A complex carbonitride of niobium and vanadium in 9% Cr ferritic steels

Tokuno, Kazushige; Hamada, Kazushi; Uemori, Ryuji; Takeda, Tetsujiro; Itoh, Kametaro

doi:10.1016/0956-716x(91)90240-2

Cited by 38 publications

(18 citation statements)

References 4 publications

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“…12) MX particles Ta or V-rich were also reported for normalized ORNL RA steels, tempered at 750°C. 7) These three types of morphologies, including in some cases the "wing" morphology, have been observed in 9CrMoVNb, 13) 9CrWCoVNb 14) and CrWNb 15) steels after tempering but, to our knowledge, the "wing" morphology involving Ta and V has not been reported in other alloys of composition similar to Eurofer97, such as F82H or JLF1. On the other hand, "duplex" precipitates, in which many TaC particles precipitate on a rectangular TiN particle were found for the F82H RA steel.…”

Section: Morphology and Compositionmentioning

confidence: 92%

Thermodynamic Modeling in Reduced Activation Steels

Danón

Servant

2005

ISIJ Int.

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Reduced Activation (RA) martensitic steels of the 9/11CrWVTa type are promising candidates for fusion reactor applications as long as they exhibit good mechanical properties-similar to those of commercial martensitic steels of the 9/12CrMo(NbV) type-and satisfy design criteria related to the behavior under irradiation. A contribution on thermodynamic modeling in RA steels is presented. The current status of the development of a thermodynamic database in the framework of the CALPHAD approach is reported. Thermodynamic calculations concerning RA alloys are discussed which can be helpful to interpret experimental observations on phase relationships, phase compositions, transition temperatures, etc.

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Section: Morphology and Compositionmentioning

confidence: 92%

Thermodynamic Modeling in Reduced Activation Steels

Danón

Servant

2005

ISIJ Int.

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“…13,14) Other researchers reported the TEM-EDS with an noticeable peak of Cr 15,16) and without any peak of Cr. 12,17) The above reports are on the normalized and tempered specimens, so that Cr carbides should be around the V(CN) particles of interest. On the other hand, the TEM-EDS information of VN in high Cr steel in the normalized state has not yet been available.…”

Section: Optical Microscopy and Precipitatesmentioning

confidence: 99%

Solubility Product of VN in Austenite of High Cr Heat Resistant Steel

et al. 2003

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Dissolved V in austenite of 7%Cr-0.4%V-0.09%N steel (hereinafter, % means mass%) was measured and the solubility product of VN was determined as follows:where T is the absolute temperature in K. The solubility product obtained is 3 to 5 times larger than those in the literature and about one order larger than that for iron. The decrease in the activity coefficient of nitrogen due to the presence of Cr and V in the experimental steel is responsible for the increase in the solubility product of VN.KEY WORDS: precipitation; MX; thermodynamics; activity coefficient. log([% ][% ])V N 4.38 ϭ Ϫ 8 436 T stituent elements. The detectable limit for V in this study is about 0.42 ppm for the experimental steel. The solubility product of VN is calculated using the following equation assuming that chemical composition of VN is stoichiometric.[%V] [%N] Symbols, [%V] and [%N], denote the dissolved V and N in austenite, and V t , N t denote the total V and N, respectively. Symbol, [%N 0 ], denotes the dissolved N in Fe-V-N alloy which is calculated from the observed values of the dissolved V. The amount of the dissolved vanadium in the matrix, [%V], is assumed to be equal to the amount of the dissolved vanadium observed. Experimental Results and Discussion Thermal EquilibriumCharacteristic features of the present analyzing method are that the duration of heat treatment is relatively short, and that the V content of a filtered solution is directly measured. Therefore, firstly, whether the equilibrium in the precipitation of VN is satisfactorily guaranteed by 1 h heating or not becomes a problem. Therefore, the effects of heating rate and heating duration should be discussed. Figure 1 shows the Arrhenius plot of the dissolved V. Open marks correspond to rapid heating where a small coupon was put into a pre-heated furnace and temperature of the coupon was reached to an aiming temperature within 5 min at least. Closed marks correspond to slow heating where a coupon was set in a cold furnace and gradually heated up to an aiming temperature taking 3 h. All coupons were held for 1 h at a temperature in both cases. The figure shows that a linear relationship is found in a wide range of temperature by the rapid heating and the regression line may probably correspond to the equilibrium solubility limit of V in austenite. On the other hand, the amount of the precipitates by the slow heating is insufficient at low temperatures as compared with those of the rapid heating. Figure 2 shows the time dependence of the dissolved V of the rapidly heated specimens at 1 100°C. This figure shows that the enough precipitation has been roughly accomplished by the 1 h rapid heating. Therefore, from Figs. 1 and 2 it is found that the equilibrium of the precipitation of VN in austenite is practically realized by a technique of the rapid heating of a small coupon followed by the short time holding at a temperature. The authors have studied the precipitation behavior of TaC and NbC and concluded that the precipitation of MX in austenite is accomplished wit...

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“…[2][3][4] Many researches have been conducted on features and role of MX carbonitrides. 2,[5][6][7][8][9][10] A possibility of further improvement in creep strength by controlling MX carbonitride has been also investigated. 11) Recently, Inoue et al reported that two-phase separation behavior of primary MX into Nb-rich MX and V-rich MX was caused by the miscibility gap between primary MX and another two phases at the temperature.…”

Section: Introductionmentioning

confidence: 99%

Phase Equilibrium between Austenite and MX Carbonitride in a 9Cr-1Mo-V-Nb Steel

et al. 2005

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Precipitation behavior during normalizing heat treatment has been investigated on a 9Cr-1Mo-V-Nb steel. Heterogeneously distributed spherical MX (MϭNb, V, Cr and XϭC, N) carbonitride particles and platelet M 3 C (MϭFe, Cr) carbide were observed in the as normalized condition. Number of the precipitates decreased with increasing normalizing temperature and no precipitates was observed after normalizing at 1 250°C. Although the size of M 3 C was almost constant independent of normalizing temperature, that of MX increased with increase in normalizing temperature up to 1 200°C. For MX carbonitride, not only size, but also composition of metallic elements was influenced by normalizing temperature. Since equilibrium composition of MX carbonitride depends on temperature, MX particle with non-equilibrium composition dissolves and precipitation of it takes place with its equilibrium composition at the normalizing temperature. A phase field diagram of NbX-VX quasi binary system in a 9Cr-1Mo-V-Nb steel was experimentally determined. It has been supposed that precipitation of M 3 C takes place during cooling from normalizing temperature in the surrounding area of MX particles where the concentration of niobium and vanadium in matrix is poor.KEY WORDS: ferritic creep resistant steel; 9Cr-1Mo-V-Nb steel; MX carbonitrides; cementite; phase equilibrium; precipitation behavior; two-phase separation; normalizing.quency vacuum induction furnace. The ingot was heated to 1 150°C for 1.5 h and hot rolled in a range of temperatures from 1 150°C to 900°C into bar with a diameter of 16 mm. Normalizing heat treatment conditions are shown in Table 2, together with prior austenite grain size number and Vickers hardness in the as normalized condition. Normalizing heat treatments were performed for 600 s in a range of temperatures from 1 050 to 1 250°C and for 3 600 s at 1 100 and 1 200°C, followed by air cooling. Prior austenite grain size of the steel coarsened with increase in normalizing temperature, but hardness of about HV400 was almost the same independent of normalizing temperature. Presence of d-ferrite was not detected for all the normalizing temperatures investigated.Distribution of precipitates was observed on carbon extracted replica under Field Emission Transmission Electron Microscope (FE-TEM). Each precipitates were analyzed by Energy Dispersion X-ray Spectroscopy attached to FE-TEM (TEM-EDS). Mechanically polished specimen surface was etched in a saturated solution of picric acid in ethyl alcohol with 1 % hydrochloric acid (Villela's reagent). The carbon was deposited on the etched surface, and the carbon film was detached from the specimen surface in a Villela's reagent. The carbon extracted replica was cleaned in ethyl alcohol and collected on copper grids for TEM examination. Precipitates were identified by means of X-ray diffraction analysis on an electrolytically extracted residue. Figure 1 shows a TEM micrograph of the carbon extracted replica prepared from the steel in the as received condition. Figure 1(b) is a high...

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A complex carbonitride of niobium and vanadium in 9% Cr ferritic steels

Cited by 38 publications

References 4 publications

Thermodynamic Modeling in Reduced Activation Steels

Thermodynamic Modeling in Reduced Activation Steels

Solubility Product of VN in Austenite of High Cr Heat Resistant Steel

Phase Equilibrium between Austenite and MX Carbonitride in a 9Cr-1Mo-V-Nb Steel

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