Investigations on coarsening of MX and M23C6 precipitates in 12% Cr creep resistant steels assisted by computational thermodynamics

Prat, O.; García, J.; Rojas, D.; Carrasco, Claudia; Kaysser-Pyzalla, Anke R.

doi:10.1016/j.msea.2010.05.084

Cited by 90 publications

(41 citation statements)

References 23 publications

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“…The W effect is also observed in M 23 C 6 -strengthened alloy but the effect is less pronounced. Moreover, the coarsening rate of Lave phases in alloy LavesW is close to that of the well accepted very stable MX carbonitride, [4,28] proving that indeed undesirable Laves phase can be turned into desirable precipitates. While being equally stable the volume percent of Laves phase (11.3 vol pct) is much higher than the maximum volume percent of MX carbonitride (0.5 to 1 vol pct) which increases the net strengthening contribution of the Laves precipitates significantly.…”

Section: Model Predictionssupporting

confidence: 53%

“…They have a very high-coarsening rate, which is 10 to 100 times faster than that of MX carbonitrides. [2,4,5] Their growth and coarsening not only lead to a loss of strengthening but also lead to depletion of useful elements, such as Mo and Cr, from the matrix. A common solution to prevent the formation of such undesirable phases is to decrease the Mo and Cr levels, to a level at which such precipitates do not form.…”

Section: Introductionmentioning

confidence: 99%

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The Computational Design of W and Co-Containing Creep-Resistant Steels with Barely Coarsening Laves Phase and M23C6 as the Strengthening Precipitates

Zwaag

2014

Metall Mater Trans A

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Generally, Laves phase and M 23 C 6 are regarded as undesirable phases in creep-resistant steels due to their very high-coarsening rates and the resulting depletion of beneficial alloying elements from the matrix. In this study, a computational alloy design approach is presented to develop martensitic steels strengthened by Laves phase and/or M 23 C 6 , for which the coarsening rates are tailored such that they are at least one order of magnitude lower than those in existing alloys. Their volume fractions are optimized by tuning the chemical composition in parallel. The composition domain covering 10 alloying elements at realistic levels is searched by a genetic algorithm to explore the full potential of simultaneous maximization of the volume fraction and minimization of the precipitates coarsening rate. The calculations show that Co and W can drastically reduce the coarsening rate of Laves and M 23 C 6 and yield high-volume fractions of precipitates. Mo on the other hand was shown to have a minimal effect on coarsening. The strengthening effects of Laves phase and M 23 C 6 in the newly designed alloys are compared to existing counterparts, showing substantially higher precipitation-strengthening contributions especially after a long service time. New alloys were designed in which both Laves phase and M 23 C 6 precipitates act as strengthening precipitates. Successfully combining MX and M 23 C 6 was found to be impossible.

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Section: Model Predictionssupporting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

The Computational Design of W and Co-Containing Creep-Resistant Steels with Barely Coarsening Laves Phase and M23C6 as the Strengthening Precipitates

Zwaag

2014

Metall Mater Trans A

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“…Factors such as diffusion, interfacial energy or microstructure have to be accounted for in kinetic models. Kinetic modelling of Z-phase has been attempted [36][37] but this is very complicated due to the nature of Z-phase (see nucleation and interface chapters) and cannot be covered by standard methods. Another complication is given in [38][39] which shows that for creep specimens, Z-phase would precipitate 2-4 times faster in the gauge length compared to the grip, something that would be very difficult to model.…”

Section: Thermodynamicsmentioning

confidence: 99%

Review of Z phase precipitation in 9–12 wt-Cr steels

Danielsen

2016

Materials Science and Technology

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ABSTRACT9-12wt%Cr steels for high temperature applications in fossil fired power plants rely upon precipitate strengthening from (V,Nb)N MX nitrides for long term creep strength. During prolonged exposure at service temperature another nitride precipitates: Cr(V,Nb)N Z-phase. The Z-phase slowly replaces MX, eventually causing a breakdown in creep strength. This paper reviews the Z-phase and its behaviour in 9-12wt%Cr steels including thermodynamic modelling, crystal structure, nucleation process and precipitation rate as a function of chemical composition. The influence of Z-phase precipitation upon long-term creep strength is assessed from several different 9-12wt%Cr steel grades and alloy design philosophies.

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“…The above-mentioned specimens processed by Q & P were mechanically ground and polished,then corroded with 4 voL% nitric acid alcohol solution,and the specimens were analyzed by KYKY-2800B scanning electron microscopy for microstructure and carbides observation.Each sample was selected 100 carbide particles, and carbides size distribution was counted by ImageJ software.In this paper, the method of counting the size of the carbides was the maximum length of the particles and the vertical dimension of the average as the particle diameter [13],and the specimens processed by Q&P with partition time of 1200s were extracted by electrolysis with reference to the extraction standard of carbides.The electrolyte container was made of stainless steel, which was directly used as the cathode; the electrolyte was 8% HCl and 5% citric acid, and the solution pH was about 4, the curret density was 0.05 A/cm2, the extraction time was 10 h, and The temperature was controlled at 5 °C . When the extraction was completed, the carbides powders were washed with alcohol by ultrasonic vibration, and then the carbide powders were dried.The morphology of carbide particles was observed by KYKY-2800B scanning electron microscopy, and chemical element composition was determined by EDS.…”

Section: Materials and Experiments Proceduresmentioning

confidence: 99%

“…The size statistics of two kinds of carbides were calculated respectively, and it is concluded that the size distribution of carbides of V was less than or equal to 80nm,while, the range of size distribution of Cr carbides is greater than 80nm.The content of Cr in 60Si2CrVA is higher, so its carbides tend to aggregate and grow; carbides rich in V and carbides rich in Cr have different nucleation sites, the former is mainly formed in the original austenite crystal [18][19][20],while the latter is formed at grain boundaries and martensite lath boundaries. The precipitation diffusion rate is higher in the original austenite.…”

Section: B Effect Of Carbide Size Distribution On Mechanical Propertmentioning

confidence: 99%

Study of The Precipitation Behavior and Strengthening of Carbides during the Partition Process

Jiang¹,

Zhao²

2018

Proceedings of the 4th Annual International Conference on Material Engineering and Application (ICMEA 2017)

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Abstract-In this paper, the size distribution and quantity of carbides precipitated during the partition process of 60Si 2 CrVA spring steel treated by Q&P with different partition time were statistically analyzed by SEM. Carbide particles were obtained by electrolytic extraction of 60Si 2 CrVA treated by Q&P with partition time of 1200s, and the contribution of different kinds of carbides to the yield strength was calculated. The results show: during the partition process of 60Si2CrVA spring steel, the size and volume fraction of carbides increase continuously with the extension of partition time, while the contribution of carbides to yield strength decreases gradually. Carbides rich in V(≤80nm)and carbides rich in Cr(>80nm)are mainly precipitated in the partition process, and carbides rich in V play the key role in precipitation strengthening.Keywords-60Si2CrVA spring steel; Q&P process; Partition time; Carbides; Precipitation strengthening I INTRODUCTIONSpring steel is widely used in aircraft, railway vehicles, such as automobiles and tractors transport and other industrial products. It mainly work in bending periodic, alternating torsion stress conditions, subjected to pull, pressure, shock, torsional fatigue, corrosion and other effects, sometimes bear high short-term sudden load. So the comprehensive mechanical properties of spring steel high requirements.The microstructure of martensite and retained austenite can be obtained by heat treatment of spring steel by Q&P process, and it has the advantages of both high strength and high plasticity in performance [1][2][3][4].Although the Si and Al elements in the spring steel can inhibit the precipitation of cementite in the Q&P process,E.P.Da Siva, D.De knijf, D.V.Edmods and Moor [5][6] all indicate that carbides precipitation in the partition period cannot be completely suppressed even in low carbon steels with relatively high Si and Al content, especially transition carbides [7][8].While precipitation of carbides and the diffusion of carbon in martensite into austenite are a competition mechanism.Carbides precipitation not only lead to the less content of retained austenite at room temperature, but also contribute to poor carbon in martensite,which can reduce comprehensive mechanical properties.As the second phase particle precipitation, the size of carbides will affect the mechanical properties of steel [9][10].The large size carbide particles formed in partition time are easy to cause stress concentration, reduce the plasticity and toughness,and it will result in serious brittle fracture.So,in addition to martensite,precipitation of carbides is also an important factor determining the mechanical properties of spring steel treated by Q&P process [11][12].There were no systemic study of precipitation of spring steel in the partition of carbides and its effects on the mechanical properties in the domestic and foreign literatures.The purpose of the present work was to explore the influence ofcarbides on mechanical properties by the statistics of carbides precip...

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Investigations on coarsening of MX and M23C6 precipitates in 12% Cr creep resistant steels assisted by computational thermodynamics

Cited by 90 publications

References 23 publications

The Computational Design of W and Co-Containing Creep-Resistant Steels with Barely Coarsening Laves Phase and M23C6 as the Strengthening Precipitates

The Computational Design of W and Co-Containing Creep-Resistant Steels with Barely Coarsening Laves Phase and M23C6 as the Strengthening Precipitates

Review of Z phase precipitation in 9–12 wt-Cr steels

Study of The Precipitation Behavior and Strengthening of Carbides during the Partition Process

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