RD Fiber Research Articles

Evolution of microstructure and texture in Ni49.4Ti38.6Hf12 shape memory alloy during hot rolling

This paper deals with the evolution of microstructure and texture during hot rolling of hafnium containing NiTi based shape memory alloy Ni49.4Ti38.6Hf12. The formation of the R-phase has been associated with the precipitation of (Ti,Hf)2Ni phase. The crystallographic texture of the parent phase B2 as well as the product phases R and B19′ have been determined. It has been found that the variant selection during the B2 → R phase transformation is quite strong compared to the case of the B2 → B19′ transformation. During deformation, the texture of the austenite phase evolves with strong Goss and Bs components. After transformation to martensitic structure, it gives rise to a [011]||RD fiber. Microstructure and texture studies reveal the occurrence of partial dynamic recrystallization during hot rolling. Large strain heterogeneities that occur surrounding (Ti,Hf)2Ni precipitates are relieved through extended dynamic recovery instead of particle stimulated nucleation.

Origin of the {h 1 1 }<1/h,1,2> Fiber in Single Phase Ferrite Steels

In the present work, the oriented nucleation origin of the recrystallized {h11}<1/h,1,2> fibre is characterized. Aiming to investigate the substructural evolution of <110>//RD fibre grains and {001}<110> grains in particular, a detailed microstructure and texture analysis is performed by high resolution orientation scanning microscopy on a cross-rolled sample. The reason to work with cross-rolled material is the increased incidence of rotated cube orientations after cross rolling. The present data have revealed the presence in the deformed substructure of a crystallite volume that has rotated towards the {311}<136> component in the interior of <110>//RD fibre grains as a result of a grain fragmentation process. Preliminary simulations of the deformation texture suggested that the observed orientation fragmentation might be produced by strain localizations of a shear band nature.

Tempforming in medium-carbon low-alloy steel

Abstract Deformation of tempered martensitic structure, i.e., tempforming using a caliber rolling at 500 °C was applied to a 0.4%C–2%Si–1%Cr–1%Mo steel to obtain ultrafine elongated grain structure with a strong 〈1 1 0〉//RD fiber deformation texture and then tensile and Charpy impact properties were investigated. An inverse temperature dependence of impact toughness was demonstrated in the tempformed (TF) samples in subzero temperatures, where conventionally quenched and tempered samples showed a ductile-to-brittle transition. The enhancement in the impact toughness of the TF sample was attributed to the occurrence of a delamination, where cracks branched to the longitudinal direction of the impact test bar. The delamination was shown to occur due to the microstructural anisotropy. The dominating factors controlling the delamination were considered to be the transverse grain size, the grain shape and the deformation texture.

Enhanced upper shelf energy by ultrafine elongated grain structures in 1100MPa high strength steel

Abstract The ultrafine elongated grain (UFEG) structure with strong //RD fiber deformation texture was produced by warm caliber-rolling at 500 °C and final tempering at 550 °C, namely tempforming in the 1100 MPa medium carbon-low alloy steel with ultralow phosphorus and sulfur concentrations. Charpy impact tests were performed at temperature range of −196 °C to 150 °C on the UFEG structure along with a conventional quenched and tempered (QT) structure. A remarkable increase in upper shelf energy of 150 J was obtained in the UFEG structure without delamination, while that of QT structure was 97 J. The UFEG structures tempered at higher temperatures of 625 and 700 °C showed remarkable increase in Charpy absorbed energy from 150 J to 187 J and 203 J. Also, the QT structure absorbed almost same energy as UFEG structure at 700 °C. The enhanced toughness was discussed with tensile ductility, void nucleation and growth, and their relations to microstructure including the //RD fiber deformation texture.

Low core loss non-oriented silicon steels

Low core loss non-oriented silicon steels are produced with high (Si+Al) content to reduce eddy current losses. However, high alloy content has detrimental effect on mechanical properties, saturation polarization and thermal conductivity. A new generation of medium and, particularly, low core loss non-oriented silicon steels was developed, with lower alloy content than the conventional grades, based on improved purity and texture. The development allowed the production of new low loss grades, with maximum core loss ( W 1.5/50) of 2.30 W/kg at 0.50 mm and 1.95 W/kg at 0.35 mm, with high permeability ( J 50 of 1.7 and 1.72 T, respectively). Texture improvement was based on hot band structure control and higher boundary mobility. Large hot band grain size and low [1 1 0]∥RD fiber fraction in the hot band texture contribute to reduce the intensity of [1 1 1]∥ND and slightly increase the intensity of [0 0 1]∥RD in the final product. Higher grain boundary mobility and/or a two-stage cold rolling process, with an intermediate annealing, increase the fraction of [0 0 1]∥RD and reduce the fraction of [1 1 1]∥ND on recrystallization and lead to favorable texture evolution on grain growth.

Toughening of a 1500 MPa class steel through formation of an ultrafine fibrous grain structure

A deformation of tempered martensite, namely tempforming at an elevated temperature, was applied to a medium-carbon low-alloy steel. This thermomechanical treatment led to an evolution of an ultrafine fibrous grain structure with a strong 〈1 1 0〉∥RD fiber deformation texture and to a remarkable improvement in Charpy impact strength (uE = 165 J) at a tensile strength of 1.5 GPa.

Effects of Two-step Annealing on Texture and Magnetic Properties by Addition of Co, Mo, or Ni in Silicon Steel

In 3Si–1.4Al electrical steel with addition of Co, Mo or Ni, the texture of hot bands is almost random except γ fiber which is dominant. After cold reduction, the texture shows the typical (111)//ND and (110)//RD fibers. When cold rolled sheets are annealed, it is clear that γ fiber of {111}‹110› and {111}‹112› decreases significantly, while, on the contrary, Goss texture increases but cube texture is not changed. Two-step annealing process was observed to be effective to increase grain size and decrease γ fiber texture resulting in lowering iron loss and its anisotropy. The combination of increasing grain size and decreasing γ texture by two-step annealing was able to improve magnetic properties.

Evolution of crystallinity and of crystallographic orientation in isotactic polypropylene during rolling and heat treatment

The development of the crystallinity and of the crystallographic orientation of isotactic polypropylene during rolling deformation and subsequent heat treatment is studied. The experiments are conducted by using X-ray diffraction with an area detector. The evolution of crystallographic orientation is tracked by calculating the pole figures and by applying a quantitative 3D texture component fit method. The rolling orientation after a true strain of −1.5 mainly consists of the (0 1 0)[0 0 1], (1 3 0)[0 0 1], and [0 0 1]//RD fiber components (RD: rolling direction). The results reveal that the crystallinity drastically decreases during rolling. We suggest that decrystallization (disaggregation) is a deformation mechanism which takes place as a microscopic alternative to crystallographic intralamellar shear depending on the orientation of the lamellae relative to the imposed deformation tensor. Heat treatment after rolling leads to the recrystallization of amorphous material and to a strong enhancement of the fiber orientation component. The recrystallization orientation is explained in terms of an oriented nucleation mechanism where amorphous material aligns along existing crystalline lamellae blocks which prevailed during the preceding deformation.

Development of a new generation of high permeability non-oriented silicon steels

The paper describes a new generation of the high permeability fully processed silicon steel grades developed by Acesita, with core loss ( W 1.5/60) in range of 3.10–4.20 W/kg and polarisation ( J 50) from 1.71 to 1.75 T, respectively. The new grades have lower (Si+Al) content and a better crystallographic texture, with lower fractions of [1 1 1]||ND fibre and higher fractions of [0 0 1]||RD fibre. The new grades have better mechanical and magnetic properties than conventional grades.

Effect of Rolling Temperature, Reduction and Alloying Additions on the Texture of Warm Rolled Steels

The effect of warm and cold rolling parameters on the development of annealing textures was studied in two low carbon steels containing additions of chromium. Two warm rolling temperatures (640 and 700°C) were employed together with a reduction of 65%. The effects of an additional cold rolling reduction of 40% and of decreasing the heating rate during annealing were also studied. The ND fiber, <111>//ND, of the recrystallization texture was strengthened as the warm rolling temperature was decreased. However, all the warm rolled steels contained a retained RD fiber, <110>//RD. A noticeable improvement in both the continuity and intensity of the ND fiber was obtained when the sample was submitted to an additional 40% cold rolling reduction. The ND fiber was even more continuous and intense when a low heating rate was utilized, yielding r-values of 1.1 and 1.3 for the warm rolled and warm plus cold rolled samples, respectively.

Evolution of Non-Oriented Silicon Steel Texture on Recrystallization and Grain Growth

The evolution of annealing texture of non-oriented grain silicon steel as a function of annealing temperature was investigated from hot rolled samples taken from industrial production. Hot band samples were annealed at 900°C, cold rolled to final thickness of 0.5mm in a single stage cold rolling process or in two stages with intermediate annealing at 900°C, and final annealed in the temperature range from 540°C to 980°C. The results show that the [001]||RD fibre is an important recrystallization texture component, but it may be consumed by further grain growth and become a minor component. The effect of grain growth in the temperature range investigated seems to be that of strengthening the main components at the expenses of the others. The results suggest that to avoid the reduction of the [001]||RD fibre on grain growth a volume fraction ratio between the texture components (111)[112] and (110)[001] close to unity is necessary after recrystallization. This can be obtained under conditions that enhance [001]||RD fibre on recrystallization, such as: strong [111]ND fibre in the deformation texture, large initial grain size and enhanced grain boundary mobility, by proper composition and purity.

Microstructure and Texture of Commercial Purity Aluminum Strips Produced by Melt Direct Rolling

The microstructure and texture of the aluminum strips produced by the melt direct rolling (MDR) method are inhomogeneous in the direction of strip thickness. The subsurface layer (about 30% thickness of the strips) shows fine and equiaxed grains formed by geometric dynamic recrystallization and has a strong shear texture ((110)//RD fiber texture including {111}(l10) and {001}(110) orientations), while the center layer shows elongated grains and has a typical rolling texture. This inhomogeneity is due to large shear deformation induced by friction during rolling. Near the surface, the microstructure shows no remarkable changes during annealing below 673 K, but the relative intensities of {111}(110) and {113}(110) orientations increase. Relatively large τ and very large Δr are obtained from the tensile tests of the MDR strip and they vary with the textures depending on annealing temperatures. The present study has clarified that the MDR method is useful to develop the {111} texture in aluminum strip by introduction of large shear deformation during rolling.

Influence of Ferrite Rolling Temperature on Grain Size and Texture in Annealed Low C and IF Steels.

Single pass rolling experiments were carried out on two low carbon steels and an IF grade at temperatures between ambient and 700°C. These were followed by salt bath annealing treatments. The main aim was to investigate the effect of the transition from cold to warm rolling on annealing behavior. Three aspects of annealing were examined: the kinetics of recrystallization; the final grain size; and the resulting texture. The sensitivity of these to the deformation temperature was markedly greater in the low C grades than in the IF grade. In the low C material, changing the rolling temperature from cold to warm resulted in an increase in time to 50% recrystallization of about 1 1/2 orders of magnitude, a two-fold increase in final grain size and a remarkably different texture (i.e. one composed of a partial RD fibre instead of the typical ND fibre). By comparison, recrystallization was only slightly influenced by deformation temperature in the IF steel. These observations are explained in terms of the influence on nucleation of the stored energy and the degree of in-grain banding. In particular, the present results suggest that in-grain shear bands play a larger role in the formation of ND fibre grains than previously thought. From an industrial standpoint, IF steels clearly lend themselves more readily to the replacement of cold by warm rolled material than do low C grades.

Model of Secondary Recrystallization in Silicon-Iron and Comparison With Experiments

A comparative analysis has been made of selective grain growth processes at different layers of a grain oriented silicon iron sheet. Shorter incubation time and best orientation selection during secondary recrystallization appear at 40 μm from the sheet surface. This has been linked to the presence of a relatively strong //RD fiber in the texture. The differences through the sheet thickness are assumed to be inherited from the hot band. Computer simulations in the framework of the statistical theory of grain growth support the proposed selection mechanisms.

Effect of Ti on the Development of Rolling Textures in High Purity Iron

With the method of the crystallite orientation distribution function analysis, the development of the rolling texture was studied in detail on a Fe-0.004%C-0.20%Ti alloy cold rolled up to 90% reduction in thickness. It was found that the effect of Ti was widely different among various rolling texture components. The addition of Ti enhanced the development of the 〈 110 〉 ‖ RD fiber rolling texture component by promoting the rotation about the 〈 110 〉 ‖ RD axis. This resulted in the development of the strong {112} 〈 110 〉 texture component. As to the 〈 110 〉 ‖ TD fiber texture component, it was found that, although the addition of Ti did not affect the rotation about the 〈 110 〉 ‖ TD axis in the range {110} 〈 001 〉 to {554} 〈 225 〉 , it strongly suppressed the rotation of {554} 〈 225 〉 into {111} 〈 112 〉 . As a result, strong {554} 〈 225 〉 rolling texture component was developed below 70% rolling reduction. This component seems to provide origins of the {554} 〈 225 〉 recrystallization texture commonly observed in the Ti-stabilized steel. Such changes in the rolling texture would be expected, since slip modes are strongly affected by scavenging of C atom by Ti, or by the presence of very fine TiC precipitate particles.