     

Individual Grain Orientation and Heterogeneous Deformation in Cold-deformed Interstitial-Free Sheet Steel

The cold rolling deformation textural evolution of an interstitial-free （IF） steel sheet is investigated by experiment and simulation. The microstructure of the IF steel is observed by transmission electron microscopy （TEM）. The relationship between the deformation behavior of individual grain and the grain orientation are connected by Taylor factor M. The results show that the grains with higher Taylor factor are deformed slighter than those with lower ones. By considering the heterogeneous deformation, the texture simulation result can be greatly improved.     

Texture comparison of an ordinary IF steel and a high-strength IF steel under ferritic rolling and high-temperature coiling

The present work was performed to investigate the texture difference of an ordinary Ti-IF steel and a high-strength Ti-IF steel under ferritic hot rolling and high-temperature coiling. Comparing with the completely recrystallized textures of the ordinary IF steel, the textures of the high-strength IF steel were still deformed textures. The texture difference for the two steels is related to high P content in the high-strength IF steel which prevents the recrystallization during the coiling process. For the ordinary IF steel, the texture components were mainly very weak {001}110 orientation at the surface, and partial 110//RD (rolling direction) textures focused on {223}110 orientation and 111/ND (normal direction) texture at the mid-section and 1/4-section. For the high-strength IF steel, the texture components were mainly of {110}001 orientation at the surface and of a sharp 110//RD texture from {001}110 to {223}110 and weak 111/ND texture at the mid-section and 1/4-section.     

Microstructure and texture evolution in low carbon steel deformed by differential speed rolling (DSR) method

The study examined the microstructural and textural evolution of low carbon steel samples fabricated using a differential speed rolling (DSR) process with respect to the number of operations. For this purpose, the samples were deformed by up to 4-pass of DSR at room temperature with a roll speed ratio of 1:4 for the lower and upper rolls, respectively. The DSR technique applied to low carbon steel samples resulted in a microstructure composed of ultrafine ferrite grains, approximately 0.4 µm in size, after 4-pass with a high-angle grain boundary fraction of ~65 %. The microstructural features of the ferrite phase indicated the occurrence of continuous dynamic recrystallization, beginning with the formation of a necklace-like structure of ultrafine equiaxed grains around the elongated grains, which were formed in the early stages of deformation, and ending with ultrafine recrystallized grains surrounded by boundaries with high angles of misorientations. In the pearlite phase, the microstructural changes associated with DSR deformation were presented by the occurrence of bending, kinking, and breaking of the cementite lamellar plates. In addition, the evolution of texture after DSR processing was affected by shear deformation and rolling deformation, leading to the formation of a texture composed of fractions of components with shear texture orientations such as {110} 〈001〉 (Goss) and orientations close to {112} 〈111〉, in addition to rolling texture components consisting mainly of α-fiber and γ-fiber.     

Promotion of texture weakening in magnesium by alloying and thermomechanical processing. II: rolling speed

In the first part of this two-part paper, the effect of increasing Ce in solid solution on the recrystallization and texture evolution of four Mg–Zn–Ce sheets was investigated in the as-deformed and annealed state. In this second part, the effect of rolling speed on the microstructure and texture development of these alloys is evaluated. The effect of rolling speed on the recrystallization and texture evolution of four Mg–Zn–Ce sheets was investigated at as-deformed and different stages of annealing. The deformation microstructure was obtained through two stages that can be characterised as rough rolling and finish rolling. To study the effect of finish rolling temperature, one rolling pass with a 65 % reduction in thickness was performed at 300 and 450 °C and at rolling speeds of 15 and 1000 m/min. The results showed that by increasing the rolling speed, more secondary and compression twins were activated, which leads to the formation of more numerous local shear bands and a more uniform microstructure. Annealing secondary twins (S-twins) and their vicinity were observed to be the preferential sites for nucleation, and it seems that recrystallization on S-twins contributes to basal texture weakening. Therefore, an increasing number of such twins increase the texture weakening. In this way, the combination of these RE additions and HSR resulted in a weaker deformed and annealed texture.     

单相组织TWIP钢的扩孔性研究

超高强钢的扩孔性能是冲压成形的重要性质.为评价980 MPa TWIP钢的扩孔性能,本文以单相铁素体IF钢和980 MPa双相钢作为参考材料,用扫描电镜观察了3个钢种的微观组织,并对3个钢种进行了拉伸实验和扩孔实验,采用背散射电子衍射(EBSD)技术分析了拉伸后和扩孔实验后TWIP钢的微观组织.实验结果表明:拉伸前TWIP钢呈现类似于IF钢均匀的单相奥氏体组织,而拉伸后TWIP钢呈现类似于DP钢不均匀的硬质变形孪晶奥氏体和软质奥氏体;扩孔后TWIP钢的开裂位置集中在奥氏体和变形孪晶奥氏体界面;虽然TWIP钢显现出更大的均匀伸长率和加工硬化,但扩孔率明显小于IF钢.TWIP钢扩孔率增加源于早期孪晶诱发塑性(TWIP效应)导致的均匀变形.同时,这种变形机制导致组织中的硬质变形孪晶奥氏体,硬质变形孪晶奥氏体与软质奥氏体匹配(类似于双相钢中马氏体铁素体匹配)将恶化局部变形,阻碍扩孔性能进一步提升.     

The effect of SiC nanoparticles on deformation texture of ARB-processed steel-based nanocomposite

In this study, the influence of SiC nanoparticles on deformation texture of steel-based nanocomposite fabricated by accumulative roll bonding process was investigated. It was found that there was a texture transition from the rolling texture to the shear texture for both pure interstitial free steel and steel-based nanocomposite. However, the texture transition occurred in different cycles for the pure steel (the third cycle) and steel-based nanocomposite (the first cycle). It was realized that the fraction of low misorientation angle grain boundaries was decreased and the fraction of high misorientation angle grain boundaries was increased by the number of cycles. Also, recrystallization occurred in the pure steel and steel-based nanocomposite samples after the third and first cycles, respectively. In addition, the occurrence of recrystallization in steel-based nanocomposite was sooner than that of pure steel. At the early stage of dynamic recrystallization in processed steels, the {011}< 100 >-oriented grains were evolved and the fraction of grains with α-fiber and γ-fiber orientations was slightly decreased. The formation of the rolling texture in the steel-based nanocomposite samples was different from the typical rolling texture for the pure steel samples, due to the presence of the SiC nanoparticles in the nanocomposite. The weak rolling texture was attributed to the high stored energy of deformation, which was, in turn, due to low deformation temperature.     

Influence of rolling temperature on static recrystallization behavior of AZ31 magnesium alloy

Poor formability of rolled magnesium (Mg) alloys extremely restricts applications in form of sheets originating from formation of strong basal texture. Recently, we found that increasing rolling temperature from 723 to 798 K for a AZ31 Mg alloy can significantly improve stretch formability due to remarkable texture weakening after annealing. In this study, static recrystallization behaviors of AZ31 alloy sheets rolled at 723 and 798 K were investigated by electron backscattered diffraction analyses at different annealing stages in order to understand the origin of high temperature rolling on texture weakening. For both sheets, similar deformation microstructures with approximately the same types and fractions of twins exist in the as-rolled condition and recrystallized grains are mainly formed at pre-existing grain boundaries due to discontinuous recrystallization during subsequent annealing. However, only the basal texture of the latter remarkably weakens due to the formation of new recrystallized grains with well-dispersed orientations. Non-basal slips enhanced during high temperature rolling at 798 K are most likely responsible for the texture randomization as a result of rotations of recrystallization nuclei.     

Promotion of texture weakening in magnesium by alloying and thermomechanical processing: (I) alloying

The recrystallization and texture evolution of four Mg–Zn–Ce sheets with a warm-rolled microstructure obtained through two stages that can be characterised as rough rolling and finish rolling were investigated at different stages of post-rolling annealing. On annealing, the same regions of the microstructure, located by hardness indentations, were examined and tracked by electron backscatter diffraction (EBSD). Furthermore, intragranular misorientation axes (IGMA) analysis was used to investigate the associated deformation mechanisms in the as-deformed material. By combining these two methods, the development of the recrystallization microstructure was investigated and important aspects, such as preferential nucleation sites, correlation between activated deformation mechanism and initial orientation of the recrystallized grains, were studied. The results showed that the Mg–1Zn–1Ce alloy, which had the highest Ce/Zn ratio, showed the weakest as-rolled texture and the most homogenous distribution of shear banding/twinning. The IGMA analysis also showed that in Mg–1Zn–1Ce, other types of dislocations rather than basal 〈a〉 were activated; in particular, prismatic 〈a〉 type was activated during deformation. Therefore, the weakening of recrystallization texture during rolling resulting from the addition of RE elements was linked with a change in dynamic recrystallization (DRX) behaviour. Since the Mg–1Zn–1Ce alloy corresponds to the highest level of Ce in solid solution, the observed texture weakening was possibly due to decreasing grain boundary mobility as a result of solute partitioning of RE elements to dislocations and grain boundaries.     

Mesoscale Simulation of Recrystallization Textures and Microstructures

The paper presents mesoscale simulations of textures and microstructures formed during recrystallization. It gives an overview of the method and demonstrates how microstructure and texture simulations can be performed by incorporating realistic input data for the boundary character and for the initial deformation microstructure. Particular attention is placed on the simulation of primary static recrystallization in a deformed aluminum polycrystal on the basis of crystal plasticity finite element data. Various nucleation scenarios are discussed also with respect to macroscopic effects such as friction and shear localization.     

Stability against coarsening in ultra-fine grained aluminum alloy AA 3103 sheet fabricated by continuous confined strip shearing

The stability of ultra-fine grained Al–Mn alloy AA 3103 against coarsening at elevated temperature is analyzed. AA 3103 sheets were produced by means of continuous confined strip shearing (CCSS), which represents an adaptation of equal channel angular pressing to impose severe plastic deformation on sheet samples. With increasing number of CCSS passages, finer and more uniform grains with an increasing fraction of high-angle grain boundaries (HAGBs) were observed. In particular, the sample subjected to 12 passages of CCSS displayed fairly uniform equiaxed grains with an average size of 1.6 μm. During subsequent annealing at 300 and 350 °C, these grains were quite stable, exhibiting a rather low growth rate. This stability is explained in terms of Humphreys’ unified theory of the stability of cellular structures, which has shown that under conditions of very large strains when HAGBs prevail intrinsically stable microstructure will be formed.     

Texture mechanism in some fcc-type soft magnetic materials

The authors have studied the mechanism for recrystallization texture in some soft magnetic materials with fcc crystal structure. The alloys used were 77% Ni-14% Fe-5% Cu-4 wt% Mo permalloys. Thin foils selected area electron diffraction (SAD) and X-ray diffraction techniques were employed using a Philips 300 Electron Microscope (EM 300) and an X-ray diffractometer, respectively. Investigations were carried out on deformed, recovered and recrystallized states of the alloys. The various results show that the cold-rolled (deformed) and recovered states of the alloys possess copper-type of rolling texture with {110} 〈112〉 texture as the predominant deformation texture though other minor components such as {112} 〈111〉, {110} 〈001〉 and {123} 〈420〉 textures were detected. No cube texture, {100} 〈001〉 was detected in any of the deformed and recovered materials though the recrystallization texture in these alloys is the cube texture, {100} 〈001〉 which forms over 80% of the annealing texture in these alloys. It is concluded here that the detection of cube texture in the deformed and recovered materials is not a prerequisite for the detection of cube texture in these alloys. The present work is not conclusive about the mechanism for recrystallization texture, but it is proposed here that recrystallization texture, in these alloys is attributed to the growth-oriented mechanism based on the following model. (1) The lattice domains which form the recrystallization texture are present in the cold-rolled matrix. (2) The favoured site for nucleation are the grain boundaries and deformation band boundaries. (3) For the nucleus to be able to grow and form the recrystallization texture it must possess the necessary free energy. (4) Grains must be capable of growth into two or more orientations between which it forms, i.e. the nuclei which form the cube texture should have a [111] pole in common with the matrix in which they grow and a rotation of about 30° around this pole.     

温轧温度对Cr-Ti-B系低碳钢组织与织构的影响

使用扫描电镜、电子背散射衍射、透射电子显微镜和固体内耗仪研究了温轧温度对Cr-Ti-B系低碳钢组织和织构的影响.结果 表明,温轧后钢的组织由变形铁素体和少量珠光体所组成,随着温轧温度的提高铁素体晶内剪切带的含量呈现先提高后降低的趋势,在450℃温轧剪切带的含量最高.剪切带的形成,与Ti和B元素的偏聚密切相关.在350℃...     

Deformation, Phase Transformation and Recrystallization in the Shear Bands Induced by High-Strain Rate Loading in Titanium and Its Alloys

α-titanium and its alloys with a dual-phase structure (α β) were deformed dynamically under strain rate of about 104 s-1. The formation and microstructural evolution of the localized shear bands were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that both the strain and strain rate should be considered simultaneously as the mechanical conditions for shear band formation, and twinning is an important mode of deformation. Both experimental and calculation show that the materials within the bands underwent a superhigh strain rate (9×105 s-1) deformation, which is two magnitudes of that of average strain rate required for shear band formation; the dislocations inthe bands can be constricted and developed into cell structures; the phase transformation from α to α2 within the bands was observed, and the transformation products (α2) had a certain crystallographic orientation relationship with their parent; the equiaxed grains with an average size of 10μm in diameter observed within the bands are proposed to be the results of recrystallization.     

Effects of Primary Annealing Condition on Recrystallization Texture in a Grain Oriented Silicon Steel

The recrystallization texture in grain oriented silicon steel sheets, which were annealed at different primary annealingtemperatures with and without an electric field, was investigated. An automated electron backscattered diffraction(EBSD) technique was used to analyze the recrystallization texture. It was found that recovery and application ofelectric field in primary annealing lead to an increase of {001} component and a decrease of {111} component afterannealing at 900℃. The development of recrystallization texture can be explained in terms of the effects of electricfield and primary annealing temperature on recovery.     

Formation of a random texture and ultrafine grains in AA 3003 aluminium alloy during the repeated shear deformation introduced by continuous confined strip shearing

Abstract

To investigate the microstructural development and corresponding texture evolution during repeated shear deformation, specimens of AA 3003 Aluminium alloy were deformed by continuous confined strip shearing based on equal channel angular pressing. Strip specimens were deformed by the shear forming process during up to eight passes, equivalent to effective strains of ~4.8. Texture evolution in the AA 3003 strips during the shear deforming process was studied by comparing the experimentally measured textures with simulated ones. Electron backscattered diffraction was employed to investigate detailed changes in microtextures and microstructures during repeated shear deformation. Softening associated with deformation is believed to be responsible for the formation of ultrafine grains and the random texture resulting from repeated shear deformation.     

无取向硅钢形变储能取向依赖性及其对再结晶织构的影响

采用晶体塑性有限元模拟与实验相结合的方式,研究无取向硅钢冷轧过程中不同初始织构组分的取向流动与形变储能累积。结果表明:冷轧后形成了较强的α,γ形变织构和较弱的λ形变织构。再结晶织构由γ,α,η和λ织构组成,其取向密度依赖于冷轧压下率。随冷轧压下率增大,λ再结晶织构逐渐增强,η织构先增强后减弱,γ织构先减弱后增强,α织构稍有弱化。冷轧过程中形变储能累积具有明显的初始取向依赖性,初始γ取向储能累积速率在低于50%压下率时与初始α取向接近,高于50%压下率时则明显大于后者,初始λ取向储能累积速率始终显著低于γ和α取向,转至同一形变取向的不同初始取向间的储能累积也会产生差异。冷轧过程中不同初始织构组分的取向流动与形变储能累积规律,决定了无取向硅钢再结晶织构组分的发展。     

Formation of textures and microstructures in asymmetrically cold rolled and subsequently annealed aluminum alloy 1100 sheets

The formation of textures and microstructures in asymmetrically cold rolled and subsequently annealed AA 1100 sheets was investigated. The asymmetrical rolling procedure in this experiment was performed in a rolling mill with different roll velocities (roll velocity ratio of 1.5/1.0). In order to enhance the shear deformation, asymmetrical rolling was performed by a large reduction per pass and without lubrication. Asymmetrical rolling led to the formation of strong shear textures. The evolution of asymmetrically cold rolled textures was analyzed by FEM simulations. After recrystallization annealing, pronounced {111}//ND orientations prevailed in all thickness layers. Intensified shear deformations by asymmetrical rolling also led to the formation of ultra-fine grains after recrystallization annealing.     

Electron backscatter diffraction study of deformation and recrystallization textures of individual phases in a cross-rolled duplex steel

The evolution of microstructure and texture during cross-rolling and annealing was investigated by electron backscatter diffraction in a ferritic–austenitic duplex stainless steel. For this purpose an alloy with nearly equal volume fraction of the two phases was deformed by multi-pass cross-rolling process up to 90% reduction in thickness. The rolling and transverse directions were mutually interchanged in each pass by rotating the sample by 90° around the normal direction. In order to avoid deformation induced phase transformation and dynamic strain aging, the rolling was carried out at an optimized temperature of 898 K (625 °C) at the warm-deformation range. The microstructure after cross warm-rolling revealed a lamellar structure with alternate arrangement of the bands of two phases. Strong brass and rotated brass components were observed in austenite in the steel after processing by cross warm-rolling. The ferrite in the cross warm-rolling processed steel showed remarkably strong RD-fiber (RD//< 011 >) component {001}< 011 >. The development of texture in the two phases after processing by cross warm-rolling could be explained by the stability of the texture components. During isothermal annealing of the 90% cross warm-rolling processed material the lamellar morphology was retained before collapse of the lamellar structure to the mutual interpenetration of the phase bands. Ferrite showed recovery resulting in annealing texture similar to the deformation texture. In contrast, the austenite showed primary recrystallization without preferential orientation selection leading to the retention of deformation texture. The evolution of deformation and annealing texture in the two phases of the steel was independent of one another.