Recovery and Precipitate Analysis of 9 Pct Cr-1 Pct MoVNb Steel during Creep

Kabadwal, A.; Tamura, Manabu; Shinozuka, Kei; Esaka, Hisao

doi:10.1007/s11661-009-0094-9

Cited by 15 publications

(7 citation statements)

References 52 publications

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“…One countermeasure for this problem is to predict the residual lives of the particular components in each power plant over a short time (Masuyama, 2013;Masuyama, Tokunaga, Shimohara, Yamamoto, & Hirano, 2009;Kimura, 2009;Maruyama, Nakamura, & Yoshimi, 2016). Therefore, variations in both the dislocation density Spiradek et al, 1994;Sawada et al, 1997;Kadoya & Shimizu, 2000;Ennis, 2002;Hayakawa et al 2003;Kassner, 2004;Aghajani Bazazi, 2009;Dudova et al 2012;Dudko et al, 2017) and sub-grain size (Sawada, 1997;Shimizu, 2000 andBlum & Gotz, 1999;Ennis & Czyrska-Filemonowicz, 2002;Qin, Gotz, & Blum, 2003;Aghajani Bazazi, 2009;Dudova et al, 2012;Dudko et al, 2017) during creep have been studied individually as indicators for material degradation together with the changes in hardness, microstructure, and mechanical properties (Kushima et al, 1991;Sawada et al, 1997;Masuyama et al, 2009;Kabadwal, Tamura, Shinozuka, & Esaka, 2010;Fedoseeva et al, 2016). The residual lives of the in-service components have been estimated based on these reported changes, and damaged parts are scheduled to be replaced by new ones based on these findings.…”

Section: The Way Of Advancesmentioning

confidence: 99%

Relation between Sub-grain Size and Dislocation Density During Steady-State Dislocation Creep of Polycrystalline Cubic Metals

Tamura¹

2018

JMSR

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The sub-grain size, d, during steady-state dislocation creep of polycrystalline metals is theoretically formulated to be inversely proportional to the dislocation density, ρ, which is defined as the number of dislocations swept out of a sub-grain divided by the cross-sectional area of the sub-grain. This dislocation density differs from the typically observed dislocation density inside a sub-grain after unloading, ρ_ob. In the current work, the ρ_ob values inside sub-grains in steadily crept specimens of Al, Cu, Fe, Fe–Mo alloy, austenitic stainless steel, and high-Cr martensitic steel reported in the literature were used to evaluate the relation ρ_ob=ηρ. It was confirmed that η≈1 for pure metals (regardless of the type of metal) crept at high temperatures and low stresses or for long durations and η>1 for Mo-containing alloys and martensitic steel crept at low temperatures and/or high stresses. Moreover, it is suggested that the condition η>1 corresponds to a state of excess immobile dislocations inside the sub-grain. The theoretical relation d_ob (≈d)∝η∙〖ρ_ob〗^(-1), where d_ob is the observed sub-grain size, essentially differs from the well-known empirical relation d_ob∝〖ρ_ob〗^(-0.5).

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Section: The Way Of Advancesmentioning

confidence: 99%

Relation between Sub-grain Size and Dislocation Density During Steady-State Dislocation Creep of Polycrystalline Cubic Metals

Tamura¹

2018

JMSR

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“…The metallurgical meanings of these parameters, 𝑄, 𝑉, and 𝐶, obtained using an exponential law are easily explained compared to the typical parameter of the stress exponent (𝑛) obtained using the commonly used power law. Some fundamental research findings have been obtained by analyzing creep data using an exponential law, such as microstructural changes during the long-term creep of typical heat-resistant steels (Tamura, Esaka, & Shinozuka, 2000), the applicability of an exponential law in the creep of metals including nickel-based alloys and solders (Tamura, Esaka, & Shinozuka, 2003), the analysis precipitates during creep of Grade 91 steel (Kabadwal, Tamura, Shinozuka, & Esaka, 2010), the Larson-Miller constant of heat-resistant steel and its physical interpretation (Tamura, Abe, Shiba, Sakasegawa, & Tanigawa, 2013), and changes in dislocation density during the creep of 9Cr-1W steel (Tamura & Abe, 2015b). Moreover, the physical meaning of dislocation density in steady-state creep were investigated by analyzing the creep data of 21 types of ferritic/martensitic and austenitic steels including pure metals using an exponential law (Tamura, 2017).…”

Section: Introductionmentioning

confidence: 99%

Analysis of the Degradation in the Creep Strength of High-Cr Martensitic Steels

Tamura¹,

Abe²

2021

JMSR

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To investigate the formation process of the Z-phase, which lowers the long-term rupture strength of high-Cr martensitic steel, the creep curves of Grades T91, T92, and P92 were analyzed along with the experimental steels of 9Cr-1W and 9Cr-4W by applying an exponential law to the temperature, stress, and time parameters. The activation energy (Q ), activation volume (V ), and Larson-Miller constant (C ) were obtained as functions of creep strain. At the beginning of creep, sub-grain boundary strengthening occurs due to dislocations that are swept out of the sub-grains, which is followed by strengthening due to the rearrangement of M23C6 and the precipitation of the Laves phase. After Q  reaches a peak, heterogeneous recovery and subsequent heterogeneous deformation begin at an early stage of transient creep in the vicinity of several of the weakest boundaries due to coarsening of the precipitates. This activity triggers an unexpected degradation in strength due to the accelerated formation of the Z-phase. Stabilization of M23C6 and the Laves phase is important for mitigating the degradation of the long-term rupture strength of high-strength martensitic steel. The stabilization of the Laves phase is especially important for the Cr-Mo systems because Fe2Mo is easily coarsened at ~600 °C as compared to Fe2W. Lowering the hardness and Si content also prevents excess hardening due to the Laves phase, which also mitigates the degradation. The online monitoring of creep curves and the QVC  analysis render it possible to detect signs of long-term degradation under targeted conditions within a relatively short period.

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“…The metallurgical meanings of these parameters, , , and , obtained using an exponential law are easily explainable as compared to a typical parameter of the stress exponent, , obtained using a power law, which is commonly used. Following fruitful research findings are presented by analyzing creep data using an exponential law; namely, changes in microstructures during long-term creep of typical heat resistant steels (Tamura, Esaka, & Shinozuka, 2000), applicability of an exponential law in creep of metals including nickel base alloys and solders (Tamura, Esaka, & Shinozuka, 2003), precipitates analysis of Grade 91 steel during creep (Kabadwal, Tamura, Shinozuka, & Esaka, 2010). Larson-Miller constant of heat resistant steel and the physical meaning of the constant (Tamura, Abe, Shiba, Sakasegawa, & Tanigawa, 2013), changes in dislocation density during creep of 9Cr-1W steel (Tamura & Abe, 2015), and physical meaning of dislocation density in steady state creep by analyzing creep data of 21 types of ferritic/martensitic and austenitic steels including pure metals using an exponential law (Tamura, 2017).…”

Section: Introductionmentioning

confidence: 99%

Analysis on Degradation in Creep Strength of 9Cr-W Martensitic Steel

Tamura¹

2021

JMSR

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In order to clarify the creep mechanism of high Cr martensitic steel, creep curves of 9Cr-1W and 9Cr-4W steels were analyzed applying an exponential law to the temperature, stress, and time parameters. The activation energy, Q, the activation volume, V, and the Larson-Miller constant, C, are obtained as functions of creep strain. At the beginning of creep, sub-grain boundary strengthening by swept dislocations out of sub-grains occurs followed by strengthening due to the rearrangement of M23C6 and the precipitation of Laves phase. After Q reaches a peak, heterogeneous recovery and subsequent heterogeneous deformation begin at an early stage of transient creep in the vicinity of some weakest boundaries due to coarsening of the precipitates, which triggers the unexpected degradation in strength due to the accelerating coarsening of precipitates. Stabilizing not only M23C6 but also Laves phase is important to mitigate the degradation of rupture strength of martensitic steel. The above creep mechanism for martensitic steel can be applicable to the explanation for the degradation in long term rupture strength of high Cr martensitic steel, Grades 91 and 92.

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Recovery and Precipitate Analysis of 9 Pct Cr-1 Pct MoVNb Steel during Creep

Cited by 15 publications

References 52 publications

Relation between Sub-grain Size and Dislocation Density During Steady-State Dislocation Creep of Polycrystalline Cubic Metals

Relation between Sub-grain Size and Dislocation Density During Steady-State Dislocation Creep of Polycrystalline Cubic Metals

Analysis of the Degradation in the Creep Strength of High-Cr Martensitic Steels

Analysis on Degradation in Creep Strength of 9Cr-W Martensitic Steel

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