Modelado termo-metalúrgico del enfriamiento de una fundición nodular

Tesis (DCI)--FCEFN-UNC, 2012En esta tesis se desarrolla un nuevo modelo termo-metalúrgico de los cambios de fase difusionales de la austenita que ocurren durante el enfriamiento continuo de una fundición nodular. El modelo se implementa en un programa de elementos finitos y se aplica en un estudio paramétrico y en la simulación del enfriamiento de una fundición nodular eutéctica colada en dos probeteros: uno de sección circular y otro cuadrada. Los resultados numéricos obtenidos y su comparación con los resultados experimentales ponen de manifiesto la necesidad de modelar los procesos termometal úrgicos en múltiples escalas y la validez de algunas de las hipótesis propuestas en esta tesis.Fil: Carazo Rodríguez, Fernando Diego. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.

About Equilibrium Mode Ruling Ferritic Transformation in Low-Alloy SGI

Ferrite precipitating around the graphite nodules shaping the typical bull’s-eye microstructure could grow under negligible partitioning local equilibrium or under paraequilibrium conditions, as both imply that ferrite inherits the composition of the parent austenite. The first mechanism has been rejected by other researchers by means of simple calculations of the silicon spike width necessary for local equilibrium conditions to take place. Nevertheless, experimental analyses are necessary to verify this conclusion. In this study, transmission electron microscopy has been used to assess the presence of a silicon spike in front of the growing ferrite interface. The outcome allowed the authors to confirm that a paraequilibrium mode governs the transformation, supporting the conclusions of previous calculations. In addition, some issues about ferrite growth modeling are discussed.Fil: García, Laura Noel. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Mecánica Aplicada; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Carazo, Fernando Diego. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Mecánica Aplicada; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Boeri, Roberto Enrique. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Mecánica Aplicada; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentin

Metamodelling the hot deformation behaviour of titanium alloys using a mean-field approach

During the thermomechanical processing of titanium alloys in the β-domain, the β-phase undergoes restoration phenomena. This work describes them by a mean-field physical model that correlates the flow stress with the microstructural evolution. To reduce the computational time of process simulations, metamodels are developed for specific outputs of the mean-field physical model using Artificial Neural Network (ANN) and Decision Tree Regression (DTR). The performance of the obtained metamodels is evaluated in terms of the coefficient of determination (R²), the root-mean-square error (RMSE), and the mean relative error (MRE). No significant difference was observed between R2training and R2testing, meaning that all the metamodels correctly generalise the overall behaviour of the outputs for a wide range of inputs. The evolution of the metamodel outputs is compared with the model predictions in two different situations: 1) at a constant strain rate and temperature, and 2) during Finite Element (FE) simulations of the hot deformation of a hat-shaped sample, where temperature and effective strain rate vary at each element during deformation. The evolution of the outputs at constant and non-constant strain rates and temperature demonstrated the robustness of the metamodels in predicting the heterogeneous deformation within a workpiece. The computational time required by the metamodels to calculate selected outputs can be more than 100 times less than that of the model itself at a constant strain rate using MATLAB® and up to 19% less when coupled with FE simulations. The simulation results combined with microstructural analysis are used to visualise the different restoration mechanisms occurring in different regions of the hat-shaped sample as a function of the local thermomechanical history. The changes in strain rate and temperature during deformation influence the evolution of the wall dislocation density and the immobilisation rate of mobile dislocations at subgrain boundaries, leading to different kinetics of microstructure evolution.Fil: Miller Branco Ferraz, Franz. Graz University Of Technology.; AustriaFil: Sztangret, Lukasz. AGH University of Science and Technology; PoloniaFil: Carazo, Fernando Diego. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Mecanica Aplicada; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Buzolin, Ricardo Henrique. Graz University Of Technology.; AustriaFil: Wang, Peng. Graz University Of Technology.; AustriaFil: Szeliga, Danuta. AGH University of Science and Technology; PoloniaFil: dos Santos Effertz, Pedro. No especifíca;Fil: Macio, Piotr. AGH University of Science and Technology; PoloniaFil: Krumphals, Alfred. No especifíca;Fil: Poletti, Maria Cecilia. Graz University Of Technology.; Austri

Reply to the Letter to the Editor. Regarding the Paper "Stable Eutectoid Transformation in Nodular Cast Iron: Modeling and Validation" F. D. Carazo, P. M. Dardati, D. J. Celentano, and L. A. Godoy: MMTA 2017

Respuesta a una carta al Editor del Journal o discusión planteada por el Prof. Jacques Lacaze al artículo de mi autoría "Stable eutectoid transformation in nodular cast iron: modeling and validation" (DOI: http://dx.doi.org/10.1007/s11661-016-3827-6)Fil: Carazo, Fernando Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan; Argentin

Determination of the PLE/NPLE transition boundary in the Fe-C-Si system: Application to ferrite growing in bull-eye structure in spheroidal graphite cast irons under continuous cooling conditions

The ferrite growth in SG cast irons is expected to take place at temperatures lower than T_α, when C_α/γ−C_α/G turns to positive values. Nevertheless, once the alloy reaches T_αo it could grow driven by C_γ/α−C_γ. In spite of the presence of C_γ/α−C_γ at temperatures lower than T_αo, no ferrite growth is evidenced for intermediate temperatures between T_αo and T_α under continuous cooling conditions. Carbon flux driven by C_γ/α−C_γ recalls the one that rules proeutectoid ferrite in steels. Nevertheless, unlike steels, in case of SG cast irons, silicon and alloying elements (Mn and Cu are the more common ones) develop a segregation profile that is inherited by austenite; later on these profiles are acquired by the final microstructure since no diffusion of alloying elements is expected to take place during solid-state transformations [1]. Considering all this, growth in SG cast irons was studied at austenite in contact with graphite, as it is accepted to start right there [1,2]. To set the composition at this point for the different samples, measured microsegregation profiles from a previous work [3] were employed. On the other hand, Thermo-Calc software (TC) was used for calculating carbon at the beginning of the solid-state transformation. Later, isopleth FeCSi isotherm sections were built using TC for determining the transition temperatures from – slow– partitioning local equilibrium (PLE) to –fast– negligible partitioning local equilibrium (NPLE) [4]. These constructions were necessary since no data was available neither for the temperature range of interest in SG cast irons and nor for the high silicon contents registered at austenite in contact with graphite. In the calculation of these transition temperatures is the answer to the absence of ferrite growth during the referenced temperature gap for continuous cooling conditions. This should be taken into account when developing solid-state growth models to get a more accurate description of ferrite growth during continuous cooling in SG cast irons. In addition, an explanation for the pearlite promoting effect of alloying elements is proposed.Fil: García, Laura Noel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Mecanica Aplicada; ArgentinaFil: Carazo, Fernando Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Mecanica Aplicada; ArgentinaXLVII International Conference on Computer Coupling of Phase Diagrams and ThermochemistryJuriquillaMéxicoCentro de Ingeniería y Desarrollo IndustrialCentro de Tecnología AvanzadaTexas A&M University. Material Science & EngineeringCentro de Investigación en Materiales Avanzado

Metastable Eutectoid Transformation in Spheroidal Graphite Cast Iron: Modeling and Validation

This paper presents a new microstructural model of the metastable eutectoid transformation in spheroidal graphite cast irons. The model takes into account the nucleation and growth of pearlite nodules. The nucleation is assumed to be continuous and dependent on the metastable undercooling associated with the upper limit of the three-phase field, while the growth rate is considered to be ruled by the silicon partitioning between ferrite and cementite at the pearlite/austenite front. The initial conditions for the metastable transformation are obtained from a microstructural simulation of solidification, graphite growth, and stable eutectoid transformation. These microstructural models are coupled with the thermal balance solved at a macroscopic level via the finite element method. The experimental validation of the metastable eutectoid model achieved by comparison with measured values of ferrite, graphite, and pearlite fractions at the end of the cooling process demonstrates the sound predictive capabilities of the proposed model

Ferrite Growth During Cooling Through the Ferrite-Austenite-Graphite Field in SGI

This investigation examines the growth of ferrite during the cooling of spheroidal graphite cast irons through the ferrite-austenite-graphite phase field as conditioned by the partitioning of Silicon. Two different melts are examined. Ferrite growth was assumed to take place under paraequilibrium conditions. The study involves the measurement of the temperature of ferrite precipitation start under slow cooling conditions by DSC. Thermo-Calc was used to calculate the equilibrium concentration of Si at the ferrite precipitation start temperature. Calculated Si concentrations are compared to microsegregation profiles measured on the same alloys in a previous study. The results led to conclude that partitioning of Silicon does not represent a constraint for ferrite to grow between the upper and lower limits of the three-phase field, contradicting some of the existing literature.Fil: García, Laura Noel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Mecanica Aplicada; ArgentinaFil: Carazo, Fernando Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Mecanica Aplicada; ArgentinaFil: Boeri, Roberto Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina. Universidad Nacional de Mar del Plata; Argentin

The transition from stable to metastable system and its relation with the ferrite halo extension in SG cast irons

Microsegregations of alloying elements developed during solidification are known to affect solid state transformations in spheroidal graphite cast irons. However, no clear relation between them and the presence and extension of ferrite halos has been established until now. The aim of the present work is to expose how the microsegregations of Si, Mn and Cu influence in the transition from stable to metastable system during solid state transformations and how the extension of the ferrite halo is affected accordingly. The study was carried out on samples cast at a cooling rate of 20 K/min, which allowed the diffusion of carbon under equilibrium conditions.Fil: García, Laura Noel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Mecanica Aplicada; ArgentinaFil: Carazo, Fernando Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Mecanica Aplicada; ArgentinaFil: Dardati, Patricia Mónica. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Departamento de Ingeniería Mecanica; Argentin

Thermomechanical–microstructural modelling of nodular cast iron solidification

This paper presents a thermomechanical–microstructural formulation for the analysis of the solidification process of nodular cast irons of eutectic composition. This formulation is defined in a finite strain thermoplasticity framework considering multinodular microstructure based liquid– solid phase change effects. The performance of this model is evaluated in the analysis of a solidification test for which some laboratory measurements are available. Computed temperature and displacement evolutions together with final values of austenite and graphite volumetric fractions and density of graphite nodules are all found to reasonably agree with the corresponding experimental measurements. This analysis illustrates the possibility of tackling different coupled and complex phenomena occurring in casting problems.Fil: Celentano, Diego Javier. Pontificia Universidad Catolica de Chile. Escuela de Ingeniería. Departamento de Ingeniería Mecanica y Metalurgica; ChileFil: Dardati, Patricia Mónica. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Departamento de Ingeniería Mecanica; ArgentinaFil: Carazo, Fernando Diego. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Departamento de Ingeniería Mecanica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Godoy, Luis Augusto. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Estructuras; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Effective properties of nodular cast-iron: A multi-scale computational approach

A numerical approach based on a computational constitutive multi-scale model is used in this work to predict the effective Young’s modulus and Poisson’s ratio of a pearlitic nodular cast iron. The Representative Volume Element (RVE) is defined based on a set of micrographs acquired from an optical device. For each micrograph, two RVE with different shape, rectangular and hexagonal, are defined. The volume fraction of graphite and metal matrix and the boundary of each object were identified on each RVE by using a procedure of image enhanced and segmentation. The set of RVE obtained was meshed with triangular finite elements. The numerical results obtained with rectangular and hexagonal RVE are compared with results obtained by means of an analytical expression. The influence of graphite fractions, aspect ratios and nodularity are investigated. The results show that graphite fraction has the largest influence on the effective modulus E. This feature is independent of the external shape of the RVE. Only one multi-scale model show a good agreement with the analytical expression in the effective modulus E. Also, the influence of the graphite volume fraction on the effective Poisson’s ratio is investigated by means of multi-scale simulation.Fil: Carazo, Fernando Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Mecanica Aplicada; ArgentinaFil: Giusti, Sebastian Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Departamento de Ingeniería Civil; ArgentinaFil: Boccardo, Adrian Dante. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Departamento de Ingeniería Civil; ArgentinaFil: Godoy, Luis Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentin