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Journal Articles

Precipitation of ferromagnetic phase induced by defect energies during creep deformation in Type 304 austenitic steel

Tsukada, Yuki*; Shiraki, Atsuhiro*; Murata, Yoshinori*; Takaya, Shigeru; Koyama, Toshiyuki*; Morinaga, Masahiko*

Journal of Nuclear Materials, 401(1-3), p.13 - 16, 2010/06

 Times Cited Count:3 Percentile:24.16(Materials Science, Multidisciplinary)

The correlation of defect energies with precipitation of the ferromagnetic phase near M$$_{23}$$C$$_{6}$$ carbide during creep tests at high temperature in Type 304 austenitic steel was examined by estimating the defect energies near the carbide, based on micromechanics. As one of the defect energies, the precipitation energy was calculated by assuming M$$_{23}$$C$$_{6}$$ carbide to be a spherical inclusion. The other defect energy, creep dislocation energy, was calculated based on dislocation density data obtained from transmission electron microscopy observations of the creep samples. The dislocation energy density was much higher than the precipitation energy density in the initial stage of the creep process, when the ferromagnetic phase started to increase. Creep dislocation energy could be the main driving force for precipitation of the ferromagnetic phase.

Journal Articles

Phase-field simulation of nucleation and growth of M$$_{23}$$C$$_{6}$$ carbide and ferromagnetic phases during creep deformation in Type 304 steel

Tsukada, Yuki*; Shiraki, Atsuhiro*; Murata, Yoshinori*; Takaya, Shigeru; Koyama, Toshiyuki*; Morinaga, Masahiko*

Journal of Nuclear Materials, 401(1-3), p.154 - 158, 2010/06

 Times Cited Count:6 Percentile:40.42(Materials Science, Multidisciplinary)

A phase-field method was applied to the simulation of simultaneous nucleation and growth of both M$$_{23}$$C$$_{6}$$ carbide and ferromagnetic $$alpha$$ phases during the creep process in Type 304 steel. The defect energy of the creep dislocations near the carbides, which increases during creep, was integrated into the nucleation driving force for the $$alpha$$ phase. The simulation used in this study accurately reproduced changes in the amounts of the precipitated phases as a function of creep time. Furthermore, we examine the effect of the dislocation density on precipitation of the $$alpha$$ phase, and show that the phase-field method is useful for examining the stochastic and kinetic phenomenon of phase transformation.

Oral presentation

Relationship between phase transformation in SUS304 stainless steel and strain stored in it during creep tests

Shiraki, Atsuhiro*; Wada, Takumi*; Murata, Yoshinori*; Morinaga, Masahiko*; Takaya, Shigeru; Koyama, Toshiyuki*

no journal, , 

no abstracts in English

Oral presentation

Evaluation of creep strain energy related to formation of ferro-magnetic phase in SUS304

Tsukada, Yuki*; Shiraki, Atsuhiro*; Murata, Yoshinori*; Morinaga, Masahiko*; Takaya, Shigeru; Koyama, Toshiyuki*

no journal, , 

no abstracts in English

Oral presentation

Formation of the ferromagnetic phase in SUS304 steel induced by strain energy stored during creep tests

Shiraki, Atsuhiro*; Tsukada, Yuki*; Murata, Yoshinori*; Morinaga, Masahiko*; Takaya, Shigeru; Koyama, Toshiyuki*

no journal, , 

This study demonstrates the mechanism of $$gamma$$$$rightarrow$$$$alpha$$ transformation in creep test on the basis of the energy of the system. The experimental result shows that the strain energy around M$$_{23}$$C$$_{6}$$ carbide becomes very high due to dislocations stored during creep. As a result, the system free energy in the local region near the carbide increases with increasing creep time but it decreases by the formation of ferromagnetic $$alpha$$ phase.

Oral presentation

Formation of ferromagnetic phase in SUS304 stainless steel due to the strain energy stored in it during creep test

Shiraki, Atsuhiro*; Tsukada, Yuki*; Murata, Yoshinori*; Morinaga, Masahiko*; Takaya, Shigeru; Koyama, Toshiyuki*

no journal, , 

We evaluated the system free energy of SUS304 for understanding the phenomenon that ferromagnetic phase is formed in austenitic stainless steel during creep test. As result, it was thought that there are regions with high system free energy due to increase in strain energy locally, where ferromagnetic phase may be formed.

Oral presentation

Analysis and prediction of microstructure of heat resistant steels based on system free energy

Murata, Yoshinori*; Shiraki, Atsuhiro*; Takeda, Kotaro*; Tsukada, Yuki*; Saito, Yoshihiro*; Morinaga, Masahiko*; Koyama, Toshiyuki*; Takaya, Shigeru

no journal, , 

no abstracts in English

Oral presentation

Phase-field simulation of the formation of $$M_{23}C_{6}$$ carbide in SUS304 austenitic steel

Shiraki, Atsuhiro*; Tsukada, Yuki*; Murata, Yoshinori*; Morinaga, Masahiko*; Takaya, Shigeru; Koyama, Toshiyuki*

no journal, , 

Authors have shown that ferromagnetic phases are induced in SUS304 by strain concentration during creep test. In this paper, we simulate the formation of $$M_{23}C_6$$ carbide which is important as trapping site of dislocation by using the phase-field method.

Oral presentation

Phase-field simulation on the formation of ferromagnetic phase during creep deformation in SUS304 steel

Tsukada, Yuki*; Shiraki, Atsuhiro*; Murata, Yoshinori*; Morinaga, Masahiko*; Takaya, Shigeru; Koyama, Toshiyuki*

no journal, , 

The formation of the ferromagnetic $$alpha$$ phase during creep deformation in SUS304 steel was simulated by aphase-field method. In order to consider the precipitation and growth of the phase simultaneously, we haveconstructed a model based on experimental results. In this model, strain energy stored near $$M_{23}C_6$$ carbideduring creep deformation increases the driving force for precipitation of the $$alpha$$ phase. This strain energy isestimated on the basis of distribution function of dislocation density in space near the carbide and is used inthe calculation of the activation energy for nucleation of the $$alpha$$ phase. Changes in mole fraction of both $$M_{23}C_6$$ carbide and the $$alpha$$ phase are reproduced well in this simulation. Furthermore, it is found that theincrease rate of dislocation density during creep process affects the manner of the change in mole fraction ofthe $$alpha$$ phase.

Oral presentation

Formation of ferromagnetic phase in nuclear grade austenitic stainless steel and evaluation based on system free energy

Shintani, Tsuyoshi*; Tsukada, Yuki*; Shiraki, Atsuhiro*; Murata, Yoshinori*; Morinaga, Masahiko*; Takaya, Shigeru; Koyama, Toshiyuki*

no journal, , 

The magnetic flux density of SUS316 changes lesser than that of SUS304 during creep deformation. In this study, the reason of this difference was investigated based on system free energy. As result, it was revealed that the strain energies of both steels, which contribute to the formation of ferromagnetic bcc phase, were almost the same. Therefore, the dependency of magnetic flux density change on steel grades will be related to that activation energy for the formation of ferromagnetic phase of SUS316 is larger than that of SUS304.

Oral presentation

Phase-field simulation on the formation of ferromagnetic phase induced by creep strain in SUS304 steel

Tsukada, Yuki*; Shiraki, Atsuhiro*; Murata, Yoshinori*; Koyama, Toshiyuki*; Takaya, Shigeru; Morinaga, Masahiko*

no journal, , 

Phase-field simulation was conducted based on thermodynamic data base and experimental data on dislocation density near carbides to reveal the relationship between carbide and the formation of ferromagnetic phase in SUS304. The results showed that it is important to consider change in dislocation density near carbides and threshold stress for the formation of ferromagnetic phase to show quantitative relationship between damage at elevated temperature and the content of ferromagnetic phase.

Oral presentation

Phase-field simulation on phase transformation during creep deformation in type 304 steel

Tsukada, Yuki*; Shiraki, Atsuhiro*; Murata, Yoshinori*; Takaya, Shigeru; Koyama, Toshiyuki*; Morinaga, Masahiko*

no journal, , 

Phase-field simulation of phase transformation during creep in Type 304 austenitic steel is performed and simultaneous nucleation and growth of both $$M_{23}C_6$$ carbide and ferromagnetic $$alpha$$ phases are reproduced. Nucleation events of these product phases are explicitly introduced through a probabilistic Poisson seeding process based on the classical nucleation theory. Creep dislocation energy near the carbide is integrated into the nucleation driving force for the $$alpha$$ phase. We examine the effect of the dislocation density on precipitation of the $$alpha$$ phase, and it is found that a small difference in the dislocation density leads to a significant change in precipitation behavior of the $$alpha$$ phase.

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