Browsing by Author "Jimbert, Pello"
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Item Different Phenomena Encountered during Dilatometry of Low-density Steels(2021-11-22) Jimbert, Pello; Guraya, Teresa; Kaltzakorta, Idurre; Gutiérrez, Teresa; Elvira, Roberto; Tafaghodi Khajavi, Leili; CIRMETALIn recent decades, highly alloyed low-density steels are being developed to reduce the weight of different automotive parts. Dilatometry can be a very useful experimental technique to understand phase transformations during heating or cooling of new low-density steel alloys. When performing dilatometry measurements some assumptions are made such as the homogeneity of the sample material tested during the experiment. In this study, dilatometry tests were performed for two different low-density steels, and the variations of the composition between the surface and the inner part of the sample were analyzed. The migration of manganese by diffusion from the interior of the samples and finally its evaporation on the surface under vacuum were observed. This compositional gradient generated in the samples may influence the veracity and interpretation of the results obtained in dilatometry when working with high manganese steel alloys. The detachment of surface grains created by this compositional change near the surface of the samples is also investigated.Item Evolution of Microstructure during Isothermal Treatments of a Duplex-Austenitic 0.66C11.4Mn.9.9Al Low-Density Forging Steel and Effect on the Mechanical Properties(Multidisciplinary Digital Publishing Institute (MDPI), 2021-01-26) Kaltzakorta, Idurre; Gutierrez, Teresa; Elvira, Roberto; Jimbert, Pello; Guraya, TeresaIn the last decades, low-density steels for forging have increasing interest in the automotive industry, and good mechanical properties are required for their real application. This paper describes the results obtained for a 0.66C11.4Mn9.9Al duplex austenitic low-density steel after applying a set of isothermal treatments at different combinations of time and temperature, aimed to promote kappa carbide precipitation, and improve the mechanical properties obtained with a water quenching treatment. The effects of the different isothermal treatments on the microstructure and on the mechanical properties have been analyzed and compared to those obtained from a quenching heat treatment. We found that isothermal treatments in the range temperature between 550–750 °C promoted the profuse precipitation of coarse kappa carbides at grain boundaries, which dramatically reduced the ductility of the alloy, whereas a traditional quenching treatment resulted in a better combination of ductility and mechanical strength.Item Manufacturing and forging issues encountered while upscaling 1.3C30Mn10Al-austenitic and 0.65C12Mn-duplex low-density steels(2021-07) Kaltzakorta, Idurre; Gutierrez, Teresa; Elvira, Roberto; Jimbert, Pello; Guraya, Teresa; CIRMETALDifficulties found when manufacturing and forging two low density steels in different scales are described in this work. Austenitic and duplex low-density steels have attracted a lot of interest due to their good combination of mechanical properties and density reduction. In this work, the fabrication of 1.3 C30Mn10Al austenitic low-density steel and 0.65 C12Mn10Al duplex low-density steel have been studied. The scaling up of the manufacturing process from 1 Kg to 35 Kg ingots of both materials and the subsequent hot forging of the ingots is described, showing the difficulties encountered during the production and transformation of these steels. Only the small ingots were successfully forged, but not the larger ones, showing the important differences in the forging properties depending on the geometry and dimensions of the final part to be forged, and the homogenization temperatures. The possible causes of this scale dependence are proposed from the experimental results obtained, as well as from the hot axial compression tests and the thermodynamic simulations carried out.Item Material Fracture Life Prediction Under High Temperature Creep Conditions Using Support Vector Machines And Artificial Neural Networks Techniques(Institute of Electrical and Electronics Engineers Inc., 2021) Martinez, Roberto Fernandez; Jimbert, Pello; Callejo, Lorena M.; Barbero, Jose Ignacio; CIRMETAL; Tecnalia Research & Innovation; PROMETALOne of the most applied materials to manufacture critical components in power plants are martensitic steels due to their high creep and oxidation resistance. In this work, the fracture life of martensitic steels that are designed based on the P92 standard is modeled in order to better understand the relation between its service life and its composition and its thermal treatment. This feature is usually studied by performing creep tests, although carrying out tests of this type are really cost and time consuming. To solve this problem, a multivariate analysis and a training-testing model methodology were performed using a dataset formed by 344 creep tests with the final goal of obtaining a model to predict the fracture life of the material based on several nonlinear techniques like support vector machines and artificial neural networks. Once the models were defined based on predicting with the better generalization capability to cover the whole scenario of the problem, those were compared to determine which one was the most accurate among them. Finally, it was concluded that the model's performance using the proposed methodology based on artificial neural networks got the most accurate results, achieving low errors of approximately 6.14% when predicting creep behavior under long service times.Item Material Fracture Life Prediction Using Linear Regression Techniques Under High Temperature Creep Conditions(Springer Nature, 2019-10-22) Fernandez Martinez, Roberto; Jimbert, Pello; Barbero, Jose Ignacio; Callejo, Lorena M.; Somocueto, Igor; Nyström, Ingela; Hernández Heredia, Yanio; Milián Núñez, Vladimir; PROMETAL; CIRMETAL; Tecnalia Research & Innovation9–12% Cr martensitic steels are widely used for critical components of new, high-efficiency, ultra-supercritical power plants because of their high creep and oxidation resistances. Due to the time consuming effort of obtaining creep properties for new alloys under high temperature creep conditions, in both short-term and long-term testing, it is often dealt with simplified models to assess and predict the future behavior of some materials. In this work, the total time to produce the material fracture is predicted according to models obtained using several linear techniques, since this property is really relevant in power plants elements. These models are obtained based on 344 creep tests performed on modified P92 steels. A multivariate analysis and a feature selection were applied to analyze the influence of each feature in the problem, to reduce the number of features simplifying the model and to improve the accuracy of the model. Later, a training-testing validation methodology was performed to obtain more useful results based on a better generalization to cover every scenario of the problem. Following this method, linear regression algorithms, simple and generalized, with and without enhanced by gradient boosting techniques, were applied to build several linear models, achieving low errors of approximately 6.75%. And finally, among them the most accurate model was selected, in this case the one based on the generalized linear regression technique.Item New chromium steel grade for creep applications(2022-10-11) Callejo, Lorena M; Barbero, José Ignacio; Serna-Ruiz, Mónica; Eguizabal, David; Martinez, Roberto Fernandez; Jimbert, Pello; Calleja-Saenz, Beatriz; López, Alejandra; Tecnalia Research & Innovation; CIRMETAL; PROMETAL; SGIn this study, a novel Chromium steel grade (COIN2) is produced as a result of a new steel composition and an innovative heat treatment. This new steel grade COIN2 evolves from the P92 steel grade and other novel steel grade recently created by the authors (COIN), and represents an enhancement of hardness, tensile properties, and creep behaviour with respect to them, which validates the metallurgical strategy used for further research in order to increase the efficiency of power plants and thus reduce the CO2 emissions. The characterization reveals a significant property improvement with the innovative thermal treatment, contributing to the production of a novel and more competitive steel grade for creep applications.Item Novel creep steel developed through innovative composition and thermal treatment(2021) Callejo, Lorena M.; Barbero, José Ignacio; Serna-Ruiz, Mónica; Eguizabal, David; Arregi, Bernaitz; Fernandez Martinez, Roberto; Jimbert, Pello; Calleja-Saenz, Beatriz; López, Alejandra; Tecnalia Research & Innovation; CIRMETAL; PROMETAL; SG; EXTREMATThe present investigation refers to the improvement of tensile properties, hardness, and creep resistance obtained from a high-chromium novel steel grade formulated by the combination of innovative steel composition and heat treatment. The novel steel grade has evolved from the P92 steel grade, and shows a better behaviour than that offered by the P92 steel grade, thus representing a promising metallurgical strategy for increasing the efficiency of power plants, and subsequently reducing the CO2 emissions.