Evolution of microstructure and texture during casting of AISI 304 stainless steel strip

The solidification behavior of AISI 304 stainless steel strip was studied using a melt/substrate contact apparatus, whereby a copper substrate embedded in a moving paddle is rapidly immersed into a steel melt to produce thin (∼1-mm gage) as-cast coupons. For cases where other casting conditions were kept constant, the effect of substrate topography and melt superheat on the development of microstructure and texture during solidification was studied using electron backscatter diffraction (EBSD) and optical microscopy. It was found that nucleation and growth of grains during solidification were influenced both by substrate topography and melt superheat. A ridged substrate produced a high density of randomly oriented grains at the chill surface with the preferred growth of 〈001〉-oriented grains perpendicular to the substrate wall producing a coarse columnar grain structure exhibiting a strong 〈001〉 fiber texture at the strip center. In contrast, a smooth substrate resulted in a lower nucleation density to produce a very coarse-grained columnar microstructure with moderate and essentially constant 〈001〉 fiber texture throughout the strip thickness. By the manipulation of casting parameters, it is possible to produce strip-cast austenitic stainless steel with a particular microstructure and texture.     

Effect of initial texture on texture evolution in 1050 Al alloys under simple shear

The effect of the initial textures prior to dissimilar channel angular pressing (DCAP) on the texture evolution of the 1050 Al alloy sheets, processed by the continuous confined strip shearing (C2S2) process, were studied. The four different specimens, i.e., cold rolled, heat treated, warm rolled, and as-cast 1050 Al alloy sheets, having various initial textures were prepared using different thermomechanical routes. Although the major texture types were significantly affected by the initial textures prior to DCAP, DCAP always promoted both the 〈111〉//normal direction (ND) textures and the {001}〈110〉 rotated cube texture regardless of the initial texture status. Effects of the texture evolutions due to equal channel angular pressing (ECAP) on deep drawbility and planar anisotropy were analyzed based on the -r value and the Δr value determined from the measured pole figures. A feasibility for producing the 1050 Al alloy sheets having high deep drawbility and low planar anisotropy was demonstrated.     

The influence of rolling practice on notch toughness and texture development in high-strength linepipe

The mechanical properties and notch toughnesses of an X80 linepipe steel were determined for various test directions in the plane of sheet that had been finish rolled in the γ and in the intercritical (α+γ) regions. The anisotropies of yield strength (YS) and of impact energy are correlated to the presence of various texture components, as detected by the use of an orientation distribution function (ODF) analysis. The final microstructures were similar and consisted of polygonal and acicular ferrite. The textures were also similar; however, after rolling in the (α+γ) region, the intensity of the texture was significantly higher. These textures were mainly comprised of two fibers, the rolling direction (RD), 〈110〉//RD, and the normal direction (ND), 〈111〉//ND, fibers. The observations show that the RD fiber centered at {112}〈110〉 and the {110}〈001〉 orientation were responsible for the YS anisotropy. The relationships between notch toughness and texture were considered for the brittle or cleavage (−196 °C), mixed brittle-ductile (−60 °C), and ductile (room temperature (RT)) modes of fracture. This work shows that the anisotropy of impact energy associated with ductile fracture at the higher temperatures is caused by the {112}〈110〉 component, and that the {001}〈110〉 and {110}〈001〉 components (if present) are responsible for the anisotropy of the impact energy associated with cleavage at low temperatures. The lack of anisotropy of the impact energy observed at −196 °C and the increase in toughness at higher temperatures are interpreted in terms of the volume fractions of textured grains present in the sheet and the intensities of specific texture components.     

Orientation distribution function analysis of the recrystallization texture in a boron-treated deep-drawing steel

The textural components present in a boron-treated deep-drawing quality nonaging steel, processed and annealed in the mill, have been determined using the orientation distribution function (ODF) analysis technique. The main components are a 〈111〉 fiber parallel to sheet plane normal or normal direction, ND, and an incomplete 〈337〉∥ND fiber. Minor {110}〈001〉, {310}〈001〉, {001}〈110〉, and {110} 〈110〉 orientations were also found. The texture on the whole is somewhat similar to that in A1-killed steels, but not as strongly developed. It is expected that this boron-treated steel would be suitable for moderate forming applications.     

Approach to saturation in textured soft magnetic materials

A model has been developed for calculating the anisotropic magnetic properties of soft magnetic materials with the objective of accounting for variations in permeability in textured materials. The model in its current form takes account of the rotation of the magnetization direction in each domain of a textured polycrystal and, thus, is applicable to large applied fields. The magnetization direction is determined by minimizing the sum of the magnetocrystalline anisotropy energy and the energy of interaction between the applied field and local magnetization. Examples are given of the application to idealized textures, such as fiber textures, in which all grains share a common axis parallel to the sheet normal (ND). The cube fiber (〈100〉‖ND) has the highest permeability at any applied field, followed by a randomly oriented polycrystal, with the gamma fiber (〈111〉‖ND) having the lowest permeability. Two further examples are given of textured steel sheets, often referred to as “nonoriented electrical steels,” intended for use as laminations in rotating electrical machinery. In one case, the two samples show that a random texture is preferable to one in which the rolling texture is retained. The second example demonstrates the importance of a particular texture component, the Goss or 〈001〉{110}, for producing an anisotropic permeability.     

Electropulsing Induced Texture Evolution in the Recrystallization of Fe-3 Pct Si Alloy Strip

Electropulsing induced texture evolution in the primary recrystallization of a Fe-3 pct Si alloy strip was studied using the electron backscattered diffraction technique. The results revealed that the electropulsing strengthened considerably the recrystallization of a cold-rolled Fe-3Si alloy strip. Various textures with high-energy storages, such as α (100)〈110〉, γ (111)〈110〉, γ (111)〈112〉, and G-texture (110)〈001〉, formed after several seconds of electropulsing treatment (EPT), depending on the intensity of electropulsing. The athermal effect of electropulsing is 319 times stronger than the thermal effect of electropulsing for the formation of the G texture. The mechanism of electopulsing induced texture evolution is discussed from the point of view of Gibbs free energy and dislocation dynamics.     

Effect of texture and microstructure on resistance to cracking of high-strength hot-rolled Nb-Ti microalloyed steels

Significant texture gradient in the through-thickness direction was observed in high-strength hot-rolled 560 and 770 MPa Nb-Ti microalloyed steels, characterized by polygonal ferrite and ferrite bainite microstructures, respectively. {113}〈110〉 was the most intense deformation texture in the two high-strength grades of Nb-Ti steels and was dominant in the midthickness region compared to 10 and 25 pct depth below the surface. The recrystallization texture of austenite, {100}〈001〉, transformed into {100}〈011〉 component in the ferrite and indicated an increase in the intensity with increase in depth for the Nb-Ti microalloyed steels. The {100}〈011〉 texture has a detrimental effect on the edge formabiity of steels. However, the midthickness plane contained considerable intensity of desired texture, {332}〈113〉, which is expected to offset the undesirable {100}〈011〉 texture resulting in superior edge formability and impact toughness of Nb-Ti steels, consistent with experimental observations.     

Atmosphere change of vacuum to hydrogen and sharpness of {110}〈001〉 texture in thin-gaged 3 Pct Si-Fe alloy strips

Heating in vacuum finally resulted in a main {100}〈uvw〉 texture and a trace of {111}〈uvw〉 texture. However, the texture was changed to the {110}〈001〉 texture when the strip was heated in hydrogen or when the vaccuum was changed to hydrogen at a temperature T_c. As T_c increased, the sharpness of the {110}〈001〉 texture increased, resulting in the high magnetic induction. This can be understood in the light of surface segregation kinetics of sulfur.     

Surface segregation and directionality of {110} grains in electrical steels containing Sn and Sb

A repulsive segregation behavior between sulfur and tin or antimony was observed. Tin and antimony as well as sulfur governed the selective grain growth. In the tin- and the antimony-added strips, the deviation angle distributions between the 〈001〉 crystal direction of {110} grains and the rolling direction after final annealing were broad, compared to that in the strip without the solutes. This is due to a {001} cold-rolling texture with a deviation angle between the 〈001$x232A; crystal and the rolling directions that results in the initial annealing texture detrimental to the formation of sharp {110} 〈001〉 texture. This research was supported by a grant from the Center for Advanced Materials Processing (CAMP) of the 21st Century Frontier R&D Program funded by the Ministry of Science and Technology, Republic of Korea.     

Investigation of Prism ?a? Slip in Warm-Rolled AZ31 Alloy

Based on analysis of texture and in-grain misorientation axes (IGMA) distribution, we investigate the effects of initial orientation and deformation temperature on the rollability of magnesium alloy AZ31 and the associated deformation mechanisms. Plate samples oriented favorably for basal 〈a〉 slip exhibited the best rollability at room temperature, whereas under the warm-rolling condition, surprisingly, the plate oriented for prism 〈a〉 slip exhibited the best rollability. The enhanced rollability of the latter plate is attributed to increased activity of prism 〈a〉 slip, which exhibits a lower texture hardening rate than basal 〈a〉 slip. The increased activity of prism 〈a〉 slip is shown experimentally by the development of the á10[`1]0 ? \langle 10\bar{1}0 \rangle //RD texture and 〈0001〉-type IGMA distribution. Asymmetric texture is also suggested to impair the rollability of plate oriented for basal 〈a〉 slip.     

Room-temperature deformation behavior of a directionally solidified β (B2)-(Ni-Fe-Al) intermetallic alloy

The room-temperature mechanical behavior of a directionally solidified columnar-grained, single-phase β (B2)-(Ni-20 at. pct Fe-30 at. pct A1) intermetallic alloy deformed along the “hard” 〈001〉 direction has been characterized. The 0.2 pct offset compressive yield stress was found to be comparable to that of 〈001〉 single crystals of stoichiometric NiAl. The dislocation substructure consisted of a preponderance of long, straight a〈111〉 screw dislocations on {112} planes, with cross-slip on {123} and {110} planes. The superpartials were not resolved by weak-beam imaging conditions, indicating that the antiphase boundary (APB) energy of NiAl is not reduced significantly by the Fe addition. The dislocation substructure was analyzed as a function of strain and compared to the dislocation substructure in 〈001〉 NiAl and body-centered cubic (bcc) metals deformed at low homologous temperatures. The debris left behind by a〈111〉 screw dislocations consisted of prismatic edge dipole loops 5 to 25 nm in diameter.     

Annealing behavior of alumina dispersion-strengthened copper strips rolled under different conditions

A study has been made of annealing behavior of a boron-added alumina dispersion-strengthened copper (ADSC) strip, Glidcop Al-25, and specimens fabricated by rolling of the strip by 25 to 28 pct under various conditions. All the specimens, including the starting strip, had similar microstructures consisting of microbands aligned parallel to the rolling direction. The textures of the specimens were characterized by β fiber, which runs from the copper orientation {112}〈111〉 over the S orientation {123}〈634〉 to the brass orientation {110}〈112〉 in the Euler orientation space, with the intensities in the S and the brass components being higher than the copper component and with the S components having higher intensities than the brass component in the surface layers. When annealed at 1123 K for 1 hour, the center region of the starting strip and cold-rolled specimens underwent recrystallization, with recrystallization texture being approximated by {112}〈312〉, whereas the specimens rolled at 813 K did not undergo recrystallization through the thickness. These results have been discussed based on detailed microstructures and microtextures.     

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.     

Microscale and Mesoscale Crystallographic Textures of Nanocrystalline Ni-Based Electrodeposits

The microscale and mesoscale crystallographic textures observed in nanocrystalline Ni, Ni-20 pct Fe, and Ni-50 pct Fe electrodeposits are described. The nanosized grains are arranged in coarse mesoscale colonies. In the as-deposited state, the bulk texture of the Ni-20 pct Fe alloy displays a dominant 〈001〉 fiber parallel to the macroscopic deposition direction (DD). The grains are elongated along the 〈001〉 crystal lattice direction, which is mostly parallel to the local DD, producing a well-defined 〈001〉//DD fiber microtexture on a local scale. The grain misorientation histograms show some content of low-angle boundaries, frequently associated with the presence of grain clusters, and are dominated by high-angle boundaries with a possible enhanced frequency of ∑5 and ∑7 coincident site lattice boundaries and a significant content of ∑3 twin boundaries. For all three alloys, the coarsened grains, obtained by annealing, within the mesoscale colonies show a fiber mesotexture characterized by a 〈111〉 axis approximately perpendicular to the colony hemispherical growth surface (parallel to the local DD). It is surmised that a similar “cobblestone” mesotexture with a 〈001〉 fiber axis already exists in the as-received state, as previously proposed by a number of the present authors and as supported by the results on the Ni-20 pct Fe alloy presented here.     

Recrystallization and grain growth of cold-drawn gold bonding wire

Recrystallization and grain growth of gold bonding wire have been investigated with electron back-scatter diffraction (EBSD). The bonding wires were wire-drawn to an equivalent strain greater than 11.4 with final diameter between 25 and 30 μm. Annealing treatments were carried out in a salt bath at 300 °C, and 400 °C for 1, 10, 60 minutes, and 1 day. The textures of the drawn gold wires contain major 〈111〉, minor 〈100〉, and small fractions of complex fiber components. The 〈100〉 oriented regions are located in the center and surface of the wire, and the complex fiber components are located near the surface. The 〈111〉 oriented regions occur throughout the wire. Maps of the local Taylor factor can be used to distinguish the 〈111〉 and 〈100〉 regions. The 〈111〉 oriented grains have large Taylor factors and might be expected to have higher stored energy as a result of plastic deformation compared to the 〈100〉 regions. Both 〈111〉 and 〈100〉 grains grow during annealing. In particular, 〈100〉 grains in the surface and the center part grow into the 〈111〉 regions at 300 °C and 400 °C. Large misorientations (angles >40 deg) are present between the 〈111〉 and 〈100〉 regions, which means that the boundaries between them are likely to have high mobility. Grain average misorientation (GAM) is greater in the 〈111〉 than in the 〈100〉 regions. It appears that the stored energy, as indicated by geometrically necessary dislocation content in the subgrain structure, is larger in the 〈111〉 than in the 〈100〉 regions.     

The origin of transformation textures in steel weld metals containing acicular ferrite

The present investigation is concerned with basic studies of the development of transformation textures in steel weld metals, using the electron backscattering pattern (EBSP) technique. It is shown that the acicular ferrite (AF) plates exhibit an orientation relationship with both the austenite and the prior delta ferrite columnar grains in which they grow. The observed orientation relationship lies within the Bain orientation region and can be described by three texture components,i.e., a 〈100〉 component and two complementary 〈111〉 components. Each of these texture components is orientated approximately parallel with the original cell/dendrite growth direction. Measurements of the spatial misorientation between neighboring plates confirm that the morphology of AF in low-alloy steel weld metals bears a close resemblance to upper bainite.     

The evolution of annealing textures in 90 Pct drawn copper wire

An electrolytic copper rod was drawn in 24 passes to a 90 pct reduction in area and subsequently annealed under various conditions. The global texture of the drawn wire, as measured by X-ray methods, showed a fiber texture approximated by a strong 〈111〉 and a weak 〈100〉 component. However, its microtexture, as measured by electron backscattered diffraction (EBSD), indicated that the major 〈111〉+minor 〈100〉 duplex fiber texture was dominant only in the center region, while a relatively diffuse texture developed with a somewhat higher density of orientations having a 〈11w〉//wire axis in the middle and surface regions. The inhomogeneous texture in the as-deformed wire gave rise to an inhomogeneous microstructure and texture after annealing. When annealed at 300 °C or 600 °C for 3 hours, the wire developed a duplex fiber texture consisting of major 〈100〉+minor 〈111〉 components in the center region, a strong 〈100〉 fiber texture in the middle region, and a weak texture consisting of 〈111〉 and 〈100〉 components with the 〈111〉 component being slightly stronger in the surface region. When the drawn wire was annealed at the high temperature of 700 °C, the texture at short annealing times was similar to that of the wire annealed at the lower temperatures of 300 °C and 600 °C for 3 hours, but prolonged annealing gave rise to a texture ranging from the 〈111〉 to 〈112〉 components due to abnormal grain-growth that started in the surface region. The recrystallization texture consisting of the major 〈100〉+minor 〈111〉 components was explained by the strain-energy-release maximization (SERM) model, in which the recrystallization texture is determined such that the absolute maximum principal stress direction due to dislocations in the deformed state is along the minimum elastic-modulus direction in recrystallized grains. On the other hand, the abnormal grain-growth texture was attributed to grain-boundary mobility differences between differently oriented grain.     

〈110〉 dendrite growth in aluminum feathery grains

Automatic indexing of electron backscattered diffraction patterns, scanning electron microscopy, and optical microscopy observations have been carried out on aluminum-magnesium-silicon, aluminum-copper, and aluminum-silicon alloys directionally solidified or semicontinuously cast using the direct chill casting process. From these combined observations, it is shown that the feathery grains are made of 〈110〉 primary dendrite trunks (e.g., [01 ]) split in their centers by a coherent (111) twin plane. The average spacing of the dendrite trunks in the twin plane (about 10 to 20 μm) is typically one order of magnitude smaller than that separating successive rows of trunks (or twin planes). The [01 ] orientation of these trunks is close to the thermal gradient direction (typically within 15 deg)—a feature probably resulting from a growth competition mechanism similar to that occurring during normal 〈100〉 columnar dendrite growth. On both sides of these trunks, secondary dendrite arms also grow along 〈110〉 directions. Their impingement creates wavy noncoherent twin boundaries between the coherent twin planes. In the twin plane, evidence is shown that 〈110〉 branching mechanisms lead to the propagation of the twinned regions, to the regular arrangement of the primary dendrite trunks along a [ 11] direction, and to coherent planar twin boundaries. From these observations, it is concluded that the feathery grains are probably the result of a change from a normal 〈100〉 to a 〈110〉 surface tension/attachment kinetics anisotropy growth mode. This change might be induced by the added solute elements, by the local solidification conditions (thermal gradient, growth rate, and melt convection), and possibly by the help of the twin plane itself. Convection in the melt could also play a role in the symmetrization of the 〈110〉 growth directions of the side arms. Finally, the proposed mechanisms of feathery grain growth are further supported by the observation of 〈110〉 dendrite growth morphologies in thin aluminum-zinc coatings.     

Effects of heating rate and hydrogen flow rate on magnetic induction and final grain texture of 3 pct silicon steel

In inhibitor-free 3 pct silicon steel of 0.1-mm thickness, magnetic induction after final annealing decreased roughly with increasing heating rate and hydrogen flow rate. This is mainly due to the increase in the number of the {110}〈uvw〉_≠〈001〉 grains.     

A theoretical examination of the plastic deformation of ionic crystals: III. Mixed {110}, {100}, {111} 〈110〉 slip and approximate 〈110〉 pencil glide

Calculations have been made of the Taylor factorM and of the lattice rotation for crystals undergoing axisymmetric flow and deforming by approximate 〈110〉 pencil glide. Two types of approximate 〈110〉 pencil glide were considered: 1) mixed slip on {110}, {l00}, and {111} 〈110〉 systems and 2) slip on a set of equally spaced slip planes containing each (110) slip direction. The results indicate that the pencil glide mode tends to reduce the plastic anisotropy in axisymmetric flow in contrast to the 〈111〉 slip modes in bcc metals. The lattice rotation is such that the fiber axis tends toward 〈111〉 in tension (〈lOO〉minor tendency) and toward 〈110〉 in compression. This result is similar to that of {lll}〈110〉 slip in fcc metals. We have also calculated the Taylor factors for mixed {110}〈110〉 + {lll}〈110〉 slip and for mixed {l00}(110) + {lll}〈110〉 slip. These mixed modes, together with the {lll}〈110〉 and the mixed {l00}〈110〉 + {110}〈110〉 slip modes previously analyzed, constitute all possible slip modes among {lll}〈110〉, {l00}(110), and {ll0}〈110〉 systems accommodating an arbitrary shape change. The conditions governing the activation of the various mixed modes have also been determined.