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小山 元道*; 山下 享介*; 諸岡 聡; 澤口 孝宏*; Yang, Z.*; 北條 智彦*; 川崎 卓郎; Harjo, S.
鉄と鋼, 110(3), p.197 - 204, 2024/02
被引用回数：0The local plasticity and associated microstructure evolution in Fe-5Mn-0.1C medium-Mn steel (wt.%) were investigated in this study. Specifically, the micro-deformation mechanism during L
ders banding was characterized based on multi-scale electron backscatter diffraction measurements and electron channeling contrast imaging. Similar to other medium-Mn steels, the Fe-5Mn-0.1C steel showed discontinuous macroscopic deformation, preferential plastic deformation in austenite, and deformation-induced martensitic transformation during Lders deformation. Hexagonal close-packed martensite was also observed as an intermediate phase. Furthermore, an in-situ neutron diffraction experiment revealed that the pre-existing body- centered cubic phase, which was mainly ferrite, was a minor deformation path, although ferrite was the major constituent phase.
小山 元道*; 山下 享介*; 諸岡 聡; Yang, Z.*; Varanasi, R. S.*; 北條 智彦*; 川崎 卓郎; Harjo, S.
鉄と鋼, 110(3), p.205 - 216, 2024/02
被引用回数：0
deformation experiments with cold-rolled and intercritically annealed Fe-5Mn-0.1C steel were carried out at ambient temperature to characterize the deformation heterogeneity during Lders band propagation. Deformation band formation, which is a precursor phenomenon of Lders band propagation, occurred even in the macroscopically elastic deformation stage. The deformation bands in the Lders front grew from both the side edges to the center of the specimen. After macroscopic yielding, the thin deformation bands grew via band branching, thickening, multiple band initiation, and their coalescence, the behavior of which was heterogeneous. Thick deformation bands formed irregularly in front of the region where the thin deformation bands were densified. The thin deformation bands were not further densified when the spacing of the bands was below 
10 
m. Instead, the regions between the deformation bands showed a homogeneous plasticity evolution. The growth of the thin deformation bands was discontinuous, which may be due to the presence of ferrite groups in the propagation path of the deformation bands. Based on these observations, a model for discontinuous Lders band propagation has been proposed.
興津 貴隆*; 北條 智彦*; 諸岡 聡; 宮本 吾郎*
鉄と鋼, 110(3), p.260 - 267, 2024/02
被引用回数：0We have investigated the dynamic tensile properties of 4, 5, 6-mass%-Mn-containing low carbon steels with multi-phase microstructures containing retained austenite. The five materials used were classified into two groups. The first group of materials, with around 10% of retained austenite, showed normal strain rete dependence of yield strength (YS) and tensile strength (TS) as in conventional high strength steels. The second group of materials, containing 25-36% of retained austenite, exhibited Lders elongation showed also normal strain rate dependence in YS and flow stress at Lders deformation, but TS varied in a complex manner. Among the second group, in the 4 Mn steel, TS was nearly constant at strain rates below 1 s
but increased slightly at higher strain rates. In the 5 and 6 Mn steels, TS once decreased up to the strain rate of 1 or 10 s, and then began to increase at higher strain rates. These behaviors were discussed in terms of temperature rise during plastic deformation causing suppression of martensitic transformation, and thermal stability of retained austenite. In the 4 Mn steel with relatively unstable retained austenite, almost all the austenite transforms regardless of strain rate. In the 5 and 6 Mn steels, where the retained austenite is moderately stable, strain induced transformation of austenite continues up to high plastic strain, providing a good balance of strength and ductility. At high strain rate, TS decreases slightly due to temperature rise, but at higher strain rates than 1 s, the strain rate sensitivity of flow stress in ferrite become prominent and the flow stress increases.
ders deformation in an Fe-5Mn-0.1C medium-Mn steel小山 元道*; 山下 享介*; 諸岡 聡; 澤口 孝宏*; Yang, Z.*; 北條 智彦*; 川崎 卓郎; Harjo, S.
ISIJ International, 62(10), p.2036 - 2042, 2022/10
被引用回数：11 パーセンタイル：64.46(Metallurgy & Metallurgical Engineering)The local plasticity and associated microstructure evolution in Fe-5Mn-0.1C medium-Mn steel (wt.%) were investigated in this study. Specifically, the micro-deformation mechanism during Lders banding was characterized based on multi-scale electron backscatter diffraction measurements and electron channeling contrast imaging. Similar to other medium-Mn steels, the Fe-5Mn-0.1C steel showed discontinuous macroscopic deformation, preferential plastic deformation in austenite, and deformation-induced martensitic transformation during Lders deformation. Hexagonal close-packed martensite was also observed as an intermediate phase. Furthermore, an in-situ neutron diffraction experiment revealed that the pre-existing body-centered cubic phase, which was mainly ferrite, was a minor deformation path, although ferrite was the major constituent phase.
ders band propagation in an Fe-5Mn-0.1C medium Mn steel clarified through 
scanning electron microscopy小山 元道*; 山下 享介*; 諸岡 聡; Yang, Z.*; Varanasi, R. S.*; 北條 智彦*; 川崎 卓郎; Harjo, S.
ISIJ International, 62(10), p.2043 - 2053, 2022/10
被引用回数：7 パーセンタイル：32.54(Metallurgy & Metallurgical Engineering) deformation experiments with cold-rolled and intercritically annealed Fe-5Mn-0.1C steel were carried out at ambient temperature to characterize the deformation heterogeneity during Lders band propagation. Deformation band formation, which is a precursor phenomenon of Lders band propagation, occurred even in the macroscopically elastic deformation stage. The deformation bands in the Lders front grew from both the side edges to the center of the specimen. After macroscopic yielding, the thin deformation bands grew via band branching, thickening, multiple band initiation, and their coalescence, the behavior of which was heterogeneous. Thick deformation bands formed irregularly in front of the region where the thin deformation bands were densified. The thin deformation bands were not further densified when the spacing of the bands was below 10 m. Instead, the regions between the deformation bands showed a homogeneous plasticity evolution. The growth of the thin deformation bands was discontinuous, which may be due to the presence of ferrite groups in the propagation path of the deformation bands. Based on these observations, a model for discontinuous Lders band propagation has been proposed.
ders band propagation in a medium Mn steel小山 元道*; 山下 享介*; 諸岡 聡; Yang, Z.*; Varanasi, R.*; 北條 智彦*; 川崎 卓郎; Harjo, S.
no journal, ,
The micro-deformation of an Fe-5Mn-0.1C medium Mn steel consisting of face-centered cubic and body-centered cubic phases was characterized through multi-scale in situ scanning electron microscopy. Specifically, multiscale in situ back-scatter electron imaging coupled with ex situ electron backscatter diffraction measurements was conducted under tensile testing. The Fe-Mn-C alloy showed macroscopically localized deformation (i.e., Lders deformation), and the deformation-localized region consisted of multiple find deformation bands. The hierarchical structure of the deformation bands initiated from a specimen side edge and propagated to the other side edge. More microscopically, the plastic deformation preferentially progressed in a face-centered cubic phase, and temporarily stopped when the fine deformation band encountered a group of body-centered cubic grains, which resulted in zigzag propagation of the fine deformation bands. Through coalescence of fine deformation bands, a thick macroscopic deformation band formed. By repetition of the micro-deformation process, the thick deformation band front moved along the tensile direction from an end of the gauge portion to the other end.
諸岡 聡; 小山 元道*; 川崎 卓郎; Harjo, S.
no journal, ,
Medium Mn steels have been actively investigated due to their excellent balance between material cost and mechanical properties. In particular, medium Mn steel with a nominal chemical composition of Fe-5.0Mn-0.1C (mass%) fabricated by intercritical annealing 923 K for 1.8 ks after cold-rolling, was the high-strength mechanical properties at low temperature. This strengthening mechanism evaluated by means of in-situ neutron diffraction under low temperature (engineering materials diffractometer (TAKUMI) at Japan Proton Accelerator Research Complex (J-PARC)), electron back scatter diffraction (EBSD), low temperature differential scanning calorimetry (DSC) and low temperature magnetic susceptibility measurement. We found that as the sample temperature decreases, face-centered cubic (FCC) structure transferred face-centered tetragonal (FCT) structure. Namely, it suggests that austenite transformed martensite like Fe-Pd or Fe-Pt alloy. Therefore, the origin of the high-strength mechanical properties at low temperature was in the presence of FCT martensite. This study got partially support from MEXT Program: Data Creation and Utilization Type Material Research and Development (JPMXP1122684766).
