Uniaxial tensile tests were conducted for measuring the plastic deformation behavior of low carbon bainite steels before and after aging. Small pieces were cut from the inside of the tensile specimens subjected to several plastic strains, and microstructural observation and X-ray diffraction were conducted. The bainite steel before aging has island-dispersed martensite and austenite (MA) constituents. The proof strength of the bainite steel before aging was found to be 600 MPa. The steel before aging began to deform plastically at 83 % of 700 MPa, which is the proof strength of the bainite steel after aging. The yield ratio before aging was 0.64. The bainite steel having MA-constituents is easy to deform plastically. The bainite steel consists of 89 vol% pro-eutectoid ferrite grains and 11 vol% MA-constituents. The ratio of volume fractions is constant up to 2 % plastic strain. The volume fraction of martensite phase in the MA- constituents is also constant up to fracture. On the other hand, it was newly found that the austenite phase disappears and the volume fraction of ferrite phase increases in the necking portion. Most of the carbon content in the bainite steel is solidly soluble in MA-constituents, and there is no cementite in the bainitic steel before aging. The MA-constituents disappears with aging treatment. The bainite steel after aging consists of 98 vol% ferrite grains and 2 vol% cementite. The ratio of volume fractions remains constant until fracture. And then, the low-carbon bainite steel having the original microstructure induced by aging treatment are returning to reinforce the proof strength of 700 MPa and the yield ratio of 0.76.

A thermally sprayed MCrAlY alloy coating in a thermal barrier coating system, called a “bond coat” (BC), is applied to the hot sections of gas turbines and jet engines. Residual stress in the BC is generated during spraying and after thermal exposure. Residual stress in sprayed coatings is an important characteristic that determines the development of high-performance materials and processes. X-ray diffraction is useful for evaluating the residual stress as well as the in situ stress change during thermal exposure. The X-ray elastic constants, which are necessary for evaluating the residual stress using this method, result in an accurate evaluation of the residual stress of a thin coating layer. However, systematic research on the effects of microstructural changes has yet to be conducted. In this study, the influence of high-temperature exposure on the X-ray elastic constants of an atmospheric-plasma-sprayed (APSed) BC was investigated by bending a two-layer specimen. Additionally, a dense high-velocity oxygen fuel (HVOF) BC was evaluated to elucidate the influence of sliding splat particles. Finally, the relationship between the X-rays and mechanical elastic constants of the BC was studied. It was found that the X-ray elastic constants of the as-sprayed APS BC were higher than the mechanical elastic constants due to the sliding deformation between the splat particles. Similarly, the X-ray elastic constants of HVOF BC were higher than the mechanical constants, as same as APS BC. However, the difference between the elastic constants was smaller than that of APS BC. The influence of sliding deformation of both coatings was suppressed by thermal exposure, and the X-ray elastic constants approached the mechanical constants.

In X-ray stress measurement using the sin²ψ method, there are directions and locations where residual stress cannot be measured due to interference between the stress equipment and long parts. In such cases, the long parts are often cut into small pieces before measurement. However, nondestructive measurement without cutting is indispensable for measurement objects with high cultural and historical values, such as long Japanese swords such as Wakizashi. On the other hand, X-ray stress measurement using the cosα method allows nondestructive evaluation of stress from the lattice strains measured from a Debye-Scherrer ring recorded by an area detector under a single X-ray exposure at an oblique angle. This method has an advantage that its simple optical system prevents interference between stress equipment and long parts. In this study, a nondestructive technique was developed for measuring the residual stress filed near the tang (Nakago-jiri) of a long Japanese Wakizashi sword using the optics of the cosα method without cutting the sword. As a result, using the Debye-Scherrer rings recorded by the cosα method, the 2θ - sin²ψ graphs were obtained from the Nakago surface, where the 2θ - sin²ψ graph parallel to the longitudinal direction of Japanese sword cannot be measured by X-ray stress measurement using the sin²ψ method. The obtained eight 2θ - sin²ψ graphs were used to evaluate the residual stress field near the Nakago surface. It was found that there was a clear stress gradient in the vertical stress component in the plane, which was not observed in the Nakago surface without Shinogi. The residual strain information in the directions that cannot be measured due to the interference between the stress equipment and parts is important, and the residual strain information should be measured as much as possible using this developed method.

Memory disks for a hard disk drives are required to achieve higher recording densities. To achieve this, there is a demand for thinner aluminum alloy blank disks. As the thickness of the blank disk becomes thinner, the stiffness of the blank disk decreases and its flatness deteriorates. To achieve excellent flatness, it is necessary to know the residual stress in the blank disk. For this reason, we developed a technique for measuring the residual stress in blank disks. In this study, we measured the diffraction spots of coarse grains using a double exposure method, completed the image processing procedure, and established a method for measuring the residual stress in the blank disks. When the residual stresses in the blank disks were measured using this method, it was found that the tensile residual stress was generated on the outside of the blank disk with press-annealing. This suggests that a slightly larger compressive force was applied to the outside of the blank disk under press-annealing. Furthermore, the residual stress was divided into compressive and tensile residual stresses on the front and back of the blank disks, respectively.

In this study, martensitic stainless steel SUS420J2 (AM material) was fabricated by laser powder bed fusion (LPBF), one of the additive manufacturing (AM) methods, using the laser scanning pattern that was selected in our previous study as a suitable one to reduce residual stress. AM material was heat-treated under two conditions, that is, conventional quenching and tempering (H1 treatment) and only tempering at low temperature for a long time (H2 treatment), and their effects were systematically investigated. The results showed that the amount of the retained γ phase in the microstructure of AM material significantly reduced with the H1 treatment and the microstructure became almost the same to that of the H1-treated wrought material (W material). Hardness, static strength and wear resistance of the H1-treated AM material were comparable to those of the H1-treated W material. Moreover, the H1 treatment gave the effect to markedly reduce the directional dependence and the absolute value of residual stress generated in AM material. On the other hand, the microstructure of AM material was unchanged by the H2 treatment. Further, its hardness and static strength were lower than those of the untreated AM material, besides the directional dependence and the absolute value of residual stress remained almost unchanged. The fatigue strength of W material was greatly improved by the H1 treatment, but the improvement of the fatigue strength of the H1-treated AM material was smaller than that of the H1-treated W material because the fatigue strength of AM material was significantly affected by molding defects, and the fatigue strength of the H2-treated AM material was not improved.

The Tamagawa acidic water originates from the Tamagawa hot springs in eastern Akita Prefecture. Currently, the pH of Lake Tazawa has increased from 4.6 to about 5.8 due to the operation of a neutralization treatment facility. However, it has not recovered to 6.8, and the water environment and ecosystem have not yet recovered. In this study, a neutralizer was prepared four kinds of iron and steel slag for using to improve Tamagawa acidic water and to expand the use of them. Neutralization experiments were conducted to evaluate the effectiveness of the neutralizer by analyzing pH changes and concentration of several metal ions about treated water and surface composition of used neutralizer. The results showed the pH of acidic water was raised by these neutralizers, and did not leach heavy metal ions, suggesting that the neutralizer could be used stably.