Materials Science Forum Vols. 558-559

Abstract: The variations of in plane Charpy toughness anisotropy as a function of the microstructure and texture of an industrial grade of API –X80 pipeline steel was studied. Standard size Charpy samples with a long axis orientated at 0, 22.5, 45, 67.5 and 90° with respect to the rolling direction of the plate were tested at different temperatures varying from -196°C to 20°C. Microstructure and texture of the plates were investigated by means of electron backscattering diffraction (EBSD), XRD and the recently developed 3D EBSD technique. The spatial grain shape orientation distribution was examined on samples which were cut from the middle thickness of an industrial rolled plate by means of 3D EBSD and following grain shape reconstruction and approximation of the grain shape with ellipsoids. It was found that the experimentally observed 3D microstructures could well be correlated to the anisotropy of the measured Charpy impact toughness of the steel for the Charpy samples. The Charpy toughness anisotropy of the plates in the transition region where both ductile and brittle fractures take place can be related to the microstructural anisotropy characterized by the grain shape orientation and the spatial distribution of the 2nd phase.

Abstract: To identify the characteristic microstructural length determining the mechanical properties of a quenched and tempered medium-C steel and its dependence on the prior austenite grain size, different tempering treatments have been carried out after a fully martensitic quenching. The resulting microstructures have been analyzed by Orientation Imaging Microscopy (OIM) and two kind of features have been taken into consideration: packets (i.e. domains delimited by high-angle boundaries) and cells (domains bounded by low-angle grain boundaries). The main results can be summarized as follows: 1. A very weak effect of austenite grain size on packet size was found. 2. A finer packet size was measured at mid-thickness with respect to surface after external and internal water quenching process. This phenomenon was attributed to the effect of the strain path on the phase transformation during quenching. 3. The through-thickness microstructural gradient remains substantially unchanged after tempering. 4. Grains with high-angle boundaries do not significantly grow after tempering; on the contrary, low-angle grain boundaries move, fully justifying the hardness evolution with the tempering temperature.

Abstract: It is known that well developed <111>//ND texture increases Lankford value (r-value) of not only bcc metals but also fcc metals and alloys. However, <111>//ND texture cannot be formed in fcc metals by conventional rolling and annealing processes. The <111>//ND orientation is one of the major components of shear texture. Accordingly, this orientation develops in aluminum sheet when shear deformation is introduced. Al-Mg-Si alloy 6016 sheet was processed by two-pass differential speed rolling at room temperature under a high friction conditions. The rolling direction of the second pass was so selected that the direction of shear deformation introduced in the second pass was either similar (unidirectional shear rolling) to or opposite (reverse shear rolling) to that in the first pass. The roll speed ratio was 2.0. Large shear strain was successfully introduced through the thickness uniformly by the differential speed rolling. The shear texture with major components of {001}<110> and {111}<110> were developed throughout the thickness. Though large reduction in thickness of 75% was applied to the sheets by the rolling, conventional rolling texture such as {112}<111> or {123}<643> orientation was not detected in any part of the thickness. By solution treatment after the rolling, intensity of shear texture weakened and grain size decreased. It has been found that r-value is improved by the differential speed rolling subsequently followed by solution treatment.

Abstract: High-temperature plastic flow and tensile ductility in pre-annealed Zr65Al10Ni10Cu15 bulk metallic glass are examined in a supercooled liquid region. The specimen annealed at 673K for 1.8ks before the tensile test exhibits uniform deformation, and large elongation of 1100% is obtained in the tensile test at 673K and in a constant true strain rate of 1×10-2s-1. In the specimen, initial stress decreases in comparison with that of the specimen without annealing, but apparent strain hardening arise during deformation. SEM analysis after the deformation reveals that the cavitation is very limited even at the fracture tip. XRD and TEM analyses reveal that icosahedral phase is observed only in gage section but not in grip section after the deformation. The limited cavitation due to the accommodation of stress concentration through the grain boundary amorphous phase possibly makes a positive contribution to the large elongation in the annealed specimen, as well as the neck stability due to the strain hardening by the interaction between the icosahedral phase particles increasingly crystallized by the local strain.

Abstract: The distribution of the precipitates on the grain boundaries in Fe-3%Si steel during secondary recrystallization annealing were studied using high-angle annular dark filed (HAADF) scanning transmission electron microscopy (STEM). Because HAADF image can show both grain boundaries and precipitates clearly, the change of precipitate distribution on grain boundaries can be quantitatively analyzed. It was observed that the total area of the precipitates on grain boundaries increased in the order of non-annealed, 600°C, and 900°C sample and the total area of precipitates on grain boundaries in the 1000 °C sample was much lower than that in the 900 °C sample. The compositions of the precipitates were also analyzed using X-ray energy-dispersive spectrometer (XEDS). The most precipitates were multi-phase ones, mainly composed of AlN and MnS. Our analysis results suggest that such a precipitate behavior is responsible for the abnormal grain growth of Fe-3%Si steel occurring under the temperature above 900 °C.

Abstract: In this study, microwave (MW) heating of Fe powder in the separated electric (E-) and magnetic (H-) fields was performed first, and the heating behaviors on the field dependence were investigated. It was shown that they are heated better in H- field than in E- field. The MW heating mechanism of metals were briefly discussed. MW heating of soda-lime glass alone was not easy, however addition of iron powder enhanced the heating, depending on the volume fraction of the powder. Occurrence of deformation and melting of the glass spheres was observed. This technique is applicable to fabrication of glass-metal composites and vitrification of waste matters. MW heating of Ni-based metal glass was attempted with no external pressure and in an inert atmosphere, it was also shown that heating was better accomplished in H- field. Weakly sintered body was possibly obtained with retention of the amorphous phase.