Gonzalez-Ojeda, Roberto
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Gonzalez-Ojeda, Roberto
Official Name
Gonzalez Ojeda, Roberto
Alternative Name
robglez
González-Ojeda, R.
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ORCID
Scopus Author ID
56314856300
Researcher ID
DTL-2716-2022

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Cooling efficiency in furnace design

2013-12 , Gonzalez-Ojeda, Roberto , Quintana Hernández, María José , Ruiz Bustinza, Iñigo , García Carcedo, Fernando , Barbés, Miguel Ángel , Florentina Barbés, María

During melting, reduction or thermal treatment of a steel charge, the input of energy (either chemical or electrical) is indispensable to guarantee the viability of the process. Under these circumstances, it will be reasonable to design the furnace lining in such a way that heat loss through the walls is minimized. Nevertheless, it can be proved that, for some situations, it is more efficient to withdraw as much heat as possible from the walls than trying to thermally isolate the system. The work presents recommendations for the design of walls and cooling systems in furnaces obtained by quantitative analysis of temperatures reached in specific locations of the furnace using the nodal wear model. The analysis indicates that the wear process of the lining may be controlled if all the elements that intervene in the process are known.

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High temperature mechanical behavior and microstructural evolution of 304 stainless steel

2010-05 , Quintana Hernández, María José , 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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Ultrafine-grain Steels: Mechanical Behavior

2016 , Quintana Hernández, María José , Gonzalez-Ojeda, Roberto , 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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Grain Size Distribution on a Forged Ni-Cr-Mo Low-Alloy Steel

2018 , Quintana Hernández, María José , Ales, T. , Gonzalez-Ojeda, Roberto , Collins, P. , Kenney, M.

Microalloyed Ni-Cr-Mo steel (8620) combines good characteristics of formability during forging at 1100°C with the capacity to transform into martensite, while distributing residual stresses and allowing surface treatments and modifications in mechanical parts such as gears and cams. The work presents grain size measurements at different locations of a hot forged gear analyzing it by quantitative metallography techniques and simulating deformation by finite element modeling to estimate local strain and strain rate. Dynamic recrystallization mathematical models for the austenitic initial grain size before forging were applied to calculate theoretical final grain size and correlate the results with microstructural observations, taking also into account the role of precipitation of Cr and Mo carbides. Copyright © 2018 MS&T18®

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