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  • Efecto de la microestructura inicial en la precipitación del Inconel 718 a a 900ºC

     Calvo Muñoz, Jessica; Cabrera Marrero, Jose Maria
    Congreso Nacional de Tratamientos Térmicos y de Superficie
    Presentation's date: 2014-04-22
    Presentation of work at congresses

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  • Dynamic recovery and dynamic recrystallization competition on a Nb- and N-bearing austenitic stainless steel biomaterial: Influence of strain rate and temperature

     Souza, R.C.; Silva, E.S.; Jorge, A.M.; Cabrera Marrero, Jose Maria; Balancin, O.
    Materials science and engineering A. Structural materials properties microstructure and processing
    Date of publication: 2013-10
    Journal article

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    he objective of this study was to investigate the dynamic softening behavior of an austenitic stainless steel with high nitrogen (type ISO 5832-9) through hot torsion tests, in the temperature range of 900 1200 degrees C and in the strain rate range of 0.01-10 s(-1). The shape of flow stress curves indicated that the softening was promoted by dynamic recovery followed by dynamic recrystallization with high level of recovery. The microstructure evolution indicated that even though after large straining as that of the steady state stresses a combination of strained and recrystallized grains was observed. The delay of dynamic reaystallization, which is a consequence of the intermediate level of stacking fault energy of this steel, and the presence of large recrystallized grains, inside of necklace formed by small grains, were associated with extended recovery regions.

    The objective of this study was to investigate the dynamic softening behavior of an austenitic stainless steel with high nitrogen (type ISO 5832-9) through hot torsion tests, in the temperature range of 900–1200 °C and in the strain rate range of 0.01–10 s−1. The shape of flow stress curves indicated that the softening was promoted by dynamic recovery followed by dynamic recrystallization with high level of recovery. The microstructure evolution indicated that even though after large straining as that of the steady state stresses a combination of strained and recrystallized grains was observed. The delay of dynamic recrystallization, which is a consequence of the intermediate level of stacking fault energy of this steel, and the presence of large recrystallized grains, inside of necklace formed by small grains, were associated with extended recovery regions.

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    Texture analysis in ultrafine grained coppers processed by equal channel angular pressing  Open access

     Higuera Cobos, Oscar Fabián; Cabrera Marrero, Jose Maria
    Materials research-Ibero-american journal of materials
    Date of publication: 2013-05
    Journal article

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    lectrolytic tough pitch (ETP) and fire refined high conductivity (FRHC) copper samples were severely deformed at room temperature by equal channel angular pressing (ECAP) up to 16 passes (e ~ 1 per pass), following route Bc. The effect of the initial texture on the evolution of texture after the ECAP process for both materials was analyzed. The annealed materials present a marked anisotropy, with a texture controlled by the <110> fiber. According to the orientation distribution function (ODF), this initial behavior allows the presence of a strong C ({001} <110>) component after the first two ECAP passes in both coppers. However in the second pass the C component significantly increases in the FRHC copper, whereas the ETP copper presents a much more balanced behavior of the A1* (111)[112] and A 2* (111)[112] components. The textures obtained for both coppers after each ECAP pass exhibit predominant orientations with continuous distributions along the orientation fiber with simple shear texture

    Electrolytic tough pitch (ETP) and fire refined high conductivity (FRHC) copper samples were severely deformed at room temperature by equal channel angular pressing (ECAP) up to 16 passes ( ε ~ 1 per pass), following route Bc. The effect of the initial texture on the evolution of texture after the ECAP process for both materials was analyzed. The annealed materials present a marked anisotropy, with a texture controlled by the <110> fiber. According to the orientation distribution function (ODF), this initial behavior allows the presence of a strong C ({001} <110>) component after the first two ECAP passes in both coppers. However in the second pass the C component significantly increases in the FRHC copper, whereas the ETP copper presents a much more balanced behavior of the A 1 * (111) [ 11 2] and A 2 * (111)[11 2 ] components. The textures obtained for both coppers after each ECAP pass exhibit predominant orientations with continuous distributions along the orientation fiber with simple shear texture.

  • Effect of boron on the continuous cooling transformation kinetics in a low carbon advanced ultra-high strength steel (A-UHSS)

     Altamirano, G.; Mejía, Ignacio; Hernandez Exposito, Ana; Cabrera Marrero, Jose Maria
    International Materials Research Congress
    Presentation of work at congresses

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    he aim of the present research work is to investigate the influence of B addition on the phase transformation kinetics under continuous cooling conditions. In order to perform this study, the behavior of two low carbon advanced ultra-high strength steels (A-UHSS) is analyzed during dilatometry tests over the cooling rate range of 0.1-200C/s. The start and finish points of the austenite transformation are identified from the dilatation curves and then the continuous cooling transformation (CCT) diagrams are constructed. These diagrams are verified by microstructural characterization and Vickers micro-hardness. In general, results revealed that for slower cooling rates (0.1-0.5C/s) the present phases are mainly ferritic-pearlitic (F+P) structures. By contrast, a mixture of bainitic-martensitic structures predominates at higher cooling rates (50-200C/s). On the other hand, CCT diagrams show that B addition delays the decomposition kinetics of austenite to ferrite, thereby promoting the formation of bainitic-martensitic structures. In the case of B microalloyed steel, the CCT curve is displaced to the right, increasing the hardenability. These results are associated with the ability of B atoms to segregate towards austenitic grain boundaries, which reduce the preferential sites for nucleation and development of F+P structures.

  • Prediction of hot flow curves of construction steels by physically-based constitutive equations

     Varela Castro, Gonzalo; Cabrera Marrero, Jose Maria
    International Materials Research Congress
    Presentation's date: 2013
    Presentation of work at congresses

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    The development of accurate constitutive equations is important for the success of computer simulations of high temperature forming operations. Often, these simulations must be made on alloys that have not been completely characterized. For that reason physically-based constitutive equations taking the chemical composition into consideration, involving deformation mechanisms and characteristic properties of the material are necessary. The influence that exerts the solute elements to an alloy on the mechanisms of diffusion on deformation processes at high temperatures is not an easy subject and the available information in literature is scarce. This study examines that influence working on the basis of eight structural plain carbon steels with the chemical composition ranging between 0.15-0.45%C, 0.2-0.4%Si and 0.6-1.6%Mn produced by Electro-Slag Remelting ESR process and tested by isothermal uniaxial compression technique. The studied deformation conditions include strain rates ranging between 5·10-4 to 1·10-1 s -1 and temperatures between 0.6-0.75Tm, with Tm the melting temperature. A constitutive expression for the hot working behavior is proposed, it includes the variation of the diffusion parameters with the chemical composition. To such aim the effect of the chemical composition of the alloy on the pre-exponential factor D0 of the gamma iron self-diffusion coefficient Dsd is included. Finally, a comparison of the experimental and predicted results shows the good agreement of the model with experimental flow data.

  • Dynamically recrystallized austenitic grain in a low carbon advanced ultra-high strength steel (A-UHSS) microalloyed with boron under hot deformation conditions

     Mejía, Ignacio; Garcia Mora, E.; Altamirano, G.; Bedolla Jacuinde, Arnoldo; Cabrera Marrero, Jose Maria
    International Materials Research Congress
    Presentation of work at congresses

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    This research work studies the dynamically recrystallized austenitic grain size (Drec) in a new family of low carbon NiCrCuV advanced ultra-high strength steel (A-UHSS) microalloyed with boron under hot deformation conditions. For this purpose, uniaxial hot-compression tests are carried out in a low carbon A-UHSS microalloyed with different amounts of boron (14, 33, 82, 126 and 214 ppm) over a wide range of temperatures (950, 1000, 1050 and 1100C) and constant true strain rates (10-3, 10-2 and 10-1 s-1). Deformed samples are prepared and chemically etched with a saturated aqueous picric acid solution at 80C in order to reveal the Drec and examined by light optical (LOM) and scanning electron microscopy (SEM). The Drec is related to the Zener-Hollomon parameter (Z), and thereafter the Drec divided by Burger's vector (b) is related to the steady state stress (ss) divided by the shear modulus () (Derby model). Results shown that the Drec in the current steels is fine ( 23 m) and almost equiaxed, and the recrystallized grain size-flow stress relationship observed after of plastic deformation is consistent with the general formulation proposed by Derby. It is corroborated that boron additions to the current A-UHSS do not have meaningful influence on the Drec.

  • Mechanical, microstructural and electrical evolution of commercially pure copper processed by equal channel angular extrusion

     Higuera Cobos, Oscar Fabián; Cabrera Marrero, Jose Maria
    Materials science and engineering A. Structural materials properties microstructure and processing
    Date of publication: 2013-06-01
    Journal article

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    Samples of commercially pure copper (ETP copper) were subjected to equal-channel angular pressing (ECAP) for up to 16 passes at room temperature following route Bc. Microstructural evolution was determined by oriented image microscopy (OIM) and differential scanning calorimetry (DSC) was used to estimate the stored deformation energy and the recrystallization temperature after each ECAP pass. On the other hand, electrical properties were correlated with the associated energy that results from the defects induced by ECAP. Results show that the stored energy rises on increasing ECAP deformation, while the recrystallization temperature decreases significatively. Also, mechanical properties after each pass were evaluated by tensile tests. Microstructural and mechanical features display that a stable microstructure is attained after four passes. Similarly, electrical conductivity decreases up to a saturation state at increasing ECAP passes

    Samples of commercially pure copper (ETP copper) were subjected to equal-channel angular pressing (ECAP) for up to 16 passes at room temperature following route Bc. Microstructural evolution was determined by oriented image microscopy (OIM) and differential scanning calorimetry (DSC) was used to estimate the stored deformation energy and the recrystallization temperature after each ECAP pass. On the other hand, electrical properties were correlated with the associated energy that results from the defects induced by ECAP. Results show that the stored energy rises on increasing ECAP deformation, while the recrystallization temperature decreases significatively. Also, mechanical properties after each pass were evaluated by tensile tests. Microstructural and mechanical features display that a stable microstructure is attained after four passes. Similarly, electrical conductivity decreases up to a saturation state at increasing ECAP passes.

  • Effect of microalloying elements (Nb, V and Ti) on the hot flow behavior of high-Mn austenitic twinning induced plasticity (TWIP) steel

     Reyes Calderón, F.; Mejía Granados, Ignacio; Boulaajaj, Ahmed; Cabrera Marrero, Jose Maria
    Materials science and engineering A. Structural materials properties microstructure and processing
    Date of publication: 2013
    Journal article

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    This research work studies the effect of microalloying elements such as Nb, V and Ti on the hot flow behavior of high-Mn austenitic TWIP steel. For this purpose, isothermal uniaxial hot compression tests were carried out at three temperatures (900, 1000 and 1100 1 C) and four constant strain rates (10 1 , 10 2 ,10 3 and 10 4 s 1 ). Experimental results revealed that hot flow curves of microalloyed TWIP steels show single peak curves for all test conditions. Results are discussed in terms of the peak stress ( s p ) and peak strain ( e p ) and its dependence on the strain rate ( _ e ) and temperature. The addition of microalloying elements such as Nb, V and Ti in TWIP steels generates a slight increase in the s p value, and Ti microalloyed TWIP steel exhibits the highest s p value. Hot deformed microstructures were analyzed by the Electron Back-Scattering Diffraction Technique (EBSD). The most important results of the austenitic recrystallized grain refinement were obtained for V and Ti microalloyed TWIP steels.

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    Microstructural, thermical and mechanical characterization of ZK60 alloy processed through ECAP  Open access

     Dumitru, Florina Diana; Ghiban, Brândusa; Cabrera Marrero, Jose Maria; Higuera Cobos, Oscar Fabián; Ghiban, Nicolae; Gurau, Gheorghe H.
    Metalurgia International
    Date of publication: 2013
    Journal article

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  • Hot deformation activation energy (Q(HW)) of austenitic Fe-22Mn-1.5Al-1.5Si-0.4C TWIP steels microalloyed with Nb, V, and Ti

     Reyes Calderón, F.; Mejía Granados, Ignacio; Cabrera Marrero, Jose Maria
    Materials science and engineering A. Structural materials properties microstructure and processing
    Date of publication: 2013-02-01
    Journal article

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    The activation energy for hot deformation ( Q HW ) of high-Mn microalloyed TWIP steels was determined from experimental uniaxial hot compression curves. The presence of microalloying elements such as Nb, V, and Ti, increases the Q HW value from 366 in the non-microalloyed one to 446 kJ/mol in the V-microalloyed TWIP steel. This change represents an increase from 16% up to 22% of Q HW values.

  • Effect of the Si and Al content in ferritic electrical steels on the flow behaviour and dynamic softening in hot rolling

     Rodríguez Calvillo, Pablo; Perez Sine, Mariona; Schneider, Juergen; Cabrera Marrero, Jose Maria; Hermann, Harti; Kawalla, Rudolf
    Materials science forum
    Date of publication: 2013
    Journal article

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    FeSi steels with and without addition of Al are widely used as electrical steels. To improve the knowledge of the effects by the addition of Si and Al on the hardening and softening under hot rolling conditions, the behaviour of the flow curves in a wide range of temperatures and deformation velocities have been studied.

  • Texture analysis in ultrafine grained copper processed by equal channel angular pressing

     Higuera Cobos, Oscar Fabián; Cabrera Marrero, Jose Maria
    Materials research-Ibero-american journal of materials
    Date of publication: 2013-05
    Journal article

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    Electrolytic tough pitch (ETP) and fire refined high conductivity (FRHC) copper samples were severely deformed at room temperature by equal channel angular pressing (ECAP) up to 16 passes (e ~ 1 per pass), following route Bc. The effect of the initial texture on the evolution of texture after the ECAP process for both materials was analyzed. The annealed materials present a marked anisotropy, with a texture controlled by the <110> fiber. According to the orientation distribution function (ODF), this initial behavior allows the presence of a strong C ({001} <110>) component after the first two ECAP passes in both coppers. However in the second pass the C component significantly increases in the FRHC copper, whereas the ETP copper presents a much more balanced behavior of the A1 * (111)[ 1 1 2] and A2* (111)[11 2 ] components. The textures obtained for both coppers after each ECAP pass exhibit predominant orientations with continuous distributions along the orientation fiber with simple shear texture.

  • Microstructure influencing physical and mechanical properties of electrolytic tough pitch copper produced by equal channel angular pressing

     Higuera Cobos, Oscar Fabián; Cabrera Marrero, Jose Maria
    Mechanics of materials
    Date of publication: 2013-11
    Journal article

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    Samples of electrolytic tough pitch (ETP) copper were subjected to equal-channel angular pressing (ECAP) for up to 16 passes at room temperature following route Bc. The microstructural evolution was followed by Oriented Image Microscopy (OIM) and Differential Scanning Calorimetry (DSC) was used to estimate the activation energy and the recrystallization temperature after each ECAP pass. Also, mechanical properties after each pass were evaluated by tensile tests. Finally, electrical properties were analyzed. Results show that the stored energy increases on increasing ECAP deformation, while the recrystallization temperature decreases signi¿cantly. From a mechanical point of view a stable state is attained after 4 passes. Similarly, electrical conductivity slightly decreases down to a saturation state.

  • Microstructural and calorimetric analysis of ZK60 alloy processed by ECAP

     Dumitru, Florina Diana; Ghiban, Brândusa; Cabrera Marrero, Jose Maria; Higuera Cobos, Oscar Fabián; Gurau, Gheorghe; Ghiban, Nicolae
    Advanced materials research (online)
    Date of publication: 2013
    Journal article

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    In the last years many research efforts have been made in order to extend the application of wrought magnesium to structural components. One of the methods to improve the mechanical properties of the processed materials is through severe plastic deformation (SPD). ZK60 magnesium alloy samples were subjected to 6 passes of equal-channel angular pressing (ECAP) decreasing the temperature after the fourth pass, following an alternative route A. The structural characterization was realized by microstructural evolution using Oriented Image Microscopy (OIM) and XRD analysis. Differential Scanning Calorimetry (DSC) was used to estimate the stored energy and the recrystallization temperature after each ECAP pass.

  • Effect of boron on the hot ductility behavior of a low carbon advanced ultra-high strength steel (A-UHSS)

     Mejía, Ignacio; Altamirano, G.; Bedolla Jacuinde, Arnoldo; Cabrera Marrero, Jose Maria
    Metallurgical and materials transactions A-Physical metallurgy and material
    Date of publication: 2013-11
    Journal article

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    This research work studied the effect of boron additions (14, 33, 82, 126, and 214 ppm) on the hot ductility behavior of a low carbon advanced ultra-high strength steel. For this purpose, specimens were subjected to a hot tensile test at different temperatures [923 K, 973 K, 1023 K, 1073 K, 1173 K, and 1273 K (650 °C, 700 °C, 750 °C, 800 °C, 900 °C, and 1000 °C)] under a constant true strain rate of 10-3 s-1. The reduction of area (RA) of the tested samples until fracture was taken as a measure of the hot ductility. In general, results revealed a marked improvement in hot ductility from 82 ppm B when the stoichiometric composition for BN (0.8:1) was exceeded. By comparing the ductility curve of the steel with the highest boron content (B5, 214 ppm B) and the curve for the steel without boron (B0), the increase of hot ductility in terms of RA is over 100 pct. In contrast, the typical recovery of hot ductility at temperatures below the Ar3, where large amounts of normal transformation ferrite usually form in the structure, was not observed in these steels. On the other hand, the fracture surfaces indicated that the fracture mode tends to be more ductile as the boron content increases. It was shown that precipitates and/or inclusions coupled with voids play a meaningful role on the crack nucleation mechanism, which in turn causes hot ductility loss. In general, results are discussed in terms of boron segregation and precipitation on austenitic grain boundaries during cooling from the austenitic range and subsequent plastic deformation.

  • Printed circuit boards: a review on the perspective of sustainability

     Canal Marques, André; Cabrera Marrero, Jose Maria; Malfatti, Célia de Fraga
    Journal of environmental management
    Date of publication: 2013-12
    Journal article

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    Modern life increasingly requires newer equipments and more technology. In addition, the fact that society is highly consumerist makes the amount of discarded equipment as well as the amount of waste from the manufacture of new products increase at an alarming rate. Printed circuit boards, which form the basis of the electronics industry, are technological waste of dif fi cult disposal whose recycling is complex and expensive due to the diversity of materials and components and their dif fi cult separation. Currently, printed circuit boards have a fi xing problem, which is migrating from traditional Pb e Sn alloys to lead-free alloys without de fi nite choice. This replacement is an attempt to minimize the problem of Pb toxicity, but it does not change the problem of separation of the components for later reuse and/or recycling and leads to other problems, such as temperature rise, delamination, fl aws, risks of mechanical shocks and the formation of ¿ whiskers ¿ . This article presents a literature review on printed circuit boards, showing their structure and materials, the environmental problem related to the board, some the different alternatives for recycling, and some solutions that are being studied to reduce and/or replace the solder, in order to minimize the impact of solder on the printed circuit boards.

  • Predicción microestructural de palanquillas de acero al carbono obtenidas por colada continua empleando una aproximación macro-micro.  Open access

     Acevedo Cabello, Jorge Luis
    Defense's date: 2013-02-08
    Department of Materials Science and Metallurgy, Universitat Politècnica de Catalunya
    Theses

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    Se desarrolla un estudio numérico-experimental de la microestructura de solidificación y la segregación en palanquillas de aceros hipoeutectoides fabricadas con el proceso de colada continua. Un programa desarrollado en FORTRAN, resuelve con el método de los elementos finitos la transferencia de calor. Con los resultados del problema térmico y los parámetros microestructurales se simulan los espaciados dendríticos primarios y secundarios, y la cantidad de segregación que son generados durante el proceso de colada continua. La simulación numérica de la transferencia de calor, se valida con problemas industriales propuestos en bibliografía. Con las condiciones reales de operación, la composición química de cada acero y los modelos de cada zona de enfriamiento, se determina la evolución del campo de temperaturas y los espesores de las zonas líquida y sólida, las velocidades de enfriamiento y el gradiente térmico. En la medida en que se incrementa la velocidad de colada se observa que, la solidificación comienza más tarde y la longitud metalúrgica crece. El efecto de la temperatura de colada en los nodos internos es más apreciable que en los nodos superficiales. Si el flujo de agua de los rociadores se incrementa la temperatura en los nodos superficiales disminuye y el efecto demora más tiempo en llegar al centro de la palanquilla. La variación del porcentaje de C en la evolución de la temperatura afecta sólo en los nodos internos. Asumiendo condiciones de simetría la caracterización de los espaciados dendríticos se realiza en un cuarto de palanquilla. La simulación numérica de éstos se valida con los resultados experimentales de bibliografía y del presente estudio. Se realiza un ajuste numérico-experimental de los parámetros termo-físicos M y N que dan lugar a las ecuaciones que describen la evolución de los espaciados dendríticos. Se concluye que cerca de la superficie de la palanquilla no hay efecto de la variación de la velocidad de colada y del flujo de agua de los rociadores sobre los espaciados dendríticos, y, por otra parte, se observa que si hay efecto de la variación de la temperatura de colada y del contenido de C sobre los espaciados dendríticos. La predicción de la segregación en aleaciones de acero, se realiza con una metodología original no reportada en bibliografía denominada formulación mixta. Como primer paso se estudian los modelos analíticos de la microsegregación y la macrosegregación, y como éstos se relacionan con el problema térmico y microestructural. La caracterización en palanquillas de acero para los elementos químicos C, Mn, P, Si, S y Cr se realiza por espectrometría. Entre los resultados numéricos del problema térmico y los espaciados dendríticos, y los resultados experimentales de la segregación, la tendencia no es evidente. Por lo tanto, en la formulación mixta, un parámetro de ajuste θ que varía entre 0 y 1, permite combinar de modo proporcional la influencia de los fenómenos de microsegregación y macrosegregación. La predicción de la segregación se realiza con un parámetro de ajuste promedio obtenido de siete aceros. En la mayoría de los casos para los elementos químicos C, Si, Mn, P, S y Cr se ha observado que el parámetro de ajuste promedio fluctúa entre 0.4 y 0.5. En el borde de la palanquilla la segregación es negativa para los elementos químicos C y P, sucediendo lo contrario cerca del origen en donde predomina la segregación positiva para los elementos químicos C, Si, P y S. En la simulación del proceso son omitidos el campo de velocidades, la agitación electromagnética, la aceleración de gravedad y las asimetrías del proceso. Se obtienen buenos resultados de la transferencia de calor y los espaciados dendríticos. Sin embargo, desde una perspectiva numérica la simulación de la segregación presentó más dificultades, dado que la distribución de la composición química experimental es más heterogénea, sin implicar un problema de calidad en el material.

    A numerical-experimental study of the solidification microstructure of a continuous casting process of seven steel billets is carried out. The heat transfer problem is solved by the finite element method with a FORTRAN developed program. In the continuous casting process, the primary and secondary dendritic arm spacing and segregation that are generated are simulated based on the results of the thermal problem and microstructural parameters. The heat transfer numerical simulation, is validated with analytic solutions and two industrial problems proposed in literature. The temperature field evolution, liquid and solid areas thicknesses, the cooling rates and thermal gradient are determined with real operating conditions, the chemical composition of each steel and the models of each cooling zone. If the casting speed increases, the solidification starts later and the metallurgical length increase. The effect of the casting temperature in the internal nodes is greater than in the surface nodes. If the spray water flow is increased, the surface nodes temperature decreases and the cooling effect suffer a delay in reaching the center of the billet. The effect of carbon content on temperature is observed only in the internal nodes. Assuming conditions of symmetry, characterization of the primary and secondary dendritic arm spacing is performed in a quarter of the billet. The numerical simulation of these dendritic arm spacings is validated with experimental results of literature and the present study. Coupling experimental measurements with numerical simulation a fit of the parameters M and N give rise to equations predicting the dendritic arm spacing. A good prediction is obtained. No effects are observed in the variation of the casting speed and spray water flow on dendritic arm spacing near the billet surface, while an effect is experimented with a variation of the superheat and carbon content on dendritic arm spacing. The prediction of segregation is performed with an original methodology not reported in literature, and here called mixed formulation. As a first step analytical models of microsegregation and macrosegregation, are studied. As well they are associated to the thermal and microstructural problem. In steel billets the characterization of C, Mn, P, Si, S and Cr is performed by spectrometry. There is no evident trend between the numerical results of the thermal problem and dendritic arm spacings, and the experimental results of segregation. Therefore, a fitting parameter ¿ is implemented in the mixed formulation allowing a proportional combination of the influence of microsegregation and macrosegregation phenomena. The segregation is predicted with an average fitting parameter obtained from seven steels. In most cases, for the chemical elements C, Mn, P, Si, S and Cr, it has been observed that average fitting parameter ranges between 0.4 and 0.5. At the edge of the billet, negative segregation is obtained for C and P, while close to the center, positive segregation predominates for the chemical elements C, Si, P and S. In the continuous casting process simulation, velocity field, electromagnetic stirring, acceleration of gravity and asymmetries of the process are omitted. Good results of heat transfer and dendritic arm spacings have been obtained. However, the numerical simulation of segregation presented more difficulties, since the experimental chemical composition distribution is more heterogeneous.

  • Efecto de los contenidos de C, Si y Mn en el comportamiento a fluencia en caliente de aceros de construcción al carbono. Aplicación a la obtención de productos largos laminados.  Open access

     Varela Castro, Gonzalo
    Defense's date: 2013-06-07
    Department of Materials Science and Metallurgy, Universitat Politècnica de Catalunya
    Theses

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    El presente trabajo de investigación se enfoca en el estudio del comportamiento a fluencia y ductilidad en caliente de los denominados aceros de construcción y su dependencia con la composición química, concretamente el C, Si y Mn. La primera se ha analizado mediante compresión uniaxial isotérmica en el intervalo de temperaturas comprendido entre 900 y 1100℃ a velocidades de deformación verdadera en el intervalo de 5·10-4 y 1·10-1 s-1. Mientras que el comportamiento de ductilidad de las aleaciones se ha analizado estudiando el comportamiento y los mecanismos de fragilización operantes bajo diferentes ciclos térmicos en un amplio intervalo de temperaturas (650-1100℃) y a una velocidad de deformación constante (1·10-3 s-1), a través de ensayos de tracción uniaxial isotérmicos y técnicas de microscopía electrónica. Para ello se han refundido ocho (8) aceros por medio de la técnica de refusión por electro-escoria (ESR), con composiciones químicas comprendidas dentro de los siguientes intervalos: Fe (% bal.), 0.15-0.15-0.45%C, 0.20-0.40%Si y 0.70-1.60%Mn (% de masa). Finalmente se propone un modelo constitutivo genérico que describe el comportamiento a fluencia en caliente de aleaciones de tipo Fe-C-Si-Mn, en donde todos los parámetros característicos del mismo son una función de la composición química de la aleación. Además, según datos de literatura, se propone una expresión que muestra la variación del factor pre-exponencial del coeficiente de autodifusión del Fe en austenita con la composición química. Dado el buen acuerdo entre los resultados experimentales y calculados, el presente enfoque es susceptible de ser aplicado en la modelización constitutiva de operaciones de conformado termomecánico de metales y aleaciones metálicas.

    The present research work is focused on the flow and ductility behavior at elevated temperatures of structural steels and their dependence with the chemical composition, specifically C, Si and Mn. The hot flow behavior was studied by isothermal uniaxial compression tests that ranged from 900 to 1100℃, while applying true strain rates that ranged from 5·10-4 to 1·10-1 s-1. Ductility behavior of the alloys was analyzed by studying the embrittlement mechanisms that operate under different thermal cycles in a wide range of temperatures (650 to 1050℃) at a constant true strain rate (1·10-3 s-1) by means of isothermal uniaxial tensile tests and electron microscopy techniques. For this purpose, eight different steels were refined via an electro-slag remelting (ESR) process to obtain the following range of chemical composition: Fe (% bal.), 0.15- 0.45% C, 0.20-0.40%Si and 0.70-1.60%Mn (mass %). Finally a generic constitutive model is proposed that describes the flow stress behavior at elevated temperatures of Fe-C-Si-Mn alloys, where all the characteristic parameters are a function of the chemical composition of the alloy. This work also uses literature values to demonstrate the variation of the pre-exponential factor of the self-diffusion coefficient of Fe in austenite with the chemical composition. Given the good agreement observed between the experimental and calculated data the presented approach is likely to have an application in constitutive modeling of thermomechanical processes of metals and metallic alloys.

  • Caracterización termomecánica de dos aceros de construcción. Influencia de la microaleación conjunta de Nb y V  Open access

     Cartaya Ruesga, Elio Armando
    Defense's date: 2013-07-29
    Universitat Politècnica de Catalunya
    Theses

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    En este trabajo se estudia la influencia de la microadición conjunta de Nb y V sobre los fenómenos de ablandamiento dinámico y estático durante y trás la deformacion en caliente. En la primera etapa del estudio se realizaron ensayos de compresión simple para evaluar el proceso de recristalización dinámica en dos aceros de construcción. Las pruebas fueron efectuadas a temperaturas comprendidas entre 900 y 1100 ºC, a velocidades de deformación de 0.001, 0.01, 0.1, 1 y 10 s-1, y hasta una deformación de 0.8, con el fin de analizar los granos recristalizados dinámicamente. Por otra parte mediante ensayos de relajación de tensiones se determinó la cinética de recristalización estática y/o metadinámica en ambos aceros, aplicando deformaciones previas a la relajación iguales a 0.05, 0.15 y 0.25, a temperaturas desde 850 a 1050 ºC y velocidades de deformación de 0.1, 1 y 10 s-1. Empleando estos ensayos de relajación se construyeron los diagramas PTT para el acero microaleado, verificando mediante FESEM los tiempos de precipitación. Con la cinética de precipitación y con los tiempos de recristalización se elaboraron los respectivos diagramas RPTT. Partiendo de los resultados experimentales se plantearon las ecuaciones constitutivas que predicen el comportamiento de los fenómenos evaluados, teniendo en cuenta tanto los parámetros tecnológicos como la influencia de la microaleación. Vale la pena resaltar que el modelo la de la cinética de precipitación tiene en cuenta la formación de carbonitruros complejos del tipo (NbxV1-x)(Cy,N1-y), lo cual a la fecha no se ha desarrollado. Con estos modelos será más fácil analizar un proceso termomecánico adecuado para su posible aplicación a escala industrial

    In this thesis the influence of joint microaddition of Nb and V on the dynamic and static softening phenomena during and after the hot deformation was investigated. In the first part of the study, the dynamic recrystallization process of two construction steels were evaluated by simple compression tests, which were conducted at temperatures between 900 and 1100 °C, with various strain rates of 0.001, 0.01, 0.1, 1 and 10 s-1, and up to a strain of 0.8, in order to analyze the dynamically recrystallized grains. Furthermore, through stress relaxation testing, the static and / or metadynamic recrystallization kinetic was determined in both steels, by applying deformations prior to relaxation equal to 0.05, 0.15 and 0.25, at temperatures from 850 to 1050 °C and strain rates of 0.1, 1 and 10 s-1. Using these relaxation tests, the PTT diagrams were constructed for the microalloyed steel, verifying the precipitation times through FESEM. With the precipitation kinetics and recrystallization times the respective RPTT diagrams were developed. Based on the experimental results, constitutive equations were proposed to predict the behavior of the evaluated phenomena, taking into account both the technological parameters and the influence of microalloying. It is worth emphasizing that the model of the precipitation kinetics takes into account the formation of complexes carbonitrides type (NbxV1-x)(Cy,N1-y), which has not been developed neither reported in literature up to date. With the help of these models it will be easier to analyze a suitable thermomechanical process in possible industrial applications.

  • Relación microestructura y propiedades de cobre sometido a deformación plástica severa mediante presión en canal angular de sección constante  Open access

     Higuera Cobos, Oscar Fabián
    Defense's date: 2013-07-12
    Universitat Politècnica de Catalunya
    Theses

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    Muestras de cobre electrolítico (ETP) y refinado al fuego (FRHC) previamente recocidas durante 30 minutos a una temperatura de 600 ºC, fueron sometidas a presión en canal angular de sección constante (ECAP) a temperatura ambiente hasta un máximo de 16 pases (ε ~ 1 por pase) siguiendo la ruta Bc en una matriz con un ángulo interno de 90º y un ángulo exterior de 37°. La caracterización microestructural se determinó mediante la técnica de difracción de electrones retrodispersados (EBSD). Las propiedades mecánicas después de cada pase se evaluaron por ensayos de tracción, microdureza y fatiga. Además, se utilizó la calorimetría de barrido diferencial (DSC) para estimar la energía almacenada durante la deformación y la temperatura de recristalización después de cada pase por ECAP. En cuanto a las propiedades eléctricas se correlacionaron con la energía asociada a los defectos inducidos durante el proceso ECAP y con el comportamiento microestructural observado. Las características microestructurales muestran una microestructura estable para el cobre FRHC y bimodal para el cobre ETP después de cuatro pases. Se analizó el efecto de la textura inicial sobre la evolución de la textura después del proceso de ECAP para todos los materiales. Los materiales en estado de recocido presentaron una marcada anisotropía, la cual se mantiene después del proceso ECAP, observándose una preferencia hacia la fibra <110>. Las texturas obtenidas para los cobres en estudio, después de cada pasada por ECAP, presentan orientaciones predominantes con distribuciones continuas a lo largo de fibras de orientación con textura de corte simple. Desde el punto de vista mecánico, se observó que la mejora en las propiedades mecánicas de los cobres ETP y FRHC ocurre gradualmente con el número de pasadas por ECAP, obteniéndose un estado estable después de 4 pases en la sección longitudinal y después de 2 pases en la sección transversal. En cuanto al comportamiento a fatiga, se observó una mejora significativa para los dos cobres en estudio después de 8 pases por ECAP en comparación con los de cobres recocidos. Por último, los resultados de DSC mostraron que la energía almacenada en los materiales se incrementa con el grado de deformación impartida por ECAP, mientras que la temperatura de recristalización disminuye significativamente. De manera similar, se observó que la conductividad eléctrica disminuye con el incremento de la deformación. Sin embargo, esta reducción no fue muy significativa si se tiene en cuenta el grado de deformación aplicada a las muestras.

    Samples of electrolytic tough pitch (ETP) and fire refined high conductivity (FRHC) copper previously annealed for 30 minutes at a temperature of 600 °C, were subjected to equal-channel angular pressing (ECAP) for up to 16 passes (ε ~ 1 per pass) at room temperature following route Bc, using an ECAP die with an inner angle of 90° and an outer angle of 37°. The microstructural characterization was determined by electron backscattered diffraction (EBSD) technique. The mechanical properties after each pass were evaluated by tensile tests, microhardess and fatigue. Additionally, differential scanning calorimetry (DSC) was used to estimate the stored deformation energy and the recrystallization temperature after each ECAP pass, while the electrical properties were correlated with the associated energy that results from the defects induced during the ECAP process and the observed microstructural behavior. The microstructural features show a stable microstructure for the FRHC copper and a bimodal microstructure for the ETP copper after four passes. The effect of the initial texture on the evolution of texture after the ECAP process for all materials was analyzed. The annealed materials showed a marked anisotropy, which remains after the ECAP process, showing a preference for the <110> fiber. The textures obtained for the investigated coppers after each ECAP pass exhibit predominant orientations with continuous distributions along the orientation fiber with simple shear texture. From a mechanical point of view, an improvement in the mechanical properties for the ETP1 and FRHC coppers occurs gradually with the number of ECAP passes, obtaining a stable state after 4 passes in longitudinal section and after 2 passes in cross section. The fatigue behavior shows a significant improvement in the fatigue life for both the ETP2 and FRHC coppers subjected to 8 ECAP passes compared with the annealed coppers. Finally, the DSC results showed that the stored energy in materials increases with the degree of deformation imparted by ECAP, while the recrystallization temperature significantly decreases. Similarly, it was found that the electrical conductivity decreases with increasing deformation. However, this reduction was not significant when taking into account the degree of strain applied to the samples. The DSC results show that the stored energy rises on increasing ECAP deformation, while the recrystallization temperature decreases significatively. Similarly, electrical conductivity decreases up to a saturation state at increasing ECAP passes.

  • Mechanical properties and microstructure of low carbon ultra-high strength steels (UHSS) microalloyed with boron

     Mejía, Ignacio; Garcia De La Rosa, Armando; Bedolla Jacuinde, Arnoldo; Cabrera Marrero, Jose Maria
    Materials research society symposia proceedings
    Date of publication: 2012
    Journal article

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  • On the onset of dynamic recrystallization in steels

     Varela Castro, Gonzalo; Cabrera Marrero, Jose Maria; Prado Pozuelo, Jose Manuel
    Advanced materials research
    Date of publication: 2012
    Journal article

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    The knowledge of the flow behavior of metallic all oys subjected to hot forming operations is of particular interest for designers and engineers in the practice of industrial forming processes simulations (i.e. rolling mill). Nowadays dynamic recrystallization (DRX) is recognized as one of the most relevant and meaningful mechanis ms available for the control of microstructure. This mechanism occurs during hot forming operations over a wide range of metals and alloys and it is known to be as a powerful tool which can be used to the control of the microstructure and properties of alloys. Therefore is important to kno w, particularly in low stacking fault energy (SFE) materials, the precise time for which DRX is availa ble to act. At constant strain rate such time is defined by a critical strain, . Unfortunately this critical value is not directly measurable on the flow curve; as a result different methods have been developed to derive it. Focused on steels, in the present work the state of art on the critical strai n for the initiation of DRX is summarized and a review of the different methods and expressions for determining is included. The collected data is suitable to feeding constitutive models.

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    Determination of the critical parameters for the onset of dynamic recrystallization (DRX) in advanced ultrahigh strength steels (A-UHSS) microalloyed with boron  Open access

     Altamirano Guerrero, Gerardo; Mejía Granados, Ignacio; Cabrera Marrero, Jose Maria
    Computer methods in materials science
    Date of publication: 2012
    Journal article

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    In this research work, the double differentiation mathematical method was used to identify more accurately the criti- cal stress ሺ ߪ ௖ ) and critical strain ሺ ߝ ௖ ) associated with the onset of dynamic recrystallization (DRX), which is based on changes of the strain hardening rate )ߝ߲/ߪ߲ ൌ ߠሺ as a function of the flow stress (Poliak and Jonas method, simplified by Najafizadeh and Jonas). For this purpose, a low carbon advanced ultra-high strength steel (A-UHSS) microalloyed with different amounts of boron (14, 33, 82, 126 and 214 ppm) was deformed by uniaxial hot-compression tests at high tempe- ratures 1100 ݀݊ܽ ሺ950,1000,1050 ° )ܥ and constant true strain rates ሺ 10 ିଷ ,10 ିଶ 10 ݀݊ܽ ିଵ ݏ ିଵ ) . Results indicate that both ߪ ௖ and ߝ ௖ increase with decreasing deformation temperature and in creasing strain rate. On the other hand, these criti- cal parameters tend to decrease as boron content increases. Such a behavior is attributed to a solute drag effect by boron atoms on the austenitic grain boundaries and also to a solid solution softening effect.

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    EBSD texture analysis of an AlCuMg alloy for different solidification rates  Open access

     Lopez Galindo, Diana; Rodriguez, Andres; Colas, Rafael; Cabrera Marrero, Jose Maria; Talamantes Silva, Jose
    World Foundry Congress
    Presentation's date: 2012
    Presentation of work at congresses

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    The 3xx series aluminium alloys are widely used for automotive applications. However, increments in engine power density result in higher alloy mechanical properties requirements for components such as cylinder heads. These alloys should perform better at high temperatures (>200 °C). A good alternative to the traditional Al-Si alloys are the Al- Cu based alloys. However, hot tear tendency is a big obstacle for the widespread use of this family of alloys [1]. The present work focus on determine the relationship between crack occurrence and grain orientation, as a result of the solidification rate. Grain refinement elements such as Ti and Zn are added to the alloy to reduce hot tearing tendency. Two different variants of AlCuMg alloy are evaluated at different solidification rates.

  • Endurecimiento de chapa de acero TWIP durante ensayos cíclicos tracción-compresión

     Calvo Muñoz, Jessica; Benito Paramo, Jose Antonio; Cabrera Marrero, Jose Maria
    Congreso Nacional de Propiedades Mecánicas de Sólidos
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  • Hot deformation characteristics of a 18Mn-0.8Si-0.55C TWIP steel

     Calvo Muñoz, Jessica; Cabrera Marrero, Jose Maria
    International Conference on Thermomechanical Processing of Steels
    Presentation's date: 2012-09-10
    Presentation of work at congresses

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    Caracteristicas de la deformacion en caliente de aceros TWIP  Open access

     Calvo Muñoz, Jessica; Rodríguez Calvillo, Pablo; Cabrera Marrero, Jose Maria; Mateo Garcia, Antonio Manuel
    Congreso Nacional de Propiedades Mecánicas de Sólidos
    Presentation's date: 2012
    Presentation of work at congresses

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  • Characterization of precipitation kinetics of Inconel 718 superalloy by the stress relaxation technique

     Calvo Muñoz, Jessica; Cabrera Marrero, Jose Maria; Shu, Sheyu
    Materials science forum
    Date of publication: 2012
    Journal article

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    Inconel 718 is a nickel-chromium-iron superalloy which presents excellent mechanical properties at high temperatures, as well as good corrosion resistance and weldability. These characteristics can be optimized with an appropriate control of microstructural features such as grain size and precipitation. Precipitates of different nature can form in these alloys, i.e. γ’’ (a metastable metallic compound Ni3Nb), γ’ (Ni3(Ti, Al), carbides and/or δ phase (intermetallic Ni3Nb). Aging treatments are usually designed to obtain the precipitation required in order to optimize mechanical properties. However, precipitation can also appear induced by deformation and therefore interfere with hot forming operations, such as forging. Under these conditions, precipitation may lead to an increase of the loads required to carry out the process. The aim of the work was the characterization of precipitation kinetics for Inconel 718. With this purpose, stress relaxation tests were carried out at temperatures ranging from 950°C to 800°C. Moreover, different amounts of deformation were applied to the samples, prior to stress relaxation, to evaluate the effect of this variable on inducing precipitation. Some samples were quenched at different relaxation times for metallographic evaluation. The results obtained through mechanical testing, together with a proper characterization of precipitation by Scanning Electron Microscopy, were the basis for obtaining precipitation-timetemperature (PTT) diagrams after different deformation conditions.

  • EBSD study of a hot deformed austenitic stainless steel

     Mirzadeh, H.; Cabrera Marrero, Jose Maria; Najafizadeh, A.; Rodríguez Calvillo, Pablo
    Materials science and engineering A. Structural materials properties microstructure and processing
    Date of publication: 2012-01-18
    Journal article

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    The microstructural evolution of a 304 H austenitic stainless steel subjected to hot compression was studied by the electron backscattered diffraction (EBSD) technique. Detailed data about the boundaries, coincidence site lattice (CSL) relationships and grain size were acquired from the orientation imaging microscopy (OIM) maps. It was found that twins play an important role in the nucleation and growth of dynamic recrystallization (DRX) during hot deformation. Moreover, the conventional discontinuous DRX (DDRX) was found to be in charge of grain refinement reached under the testing conditions studied. Furthermore, the recrystallized fraction (X) was determined from the grain average misorientation (GAM) distribution based on the threshold value of 1.55°. The frequency of high angle boundaries showed a direct relationship with X. A time exponent of 1.11 was determined from Avrami analysis, which was related to the observed single-peak behavior in the stress–strain flow curves.

  • Equal channel angular pressing of Cu-Al bimetallic rods

     Llorca Isern, Nuria; Escobar, Ana Maria; Roca, Antoni; Cabrera Marrero, Jose Maria
    Materials science forum
    Date of publication: 2012
    Journal article

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    Coextrusion and corolling are the major processes to produce bimetallic rods, tubes and wires, the objective being to perform clad metals, bimetallic joints or seals. The aim of the present work is to produce bimetallic rods showing an ultra fine grained microstructure with enhanced properties. Bimetallic Cu-Al rods were deformed by equal channel angular pressing (ECAP) in order to study their microstructure. ECAP is an int eresting process for producing bulk materials with refined microstructure and, consequently, chan ges in physical, chemical and mechanical properties can be observed. Higher shear strength a nd dimensional stability are among the advantages of this process. A comparative experimen tal study of pure commercial copper with cylindrical inner aluminium rods of different diame ters processed by one-pass equal channel angular pressing has been carried out. The ECAP die used in this research was a 90º 2-channels intersecting angle. Electron backscattered (EBSD) a nd X-ray diffraction techniques were used for microstructure characterization (deformation, grain fragmentation and microstrain evaluation) at the interfaces and away from them. It was found that th e microstructure in the ECAP deformed Cu-Al bimetallic rods was influenced by the dimensions of the aluminium inner rod. In fact, the microstructure appeared to be much more elongated a nd refined in the samples containing smaller diameter aluminium rods.

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    Comportamiento termomecánico de un acero microaleado al Nb-V  Open access

     Cartaya, E. A.; Varela, G.; Cabrera Marrero, Jose Maria; Prado Pozuelo, Jose Manuel
    TRATER Press. Revista del tratamiento térmico
    Date of publication: 2012-06
    Journal article

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    Empleando ensayos de compresión simple en ca- liente y relajación de tensiones después de la de - formación en un dilatómetro modelo DIL805T, se obtuvieron las curvas de fluencia y relajación de dos aceros, el primero de ellos al C – Mn y otro HS- LA con idéntica composición química base, micro- aleado con Nb – V. Los ensayos de compresión simple fueron efectua- dos a temperaturas en el rango austenítico, desde 900 – 1.200 ºC y velocidades de deformación de 0.001, 0.01, 0.1, 1 y 10 s - 1 . Se obtuvieron las curvas de fluencia para las diferentes condiciones, permitien- do el estudio del efecto de los elementos microale- antes sobre la recristalización dinámica y la micro- estructura final; pudiendo comprobar mediante un análisis microestructural el efecto retardador en la cinética de recristalización que presenta el acero microaleado, el incremento en la deformación críti- ca y en la energía de activación. Se determina asi- mismo por medio del método de relajación de ten - siones la cinética de precipitación, elaborando los diagramas precipitación – temperatura – tiempo

  • The origin of microstructure inhomogeneity in Mg-3Al-1Zn processed by severe plastic deformation

     Fatemi Varzaneh, Mahmood; Zarei-Hanzaki, A.; Vaghar, R.; Cabrera Marrero, Jose Maria
    Materials science and engineering A. Structural materials properties microstructure and processing
    Date of publication: 2012-08-15
    Journal article

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    A Mg–3Al–1Zn alloy has been severely deformed by accumulative back extrusion to investigate the effects of processing parameters (temperature and deformation pass) on the microstructure homogeneity. The results indicate that the activation of different grain refinement mechanisms in magnesium may result in an inhomogeneous microstructure, i.e. a bimodal grain size distribution. However, a rapid rate of homogeneity development has been occurred through applying further subsequent passes. This has been justified considering the imposed strain reversal during accumulative back extrusion processing.

  • Effect of V on Hot Deformation Characteristics of TWIP Steels

     Reyes, Francisco; Calvo Muñoz, Jessica; Cabrera Marrero, Jose Maria; Mejía, Ignacio
    Steel research international
    Date of publication: 2012-04
    Journal article

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    Twinning induced plasticity (TWIP) steels, which rely on high Mn contents to promote twinning as the deformation mechanism, exhibit high ultimate strengths together with outstanding combinations of ultimate strength and ductility. In terms of mechanical properties, one of the most important microstructural features is grain size. The knowledge of the kinetics of recrystallization mechanisms, i.e., dynamic recrystallization (DRX) and static recrystallization (SRX), can be used in order to control the grain size of the final product by a proper rolling schedule design. The focus of this work is the characterization of the DRX kinetics of two TWIP steels. The basic composition of the steels is Fe–21Mn–0.4C–1.5Al–1.5Si, and one of them is further alloyed with 0.12% V. With this objective, compression tests were carried out at 900, 1000, and 11008C and strain rates ranging from 1 10 1 s 1 to 1 10 4 s 1. Furthermore, metallographic observation by optical microscopy (OM) was done to assess the evolution of grain size for the different deformation conditions. According to the results, the existence of V in the composition does not affect the hot flow behavior of the steel, although recrystallization fraction and recrystallized grain size decrease for the V-containing steel.

  • Modeling and prediction of hot deformation flow curves

     Mirzadeh, H.; Cabrera Marrero, Jose Maria; Najafizadeh, A.
    Metallurgical and materials transactions A-Physical metallurgy and material
    Date of publication: 2012-01
    Journal article

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    The modeling of hot flow stress and prediction of flow curves for unseen deformation conditions are important in metal-forming processes because any feasible mathematical simulation needs accurate flow description. In the current work, in an attempt to summarize, generalize, and introduce efficient methods, the dynamic recrystallization (DRX) flow curves of a 17-4 PH martensitic precipitation hardening stainless steel, a medium carbon microalloyed steel, and a 304 H austenitic stainless steel were modeled and predicted using (1) a hyperbolic sine equation with strain dependent constants, (2) a developed constitutive equation in a simple normalized stress-normalized strain form and its modified version, and (3) a feed-forward artificial neural network (ANN). These methods were critically discussed, and the ANN technique was found to be the best for the modeling available flow curves; however, the developed constitutive equation showed slightly better performance than that of ANN and significantly better predicted values than those of the hyperbolic sine equation in prediction of flow curves for unseen deformation conditions.

  • Thermal stability and microstructural behavior of ECAP processed copper

     Higuera Cobos, Oscar Fabián; Rodríguez Calvillo, Pablo; Cabrera Marrero, Jose Maria
    Conference on Material Forming
    Presentation's date: 2011-04-20
    Presentation of work at congresses

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  • Effect of V on hot deformation characteristics of TWIP steels

     Reyes Calderón, F.; Mejía, I.; Bedolla Jacuinde, A.; Calvo Muñoz, Jessica; Cabrera Marrero, Jose Maria
    International Conference on High Manganese Steels
    Presentation's date: 2011-05-18
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  • Effect of microalloying elements (B, Nb, and V) on solution heat treatment microstructure of Fe-Mn-Al-Si-C TWIP steels

     Reyes Calderón, F.; Mejía, I.; Bedolla Jacuinde, A.; Calvo Muñoz, Jessica; Cabrera Marrero, Jose Maria
    International Conference on High Manganese Steels
    Presentation's date: 2011-05-16
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  • Ultrasonics inspections and confocal microscopy to evaluate fatigue damage in fiber reinforced polymer composites

     Garcia, Vicente G.; Sala, J.; Crispi, L.; Cabrera Marrero, Jose Maria; Istúriz, Álvaro; Saez, A.; Millan, M.; Comes, C.; Trias, D.
    International Conference on Composite Materials
    Presentation's date: 2011-08
    Presentation of work at congresses

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    On this study, periodic ultrasonic inspections were performed during flexural fatigue tests, on two different composites, and under certain conditions a confocal microscope proved useful to evaluate surface damage detected by acoustic signal analysis. Rectangular bars of plain weave glass fiber/phenolic resin composite and bars of a specific sequence of carbon fiber/epoxy resin composite were subjected to four-point bending fatigue tests until reaching 20,000 cycles, but stopping every 2,000 cycles for ultrasound inspection. Software was developed to create C-scan images, but also to process each A-scan signal through one of several algorithms that helped spot internal and surface damage. The tests using the glass fiber/resin composite allowed observing the damage before failure as seen by acoustic signal analysis. The tests on the carbon fiber/resin composite showed that ultrasound can aid to pinpoint where surface damage might be occurring and where a confocal microscope can be used.

  • Characterization of the hot deformation behaviour of Nimonic 80A and 263 Ni-based superalloys

     Calvo Muñoz, Jessica; Cabrera Marrero, Jose Maria; Guerrero-Mata, M. P.; de la Garza, M.; Puigjaner, J. F.
    International Conference on Technology of Plasticity
    Presentation's date: 2011-09-29
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  • Microstructural modeling and thermomechanical analysis of an IN718 superalloy during a forging process

     Reyes, L. A.; Paramo, P. J.; Guerrero-Mata, M. P.; de la Garza, M.; Páramo, V.; Calvo Muñoz, Jessica; Cabrera Marrero, Jose Maria
    International Conference on Technology of Plasticity
    Presentation's date: 2011-09-28
    Presentation of work at congresses

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  • Hot ductility behavior of a low carbon advanced high strength steel (AHSS) microalloyed with boron

     Mejía, Ignacio; Bedolla Jacuinde, Arnoldo; Maldonado, Cuauhtémoc; Cabrera Marrero, Jose Maria
    Materials science and engineering A. Structural materials properties microstructure and processing
    Date of publication: 2011-05-24
    Journal article

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    The current study analyses the influence of boron addition on the hot ductility of a low carbon advanced high strength NiCrVCu steel. For this purpose hot tensile tests were carried out at different temperatures (650, 750, 800, 900 and 1000 ◦C) at a constant true strain rate of 0.001 s−1. Experimental results showed a substantial improvement in hot ductility for the low carbon advanced high strength steel when microalloyed with boron compared with that without boron addition. Nevertheless, both steels showed poor ductility when tested at the lowest temperatures (650, 750 and 800 ◦C), and such behavior is associated to the precipitation of vanadium carbides/nitrides and inclusions, particularly MnS and CuS particles. The fracture mode of the low carbon advanced high strength steel microalloyed with boron seems to be more ductile than the steel without boron addition. Furthermore, the fracture surfaces of specimens tested at temperatures showing the highest ductility (900 and 1000 ◦C) indicate that the fracture mode is a result of ductile failure, while in the region of poor ductility the fracture mode is of the ductile–brittle type failure. It was shown that precipitates and/or inclusions coupled with voids play a meaningful role on the crack nucleation mechanism which in turn causes a hot ductility loss. Likewise, dynamic recrystallization (DRX) which always results in restoration of ductility only occurs in the range from 900 to 1000 ◦C. Results are discussed in terms of boron segregation towards austenitic grain boundaries and second phase particles precipitation during plastic deformation and cooling.

  • Determination of the critical conditions for the initiation of dynamic recrystallization in boron microalloyed steels

     Mejía, Ignacio; Bedolla Jacuinde, Arnoldo; Maldonado, Cuauhtémoc; Cabrera Marrero, Jose Maria
    Materials science and engineering A. Structural materials properties microstructure and processing
    Date of publication: 2011-05-15
    Journal article

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    From the present research, the critical conditions associated with the onset of dynamic recrystallization (DRX) of hot deformed boron microalloyed steels were precisely determined based on changes in the strain hardening rate ( ) as a function of the flow stress. For this purpose, a low carbon steel microalloyed with four different amounts of boron (29, 49, 62 and 105 ppm) was deformed by uniaxial hot-compression tests at high temperature (950, 1000, 1050 and 1100 ◦C) and constant true strain rate (10−3, 10−2 and 10−1 s−1). Results indicate that the critical conditions for the initiation of dynamic recrystallization depend on the temperature and strain rate. In addition, both critical stress c, and critical strain εc, were noticed to decrease as boron content increased. Such a behavior is attributed to a solute drag effect by boron atoms on the austenitic grain boundaries and also to a solid solution softening effect. The critical ratios c/ p and εc/εp for all boron microalloyed steels remain fairly constant (≈0.82 and ≈0.53, respectively), such values are in agreement with those commonly reported for Al-killed, C–Mn, Nb, Nb–Ti, high carbon and stainless steels.

  • Constitutive relationships for hot deformation of austenite

     Mirzadeh, H.; Cabrera Marrero, Jose Maria; Najafizadeh, A.
    Acta materialia
    Date of publication: 2011-09
    Journal article

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    Constitutive equations were used to derive the flow stress of a 17–4 PH stainless steel during hot compression testing. Two general methods were used: (i) a conventional method of finding apparent materials constants; and (ii) a physically based approach which accounts for the dependence of the Young’s modulus and the self-diffusion coefficient of austenite on temperature. Both methods were critically discussed and some modifications and easy-to-apply methods were also introduced. The second approach was also performed for peak and critical stresses to find out the effect of dynamic recrystallization on the ideal theoretical values. The discussion of results proved that when the deformation mechanism is controlled by the glide and climb of dislocations, a constant creep exponent (n) of 5 can be used in the classical hyperbolic sine equation, and the self-diffusion activation energy can be used to describe the appropriate stress. 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  • Strain Influence on the Precipitation Kinetic Nb-V Microalloyed HSLA Steel

     Cartaya Ruesga, Elio Armando; Cabrera Marrero, Jose Maria; Prado Pozuelo, Jose Manuel
    Journal of iron and steel research international
    Date of publication: 2011-05
    Journal article

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  • Precipitation Kinetics on a Nb-V Microalloyed Steel

     Cartaya Ruesga, Elio Armando; Cabrera Marrero, Jose Maria; Prado Pozuelo, Jose Manuel
    Journal of iron and steel research international
    Date of publication: 2011-05
    Journal article

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  • Hot deformation behavior of a medium carbon microalloyed steel

     Mirzadeh, H.; Cabrera Marrero, Jose Maria; Prado Pozuelo, Jose Manuel; Najafizadeh, A.
    Materials science and engineering A. Structural materials properties microstructure and processing
    Date of publication: 2011-04-25
    Journal article

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  • Deformation behaviour of a twinning induced plasticity (TWIP) steel

     Calvo Muñoz, Jessica; Cabrera Marrero, Jose Maria; Pineda, R.; Delor, A.; Mejía, Ignacio; Bedolla Jacuinde, Arnoldo
    Metallurgia Italiana
    Date of publication: 2011-08
    Journal article

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  • Shear banding phenomenon during severe plastic deformation of an AZ31 magnesium alloy

     Cabrera Marrero, Jose Maria; S.M. Fatemi-Varzaneh, S.M.; Zarei-Hanzaki, A.
    Journal of alloys and compounds
    Date of publication: 2011-02
    Journal article

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  • Mechanical properties of different coppers processed by equal channel angular pressing

     Higuera Cobos, Oscar Fabián; Muñoz, Jairo Alberto; Cabrera Marrero, Jose Maria
    Materials science forum
    Date of publication: 2011
    Journal article

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