Gonzalez-Ojeda, Roberto

Main Affiliation

Facultad de Ingeniería - CampCM

Preferred name

Official Name

Gonzalez Ojeda, Roberto

ORCID

0000-0003-2319-1631

Researcher ID

DTL-2716-2022

Scopus Author ID

56314856300

Now showing 1 - 10 of 38

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Warm-stamping mechanical behavior and microstructural characterization of Al-Si metal sheets using water refrigerated tooling
(IEEE, 2026-01-11)
P, Estrada-Warn
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GJ, Garcia-Santibañez
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M, Jauregui-Pablos
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S, Vazquez-Gomez-Orduña
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Gonzalez-Ojeda, Roberto
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Ultrafine-grain Steels: Mechanical Behavior
(2016)
Quintana Hernández, María José
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Gonzalez-Ojeda, Roberto
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MARÍA JOSÉ QUINTANA HERNÁNDEZ;576914
In recent years, both the steelmaking industry and laboratories in different parts of the world, have shown an increasing interest in reaching an industrial-level production of ultrafine grained steels (also known as ultrafine ferrite), which have a grain size d lower than 5 μm, and enhanced mechanical resistance and fracture toughness. At room temperature, the capacity of the material to be deformed during bending or drawing operations (typical of requirements for automotive parts applications) depends on the interaction of a hard and a soft phase in the microstructure. On the other hand, at high temperatures, these steels may show superplastic behavior if deformed at a precise combination of temperature and strain rate.
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Machinability Improvement Through Heat Treatment In 8620 Low-Carbon Alloyed Steel
(2009)
Verdeja, Luis Felipe
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Verdeja, José Ignacio
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Gonzalez-Ojeda, Roberto
The effect of different heat treatments is evaluated on SAE 8620 low-carbon alloyed steel by means of drilling tests. Improving machinability through prior heat treatment in steels used for nitro-carburizing surface treatments is very important in the manufacturing of large series of parts, due to its impact in production costs. This is the case for the commonly used SAE 8620 grade, in its carburized and quenched and tempered state, for the production of gears, shafts and other transmission box components for the automobile industry. The machinability of the steel, determined by simple drilling tests (which are typical in industry labs), is a function of microstructure, which is determined by the state in which the steel is received and/or heat treatments prior to carburizing. This work shows that by employing some inter-critic annealing treatments, followed by sub-critic isothermal ones, the machinability of 8620 steel can be improved by ∼16% over the typical as-received cold drawn state.
Scopus© Citations 6 60 2
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Superplastic HSLA Steels: Microstructure and Failure
(2013)
Fernández, Sara
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García García, José Ovidio
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Verdeja González, Luis Felipe
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Verdeja González, José Ignacio
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Quintana, María José
Certain materials can show superplasticity when traction tested at temperatures higher than 50% of their melting point and with low strain rates ( < 10−2 s−1), showing very high elongations (>100%) without localized necking and mainly intergranular fractures. This behavior requires that the starting grain size is small (<10 μm) so the flow of matter can be non-homogeneous (sliding and rotating of the grain boundaries, accommodated by diffusion). This work presents the superplastic characteristic of shipbuilding steel deformed at 800 °C and a strain rate slower than 10−3 s−1. The fine grain size (5 μm) is obtained when using Nb as a microalloying element and manufactured by controlled rolling processes (three stages). After the superplastic deformation, the steel presents mixed fractures: by decohesion of the hard (pearlite and carbides) and ductile (ferrite) phases and by intergranular sliding of ferrite/ferrite and ferrite/pearlite, just as it happens in stage III of the creep behavior. This is confirmed through the Ashby–Verrall model, according to which the dislocation creep (power-law creep) and diffusion creep (linear-viscous creep) occur simultaneously.
Scopus© Citations 4 7 1
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Effect of pressure in the microstructure of die cast Al-8.5Si-3.5cu alloys
(2014)
Barbés Fernández, Miguel Ángel
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Verdeja González, José Ignacio
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Quintana, María José
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Verdeja González, Luis Felipe
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Gonzalez-Ojeda, Roberto
The microstructure of Pressure Die Casting of an Al-8.5 Si-3.5 Cu alloy used for clean room tiles shows amount of constituents (eutectic and Si phases) that do not correspond to the ones indicated by the phase diagram. Furthermore, there are differences in amount of constituents between the core and the surface zones of parts produced by this process. The work presents quantitative microstructural analysis of this type of industrially produced part, and as a possible cause for these differences, simulations of the effect of pressure on the eutectic (temperature and chemical composition) in the Al-Si system. As the production rate of these parts is very high, and solidification is very fast, microstructural heterogeneity may be related to local entrapment of gasses unable to escape during casting.
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High temperature mechanical behavior and microstructural evolution of 304 stainless steel
(2010-05)
Quintana Hernández, María José
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Gonzalez-Ojeda, Roberto
The use of stainless steel at very high temperatures requires a detailed study of stress-strain and microstructure relationships. The tests made with a 304 type stainless steel are presented in order to study tensile properties at both 700 and 850oC, as well as microstructure characteristic such as austenite grain size (predominant phase in this steel), twinning and carbide M23C6 precipitates distribution and size, comparing them also to room temperature data. Though the resistance is reduced in considerable amount, the results indicate that the time the samples are maintained at the test temperature is a critical factor in the stress-strain curve, which is related to the presence of twins and its different concentration at the core or exterior part of the sample, as well as the amount of carbide precipitates at the interior or borders of the austenite crystals.
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Presintering of TiCN-TiC-WC-Cr 3 C 2 -Ni cermets under N 2 -H 2 atmospheres
(2017)
López-Ezquerra, Belén
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Gonzalez-Ojeda, Roberto
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Iparraguirre, I.
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Rodríguez, N.
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Sánchez-Moreno, José Manuel
C/N ratios in TiCN-TiC-WC-Cr3C2-Ni cermets can be intentionally modified by changing the composition of the presintering atmosphere. This affects not only the sinterability but also the final microstructure of these materials. Melting occurs at lower temperatures as the nitrogen content of the presintering atmosphere rises. However, the final densities are lower due to the precipitation of free carbon. Grain growth of the carbonitride phase is accelerated in samples presintered in N2 due to the activation of solution reprecipitation kinetics. Finally, the precipitation of the Cr-rich M7C3 carbide can also be controlled by the appropriate selection of the presintering atmosphere up to 7.8 wt.% Cr contents. © 2016 Elsevier Ltd
Scopus© Citations 14 36 1
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Mechanical properties of newly developed TiB2 based cermets
(1997)
Gonzalez-Ojeda, Roberto
23 2
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New binder phases for the consolidation of TiB2 hardmetals
(1996)
Gonzalez-Ojeda, Roberto
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Barandika, M.G.
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Oña, D.
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Sánchez, J.M.
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Villellas, A.
New TiB2-based cermets have been consolidated by hot isostatic pressing of powder mixtures of TiB2 and metallic alloys based on Fe, Ni and Co additions. Relevant thermodynamic aspects of the systems B-Ti-Ni, B-Ti-Fe and B-Ti-Co, essential for avoiding the formation of extremely brittle secondary borides, especially the secondary boride M23B6, are discussed in this work. The role of contaminants like oxygen, carbon and nitrogen, which can also lead to the formation of these compounds is also explained. The hardness, toughness and cutting behaviour of the cermets produced with these new binder phases are comparable with the highest commercial WC-Co grades.
Scopus© Citations 49 38 1
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Microscale mechanical properties testing and simulation
(2018)
Gonzalez-Ojeda, Roberto
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Sánchez-Moreno, José M.
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Quintana, María José
Characterization of mechanical properties at a micro and nano scale has become increasingly important for manufactured parts, though facilities with accurate and state-of-the-art equipment are scarce, expensive and not always available. For this reason, equipment already in use for traditional characterization can be used to analyze micro and even nano phenomena if calculations and simulations are combined with models representing testing procedures, such as hardness indentation or micro-machining of bending beams. The understanding of the interaction between phases in the material and more accurate finite element models of grains or precipitates with different geometries can contribute in measuring the behavior of very small zones of a manufactured part and design quality control or inspection protocols. © 2018 IEEE.
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Gonzalez-Ojeda, Roberto

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