Ferrite Texture Research Articles

Biaxial deformation behaviour of duplex stainless steels: Experiments and crystal plasticity based stress predictions

Biaxial tensile tests are performed on two phase duplex stainless steel using a newly developed multiaxial testing rig integrated with a digital image correlation mapping facility. A cruciform-shaped specimen geometry is subjected to equibiaxial tensile (EBT) loading, and the load–strain response is captured. Unlike uniaxial tensile testing, a well-defined gauge area is absent in biaxial specimens; hence, stress cannot be estimated directly. Finite element analysis is used to calculate the stress state. The phenomenological finite element model failed to capture the inherent anisotropy of the material; hence, a crystal plasticity finite element based method is used to estimate the stresses. It is observed that the 0.2% proof stress increased, but the strain to failure remained constant in comparison with uniaxial tensile properties. The work hardening behaviour is isotropic similar to that observed during uniaxial testing. The goss and rotated goss orientations in austenite accommodated most of the strain along RD and TD, respectively. During EBT, the change in austenite and ferrite textures is minimal and similar to their single phase counterparts reported in the literature. The EBT test results indicate that the influence of micromechanical interactions between the phases on the work hardening behaviour and texture evolution is weak.

Interfacial Microstructure and Properties of Clad Rebar Prepared by Clean-Interface Assembly and Vacuum Hot-Rolling

Stainless steel cladded rebars were successfully prepared by clean-interface assembly and vacuum hot-rolling process. The interfacial microstructure and properties of the clad rebars were investigated by scanning electron microscope (SVM), transmission electron microscope (TEM), and electron probe X-ray microanalyser (EPMA). The results demonstrated that owing to the diffusion of carbon, decarburised (roughly 50 μm) and composite zones (roughly 60 μm) formed on each side of the composite interface. The decarburized zone features a single ferrite texture, hence, a relatively low micro-hardness of 138HV while, due to the large amount of martensite formed within it, the composite zone has a relatively high micro-hardness of 218HV. The salt spray test showed that the corrosion rate of the clad rebars is close to that of the round stainless bars, and is approximately one-tenth that of the carbon rebars. In addition, a layered multipass welding process was used to produce a cladding joint, which was determined to have a tensile strength greater than the standard value of the parent material and excellent corrosion resistance.

Anisotropic work hardening behaviour in duplex stainless steel under uni-axial loading: Interplay between phase morphology and crystallographic texture

Duplex stainless steels (DSS) are characterised by vivid phase morphology and crystallographic textures. The typical microstructure consists of elongated phases (along rolling direction, RD) stacked alternatively along the normal direction (ND). In this study, uni-axial testing in multiple macroscopic directions is used to explore the anisotropic evolution of work hardening. Crystal plasticity simulations are used to gain insights into the same. The compressive stress and work hardening of samples loaded in the transverse direction (TD) are observed to be higher than those loaded in the RD and ND. Austenite and ferrite developed [110] and [111] parallel to the loading direction type fibre textures during uni-axial compression. The weak austenite texture behaves similarly to its single-phase counterparts regarding reorientation. The plastic anisotropy evolution is aided by the strong ferrite texture, which deviates from its single-phase behaviour. When loaded along TD compared to other directions, microstructural characterisation revealed the formation of deformation twins in austenite and lower effective slip length of both the phases.

Strength Enhancement of Superduplex Stainless Steel Using Thermomechanical Processing

The impact of microstructure evolution on mechanical properties in superduplex stainless steel UNS S32750 (EN 1.4410) was investigated. To this end, different thermomechanical treatments were carried out in order to obtain clearly distinct duplex microstructures. Optical microscopy and scanning electron microscopy, together with texture measurements, were used to characterize the morphology and the preferred orientations of ferrite and austenite in all microstructures. Additionally, the mechanical properties were assessed by tensile tests with digital image correlation. Phase morphology was not found to significantly affect the mechanical properties and neither were phase volume fractions within 13% of the 50/50 ratio. Austenite texture was the same combined Goss/Brass texture regardless of thermomechanical processing, while ferrite texture was mainly described by α-fiber orientations. Ferrite texture and average phase spacing were found to have a notable effect on mechanical properties. One of the original microstructures of superduplex stainless steel obtained here shows a strength improvement by the order of 120 MPa over the industrial material.

Microstructural development and texture evolution in the stir zone and thermomechanically affected zone of a ferrite-martensite steel friction stir weld

The microstructure development and texture evolution during friction stir welding of a dual-phase DP700 steel were investigated. Based on electron backscattered diffraction analysis, it was found that continuous dynamic recrystallization and discontinuous dynamic recrystallization are the operative recovery mechanisms for the ferrite phase in the stir zone. However, in addition to these mechanisms, geometrically dynamic recrystallization is also involved within the thermomechanically affected zone which is due to the lower strain rates in the thermomechanically affected zone. However, the continuous dynamic recrystallization was the predominant recovery mechanism for ferrite in both the stir zone and thermomechanically affected zone. Micro-texture examination showed that FSW develops typical shear texture components such as D1, D2 and F as well as the cube recrystallization texture for the ferrite phase within the stir zone. However, because of different thermomechanical conditions in various regions of the thermomechanically affected zone, additional shear texture components are developed, such as E, J and J¯ together with as D1, D2 and F, which were already observed in the stir zone. The absence of the cube recrystallization texture of ferrite in thermomechanically affected zone is attributed to insufficient recrystallization due to lowered strain and temperature in this zone. Study of the retained austenite constituent revealed that both shear textures, B and B¯ as well as recrystallization textures are developed in this phase within both the stir zone and thermomechanically affected zone.

Explaining the dilatometric behavior during bainite transformation under the effect of variant selection

The selection of crystallographic variants in bainitic microstructures is a deeply studied topic which can be attributed to several reasons. In the cases where the prior austenite is textured, stressed or plastically deformed, the final ferrite texture and the dilatometry signal may change, being anisotropic. Although the causality between variant selection and the variation of the dilatometric signal has been previously assumed, it has not been thoroughly proved. In this work, the phenomenological theory of martensite was combined with a continuum mechanics analysis to calculate the relative length changes associated to the bainitic transformation during different bainitic transformations in order to prove the connection between the selection of crystallographic variants and the distortion of the dilatometry signal. To do so, four different bainitic microstructures were analyzed: one of them obtained by a pure isothermal treatment and the rest of them obtained by ausforming treatments. Some of the mentioned microstructures had shown to lead to negative longitudinal dilatometry signals and to present a strong variant selection. Results showed that the experimental trends could be explained by theoretical means, which enables to further understand the bainitic transformation.

Effect of Annealing on the Microstructure, Texture and Mechanical Properties of a Dual-Phase Ultrahigh-strength TWIP Steel

The present study investigates the effect of annealing time and temperature on the microstructural restoration (by recovery and recrystallization), texture evolution and tensile properties of a dual-phase TWIP steel. The samples, which were initially hot rolled-air cooled followed by being in solution treated condition, subsequent 50 pct cold rolled condition and different annealing conditions (temperatures ranging from 500 °C to 1000 °C for 5 minutes to 2 hours), were subjected to microstructural characterization using optical and transmission electron microscopy, electron backscatter diffraction analysis, tensile testing and fractographic study. The deformation-induced ferrite (DIF) transformation due to cold deformation, the evolution of the grain structure and texture in both austenite and ferrite, and the change in the DIF fraction (accompanying the recrystallization annealing treatment) are critically analyzed. The optimum combination of strength and ductility is achieved in the partially recrystallized samples annealed at 700 °C for 30 minutes (UTS: 859 MPa, total elongation: 37 pct) and 900 °C for 30 minutes (UTS: 708 MPa, total elongation: 63 pct).The effects of DIF on the evolution of microstructure and texture during annealing and the final properties are discussed.

Tnr Dependent Hot Rolling Microstructure and Texture Development in C-Mn Dual Phase and HSLA Steels

No recrystallization of austenite, Tnr, has an important influence on the transformed phase fractions and the final crystallographic texture after hot deformation. This paper investigates the evolution of microstructure and texture components during hot-rolling in two austenitic region based on Tnr along with three different cooling trajectory and coiling in dual-phase steels and high strength low alloys steel. The recrystallization of the austenite, the austenite deformation followed by the austenite-to-ferrite transformation influence the final microstructure and texture in dual phase steels, have been examined by means of optical microscopy, X-ray diffraction (XRD) measurements. Recrystallized and deformed austenite have clearly different texture components and, due to the specific lattice correspondence relations between the parent austenite phase and its transformation products, the resulting ferrite textures are different as well.

Evolution of Microstructure and Crystallographic Texture During Dissimilar Friction Stir Welding of Duplex Stainless Steel to Low Carbon-Manganese Structural Steel

Electron backscattered diffraction (EBSD) was used to analyze the evolution of microstructure and crystallographic texture during friction stir welding of dissimilar type 2205 duplex stainless steel (DSS) to type S275 low carbon-manganese structural steel. The results of microstructural analyses show that the temperature in the center of stirred zone reached temperatures between Ac1 and Ac3 during welding, resulting in a minor ferrite-to-austenite phase transformation in the S275 steel, and no changes in the fractions of ferrite and austenite in the DSS. Temperatures in the thermomechanically affected and shoulder-affected zones of both materials, in particular toward the root of the weld, did not exceed the Ac1 of S275 steel. The shear generated by the friction between the material and the rotating probe occurred in austenitic/ferritic phase field of the S275 and DSS. In the former, the transformed austenite regions of the microstructure were transformed to acicular ferrite, on cooling, while the dual-phase austenitic/ferritic structure of the latter was retained. Studying the development of crystallographic textures with regard to shear flow lines generated by the probe tool showed the dominance of simple shear components across the whole weld in both materials. The ferrite texture in S275 steel was dominated by D1, D2, E, bar{E} , and F, where the fraction of acicular ferrite formed on cooling showed a negligible deviation from the texture for the ideal shear texture components of bcc metals. The ferrite texture in DSS was dominated by D1, D2, I, bar{I} , and F, and that of austenite was dominated by the A, bar{A} , B, and bar{B} of the ideal shear texture components for bcc and fcc metals, respectively. While D1, D2, and F components of the ideal shear texture are common between the ferrite in S275 steel and that of dual-phase DSS, the preferential partitioning of strain into the ferrite phase of DSS led to the development of I and bar{I} components in DSS, as opposed to E and bar{E} in the S275 steel. The formations of fine and ultrafine equiaxed grains were observed in different regions of both materials that are believed to be due to strain-induced continuous dynamic recrystallization (CDRX) in ferrite of both DSS and S275 steel, and discontinuous dynamic recrystallization (DDRX) in austenite phase of DSS.

Enhancement in magnetostrictive properties of cobalt ferrite by magnetic field assisted compaction technique

Sintered polycrystalline cobalt ferrite is a potential magnetostrictive material for torque sensor application. Significant enhancement in magnetostriction of cobalt ferrite by magnetic field assisted compaction has been reported. Nano crystalline cobalt ferrite powder was prepared by combustion synthesis method using glycine as fuel. Phase pure cobalt ferrite powder was pressed into cylindrical pellets at an applied pressure of 200 MPa using a uniaxial hydraulic press with and without magnetic field of 1 Tesla. The green pellets were sintered at 1350 °C for 12 h which resulted in sintered pellets with ∼85% of the theoretical density. The SEM micrographs of the sintered pellets revealed the microstructure to be composed of grains with average size of ∼4 μm. EBSD analysis showed that significant change in texture of cobalt ferrite has not been observed in the sample compacted in presence of magnetic field. Maximum magnetizations of 70.2 emu/g and 69.8 emu/g were observed for cobalt ferrite processed with and without magnetic field pressing, respectively. A significant enhancement in magnetostriction, (195 ppm–325 ppm) ∼65% and strain sensitivity, 35% (1.3 × 10−9 m/A to 1.8 × 10−9 m/A) have been observed for the sample pressed under magnetic field than the sample pressed without magnetic field.

“Flash” Annealing in a Cold‐Rolled Low Carbon Steel Alloyed with Cr, Mn, Mo, and Nb: Part II—Anisothermal Recrystallization and Transformation Textures

The aim of the present investigation is to study the microstructure and texture evolution in a cold‐rolled low carbon steel subjected to continuous heating and subsequent quenching. Peak‐annealing and quenching experiments are carried out at different temperatures at three heating rates (10, 400, and 1000 °C s−1). The texture evolution in ferrite and martensite is analyzed separately via Electron Backscattered Diffraction (EBSD) measurements. It is observed that the recrystallization is virtually completed at 771 °C in samples heated at 10 °C s−1. Conversely, the recrystallization is suppressed in samples heated at rates ≥400 °C s−1. In samples heated at 10 °C s−1, the ferrite texture evolves according to the well‐known recrystallization behavior, showing a maximum in {113}<110> components, whereas in samples heated at rates ≥400 °C s−1, the texture is similar to the one of the cold‐rolled material. It is concluded that the texture evolution in martensite is strongly dependent on the evolution of recrystallization textures in ferrite. A particular grain substructure product of the interaction between the recrystallization of ferrite and massive austenite formation is observed after heating at rates ≥400 °C s−1. However, this substructure seems to have effect neither on the textures of ferrite nor on the work hardening behavior.

The effect of thermomechanical controlled processing on recrystallisation and subsequent deformation-induced ferrite transformation textures in microalloyed steels

The evolution of texture components for two experimental 0.06 wt% C steels, one containing 0.03 wt% Nb (Nb steel) and the second containing both 0.03 wt% Nb and 0.02 wt% Ti (Nb–Ti steel), was investigated following a new thermomechanical controlled process route, comprising first deformation, rapid reheat to 1200 °C and final deformation to various strains. Typical deformation textures were observed after first deformation for both steels. Following subsequent reheating to 1200 °C for various times, the recrystallisation textures consisted primarily of the α- leftlangle {011} rightrangle //RD texture fibre with a weak γ-{111}//ND texture fibre, similar to deformation textures, indicative of the dominance of a strain-induced boundary migration mechanism. The texture components after finish deformation were different from the rough deformation textures, with a strong α- leftlangle {011} rightrangle //RD texture fibre at the beginning, and then the strong peaks move to (111) leftlangle {1bar{2}1} rightrangle and (111) leftlangle {bar{1}bar{1}2} rightrangle textures due to the deformation-induced ferrite (DIF) transformation. The effect of Ti on the recrystallisation textures and deformation textures has also been analysed in this study. The results illustrate that Ti significantly influences the γ-{111}//ND texture fibre. Finally, the textures after deformation and recrystallisation in the austenite were calculated based on the K–S orientation relationship between the austenite and ferrite. This allowed the understanding of the mechanism of recrystallisation between first and final deformation and the DIF textures during phase transformation.

Influence of heat input in electron beam process on microstructure and properties of duplex stainless steel welded interface

The influence of heat input in electron beam (EB) process on microstructure, mechanical properties, and pitting corrosion resistance of duplex stainless steel (DSS) welded interface was investigated. The rapid cooling in EB welding resulted in insufficient austenite formation. The austenite mainly consisted of grain boundary austenite and intragranular austenite, and there was abundant Cr2N precipitation in the ferrite. The Ni, Mo, and Si segregation indicated that the dendritic solidification was primarily ferrite in the weld. The weld exhibited higher hardness, lower toughness, and poorer pitting corrosion resistance than the base metal. The impact fractures of the welds were dominated by the transgranular cleavage failure of the ferrite. The ferrite was selectively attacked because of its lower pitting resistance equivalent number than that of austenite. The Cr2N precipitation accelerated the pitting corrosion. In summary, the optimised heat input slightly increased the austenite content, reduced the segregation degree and ferrite texture intensity, decreased the hardness, and improved the toughness and pitting corrosion resistance. However, the effects were limited. Furthermore, optimising the heat input could not suppress the Cr2N precipitation. Taking into full consideration the microstructure and properties, a heat input of 0.46 kJ/mm is recommended for the EB welding of DSS.

Influence of Temperature on the Texture Distribution in Two-Phase Region Hot Deformation of Grain-Oriented Silicon Steel

Hot deformation simulation test of 3% Si grain-oriented silicon (CGO) steel was carried out at different temperatures, and evolution of microstructures and recrystallized textures in two-phase region was analyzed by electron backscatter diffraction and optical microscopy. The “δ → γ” and “γ → α” phase transformation points of the two-phase region measured by differential scanning calorimetry method are 1272 and 819 °C, respectively, which are within the ranges of 1300-1350 and 800-850 °C, measured by water quenching. The hot deformation temperature has a large effect on the microstructure and texture in the steel. A higher hot deformation temperature leads to higher degree of recrystallization and larger average grain size, more γ-fiber textures and cube {100} texture, but the rotated cube {100} texture is stable. The recrystallized microstructure was also affected by the phase compositions. While the cube {100} texture results in typical austenite recrystallization texture, {111} textures lead to typical ferrite rolling textures.

Microstructures and Mechanical Properties of as-Drawn and Laboratory Annealed Pearlitic Steel Wires

Near eutectoid fully pearlitic wire rod (5.5 mm diameter) was taken through six stages of wire drawing (drawing strains of 0 to 2.47). The as-drawn (AD) wires were further laboratory annealed (LA) to re-austenitize and reform the pearlite. AD and LA grades, for respective wire diameters, had similar pearlite microstructure: interlamellar spacing (λ) and pearlite alignment with the wire axis. However, LA grade had lower hardness (for both phases) and slightly lower fiber texture and residual stresses in ferrite. Surprisingly, essentially identical tensile yield strengths in AD and LA wires, measured at equivalent spacing, were found. The work hardened AD had, as expected, higher torsional yield strengths and lower tensile and torsional ductilities than LA. In both wires, stronger pearlite alignment gave significantly increased torsional ductility.

Correlation of Microstructure and Texture in a Two-Phase High-Mn Twinning-Induced Plasticity Steel During Cold Rolling

The evolution of microstructure and texture of a two-phase austenite-ferrite twinning-induced plasticity steel during cold rolling was investigated and different deformation mechanisms were found to become active with increasing thickness reductions. Optical microscopy showed the formation of brass-type shear bands across several austenite grains at reductions greater than 50 pct. TEM observations reveal the presence of deformation twinning in austenite. The austenite phase initially shows the Cu-type texture, i.e., Cu {1 1 2}〈1 1 1〉, Goss {0 1 1}〈1 0 0〉 with a spread toward Brass {1 1 0}〈1 1 2〉. With continued cold rolling, the Cu {1 1 2}〈1 1 1〉 component moves toward CuT component {552}〈115〉 and the other two components increase in intensity. There is also emergence of {111} fiber after 90 pct cold rolling. The ferrite phase exhibits the evolution of ND-rotated Cube component {001}〈110〉 along with 〈110〉 fiber at lower as well as at higher rolling reductions. An exception is at 75 pct reduction, when the ferrite texture contains {111} fiber in place of 〈110〉 fiber with a weak rotated-Cube component. Phase fraction analysis by X-ray diffraction indicates a decrease in the austenite fraction up to 75 pct reduction followed by an increase at 90 pct reduction. After 90 pct cold rolling, the phase fraction is similar to that of the “as-received” state. Elongated grains of ferrite phase in finer dimensions after 90 pct cold rolling indicate softening within that phase; at similar stage, there are finer scale austenite grains mostly at the grain boundaries. The above has been suggested to be related with the adiabatic heating during cold rolling due to the high strain hardening of the austenite phase.

The effect of the pre-heating stage on the microstructure and texture of a cold rolled FeCMnAlSi steel under conventional and ultrafast heating

This work focuses on the effect of a pre-heating stage on the microstructure evolution during continuous heating of 50% and 75% cold-rolled low carbon steel under conventional and ultrafast heating rates. Peak annealing experiments under two heating rates (10°C/s and 400°C/s) are applied to the samples after a pre-heating stage of 10s. The selected pre-heating temperatures (300°C and 400°C) show an influence on the phase fraction of austenite formed after a short holding time in the intercritical (α+γ) phase field, and an effect on the intensity of recrystallized ferrite texture components. A refinement of ferritic average grain diameter is observed after increasing the heating rate from 10°C/s to 400°C/s. It is concluded that a pre-heating stage has a negligible impact on the microstructure and texture of cold-rolled low carbon steel. Therefore, a suitable technological window for the application of ultrafast heating rates in steel processing is enabled.

Texture development during cold rolling of Fe–Cr–Ni alloy-experiments and simulations

In the present work, evolution of microstructure and crystallographic texture during cold rolling of two phase Fe–Cr–Ni alloy was investigated. Fe–Cr–Ni alloy (in initially solution annealed condition) was uni-directionally cold rolled in a laboratory rolling mill to different thickness reductions. Scanning electron microscopy was used to observe the changes in microstructure, while X-ray diffraction was used to investigate changes in crystallographic texture of austenite and ferrite (through changes in orientation distribution function). Crystallographic texture was also simulated using different crystal plasticity models (Full constraint Taylor, relaxed constraint Taylor (lath and pancake) and co-deformation Visco Plastic Self Consistent (VPSC)). With the increase in plastic deformation, there were morphological as well as crystallographic changes in the microstructure. Strong α-fibre (RD//〈1 1 0〉) texture was developed in ferrite, while brass ({1 1 0}〈1 1 2〉) and Goss ({1 1 0}〈0 0 1〉) was dominant in austenite after 80% cold rolling. The formation of brass type texture after deformation has been attributed to the formation of shear bands and presence of strong crystallographic texture in the initial solution annealed material. Both Taylor as well as VPSC models could not capture the changes in texture with deformation accurately. For ferrite: γ-fibre (ND//〈1 1 1〉) and for austenite: Cu ({1 1 2}〈1 1 1〉) component was always present in the simulated textures. Possible reason for this could be the pining effect of interface boundaries and non-incorporation of non-crystallographic shear banding in the Taylor and VPSC models.

Microstructural characterization and electron backscatter diffraction analysis across the welded interface of duplex stainless steel

The microstructural evolution, orientation relationships, boundary characteristics, grain type, local deformation, and microhardness across the welded interface of duplex stainless steel (DSS) were investigated. The DSS welded joint consisted of four typical zones: base metal (BM), low-temperature heat-affected zone (LTHAZ), high-temperature heat-affected zone (HTHAZ), and weld metal (WM). The apparent microstructural changes in the HTHAZ and LTHAZ were secondary austenite and Cr2N precipitation. A modified cooperative precipitation mechanism of secondary austenite and Cr2N at the interface was proposed. Furthermore, the ferrite in both the HTHAZ and LTHAZ maintained the same distribution as the ferrite texture in the BM, while this ferrite texture disappeared completely in the WM. Different austenite grains in the different zones exhibited different orientation relationships with the ferrite matrix. Special grain boundaries were mainly distributed between the austenite grains, while the ferrite grains primarily contained random grain boundaries. Austenite twins constituted the largest proportion of the special boundaries. The special austenite grain boundaries in the BM and LTHAZ were higher in relative frequency than those in the HTHAZ and WM. The ferrite grains in the HTHAZ and WM mainly consisted of substructured grains. In the BM, the recrystallization degree of ferrite was significantly lower than that of austenite grains. The local deformations were mainly generated in the grain boundaries and within the deformed grains. The HTHAZ exhibited the highest hardness, while the BM had the lowest hardness. The LTHAZ had a lower hardness than the HTHAZ and higher hardness than the BM.

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.