Orientation imaging microscopy studies of recrystallization in interstitial-free steel

The origin of the γ fiber recrystallization texture in interstitial-free (IF) steel developed during continuous annealing has been investigated by scanning electron microscopy (SEM) and orientation imaging microscopy (OIM). Nucleation of {111∼<uvw> oriented crystals occurs in deformation banded γ grains and therefore a comprehensive study of microstructure of cold-rolled IF steel in the sections perpendicular to the rolling and transverse directions (TDs) and the rolling plane (RP) has been carried out to understand the formation, geometry, and microstructural features of recrystallization. The RP section gave abundant evidence of orientation gradients formed in γ oriented grains that had been subject to orientation splitting to give deformation bands. These orientation gradients across a single grain are around 5 to 30 deg and this orientation difference is sufficient to form nuclei with mobile interfaces during annealing and hence to create chains of γ oriented new grains in the original hot band γ grain envelopes. A grain impingement model requiring orientation pinning is then proposed to explain how these grains, contained in deformed γ grain envelopes, grow out into their neighbors to dominate the final recrystallization texture of IF steel. The α deformed grains contain only small lattice curvatures, and therefore in-grain nucleation is rare. These grains are mostly consumed by invading γ grains toward the end of the recrystallization process.     

Orientation imaging microscopy studies of recrystallization in interstitial-free steel

The origin of the γ fiber recrystallization texture in interstitial-free (IF) steel developed during continuous annealing has been investigated by scanning electron microscopy (SEM) and orientation imaging microscopy (OIM). Nucleation of {111} «uvw» oriented crystals occurs in deformation banded γ grains and therefore a comprehensive study of microstructure of cold-rolled IF steel in the sections perpendicular to the rolling and transverse directions (TDs) and the rolling plane (RP) has been carried out to understand the formation, geometry, and microstructural features of recrystallization. The RP section gave abundant evidence of orientation gradients formed in γ oriented grains that had been subject to orientation splitting to give deformation bands. These orientation gradients across a single grain are around 5 to 30 deg and this orientation difference is sufficient to form nuclei with mobile interfaces during annealing and hence to create chains of γ oriented new grains in the original hot band γ grain envelopes. A grain impingement model requiring orientation pinning is then proposed to explain how these grains, contained in deformed γ grain envelopes, grow out into their neighbors to dominate the final recrystallization texture of IF steel. The α deformed grains contain only small lattice curvatures, and therefore in-grain nucleation is rare. These grains are mostly consumed by invading γ grains toward the end of the recrystallization process.     

退火工艺对冷轧高强IF钢组织及织构的影响

为了观察高强IF钢退火处理后的显微组织和再结晶织构的变化规律,采用两种不同退火工艺对高强IF钢进行热处理。结果表明,IF钢在两种退火方式下均形成了γ-{111}纤维织构,快速升温(350℃/min)退火时,再结晶新核呈等轴状,由变形带内的亚晶合并形成,与冷轧变形基体保持相同取向。慢速升温(2℃/min)退火时,新核在晶界弓出形成,且沿轧制方向呈饼形分布,与基体没有明显取向关系。慢速升温退火样品的γ-{111}取向密度强于快速升温的。对进一步改善薄板钢深冲性能具有指导作用。     

Development of recrystallization textures in 0.08%C steel

The present work investigates the effect of cold deformation on the evolution of microstructure and textures during recrystallization in 0.08%C steel. The cold rolling texture consists of partial α-fiber (RD//〈110〉) and complete γ-fiber (ND//〈111〉) along with Goss ({110}〈001〉) and cube ({100}〈100〉}) texture components. The sharpness of α-fiber, γ-fiber and cube component increases with the increase in rolling reduction from 70 to 85% while that of Goss component decreases. After recrystallization (750 and 800°C), the textures were composed of α and γ-fiber along with significant Goss components. The strength of γ-fiber decreases after annealing. The presence of Goss component in recrystallization textures is attributed to preferential nucleation in {111}〈112〉 type deformed grains.     

异步轧制取向硅钢的织构形成与转变机理

采用异步轧制方式将０．７５ ｍ ｍ 厚的工业取向硅钢板材冷轧至０．３５ ｍ ｍ ,然后用工业退火工艺对板材进行热处理,研究了剪切变形条件下的织构形成与转变机理。结果表明：双向轧制能有效地消除剪切应力导致织构组分偏离的影响,并获得比常规轧制板材更为理想的冷轧织构组态;亚表层上形成较强的｛１１１｝＜ １１２＞ 织构可能是源于不同于其它层的特殊形变方式;脱碳退火后板材亚表层上的Ｇｏｓｓ晶粒与绝大多数晶粒都有单轴重合的取向关系,这种特殊性可能是Ｇｏｓｓ晶粒在二次再结晶退火中能够异常长大的一种机制。     

Aspects of orientation-dependent grain growth in extra-low carbon and interstitial-free steels during continuous annealing

The present work concentrates on the application of orientation imaging microscopy (OIM) based on the electron backscattered diffraction (EBSD) technique to the investigation of the microstructural evolution of an extra-low carbon (ELC) steel and a Ti-Nb-bearing interstitial-free (IF) steel, during continuous annealing. Aspects like the nucleation, the evolution of the recrystallized volume fraction and grain size of grains with different orientations, the interface area limiting recrystallized {111} regions, and the apparent growth rates have been considered. Different criteria have been applied in order to identify crystallites produced during annealing. During the first stages of annealing, a network of grain boundaries with misorientations higher than 10 deg is produced, mainly inside the deformed γ-fiber grains. The crystallites formed within this network, free from cells or subgrains at their interiors, can be considered as potential nuclei. However, among all, only some of them become effective due to an important selection. The {111} recrystallized grains have a significant size and number advantage as compared with other texture components, and a hard impingement between clusters of {111} grains is produced during grain growth. The effect of grain growth behind the recrystallization front seems to be negligible as compared with the grain coarsening produced by the migration of this front, driven by the cold-work stored energy.     

Aspects of Orientation-Dependent grain growth in extra-low carbon and interstitial-free steels during continuous annealing

The present work concentrates on the application of orientation imaging microscopy (OIM) based on the electron backscattered diffraction (EBSD) technique to the investigation of the microstructural evolution of an extra-low carbon (ELC) steel and a Ti-Nb-bearing interstitial-free (IF) steel, during continuous annealing. Aspects like the nucleation, the evolution of the recrystallized volume fraction and grain size of grains with different orientations, the interface area limiting recrystallized {111} regions, and the apparent growth rates have been considered. Different criteria have been applied in order to identify crystallites produced during annealing. During the first stages of annealing, a network of grain boundaries with misorientations higher than 10 deg is produced, mainly inside the deformed γ-fiber grains. The crystallites formed within this network, free from cells or subgrains at their interiors, can be considered as potential nuclei. However, among all, only some of them become effective due to an improtant selection. The {111} recrystallized grains have a significant size and number advantage as compared with other texture components, and a hard impingement between clusters of {111} grians is produced during grain growth. The effect of grain growth behind the recrystallization front seems to be negligible as compared with the grain coarsening produced by the migration of this front, driven by the cold-work stored energy. J.L. Bocos, formerly Researcher with CEIT     

Evolution of Microstructure and Texture During Deformation and Recrystallization of Heavily Rolled Cu-Cu Multilayer

A Cu-Cu multilayer processed by accumulative roll bonding was deformed to large strains and further annealed. The texture of the deformed Cu-Cu multilayer differs from the conventional fcc rolling textures in terms of higher fractions of Bs and RD-rotated cube components, compared with the volume fraction of Cu component. The elongated grain shape significantly affects the deformation characteristics. Characteristic microstructural features of both continuous dynamic recrystallization and discontinuous dynamic recrystallization were observed in the microtexture measurements. X-ray texture measurements of annealing of heavily deformed multilayer demonstrate constrained recrystallization and resulted in a bimodal grain size distribution in the annealed material at higher strains. The presence of cube- and BR-oriented grains in the deformed material confirms the oriented nucleation as the major influence on texture change during recrystallization. Persistence of cube component throughout the deformation is attributed to dynamic recrystallization. Evolution of RD-rotated cube is attributed to the deformation of cube components that evolve from dynamic recrystallization. The relaxation of strain components leads to Bs at larger strains. Further, the Bs component is found to recover rather than recrystallize during deformation. The presence of predominantly Cu and Bs orientations surrounding the interface layer suggests constrained annealing behavior.     

Twinning-induced sluggish evolution of texture during recrystallization in AISI 316L stainless steel after cold rolling

This paper deals with the evolution of texture in AISI 316L austenitic stainless steel during annealing after 95 pct cold rolling. After 95 pct cold rolling, the texture is mainly of the brass type {110}〈112〉, along with a scatter toward the S orientation {123}〈634〉 and Goss orientation {011}〈100〉. Weak evidence of Cu component is observed at this high deformation level. During annealing, recovery is observed before any detectable recrystallization. Recrystallization proceeds through nucleation of subgrain by twinning within the deformed matrix and, later, preferential growth of those to consume the deformed matrix. After recrystallization, the overall texture intensity was weak; however, there are some discernible texture components. There was no existence of the brass component at this stage. Major components are centered on Goss orientation and Cu component {112}〈111〉 as well as the BR component {236}〈385〉. Also, a few orientations come up after recrystallization (i.e., {142}〈2−11〉 and {012}〈221〉). With increase in annealing temperature, the textural evolution shows emergence of weak texture with another new component, {197}〈211〉. The evolution of texture was correlated with the deformation texture through twin chain reaction.     

Formation of Nuclei With {111}<110> and {111}<112> Orientations of IF Steel at Early Stage of Recrystallization Using EBSD Analysis

The excellent deep drawability of interstitial free steel (IF steel) is closely related to its texture formed during recrystallization. The nucleation process of cold rolled IF steel at the early stage of recrystallization was investigated by electron back scattered diffraction (EBSD). The characteristics of the microstructure after deformation and the orientation of nucleation were observed. The results show that the deformed microstructure with 80% reduction could be subdivided into two groups. These two types of microstructure were characterized by their orientation and internal local misorientations. The nuclei with γ-orientation preferred to form in deformed bands with γ-orientation and at the boundaries between deformed grains with different orientations. The recrystallized grains with {111}<110> orientation appeared firstly in deformed matrix with {111}<112> orientation and consumed the matrix with {111}<112> to grow up, while the recrystallized grains with {111}<112> orientation were observed secondly in deformed matrix with {111}<110> orientation and consumed matrix with {111}<110> to grow up.     

Evolution of Microstructure and Texture during Annealing of Aluminum AA1050 Cold Rolled to High and Ultrahigh Strains

The microstructure and texture of commercial purity aluminum (AA1050) have been investigated after cold rolling to von Mises strains of 3.6 to 6.4 followed by recovery and recrystallization during annealing. The evolution of structural parameters of the deformed microstructure, such as boundary spacing and fraction of high-angle boundaries (HABs), did not reach saturation in the given strain range. Recovery was accompanied by structural coarsening and by a decrease in the fraction of HABs. The coarsening rate increased with increasing strain prior to annealing. Recrystallization nuclei were found to form both in deformation zones around coarse particles and in recovered lamellar structures. The process of recrystallization in the present material can thus be characterized as discontinuous recrystallization. In recrystallized conditions, the average grain size was related to the grain orientation: the mean size of grains having orientations of the rolling texture was smaller than the size of grains with other orientations. The orientation dependence of the recrystallized grain size was more pronounced in the samples rolled to ultrahigh strains.     

Observation of cold-rolling texture and partially recrystallized texture in polycrystalline 3 pct Si-Fe by high-resolution electron backscattered diffraction

Cold-rolling texture and partially recrystallized texture of polycrystalline 3 pct Si-Fe were investigated using high-resolution electron backscattered diffraction (EBSD) method. From the measurement on a deformed grain with {211}〈011〉∼{111}〈011〉 orientations, deformation bands with {12 4 1}〈014〉 orientation were found. It turned out that the orientation rotation relationship between deformation bands and surrounding deformed grain can be explained by the activation of the slip system, which has a common slip plane with an adjacent grain. Oriented nucleation of recrystallized grains with {12 4 1}〈014〉 orientation was observed in a deformed grain with {211}〈011〉∼{111}〈011〉 orientation. Exactly the same orientation relationship that was observed between deformed grain and the deformation bands was also observed between the deformed grain and the recrystallized grain. A hypothesis that recrystallization nuclei are generated directly from the deformation bands formed by an activation of the slip system that has a common slip plane of neighboring deformed grains was proposed from the present experimental results.     

Effect of cold rolling and mode of annealing on textures,mechanical properties and formability limit diagrams in interstitial free steel sheets

Formability limit diagram (FLD) and strain limits are determined along with mechanical properties and the same are correlated with textural characterization as a function of degree of rolling in an interstitial free (IF) steel. Around 65–70% and 85–90% hot deformation were given in austenitic region. It was found that 85–90% deformation developed strong hot band texture and the texture was dominated by {112}〈110〉 and {332}〈113〉 orientations. Hot rolled steel sheets were then cold rolled to 50%, 70%, 80% and 90%, where the perfect α-fiber and γ-fiber textures were developed at 80% cold reduction. Excellent formability was obtained by batch as well as continuous mode of annealing. The new γ-fibers were developed after annealing. It was observed that IF steel sheet has to be cold rolled between 80% and 90%. From FLD plots, it was observed that IF steel sheets were highly formable.     

中温含铜取向硅钢的形变和再结晶织构特征

通过对比中温含铜取向硅钢与普通取向硅钢和高磁感取向硅钢的组织和织构特征,分析中温含铜取向硅钢独特的织构演变规律及其对二次再结晶行为的影响.结果表明,为了获得有利于高斯晶粒长大的强γ取向线织构,中温含铜钢需经过回复退火处理和高温退火阶段慢速升温.回复过程中γ取向线晶粒储能降低,同时慢速升温有利于γ取向线晶粒的形核和再结晶.中温含铜钢的二次再结晶开始温度超过1000℃,由于初次再结晶晶粒组织以γ织构为主且非γ取向线晶粒较少,导致最终二次晶粒尺寸超大且晶界圆滑,二次再结晶机理以择优长大为主导,超大的二次晶粒尺寸导致最终成品的铁损升高,但通过激光刻痕处理后,整体铁损的降低效果比二次晶粒较小的高磁感取向硅钢更加显著.      

Effect of two step cold rolling — continuous annealing on micro-structures,textures and mechanical properties in IF and IF-HS steel sheets

In the present work, the objectives were to investigate the type of microstructure and texture that developed after two step cold rolling — continuous annealing. Further, an attempt has been made to correlate the microstructure and texture with mechanical properties. Interstitial free (IF) and interstitial free — high strength (IF-HS) steel sheets which contain almost γ-fiber textures, were subjected to two step cold rolling for different percentage of reduction and further continuously annealed. It was observed that cold rolling strengthened the region of (223)[1$ \bar 1 $ \bar 1 0] and 335[1$ \bar 1 $ \bar 1 0] orientations of α-fiber as well as γ-fiber. After continuous annealing, cold rolled γ-fiber as well as (223)[1$ \bar 1 $ \bar 1 0] and 335[1$ \bar 1 $ \bar 1 0] orientations transformed to extremely strong new γ-fiber. It was found that at two steps 80% cold rolling -continuous annealing, drawability of IF steel sheet was exceptionally high i.e. around 3.15, whereas for IF-HS steel sheets, it was around 2.7. Although, two steps cold rolling -continuous annealing enhanced percentage elongation and stretchability exceptionally, but it reduced the yield strength substantially. However, ultimate tensile strength was hardly affected. In addition, it is also observed that two steps cold rolling — continuous annealing developed uniform grain size in both the grades of steel sheets.     

Modeling texture change during the static recrystallization of interstitial free steels

A recrystallization model was developed based on the principal features of oriented nucleation and selective growth. The nucleation mechanism that is adopted assumes that nucleation takes place in deformed grains with relatively high Taylor factors. The selective growth law is based on the assumed high mobility of {110} plane matching (PM) boundaries and also includes a variant selection rule. The two submodels enable the full recrystallization process to be simulated. The theory is applied to the annealing of a Ti-Nb alloyed interstitial free (IF) steel. It is demonstrated that the nucleation and growth algorithms can successfully account for the annealing textures observed, including the presence of a strong {111}<211> component. An important feature of the model is that it permits the role of variant selection to be assessed; it also shows the effect on the texture of the low mobility of low-angle grain boundaries (LAGBs).     

Quantitative Analysis of Micro‐Textures during Recrystallization in an Interstitial‐Free Steel

Two interstitial‐free steel samples were prepared by normal and by cross rolling. The effect of the resulting different deformation textures and microstructures on the subsequent recrystallization behavior was studied by micro‐texture analysis. The differences in recrystallization textures of the two differently rolled samples can be attributed to the microstructural differences in the as‐deformed state. The orientation distribution of the recrystallized grains forming at the early stages of the recrystallization dominated the final recrystallization textures, pointing to the importance of oriented nucleation in the formation of recrystallization textures of interstitial‐free steels.     

On the origin of the R orientation in the recrystallization textures of aluminum alloys

The crystallographic textures of most Al alloys, after rolling and recrystallization, are composed of two components, the cube orientation {001}〈100〉 and a component similar to the former rolling texture, the so-called R orientation {124}〈211〉. The R orientation can be retained from the rolling texture in cases where the stored dislocation energy is being reduced merely through extended recovery reactions, which is referred to as continuous recrystallization. In addition, R-oriented grains can form through genuine, discontinuous recrystallization by nucleation within S-oriented grains at the grain boundaries between the deformed bands and a subsequent growth selection as caused by orientation pinning. The strength of the R orientation in the recrystallization textures strongly depends on the pretreatment and processing parameters of the material and, in particular, on the alloy investigated. The present article gives a survey of the factors affecting the R orientation and reviews recent results on the formation mechanisms of this orientation, which have been obtained by local texture analysis. The results are discussed with regard to the competition of the R orientation with the cube orientation during the evolution of the recrystallization textures in Al alloys.     

高性能取向硅钢的工业化生产研究

采用光学显微镜、X射线衍射仪等分析了宁波钢铁有限公司生产的取向硅钢不同工序下的组织及织构演变规律.结果 表明:铸坯经过热轧后,沿着厚度方向组织不均匀;一次冷轧并经脱碳退火后,组织由条状纤维状变成等轴状的初次再结晶晶粒,初次再结晶平均晶粒尺寸为18.17 μm,织构主要以α织构和γ织构为主;在二次冷轧后,晶粒再次被压缩,转变为纤维状,织构主要为γ织构;经过高温退火后,发生二次再结晶,晶粒异常长大,晶粒尺寸达到厘米级,织构成分为单一且锋锐的Goss织构.     

Fe-6.5%Si合金温轧后退火过程中再结晶行为

用电子背散射技术观察了700℃温轧板在退火过程中的组织及织构演变以了解其再结晶行为.结果表明,温轧织构由强的（111）〈112〉、较弱的〈110〉∥RD及Goss组成,再结晶织构与之相似.〈110〉∥RD及（111）〈112〉新晶粒首先形成于与之构成小角度晶界的形变晶粒的晶界附近,而在角隅及组织不均匀区等位置孕育出与周围晶粒构成大角度晶界的晶核,择优取向不明显.退火过程中（111）〈112〉在形变组织中累积,最终转化为（111）〈112〉再结晶晶粒.分析认为,温轧后退火是不均匀组织在低储存能驱动下的再结晶过程.（112）〈110〉及（111）〈112〉形变拉长晶粒多发生连续再结晶从而退火织构与形变态相似.在角隅区形成核心进而发生不连续再结晶,核心取向的统计性及不连续晶核的长大弱化再结晶织构,其中Goss晶粒多以此方式形成于（111）〈112〉晶粒内部.