著者

小山 元道 澤口 孝宏 津﨑 兼彰

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.104, no.4, pp.187-200, 2018 (Released:2018-03-31)

参考文献数

86

被引用文献数

6

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This paper presents an overview of the recent works on dynamic strain aging (DSA) of Fe-Mn-C austenitic steels including Hadfield and twinning-induced plasticity (TWIP) steels. First, a model of the DSA mechanism and its controlling factors are briefly explained in terms of Mn-C coupling and dislocation separation. Then, we introduce the effects of DSA on mechanical properties such as work hardening capability, uniform elongation, post-uniform elongation, and fatigue strength. Specifically, we note the pinning effect on extended dislocation for the work hardening, the Poretvin-Le Chatelier banding effect on damage evolution for the elongation, and the crack tip hardening/softening effect on crack resistance for the fatigue strength. We believe that this overview will help in designing advanced high-strength steels with superior ductility and fatigue resistance.

著者

小山 元道 秋山 英二 津﨑 兼彰

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.1132-1139, 2014 (Released:2014-08-31)

参考文献数

36

被引用文献数

4

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Al effects on strain aging and resistance against hydrogen embrittlement were examined in Fe-18Mn-0.6C-based twinning-induced plasticity steels deformed at different strain rates. The Fe-18Mn-0.6C steel showed hydrogen-induced fracture when it had been pre-deformed at a strain rate of 1.7×10–6 s–1. The hydrogen-induced fracture was suppressed by increasing strain rate and increasing Al content. From the viewpoint of material strengthening by strain aging, we found two important factors improving the resistance to the hydrogen embrittlement; (1) suppression of dynamic strain aging by increasing strain rate and Al content, and (2) suppression of static strain aging under loading by the Al addition.

著者

大塚 秀幸 V.A. Dinh 大野 隆央 津﨑 兼彰 土谷 浩一 佐原 亮二 北澤 英明 中村 照美

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.10, pp.1329-1338, 2014 (Released:2014-09-30)

参考文献数

22

被引用文献数

10

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The effects of carbon content on tetragonality and magnetic moment of bcc iron have been evaluated by first-principles calculation. Three kinds of supercells, Fe54C1, Fe54C2 and Fe128C1 (which correspond to Fe-0.40C, Fe-0.79 and Fe-0.17C mass%, respectively) are used for the calculation of tetragonality and magnetic moment of Fe-C system. Main results obtained are as follows. (1) The total energy and mechanical energy of the Fe-C system with carbon atom at the octahedral sites are smaller than those with carbon atom at the tetragonal sites. The carbon atom at octahedral site produces fairly large expansion in one direction. (2) Tetragonality of Fe-C system obtained by first-principles calculation increases linearly with increasing carbon content and agrees well with experimental results. The average magnetic moment of an Fe atom increases with increasing carbon content. (3) The magnetic moment of an Fe atom at the nearest neighbor of carbon atom is lower than that of pure iron and increases with increasing distance between the iron and carbon atoms. The projected density of states shows a hybridization with main contributions from Fe d and C p states which leads to the above mentioned decrease of the magnetic moment of an Fe atom. (4) In Fe54C2, tetragonality and magnetic moment of iron atom change with the distance between two carbon atoms. The value of tetragonality is either 0.981, 1.036 or 1.090. When the dumbbell structure which consists of the first carbon atom and its two nearest neighbor iron atoms is perpendicular to the second dumbbell structure which consists of the second carbon atom and its two nearest neighbor iron atoms, the tetragonality is 0.981 and does not agree with experimental value. The mechanical energy is relatively large. On the other hand, when the first dumbbell structure is parallel to the second dumbbell structure, the tetragonality is 1.036 which agrees well with experimental data. The mechanical energy is relatively small. When straight C-Fe-C pair is formed, tetragonality is 1.090. (5) In Fe54C2, formation enthalpy is relatively low when the calculated tetragonality is 1.036, and the existence probability under the assumption of Boltzmann distribution is high. In other cases, the existence probability is nearly zero. (6) The average magnetic moment of an Fe atom is proportional to volume, but not in a clear relation with tetragonality. It is considered that the increase of magnetic moment of an Fe atom by the addition of carbon atom is mainly due to the magneto-volume effect but not due to the tetragonality effect.