著者

牧 正志 古原 忠 辻 伸泰 森戸 茂一 宮本 吾郎 柴田 曉伸

出版者

一般社団法人 日本鉄鋼協会

雑誌

鉄と鋼 (ISSN:00211575)

巻号頁・発行日

vol.100, no.9, pp.1062-1075, 2014 (Released:2014-08-31)

参考文献数

72

被引用文献数

24 30

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After ausforming appeared as the first thermomechanical processing of steels in the first half of the 1960 s, various thermomechanical processings have been developed for the improvement of mechanical properties over the last fifty years. Their application was mainly to martensitic steels in the 1960 s such as ausforming and TRIP, and moved to ferrite (+ pearlite) structures by the development of controlled rolling and accelerated cooling of HSLA steels in the 1970~1980 s. However, recently, interest has returned to martensite (and also bainite) because of the demand for higher strength, and the ausforming and TRIP have been revived and successfully applied to commercial practice. Very recently, severe plastic deformation (SPD) is the focus of attention as a new method of producing a very fine-grained structure with grain size of less than 1 μm. By the application of SPD, dynamic phenomena such as dynamic recrystallization and dynamic ferrite transformation occur in the process. We need more systematic studies on such phenomena for the development of new type of thermomechanical processing in steels.

著者

宮本 吾郎 金下 武士 知場 三周 古原 忠

出版者

公益社団法人 日本金属学会

雑誌

日本金属学会誌 (ISSN:00214876)

巻号頁・発行日

vol.79, no.7, pp.339-347, 2015 (Released:2015-07-01)

参考文献数

38

被引用文献数

8 21

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Attention to lath martensite and bainite in steels has been increasing due to their good mechanimcal properties. Various boundaries bewteen K-S variants contained in those microstructures contribute to their high strength and toughness so that deeper understand of nature of those boundaries is required. EBSD analyses have revealed that different variant grouping tendencies appear depending on composition and transformation temperature, such as variants belonging to the same Bain group, variants sharing the same close-packed plane parallel relationship. Kinematical compatibility (KC) condition can explain variant pairs coupled preferentially in lenticular and thin plate martensite satisfactory. In addition, it is revealed that some of the variant pairs observed in lath martensite and bainite are favorable for the KC condition when double shears are assuemd for lattice invariant shear.

著者

紙川 尚也 阿部 吉剛 宮本 吾郎 船川 義正 古原 忠

出版者

一般社団法人 日本鉄鋼協会

雑誌

鉄と鋼 (ISSN:00211575)

巻号頁・発行日

vol.99, no.5, pp.352-361, 2013 (Released:2013-04-30)

参考文献数

46

被引用文献数

3 6

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Tensile behavior and structure-property relationship of ferritic steels with nano-sized carbide dispersion were invesigated using Ti-added steel and Ti,Mo-added low carbon steels. By austenitizing followed by isothermal heat treatment at 700°C, polygonal ferrites containing very fine carbides of TiC and (Ti,Mo) C were obtained in the Ti-added and the Ti,Mo-added steels, respectively. The size of such carbides was finer in the Ti,Mo-added steel than in the Ti-added steel at the same holding period of isothermal heat treatment. The results of tensile tests for these samples showed that the strength is higher as the diameter of the carbides is smaller. The structure-based strength calculation led to a good agreement with the experiments, when it was assumed that the Ashby-Orowan mechanism is dominant for precipitation strengthening of nano-sized alloy carbides. It was also suggested that a relatively large tensile ductility is related to enhanced recovery during the tensile deformation, accompanied with promotion of secondary slips or cross slips in a finer scale due to the nano-sized particles.