Creep-damage assessment of high chromium heat resistant steels and weldments

Fujiyama, Kazunari; Mori, Keita; Matsunaga, Takahide; Kimachi, Hirohisa; Saito, Takashi; Hino, Takehisa; Ishii, Ryuichi

doi:10.1016/j.msea.2008.08.045

Cited by 42 publications

(11 citation statements)

References 2 publications

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“…The average KAM and area-weighted average GOS values calculated from each location of EXL and EXH specimens are shown in Figure 12a,b, respectively. As Fujiyama et al [42] found that the mean KAM values decrease with increased creep exposure and correlate with a decrease in dislocation density and subsequently hardness, it can be concluded from Figure 12 that EXH demonstrates higher damage accumulation possibly due to competing processes of migration of micro-grain boundaries during grain growth and an increase in frequency of subgrain boundaries, which is also manifested as a reduction in hardness, as shown in Figure 6.…”

Section: Resultsmentioning

confidence: 77%

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Creep Damage Assessment of Ex-Service 12% Cr Power Plant Steel Using Digital Image Correlation and Quantitative Microstructural Evaluation

et al. 2019

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The lifetime of steam pipelines in long-term operation in coal-fired power plants are limited due to material damage that resulted from creep exposure. In the present study, the authors comparatively assess the damage of ex-service 12% Cr piping steel with varying degrees of exposure while using accelerated creep tests that employ digital image correlation (DIC) as well as microstructural investigation that is based on electron microscopy. The DIC technique, which allows multiple creep curves to be measured at temperatures ranging from 550–600 °C from a single specimen, revealed higher Zener–Hollomon parameters for a high damage material with a high void density when compared to a material with lower damage and lower void density. Both of the material states showed similar hardness values, subgrain sizes, and boundary character, despite the difference in void densities. Slightly higher inter-particle spacing of MX precipitates results in a lower threshold stress of 79 MPa for the high damage steel when compared to 97 MPa for the low damage material. Besides large Laves phase particles (>0.2 µm) that are found in the higher damaged materials that result in solid solution depletion, the most prominent microstructural damage indicator was a lower density of M23C6 precipitates. Therefore, the observations indicate that the Zener–Hollomon parameter and M23C6 particles are good damage assessment indicators between the most extreme damage states and they predict a lower damage level for a medium void density material.

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Section: Resultsmentioning

confidence: 77%

“…TKD maps were used to investigate another means of assessing creep damage, as proposed by Fujiyama et al [42], for high Cr steels involving the analysis of Kernel Average Misorientation (KAM), which is the accumulated misorientation angle measured over a kernel of pixels surrounding each measurement point.…”

Section: Resultsmentioning

confidence: 99%

Creep Damage Assessment of Ex-Service 12% Cr Power Plant Steel Using Digital Image Correlation and Quantitative Microstructural Evaluation

et al. 2019

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“…One method for analyzing strain stored energy is to consider kernel average misorientation (KAM) map obtained by processing EBSD data. KAM is defined as the average misorientation angle between a measurement point and all its neighbors at a certain distance, excluding misorientation angles above 5° . Figure shows image quality (IQ) map of the microstructure as well as its KAM map.…”

Section: Resultsmentioning

confidence: 99%

Evaluation of Fracture Micromechanisms in a Fine‐Grained Dual Phase Steel during Uniaxial Tensile Deformation

Saeidi

Ashrafizadeh

Niroumand

et al. 2014

steel research int.

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Ductile fracture mechanism in fine‐grained high‐strength dual phase steel in sheet form, which incorporated martensite particles in a soft ferrite matrix, was studied through extensive quantitative metallography, scanning electron microscopy (SEM), and electron backscattered diffraction (EBSD) observations of polished sections as well as fracture surfaces analysis of failed specimens. The void characteristics in terms of area fraction, density, and average size were examined as a function of thickness strain in the sectioned specimens. Detailed microstructural analysis revealed that interface decohesion at triple junctions of ferrite–ferrite–martensite was the dominant void nucleation mechanism. EBSD analysis also revealed that void nucleation was predominantly promoted by the increase of ferrite–ferrite grain boundary misorientation with strain, especially at the boundaries incorporating adjacent martensite particles. Moreover, the study of voids nucleation and evolution behavior suggested that ductile fracture in this steel was nucleation controlled such that just before the final fracture incidence, a high density of voids would be nucleated or a sudden accelerated void nucleation could happen. Microscopic observations as well as statistical analysis confirmed this phenomenon.

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“…KAM value for each pixel is defined as the average misorientation that a pixel has with its neighbors (6 in our case), while boundaries with orientation difference over 5°are recognized as grain boundaries. KAM value is an appropriate quantity used to evaluate the strain or the stored energy at a given point (Ref 13,14).…”

Section: Methodsmentioning

confidence: 99%

EBSD Study of Damage Mechanisms in a High-Strength Ferrite-Martensite Dual-Phase Steel

Saeidi

Ashrafizadeh

Niroumand

et al. 2014

J. of Materi Eng and Perform

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Electron backscattered diffraction (EBSD) analyses were performed on a fine-grained dual-phase (DP) sheet steel subjected to uniform tensile deformation and the preferred void nucleation sites as well as the micro-mechanisms of void formation were examined. EBSD study of grain average misorientation, grain orientation spread and kernel average misorientation of the deformed microstructure revealed that voids nucleation initially happened at ferrite-martensite interfaces neighboring rather large ferrite grains. This is believed to be mainly due to the higher shear deformation ability of the larger ferrite grains, the higher number of dislocation pile-ups at the martensite particles and the less uniform strain distribution within the larger ferrite grains compared to the smaller ones. The results demonstrated the impact of increasing uniform strain distribution within the DP microstructure on lowering the void nucleation probability.

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Creep-damage assessment of high chromium heat resistant steels and weldments

Cited by 42 publications

References 2 publications

Creep Damage Assessment of Ex-Service 12% Cr Power Plant Steel Using Digital Image Correlation and Quantitative Microstructural Evaluation

Creep Damage Assessment of Ex-Service 12% Cr Power Plant Steel Using Digital Image Correlation and Quantitative Microstructural Evaluation

Evaluation of Fracture Micromechanisms in a Fine‐Grained Dual Phase Steel during Uniaxial Tensile Deformation

EBSD Study of Damage Mechanisms in a High-Strength Ferrite-Martensite Dual-Phase Steel

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