Physical Meaning of the New Creep Rupture Equation for Heat Resisting Steels

Tamura, Manabu; Esaka, Hisao; Shinozuka, Kei

doi:10.2320/matertrans1989.41.272

Cited by 12 publications

(32 citation statements)

References 9 publications

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“…The 15) It is also reported in the previous work 15) that the values of d/p of a low carbon steel were calculated using a few independent data within a narrow range of temperature and stress and the values were analyzed as a function of time and temperature and, as a result, the precipitation of Mo 2 C during creep was predicted.…”

Section: Equivalent Obstacle Spacingmentioning

confidence: 99%

“…(1) have been discussed in the previous work. 15) It is well known that the apparent activation energy is close to the activation energy of self-diffusion for many pure metals.…”

Section: Equivalent Obstacle Spacingmentioning

confidence: 99%

“…The new theory and related equations 14,15) have not been so general, an essence of the theory has been reviewed as follows. According to the new theory time to rupture, t r , is where s, T, R, Q, V and t r0 are the applied stress, the testing temperature in K, the gas constant, the activation energy in the absence of the applied stress (apparent activation energy for simplicity), the activation volume and the material constant, respectively.…”

Section: Equivalent Obstacle Spacingmentioning

confidence: 99%

“…For these circumstances, some of the authors have developed a new creep concept and related equations 14,15) which can predict the equivalent obstacle spacing for mobile dislocations using only time to rupture. A previous work 16) reported that an average inter-particle distance of a ferritic steel containing small amount of TaN measured using TEM roughly coincided with the equivalent obstacle spacing calculated from rupture data.…”

Section: Introductionmentioning

confidence: 99%

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Relation between Creep Rupture Strength and Substructure of Heat Resistant Steel.

et al. 2002

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Creep rupture tests were performed at around 650°C on a low carbon steel, a W-bearing low carbon steel, a low carbon steel containing 0.1 % of TaN and a 0.1%C-8%Cr-2%W-0.2%V-0.04%Ta steel (F-82H), structural material for fusion reactors. The equivalent obstacle spacing for mobile dislocations is calculated using only rupture data according to the creep theory developed by some of the authors. Thin films taken from the ruptured specimens were examined under a transmission electron microscope (TEM). The observed sub-grain size or the calculated inter-particle distance roughly coincides with the equivalent obstacle spacing. This indicates that the microscopic variable, i.e. the obstacle spacing for mobile dislocations, such as sub-grain size or inter-particle distance, can be directly calculated from only the macroscopic variable, i.e. time to rupture or creep rate.

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Section: Equivalent Obstacle Spacingmentioning

confidence: 99%

“…(1) have been discussed in the previous work. 15) It is well known that the apparent activation energy is close to the activation energy of self-diffusion for many pure metals.…”

Section: Equivalent Obstacle Spacingmentioning

confidence: 99%

Section: Equivalent Obstacle Spacingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Relation between Creep Rupture Strength and Substructure of Heat Resistant Steel.

et al. 2002

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“…Tamura et al 28) showed that the actual obstacle spacing to the dislocation motion, d, can be calculated using the values of Q and V obtained from rupture data. If this idea can be expanded to the creep rate observed, then we obtain…”

Section: Microstructual Changes For F82hd During Creepmentioning

confidence: 99%

Creep Behavior of Double Tempered 8%Cr-2%WVTa Martensitic Steel

Tamura

Nowell²,

Shinozuka

et al. 2006

Mater. Trans.

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Creep testing was carried out at around 650 C for a martensitic 8Cr-2WVTa steel (F82H), which is a candidate alloy for the first wall of the fusion reactors of the Tokamak type. Rupture strength of the double tempered steel (F82HD) is lightly higher than that of simply tempered steel (F82HS). On the other hand, creep rate of F82HD is obviously smaller than that of F82HS in acceleration creep, though creep strain of F82HD in transition creep, where creep rate decreases with increasing strain, is larger than that of F82HS. Hardness of the crept F82HD decreases with increasing creep strain, which corresponded with the transmission electron microscopy (TEM) observation. On the contrary, X-ray diffraction and electron back-scattered diffraction pattern measurements show that fine sub-grains are created during transition creep. The creep curves were analyzed using an exponential type creep equation and the apparent activation energy, the activation volume and the pre-exponential factor were calculated as a function of creep strain. Then, these parameters were converted into two parameters, i.e. equivalent obstacle spacing (EOS) and mobile dislocation density parameter (MDDP). While EOS decreases with increasing creep strain, MDDP increases with increasing strain during transition creep. The decrease in EOS and the increase in either EOS or MDDP are rate-controlling factors in transition and acceleration creep, respectively. On the other hand, in case of F82HS, EOS increases and MDDP decreases during transition creep. In this case, the decrease in MDDP controls the creep rate during transition creep of F82HS. It is concluded that both EOS and MDDP are representative parameters of the change in substructure during creep.

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The Synergistic Effects among Crystal Orientations, Creep Parameters, Local Strain, Macro–Microdeformation, and Polycrystals’ Hardness of Boron Alloyed P91 Steels

Ахтар

Khajuria

2022

steel research int.

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The prerequisite to increase steam pressure and temperature, leading to improve the thermal efficiency of thermal/nuclear power plants, invited the development of high creep-resistant steels capable of serving a minimum of 100 000 h in intense conditions. [1] With the belief of weldability, manufacturability, cost, oxidation, corrosion resistance, thermal fatigue, and creep strength, P91 steel is capable of fulfilling these demands for applications in piping and tubing in ultra-supercritical powerplant technology. [2,3] Its microstructure consists of various substructures in the form of several grain boundaries (GBs), dislocations, precipitates, etc. These caused its creep strength to be sensitive and versatile to pre-/postheat treatment, parameters of welding practices, operating conditions, etc. [4,5] Previous research works have optimized these parameters for 9Cr steels to achieve maximum creep strength. [2][3][4][5] Nevertheless, boron addition in this material is a cause of great interest that contributes to extenuating creep-microstructure damages further. [6][7][8][9][10][11][12][13] Owing to long experimentation time and high costs of uniaxial creep testing, impression creep measurement (ICM) is a favored method because of its small testing time, economical technique, and small-sized testing material. This method produces impression crept zones that could be thoroughly investigated and correlated with the material's performance. [14,15] Moreover, creep properties such as n, σ Th , V eff , and activation energy could be also calculated fast.Electron backscatter diffraction (EBSD) parameters such as kernel average misorientation (KAM), grain reference orientation deviation (GROD), Taylor factor (M), and elastic stiffness are potential parameters in generating novelly in-depth knowledge of creep-microstructure reciprocity of martensitic boron alloyed 9Cr steels. [16,17] In polycrystalline materials, M refers to flow stress with respect to critical resolved shear stress and depends on strength of crystallographic orientations (entailing hardness of orientations). M considers an individual grain present among an aggregate to take the similar deformation. If it violates the state of equilibrium over GBs, then stresses at vertex points arouse multiple slips within a grain differing from crystallite to crystallite. In a stress-strain plot, the expression of M is for crystallographic strain macroscopically because the slope of strain hardening is in direct proportionality to M 2 . Therefore, microscopic and

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Physical Meaning of the New Creep Rupture Equation for Heat Resisting Steels

Cited by 12 publications

References 9 publications

Relation between Creep Rupture Strength and Substructure of Heat Resistant Steel.

Relation between Creep Rupture Strength and Substructure of Heat Resistant Steel.

Creep Behavior of Double Tempered 8%Cr-2%WVTa Martensitic Steel

The Synergistic Effects among Crystal Orientations, Creep Parameters, Local Strain, Macro–Microdeformation, and Polycrystals’ Hardness of Boron Alloyed P91 Steels

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