Effect of Boron in the Coarsening Rate of Chromium-Rich Carbides in 9%–12% Chromium Martensitic Creep-Resistant Steel: Experiment and Modeling at 650 °C

Sanhueza, Juan Pablo; Rojas, D.; García, J.; Meléndrez, Manuel; Toledo, E.; Cerda, Felipe Manuel Castro; Montalba, C.; Jaramillo, Alberto

doi:10.1007/s12540-020-00676-y

Cited by 14 publications

(7 citation statements)

References 35 publications

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“…[ 33–35 ] Boron nitrides, BN, might be also formed during the heat treatment. Even though it was reported that B and N addition without BN formation enhances creep rupture strength by decelerating the coarsening rate of M 23 C 6 , [ 36–39 ] the BN formation during forging or normalizing frequently observed in heat‐resistant 9–12Cr steels. [ 36,40,41 ] However, it was reported that the BN formation was highly dependent on cooling rates.…”

Section: Resultsmentioning

confidence: 99%

Influence of Partial Replacement of Co with Cu on Isothermal Transformation Kinetics in Ferritic/Martensitic Heat‐Resistant Steel

Lee

Shin

et al. 2022

steel research int.

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Ferritic/martensitic 9-12Cr heat-resistant steels have been in the spotlighted as a promising material for ultrasupercritical (USC) power plants application for its excellent creep-resistant properties thanks to high thermal stability of microstructure at service temperatures above 600 °C. [1][2][3] Outstanding thermal stability of 9-12Cr steels stems from the formation of the various types of precipitates, such as M 23 C 6 , MX, and Laves phase, which decelerates the movement of subgrain boundaries or dislocations. [4,5] Recently, in addition to the optimization of chemical composition, the control of prior austenite grain size (PAGS) via a modification of heat treatment path has been adopted as one of strategies for enhancing creep-resistant properties. [3] A general practice for the refinement of PAGS is a repeated austenitizing and quenching process. [6][7][8][9][10] Karthikeyan et al. [7,9] showed that normalizing and tempering after double austenitization could render smaller PAGS compared to the conventional normalizing and tempering process in 9Cr-1Mo-0.1C steel, contributing to the improvement of impact toughness and creep rupture strength. On the other hand, it was also reported that grain refinement could be achieved through the application of isothermal γ ! α transformation before normalizing and tempering process. [11,12] Moon et al. [12] presented the grain refinement mechanism by the application of isothermal transformation before normalizing and tempering process in 9Cr-1.5Mo-1.25Co-0.1C-VNb steel. It is worth mentioning that the isothermal γ ! α transformation is often applied in the manufacturing process of various parts using heat-resistant steels for ensuring machinability. [11] Although the application of isothermal transformation was known as an effective way for grain refinement in martensitic steels, it requires prolonged time for the completion of transformation due to the high hardenability. Hence, the nose temperature in time-temperature-transformation diagram (TTT diagram), at which transformation is the fastest, should be quantitatively evaluated to minimize the process time for the isothermal transformation.The 9-12Cr steels contain alloying elements, like Cr, Nb, V, Mo, and W, to utilize the various types of precipitates. However, they are mostly ferrite forming elements which can induce the formation of δ-ferrite, which is detrimental to impact toughness and tensile properties. [13][14][15][16] Thus, the austenite stabilizing elements, such as Co, Cu, or Ni, are added to guarantee a fully austenitic microstructure during austenitization. [1] Among them, Co has been most widely used for suppressing δ-ferrite. Co also contributes to decreasing the coarsening rate of M 23 C 6 because it increases Curie temperature (T C ) in steel; it has been known that ferromagnetic ordering of iron below T C delays diffusion process. [17] However, the Co is far more expensive than other alloying elements, thus less Co content is favorable to reduce the materials cost. For that purpose, Cu can be con...

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Section: Resultsmentioning

confidence: 99%

Influence of Partial Replacement of Co with Cu on Isothermal Transformation Kinetics in Ferritic/Martensitic Heat‐Resistant Steel

Lee

Shin

et al. 2022

steel research int.

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“…Although thermodynamic databases are actualized year by year, the method considers the same formalism. The approach consists of the parametrization of Gibbs free energy of a phase as a function of temperature (T), pressure (P), and composition (x) together with experimentally determined parameters related to a specific system (see equation (1)). This approach is summarized and shown in figure 4.…”

Section: Thermodynamic Descriptionmentioning

confidence: 99%

“…Ferritic and martensitic 9%-12% Cr steels are commonly used for high-temperature applications (500 °C-620 °C) due to their excellent creep resistance based on a combination of solid solution, grain boundaries, dislocations, and precipitation hardening. In martensitic/ferritic steels, M C 23 6 and MX carbides are the main reinforcement particles, that prevent the degradation of tempered martensite [1,2]. It is well known the anchoring effect over grain and sub-grain boundaries promoted by the strengthening particles, which causes a reduction in the creep strain rate [3,4].…”

Section: Introductionmentioning

confidence: 99%

Laves phase formation in Fe-based alloys from strengthening particle to self-healing agent: a review

Wackerling,

Rojas,

Oñate

et al. 2023

Mater. Res. Express

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In this study, were extensively reviewed the hardening and self-healing properties of Laves-phase in Fe-based alloys. First, the microstructural features of different polytypes of the Laves-phase, focusing on the thermodynamics and kinetics of formation in ferritic and martensitic steels were revised. C14 was identified as the dominant polytype in steels, providing strengthening by precipitation, anchoring of dislocation, and interphase boundaries, thereby increasing the creep resistance. Although the Laves phase is widely known as a reinforcement particle (or even a detrimental phase in some systems) in martensitic/ferritic and ferritic steels, recent findings have uncovered a promising property. Particles with self-healing characteristics provide creep resistance by delaying creep cavities formation. In this regard, different elements such as tungsten and molybdenum are known to provide this feature to binary and tertiary ferrous alloys due to their ability to diffuse into the creep cavities and form Laves-phase Fe(Mo,W)2. To date, self-healing by precipitation has only been reported in commercial stainless steel AISI 312, 347, and 304 modified with boron, nevertheless with a little contribution to creep rupture life. Although, commercial computational tools with thermodynamic and kinetic databases are available for researchers, to tackle the self-healing process with exactitude, genetic algorithms arise as a new tool for computational design. The two properties of Laves phase reported in the literature, precipitation hardening and self-healing agent, is a mix that can bring out a new research field. Therefore, it is not unreasonable to think of tailor-made high chromium creep-resistant steels reinforced by Laves-phase coupled with self-healing properties. However, owing to the characteristic of Laves-phase seems to be a complex challenge, mainly due to the crystallographic features of this phase in comparison with the host matrix, available computational tools, and databases.

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“…[6] Trace element additions have been employed to slow the coarsening of those features, e.g., B used to stabilize the M 23 C 6 carbides. [7,8] While fine Laves have been utilized for their potential to pin boundaries such as PAG, packets, blocks, and laths, their formation is often mitigated due to the likelihood of the Laves particles coarsening faster than M 23 C 6 carbides, thereby degrading creep performance. [9] The specification of trace elements for 9-12Cr martensiticferritic steels, such as B, in the alloy's composition range may be too broad and in turn allows the formation of phases, or inclusions, for example, when N is present, that can be detrimental to the performance of the material.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Variations in Creep Performance of P92 Steel Within Its Composition Range: Influence of N Solubility

Detrois

Antonov

Hawk

et al. 2023

steel research int.

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Underspecified composition ranges often lead to alloys with unpredictable mechanical performance. To better understand the changes in microstructure and mechanical performance associated with variations of key elements, three versions of P92 are formulated within, or close to, the specified allowable for N, B, and C ranges. Chromium and Si are also varied to influence N solubility. Different service conditions (i.e., temperature and stress) are explored. It is observed that >80% decrease in creep life occurs at 625 °C and 155 MPa for the highest B and N containing alloy. Multiscale characterization reveals key changes due to the trace element variation. The high B and N containing alloy forms deleterious BN precipitates with morphology that promotes crack nucleation and damage accumulation, but this alloy additionally forms higher fractions of beneficial MX precipitates. The alloy with the lowest B and N concentrations but greater C content shows the best creep performance—a consequence of the refined M23C6 carbide precipitate population and the absence of large‐scale inclusions or BN precipitates. Calculations of creep activation energy reveal that the high B and N containing alloy is more prone to damage accumulation which causes an early onset of accelerating creep and greater minimum creep rate.

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Effect of Boron in the Coarsening Rate of Chromium-Rich Carbides in 9%–12% Chromium Martensitic Creep-Resistant Steel: Experiment and Modeling at 650 °C

Cited by 14 publications

References 35 publications

Influence of Partial Replacement of Co with Cu on Isothermal Transformation Kinetics in Ferritic/Martensitic Heat‐Resistant Steel

Influence of Partial Replacement of Co with Cu on Isothermal Transformation Kinetics in Ferritic/Martensitic Heat‐Resistant Steel

Laves phase formation in Fe-based alloys from strengthening particle to self-healing agent: a review

Variations in Creep Performance of P92 Steel Within Its Composition Range: Influence of N Solubility

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