Faculty Profiles - TAKEMOTO Yoshito

Papers - TAKEMOTO Yoshito

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Influence of Ti and Nb on the Strength-Ductility-Hole Expansion Ratio Balance of Hot-rolled Low-carbon High-strength Steel Sheets Reviewed

Kyohei Kamibayashi, Yutaka Tanabe, Yoshito Takemoto, Ichirou Shimizu, Takehide Senuma

ISIJ INTERNATIONAL 52 ( 1 ) 151 - 157 2012

Language：English Publishing type：Research paper (scientific journal) Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN

To satisfy the demand for high-strength steel sheets with excellent strength-ductility-hole expansion ratio balance, high-strength steels consisting of a ferrite or bainitic ferrite matrix strengthened by a large amount of finely dispersed precipitates have been developed.
In this study, the influence of the precipitation-forming elements Ti and Nb on the strength-ductility-hole expansion ratio balance of these steels has been investigated. The strength-ductility-hole expansion ratio balance of steel with Ti added was superior to that with Nb added. The reason for the superiority of steel with added Ti was discussed from various viewpoints such as microstructure, texture, the condition of the pierced surface, sulphide formation, the nucleation and propagation behaviour of cracks during hole expansion, etc. We concluded that the inferior strength-ductility-hole expansion ratio balance of the steel with added Nb was mainly caused by the formation of large textural colonies and a detrimental influence of MnS. From these inferences, we proposed a combined addition of Ti and Nb, and succeeded in improving the strength-ductility-hole expansion ratio balance of the advanced high-strength steel.

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Effect of Rapid Heating on Evolution of Microstructures and Coating Layers in Hot Stamping Processes Reviewed

Proc. of the 3nd Int.Conf. Hot Sheet Metal Forming of High-Performance Steel 465 - 472 2011.6

極低炭素冷延鋼板の再結晶モデル Reviewed

鉄と鋼 97 ( 4 ) 238 - 244 2011.4

Model for Predicting Recrystallization Behavior of Colled Rolled Extralow Carbon Steel Sheets Reviewed

Norihisa Nishitani, Takafumi Hiramoto, Yoshito Takemoto, Takehide Senuma

TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN 97 ( 4 ) 238 - 244 2011.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN

Microstructual observations indicate that the recrystallization of cold rolled extralow carbon steel sheets occurs due to the abnormal growth of selected subgrains in recovered subgrain microstructures. Based on this recrystallization mechanism, a new model for predicting the recrystallization behavior of a material with idealized microstructure was proposed by Humphreys. The model cannot, however, predict the recrystallization behavior of cold rolled steel sheets in the practice because of the complexities of their microstructure.
In this study, a model for predicting the recrystallization behavior of cold rolled extralow carbon steels has been developed based on the model by Humphreys. The feature of the present model is that the pinning and solute drag effects on the recrystallization behavior can be evaluated quantitatively.
Using the model, the influence of Ti addition on the recrystallization in extralow carbon steel sheets was discussed. The result indicates that the retardation of the recrystallization due to the addition of Ti is attributed mainly to the retardation of the subgrain formation in the recovery process, and the effect of the pinning of precipitates and the dragging of solute Ti atoms on the progress of recystallization are relatively small.

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Influence of Alloying Elements on Precipitation Behavior of VCN in Middle Carbon Steels Reviewed

Takehide Senuma, Yoshito Takemoto

SOLID-SOLID PHASE TRANSFORMATIONS IN INORGANIC MATERIALS, PTS 1-2 172-174 408 - + 2011

Language：English Publishing type：Research paper (international conference proceedings) Publisher：TRANS TECH PUBLICATIONS LTD

For lightening the hot forged automotive components such as connecting rods, crank shafts etc. the increase in their yield strength is an important technical issue. Recent developments indicate that it is a promising way to increase the yield strength of the components using the ferrite-pearlite microstructure strengthened by precipitation hardening of VC.
In this study, the influence of alloying elements, cooling rate and aging temperature on the precipitation hardening behavior of V containing middle carbon steels was investigated. The precipitation hardening is very sensitive to cooling rate and aging temperature. The addition of Si reduced the sensitivity of the cooling rate. The deformation in the austenite region slightly decreases the precipitation hardening. From a detailed analysis, it was found out that the precipitation hardening is strongly influenced by the gamma ->alpha transformation behavior, which indicates that the interphase precipitation plays a significant role for the precipitation hardening.

DOI： 10.4028/www.scientific.net/SSP.172-174.408

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高効率多段ホットスタンピング技術 Reviewed

瀬沼武秀,馬込英明,葉賀一太,藤岡尚浩,竹元嘉利,清水憲一

塑性と加工 51 ( 7 ) 54 - 58 2010.7

Present Status and Future Perspective of Hot Stamping Technology : Key Technology for Lightening Automotive Bodies Reviewed

SENUMA Takehide, TAKEMOTO Yoshito

Journal of the JSTP 51 ( 592 ) 410 - 415 2010.5

組織と特性予測の計算工学共通試料試験結果 Reviewed

計算工学による組織と特性予測技術の最前線日本鉄鋼協会編 249 - 250 2010.5

Influence of Thermal History on Microstructure and Mechanical Properties of Steels for Hot Stamping Reviewed

Takehide Senuma, Yoshito Takemoto

PRICM 7, PTS 1-3 654-656 330 - 333 2010

Language：English Publishing type：Research paper (international conference proceedings) Publisher：TRANS TECH PUBLICATIONS LTD

Hot stamping is an attractive method to produce extra high strength automotive components. in the conventional hot stamping, the furnace heating is employed and the heating rate is quite low. To improve the productivity of the hot stamping technology, the reduction of time for the heating process is required. In this study, the influence of the heating rate in a range up to 200 degrees C/s, heating temperatures between 650 degrees C and 950 degrees C and cooling condition on microstructure and mechanical properties of 0.22% C -3%Mn steel has been investigated. The steel is a promising material for the highly productive new hot stamping technology because this steel transformed into martensite from austenite even at cooling in free air. The specimens heat-treated at a high heating rate and for short holding time at the heating temperature just above Ac3 show significantly fine martensite microstructure and a good strength-toughness balance. In this paper, the alpha --> gamma transformation behavior and the gamma --> alpha transformation behavior after inter-critical annealing are discussed to explain the evolution of the microstructures and mechanical properties.

DOI： 10.4028/www.scientific.net/MSF.654-656.330

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S0304-1-3 Evaluation of Crystal Orientation of Ti-Mo Alloys Using Micro Indentation Test

KIMURA Noriaki, SHIMIZU Ichiro, TADA Naoya, TAKEMOTO Yoshito

The proceedings of the JSME annual meeting 2010 265 - 266 2010

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

In recent years, β-type Ti alloys have been attracting much attention for industrial applications, not only by its high specific strength and superior formability but also by special features such as low elastic modulus and extraordinary plastic deformation behavior. However, the studies on β-Ti alloys are still less than those on other types of Ti alloys. Hence, the evaluation processes of various properties of β-Ti alloys have still not been established nevertheless of their importance for industrial applications. The aim of the present study is to evaluate the crystal orientation of grains of β-Ti alloys by means of micro indentation technique. Ti-14Mo and Ti-20Mo alloys, whose primary deformation mechanisms are mechanical twin and coarse slip, respectively, were employed as typical β-Ti alloys. The detailed investigations were performed on the relationship between the crystal orientation and the indentation behavior. The results revealed that the lines which appeared around the indentation of Ti-14Mo almost corresponded to twin boundaries, while those of Ti-20Mo were slip lines. The distortion of indentation shapes also appeared on both Ti-Mo alloys. Based on these results, the procedure of crystal orientation evaluation by micro indentation test was discussed.

DOI： 10.1299/jsmemecjo.2010.1.0_265

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Ti-MoおよびTi-6Mo-X-Y合金の微細組織と機械的性質 Reviewed

竹元嘉利, 三宅章義, 瀬沼武秀

日本金属学会誌 73 ( 9 ) 752 - 757 2009

Influence of Press Forming Conditions on the Shape Fixability of Hot Stamped Hat-type Parts Reviewed

Proc. of the 3rd Int. Conf. on Steels in Cars and Tracks 230 - 235 2008.6

Elasto-plastic behavior and its composition dependency of β-type Ti-Mo alloys Reviewed

Proceedings of JSEM ( 8 ) 274 - 276 2008.6

ホットスタンピング部品の形状凍結性に及ぼす成形条件の影響 Reviewed

瀬沼武秀, 馬込英明, 田邉章宏, *竹元嘉利

塑性と加工 49 ( 567 ) 321 - 325 2008.4

Model for Predicting the Microstructural Evolution of Extralow Carbon Steels Reviewed

Takehide Senuma, Yoshito Takemoto

ISIJ INTERNATIONAL 48 ( 11 ) 1635 - 1639 2008

Language：English Publishing type：Research paper (scientific journal) Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN

The microstructural evolution of extralow carbon steels in hot working processes has been studied. Considering the experimental results of the microstructural evolution of austenite and the transformation behavior, a metallurgical model for predicting the microstructural evolution of extralow carbon steels in hot working processes was developed. The model was applied to hot rolling processes to evaluate the quantitative effect of various operation conditions on the grain refinement of ferrite and the calculated results were found to correlate relatively well to experimental ones.

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Grain refinement of extralow-carbon steels in hot strip rolling

Takehide Senuma, Yoshito Takemoto

3rd International Conference on Thermomechanical Processing of Steels, TMP 2008 2008

Language：English Publishing type：Research paper (international conference proceedings)

The effect of various operational parameters such as the finishing temperature, the final reduction, the cooling rate, the onset time for cooling after the final rolling in a hot strip rolling process on the grain refinement of hot rolled extralow carbon steel bands has been investigated. To analyze the experimental results, a metallurgical model for predicting the microstructural evolution of extralow carbon steels in hot working processes was developed. The calculated results were found to correlate relatively well to experimental ones and indicate that the effect of various operation conditions on grain refinement can be explained by considering the evolution of the dislocation density in austenite and the transformation temperature.

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Analysis of Fine Stress Fields in Metal Matrix Composites Using HOLZ Patterns Reviewed

M. Shibata, Y. Takemoto and I. Shimizu

Materials Science Forum 539-543 848 - 853 2007.7

The effect of deformation mechanism on plastic behavior of β-type Ti-Mo alloys Reviewed

Ichiro Shimizu and Yoshito Takemoto

Ti-2007 Science and Technology 1 543 - 546 2007.6

Anelastic behavior of Ti-8mass%Mo alloy by pre-deformation Reviewed

Yoshito Takemoto, Akira Sakakibara and Takehide Senuma

Ti-2007 Science and Technology 1 539 - 542 2007.6

Recrystallization behavior and texture formation of rapidly annealed cold-rolled extralow carbon steel sheets Reviewed

Takehide Senuma, Kaoru Kawasaki, Yoshito Takemoto

MATERIALS TRANSACTIONS 47 ( 7 ) 1769 - 1775 2006.7

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

The influence of a heating rate up to 1000 degrees C/s on recrystallization behavior and texture formation of an extralow carbon steel sheet was investigated. To discuss the experimental results of this investigation, a mathematical model for predicting recrystallization behavior was developed. An analysis using the model shows that the heating rate influences the apparent thermal activation energy of recrystallization. At a higher heating rate, C dissolved from cementite and AlN precipitated during heating decreases and as a consequence the apparent thermal activation energy is lower. This can also be a valid explanation for the fact that recrystallization of a steel sheet coiled at low temperature is retarded. The main orientations of the recrystallization texture are weakened if the heating rate is increased. This tendency has already been observed at the initial stage of recrystallization. If the specimen is heated slowly up to the initial stage of recrystallization, the decrease in the intensity of the main orientations is reduced even though the heating rate subsequently increases. This result indicates that, concerning formation of the recrystallization texture, the heating rate mainly influences the nucleation process.

DOI： 10.2320/matertrans.47.1769

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