API X80 steel transformation microstructures

The data includes EBSD orientation maps of the specimens preheated at 1200 degrees celsius, and deformed at 1100 degrees celsius with 30% reduction and control cooled at the rates of 1, 18, and 95 degrees per second. The resultant microstructures correspond to quasipolygonal ferrite plus granular bainite, and lath bainite, respectively.

21Cr - 10Ni - 3Mo duplex stainless steel high temperature deformation microstructures

Data includes EBSD orentation maps of the specimens deformed in torsion at 1200 degrees celsius to strains of 0.1, 0.5, 0.9 and 1.3. The phase ratio is about 60% austenite and 40% ferrite. The miscrostructure is dynamically recovered and there is also some dynamic recrystallisation at strains of 0.9 and 1.3. The main portion of softening can be attributed to dynamic subgrain coalescence in austenite.

Substructure and texture development in austenite through thermomechanical processing

The data collection was performed using EBSD and TEM techniques. The objective was to characterise the substructure and crystallographic texture development during dynamic and post-dynamic deformation. The work reveals the role of the initial dislocation structure and texture on the softening characteristics in austenite and how these evolve during softening. It is also shown that the differences in the deformation dislocation structures between the dynamically recrystallized and deformed regions play a major role in determining the extent of recovery. An enhanced static recovery can be seen during post dynamic softening.

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.

Influence of grain size and training temperature on strain of polycrystalline Ni50Mn29Ga21 samples

The alloy Ni-Mn-Ga aroused great interest for application as a magnetic shape memory (MSM) material. This effect is caused by reorientation of twin variants by an external magnetic field. So far, most of the experiments were concentrated on single crystals. But, the MSM effect can also be realised in polycrystals which can be prepared much more efficiently. Here, polycrystalline samples were prepared by directional solidification with a <100> fibre texture of the high temperature cubic austenitic phase parallel to the heat flow. Afterwards, a heat treatment was applied for chemical homogenisation and stress relaxation in the austenitic state. Then the samples were heated up to the austenitic state and cooled down under load. The microstructure was analysed by Electron Back Scatter Diffraction (EBSD) before and after that treatment. Mechanical training at room temperature and 40°C was tracked by recording stress-strain curves. By increasing the number of training cycles the strain also increases. The influence of different training temperatures was investigated on samples with different grain sizes.

Determination of crystal structure and crystallographic characteristics in Ni-Mn-Ga ferromagnetic shape memory alloys

Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs) have received great attention during the past decade due to their giant magnetic shape memory effect and fast dynamic response. The crystal structure and crystallographic features of two Ni-Mn-Ga alloys were precisely determined in this study. Neutron diffraction measurements show that Ni48Mn30Ga22 has a Heusler austenitic structure at room temperature; its crystal structure changes into a seven-layered martensitic structure when cooled to 243K. Ni53Mn25Ga22 has an I4/mmm martensitic structure at room temperature. Electron backscattered diffraction (EBSD) analyses reveal that there are only two martensitic variants with a misorientation of ~82° around <110> axis in each initial austenite grain in Ni53Mn25Ga22. The investigation on crystal structure and crystallographic features will shed light on the development of high-performance FSMAs with optimal properties.

Characterization of nano-structured bainitic steel

A 0.79C-1.5Si-1.98Mn-0.98Cr-0.24Mo-1.06Al-1.58Co (wt%) steel was isothermally heat treated at 200°C for 10 days to produce a nano-structured bainitic steel. The microstructure consisted of nanobainitic ferrite laths with a high dislocation density and retained austenite films having extensive twins. The crystallographic analysis using TEM and EBSD revealed that the bainitic ferrite laths are close to the Nishiyama-Wassermann orientation relationship with their parent austenite. There was only one type of packet identified in a given transformed austenite grain. Each packet consisted of two different blocks having variants with the same habit plane, but different crystallographic orientations. Atom Probe Tomography (APT) revealed that the carbon content of nanobainitic ferrite laths was much higher than expected from the para-equilibrium level. This was explained due to the long heat treatment time, which led to the formation of fine Fe-C clusters on areas with high dislocation densities in bainitic ferrite laths.

Asymmetric rolling of interstitial-free steel using differential roll diameters. Part I : mechanical properties and deformation textures

IF steel sheets were processed by conventional symmetric and asymmetric rolling (ASR) at ambient temperature. The asymmetry was introduced in a geometric way using differential roll diameters with a number of different ratios. The material strength was measured by tensile testing and the microstructure was analyzed by optical and transmission electron microscopy as well as electron backscatter diffraction (EBSD) analysis. Texture was also successfully measured by EBSD using large surface areas. Finite element (FE) simulations were carried out for multiple passes to obtain the strain distribution after rolling. From the FE results, the velocity gradient along selected flow lines was extracted and the evolution of the texture was simulated using polycrystal plasticity modeling. The best mechanical properties were obtained after ASR using a roll diameter ratio of 2. The textures appeared to be tilted up to 12 deg around the transverse direction, which were simulated with the FE-combined polycrystal plasticity modeling in good agreement with measurements. The simulation work revealed that the shear component introduced by ASR was about the same magnitude as the normal component of the rolling strain tensor.