Calculation of Phase Equilibria between Austenite and (Nb, Ti, V)(C, N) in Microalloyed Steels.

Inoue, Kojikoji; Ishikawa, Nobuyuki; Ohnuma, Ikuo; Ohtani, Hiroshi; Ishida, K.

doi:10.2355/isijinternational.41.175

Cited by 89 publications

(44 citation statements)

References 20 publications

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“…Solid circle indicates average niobium concentration in MX precipitates and error bar means range of the data. Solubility limit temperature of MX carbonitride indicated by dashed line was determined by Thermo-calc calculation for NbX that was 1 216°C and experimental results on NbX and VX reported by Iseda et al 21) Peak temperature of binodal curve between 1 100 and 1 150°C is significantly lower than the result reported by Inoue et al 9) in which that is about 1 530°C. The difference in peak temperature of binodal curve should be derived from difference in niobium, vanadium, carbon and nitrogen concentrations.…”

Section: Influence Of Normalizing Temperatures On MXcontrasting

confidence: 50%

“…The difference in peak temperature of binodal curve should be derived from difference in niobium, vanadium, carbon and nitrogen concentrations. Concentrations of 0.61-2.08 mass% Nb, 0.45-2.29 mass% V, 0.18-0.42 mass% C and 0.057-0.119 mass% N for the steels used in the study of Inoue et al 9) are significantly higher than those of the steel used in the present study. During normalizing heat treatment, dissolving of MX carbonitride with nonequilibrium composition and precipitation of it with equilibrium composition takes place corresponding to binodal curve.…”

Section: Influence Of Normalizing Temperatures On MXcontrasting

confidence: 43%

“…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. 9) Such two-phase separation behavior has been clearly demonstrated by experimental results during tempering heat treatment at 765°C in a 9Cr-1Mo-V-Nb steel by Suzuki et al 10) Since MX particles are major strengthener, precipitation behavior in cooperate with two-phase separation of those during normalizing and tempering heat treatment strongly influences on creep strength. However, it has not yet been clearly understood, and presence of cementite (M 3 C) in the as normalized condition in 9-12Cr ferritic creep resistant steels [12][13][14][15][16][17] has not yet been authorized.…”

Section: Introductionmentioning

confidence: 91%

“…[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%

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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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Section: Influence Of Normalizing Temperatures On MXcontrasting

confidence: 50%

Section: Influence Of Normalizing Temperatures On MXcontrasting

confidence: 43%

Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

et al. 2005

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“…22) Tie lines between NbC and V(C, N) have been reported on (Nb, V)(C, N) complex carbonitride in Fe-Nb-V-C-N system. 23) At the temperature higher than binodal curve, chemical composition of complex carbonitride varies along the tie line. Such carbonitrides are observed as primary precipitates after normalizing heat treatment.…”

Section: Discussionmentioning

confidence: 99%

Two-phase Separation of Primary MX Carbonitride during Tempering in Creep Resistant 9Cr1MoVNb Steel

et al. 2003

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Precipitation behaviour during heat treatment has been investigated on 9Cr1MoVNb steel. Coarse primary and fine secondary MX carbonitrides are observed in the as normalized condition. On the other hand, coarse primary MX is not detected after tempering at 1 038 K, and Nb-rich and V-rich fine secondary MX carbonitrides and M 23 C 6 carbide are observed in the as tempered condition. Variations of metallic elements concentrations of Nb-rich MX and V-rich MX in the as tempered condition are within the relatively small ranges. Average diameter of 34 nm for V-rich MX is slightly larger than that of 24 nm for Nb-rich MX in the as tempered condition. Both size and metallic elements concentrations of the fine secondary MX observed in the as normalized condition are almost the same as those of Nb-rich MX observed in the as tempered condition. A composition of metallic elements of the coarse primary MX varies along the line between those of Nb-rich MX and V-rich MX in a Cr-Nb-V ternary phase diagram. It has been considered that, at normalizing temperature of 1 323 K, Nb-rich MX and V-rich MX forms solid solution and composition of the primary MX varies along the tie line between those two phases. Two-phase separation of primary MX into Nb-rich MX and V-rich MX may be caused by the miscibility gap in primary MX and another two phases at the tempering temperature of 1 038 K.

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