Toshihiro Tsuchiyama - Academia.edu (original) (raw)
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Papers by Toshihiro Tsuchiyama
ISIJ International, 2001
* 1 In this paper, the term 'recrystallization' has been defined as a discontinuous process, that... more * 1 In this paper, the term 'recrystallization' has been defined as a discontinuous process, that is, new dislocation-free grains are formed within a recovered structure and they grow consuming old grains. Continuous processes such as the formation of subgrain structure or the increase in misorientation of grain boundaries have been referred to as 'recovery'.
ISIJ International, 2005
Ridging phenomenon was successfully suppressed in a ferritic stainless steel by controlling micro... more Ridging phenomenon was successfully suppressed in a ferritic stainless steel by controlling microstructure through recrystallization of lath martensitic structure. Fe-12Cr-1Ni alloy was quenched after the solution treatment in an austenite single phase region to obtain lath martensitic structure. Cold rolling was performed to the quenched materials up to 80 % reduction in thickness before the annealing for recrystallization. With increasing the reduction by cold rolling, the recrystallization was promoted and ferrite grain size was decreased to 20 mm after recrystallization in the 80 % pre-cold-rolled material. A weak ͗111͘//ND recrystallization texture was formed by the cold rolling, but no grain colonies existed in the microstructure. As a result, the materials produced through the recrystallization of lath martensite did not cause ridging during tensile deformation, although an orange peel appeared when the grain size was not refined enough.
ISIJ International, 2007
The microstructure of partially reversed lath martensite in 13%Cr-6%Ni steel was examined by elec... more The microstructure of partially reversed lath martensite in 13%Cr-6%Ni steel was examined by electron backscatter diffraction, and the crystallographic character of the reversed austenite is discussed in relation to the mechanism of 'austenite memory'. Most of the reversed austenite grains had the same orientation as the original austenite matrix before martensitic transformation. However, some austenite grains had a different orientation in a twin relationship to the other major austenite grains, although all the reversed austenite grains retained a Kurdjumov-Sachs relationship to the martensite matrix. On the basis of the crystallographic relationships among the habit plane, the close packed direction of austenite and the martensite lath boundary, we suggest that the austenite variants are theoretically limited to two kinds within one packet and five kinds within one original austenite grain. In addition, we found that internal stress introduced by martensitic transformation plays an important role in determining the austenite variant: internal stress operates so that reversed austenite selects the same variant as that present in the original austenite matrix before martensitic transformation. This phenomenon is understood as the austenite memory.
MATERIALS TRANSACTIONS, 2004
ISIJ International, 2000
A High carbon martensitic stainless steel (Fe-1 2•/•Cr-0.7•1•C) was subjected to isothermal aging... more A High carbon martensitic stainless steel (Fe-1 2•/•Cr-0.7•1•C) was subjected to isothermal aging after tull solution treatment, and then solution-treated again in the two phase region ot austenite and M*C* carbide; partial solution (PS) treatment. Microstructural deve]opmentduring these heat treatment was investigated, and mechanical properties for the PStreated steel were evaluated by comparison with a referencial steel without isothermal aging. During the isothermal aging at 923K, the supercooled austenite undergoes eutectoid transformation and decomposes to territe and M*C, carbide, and the carbide particles are finely dispersed within the matrix. Insoluble carbide particles retained during the following PStreatment contribute to suppressing austenite grain growth effectively through the grain boundary pinning eftect. Ductile-brittle transition in the PS treated steel is characterized by a lower transition temperature and a higher upper-sheff energy compared with the referencial steel. This is due to the grain retining ot prior austenite as well as the homogeneous dispersion of carbide particles through the PStreatment with isothermal aging.
Advanced Steels, 2011
... Hence, it was concluded that Seah-Hendros model is reasonable to explain the carbon concentra... more ... Hence, it was concluded that Seah-Hendros model is reasonable to explain the carbon concentration dependence of the HallPetch coefficient in ferritic iron ... pure iron but enhanced to 600 MPaÁμm1/2 by adding 60 ppm of carbon [2]. On the other hand, yield stress (ry) of ferritic ...
ISIJ International, 2001
Reiation between microstructure and creep deformation behavior was investigated in 9•1•Cr base Cu... more Reiation between microstructure and creep deformation behavior was investigated in 9•1•Cr base Cu bearing martensitic steels, and the strengthening mechanismby Cu particles was discussed in connection with the microstructure of lath martensite. All of as-quenched 9•/•Cr-(O-4)•1•Cu steels have typical lath-martensite single structure characterized by martensite-block and-packet structures, with high density of dislocation. As a result of creep testing at 873K-140MPa, it is found that minimumcreep rate of these martensitic specimens is lowered and the rupture time is prolonged with increasing Cu content. The 9•/•Cr-4•1•Cu steel has about seven times as fong creep-rupture time as the 9•1•Cr base steel. TEM observations in the crept 9•/•Cr-4•1•Cu steel revealed that dislocations tangled with fine Cu particles which precipitated within laths. This dislocation pinning effect by Cu particles contributes to retarding the recovery of martensite. Hence the dislocation density is kept higher in the 9•/•Cr-4•1•Cu steel than the 9•1•Cr base steel during creep deformation. The relation between the recovery and the creep deformation behaviors was successfully explained by the change in pinning force by Cu particles in all of 9•/•Cr-Cu steels. Discussed in detail, once the pinning force falls below the applied stress, the recovery rapidly proceeds and the creep strain rate is accelerated corresponding to the recovery behavior. KEYWORDS: heat reslstant steel martenslte lath structure mlcrostructural change Cu partlcle pmnmg force recovery; creep
ISIJ International, 2013
† The definition to distinguish 'low' and 'high' alloy steels varies among countries and among st... more † The definition to distinguish 'low' and 'high' alloy steels varies among countries and among standard-setting organizations. As a general indication, low-alloy steel can be regarded as alloy steels containing 1-5% of elements except carbon by the ISO definition.
ISIJ International, 2001
* 1 In this paper, the term 'recrystallization' has been defined as a discontinuous process, that... more * 1 In this paper, the term 'recrystallization' has been defined as a discontinuous process, that is, new dislocation-free grains are formed within a recovered structure and they grow consuming old grains. Continuous processes such as the formation of subgrain structure or the increase in misorientation of grain boundaries have been referred to as 'recovery'.
ISIJ International, 2005
Ridging phenomenon was successfully suppressed in a ferritic stainless steel by controlling micro... more Ridging phenomenon was successfully suppressed in a ferritic stainless steel by controlling microstructure through recrystallization of lath martensitic structure. Fe-12Cr-1Ni alloy was quenched after the solution treatment in an austenite single phase region to obtain lath martensitic structure. Cold rolling was performed to the quenched materials up to 80 % reduction in thickness before the annealing for recrystallization. With increasing the reduction by cold rolling, the recrystallization was promoted and ferrite grain size was decreased to 20 mm after recrystallization in the 80 % pre-cold-rolled material. A weak ͗111͘//ND recrystallization texture was formed by the cold rolling, but no grain colonies existed in the microstructure. As a result, the materials produced through the recrystallization of lath martensite did not cause ridging during tensile deformation, although an orange peel appeared when the grain size was not refined enough.
ISIJ International, 2007
The microstructure of partially reversed lath martensite in 13%Cr-6%Ni steel was examined by elec... more The microstructure of partially reversed lath martensite in 13%Cr-6%Ni steel was examined by electron backscatter diffraction, and the crystallographic character of the reversed austenite is discussed in relation to the mechanism of 'austenite memory'. Most of the reversed austenite grains had the same orientation as the original austenite matrix before martensitic transformation. However, some austenite grains had a different orientation in a twin relationship to the other major austenite grains, although all the reversed austenite grains retained a Kurdjumov-Sachs relationship to the martensite matrix. On the basis of the crystallographic relationships among the habit plane, the close packed direction of austenite and the martensite lath boundary, we suggest that the austenite variants are theoretically limited to two kinds within one packet and five kinds within one original austenite grain. In addition, we found that internal stress introduced by martensitic transformation plays an important role in determining the austenite variant: internal stress operates so that reversed austenite selects the same variant as that present in the original austenite matrix before martensitic transformation. This phenomenon is understood as the austenite memory.
MATERIALS TRANSACTIONS, 2004
ISIJ International, 2000
A High carbon martensitic stainless steel (Fe-1 2•/•Cr-0.7•1•C) was subjected to isothermal aging... more A High carbon martensitic stainless steel (Fe-1 2•/•Cr-0.7•1•C) was subjected to isothermal aging after tull solution treatment, and then solution-treated again in the two phase region ot austenite and M*C* carbide; partial solution (PS) treatment. Microstructural deve]opmentduring these heat treatment was investigated, and mechanical properties for the PStreated steel were evaluated by comparison with a referencial steel without isothermal aging. During the isothermal aging at 923K, the supercooled austenite undergoes eutectoid transformation and decomposes to territe and M*C, carbide, and the carbide particles are finely dispersed within the matrix. Insoluble carbide particles retained during the following PStreatment contribute to suppressing austenite grain growth effectively through the grain boundary pinning eftect. Ductile-brittle transition in the PS treated steel is characterized by a lower transition temperature and a higher upper-sheff energy compared with the referencial steel. This is due to the grain retining ot prior austenite as well as the homogeneous dispersion of carbide particles through the PStreatment with isothermal aging.
Advanced Steels, 2011
... Hence, it was concluded that Seah-Hendros model is reasonable to explain the carbon concentra... more ... Hence, it was concluded that Seah-Hendros model is reasonable to explain the carbon concentration dependence of the HallPetch coefficient in ferritic iron ... pure iron but enhanced to 600 MPaÁμm1/2 by adding 60 ppm of carbon [2]. On the other hand, yield stress (ry) of ferritic ...
ISIJ International, 2001
Reiation between microstructure and creep deformation behavior was investigated in 9•1•Cr base Cu... more Reiation between microstructure and creep deformation behavior was investigated in 9•1•Cr base Cu bearing martensitic steels, and the strengthening mechanismby Cu particles was discussed in connection with the microstructure of lath martensite. All of as-quenched 9•/•Cr-(O-4)•1•Cu steels have typical lath-martensite single structure characterized by martensite-block and-packet structures, with high density of dislocation. As a result of creep testing at 873K-140MPa, it is found that minimumcreep rate of these martensitic specimens is lowered and the rupture time is prolonged with increasing Cu content. The 9•/•Cr-4•1•Cu steel has about seven times as fong creep-rupture time as the 9•1•Cr base steel. TEM observations in the crept 9•/•Cr-4•1•Cu steel revealed that dislocations tangled with fine Cu particles which precipitated within laths. This dislocation pinning effect by Cu particles contributes to retarding the recovery of martensite. Hence the dislocation density is kept higher in the 9•/•Cr-4•1•Cu steel than the 9•1•Cr base steel during creep deformation. The relation between the recovery and the creep deformation behaviors was successfully explained by the change in pinning force by Cu particles in all of 9•/•Cr-Cu steels. Discussed in detail, once the pinning force falls below the applied stress, the recovery rapidly proceeds and the creep strain rate is accelerated corresponding to the recovery behavior. KEYWORDS: heat reslstant steel martenslte lath structure mlcrostructural change Cu partlcle pmnmg force recovery; creep
ISIJ International, 2013
† The definition to distinguish 'low' and 'high' alloy steels varies among countries and among st... more † The definition to distinguish 'low' and 'high' alloy steels varies among countries and among standard-setting organizations. As a general indication, low-alloy steel can be regarded as alloy steels containing 1-5% of elements except carbon by the ISO definition.