Improvement of &amp;Omega; Method to Estimate Creep Behavior of a Mod.9Cr-1Mo Steel

Park, Kyu Seop; Masuyama, Fujimitsu; Endo, Takao

doi:10.2355/tetsutohagane1955.85.6_492

Cited by 4 publications

(2 citation statements)

References 15 publications

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“…The  ε 0 of Formula (8) was able to be calculated by substituting any strain rate (  ε ) and time (t) in the most linear region mentioned above, in addition to the Ω. The Ω and  ε 0 were determined directly from the creep curves, but the indirect method 19,20) of obtaining these two was not used. Figure 13 shows the relationship between rupture life and the product of Ω and  ε 0.…”

Section: ω Methodsmentioning

confidence: 99%

Creep-Rupture Life Prediction for 9Cr-1Mo-Nb-V Weld Metal

et al. 2015

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Creep tests were carried out with shielded-metal-arc weld metal for 9Cr-1Mo-Nb-V steel. The testing temperature and stress levels were chosen so that rupture would occur around 1 000 hours. The three creep-rupture life prediction methodologies, namely the Monkman-Grant law, the modified θ projection, and the Ω method, were applied to each experimental creep curve, and the constant numbers for individual equations were obtained. All these three were proven to be practical for weld metals similar to the base metal. However, the Monkman-Grant law has been proven to be the most effective when predicting creep rupture life at an early stage of creep test. The equation, obtained in this study, was relevant also when the Mn + Ni content varied in 9Cr-1Mo-Nb-V weld metal.KEY WORDS: weld metal; 9Cr-1Mo-Nb-V steel; creep; creep resistant steel; life prediction; minimum creep rate; Monkman-Grant law; Modified θ projection; Ω method.

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Section: ω Methodsmentioning

confidence: 99%

Creep-Rupture Life Prediction for 9Cr-1Mo-Nb-V Weld Metal

et al. 2015

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“…In order to meet the requirements for creep life assessment, studies on the constitutive equations, [3][4][5][6] the substructural evolution, [7][8][9] the growth of precipitates during creep, 10) and also the relation between creep strength and structures [11][12][13][14][15] have been investigated. Among these works, the observation reported by Kushima et al 14) is worthy of attention.…”

Section: Introductionmentioning

confidence: 99%

Change in Vickers Hardness and Substructure during Creep of a Mod.9Cr-1Mo Steel

2003

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In order to investigate the structural degradation during creep, interrupted creep tests were conducted of a Mod.9Cr-1Mo steel in the range of stress and temperature from 71 to 167 MPa and 873 to 923 K. The change of hardness and tempered martensitic lath width were measured in grip and gauge parts of interrupted specimens. The lath structure was thermally stable in static conditions, however, it was not stable during creep and the structural change was enhanced by creep strain. The relation between the change in lath width and strain was described quantitatively. The change in Vickers hardness was expressed by a single valued function of creep life consumption ratio. Based on the empirical relation between strain and lath width, a model was proposed to describe the relation between change in hardness and creep life consumption ratio. The comparison of the model with the empirical relation suggests that about 65% of hardness loss is due to the decrease of dislocation density accompanied by the movement of lath boundaries. The role of precipitates on subboundaries was discussed in connection with the abnormal subgrain growth appearing in low stress regime.

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Creep strength of Mod.9Cr1Mo steel under biaxial stress states

直巳

雅弘²,

洋

2014

Transactions of the JSME (In Japanese)

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This paper describes the development of tension, torsion, and combined tension-torsion creep testing machine with hydro static thrust bearing, criterion on creep rupture strength under biaxial stress states was examined. Tension, torsion, and combined tension-torsion creep tests were carried out at 873 K in air employing the developed creep testing machine and hollow cylindrical specimen of Mod.9Cr1Mo steel. Ratio of rupture time t R /t R * increased with the decreasing principal stress ratio λ at constant Mises' equivalent stress, where t R , and t R * denote rupture times for biaxial and tension creep tests, and λ expresses ratio of minimum principal stress to maximum principal stress. Hayhurst's stress successfully correlated with tension, torsion, and combined tension-torsion loading creep lives but Mises' type equivalent stress and maximum principal stress were inadequate to predict creep lives of Mod.9Cr1Mo steel. Oxide film and micro cracks on specimen surfaces were observed using SEM. Micro cracks and oxide film cracks initiated to the perpendicular direction to maximum principal stress axis for 1≦λ≦0. Main crack grew in direction perpendicular to specimen axis independent on the maximum stress ratio λ. The residual lives under biaxial stress states were estimated using Omega method. The Omega method was able to estimate the residual lives within a factor of 4 under biaxial stress states.

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Improvement of Ω Method to Estimate Creep Behavior of a Mod.9Cr-1Mo Steel

Cited by 4 publications

References 15 publications

Creep-Rupture Life Prediction for 9Cr-1Mo-Nb-V Weld Metal

Creep-Rupture Life Prediction for 9Cr-1Mo-Nb-V Weld Metal

Change in Vickers Hardness and Substructure during Creep of a Mod.9Cr-1Mo Steel

Creep strength of Mod.9Cr1Mo steel under biaxial stress states

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