Papers by Author: Yoshiaki Horimoto

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.

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.

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.