記述言語：日本語   出版者・発行元：一般社団法人 日本鉄鋼協会  

DOI： 10.2355/tetsutohagane.tetsu-2023-019

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Engineering and Performance  

The tensile properties of vanadium-added steels with different ferrite and pearlite hardness ratios were evaluated. In this study, four types of specimens were prepared. The specimen without vanadium (specimen A) was cooled from 1359 K to room temperature (298 K ± 2 K) in a furnace. The specimens containing vanadium (specimens B, C, and D) were cooled from 1359 to 1073, 1023, and 923 K, held for 60 min, and then cooled to room temperature in the furnace. The microstructures of all specimens consisted of ferrite and pearlite, and the volume fraction of each phase in all specimens was nearly the same. Compared to specimen A, the size and morphology of each phase in the vanadium-added steels were finer and more equiaxed, and the hardness of ferrite and pearlite increased. The increase in the ferrite hardness was attributed to the precipitation strengthening due to vanadium carbide, whereas that of pearlite was attributed not only to the precipitation strengthening due to vanadium carbide but also the ferrite/cementite misfit causing lattice strain increment. The ferrite hardness of specimen B was the highest, and that in pearlite of specimen D was the lowest. As a result, the hardness ratios of B and D were lower than those of A and C. Strength–ductility balance was improved by adding vanadium. Moreover, it was further enhanced by improving local elongation due to the decrease in ferrite and pearlite hardness ratio.

DOI： 10.1007/s11665-023-08436-w

Web of Science

Scopus

その他リンク： https://link.springer.com/article/10.1007/s11665-023-08436-w/fulltext.html

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Engineering and Performance  

We attempted to improve the strength–ductility balance of tempered martensite steel by controlling cementite particle size distribution. Four types of samples of varying tempering temperatures were prepared: T973-60m and T823-60m samples were heated to 973 and 823 K and isothermally held for 1 h, while DT-60m and DT-15m samples were heated to 973 K and isothermally held for 1 h and 15 min and cooled to 823 K and isothermally held for 15 min and 1 h. As a result, the strength–ductility balance of DT-60m and DT-15m samples using two-stage tempering was superior to that of T973-60m and T823-60m samples. From microstructural observations, T973-60m sample mainly included large cementite particles in contrast to T823-60m sample which mainly included small cementite particles. DT-60m and DT-15m samples included both small and large cementite particles. The larger the area fraction of the small cementite particles, the higher was the tensile strength and the larger the area fraction of the large cementite particles, the higher was the total elongation. In the case of DT-60m and DT-15m samples, the nucleated voids were hard to coalesce due to the suppression of strain concentration at the interface between the matrix and coarse cementite particles. From these results, we concluded that strength–ductility balance could be improved by dispersing both small and large cementite particles.

DOI： 10.1007/s11665-023-08428-w

Web of Science

Scopus

その他リンク： https://link.springer.com/article/10.1007/s11665-023-08428-w/fulltext.html

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本金属学会  

Metal additive manufacturing enables producing complex geometric structures with high accuracy and breaks the design constraints of traditional manufacturing methods. Laser powder bed fusion, a typical additive manufacturing process, presents a challenge in experimentally understanding the nano-scaled microstructure-process relationship regarding the wide range of process parameters. In this study, we aim to reveal the novel nanoscale structural features by advanced scanning transmission electron microscopy to clarify the formation mechanisms in 316L stainless steel by laser powder bed fusion. Here we show that the slender columnar grains were confined to the centreline of the melt pool along the build direction, and the columnar cell structure at the side branching of the melt pool grew along orthogonal directions to follow drastic changes in thermal gradient across adjacent melt pools. Novel nano-scaled modulated structures have been observed in the dislocation cells parallel to the laser scan direction, which were mainly caused by the elastic strain involving the thermal gradient inside the melt pool and across adjacent melt pools as well as the effective strain field in the dislocation cell interiors. An in-depth understanding of microstructure developments is worthy of fabricating high-performance materials by controlling the additive manufacturing process.

DOI： 10.2320/matertrans.mt-me2022004

Scopus

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials Letters  

We investigated the initial grain size effect on the tensile-deformed microstructure in Type 310S austenitic stainless steel. Specimens A and B were prepared with different initial grain sizes (25 and 67 μm). With increasing strain in both specimens, dislocation density increased and the crystallite size decreased. Moreover, the dislocation density difference of specimens A and B gradually increased with increasing strain. Kernel average misorientation (KAM) values at the grain boundaries were high and increased with increasing strain in both specimens. Additionally, the KAM value of specimen B was lower than that of specimen A. This is because the grain boundary area in specimen B was lower than that in specimen A. On the other hand, characteristics of dislocation cell structures, such as the dislocation cell size and the misorientation between dislocation cells, were almost the same in both specimens. From these results, we concluded that the dislocation density difference of strained specimens A and B is attributed to the difference in the dislocation cell structure amount formed in specimens A and B.

DOI： 10.1016/j.matlet.2023.134285

Scopus