Thermodynamic calculation and experimental verification of the carbonitride-austenite equilibrium in Ti-Nb microalloyed steels

Zou, H.; Kirkaldy, J. S.

doi:10.1007/bf02801182

Cited by 38 publications

(17 citation statements)

References 11 publications

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“…There have been reports on the thermodynamic analysis of complex carbonitrides in microalloyed steels. [1][2][3][4][5][6] These analyses are in reasonable agreement with the experimental values in the area where complex carbonitrides form homogeneous solutions. However, it is known that phase separation occurs in the precipitates depending on the difference of thermodynamic stabilities of terminal components in the (M 1 , M 2 )(X 1 , X 2 ) double pseudobinary system.…”

Section: Introductionsupporting

confidence: 81%

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

et al. 2001

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Thermodynamic calculations of the phase equilibria between austenite (g) and complex carbonitrides containing Nb, Ti and V, (Nb, Ti, V)(C, N), were performed. The solubility product and formation energy of each carbide and nitride as well as the interaction parameters between components were evaluated. Experimental investigation on phase separation in the complex carbonitrides was also carried out using STEM-EDX and X-ray diffraction. The immiscibility of carbonitride was found to strongly affect the phase equilibria even when the content of microalloying elements in IF steels was very low.

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Section: Introductionsupporting

confidence: 81%

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

et al. 2001

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“…These authors found good agreement between their equilibrium calculations and experimental data on the precipitated weight fraction of (Nb, Ti, V)(C, N) precipitates in hot rolled microalloyed steels. Moreover, Zou and Kirkaldy 11) showed quantitative agreement between equilibrium calculations and the experimentally determined stoichiometry of (Nb, Ti)(C, N) precipitates in a non-deformed material. So far, the present authors found no direct comparison between the calculated equilibrium mole fraction of elements in a precipitate and experimental observations of the stoichiometry of precipitates during or after hot deformation, except a recent publication by Liu 12) who compared his calcula-tions with experimental data from Craven et al 13) The objective of the present paper is to separate both retarding mechanisms, i.e.…”

Section: Introductionsupporting

confidence: 53%

“…For this approach, which was already used by Zou and Kirkaldy, 11) it was assumed that in the austenitic phase, i.e. the fcc#1 phase, there was only one type of precipitate.…”

Section: Precipitation Under Thermodynamical Equilibrium Conditionsmentioning

confidence: 99%

Austenite Recrystallization–Precipitation Interaction in Niobium Microalloyed Steels

et al. 2009

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A good combination of strength and toughness in HSLA steels can be achieved by the addition of microalloying elements such as Nb. Nb can retard the static recrystallization of austenite at lower temperatures by solute drag or by precipitation pinning. In this study, the recrystallization behavior of four Nb-microalloyed model alloys which were designed to show either extensive or almost no precipitation, was compared by multi-hit torsion tests and double hit compression tests. A good consistency between the different types of tests was found and the results were verified by optical micrographs. Further, by construction of softeningtime-temperature diagrams the recrystallization behavior was linked to the precipitation state of the material which was investigated by thermodynamical equilibrium calculations and by experimental observations from TEM-EDX, Inductively Coupled Plasma Mass Spectroscopy and X-ray Diffraction. Quantitative agreement between the experimental measurements and the calculations for precipitated mass fraction and precipitate composition as a function of temperature and steel composition is demonstrated.KEY WORDS: recrystallization; microalloyed steels; precipitation; solute drag. 911© 2009 ISIJ tions with experimental data from Craven et al. 13)The objective of the present paper is to separate both retarding mechanisms, i.e. solute drag and precipitation pinning, by investigating model alloys designed to show either extensive or almost no precipitation. Moreover, the recrystallization kinetics of four Nb-microalloyed steels during hot deformation is linked to the morphology and composition of the precipitates and the amount of Nb-solutes found in these materials. The recrystallization kinetics were investigated combining different hot deformation testing techniques while information on the precipitation state of the material was obtained from thermodynamic equilibrium calculations and from a combination of experimental observation techniques. With this work, a contribution to the understanding of the fundamental mechanisms responsible for the retardation of austenite recrystallization in Nb-microalloyed steels is achieved. Experimental ProcedureFour model alloys were designed and casted as 100 kg ingots in a Pfeiffer vacuum furnace operated under argon gas atmosphere. The chemical composition of these alloys can be found in Table 1. The C-Mn-reference alloy, without additional Nb, represents a reference steel. The second alloy, a lowC-Mn-Nb alloy containing only a few ppm C, allowed to study the effect of Nb in solid solution. The third alloy (C-Mn-Nb) was designed to study the effect of NbC-precipitates on the recrystallization kinetics. To have the highest fraction of NbC precipitates possible, a stoichiometric Nb/C-ratio of 8/1 was chosen. Finally, the fourth alloy (C-Mn-Nb-N) was designed to study the influence of N on the recrystallization and precipitation behavior. The cast blocks were thermomechanically processed under conditions comparable to those during industrial steel plate rolli...

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“…1) A lot of work has been done on high strength steel sheet, 2) high toughness steel plate, 3) high strength heat resistant steel. 4) Therefore, the solubility products of MX in carbon steel have been systematically studied and the results have been summarized elsewhere.…”

Section: Introductionmentioning

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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Thermodynamic calculation and experimental verification of the carbonitride-austenite equilibrium in Ti-Nb microalloyed steels

Cited by 38 publications

References 11 publications

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

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

Austenite Recrystallization–Precipitation Interaction in Niobium Microalloyed Steels

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

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