The nucleation of Mo-rich Laves phase particles adjacent to M23C6 micrograin boundary carbides in 12% Cr tempered martensite ferritic steels

Isik, M. I.; Kostka, Aleksander; Yardley, Victoria A.; Pradeep, Konda Gokuldoss; Duarte, María Jazmin; Choi, Pyuck‐Pa; Raabe, Dierk; Eggeler, Gunther

doi:10.1016/j.actamat.2015.01.027

Cited by 156 publications

(66 citation statements)

References 53 publications

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“…[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] This has been attributed to phase separation mechanisms, primarily in the ferrite phase, due to the existing miscibility gap in the Fe-Cr equilibrium phase diagram. 7,29,30 Dependent on the chemical composition of the alloy, the ferrite either decomposes based on nucleation and growth or spinodal decomposition 5,22,23,[31][32][33][34] to Cr-enriched α and Fe-enriched α , or by nucleation of further precipitates such as G-phase, 5,[35][36][37][38][39][40] R-phase, 5,39,[41][42][43][44] secondary austenite (γ 2 ), 5,7 Laves phases, 41,44,45 chromium carbides, 5,7 and nitrides. 5,7,12,…”

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confidence: 99%

Characterization of 475°C Embrittlement of Duplex Stainless Steel Microstructure via Scanning Kelvin Probe Force Microscopy and Magnetic Force Microscopy

Örnek

Walton

Hashimoto³

et al. 2017

J. Electrochem. Soc.

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Scanning Kelvin probe force microscopy (SKPFM) measured local Volta potentials in microstructure of 22Cr-5Ni duplex stainless steel have been correlated to microstructure development with aging treatments at 475 • C. Magnetic force microscopy (MFM) was employed to differentiate crystallographic phases to provide complementary information. The absolute Volta potentials of both ferrite and austenite increased after 5 hours of aging, indicating electrochemical ennoblement of the entire microstructure. Longer aging resulted in a gradual decrease of measured Volta potentials in both phases. The microstructure showed after 255 hours aging up to 2.5-times larger potential differences than in the as-received condition, indicating impaired electrochemical nobility. In the as-received microstructure, the ferrite phase was less noble than the austenite, whereas after 5 hours aging both phases had similar, balanced Volta potentials which indicated a balanced nobility of ferrite and austenite. Longer aging treatment caused severe loss of nobility for the entire microstructure, with ferrite showing larger changes in Volta potential than the austenite. Spinodal microstructure decomposition and associated phase reactions of the ferrite, with elemental redistribution in the austenite, are the reason for the observed changes in microstructure nobility. Duplex Stainless Steels (DSSs) have been used for structural and functional applications in a broad range of industry sectors.1 Their two-phase microstructure typically consists of a balanced fraction of ferrite (δ) and austenite (γ) resulting in beneficial properties, such as high strength and toughness, with outstanding corrosion and stress corrosion cracking resistance. However, when exposed to higher temperature regimes DSSs suffer from microstructure changes due to phase transformations arising from strong interactions of alloying elements.2-4 These microstructure changes can be accompanied by the occurrence of embrittlement and loss in corrosion resistance, which restricts their use in high-temperature applications.When the material is exposed to temperatures between 600 • C and 1000• C, the microstructure can decompose into several secondary phases.5-7 Ferrite can undergo eutectoid transformations into several phases, including σ-phase with secondary austenite (γ 2 ), χ-phase, carbides (mainly M 23 C 6 ), nitrides (CrN and Cr 2 N), or carbonitrides. 1,5,[7][8][9] Chromium nitrides can cause significant changes in microstructure performance 10,11 and hardness, 12 despite their small volume fractions and sizes (usually below 2 μm).12,13 Precipitation is typically accompanied by significant reductions in localized corrosion resistance, and is mainly attributed to the formation of element-depleted regions adjacent to secondary phases. [5][6][7] Exposure to lower temperatures between 250• C to 550• C, often referred to "475• C embrittlement", also results in variations of mechanical and electrochemical properties.14-28 This has been attributed to phase separation mechanisms, prim...

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confidence: 99%

Characterization of 475°C Embrittlement of Duplex Stainless Steel Microstructure via Scanning Kelvin Probe Force Microscopy and Magnetic Force Microscopy

Örnek

Walton

Hashimoto³

et al. 2017

J. Electrochem. Soc.

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“…The 1 wt %W additive provides the precipitation of the W-rich М6С carbides and Laves phase even under tempering. No formation of thermodynamically stable W-rich Laves phases was reported in the conventional 9%Cr martensitic steels after tempering [1,2,[7][8][9][10][11][12], and the appearance of the less stable W-rich M6C The lath thickness was approximately 0.4 µm for both steels. The high dislocation density of approximately 2 × 10 14 m −2 was observed within the lath and subgrain interiors.…”

Section: Tempered Martensite Lath Structurementioning

confidence: 96%

“…Therefore, the solubility of (3%W + 0.5%Mo) excesses the thermodynamically equilibrium solubility limit even at the tempering temperature of 750 • C. The 1 wt %W additive provides the precipitation of the W-rich M 6 C carbides and Laves phase even under tempering. No formation of thermodynamically stable W-rich Laves phases was reported in the conventional 9%Cr martensitic steels after tempering [1,2,[7][8][9][10][11][12], and the appearance of the less stable W-rich M 6 C carbides was found only in a 10%Cr-2%W steel [23]. Under tempering, the partial transformation of M 6 C carbides into Laves phase particles may occur if M 6 C carbides are occupied by other M 6 C 6 carbides and do not have access to W segregation in the vicinity of PAG-lath boundaries [27].…”

Section: Tempered Martensite Lath Structurementioning

confidence: 99%

“…These elements provide an effective solid solution strengthening [1]. It was shown [21] that addition of 1% W gives +35 MPa increase in the creep rupture strength at 600 • C for 1000 h. However, in contrast with cobalt, the tungsten and molybdenum have limited solubility within ferrite, and their excessive content leads to precipitation of such W-and Mo-rich particles as Laves phase Fe 2 (W,Mo) or M 6 C carbides [1,7,[9][10][11][12]22,23]. This depletion does not occur in the 9%Cr steel containing no or low amount of W [7].…”

Section: Introductionmentioning

confidence: 99%

“…Stability of TMLS is provided by M 23 C 6 -type carbides and MX (where M is V and/or Nb, and X is C and/or N) carbonitrides precipitated during tempering at boundaries and within ferritic matrix, respectively, and boundary Laves phase particles precipitated during creep [1,2,[4][5][6][7][8][9][10][11][12]. MX carbonitrides, which are highly effective in pinning of lattice dislocations, play a vital role in superior long-term creep resistance of the high chromium martensitic steels, whereas boundary M 23 C 6 carbides and Laves phase particles exerting a high Zener drag force stabilize the TMLS [1,2,5,[7][8][9][10][11][12][13][14]. This dispersion of secondary phase particles withstands short-term creep [4,9,15].…”

Section: Introductionmentioning

confidence: 99%

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Effect of Tungsten on Creep Behavior of 9%Cr–3%Co Martensitic Steels

Fedoseeva

Dudova

Kaibyshev

et al. 2017

Metals

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Abstract:The effect of increasing tungsten content from 2 to 3 wt % on the creep rupture strength of a 3 wt % Co-modified P92-type steel was studied. Creep tests were carried out at a temperature of 650 • C under applied stresses ranging from 100 to 220 MPa with a step of 20 MPa. It was found that an increase in W content from 2 to 3 wt % resulted in a +15% and +14% increase in the creep rupture strength in the short-term region (up to 10 3 h) and long-term one (up to 10 4 h), respectively. On the other hand, in the long-term creep region, the effect of W on creep strength diminished with increasing rupture time, up to complete disappearance at 10 5 h, because of depletion of excess W from the solid solution in the form of precipitation of the Laves phase particles. An increase in W content led to the increased amount of Laves phase and rapid coarsening of these particles under long-term creep. The contribution of W to the enhancement of creep resistance has short-term character.

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Effect of Long‐Term Thermal Aging on Microstructure and High‐Temperature Strength of a 10% Cr Martensite Ferritic Steel

Wang

et al. 2015

steel research int.

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The effect of long-term thermal aging on microstructure and high-temperature strength of a 10% Cr martensite ferritic steel is investigated. Comparison of the long-term aging behavior at 700 8C with that at 650 8C reveals that the low angle boundary fraction increases and the coarsening of the M 23 C 6 carbide accelerates at higher temperature, thereby the speed of subgrain growth increases. Additionally, elevated aging temperature suppressed nucleation of Laves phases and did not affect the K-S orientation relationship between M 23 C 6 carbides and ferrite matrix. The yield strength at 700 8C decreases, obviously, with increase of aging time at 700 8C, but its decline trend is not fully consistent with the change of the dislocation density, which confirms that loss of high-temperature strength is not only due to decreasing of free dislocations. On the other hand, the variation on increasing of the subgrain width shows a similar abrupt trend to that on decreasing of the yield strength. It is suggested that for aged steel, subgrain coarsening is also an important factor for the deterioration of yield strength.

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The nucleation of Mo-rich Laves phase particles adjacent to M23C6 micrograin boundary carbides in 12% Cr tempered martensite ferritic steels

Cited by 156 publications

References 53 publications

Characterization of 475°C Embrittlement of Duplex Stainless Steel Microstructure via Scanning Kelvin Probe Force Microscopy and Magnetic Force Microscopy

Characterization of 475°C Embrittlement of Duplex Stainless Steel Microstructure via Scanning Kelvin Probe Force Microscopy and Magnetic Force Microscopy

Effect of Tungsten on Creep Behavior of 9%Cr–3%Co Martensitic Steels

Effect of Long‐Term Thermal Aging on Microstructure and High‐Temperature Strength of a 10% Cr Martensite Ferritic Steel

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