Evaluation of Creep Deformation Mechanism of Heat Resistant Steel by Stress Change Test

Hayakawa, Hisao; Nakashima, Satoshi; Kusumoto, Junichi; Kanaya, Akihiro; Terada, Daisuke; Yoshida, Fuyuki; Nakashima, Hideharu

doi:10.1115/creep2007-26501

Cited by 6 publications

(17 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is thus concluded that there are no essential differences in the dislocation densities obtained by a TEM observation and an SCH method, apart from the case for a detailed investigation of causes of the differences between individual cases. However, it should be remembered that the dislocation densities measured by Hayakawa et al (1970;2007a;2007b) for alloy steels employing an SCH method are relatively low.…”

Section: Dislocation Densitymentioning

confidence: 99%

“…I and II using these parameter constants. The dislocation densities were reported for specimens that crept at temperatures higher than the test temperatures used by the NIMS, but the data point obtained at 630 ℃ and 60 MPa by Hayakawa et al (2007a) (solid square) lies near the regression line at 630 ℃ for the NIMS data. There is a difference between the MCRs of Hayakawa et al and the NIMS at 630 ℃, but such a difference should be metallurgically allowed.…”

mentioning

confidence: 99%

“…Dislocation densities have been measured employing the etch pit method (T. Hasegawa, R. Hasegawa, & Karashima, 1970), transmission electron microscopy (TEM) (Ham, 1961), scanning electron microscopy (Kamaladasa & Picard, 2010), X-ray diffraction (XRD) analysis (Shintani & Murata, 2011), and the stress or strain rate change test (SCH) (Yoshinaga, Matsuo, & Kurishita, 1984). However, it is not unusual that the differences among the dislocation densities of the same specimen measured employing the different methods are more than an order of magnitude (Hayakawa et al, 2007a;Umezaki, Murata, Nomura, & Kubushiro, 2014;Roodposhti, Sarkar, Murty, & Scattergood, 2015). This suggests the importance of not only selecting an appropriate method for a given specimen but also of considering the physical meanings of the observed values (Yoshinaga, Horita, & Kurishita, 1981;Pesicka, Kuzel, Dronhofer, & Eggeler, 2003).…”

Section: Introductionmentioning

confidence: 99%

“…The dislocation densities at 600 and 650 ℃ were observed employing TEM and that at 630 ℃ was calculated employing an SCH method. Hayakawa et al (2007a) reported the dislocation densities as functions of creep strain to rupture at 600 to 650 ℃ and indicated that the dislocation densities observed by TEM were approximately one order of magnitude higher than those by SCH over the whole range of creep strain. Therefore, when the dislocation density is observed at 630 ℃ employing TEM, the dislocation density may become larger than that shown in the figure measured employing an SCH method.…”

mentioning

confidence: 99%

“…There is a difference between the MCRs of Hayakawa et al and the NIMS at 630 ℃, but such a difference should be metallurgically allowed. Other data obtained by Hayakawa et al (2007a) were reported without a strain rate, and therefore, the data are plotted on each regression line with cross marks at the reported temperatures and stresses. The observed dislocation densities and the values of calculated for each data point using Equation 13 are listed in Figure 2.…”

mentioning

confidence: 99%

See 4 more Smart Citations

Verification of Equation for Evaluating Dislocation Density during Steady-state Creep of Metals

Tamura¹

2017

JMSR

View full text Add to dashboard Cite

Ninety-two sets of observed dislocation densities for crept specimens of 21 types of ferritic/martensitic and austenitic steels, Al, W, Mo, and Mg alloys, Cu, and Ti including germanium single crystals were collected to verify an equation for evaluating the dislocation density during steady-state creep proposed by Tamura and Abe (2015). The activation energy, , activation volume, , and Larson-Miller constant, , were calculated from the creep data. Using these parameter constants, the strain rate, and the temperature dependence of the shear modulus, a correction term, , was back-calculated from the observed dislocation density for each material. is defined in the present paper as a function of the temperature dependences of both the shear modulus and pre-exponential factor of the strain rate. The values of range from −394 to 233 kJmol and average 2.1 kJmol , which is a value considerably lower than the average value of (410.4 kJmol ), and values of are mainly within the range from 0 to 50 kJmol . The change in Gibbs free energy, ∆ , for creep deformation is obtained using the calculated value of , and the empirical relation ∆ ≅ ∆ is found, where ∆ is the change in Gibbs free energy for self-diffusion of the main componential element of each material. Experimental data confirm the validity of the evaluation equation for the dislocation density.

show abstract

Section: Dislocation Densitymentioning

confidence: 99%

mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Verification of Equation for Evaluating Dislocation Density during Steady-state Creep of Metals

Tamura¹

2017

JMSR

View full text Add to dashboard Cite

show abstract

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

Tamura¹,

Abe²

2021

JMSR

View full text Add to dashboard Cite

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.

show abstract

Root Cause of Degradation in the Creep Strength of Martensitic Steel

Tamura¹

2021

JMSR

View full text Add to dashboard Cite

Creep curves of Grade 91 and 92 steels were analyzed by applying an exponential law to the temperature, stress, and time parameters to investigate the formation process of the Z-phase, which lowers the long-term rupture strength of high-Cr martensitic steel. 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 because of dislocations that are swept out of the sub-grains, and this is followed by strengthening owing to the rearrangement of M23C6 and the precipitation of the Laves phase. Heterogeneous recovery and subsequent heterogeneous deformation start at an early stage of transient creep near several of the weakest boundaries because of the coarsening of the precipitates; this results in the simultaneous decreases in Q, V, and C even in transient creep. Further, this activity triggers an unexpected degradation in strength because of the accelerated formation of the Z-phase even in transient creep. The stabilization of M23C6 and the Laves phase is important to mitigate the degradation of the long-term rupture strength of high-strength martensitic steel. The stabilization of the Laves phase is especially important for Cr-Mo systems because Fe2Mo is easily coarsened at approximately 600 °C compared to Fe2W in Grade 92 steel.

show abstract

Evaluation of Creep Deformation Mechanism of Heat Resistant Steel by Stress Change Test

Cited by 6 publications

References 0 publications

Verification of Equation for Evaluating Dislocation Density during Steady-state Creep of Metals

Verification of Equation for Evaluating Dislocation Density during Steady-state Creep of Metals

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

Root Cause of Degradation in the Creep Strength of Martensitic Steel

Contact Info

Product

Resources

About