TRIP Steel Deformation Behavior by Neutron Diffraction
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TRIP Steel Deformation Behavior by Neutron Diffraction Stefanus Harjo 1, Noriyuki Tsuchida 2, Wu Gong 1, Jun Abe 1 and Kazuya Aizawa 1 1 J-PARC Center, Japan Atomic Energy Agency, Shirane 2-4, Shirakata, Tokaimura, Nakagun, Ibaraki, 319-1118, Japan 2 Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280, Japan ABSTRACT Deformation behaviors of two TRIP-type multiphase steels with different carbon contents were studied by in situ neutron diffraction measurement during tensile deformation at RT. The tensile test was conducted in a step-load controlling manner during the elastic region, and in a continuous manner with a constant crosshead speed by an initial strain rate of 1.8×10-5 s-1 during the plastic region. Austenite grains were observed to bear higher phase stresses than ferrite grains in both steels. Austenite peak intensities started to decrease at the onsets of plastic deformation in both steels, showing the occurrence of stress induced martensitic transformations. Martensite peaks were carefully analyzed to estimate phase strains, and as the results martensite grains were found to bear largest phase stresses during plastic deformation. INTRODUCTION Transformation Induced Plasticity (TRIP) is one of important effects in steel strengthening mechanism to improve strength, ductility and excellent high-speed deformation behavior [1]. To measure strengthening mechanisms of multiphase steels including TRIP-type steels during deformations, in situ neutron and X-ray diffraction measurements during deformations have been demonstrated as powerful tools [2-4]. However, the stress partitioning among the constituent phases in TRIP-type steels with average grain sizes of 2 and 5 μm were evaluated only between ferrite matrix and retained austenite, even martensitic transformations occurred during deformation [3]. Recently, lattice plane strains of martensites formed by the transformation were successfully observed in a TRIP-aided ultra-fine grained steel, when a neutron time-of-flight type diffractometer with high neutron beam intensity and high resolution was used for the measurement [5]. In this study, phase strains generations including that in the martensite during tensile deformation were studied by means of in situ neutron diffraction in two TRIP-type multiphase steels with different carbon contents and moderate grains. EXPERIMENTAL DETAILS Samples used in this study were TRIP type multiphase steels with different carbon contents (0.2C TRIP and 0.4C TRIP steels). The detail chemical compositions are listed in table I. After a solution treatment, hot-rolling and cold-rolling, these plate steels were heat-treated to produce microstructures containing bainitic ferrite (called as ferrite after this) and high carbon contained retained austenite (called as austenite after this), as follows. Heating and holding at 1073 K for 180 s, air cooling to 998 K, cooling and holding at 673 K for 180 s, and then air cooling to RT. These plate steels were grinded to remove 0.2 mm thick parts from both s
