Formation of the Z-phase and prospects of martensitic steels with 11% Cr for operation above 590°c

Kaibyshev, Rustam; Skorobogatykh, V. N.; Shchenkova, I. A.

doi:10.1007/s11041-010-9239-0

Cited by 26 publications

(33 citation statements)

References 19 publications

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“…[10,11] The degradation is summarized as follows. Z phase forms in ferritic/martensitic steels containing large amounts of Cr and N, V, and Nb after long thermal exposure similar to the case for austenitic steel; [26,30] the nose temperature of Z-phase precipitation (i.e., the temperature at which precipitation occurs earliest) is 923 K (650°C); [27] the composition of Z phase is Cr(Nb,V)N, and small amounts of Fe and Si are dissolved; [27,28] a thermodynamic calculation system showed that Z phase is more stable than MX in high-Cr ferritic/martensitic steel; [30][31][32] the nucleation mechanism is not well understood, but Z phase easily nucleates on VN and Z phase is further stabilized by dissolving Nb; [32][33][34] Nb precipitates forming MX on PAGB during normalization, and Z phase is found on PAGB near Nb containing MX; [28,35,36] Z-phase particles grow and/or become coarse by collecting nearby Cr, and dissolving and consuming finely dispersed MX particles in grains [35,36] ; and a region several microns in width along and adjacent to PAGB on which coarse M 23 C 6 and Z-phase particles grow is preferentially recovered, the timing of which corresponds to an unexpected and sharp drop in strength. [10,[35][36][37] According to the previous work shown above, the unexpected drop in strength in the times to rupture and specified strain observed at 873 K (600°C) after several thousands of hours for 11Cr-2W-0.4Mo-1Cu-Nb-V steel (shown in Figures 2, 7, and 11) is considered to be mainly because of the formation of Z phase on PAGB and the resulting local and heterogeneous recovery along PAGB.…”

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confidence: 99%

Method of Estimating the Long-term Rupture Strength of 11Cr-2W-0.4Mo-1Cu-Nb-V Steel

Tamura

2015

Metall Mater Trans A

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Long-term rupture data of 11Cr-2W-0.4Mo-1Cu-Nb-V steel were analyzed using an exponential equation for stress regarding time to rupture as a thermal activation process. The fitness was compared with the usually employed method assuming power-law creep. In the exponential method, rupture data are classified into several groups according to the thermal activation process; the activation energy, Q; the activation volume, V; then, the Larson-Miller constant, C, values are calculated, and a regression equation is obtained for each data group. The fitness level of the equation was satisfactorily high for each group. The values of Q, V, and C were unusually small for a data group where an unexpected drop in rupture strength was observed. The critical issue is how to comprehend signs of degradation within the short term. We can observe several signs at a creep time of approximately one-tenth of the times of the degradation events. The small values of Q and V indicate that completely softened regions form and creep locally, which is consistent with previous observations. From both metallurgical considerations and the variations of Q and V, it is suggested that the rate of the unexpected drop in strength is mitigated after further long-term creep.

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confidence: 99%

Method of Estimating the Long-term Rupture Strength of 11Cr-2W-0.4Mo-1Cu-Nb-V Steel

Tamura

2015

Metall Mater Trans A

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“…At rupture time ≤5000 h, in the 9Cr2W steel, the V and Cr contents were essentially independent on the rupture time. Therefore, no gradual increase in Cr content within the V-rich MX particles resulting in transformation of their cubic lattice into tetragonal lattice of Z-phase [20,32,34] was detected.…”

Section: Crept Microstructuresmentioning

confidence: 93%

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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“…When the particles are small, they tend to decrease the mobility of grain boundaries formed upon straining by dynamic recrystallization and during the interpass time by static and metadynamic recrystallization. In turn, when precipitates coalesce, a degradation of fatigue properties and corrosion resistance of the material is noticed [11][12][13][14][15][16]. The formation of Z-phase is unclear at present and not well established whether it is formed from prior nitride precipitates as proposed by some authors [13,[17][18][19] or directly nucleated as suggested by others [8,20,21].…”

Section: Accepted Manuscriptmentioning

confidence: 97%

Thermomechanical controlled processing to achieve very fine grains in the ISO 5832-9 austenitic stainless steel biomaterial

Silva

Cabrera

Balancin

et al. 2017

Materials Characterization

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Simulations of thermomechanical processing of a high niobium-and nitrogen-bearing austenitic stainless steel for orthopedic implants (ISO 5832-9) were conducted using hot torsion test with multiple deformations under continuous cooling conditions. Samples were reheated to 1250 o C and subjected to deformation schedules with pass strain of 0.3, strain rate of 1 s -1 and interpass times of 5, 20 and 50 seconds. Optical microscopy, TEM, EDS and EBSD were used to characterize the samples. Characterization of precipitates indicated that only TiNbN was undissolved after soaking, while Z-phase and NbN precipitated during on cooling deformation schedules. The evolution of grain and precipitate sizes with deformation conditions were studied and related to both grain refinement, and mechanical behavior observed. The critical grain size limited by precipitates was calculated using the values obtained for size and volume fraction of precipitates. Differences observed between calculated and measured values were discussed.Keywords: Thermomechanical controlled processing, Niobium, Strain-induced precipitation, Recrystallization, Grain Refinement, Stainless steel. ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T2 Thermomechanical controlled processing to achieve very fine grains in the ISO 5832-9 Austenitic Stainless Steel Biomaterial AbstractSimulations of thermomechanical processing of a high niobium-and nitrogen-bearing

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Formation of the Z-phase and prospects of martensitic steels with 11% Cr for operation above 590°c

Cited by 26 publications

References 19 publications

Method of Estimating the Long-term Rupture Strength of 11Cr-2W-0.4Mo-1Cu-Nb-V Steel

Method of Estimating the Long-term Rupture Strength of 11Cr-2W-0.4Mo-1Cu-Nb-V Steel

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

Thermomechanical controlled processing to achieve very fine grains in the ISO 5832-9 austenitic stainless steel biomaterial

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