Microstructural Evolution of Boron Nitride Particles in Advanced 9Cr Power Plant Steels

Li, Letian; MacLachlan, Ryan C.; Jepson, Mark A.; Thomson, Rachel C.

doi:10.1007/s11661-013-1642-x

Cited by 31 publications

(20 citation statements)

References 12 publications

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“…The 9%Cr steel with 120 ppm of B exhibits good toughness because the BN-free microstructure was achieved using the ratio of B/N¼ 1.7. No annealing at T Z1150°C is necessary to prevent the precipitation of coarsened BN inclusions [17]. Embrittlement during tension was not observed.…”

Section: Mechanical and Fracture Behaviormentioning

confidence: 97%

“…Boron replaces carbon in M 23 C 6 carbides, i.e., it forms a M 23 (B,C) 6 phase, which is more resistant to coarsening under creep conditions than the B-free carbides [1,13,15]. However, high boron concentrations lead to embrittlement due to the formation of coarse BN particles or segregation to boundaries [16][17][18]. Moreover, the precipitation of BN phase decreases the amount of effective boron and nitrogen in M 23 C 6 carbides and M(C,N) carbonitrides, respectively.…”

Section: Introductionmentioning

confidence: 99%

“…This reduces the fraction of carbonitrides and rises the coarsening rate and, therefore, results in creep resistance degradation [10]. A BNfree microstructure is achieved by balancing the Nþ B content according to a BN solubility diagram in 9-12%Cr steels or by hightemperature annealing that dissolves these nitrides into an austenitic matrix [9,[16][17][18]. The absorption of ∼0.05 wt%N in 9-12%C steels occurs during the electric arc furnace melting followed by air casting [1].…”

Section: Introductionmentioning

confidence: 99%

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Tempering behavior of a low nitrogen boron-added 9%Cr steel

Fedorova

Kostka

Tkachev

et al. 2016

Materials Science and Engineering: A

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The effect of tempering temperature on microstructure and mechanical properties was studied in a lownitrogen, high-boron, 9%Cr steel. After normalizing and low-temperature tempering, cementite platelets precipitated within the martensitic matrix. This phase transformation has no distinct effect on mechanical properties. After tempering at 500°C, M 23 C 6 carbides appeared in the form of layers and particles with irregular shapes along the high-angle boundaries. Approximately, 6% of the retained austenite was observed after normalizing, which reduced to 2% after tempering at 550°C. This is accompanied by reduction in toughness from 40 J/cm 2 to 8.5 J/cm 2. Further increase of the tempering temperature led to spheroidization and coagulation of M 23 C 6 particles that is followed by a significant increase in toughness to 250 J/cm 2 at 750°C. Three-phase separations of M(C,N) carbonitrides to particles enriched with V, Nb and Ti were detected after high-temperature tempering.

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Section: Mechanical and Fracture Behaviormentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Tempering behavior of a low nitrogen boron-added 9%Cr steel

Fedorova

Kostka

Tkachev

et al. 2016

Materials Science and Engineering: A

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“…Studies of boron in 9-12%Cr steels have mainly focused on the as-tempered or creep exposed conditions [4,[16][17][18][19]. In such martensitic steels, borides have been found as large particles presumably formed from the melt during solidification, and particularly, the formation of BN particles has been described in detail [4,16,[18][19][20][21]. In the present work, we focus on studying boron behaviour at GBs in a 10%Cr steel during the normalization using a variety of advanced experimental techniques for specimen preparation and characterization.…”

mentioning

confidence: 99%

Fine (Cr,Fe)2B borides on grain boundaries in a 10Cr–0.01B martensitic steel

et al. 2018

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A 10Cr creep resistant martensitic steel with 108 ppm B was normalized at 1100°C for 1h and air cooled. Fine (Cr,Fe) 2 B borides were observed on the majority of prior austenite grain boundaries, all of which were high angle boundaries, as revealed by EBSD-based reconstruction of parent austenite grains. Some high angle boundaries including twin boundaries were boride-free. Segregation of boron to austenite grain boundaries during slow cooling from 1100⁰C led to boride nucleation and growth. Their size increased with decreasing cooling rate. Borides were verified by atom probe tomography, auger spectroscopy, transmission and scanning electron microscopy.

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“…A sophisticated approach involving serial ion beam sectioning followed by documentation was therefore applied. 20 This approach allowed both the void shape and the associated particles to be reconstructed in three dimensions. An example of a reconstruction is shown in Figure 9.…”

Section: Damage In Grade 92 Steelmentioning

confidence: 99%

Creep fracture in tempered martensitic steels

Parker¹,

Siefert²

2018

IPCSE

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As long term laboratory creep data became available the original estimates of the allowable design stresses for creep strength enhanced ferritic steels (CSEF) were reduced. Thus, even in properly processed steel, the long term performance and creep rupture strength reported is below that originally predicted from a simple extrapolation of short term data. In addition, the typical alloy compositions for these steels specified by Codes provide reasonable strength but can steels can exhibit brittle creep behavior. This inherent brittle behavior results in notch weakening and the need to invoke weld strength reduction factors. Moreover, creep brittle behavior, and the associated micro void development, promotes burst rather than leak type fracture in components. The existence of significant densities of voids further complicates in-service assessment of condition and weld repair of these steels. It is now clear that the levels of ductility required in engineering applications necessitate proper control of composition (including trace elements), steel making and processing and all heat treatments. This paper examines background on the development of creep voids in martensitic steels and discusses metallurgical and stress state factors which promote brittle behavior.

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Microstructural Evolution of Boron Nitride Particles in Advanced 9Cr Power Plant Steels

Cited by 31 publications

References 12 publications

Tempering behavior of a low nitrogen boron-added 9%Cr steel

Tempering behavior of a low nitrogen boron-added 9%Cr steel

Fine (Cr,Fe)2B borides on grain boundaries in a 10Cr–0.01B martensitic steel

Creep fracture in tempered martensitic steels

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