Γ-fiber Recrystallization Texture Research Articles

Correlation between formability, ridging and recrystallization texture development in ferritic stainless steel fabricated by introducing intermediate annealing during cold rolling

Introducing intermediate annealing (IA) during cold rolling is a most promising approach for reinforcing ridging resistance and r-value of ferritic stainless steels, but it usually deteriorates anisotropy of r-value. To solve this problem, the texture evolution, especially recrystallization texture formation at various IA temperatures and its effect on formability and ridging was investigated. During cold rolling, the crystallite appeared along shear band because of the sequential starting of multislip systems, and due to high rotation tendency of shear component {110}〈001〉 towards stable {111}〈112〉 it owned sharp {111}<112 > and {110}<001 > components, and then during annealing, it preferentially induced recrystallized nuclei, and the γ-fiber recrystallization texture having peak intensity near {111}<112 > was formed owing to high grow tendency of preferentially formed {111}<112 > recrystallized grain. Moreover, IA at 850 °C promoted the rotation of crystallites towards stable {111}<112 > during cold rolling before final annealing compared with IA at 950 °C and above, while for IA at 950 °C and above, higher IA temperature was conducive to nucleating randomly oriented grain, and adverse to consuming other deformed grain by {111}<112 > recrystallized grains during final annealing. Therefore, the γ-fiber recrystallization texture in the final sheet gradually weakened and {110}<001 > component first strengthened and then weakened with increasing IA temperature. In addition, the banded grain clusters having similar r-value or those having same orientation and its variants with same sign of ε23 were less distinct and their size was finer in the final sheet after IA at 950 °C than those after other IA temperatures by reason of the occurrence of partial recrystallization at lower temperature and significant grain growth at higher temperature during IA. With increasing IA temperature, average r-value increasingly reduced, while anisotropy of r-value and ridging resistance first heightened and then lowered, which were lower at 850 °C and the optimal matching was realized at IA temperature of 850 °C.

Formation of recrystallization texture and its effect on deep drawability for high-purified ferritic stainless steel by two step cold rolling

For working out the approach of acquiring low planar anisotropy while achieving high ridging resistance and r-value, during two step cold rolling processes with different total reductions the texture evolution and corresponding mechanism were investigated for ferritic stainless steel. During cold rolling, the crystallites having orientations near {111} 〈112〉 and Goss were induced by shear bands and with further deformation Goss orientation tended to rotate towards more stable {111} 〈112〉. During subsequent annealing, these crystallites induced the recrystallized nuclei and {111} 〈112〉 nuclei consumed preferentially the adjacent matrixes, generating the γ-fiber recrystallization texture having the main component of {111} 〈112〉. With increasing total cold rolling reduction, the γ-fiber recrystallization textures were gradually intensified and band-like grain colonies having approximate r-value and those having variant with ε23 of same sign became more obvious and their distribution more uneven, the average r-value and ridging resistance exhibited a monotonous upward and downward trend, respectively, and the planar anisotropy of r-value first deteriorated and then improved and reached lowest value at 90 %. Considering acceptable ridging resistance in practical application, the excellent deep drawability can be acquired at the total reduction of 90 %.

Comparative study on microstructure and texture evolution of low silicon non-oriented electrical steels along one-stage and two-stage cold rolling processes

Fe-0.9% Si-0.3% Al non-oriented electrical steels were fabricated by two-stage cold rolling process including hot rolling, first cold rolling, intermediate batch annealing, second cold rolling and final annealing, in which the first cold rolling reduction varied from 15% to 54%. One-stage cold rolling process with hot band normalization was also investigated for comparison. The findings revealed that, in two-stage cold rolling process, the final recrystallization texture and magnetic properties heavily relied on the rolling reduction schedule. As the first rolling reduction increased, the core loss increased and the magnetic induction decreased owing to the enhanced γ-fiber (〈111〉//ND) texture in the final annealed sheets. Relatively lower first cold rolling reduction (15%) was beneficial to generate coarse grains during intermediate annealing and led to large grains with weakened γ-fiber and enhanced Goss textures in final sheets. By contrast, relatively higher first cold rolling reduction (30% and 54%) caused small grains by promoting the occurrence of recrystallization during intermediate annealing and resulted in small grains with stronger γ-fiber texture after final annealing. The hot band normalization in one-stage cold rolling process could also effectively improve the grain size prior to cold rolling, though MnS precipitate and sharp γ-fiber recrystallization texture were promoted in the final sheets due to the high normalization temperature and much higher cold rolling reduction, respectively. Therefore, two-stage cold rolling process was propitious to reduce γ-fiber recrystallization texture and MnS precipitate compared with one-stage cold rolling process. The appropriate rolling reduction schedule (15%+75.6%) and suitable intermediate annealing process (750 °C for 1.5 h) were propitious to produce high-performance non-oriented silicon steel with lowest core loss and highest magnetic induction.

Effects of processing routes on recrystallization texture development and magnetic properties of 0.10 mm ultrathin non-oriented electrical steel sheets for high-frequency application

Fabricating ultrathin non-oriented electrical steels (NOES) sheets has been a challenge because the severe plastic deformation inevitably results in undesirable texture such as intensive γ-fiber (<111>//ND). In the present work, both one-stage rolling route with severe plastic deformation and two-stage rolling route combining different rolling process and the intermediate annealing were used to prepare 0.10 mm-thick 3.1Si-0.8Al NOES. A rare phenomenon was found that severe plastic deformation in one-stage rolling route split the orientations of α (<110>//RD) grains through deformation banding and caused lattice curvature, exhibiting the similar microstructure characteristic and stored energy distribution as the deformed γ-grains. As a result, dominant α*-fiber ({1 1 h} <1 2 1/h>) and relatively soft α-fiber textures besides sharp γ-fiber recrystallization texture were formed, which seriously deteriorated the magnetic induction and led to high magnetic anisotropy. By comparison, the two-stage rolling route favored the development of shear bands and increased the final grain size. As the second rolling reduction decreased, detrimental γ- and α*‐fiber recrystallization textures were significantly weakened, whereas λ-fiber (<001>//ND) and {117}<291> recrystallization textures were enhanced. Besides, the final grain size was gradually increased. Therefore, the magnetic induction was continuously improved and the core loss was gradually decreased. Another new finding was that magnetic anisotropy was simultaneously improved as a result of the occurrence of {117}<291> texture and the weakening of α*-fiber texture. The recrystallization mechanism of specific texture components was investigated in detail.

Dependence of recrystallization behavior and magnetic properties on grain size prior to cold rolling in high silicon non-oriented electrical steel

The present work aimed to investigate the roles of prior grain size of the hot rolled sheets after normalization on final recrystallization behavior and magnetic properties in 3.1%Si + 0.9%Al non-oriented electrical steel. Bigger prior grain size produced coarser deformed grains and promoted the development of in-grain shear bands, which together resulted in distinct recrystallization behavior. The prior small-grained microstructure caused relatively slow kinetics at the early stage of recrystallization, while fast kinetics was displayed at the later stage due to the growth of new γ(<111>//normal direction (ND))-grains and led to strong γ-fiber recrystallization texture. By contrast, the prior big-grained microstructure gave rise to relatively fast recrystallization kinetics at the early stage due to the diversified nucleation orientation and rapid grain growth in the interior of coarse deformed γ-grains with the help of in-grain shear bands. However, relatively slow kinetics was displayed at the later stage because the coarse deformed λ(<001>//ND)-grains were sluggish to recrystallize. Hence, continuous recrystallization and shear bands induced nucleation contributed to strong λ-fiber texture. Magnetic induction B50 continuously improved as the prior grain size increased, while both the low-frequency core loss P15/50 and the high-frequency core loss P10/400 decreased firstly and then increased with different critical prior grain size.

Texture Evolution of Modified 12%Cr Steel in High-Temperature Compression

The texture evolution of modified 12%Cr steel in high-temperature compression was investigated under a 10, 25, 35, and 50% reduction at 1150°C by using Gleeble-1500 D thermal simulation machine. Electron backscattering diffraction analysis showed that the texture of modified 12%Cr steel varied within α, γ, and e and Goss fibers coexisting to γ and e , then to α and e , with the {hkl} orientation always existing in compression. Recrystallization nuclei contribute to γ-fiber strengthening due to their high-energy mechanism. First activated. α-fibers can be consolidated owing to the interaction of deformation and recrystallization. In the compression procedure of an ultrasupercritical high-pressure rotor made of modified 12%Cr steel, the deformation should be controlled under the recrystallization activation energy of α-fibers to obtain the microstructure featured by the γ-fiber recrystallization texture, and vice versa.

Effect of Ferritic Hot Rolling Process on Microstructure and Properties of IF Steel

The effect of ferritic hot rolling process on microstructure and properties of Ti microalloyed IF steel was investigated. The hot rolling-coiling, cold rolling and continuous annealing processes of ferritic zone were physically simulated. The influence of thermal deformation (finishing rolling temperature, coiling temperature) on the structure, texture and forming properties of Ti-If steel was studied through tensile test, EBSD, XRD and other analytical methods. The results showed that the recrystallization occurred after hot rolling and coiling in the ferritic region. Weak α-fiber and weak γ-fiber were obtained in the central layer of hot rolling plates, and the strength of γ-fiber was higher when finished rolling at low temperature. α-fiber and weak γ-fiber were strengthened after cold rolling. After annealing, the α-fiber was weakened and the γ-fiber was strengthened, and the γ-fiber became the main texture. The larger and more uniform grain size and better mechanical properties were obtained by IF steel finished rolling and coiling at high temperature and after continuous annealing, reaching yield strength of 106 MPa, tensile strength of 297 MPa, elongation rate of 52%, n value of 0.26 and r value of 2.3. The hot rolling texture is hereditary. If the more γ-fiber is formed after hot rolling, the more γ-fiber recrystallization texture is formed after cold rolling and annealing.

Effect of crystallographic orientations on the corrosion resistance of Fe-17Cr ferritic stainless steel

Effect of crystallographic orientations on the corrosion resistance of the Fe-17Cr ferritic stainless steel sheets was investigated by electron backscatter diffraction and electrochemical measurements. Nearly homogeneous {111}〈112〉 γ-fiber recrystallization texture is produced in the Fe-17Cr ferritic stainless steel sheets. Comparison between the inverse pole figure orientation map and scanning electron microscopy microstructures etched by aqua regia reveals that the severest corrosion occurs on the sheet rolling surface where {111} crystal plane dominates. Electrochemical measurements demonstrate that the plane perpendicular to transverse direction displays the lowest corrosion current density. This indicates that this plane, where {110} plane dominates, exhibits the best corrosion resistance.

Microstructural evolution in warm-rolled and cold-rolled strip cast 6.5 wt% Si steel thin sheets and its influence on magnetic properties

6.5wt% Si steel thin sheets were usually fabricated by warm rolling. In our previous work, 6.5wt% Si steel thin sheets with good magnetic properties had been successfully fabricated by cold rolling based on strip casting. In the present work, the main purposes were to find out the influences of warm rolling and cold rolling on microstructures and magnetic properties of the thin sheets with the thickness of 0.2mm, and to confirm which rolling method was more suitable for fabricating 6.5wt% Si steel thin sheets. The results showed that the cold rolled sheet could obtain good surface quality and flatness, while the warm rolled sheet could not. The intensity of γ-fiber rolling texture (<111>//ND) of cold rolled specimen was weaker than that of the warm rolled specimen, especially for the {111}<112> component at surface layer and {111}<110> component at center layer. After the same annealing treatment, the cold rolled specimen, which had higher stored energy and weaker intensity of γ-fiber rolling texture, could obtain smaller recrystallization grain size, weaker intensity of γ-fiber recrystallization texture and stronger intensity of λ-fiber recrystallization texture. Therefore, due to the good surface quality, smaller recrystallization grain size and optimum recrystallization texture, the cold rolled specimen possessed improved magnetic properties, and cold rolling should be more suitable for fabricating 6.5wt% Si steel thin sheets.

Effects of Coiling Temperature after Hot Rolling on Microstructure, Texture, and Magnetic Properties of Non-Oriented Electrical Steel in Strip Casting Processing Route

Low silicon non-oriented electrical steel is produced using a novel strip casting processing route. The focus is on investigating the effects of coiling temperature after hot rolling on microstructure, texture evolution, and magnetic properties. A fine microstructure with weak λ-fiber texture is formed after coiling at 650 °C. By contrast, a much coarser microstructure with a much stronger λ-fiber texture is produced after coiling at 750 °C. After cold rolling and annealing, a fine and inhomogeneous recrystallization microstructure dominated by mild λ-fiber, α-fiber, and γ-fiber recrystallization texture is formed in the case of coiling at 650 °C. By contrast, a coarse and inhomogeneous recrystallization microstructure characterized by strong Goss, α-fiber, and weak λ-fiber together with extremely weak γ-fiber recrystallization texture is formed in the case of coiling at 750 °C. Much lower iron loss and higher magnetic induction are obtained in the latter case as a result of the more desirable recrystallization microstructure and texture. It underscores that the relatively higher temperature of coiling has a similar effect as the conventional hot-band normalizing. Hence, the hot-band normalizing might be omitted in the fabrication of high-performance non-oriented electrical steels using this novel and compact strip casting production route.

Effects of initial microstructure and texture on microstructure, texture evolution and magnetic properties of non-oriented electrical steel

An equiaxed grained as-cast strip and a columnar grained as-cast strip was produced by using twin-roll strip casting, respectively. Both as-cast strips mainly containing 0.71wt%Si and 0.44wt%Al were cold rolled and annealed with or without the hot rolling prior to cold rolling. Microstructure, texture evolution along the whole processing routes and the magnetic properties were investigated in detail. It was found that the equiaxed grained strip was characterized by almost random texture while the columnar grained strip was dominated by strong λ-fiber (<001>‖ND) texture. After cold rolling and annealing, all the final sheets of both the as-cast strips showed extremely weak γ-fiber (<111>‖ND) recrystallization texture. In addition, the finally annealed sheets of the equiaxed grained strip were dominated by relatively weak λ-fiber and strong Goss ({110}<001>) recrystallization texture while those of the columnar grained strip were dominated by much stronger λ-fiber and much weaker Goss recrystallization texture regardless of whether the hot rolling was adopted before cold rolling, thus the former showed much lower magnetic induction than the latter. On the other hand, even though the finally annealed sheets of the equiaxed grained strip showed a little more homogeneous recrystallization microstructure with a little bigger grain size than those of the columnar grained strip in the case of no hot rolling, a much higher iron loss was displayed. By contrast, in the case of hot rolling, the former exhibited a little lower iron loss than the latter as a result of the more significant increase in grain size and λ-fiber recrystallization texture. The introduction of the hot rolling could increase the grain size, strengthen λ-fiber texture and weaken Goss texture of the finally annealed sheets of both the as-cast strips, leading to a much improvement in both the magnetic induction and iron loss.

Microstructure, Texture, and Deep Drawability Under Two Different Cold-Rolling Processes in Ferritic Stainless Steel

In the present study, the through-thickness texture evolution and grain colony distribution in ferritic stainless steel under two different cold-rolling processes have been investigated with the aim to enhance deep drawability. It was shown that in the case of conventional cold-rolling process, at the surface, mid-thickness between the surface and the center, and center layers, all the textures consisted of very sharp α-fiber and weak γ-fiber with a peak at {111}〈110〉 after cold rolling, and non-uniform γ-fiber recrystallization textures were formed after final annealing. In case of two-step cold-rolling process, by contrast, all the textures were dominated by sharp α-fiber and weak γ-fiber after cold rolling to 50% reduction, and {111}〈112〉 became the prominent component after subsequent annealing. The α-fiber and γ-fiber with a peak at {111}〈112〉 were intensified after cold rolling to 60% reduction, resulting in the formation of uniform γ-fiber recrystallization textures after final annealing. Furthermore, after two-step cold-rolling process, the final sheet exhibited a more homogeneous distribution of grain colonies. Therefore, the deep drawability of final sheet was significantly improved after two-step cold-rolling process. It was elucidated that the selective growth mechanism was responsible for the characteristics of γ-fiber recrystallization texture under conventional cold-rolling process, whereas γ-fiber recrystallization texture development was controlled by the oriented nucleation mechanism in the two-step cold-rolling process.

Evolution of Through-Thickness Texture in Ultra Purified 17% Cr Ferritic Stainless Steels

Texture inhomogeneity usually takes place in ferritic stainless steels due to the lack of phase transformation and recrystallization during hot strip rolling, which can deteriorate the formability of final sheets. In order to work out the way of weakening texture inhomogeneity, conventional hot rolling and warm rolling processes have been carried out with an ultra purified ferritic stainless steel. The results showed that the evolution of through-thickness texture is closely dependent on rolling process, especially for the texture in the center layer. For both conventional and warm rolling processes, shear texture components were formed in the surface layers after hot rolling and annealing; sharp a-fiber and weak γ-fiber with the major component at {111}<110> were developed in both cold rolled sheet surfaces, leading to the formation of inhomogeneous γ-fiber dominated by {111}<112> after recrystallization annealing. In the center layer of conventional rolled and annealed bands, strong a-fiber and weak γ-fiber textures were formed; the cold rolled textures were comprised of sharp a-fiber and weak γ-fiber with the major component at {111}<110>, and inhomogeneous γ-fiber dominated by {111}<112> was formed after recrystallization annealing. By contrast, in the centre layer of warm rolled bands, the texture was comprised of weak a-fiber and sharp γ-fiber, and γ-fiber became the only component after annealing. The cold rolled texture displayed a sharp γ-fiber with the major component at {111}<112> and the intensity of γ-fiber close to that of a-fiber, resulting in the formation of a nearly homogeneous γ-fiber recrystallization texture in the center layer of the final sheet.

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.

Texture evolution and formability under different hot rolling conditions in ultra purified 17%Cr ferritic stainless steels

A very non-uniform γ-fiber recrystallization texture usually takes place in ferritic stainless steels, which can deteriorate the formability of final sheets. In order to work out the way of improving the uniformity of γ-fiber recrystallization texture, conventional rolling and warm rolling processes have been carried out with an ultra purified ferritic stainless steel. Texture evolution under different hot rolling conditions was investigated by using macro and micro-texture analyses. It was observed that a non-uniform γ-fiber recrystallization texture was obtained in the final sheet after conventional rolling process, while a nearly uniform γ-fiber recrystallization texture was formed in the final sheet after warm rolling process. Therefore, the formability of the final sheet was significantly improved after warm rolling process. It was indicated that the formation of non-uniform γ-fiber recrystallization texture was attributed to oriented nucleation, whereas the formation of uniform γ-fiber recrystallization texture was explained by a combination of oriented nucleation and preferred growth. ► Effect of hot rolling conditions on texture evolution was studied. ► Uniform γ-fiber recrystallization texture was formed after warm rolling process. ► Formability was improved by employing the warm rolling process. ► The development mechanism of recrystallization texture was explored.

Texture Development and Formability of Strip Cast 17% Cr Ferritic Stainless Steel

In order to optimize the formability of ferritic stainless steel (FSS), control of the crystallographic texture is essential. In the present work, texture development of cast strips with different initial solidification structure during rolling and subsequent annealing and the formability of final sheets were investigated. Fully equi-axed and columnar grained cast strips of Fe17%Cr FSS were fabricated by a pilot twin-roll strip caster. The equi-axed and columnar grained bars cut from a conventional continuous cast slab were used as comparable specimens. It was shown that in the cold rolled and annealed sheet of fully equi-axed cast strip, uniform and strong γ-fiber recrystallization texture was formed and {001}‹110› component was almost eliminated. By contrast, the recrystallization texture in the conventional sheets with equi-axed and columnar initial solidification structures exhibited typical shift towards high-index {334}‹483›, which led to a reduced r-value as compared to that of the equi-axed cast strip. The final annealed sheet of fully columnar cast strip, however, showed weaker γ-fiber recrystallization texture and lower r-value than those of conventional sheets. It is, therefore, believed that twin-roll strip casting can improve the formability of 17% Cr FSS only under the pre-condition that appropriate solidification structure is obtained.

Texture and microstructure development in cold-rolled interstitial free (IF) steel sheet during electric field annealing

The effects of electric field annealing on the development of recrystallization texture and microstructure in a cold-rolled IF steel sheet were studied by means of ODF analysis and optical microscopy. Results showed that the applied external electric field might retard recrystallization, and enhance the γ-fiber recrystallization texture that is beneficial to the deep-drawability.

Origin of the Recrystallization Texture Formation in an Interstitial Free Steel.

A laboratory investigation has been carried out to reveal the mechanism of recrystallization texture formation in an interstitial free (IF) steel, based on the assumption that the reduced grain boundary constraint for a grain rotation during cold-rolling plays an important role on the mechanism. As a parameter of grain boundary constraint, the ratio of deformation strengths of grain boundary area and grain matrix were varied by changing the cold-rolling temperature (–100–200°C) and microalloying of boron into IF steel. The paper revealed that the reduced grain boundary constraint by scavenging the interstitial elements from grain boundaries not only enhanced a development of γ-fiber texture but also suppressed a formation of deformation bands inside the γ-fiber matirix during cold-rolling in IF-steel. In-situ like recrystallization from the strong {111} γ-fiber texture, which is caused by a reduction of nucleation frequency of //ND grains from deformation bands, is the origin of the strong {111} γ-fiber recrystallization texture formation in IF steel.