Wu Gong

In Situ Neutron Diffraction Study on Microstructure Evolution During Thermo-Mechanical Processing of Medium Manganese Steel

The microstructure evolution of medium manganese steel (Fe-5Mn-2Si-0.1C (wt%)) during thermo-mechanical processing in ferrite + austenite two-phase region was investigated by in situ neutron diffraction analysis and microstructure observations. When the specimens were isothermally held at a temperature of 700 °C, the fraction of reversely transformed austenite increased gradually with an increase in the isothermal holding time. However, it did not reach the equilibrium fraction of austenite even after isothermal holding for 10 ks. On the other hand, the fraction of reversely transformed austenite increased rapidly after the compressive deformation at a strain rate of 1 s−1 at 700 °C and reached the equilibrium state during subsequent isothermal holding for around 3 ks. Moreover, microstructure observations suggested that the austenite, which was reversely transformed during isothermal holding at 700 °C, exhibited film-like shape and existed between pre-existing martensite laths. In contrast, when the compressive deformation was applied during isothermal holding at 700 °C, most of the reversely transformed austenite had globular shapes with grain sizes less than 1 μm.

Influence of Grain Size on Work-Hardening Behavior of Fe-24Ni-0.3C Metastable Austenitic Steel

In this study, the effect of grain size on the work-hardening behavior of Fe-24Ni-0.3C metastable austenitic steel was investigated by the use of in situ neutron diffraction during tensile tests in Japan Proton Accelerator Research Complex (J-PARC). The effect of grain size on the work-hardening behavior was considered from viewpoints of martensite formation and stress partitioning between different phases. The result revealed that when the grain size changed within the coarse grained region the influence of the grain size on the stress partitioning was relatively small, thus the work-hardening behavior was mainly determined by the increasing rate of martensite volume fraction. On the other hand, when the grain size decreased down to ultrafine grained scale, the internal stress (phase stress) in martensite significantly increased, which contributed to the increasing work-hardening rate.

Enhanced mechanical properties in fully recrystallized ultrafine grained ZKX600 Mg alloy

Mg-Zn-Zr-Ca (ZKX600) alloy specimens with various fully recrystallized grain sizes ranging from 0.77 μm to 23.3 μm were fabricated by high pressure torsion (HPT) followed by subsequent annealing. Tensile tests carried out at room temperature revealed that ultrafine grained (UFG) specimens exhibited enhanced combinations of strength and ductility compared to their coarse-grained counterparts. Observation of deformation microstructures suggested that basal slip and {10-12} extension twinning were the dominant mechanisms during deformation of coarse grained specimens, while deformation twinning was significantly inhibited in the UFG specimens. Based on the observations it is proposed that non-basal slip activity is responsible for the enhanced mechanical properties, and should be the focus of further investigations.

Progress in Bulk Texture Measurement Using Neutron Diffraction

Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan; J-PARC Center, Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan; Research Center for Neutron Science and Technology, Comprehensive Research Organization for Science and Society, Tokai, Ibaraki, 319-1106, Japan; Department of Neutron Application Technology, Radiation Application Development Association, Tokai, Ibaraki, 319-1106, Japan; College of Engineering, Ibaraki University, Hitachi, Ibaraki, 316-8511, Japan; Department of Materials Engineering and Industrial Technologies, University of Trento, 7738123 Trento, Italy.