Alberto Bacilio Quispe Cohaila - Academia.edu (original) (raw)
Papers by Alberto Bacilio Quispe Cohaila
Crystals, May 23, 2024
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Fondo Editorial - UNAM, Dec 1, 2020
ISIJ International, 1999
The simulation methodapplied to determine no-recrystallization temperature (T**) has also been us... more The simulation methodapplied to determine no-recrystallization temperature (T**) has also been used to simultaneously determine phasetransformation temperatures on cooling (A*3, A*1) in a set of six steels with different Ti and N contents. A study has been made of the influence of Ti and Ncontents on these parameters for different strain conditions, and the results permit an estimation of what would be the most appropriate contents depending on the type of rolling (hot strip mill, near net shape casting). Austenite grain size was also determined at 11 OO'Cand 1 300'C for all the steels, it being found that a Ti/N ratio close to two gave the finest grain,
Revista de Metalurgia, 1997
Resumen Se describe un método desarrollado en el CENIM, que permite estudiar la interacción de la... more Resumen Se describe un método desarrollado en el CENIM, que permite estudiar la interacción de la recristalización-precipitación inducida por deformación de un acero microaleado al vanadio. Mediante ensayos de torsión, y aplicando el método back extrapolation, se ha determinado la fracción recristalizada a diferentes temperaturas. Cuando la precipitación comienza, la fracción recristalizada se desvía de la ecuación de Avrami y esto permite conocer el instante en que la precipitación comienza (P s) y el instante en que termina (P f). De este modo, se pueden trazar los diagramas Recristalización-Precipitación-Tiempo-Temperatura (RPTT), que muestran gráficamente la interacción Recristalización-Precipitación y que simultáneamente permiten la determinación de la temperatura crítica de recristalización estática (SCRT). Dicha temperatura crítica representa el límite entre las dos fases, antes y después de la precipitación. Palabras clave: Torsión. Interacción. Recristalización. Precipitación inducida. Diagramas RPTT. Recrystallization-Precipitation-Time-Temperature (RPTT) diagram of a vanadium microalloyed steel Abstract A method developed in the CENIM is described which allows to study the interaction recrystallization-induced precipitation by the deformation of vanadium microalloyed steel. By means of torsión test and applying the back extrapolation method, has been determined the recristallized fraction to diferent temperatures. When the precipitation begins, the recristallized fraction is separated of the Avrami's equation and this allows to know the instant the precipitation begins (P s) and the instant the precipitation finishes (P f). Thereby can be traced the Recrystallization-Precipitation-Time-Temperature (PTT) diagrams, which graphically show the interaction Recrystallization-Precipitation and simultaneously allows the determination of the static recrystallization critical temperature (SCRT). The mentioned temperature represents the limit between the two phases, before and after of the precipitation.
Biochemical Journal, 1988
The resistance of transferrin, lactoferrin and caeruloplasmin to oxidative damage: a reply Halliw... more The resistance of transferrin, lactoferrin and caeruloplasmin to oxidative damage: a reply Halliwell and his colleages [1] agree with our conclusion [2] that apolactoferrin and apotransferrin are relatively resistant to inactivation by myeloperoxidase-derived hypochlorous acid (HOCI). However, in our study we did observe some loss of binding capacity (approx. 70 %
Resumen Para aplicar el proceso de electroescoria a la fabricación de aceros es necesario compren... more 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
ISIJ International, 1996
Using torsion tests and applying the back extrapolation method, the statically recrystallized fra... more Using torsion tests and applying the back extrapolation method, the statically recrystallized fraction of low carbon microalloyed steels contai n ing vanadium, n iobium andtitanium, respectivel y, has beendetermined for different temperatures and strains. Fromthe recrystallized fraction against time curves it is possible to draw pre,cipitation-time-temperature (PTT) diagrams. These diagrams show that the strain does not affect precipitation kinetics in an independent manner, but that this influence is related with the microalloy content. The greater the strain applied, the shorter the incubation time of induced precipitation, but this influence diminishes as the microalloy content increases. It is also demonstrated that the incubation time is practically independent of the nature of the metal microalioy (V, Ti, Nb). In this sense, new expressions are proposed to relate the incubation and precipitation end times with the strain and the microalloy content. A model is also estabiished for precipitation kinetics at the curve nose temperature.
Revista de Metalurgia, 2003
Resumen Se fabricaron varias coladas del acero 38MnSiVS5 con diferentes contenidos de titanio y a... more Resumen Se fabricaron varias coladas del acero 38MnSiVS5 con diferentes contenidos de titanio y aluminio, y se determinó el tamaño del grano austenítico a temperaturas comprendidas entre 900 y 1.200 °C. Se cuantificaron las fracciones de volumen de crecimiento normal y anormal, respectivamente. Los resultados muestran que el crecimiento anormal del grano austenítico ocurre independientemente de los contenidos de titanio y aluminio, debido, fundamentalmente, a la disolución parcial de los precipitados TiN. Aquellos aceros con porcentajes altos de aluminio mostraron un peor comportamiento debido a que la formación de un segundo tipo de precipitados, concretamente AIN, y su pronta disolución entre 1.000 y 1.100 °C, ocasiona un descenso drástico en las fuerzas de anclaje locales, lo que produce un crecimiento anormal más pronunciado de los granos afectados. Paralelamente, se realizó un estudio de los precipitados por Microscopía de Transmisión y de Barrido (MTB), que permitió calcular las fuerzas de anclaje de acuerdo con las expresiones de Zener y Gladman y establecer una comparación con las fuerzas impulsoras de crecimiento de grano. Dicha comparación permite explicar las diferencias encontradas entre las distintas coladas. Palabras clave Crecimiento anormal de grano. Distribución de tamaños de precipitados. Fuerzas de anclaje. Fuerzas impulsoras. Austenite grain abnormal growth in the microalloyed steel SSIVlnSiVSS and determination of driving and pinning forces Abstract Several castings of 38MnSiVS5 steel have been manufactured with different titanium and aluminium contents and the austenitic grain size has been determined at temperatures between 900 and 1200 °C. The volume fraction of normal and abnormal grain growth have been quantified. The results show that abnormal growth of the austenitic grain occurs irrespective of the titanium and aluminium contents, due fundamentally to the partial dissolution of TiN precipitates. The steels with high aluminium contents have presented worse behaviour due to the formation of a second type of precipitates, namely AIN, which quickly dissolve between 1000 and 1100 °C, causing a drastic decline in the local pinning forces which gives rise to more pronounced abnormal growth of the affected grains. In parallel, a study of the precipitates has been carried out by transmission and scanning microscopy, allowing the calculation of pinning forces according to Zener and Gladman expressions and the establishment of a comparison with driving forces. This comparison makes it possible to explain the differences encountered between the different castings.
ISIJ International, 1999
The austenite grain size of six steeis with different Ti and N contents has been determined at 1 ... more The austenite grain size of six steeis with different Ti and N contents has been determined at 1 300'C x I O min and at 11 OO'C x I Omin, The most stable grain was achieved for a Ti/N ratio close to 2. In parallel, a study of precipitate sizes was carried out using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results indicate that the steels with a lower N content and approximately the same Ti content show a distribution of precipitates of larger size, which increases with the Ti content in solution at the austenitization temperature applied, As the austenitization temperature increases, the double effect of precipltate dissolution and coarsening appears, and only with a hipostoichiometric Ti/N ratio and as precipitated Ti content above 0.010 (wt'/•) are they capable of controlling the austenite grain up to high temperatures, KEYWORDS: titanium nitride size; austenite grain size; Ostwald ripening; Ti/N ratio. 1.
Materials Science Forum, 2013
Under certain conditions of temperature, time and deformation, static recrystallization of austen... more Under certain conditions of temperature, time and deformation, static recrystallization of austenite in microalloyed steels can be temporarily inhibited by means of the strain-induced precipitation of nanoparticles that cause a pinning effect on austenite grain boundaries in motion. This inhibition can be seen by the formation of a “plateau” in the curves of static recrystallization of austenite obtained from double-deformation tests carried out under isothermal conditions. In this work, several microalloyed steels with different compositions are studied by hot torsion tests in order to characterize the kinetics of recrystallization and its inhibition. The precipitation state in austenite is studied in several samples by means of transmission electron microscopy. The influence of the type of microalloying element (Al, Nb, V) and the mean size of the precipitates on the duration time of the plateau is studied and relationships between these variables can be obtained. Particularly, it...
Revista de Metalurgia, 2005
Resumen Mediante ensayos de torsión y usando el método hack extrapolation se ha determinado la ci... more Resumen Mediante ensayos de torsión y usando el método hack extrapolation se ha determinado la cinética de recristalización estática de aceros microaleados con vanadio (V), niobio (Nb) y titanio (Ti) y, a partir de las mismas, ha sido posible dibujar los diagramas recristalizaciónprecipitación-tiempo'temperatura (RPTT), que muestran gráficamente la interacción recristalización-precipitación. Estos diagramas muestran que el efecto de la deformación en la cinética de precipitación depende del contenido de microaleante. En este sentido, se propone una nueva expresión para relacionar la influencia de la deformación y del contenido de microaleante sobre el periodo mínimo de incubación de la precipitación inducida. Palabras clave Deformación. Acero microaleado. Diagrama RPTT Cinética de precipitación. Periodo de incubación. Influence mutual of the deformation and chemical composition on induced precipitation in microalloyed steels Abstract By means of torsion tests and applying the "back extrapolation" method, the static recrystallization kinetics in microalloyed steels with vanadium (V), niobium (Nb) and titanium (Ti) has been determined and, recrystallization-precipitation-time-temperature (RPTT) diagrams have been plotted also graphically, which show the Recrystallization-Precipitation interaction. These diagrams show that the effect of the deformation on the precipitation kinetics depends of the microalloy content. In this sense, a new expression is proposed to relate the influence of the deformation and the chemical composition on the minimum incubation of the precipitation kinetics.
Materials Science Forum, 2003
Hot torsion tests were used to simulate hot rolling of a Nb-microalloyed steel. Subsequent graphi... more Hot torsion tests were used to simulate hot rolling of a Nb-microalloyed steel. Subsequent graphic representation of Mean Flow Stress (MFS) versus the inverse of absolute temperature for each pass allowed to know the critical rolling temperatures (T nr , A r3 , A r1) and residual stress accumulated in austenite just before austenite to ferrite phase transformation. It has been found that, as successive rolling passes are applied at temperatures below T nr , mean precipitate size decreases as a result of deformation applied and hardening by incomplete recrystallization of austenite.
Revista de Metalurgia, 1998
Metallurgical and Materials Transactions A, 2013
Steel Research, 1996
Using torsion tests, and applying the back extrapolation method, the statically recrystallized fr... more Using torsion tests, and applying the back extrapolation method, the statically recrystallized fraction has been determined for low carbon microalloyed steels with different V, Nb and Ti contents, at different temperatures and an equivalent strain of 0.20%. At temperatures below the static recrystallization critical temperature (SRCT), or the temperature at which strain induced precipitation commences, recrystallized fraction against time curves show a plateau caused by precipitations. The formation of the plateau makes it possible to evaluate precipitation-time-temperature (PTT) diagrams, and thus to know the precipitation kinetics. The PTT diagrams show that an increase in the microalloy content raises SRCT and reduces incubation time. For similar Nb, V and Ti contents, Nb is the element which raises SRCT the most.
ISIJ International, 1997
Using torsion tests, a study has been made of Recrystallization-Precipitation (R-P) interaction i... more Using torsion tests, a study has been made of Recrystallization-Precipitation (R-P) interaction in a vanadium microalloyed steel for two strains (0.20 and 0.35). When strain induced precipitation starts, the recrystallized fraction deviates from Avrami's equation, giving rise to the formation of a plateau on the curves which represent the recrystallized fraction against time. This makes it possible to know the moment at which precipitation starts (P*) and the moment at which it finishes (Pf)' After the end of precipitation, recrystallization continues to progress in accordance with Avrami's [aw. Recrystallization-Precipitation-Time-Temperature (RPTT) diagrams have been drawn, superposing on them the lines corresponding to different recrystallized fractions. This makes it possible to represent in graph form the Recrystallization-Precipitation interaction and the determination of the static recrystallization critical temperature (SRCT), It is demonstrated that during the interval of time in which precipitation occurs (Pf~P*), recrystallization does not advance, The work which has been carried out establishes new aspects in the phenomenon of R-P interaction.
ISIJ International, 2002
By simulation of hot rolling using torsion tests and subsequent graphic representation of mean fl... more By simulation of hot rolling using torsion tests and subsequent graphic representation of mean flow stress (MFS) versus the inverse of temperature for each pass, no-recrystallization temperature (T nr) was determined for a low niobium microalloyed steel at different interpass times and two strains of 0.20 and 0.35. Recrystallized fraction (X a) against time curves and RPTT diagrams were also determined for these two strains. This work has allowed evaluation of the influence of a very low Nb content on three aspects: T nr , the residual stress accumulated in the austenite just before the γ→α transformation (Δσ r), and recrystallization-precipitation interaction. It was found that when the strain applied was 0.2 and the interpass times were less than 30 seconds, the values of T nr and Δσ r were rather high. However, greater strains and interpass times brought about very small values of T nr and Δσ r. In addition to this, new aspects about the definition of T nr are also discussed in this paper.
Crystals, May 23, 2024
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Fondo Editorial - UNAM, Dec 1, 2020
ISIJ International, 1999
The simulation methodapplied to determine no-recrystallization temperature (T**) has also been us... more The simulation methodapplied to determine no-recrystallization temperature (T**) has also been used to simultaneously determine phasetransformation temperatures on cooling (A*3, A*1) in a set of six steels with different Ti and N contents. A study has been made of the influence of Ti and Ncontents on these parameters for different strain conditions, and the results permit an estimation of what would be the most appropriate contents depending on the type of rolling (hot strip mill, near net shape casting). Austenite grain size was also determined at 11 OO'Cand 1 300'C for all the steels, it being found that a Ti/N ratio close to two gave the finest grain,
Revista de Metalurgia, 1997
Resumen Se describe un método desarrollado en el CENIM, que permite estudiar la interacción de la... more Resumen Se describe un método desarrollado en el CENIM, que permite estudiar la interacción de la recristalización-precipitación inducida por deformación de un acero microaleado al vanadio. Mediante ensayos de torsión, y aplicando el método back extrapolation, se ha determinado la fracción recristalizada a diferentes temperaturas. Cuando la precipitación comienza, la fracción recristalizada se desvía de la ecuación de Avrami y esto permite conocer el instante en que la precipitación comienza (P s) y el instante en que termina (P f). De este modo, se pueden trazar los diagramas Recristalización-Precipitación-Tiempo-Temperatura (RPTT), que muestran gráficamente la interacción Recristalización-Precipitación y que simultáneamente permiten la determinación de la temperatura crítica de recristalización estática (SCRT). Dicha temperatura crítica representa el límite entre las dos fases, antes y después de la precipitación. Palabras clave: Torsión. Interacción. Recristalización. Precipitación inducida. Diagramas RPTT. Recrystallization-Precipitation-Time-Temperature (RPTT) diagram of a vanadium microalloyed steel Abstract A method developed in the CENIM is described which allows to study the interaction recrystallization-induced precipitation by the deformation of vanadium microalloyed steel. By means of torsión test and applying the back extrapolation method, has been determined the recristallized fraction to diferent temperatures. When the precipitation begins, the recristallized fraction is separated of the Avrami's equation and this allows to know the instant the precipitation begins (P s) and the instant the precipitation finishes (P f). Thereby can be traced the Recrystallization-Precipitation-Time-Temperature (PTT) diagrams, which graphically show the interaction Recrystallization-Precipitation and simultaneously allows the determination of the static recrystallization critical temperature (SCRT). The mentioned temperature represents the limit between the two phases, before and after of the precipitation.
Biochemical Journal, 1988
The resistance of transferrin, lactoferrin and caeruloplasmin to oxidative damage: a reply Halliw... more The resistance of transferrin, lactoferrin and caeruloplasmin to oxidative damage: a reply Halliwell and his colleages [1] agree with our conclusion [2] that apolactoferrin and apotransferrin are relatively resistant to inactivation by myeloperoxidase-derived hypochlorous acid (HOCI). However, in our study we did observe some loss of binding capacity (approx. 70 %
Resumen Para aplicar el proceso de electroescoria a la fabricación de aceros es necesario compren... more 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
ISIJ International, 1996
Using torsion tests and applying the back extrapolation method, the statically recrystallized fra... more Using torsion tests and applying the back extrapolation method, the statically recrystallized fraction of low carbon microalloyed steels contai n ing vanadium, n iobium andtitanium, respectivel y, has beendetermined for different temperatures and strains. Fromthe recrystallized fraction against time curves it is possible to draw pre,cipitation-time-temperature (PTT) diagrams. These diagrams show that the strain does not affect precipitation kinetics in an independent manner, but that this influence is related with the microalloy content. The greater the strain applied, the shorter the incubation time of induced precipitation, but this influence diminishes as the microalloy content increases. It is also demonstrated that the incubation time is practically independent of the nature of the metal microalioy (V, Ti, Nb). In this sense, new expressions are proposed to relate the incubation and precipitation end times with the strain and the microalloy content. A model is also estabiished for precipitation kinetics at the curve nose temperature.
Revista de Metalurgia, 2003
Resumen Se fabricaron varias coladas del acero 38MnSiVS5 con diferentes contenidos de titanio y a... more Resumen Se fabricaron varias coladas del acero 38MnSiVS5 con diferentes contenidos de titanio y aluminio, y se determinó el tamaño del grano austenítico a temperaturas comprendidas entre 900 y 1.200 °C. Se cuantificaron las fracciones de volumen de crecimiento normal y anormal, respectivamente. Los resultados muestran que el crecimiento anormal del grano austenítico ocurre independientemente de los contenidos de titanio y aluminio, debido, fundamentalmente, a la disolución parcial de los precipitados TiN. Aquellos aceros con porcentajes altos de aluminio mostraron un peor comportamiento debido a que la formación de un segundo tipo de precipitados, concretamente AIN, y su pronta disolución entre 1.000 y 1.100 °C, ocasiona un descenso drástico en las fuerzas de anclaje locales, lo que produce un crecimiento anormal más pronunciado de los granos afectados. Paralelamente, se realizó un estudio de los precipitados por Microscopía de Transmisión y de Barrido (MTB), que permitió calcular las fuerzas de anclaje de acuerdo con las expresiones de Zener y Gladman y establecer una comparación con las fuerzas impulsoras de crecimiento de grano. Dicha comparación permite explicar las diferencias encontradas entre las distintas coladas. Palabras clave Crecimiento anormal de grano. Distribución de tamaños de precipitados. Fuerzas de anclaje. Fuerzas impulsoras. Austenite grain abnormal growth in the microalloyed steel SSIVlnSiVSS and determination of driving and pinning forces Abstract Several castings of 38MnSiVS5 steel have been manufactured with different titanium and aluminium contents and the austenitic grain size has been determined at temperatures between 900 and 1200 °C. The volume fraction of normal and abnormal grain growth have been quantified. The results show that abnormal growth of the austenitic grain occurs irrespective of the titanium and aluminium contents, due fundamentally to the partial dissolution of TiN precipitates. The steels with high aluminium contents have presented worse behaviour due to the formation of a second type of precipitates, namely AIN, which quickly dissolve between 1000 and 1100 °C, causing a drastic decline in the local pinning forces which gives rise to more pronounced abnormal growth of the affected grains. In parallel, a study of the precipitates has been carried out by transmission and scanning microscopy, allowing the calculation of pinning forces according to Zener and Gladman expressions and the establishment of a comparison with driving forces. This comparison makes it possible to explain the differences encountered between the different castings.
ISIJ International, 1999
The austenite grain size of six steeis with different Ti and N contents has been determined at 1 ... more The austenite grain size of six steeis with different Ti and N contents has been determined at 1 300'C x I O min and at 11 OO'C x I Omin, The most stable grain was achieved for a Ti/N ratio close to 2. In parallel, a study of precipitate sizes was carried out using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results indicate that the steels with a lower N content and approximately the same Ti content show a distribution of precipitates of larger size, which increases with the Ti content in solution at the austenitization temperature applied, As the austenitization temperature increases, the double effect of precipltate dissolution and coarsening appears, and only with a hipostoichiometric Ti/N ratio and as precipitated Ti content above 0.010 (wt'/•) are they capable of controlling the austenite grain up to high temperatures, KEYWORDS: titanium nitride size; austenite grain size; Ostwald ripening; Ti/N ratio. 1.
Materials Science Forum, 2013
Under certain conditions of temperature, time and deformation, static recrystallization of austen... more Under certain conditions of temperature, time and deformation, static recrystallization of austenite in microalloyed steels can be temporarily inhibited by means of the strain-induced precipitation of nanoparticles that cause a pinning effect on austenite grain boundaries in motion. This inhibition can be seen by the formation of a “plateau” in the curves of static recrystallization of austenite obtained from double-deformation tests carried out under isothermal conditions. In this work, several microalloyed steels with different compositions are studied by hot torsion tests in order to characterize the kinetics of recrystallization and its inhibition. The precipitation state in austenite is studied in several samples by means of transmission electron microscopy. The influence of the type of microalloying element (Al, Nb, V) and the mean size of the precipitates on the duration time of the plateau is studied and relationships between these variables can be obtained. Particularly, it...
Revista de Metalurgia, 2005
Resumen Mediante ensayos de torsión y usando el método hack extrapolation se ha determinado la ci... more Resumen Mediante ensayos de torsión y usando el método hack extrapolation se ha determinado la cinética de recristalización estática de aceros microaleados con vanadio (V), niobio (Nb) y titanio (Ti) y, a partir de las mismas, ha sido posible dibujar los diagramas recristalizaciónprecipitación-tiempo'temperatura (RPTT), que muestran gráficamente la interacción recristalización-precipitación. Estos diagramas muestran que el efecto de la deformación en la cinética de precipitación depende del contenido de microaleante. En este sentido, se propone una nueva expresión para relacionar la influencia de la deformación y del contenido de microaleante sobre el periodo mínimo de incubación de la precipitación inducida. Palabras clave Deformación. Acero microaleado. Diagrama RPTT Cinética de precipitación. Periodo de incubación. Influence mutual of the deformation and chemical composition on induced precipitation in microalloyed steels Abstract By means of torsion tests and applying the "back extrapolation" method, the static recrystallization kinetics in microalloyed steels with vanadium (V), niobium (Nb) and titanium (Ti) has been determined and, recrystallization-precipitation-time-temperature (RPTT) diagrams have been plotted also graphically, which show the Recrystallization-Precipitation interaction. These diagrams show that the effect of the deformation on the precipitation kinetics depends of the microalloy content. In this sense, a new expression is proposed to relate the influence of the deformation and the chemical composition on the minimum incubation of the precipitation kinetics.
Materials Science Forum, 2003
Hot torsion tests were used to simulate hot rolling of a Nb-microalloyed steel. Subsequent graphi... more Hot torsion tests were used to simulate hot rolling of a Nb-microalloyed steel. Subsequent graphic representation of Mean Flow Stress (MFS) versus the inverse of absolute temperature for each pass allowed to know the critical rolling temperatures (T nr , A r3 , A r1) and residual stress accumulated in austenite just before austenite to ferrite phase transformation. It has been found that, as successive rolling passes are applied at temperatures below T nr , mean precipitate size decreases as a result of deformation applied and hardening by incomplete recrystallization of austenite.
Revista de Metalurgia, 1998
Metallurgical and Materials Transactions A, 2013
Steel Research, 1996
Using torsion tests, and applying the back extrapolation method, the statically recrystallized fr... more Using torsion tests, and applying the back extrapolation method, the statically recrystallized fraction has been determined for low carbon microalloyed steels with different V, Nb and Ti contents, at different temperatures and an equivalent strain of 0.20%. At temperatures below the static recrystallization critical temperature (SRCT), or the temperature at which strain induced precipitation commences, recrystallized fraction against time curves show a plateau caused by precipitations. The formation of the plateau makes it possible to evaluate precipitation-time-temperature (PTT) diagrams, and thus to know the precipitation kinetics. The PTT diagrams show that an increase in the microalloy content raises SRCT and reduces incubation time. For similar Nb, V and Ti contents, Nb is the element which raises SRCT the most.
ISIJ International, 1997
Using torsion tests, a study has been made of Recrystallization-Precipitation (R-P) interaction i... more Using torsion tests, a study has been made of Recrystallization-Precipitation (R-P) interaction in a vanadium microalloyed steel for two strains (0.20 and 0.35). When strain induced precipitation starts, the recrystallized fraction deviates from Avrami's equation, giving rise to the formation of a plateau on the curves which represent the recrystallized fraction against time. This makes it possible to know the moment at which precipitation starts (P*) and the moment at which it finishes (Pf)' After the end of precipitation, recrystallization continues to progress in accordance with Avrami's [aw. Recrystallization-Precipitation-Time-Temperature (RPTT) diagrams have been drawn, superposing on them the lines corresponding to different recrystallized fractions. This makes it possible to represent in graph form the Recrystallization-Precipitation interaction and the determination of the static recrystallization critical temperature (SRCT), It is demonstrated that during the interval of time in which precipitation occurs (Pf~P*), recrystallization does not advance, The work which has been carried out establishes new aspects in the phenomenon of R-P interaction.
ISIJ International, 2002
By simulation of hot rolling using torsion tests and subsequent graphic representation of mean fl... more By simulation of hot rolling using torsion tests and subsequent graphic representation of mean flow stress (MFS) versus the inverse of temperature for each pass, no-recrystallization temperature (T nr) was determined for a low niobium microalloyed steel at different interpass times and two strains of 0.20 and 0.35. Recrystallized fraction (X a) against time curves and RPTT diagrams were also determined for these two strains. This work has allowed evaluation of the influence of a very low Nb content on three aspects: T nr , the residual stress accumulated in the austenite just before the γ→α transformation (Δσ r), and recrystallization-precipitation interaction. It was found that when the strain applied was 0.2 and the interpass times were less than 30 seconds, the values of T nr and Δσ r were rather high. However, greater strains and interpass times brought about very small values of T nr and Δσ r. In addition to this, new aspects about the definition of T nr are also discussed in this paper.