EBSD investigation of the microstructure and texture characteristics of hot deformed duplex stainless steel

The microstructure and crystallographic texture characteristics were studied in a 22Cr-6Ni-3Mo duplex stainless steel subjected to plastic deformation in torsion at a temperature of 1000 °C using a strain rate of 1 s⁻¹. High-resolution EBSD was successfully used for precise phase and substructural characterization of this steel. The austenite/ferrite ratio and phase morphology as well as the crystallographic texture, subgrain size, misorientation angles and misorientation gradients corresponding to each phase were determined over large sample areas. The deformation mechanisms in each phase and the interrelationship between the two are discussed.

EBSD and TEM investigation of the hot deformation substructure characteristics of a type 316L austenitic stainless steel

The evolution of crystallographic texture and deformation substructure was studied in a type 316L austenitic stainless steel, deformed in rolling at 900 °C to true strain levels of about 0.3 and 0.7. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used in the investigation and a comparison of the substructural characteristics obtained by these techniques was made. At the lower strain level, the deformation substructure observed by EBSD appeared to be rather poorly developed. There was considerable evidence of a rotation of the pre-existing twin boundaries from their original orientation relationship, as well as the formation of highly distorted grain boundary regions. In TEM, at this strain level, the substructure was more clearly revealed, although it appeared rather inhomogeneously developed from grain to grain. The subgrains were frequently elongated and their boundaries often approximated to traces of {111} slip planes. The corresponding misorientations were small and largely displayed a non-cumulative character. At the larger strain, the substructure within most grains became well developed and the corresponding misorientations increased. This resulted in better detection of sub-boundaries by EBSD, although the percentage of indexing slightly decreased. TEM revealed splitting of some sub-boundaries to form fine microbands, as well as the localized formation of microshear bands. The substructural characteristics observed by EBSD, in particular at the larger strain, generally appeared to compare well with those obtained using TEM. With increased strain level, the mean subgrain size became finer, the corresponding mean misorientation angle increased and both these characteristics became less dependent on a particular grain orientation. The statistically representative data obtained will assist in the development of physically based models of microstructural evolution during thermomechanical processing of austenitic stainless steels.

An analysis of microband orientation in hot deformed aluminium alloy AA5052 using forward and reverse torsion

The effects of strain path reversal on the macroscopic orientation of microbands in AA5052 have been studied using high resolution electron backscatter diffraction. Deformation was carried using two equal steps of forward/forward or forward/reverse torsion at a temperature of 300°C and strain rate of 1s-1 to a total equivalent tensile strain of 0.5. In both cases microbands were found in the majority of grains examined with many having more than one set. The microbands appear to cluster at specific angles to the macroscopic deformation. For the forward/forward condition microbands clustered around -20° and +45° to the maximum principle stress direction and at ± 30-35° to the principal strain direction. For the forward/reverse condition significantly more spread in microband angle was observed though peaks were visible at ±35° with respect to principal stress direction and at -40° and +30° with respect to the principal strain direction of the reverse torsion. This suggests the microbands formed in the forward deformation have or are dissolving and any new microbands formed are related to the deformation conditions of the final strain path.

EBSD study of the orientation dependence of substructure characteristics in a model Fe-30wt%Ni alloy subjected to hot deformation

The aim of the present investigation was to determine the orientation dependence of substructure characteristics in an austenitic Fe−30wt%Ni model alloy subjected to hot plane strain compression. Deformation was carried out at a temperature of 950 °C using a strain rate of 10 s^₋₁ to equivalent strain levels of approximately 0.2, 0.4, 0.6 and 0.8. The specimens obtained were analysed using a fully automatic electron backscatter diffraction technique. The crystallographic texture was characterized for all the strain levels studied and the subgrain structure was quantified in detail at a strain of 0.4. The substructure characteristics displayed pronounced orientation dependence. The major texture components, namely the copper, S, brass, Goss and rotated Goss, generally contained one or two prominent families of parallel larger-angle extended subboundaries, the traces of which on the longitudinal viewing plane appeared systematically aligned along the {111} slip plane traces, bounding long microbands subdivided into slightly elongated subgrains by short lower-angle transverse subboundaries. Relatively rare cube-orientated grains displayed pronounced subdivision into coarse deformation bands containing large, low-misorientated subgrains. The misorientation vectors across subboundaries largely showed a tendency to cluster around the sample transverse direction. Apart from the rotated Goss texture component, the stored energy levels for the remaining components were principally consistent with the corresponding Taylor factor values.

In-situ observations of Widmanstätten ferrite formation in a low carbon steel

An in situ laser-scanning confocal microscopy study has been undertaken into Widmanstätten ferrite formation in an Fe–C alloy, in combination with electron backscattered diffraction. It has been found for the first time that the sympathetic nucleation of Widmanstätten ferrite on grain boundary allotriomorphs can exhibit a step wise change in orientation and growth direction until the most favourable growth conditions are achieved.

Effect of orientation stability on recrystallization textures of deformed aluminium single crystals

High purity Al single crystals of the Cube (0 0 1)[1 0 0] and rotated Cube (0 1 1)[0 1 ¯ 1] orientations have been deformed in plane strain compression in a channel die. Deformation was carried out at temperatures between 25 and 600 8C up to strains of 1.2. The as-deformed microstructure has been characterised using electron microscopy and electron backscattered diffraction (EBSD).
Annealing was carried out for various times and temperatures. The recrystallized microstructure has been studied using electron microscopy, and the orientation of recrystallized grains determined using EBSD. After cold deformation and annealing both orientations exhibited a random recrystallization texture component. After hot deformation both orientations retained a similar annealing texture to their starting deformation texture. The annealing texture of deformed single crystals was found to be more sensitive to the temperature of deformation than the stability of the orientation.

Variant selection during the c-to-ab phase transformation in hot-rolled bainitic TRIP-aided steels

The variant selection phenomenon during the austenite to bainite phase transformation in hot-rolled TRIP-aided steels was quantitatively characterized at the level of individual austenite grains. The reconstruction of the electron backscatter diffraction maps provided evidence that bainite grows by packets of laths sharing a common {1 1 1}_y plane in the austenite. The affect of hot deformation is to reduce the number of packets that form. It is suggested that slip activity is important in understanding this effect.

Designing microstructures to enhance the plasticity of wrought magnesium alloys

The data examines the design of magnesium alloys for improved ductility by the edition of rare earth elements. These elements, such as cerium and gadolinium modify the texture of wrought products and also refine the grain size.

Role of microstructure in the low cycle fatigue of multi-phase steels

The low cycle fatigue (LCF) behaviour of several commercially-produced multiphase steels was studied; including dual-phase (DP) and transformation induced plasticity (TRIP). In addition, a novel TRIP980 hybrid microstructure was examined that consisted of coarse ferrite grains along with low temperature bainite regions interspersed with retained austenite. Fully reversed strain controlled fatigue tests were conducted on the different steels to determine the cyclic stress response and strain to failure. The effects of the cyclic deformation on the microstructures were analysed using electron backscattered diffraction (EBSD) and X-ray diffraction (XRD). Results showed that the initial cyclic hardening behaviour and low cyclic softening ratio observed in the TRIP steels was not necessarily due to austenite to martensite transformation. Differences between the austenite transformation behaviour of the conventional and novel hybrid TRIP microstructures was related to the different surrounding phases and the size of the retained austenite.

Development of asymmetric rolling for the better control over structure and mechanical properties in IF steel

In the present study, the effects of kinematic and geometric asymmetries in rolling during multi-pass processing of IF steel are examined. The theoretical investigation by final element simulations and experimental investigations by means of electron-backscatter diffraction analysis and tensile tests suggest that asymmetric rolling increases the total imposed strain compared to symmetric rolling, and largely re-distributes the strain components due to additional shear. This enhances the intensity of grain refinement, strengthens and tilts crystallographic orientations, and increases mechanical strength. The effect is highest in the asymmetric rolling with differential roll diameters.

Effective grain orientation on the substructure development of 304 stainless steel and NA-30% fe

This data is the result of an investigation into the effect of grain orientation on the substructure development of 304 stainless steel and a Ni-30wt.%Fe alloy. Both alloys have been used as model alloys to study the high temperature deformation of austenite. The development of the dislocation substructure as a function of strain, temperature and grain orientation was investigated using a combination of electron backscatterd diffraction (EBSD) and transmission electron microscopy (TEM).

Experiment and theoretical prediction of martensitic transformation crystallography in a Ni–Mn–Ga ferromagnetic shape memory alloy

A detailed study of martensitic transformation crystallography and microstructural characteristics in the Ni53Mn25Ga22 ferromagnetic shape memory alloy (FSMA) was performed by both experimental observation and theoretical calculation. It is revealed that there are two microscopically twin-related martensitic variants with a misorientation of ∼82° around the 〈1 1 0〉_M axis in each initial austenite grain. The twin interface plane was determined to be {0.399 0.383 0.833}_M (1.79° away from {1 1 2}_M). The ratio of the amounts of the two variants inherited from one single austenite grain is about 1.70. The prevalent orientation relationship between austenite and martensite was found to be Kurdjumov–Sachs (K–S) relationship with (1 1 1)_A//(1 0 1)_M, [110]A//[111]_M. A successful explanation of the crystallographic features during martensitic transformation will shed light on the development of FSMAs with optimal performance.

Crystallographic features during martensitic transformation in Ni-Mn-Ga ferromagnetic shape memory alloys

The martensitic transformation crystallography in two Ni ₅₃Mn₂₅Ga₂₂ (at. %) ferromagnetic shape memory alloys (FSMAs) was investigated by means of misorientation calculation and pole figure analysis based on the orientation of the martensitic lamellae obtained from electron backscattered diffraction (EBSD) measurements. In the alloy that was first annealed at 1073K for 4h, and then cooled to 473K at ~4K/min and held for 30min, followed by cooling to room temperature at ~10K/min, there are only two kinds of differently orientated martensitic lamellae with a misorientation angle of ~82° distributed alternatively in each initial austenite grain. There is a compound twinning orientation relationship between the two lamellae. The prevalent orientation relationship between austenite and martensite is Kurdjumov-Sachs (K-S) relationship with (111)_A//(10I)_M, [1-10]_a//[11-1]_m. In the alloy that was annealed at 1173K for 4h followed by furnace cooling, nanoscale twins inside the martensitic lamellae were observed and the orientation relationships both between the nanotwins within one lamella and between the nanotwins in two neighboring lamellae were determined. The results presented in this paper will enrich the crystallographic data of the FSMAs and offer useful information for the development of novel FSMAs with optimal performances.