Effect of the size and dispersion of precipitates formed in hot rolling on recrystallization texture in ferritic stainless steels

In the present paper, the size and dispersion of precipitates in ferritic stainless steels have been varied by applying different hot rolling processes, the effect of which on the evolution of recrystallization textures was investigated. The precipitate characterization was observed and studied by transmission electron microscopy and the texture evolution processes were characterized by X-ray diffraction and electron backscattering diffraction. The results show that low temperature finish rolling can promote the formation of a large number of fine and dense TiC precipitates in hot band. These fine and dense precipitates can be inherited in the final sheet, and are beneficial to facilitating the nucleation of randomly oriented grains by promoting the formation of inhomogeneous cold rolled microstructure, strongly suppressing the growth of recrystallized grains by pinning grain boundary migration, thereby weakening the formation of γ-fiber recrystallization texture and deteriorating the formability of final sheet. By contrast, strong γ-fiber recrystallization texture is developed in the sample with sparsely distributed coarse precipitates. Therefore, the size and dispersion of precipitates formed in hot rolling have significant effects on the nucleation of randomly oriented grains and the growth of recrystallized grains during recrystallization annealing, which play important roles in controlling the γ-fiber recrystallization texture in ferritic stainless steels.     

Evolution of Microstructure and Texture during Hot Deformation of a Commercially Processed Supral100

The microstructure and texture in a commercially processed Al-6 wt% Cu-0.4 wt% Zr(Supral100) aluminium alloy have been investigated after annealing and hot tensile straining at 450 ℃,using a field emission gun scanning electron microscope(SEM) and electron backscatter diffraction(EBSD).The microstructure of commercially processed alloy had a relatively large fraction of high angle grain boundaries(HAGBs) which were aligned parallel to the rolling direction,and a strong texture.Annealing at 450 ℃ led to an increase in the fraction of HAGBs and to an increase in HAGB spacing and these changes were progressively enhanced by subsequent tensile deformation.The increasing fraction of HAGBs was due to the annihilation of low angle grain boundaries(LAGBs).A sharpening of texture during annealing was attributed to preferential textural growth,and the reduction of texture at higher tensile strains led to the development of superplastic behaviour.The present work supports the view that the evolution of the fine grain microstructure during the high temperature straining of Supral100 is primarily due to the accumulation of a large area of grain boundary during the initial thermomechanical processing,and does not involve any unusual restoration processes.     

Texture and microstructure development during hot deformation of ME20 magnesium alloy: Experiments and simulations

The influence of deformation conditions and starting texture on the microstructure and texture evolution during hot deformation of a commercial rare earth (RE)-containing magnesium alloy sheet ME20 was investigated and compared with a conventional Mg sheet alloy AZ31. For all the investigated conditions, the two alloys revealed obvious distinctions in the flow behavior and the development of texture and microstructure, which was primarily attributed to the different chemistry of the two alloys. The presence of precipitates in the fine microstructure of the ME20 sheet considerably increased the recrystallization temperature and suppressed tensile twinning. This gave rise to an uncommon Mg texture development during deformation. Texture simulation using an advanced cluster-type Taylor approach with consideration of grain interaction was employed to correlate the unique texture development in the ME20 alloy with the activation scenarios of different deformation modes.     

Microstructure and texture evolution in continuously cooled AA 3004 hot rolled sheet

Abstract

A quantitative study of variations in microstructure and texture evolution in the through thickness direction of industrially hot rolled AA 3004 aluminium alloy has been carried out. The microstructural features of the specimens were examined with the aid of the electron channelling contrast technique in conjunction with an image analysis system. The number of recrystallised grains and the size distributions of coarse and fine intermetallics were measured to evaluate the variation between surface and centre. Significant differences in the number of recrystallised grains and the average size of coarse intermetallics in the through thickness direction of the hotband were observed. After isothermal annealing of the hotband for various times the fine intermetallic area fraction increased and was higher at the centre than at the surface. Quantitative texture analysis was carried out on the specimens and various texture components estimated to characterise the through thickness texture evolution. The proportion of cube texture component was higher near the surface than at the centre and this difference increased after isothermal annealing. Since negligible change occurred in the cube content of the centre specimen, growth of cube grains was deduced to have taken place primarily near the surface region. These observations illustrate that mechanisms of cube texture formation, heterogeneous nucleation of precipitates causing retarded recrystallisation, and Zener drag are evidently applicable even to complex commercial alloys.

MST/1849     

Grain morphology and texture evolution of TC21 titanium alloy during annealing with different time

A homogeneous equiaxed‐structure TC21 titanium alloy is hot rolled and annealed for different time ranging from 1 h to 6 h. The grain morphology and texture evolution of α and β phases during annealing are mainly investigated using the electron back‐scattered diffraction characterization. In the early annealing stage, the α grain mainly maintains the elongated morphology generated in the rolling. With increasing annealing time, more and more elongated α grains become equiaxed due to enhanced static recrystallization and boundary splitting. Differently, the β grain exhibits a fully equiaxed morphology all the time due to the sufficient static recrystallization, and get a coarsening with increasing annealing time. The α phase exhibits a (0001) basal texture in the early annealing stage, and then forms a TD‐split texture with increasing annealing time. The β phase exhibits the {001}<110> texture at every annealing time. Based on the analysis about the texture of different grain sizes, the effects of recrystallization nucleation and oriented growth on texture evolution are discussed. It suggests that TD‐split texture in α phase is originated from both the recrystallization nucleation and oriented growth. The formation of {001}<110> texture in β phase is mainly originated from the oriented growth.     

Microstructure Evolution during Friction Stir Welding of Aluminum Alloy AA2219

The characterization of microstructure evolution in friction stir welded aluminum alloy was carried out by optical microscopy (OM) and transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The weld nugget consisted of very fine equiaxed grains and experienced dissolution of nearly half of metastable precipitates into the matrix during welding. Thermomechanically affected zone (TMAZ) also experienced dissolution of precipitates but to a lesser extent whereas coarsening of precip...     

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.     

Microstructure and texture evolution in hot rolled AA 3004 aluminium alloy

Abstract

The evolution of microstructure and texture in industrially hot rolled AA 3004 aluminium alloy has been studied. Specimens were subjected to isothermal annealing treatments and the recrystallisation kinetics was determined via measurement of changes in hardness at surface and centre locations. Metallographic examination of specimens was performed using electron channelling contrast. With the aid of an image processor, the Mg₂Si precipitate count and size distributions were obtained. A significant increase in the number of precipitates was observed to occur after the completion of recrystallisation. Quantitative texture analysis was performed on the tapered specimens to characterise the through thickness effect. The quantity of cube texture component was shown to be higher at the surface than at the centre location and decreased with increasing exit temperature of the hotband.

MST/1564     

Surface mechanical attrition treatment-induced dissolution of Cu4Ti precipitates in Cu–4wt-%Ti alloy

ABSTRACT

The microstructural evolution of an overaged Cu-4wt-%Ti alloy associated with surface mechanical attrition treatment (SMAT) has been studied by X-ray diffraction, scanning electron microscope and transmission electron microscopy. The results show that β-Cu₄Ti precipitates in the topmost surface layer were dissolved after SMAT, and Cu solid solution phase with a fine grain size of approximately 25?nm was observed. Dislocation activities were the main deformation mechanism of lamellar structure in the overaged Cu–4wt-%Ti alloy. The twinning in lamellar Cu phase was inhibited by the β-Cu₄Ti precipitates.     

Microstructure‐texture‐fracture toughness property correlation in annealed Al‐6Mg alloy with minor scandium and zirconium additions

The effect of minor addition of scandium and zirconium on the fracture toughness (FT) behaviour of aluminium‐6 wt% magnesium alloy is studied. Texture measurement and transmission electron microscopy have revealed that the evolution of texture in cast alloys after annealing is decided by the morphology and character of the precipitates. It is further demonstrated that the said minor addition influences the FT behaviour of Al‐6Mg alloy by manipulating in‐plane anisotropy as decided by the precipitate morphology. Textural situation in annealed state has also been related to the FT behaviour.     

预处理工艺对双辊铸轧3003铝合金再结晶行为的影响

对双辊铸轧3003铝合金板材进行了3种预处理退火,研究不同预处理工艺下的冷轧板材在380～500℃退火时晶粒组织和再结晶织构的变化规律。结果表明:最优化预处理工艺为610℃/12h+460℃/12h,高温阶段第二相尺寸发生粗化,低温阶段基体中Mn的过饱和固溶度显著降低,两者均有利于提高后续退火时的再结晶形核率。500℃退火时,在粗大第二相的附近产生了粒子诱发形核机制,降低了再结晶织构强度;并且退火时几乎不存在析出,析出相对再结晶形核的抑制作用甚微,从而得到了晶粒细小、织构弱的再结晶组织。     

形变和退火对Fe47Mn30Co10Cr10B3间隙高熵合金微观组织结构演变的影响

在不同温度对Fe₄₇Mn₃₀Co₁₀Cr₁₀B₃间隙高熵合金进行不同的形变和退火处理,使用电子背散射衍射和电子通道衬度像等手段对样品进行表征,研究了形变和退火对其微观组织结构演变的影响。结果表明,在小应变量条件下,随着形变温度的降低,主导的形变机制从位错滑移转变为相变诱导塑性;在室温形变条件下,随着应变量的增大,主导的形变机制由位错滑移转变为相变诱导塑性。对大应变量的样品退火,随着退火温度的提高,微观组织从形变态(600℃-5 min)、部分再结晶态(800℃-5 min)到完全再结晶态(1000℃-5 min)的演变。在1000℃退火条件下,随着退火时间的延长,微观组织由部分再结晶态(1 min)演变到完全再结晶态(5 min和15 min),且相组成由γ单相演变为γ+ε双相。退火不能改变形变态中第二相颗粒沿着轧向的分布。拉伸实验结果表明合金的屈服强度为326 MPa,抗拉强度为801.9 MPa,延伸率为26.8%,实现了较好的强韧化性能且其断裂机制为韧性断裂。     

Al-Mg-Sc-Ti合金中Al3(Scx,Ti1-x)粒子的析出行为

用激冷铸造法制备Al-5.5Mg-0.25Sc-0.04Ti合金,研究了在不同温度退火后其硬度随时间的变化,并用金相显微镜(OM)和透射电镜(TEM)研究了这种合金中Al₃(Sc_x,Ti_1-x)第二相粒子的存在形式和形成机制。结果表明：用急冷铸造法制备的Al-5.5Mg-0.25Sc-0.04Ti铸态合金中Sc和Ti原子主要以固溶的形式存在于α(Al)基体中,在电镜下很难观察到这些粒子。铸态合金在较低温度(低于250℃)下退火时其硬度提高得比较慢,退火较长时间才能出现硬度的峰值;而在比较高的温度(高于350℃)退火硬度提高得非常快,很快出现峰值。但是,硬度出现峰值后继续退火则大幅度降低;在300℃退火硬度的热稳定性比较高。硬度的变化,与次生Al₃(Sc_x,Ti_1-x)粒子的析出密切相关。在较低温度下次生Al₃(Sc_x,Ti_1-x)粒子的析出不充分且粒径较小,对晶界、亚晶界和位错的钉扎作用较弱;而在过高的温度下Al₃(Sc_x,Ti_1-x)粒子发生粗化,使合金的性能降低。     

Texture evolution and probability distribution of Goss orientation in magnetostrictive Fe–Ga alloy sheets

Texture evolution and the distribution of Goss orientation in polycrystalline Fe–Ga alloy were investigated as a series of rolling and subsequent annealing processes were used to develop highly textured rolled sheet. A dramatic change from the random nature of the as-rolled and primary recrystallized texture is observed when careful control of atmosphere and temperature during anneal leads to development of a sharp Goss orientation over up to 98 % of the surface of a sample during secondary recrystallization. In this work, grain boundary properties in local areas surrounding Goss grains are investigated and the evolution of Goss orientation is traced through the different stages of alloy processing using electron backscatter diffraction analysis. To evaluate the evolution of grains with Goss orientation, {011} grains are selected and separated from other texture components at each processing step and statistical analysis used to correlate the structural inheritance chain of Goss-oriented grains. The four processing stages considered are the alloy after hot rolling, the as-rolled alloy (i.e., after subsequent warm and cold rolling), the alloy after an initial anneal during which primary recrystallization occurs, and the alloy after final anneals in which secondary recrystallization with abnormal grain growth occurs. Analysis of Goss grain orientation probability distribution functions after primary and secondary recrystallization convincingly demonstrates that the orientation of the abnormally grown Goss texture that develops during secondary recrystallization is determined by the orientation of Goss components that develop during the primary recrystallization stage of alloy processing.     

Microstructural changes on high temperature treatment of a cold-worked and nitrided Fe–1%V alloy

An Fe–1.06%V alloy was used to study the control of recrystallization through fine VN precipitates in cold-worked and nitrided ferritic matrix. Nitriding was carried out at 475°C in ammonia atmosphere. Subsequent high temperature annealing process was performed in hydrogen gas for 795, 820, 860 and 880°C, respectively. The data on recrystallization indicates that kinetics of recrystallization obeys an Avrami type equation with a temperature independent time exponent. Transmission electron microscopy techniques were used to measure the precipitate sizes and to study the changes in the microstructure. The activation energy evaluated for recrystallization was found to be consistent with that governing the VN particle coarsening. From these findings it was concluded that the initiation of recrystallization is dominated by the interface reaction controlled growth of VN stringers at subgrain boundaries. After the disappearance of stringers, the interaction of fine precipitates with subgrain boundaries is minimized and hence recrystallization starts. © 1998 Chapman & Hall     

立方织构Ni-Cr-Mo-W合金薄带及其性能

为了得到高份额立方织构金属基带,同时兼顾居里温度和屈服强度的要求,设计了Ni-7.8%Cr-1.1%Mo-1.6%W(原子分数)合金。采用冷坩埚悬浮熔炼技术冶炼合金铸锭,铸锭经过锻造、热轧、冷轧和再结晶退火,最终得到厚度为100μm的合金薄带。采用电子背散射衍射(EBSD)技术对合金薄带再结晶织构进行了表征,并研究了其磁性能及力学性能。结果表明:经大变形量冷轧和优化的两步法退火后Ni-7.8%Cr-1.1%Mo-1.6%W合金薄带立方织构份额为93.4%,小角晶界体积分数为84.5%;合金薄带的居里温度为25K,远低于77K;合金薄带室温下的屈服强度为182 MPa,与Ni-5%W合金相当,且抗拉性能十分优异。     

Study on the microstructures and the magnetic properties of precipitates in a Cu75-Fe5-Ni20 alloy

The microstructural evolutions of precipitates formed in a Cu75-Fe5-Ni20 alloy on isothermal annealing at 873 K and 1073 K have been investigated by means of transmission electron microscopy (TEM). Nano-scale magnetic particles were formed randomly in the Cu-rich matrix after receiving a short annealing due to phase decomposition in the alloy. With increasing the isothermal annealing time, however, the striking features that two or more nano-scale particles with a cubic shape and a rod shape were aligned linearly along (100) directions were observed on isothermal annealing at 873 K and 1073 K, respectively. To investigate electro-magnetic properties of precipitates in a Cu-Fe-Ni alloy, the superconducting quantum interference device (SQUID) magnetometer and physical property measurement system (PPMS) were also complemented. The present study revealed significant influences that the magnetic properties of the specimens were closely related to the microstructures in the Cu-Fe-Ni alloy, which microstructures significantly depend on the isothermal annealing temperature.     

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.     

Effect of rolling temperature on microstructure and mechanical properties of 6063 Al alloy

Aluminium alloy (6063) was severely rolled upto 92% thickness reduction at liquid nitrogen temperature and room temperature to study the effect of rolling temperature on its mechanical properties and microstructural characteristics by using tensile tests and SEM/electron back scattered diffraction (EBSD), transmission electron microscope (TEM), DSC, X-ray diffraction (XRD) as compared to room temperature rolled (RTR) material with the same deformation strain. An improved strength (257 MPa) of cryorolled 6063 Al alloy was observed as compared to the room temperature rolled alloy (232 MPa). The improved strength of cryorolled alloy is due to the accumulation of higher dislocation density than the room temperature rolled material. The tensile properties of cryorolled alloy and the alloy subjected to different annealing treatments were measured. The cryorolled alloy subjected to annealing treatment at 300 °C for 5 min exhibits an ultrafine-grained (UFG) microstructure with improved tensile strength and ductility.     

Evolution of microstructure and crystallographic texture during recrystallisation of high-strength sheet steel

Ultra-low carbon steels possess an attractive combination of mechanical properties namely drawability and strength that is suitable for automotive applications. A high-strength variant of the material containing large amounts of manganese and phosphorous has been produced in the laboratory. The main objective of the present work was to study the microstructural evolution after recrystallisation, below and above the critical phase transformation temperatures of the steel. Crystallographic texture of ferrite was found to intensify with increasing the annealing temperature; surprisingly even beyond the upper transformation temperature. The texture measurement data obtained with the electron backscatter diffraction and X-ray diffraction matched very well with each other. The steel recorded an impressive strength–drawability balance mainly due to solid solution strengthening and favourable γ-fibre texture.