Thermodynamic Aspects in the Manufacturing of Microalloyed Steels by the Electroslag Remelting Process.

Medina, Sebastián F.; Cores, A.

doi:10.2355/isijinternational.33.1244

Cited by 42 publications

(27 citation statements)

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“…This technique avoids macrosegregation, both in alloying elements and impurities, and leads to considerably less microsegregation, these defects being present in conventional ingots and continuous casting billets. 40) As Table 1 shows, this steel has a very low niobium addition (0.007 % Nb). Niobium is known to be the microalloying element that most delays static recrystallization kinetics, even when it is in solution.…”

Section: Methodsmentioning

confidence: 99%

Determination of Driving and Pinning Forces for Static Recrystallization during Hot Rolling of a Niobium Microalloyed Steel

Gómez¹,

Medina²,

Vallés

2005

ISIJ Int.

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The hot rolling process of a low Nb-microalloyed steel under different interpass time conditions is simulated by means of hot torsion tests. Subsequent graphic representation of the Mean Flow Stress (MFS) versus the inverse of the absolute temperature for each pass allows us to know the critical rolling temperatures (T nr , A r3 , A r1 ) and to characterize the progressive strengthening of austenite due to incomplete recrystallization between T nr and A r3 , thanks to the measurement of a magnitude called accumulated stress (Ds). Optical and electron microscopy studies demonstrate that the evolution of the microstructure and the precipitation state-particularly the mean particle size-over the rolling schedule is strongly dependent on the interpass time. A review is made of the expressions that have been proposed to estimate the values of recrystallization driving (F R ) and pinning forces (F P ). Using these expressions and the experimental data from the hot rolling simulations performed, the evolution of F R and F P during rolling is studied. A comparative analysis of hypotheses concerning the interaction between precipitates and migrating grain boundaries is achieved and the methods for estimating the volume fraction of precipitates and the dislocation density are assessed. Though the selected criterion significantly influences the values obtained for both forces, it is found that F P always grows faster than F R as the rolling temperature drops, which helps to explain the start of inhibition of the static recrystallization of austenite at temperatures below T nr .

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Section: Methodsmentioning

confidence: 99%

Determination of Driving and Pinning Forces for Static Recrystallization during Hot Rolling of a Niobium Microalloyed Steel

Gómez¹,

Medina²,

Vallés

2005

ISIJ Int.

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“…Extendiendo la reacción [1] a los aleantes con afinidad por el oxígeno, en nuestro caso aluminio, titanio, silicio y manganeso, puede afrontarse una descripción teórica cualitativa del equilibrio termodinámico del sistema.…”

Section: X[m]+[0] = (M X O)unclassified

“…Estas ventajas convierten al proceso ESR en especialmente indicado para la fabricación de aceros microaleados (1).…”

Section: Introductionunclassified

Estudio termodinámico de las reacciones de intercambio en la fabricación de aceros por el proceso de electroescoria

Ruiz-Valdepeñas¹,

Chapa²,

Quispe³

et al. 1998

REVMETAL

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Estudio termodinámico de las reacciones de intercambio en la fabricación de aceros por el proceso de electroescoria F. Ruiz-Valdepeñas^ , M. Chapa^ , A. Quispe^ ' y S.F. Medina^ )Resumen Para aplicar el proceso de electroescoria a la fabricación de aceros es necesario comprender los complejos procesos termodinámicos que tienen lugar, en los que intervienen los óxidos componentes de la escoria, los aleantes disueltos en el acero líquido y los elementos de las ferroaleaciones y desoxidantes que se adicionan. Calculando las actividades termodinámicas de los elementos en el metal fundido y de los óxidos en la escoria, se plantean los equilibrios teóricos de oxidación de los elementos con mayor afinidad por el oxígeno, así como sus equilibrios de intercambio mutuo. Comparando los equilibrios teóricos con los resultados experimentales se puede interpretar cómo evoluciona el sistema durante la refusión y ajustar la composición de la escoria y demás parámetros para fabricar un acero de composición distinta a la del electrodo.Palabras clave: Refusión por electroescoria. Actividad. Equilibrio termodinámico.Thermodynamics of exchange reactions in the manufacturing of microalloyed steels by the ESR process AbstractMicroalloyed steels can be manufactured by electroslag remelting provided that a good understanding of the complex thermodynamics in this process is achieved. Slag components, elements dissolved in liquid steel, ferroalloys and deoxidizers play a significant role. Theoretical calculations based on the concept of thermodynamic activity are proposed which describe the oxidation and exchange reactions of the elements with affinity for oxygen. Experimental results are interpreted and it is then possible to propose an overview of the outstanting phenomena which take place. It is therefore possible to adjust the process to the manufacturing of steels with different composition from electrode.

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“…This technique avoids macrosegregation, both in alloying elements and impurities, and there is considerably less microsegregation; these defects being present in conventional ingots and continuous casting billets. 18) The decomposition of austenite in continuous cooling has been analysed using an Adamel DT 1000 high resolution dilatometer. The specimens for dilatometry had a radius of 1 mm and a length of 12 mm.…”

Section: Methodsmentioning

confidence: 99%

“…Figures 1-4 show the dilatometric curves obtained from the tests, along with the corresponding ferrite and pearlite microstructures. On each dilatometric cooling curve an indication is made of the different critical transformation temperatures which may be deduced from the curves and whose meaning is as follows [16][17][18][19][20][21][22][23][24] : AЈ r3 ϭReal transformation start temperature for proeutectoid ferrite formation A r3 ϭConventional or apparent transformation start temperature for proeutectoid ferrite formation A r1 ϭConventional or apparent transformation final temperature for proeutectoid ferrite formation (AЈ r1 ) s ϭReal transformation start temperature for pearlite formation (AЈ r1 ) f ϭReal transformation final temperature for pearlite formation All the critical transformation temperatures have been determined with the assistance of the first derived function and the second derived function, since they are more sensitive to changes in the slope than the dilatometric curve itself. The AЈ r3 temperature is given by the point on the dilatometric curve where the straight line starts to gradually diverge from the straight during cooling.…”

Section: Dilatometric Curves Microstructures and Appli-mentioning

confidence: 99%

Modelling of Phase Transformation Kinetics by Correction of Dilatometry Results for a Ferritic Nb-microalloyed Steel

2003

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Using the dilatometry technique, g→a transformation kinetics has been determined at different cooling rates in a steel with low carbon and low niobium contents (0.09 and 0.017 mass% respectively). First of all the real and the conventional transformation temperatures of the steel were determined. The real start temperature for proeutectoid ferrite formation (AЈ r3 ) corresponds to the point where the dilatometric curve starts to diverge from the straight during cooling. The conventional start and finish temperatures for proeutectoid ferrite formation (A r3 and A r1 ) are given by two points close to the minimum and the first maximum of the curve, respectively. The real start and finish eutectoid transformation temperatures -(AЈ r1 ) s and (AЈ r1 ) f -correspond to the second point of inflection and a point close to the second relative maximum of the curve, respectively. Carbon enrichment of the remaining austenite, as the transformation to ferrite advances, is corrected taking into account the dependence on the carbon content of the atomic volume of austenite. On the other hand, the dilatometric data have also been corrected with regard to the different expansion coefficients of austenite and ferrite. In this way it has been seen that the lever-rule method applied to the dilatometric curve is useful for determining transformation temperatures, but not for determining transformation kinetics, since the amount of proeutectoid ferrite calculated with this method was up to 10 % greater than the real amount measured with an image analyser. Finally a model based on Avrami's law has been developed for the real g→a transformation kinetics.

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Thermodynamic Aspects in the Manufacturing of Microalloyed Steels by the Electroslag Remelting Process.

Abstract: In this paper the possibility is demonstrated of producing microalloyed steels with Ti

Cited by 42 publications

References 1 publication

Determination of Driving and Pinning Forces for Static Recrystallization during Hot Rolling of a Niobium Microalloyed Steel

Determination of Driving and Pinning Forces for Static Recrystallization during Hot Rolling of a Niobium Microalloyed Steel

Estudio termodinámico de las reacciones de intercambio en la fabricación de aceros por el proceso de electroescoria

Modelling of Phase Transformation Kinetics by Correction of Dilatometry Results for a Ferritic Nb-microalloyed Steel

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