Papers by Keyword: Lattice Strains

Abstract: The effect of interlamellar spacing on monotonic behavior of C70 pearlitic steel was investigated. Tensile tests under X-ray diffraction coupled with self-consistent model have been used to identify the role of interlamellar spacing on the ferrite plasticity parameters and residual stresses. It has been established that yielding of pearlite is controlled by ferrite critical shear stresses ( τc 0α) which is higher for the smaller interlamellar spacing. Moreover, the residual stress level in ferrite is higher for the largest interlamellar spacing under the same imposed total strain. Lattice strains, measured by synchrotron X-ray diffraction, show an elastic and plastic anisotropy of ferrite crystallites and high stresses in cementite which confirm the self-consistent model calculation. Keywords: Pearlitic steel, X-ray diffraction, Synchrotron radiation, Self-consistent model, Critical shear stress, Lattice strains.

Abstract: Microstresses due to intergranular and inter-phase interactions in an austenitic-ferritic super duplex steel (SAF 2507) under uniaxial compressive deformation have been studied by in-situ neutron diffraction experiments. Lattice strains of several hkl planes of austenite respective ferrite were mapped as a function of sample direction at a number of load levels during loading into the plastic regime and unloading. The analysis of the experimental results has shown that during loading both grain-orientation-dependent and inter-phase stresses were generated under plastic deformation that was inhomogeneous at the microstructural level. Residual stresses depending on the grain-orientation and phase have been found after unloading. The results also indicate stronger intergranular interactions among the studied hkl planes of austenite than those of ferrite.

Abstract: The martensitic phase transformation in an ultra fine grained (UFG) TRIP (transformation induced plasticity) steel with combination of high strength and high elongation was investigated during room temperature tensile test using in situ neutron diffraction. Two types of specimens, namely coarse grained (grain size of about 50 μm) and ultra-fine-grained (grain size of about 350 nm) specimens were examined. The lattice strain evolution of the austenite and martensite phases was observed and the load partitioning between the phases was identified.

Abstract: For industrial purposes, the adhesion control of secondary scale on hot rolled steel sheet is important. A basic study was carried out to clarify the effect of scale microstructure on the scale adhesion of low carbon steel (0.03%C-0.2%Mn). When scale of FeO (about 8μm thickness) was generated at 800°C and transformed by continuous cooling from 250~600°C to 200°C, the scale transformed from 400°C showed good adhesion. The scale consisted of magnetite seam from the steel substrate, lamellar structure of magnetite and α-Fe, and magnetite layer from the scale surface. The orientation analysis by TEM showed the relationship {110}Fe // {100}Fe3O4, <110>Fe // <100>Fe3O4, and the lattice strain was calculated as 4%. On the other hand, FeO/Fe substrate showed the relationship {100}Fe // {110}FeO, <110>Fe // <110>FeO, and 25% lattice strain was calculated. It is considered that the adhesion of scale should be affected by the lattice strain, thus Fe3O4/Fe substrate showed better adhesion than FeO/Fe substrate. The temperature of FeO formation also affects the scale adhesion through the extent of Fe super saturation in FeO.