This work brie¯y describes and evaluates one of the most complete transformation models, which de... more This work brie¯y describes and evaluates one of the most complete transformation models, which deals with the nonisothermal decomposition of austenite. The model, that does not consider the effect of precipitation on phase transformations, has been experimentally validated in high strength low alloy steels in order to evaluate how it works for microalloyed steels, where precipitation may play an important role. It has been found that the simultaneous transformation model is able to predict with an excellent agreement in microalloyed steels the formation of microstructures consisting of ferrite plus pearlite. However, the bainite formation is not successfully described by the model. The calculations incorrectly predict the formation of martensite instead of bainite in many situations.
Making the transformation from austenite to martensite difficult is called stabilisation of auste... more Making the transformation from austenite to martensite difficult is called stabilisation of austenite, a phenomenon that occurs in many cases. The straightforward method to analyse the influence of a specific factor on the stabilisation of austenite is through its influence on the martensite start (M s ) temperature. This work outlines the use of an artificial neural network to model the M s temperature of engineering steels from their chemical composition and austenite grain size. The results are focussed on analysing the role in the stabilisation of austenite of alloying elements in steels including less common elements such as V and Nb, as well as the austenite grain size. Moreover, a physical interpretation of the results is presented.
García Valencia, Jenny;Arango Viana, Juan Carlos;Correa Rico, Oscar;Pérez González, Andrés Felipe... more García Valencia, Jenny;Arango Viana, Juan Carlos;Correa Rico, Oscar;Pérez González, Andrés Felipe;Agudelo, Víctor Hugo;Mejía Mosquera, Carlos Andrés;Casals, Sergi;López Calle, Gabriel Jaime;Patiño López, Juan David;Palacio Acosta, Carlos Alberto Validación de la Lista de ...
Low carbon 25Cr-35Ni steel (HP type steel) modified with titanium and zirconium has been produced... more Low carbon 25Cr-35Ni steel (HP type steel) modified with titanium and zirconium has been produced by centrifugal casting. The different phases present in the as cast and aged conditions were described by light optical and scanning electron microscopy with secondary electron imaging and energy dispersive spectroscopy. Results suggest that the use of titanium as a microalloying element reduces secondary precipitation during aging. Moreover, secondary precipitates in the microalloyed steel are much finer and more evenly distributed. On the other hand, zirconium oxides was found to be potential nucleation sites for primary titanium rich carbides contributing to an optimum distribution of these carbides in the tubes. These differences together with the higher stability of the titanium containing primary carbides are responsible for the improvement on ductility and creep resistance found in the present work.
The bainite start temperature B s is defined as the highest temperature at which ferrite can tran... more The bainite start temperature B s is defined as the highest temperature at which ferrite can transform by a displacive transformation. A common observation is that the bainite start temperature is very sensitive to the chemical composition, indicating that the influence of solutes is more than just thermodynamic. Empirical linear regression models have long been used to calculate the B s in a limited range of compositions. This paper attempts to create an empirical model of wider applicability and higher accuracy by means of neural networks. The results are compared with those calculated using the thermodynamic theory for bainite transformation, revealing that in general this theory agrees with the experimental results, but some discrepancies can still be found when the alloys are heavily alloyed.
A theoretical design procedure based on phase transformation theory alone has been successfully a... more A theoretical design procedure based on phase transformation theory alone has been successfully applied to design steels with a microstructure consisting of a mixture of bainitic ferrite and retained austenite. Using thermodynamics and kinetics models, a set of four carbide free bainitic steels with a 0.3 wt-% carbon content were designed and manufactured following a thermo-mechanical treatment consisting of hot rolling and two-step cooling. The designed steels present significant combinations of strength and ductility, with tensile strengths ranging from 1500 to 1800 MPa and total elongations over 15%. However, a carbon content of 0.3 wt% is still high for in-use properties such as weldability. In this sense, a reduction in the average carbon content of advanced bainitic steels was proposed. Improved bainitic steels with a carbon content of 0.2 wt% reached combinations of strength and ductility comparable to those in TRIP assisted steels.
... The authors would also like to express their special acknowledgement to Mrs. J. Drillet for h... more ... The authors would also like to express their special acknowledgement to Mrs. J. Drillet for her TEM–PEELS assistance and Dr. T. Iung for helpful discussions. References. [1] HG Read, Scripta Mater. 37 (1997), p. 151. ... [12] T. Iung, J. Drillet, A. Couturier, C. Olier, Int. Conf. ...
A new model for the overall transformation kinetics of bainite has been developed. Based on the d... more A new model for the overall transformation kinetics of bainite has been developed. Based on the displacive mechanism for the bainite transformation, the model distinguishes between the nucleation kinetics of bainitic ferrite in prior austenite grain boundaries, and at tips and adjacent positions of previously formed subunits. Some geometrical aspects of the development of the transformation have been used in the modelling. The theoretical results show that the tendencies obtained with the model are in agreement with experience. The second part of this work deals with the experimental validation of this model.
A través de la presentación y discusión de algunas de las más destacadas contribuciones que la so... more A través de la presentación y discusión de algunas de las más destacadas contribuciones que la sociología contemporánea plantea sobre la configuración del sistema mundo, se busca identificar ciertos elementos que contribuyan a la construcción de perspectivas analíticas que integren los modos y las formas de acercamiento que las Ciencias Sociales poseen para la comprensión de las dinámicas y procesos sociales de orden global. Para tal efecto, se expondrán y cuestionaran de manera sintética los puntos de vista de autores centrales en la configuración de campo de estudios sociológicos, tales como Peter Berger, Jürgen Habermas, Niklas Luhmann, Pierre Bourdieu, Alain Touraine y Anthony Giddens. Con esta disertación se espera contribuir hacia la construcción de miradas integradoras sobre las transformaciones sociopolíticas del convulsionado mundo contemporáneo, esgrimiendo algunos puntos de encuentro entre las disciplinas.
The volume fraction of M23C6 carbides precipitated during cooling in an X45Cr13 stainless steel h... more The volume fraction of M23C6 carbides precipitated during cooling in an X45Cr13 stainless steel has been estimated from the thermoelectric power (TEP) measurement. Likewise, the different contributions to the TEP measurement of samples cooled at different cooling rates have been determined.
García Valencia, Jenny;Arango Viana, Juan Carlos;Correa Rico, Oscar;Pérez González, Andrés Felipe... more García Valencia, Jenny;Arango Viana, Juan Carlos;Correa Rico, Oscar;Pérez González, Andrés Felipe;Agudelo, Víctor Hugo;Mejía Mosquera, Carlos Andrés;Casals, Sergi;López Calle, Gabriel Jaime;Patiño López, Juan David;Palacio Acosta, Carlos Alberto Validación de la Lista de ...
It has been broadly reported that determination of the martensite start temperature in steels, M ... more It has been broadly reported that determination of the martensite start temperature in steels, M s , requires a complete description of their chemical composition. Recently, several neural networks models considering both chemical composition and austenite grain size (AGS) have been developed. Such models predict a moderate dependence of M s with AGS. The present work examines the validity of existing neural network models, but focusing on fine AGS (below 5 m).
This work brie¯y describes and evaluates one of the most complete transformation models, which de... more This work brie¯y describes and evaluates one of the most complete transformation models, which deals with the nonisothermal decomposition of austenite. The model, that does not consider the effect of precipitation on phase transformations, has been experimentally validated in high strength low alloy steels in order to evaluate how it works for microalloyed steels, where precipitation may play an important role. It has been found that the simultaneous transformation model is able to predict with an excellent agreement in microalloyed steels the formation of microstructures consisting of ferrite plus pearlite. However, the bainite formation is not successfully described by the model. The calculations incorrectly predict the formation of martensite instead of bainite in many situations.
Making the transformation from austenite to martensite difficult is called stabilisation of auste... more Making the transformation from austenite to martensite difficult is called stabilisation of austenite, a phenomenon that occurs in many cases. The straightforward method to analyse the influence of a specific factor on the stabilisation of austenite is through its influence on the martensite start (M s ) temperature. This work outlines the use of an artificial neural network to model the M s temperature of engineering steels from their chemical composition and austenite grain size. The results are focussed on analysing the role in the stabilisation of austenite of alloying elements in steels including less common elements such as V and Nb, as well as the austenite grain size. Moreover, a physical interpretation of the results is presented.
García Valencia, Jenny;Arango Viana, Juan Carlos;Correa Rico, Oscar;Pérez González, Andrés Felipe... more García Valencia, Jenny;Arango Viana, Juan Carlos;Correa Rico, Oscar;Pérez González, Andrés Felipe;Agudelo, Víctor Hugo;Mejía Mosquera, Carlos Andrés;Casals, Sergi;López Calle, Gabriel Jaime;Patiño López, Juan David;Palacio Acosta, Carlos Alberto Validación de la Lista de ...
Low carbon 25Cr-35Ni steel (HP type steel) modified with titanium and zirconium has been produced... more Low carbon 25Cr-35Ni steel (HP type steel) modified with titanium and zirconium has been produced by centrifugal casting. The different phases present in the as cast and aged conditions were described by light optical and scanning electron microscopy with secondary electron imaging and energy dispersive spectroscopy. Results suggest that the use of titanium as a microalloying element reduces secondary precipitation during aging. Moreover, secondary precipitates in the microalloyed steel are much finer and more evenly distributed. On the other hand, zirconium oxides was found to be potential nucleation sites for primary titanium rich carbides contributing to an optimum distribution of these carbides in the tubes. These differences together with the higher stability of the titanium containing primary carbides are responsible for the improvement on ductility and creep resistance found in the present work.
The bainite start temperature B s is defined as the highest temperature at which ferrite can tran... more The bainite start temperature B s is defined as the highest temperature at which ferrite can transform by a displacive transformation. A common observation is that the bainite start temperature is very sensitive to the chemical composition, indicating that the influence of solutes is more than just thermodynamic. Empirical linear regression models have long been used to calculate the B s in a limited range of compositions. This paper attempts to create an empirical model of wider applicability and higher accuracy by means of neural networks. The results are compared with those calculated using the thermodynamic theory for bainite transformation, revealing that in general this theory agrees with the experimental results, but some discrepancies can still be found when the alloys are heavily alloyed.
A theoretical design procedure based on phase transformation theory alone has been successfully a... more A theoretical design procedure based on phase transformation theory alone has been successfully applied to design steels with a microstructure consisting of a mixture of bainitic ferrite and retained austenite. Using thermodynamics and kinetics models, a set of four carbide free bainitic steels with a 0.3 wt-% carbon content were designed and manufactured following a thermo-mechanical treatment consisting of hot rolling and two-step cooling. The designed steels present significant combinations of strength and ductility, with tensile strengths ranging from 1500 to 1800 MPa and total elongations over 15%. However, a carbon content of 0.3 wt% is still high for in-use properties such as weldability. In this sense, a reduction in the average carbon content of advanced bainitic steels was proposed. Improved bainitic steels with a carbon content of 0.2 wt% reached combinations of strength and ductility comparable to those in TRIP assisted steels.
... The authors would also like to express their special acknowledgement to Mrs. J. Drillet for h... more ... The authors would also like to express their special acknowledgement to Mrs. J. Drillet for her TEM–PEELS assistance and Dr. T. Iung for helpful discussions. References. [1] HG Read, Scripta Mater. 37 (1997), p. 151. ... [12] T. Iung, J. Drillet, A. Couturier, C. Olier, Int. Conf. ...
A new model for the overall transformation kinetics of bainite has been developed. Based on the d... more A new model for the overall transformation kinetics of bainite has been developed. Based on the displacive mechanism for the bainite transformation, the model distinguishes between the nucleation kinetics of bainitic ferrite in prior austenite grain boundaries, and at tips and adjacent positions of previously formed subunits. Some geometrical aspects of the development of the transformation have been used in the modelling. The theoretical results show that the tendencies obtained with the model are in agreement with experience. The second part of this work deals with the experimental validation of this model.
A través de la presentación y discusión de algunas de las más destacadas contribuciones que la so... more A través de la presentación y discusión de algunas de las más destacadas contribuciones que la sociología contemporánea plantea sobre la configuración del sistema mundo, se busca identificar ciertos elementos que contribuyan a la construcción de perspectivas analíticas que integren los modos y las formas de acercamiento que las Ciencias Sociales poseen para la comprensión de las dinámicas y procesos sociales de orden global. Para tal efecto, se expondrán y cuestionaran de manera sintética los puntos de vista de autores centrales en la configuración de campo de estudios sociológicos, tales como Peter Berger, Jürgen Habermas, Niklas Luhmann, Pierre Bourdieu, Alain Touraine y Anthony Giddens. Con esta disertación se espera contribuir hacia la construcción de miradas integradoras sobre las transformaciones sociopolíticas del convulsionado mundo contemporáneo, esgrimiendo algunos puntos de encuentro entre las disciplinas.
The volume fraction of M23C6 carbides precipitated during cooling in an X45Cr13 stainless steel h... more The volume fraction of M23C6 carbides precipitated during cooling in an X45Cr13 stainless steel has been estimated from the thermoelectric power (TEP) measurement. Likewise, the different contributions to the TEP measurement of samples cooled at different cooling rates have been determined.
García Valencia, Jenny;Arango Viana, Juan Carlos;Correa Rico, Oscar;Pérez González, Andrés Felipe... more García Valencia, Jenny;Arango Viana, Juan Carlos;Correa Rico, Oscar;Pérez González, Andrés Felipe;Agudelo, Víctor Hugo;Mejía Mosquera, Carlos Andrés;Casals, Sergi;López Calle, Gabriel Jaime;Patiño López, Juan David;Palacio Acosta, Carlos Alberto Validación de la Lista de ...
It has been broadly reported that determination of the martensite start temperature in steels, M ... more It has been broadly reported that determination of the martensite start temperature in steels, M s , requires a complete description of their chemical composition. Recently, several neural networks models considering both chemical composition and austenite grain size (AGS) have been developed. Such models predict a moderate dependence of M s with AGS. The present work examines the validity of existing neural network models, but focusing on fine AGS (below 5 m).
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