Properties and microstructure of modified 9 % Cr steels

Gianfrancesco, A. Di; Matera, Susanna; Tassa, O.

doi:10.1051/metal:2001158

Cited by 2 publications

(4 citation statements)

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“…where β is chosen to be 0.4 for HABs, [45,46] d is the mean lathwidth obtained using the standard intercept count method (ASTM-E112). [47] The mean lath-width for the samples crept at 140, 155, and 170 MPa are 436 AE 90, 491 AE 110, and 513 AE 150 nm, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…Accordingly, the standard deviations in the errors from the mean number density for the samples crept at 140, 155, and 170 MPa were 0.14, 0.15, and 0.14, respectively. The internal stress generated by subgrain boundaries can be described as [ 44 ]

σ_{subgrain} = β M G B / d

where β is chosen to be 0.4 for HABs, [ 45,46 ] d is the mean lath‐width obtained using the standard intercept count method (ASTM‐E112). [ 47 ] The mean lath‐width for the samples crept at 140, 155, and 170 MPa are 436 ± 90, 491 ± 110, and 513 ± 150 nm, respectively.…”

Section: Resultsmentioning

confidence: 99%

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The Coupling Effect of Hierarchical Structures and MN‐Type Precipitates on the Creep Resistance for the High N Heat‐Resistant Martensitic Steel

Shi

Sun

Ning

et al. 2022

steel research int.

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Microstructure of the high nitrogen heat‐resistant martensitic steel (HNHM) crept using 140–170 MPa loading stresses at 923 K is investigated in correlation with creep lifetime and creep rupture strength. Upon creep deformation, both recrystallized grains and the preexisted hierarchical structures grow via strain‐induced boundaries migration (SIBM) induce the degradation of strengthening. For preexisted hierarchical structures in HNHM, martensitic packets and blocks are more inclined to form at higher stresses (170 MPa), causing the degradation of strength, while laths retain easily at lower stresses (140–155 MPa), retarding the creep damage. Additionally, under all stresses and upon 923 K, the highly stabilized MN precipitates not only pin the hierarchical structural boundaries effectively, but also act as the core for the nucleation of Laves, realizing strengthening. The findings elucidate the coupling contribution of hierarchical structures and MN‐type precipitates on the creep strengthening for HNHMs, challenging the common viewpoint that the coupling coarsening of lath and precipitates dominates the degradation of strengthening, and thus, deepens the understanding of the creep resistance of the HNHM and provides the first insights into obtaining reliable predicted creep life of the novel HNHMs.

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Section: Resultsmentioning

confidence: 99%

σ_{subgrain} = β M G B / d

Section: Resultsmentioning

confidence: 99%

The Coupling Effect of Hierarchical Structures and MN‐Type Precipitates on the Creep Resistance for the High N Heat‐Resistant Martensitic Steel

Shi

Sun

Ning

et al. 2022

steel research int.

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show abstract

“…Anderson et al [3] 796 Q was assumed to be a constant independent of stress and temperature Sklenica et al [9] 792 low T, high stress Q was assumed to be a constant. Spigarelli et al [2] 680 200 MPa, 848 to 923 K 815 160 MPa, 848 to 923 K Gianfrancesco et al [35] 552 high stress and low stress domains, T = 575°C to 650°C Current study 724 low and high stress domain, T = 500°C to 600°C…”

Section: Temperature-increment Benefitmentioning

confidence: 95%

“…In the present case, the values of barrier strength coefficients would be higher than 0.2 for the subgrain and lath boundaries, due to the presence of carbides. Generally, values of a~0.4 are chosen for high-angle boundaries [35] without carbides, which are considered to be stronger obstacles than the subgrain or the lath boundaries. The values of the barrier strength coefficients for the subgrain and lath boundaries with carbides should lie between the value of the barrier strength coefficient for subgrain boundaries and high-angle boundaries without carbides, i.e., between 0.2 and 0.4.…”

Section: Internal Stress Due To Substructure and Lath Boundariesmentioning

confidence: 99%

Improved Creep Behavior of Ferritic-Martensitic Alloy T91 by Subgrain Boundary Density Enhancement

Gupta

Was

2007

Metall Mater Trans A

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The objective of this study was to increase the creep strength of the ferritic-martensitic (F-M) alloy T91 by enhancing the subgrain boundary density. A thermomechanical treatment involving a 5 pct compression treatment, followed by an annealing treatment at 1050°C for 1 hour, then air cooling, and a tempering treatment at 800°C for 0.66 hours, then another air cooling, resulted in an increase in the subgrain boundary density of~39 pct, without altering any of the other microstructural features. Creep tests were conducted on both as-received (AR) and subgrain-boundary-enhanced (SGBE) conditions of the F-M alloy T91, over a temperature range of 500°C to 600°C and in the stress range of 150 to 255 MPa in argon. The T91-AR exhibited a higher creep rate than the T91-SGBE by a factor of~2.0 to 8.0. The ratio of time to rupture for the T91-SGBE compared to the T91-AR varied from 1.0 to 5.0. In general, higher ratios were seen at higher stresses. Creep behavior was analyzed on the basis of the Orowan equation, according to which creep rate is controlled by the mobile dislocation density and dislocation velocity. Internal stress calculations performed on both conditions showed a higher internal stress in the T91-SGBE by~10 MPa. Analysis of the sources of internal stress suggest that the higher value for the SGBE condition is due to subgrain boundary density enhancement. The SGBE condition exhibited a temperature-increment benefit of between 8°C and 26°C, such that the creep strength realized for the T91-SGBE was similar to that realized for the T91-AR, but at a higher temperature. The temperature-increment benefit increased exponentially with applied stress but less so with temperature.

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Properties and microstructure of modified 9 % Cr steels

Cited by 2 publications

References 0 publications

The Coupling Effect of Hierarchical Structures and MN‐Type Precipitates on the Creep Resistance for the High N Heat‐Resistant Martensitic Steel

The Coupling Effect of Hierarchical Structures and MN‐Type Precipitates on the Creep Resistance for the High N Heat‐Resistant Martensitic Steel

Improved Creep Behavior of Ferritic-Martensitic Alloy T91 by Subgrain Boundary Density Enhancement

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