- 著者
- Toshihiro Tsuchiyama Takayuki Sakamoto Shohei Tanaka Takuro Masumura
- 出版者
- The Iron and Steel Institute of Japan
- 雑誌
- ISIJ International (ISSN:09151559)
- 巻号頁・発行日
- vol.60, no.12, pp.2954-2962, 2020-12-15 (Released:2020-12-16)
- 参考文献数
- 13
- 被引用文献数
- 7
Medium manganese steel (Fe-5.0%Mn-1.2%Si-0.10%C alloy) was subjected to interrupted quenching from the austenite single-phase region to a temperature between Ms and Mf followed by intercritical annealing in the ferrite and austenite dual-phase region at 923 K. As a result, a core-shell type second phase, which consisted of a fresh martensite core surrounded by a film-like retained austenite shell, was formed. The mechanism and kinetics of reversion for the interrupted-quenched specimens were analyzed with DICTRA simulation and TEM observation. With regard to the effect of the core-shell type second phase on mechanical properties, it was inferred that the fresh martensite core functioned as a hard second phase and enhanced work hardening by stress partitioning similar to DP steel, while the film-like retained austenite contributed to improved ductility due to the TRIP effect. As the interrupted quenching temperature decreased, the volume fraction of the fresh martensite core decreased, while the stability of the retained austenite shell increased. This showed potential for controlling the strength and ductility balance of medium manganese steel. A possible beneficial effect of the core-shell type second phase on the ductile fracture behavior was also discussed in terms of stress/strain relaxation at the interfaces between hard martensite and ferrite matrix.
- 著者
- Takayuki Sakamoto Motoyasu Ochi Yutaka Kikuchi Kyo Kobayashi Toru Tanaka Yukio Ozaki
- 出版者
- 一般社団法人 園芸学会
- 雑誌
- The Horticulture Journal (ISSN:21890102)
- 巻号頁・発行日
- pp.MI-081, (Released:2016-05-12)
- 被引用文献数
- 2
Harvesting of asparagus spears is hard work because farmers have to harvest spears in a crouching posture. We previously developed electric long-shafted shears and a large-wheeled cart to improve the harvest posture, and we reported that the visibility of spears can be improved by modified branch training using string, without any yield or quality reduction. In the present study, we investigated the harvest efficiency, harvest posture, and subjective burden with electric long-shafted shears and a large-wheeled cart under modified branch training methods (the new standing harvest method) for labor-saving asparagus spear harvesting. Two male subjects in their 30s and 60s harvested spears for 60 min using (standing harvest) and without using (control) the new standing harvest method. The harvest efficiency of the new standing harvest method was 18% lower than that of the control. In the standing harvest, subjects had to pull the shears up to take the harvested spear from the shears with their left hand after each spear was cut (“take”). The subjects needed time for the “take” action, and the time necessary to harvest a spear with the electric long-shafted shears was longer than that required for the control. We also evaluated the harvest posture using the Ovako Working Posture Analyzing System (OWAS). For the subject in his 30s, action category(AC)2 and AC3 accounted for 72% and 14% of the postures recorded in the control, respectively, whereas in the standing harvest, AC1 and AC2 accounted for 57% and 41%, respectively. For the subject in his 60s, AC2 and AC3 accounted for 41% and 58% of the postures recorded in the control, respectively, whereas in the standing harvest, AC1 and AC2 accounted for 27% and 70%, respectively. Unfavorable postures during harvest were reduced by the new standing harvest method. The subjective physical burden on the subjects was evaluated using a modified Borg scale after 60 min of harvesting using and without using the new standing harvest method. The subjective physical burden in both subjects was highest (> 8) at the waist in the control, whereas the scores were lower than 3 in the standing harvest. Thus, the new standing harvest method reduced harvest efficiency, but resulted in substantial improvements in posture and reduced the physical burden on the subjects.