Papers by Author: Masahide Gotoh

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Authors: Katsuhiro Seki, Hashimoto Munetoh, Masahide Gotoh, Hajime Hirose
Abstract: Recently, the study of fine grain steels aimed at achieving into high strength has become active. Welding is one of the most effective methods for connecting the structural components. For those cases, the negative influence of any residual tensile stress induced during the welding process must be considered. It has been proved that shot-peening can effectively solve this problem. However, the influence of the Shot-Peening process on fine grain steels after welding has only been briefly reported up to now. In this study, fine grain steels were used, and specimens were obtained after heat treatment. Residual stress distributions near the surface of the fine grain steel after shot-peening were measured by X-ray diffraction technology. Moreover, the effect of hardness on distributions near the shot-peened surface was also estimated.
Authors: T. Akita, Masahide Gotoh, Sergey V. Dobatkin, Kazuo Kitagawa, Yukio Hirose
Abstract: In the present study, ultra fine-grained low carbon steel samples were processed by equal channel angular pressing (ECAP). Mechanical properties of the specimens annealed statically at several temperatures were evaluated by tensile and hardness test. In addition, grain sizes of the specimens were measured by SEM-electron back scattering pattern (SEM-EBSP) and X-ray diffraction analysis. Differential scanning calorimetry (DSC) measurement also evaluated thermal reactions in anneal process of the specimen. As a result, the grain size was changed at the temperature between 550oC and 600oC drastically and the tensile strength also became lower at the same temperature. The relation between yield stress and averaged grain diameter of specimens obeyed the Hall-Petch relation except the normalized specimen. Behavior of grain growth and recovery in structural observation by EBSP corresponded to reaction signal of the DSC curve.
Authors: Hajime Hirose, Shinya Suzuki, Masahide Gotoh, Toshihiko Sasaki
Abstract: In depositing the TiN thin films to the substrate by Physical Vapor Deposition (PVD), it influences the substrate interface. Change of the residual stress and the full-width at half maximum (FWHM) in each process of the TiN deposition of thin film was measured by the X-ray stress measurement. As a result of the X-ray stress measurement, there are no changes in the residual stress and the FWHM. It is thought that there is a difference in the penetration depth to the substrate of X-rays and Ti ion.
Authors: Masahide Gotoh, Katsuhiro Seki, M. Shozu, Hajime Hirose, Toshihiko Sasaki
Abstract: The fine-grained rolling steels NFG600 and the conventional usual rolling steels SM490 were processed by sand paper polishing and mechanical grinding to compare the residual stress generated after processing. The average grain size of NFG600 and SM490 is 3 μm and 15μm respectively. Therefore improvement of mechanical properties for such fine-grained steels is expected, it is important to understand the residual stress state of new fine-grained materials with processing. In this study, multi axial stresses of two kinds of specimens after polishing and grinding were measured by three kinds of analysis methods including cos-ψ method. As a result, as for σ33, the stress of NFG was compression, though that of SM490 was tension.
Authors: Lei Che, Masahide Gotoh, Yoshiaki Horimoto, Yukio Hirose
Abstract: Carbon steel is the most popular engineering material, usually consisted of ferrite and cementite phases. Internal stress state of the steel under thermal or mechanical loading is strongly affected by the amount and morphology in the cementite phase. With this aim, a computational model which applies the finite element method at the microscale was used in present study. Effects of volume fraction and particle size of the spheriodal cementite on the internal stress states in carbon steels under the mechanical and thermal loadings are investigated. To verify the reliability of the computational simulations, the residual stresses in the constituent phases are measured by means of X-ray stress diffraction technique. The computational simulations fit well with the experimental data, and the microstructure-based model is validated.
Authors: Hiroshi Goto, Masahide Gotoh, Shouichi Ejiri, Yoshiaki Horimoto, Yukio Hirose
Abstract: The purpose of this study is to examine the effect of crystallite preferred orientation on the mechanical strength of TiCN thin films in highly compressive residual stress. TiCN thin films were deposited by PVD on JIS-SKH55 (AISI M35) steel. The applied substrate bias voltages were set for –50, -80, -100, -120 and –150V. Subsequently, residual stress and crystalline preferred orientation of these specimens were investigated by X-ray diffraction methodology. The crystalline preferred orientation in thin films was evaluated by the ODF calculated from pole figures. On the other hand, dynamic hardness test (DH) and scratch test were executed to evaluate the mechanical strength of thin films. In our study, it was observed that negative bias voltages had an effect on the preferred orientation. The orientation density at –120V was the highest of all specimens. In addition, the value of scratch section area at –120V was the largest of all specimens. As a conclusion, the relation between the scratch area and the negative bias voltages corresponded to the relation between the preferred orientation and the bias voltages.
Authors: Kazuo Kitagawa, T. Akita, K. Kita, Masahide Gotoh, Naoki Takata, Nobuhiro Tsuji
Abstract: Aging behavior and mechanical properties of ultra fine grained Cu-Cr-Zr alloy sheet produced by accumulative roll bonding (ARB) process were investigated. A Cu-0.85Cr-0.07Zr (in mass%) alloy was solution treated and then cold-rolled at ambient temperature in the sheet of 1 mm thick. The sheets were heavily deformed by ARB process at ambient temperature up to 5 cycles. The grain size was reduced down to 210 nm and the fraction of high angle grain boundaries (HAGB’s) in the specimen after ARB process was 63%. The proof stress ( σ 0.2) and elongation were 540 MPa and 10%, respectively. Due to the aging treatment, a little grain growth took place (240 nm) and the fraction of HAGB’s was increased to 67%. The proof stress and elongation of the aged one increased to 605 MPa and 15%, respectively. It was noteworthy that the electrical conductivity remarkably increased from 35% to 79%IACS by the aging treatment. It was concluded that the aging treatment after ARB process enhanced not only the mechanical properties but also the electrical conductivity in the Cu-Cr-Zr alloys.
Authors: Lei Che, Masahide Gotoh, Yoshiaki Horimoto, Yukio Hirose
Abstract: The low volume fraction of carbide phase in carbon steel determines that it is difficult to estimate the stress state in it by diffraction method. In the present study, different from the studies before, we improve the technique of surface treatment on specimen and have successfully finished the stress estimations of carbide phase in carbon steels by X-ray diffraction method under normal conditions. Moreover, we investigate the affection of spherical cementite particle size on the residual stress distribution in both phases during the plastic deformed steels. We observed that the steels with small-sized cementite particles showed higher stress states than the steels with relatively large-sized cementite particles.
Authors: Masahide Gotoh, Hajime Hirose, Toshihiko Sasaki
Abstract: Thin films deposited by physical vapor deposition (PVD) were studied in terms of residual stress by the authors. The final purpose of our study is to evaluate the stress state at the interface between a substrate and a thin film. In this study, JIS-SKH55 tool steel without thin-film deposition was used as the specimen. SKH55 is a dual-phase steel consisting of martensite a’Fe and alloyed carbide M6C2. The specimens were heated to 573K, 798K, 843K and 893K. Recently, the relationship between the misfit of plastic strain and stress obtained by X-ray stress measurement has been proposed by the authors using the Eshelby/Mori-Tanaka model (EMT model). The residual stress and the misfit of plastic strain were determined by X-ray stress measurement using the EMT model. Results showed that as annealing temperature increased, the compressive residual stress remained nearly constant up to about 800K, and decreased above 800K in both phases. The misfit of plastic strain also remained nearly constant up to about 800K, and reached zero above 800K.
Authors: Masahide Gotoh, Takayuki Murotani, Toshihiko Sasaki, Yukio Hirose
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