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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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Dmaic of structural steel parts through FEM and DOE

2016 , Gonzalez-Ojeda, Roberto , Quintana, María José , Verdeja, Luis Felipe

DMAIC in the automotive sector is applied to the design and manufacturing processes of structural steel parts in order to assess variability in mechanical properties of the raw materials, use of different types of steel in the same part, modifications in thickness of the steel sheet and even changes in geometry to produce lighter and stronger parts. The work presents an example of three stamped automotive structural components, mechanically interacting together when deformed under load. Minitab design of experiments module was used to evaluate two level factors, one of them being the thickness of each part, and the other the material properties: DP600, DP780 steel or a boron-based steel alloy. A FEM model of the three parts, with structural supports and loads, was performed to evaluate displacement of the system, max. equivalent stress, strain and total weight, allowing data correlation to determine best practices to accomplish low weight, high stiffness designs. Copyright © 2016 MS&T16®.

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La temperatura de la intercara arrabio/refractario como variable determinante de los mecanismos de corrosión del crisol del horno alto

1998 , Verdeja González, Luis Felipe , Pusek, P., Alfonso , Fernández, Ángel Alejandro , Gonzalez-Ojeda, Roberto

El desgaste de materiales en el horno alto puede realizarse bajo la consideración de mecanismos estrictamente abrasivos o con el predominio de las componentes químicas y erosivas resultantes de la circulación de fluidos sobre el refractario. No obstante, aunque en determinadas situaciones, la abrasión o las componentes químicas pueden resultar los mecanismos controlantes, es necesario considerar que todos ellos (abrasión, erosión, desgaste químico, adhesión y desgaste térmico-choque térmico) "cooperan" en la degradación del refractario del horno, Para cualquiera de los mecanismos que intervenga en el desgaste de los materiales, resulta conveniente conocer el valor de la temperatura a lo largo de las intercaras del refractario con los sólidos, líquidos o gases presentes en el horno. En la ponencia será desarrollada de forma específica, la importancia que tiene la temperatura en la intercara refractario-arrabio sobre el desgaste de los materiales del crisol. Se discutirán las diferentes hipótesis de transporte (energía, cantidad de movimiento y materia) más adecuadas para la obtención de la temperatura de intercara.

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The Nodal Wear Model (NWM) as an Alternative to Understand the Mechanisms of Flow and Wear in the Blast Furnace Crucible

2010 , Gonzalez-Ojeda, Roberto , Barbés Fernández, Miguel Ángel , Verdeja González, Luis Felipe , Ruiz Bustinza, Íñigo Eloy , Mochón Muñoz, Javier , Duarte, Ramón Martín , Karbowniczek, Mirosław

The presence of thermocouples in the lining of crucibles has become a general practice in the new construction of blast furnaces. The Nodal Wear Model (NWM) has also emerged as an instrument that, while using experimental data, obtains nodal variables whose experimental measurement is not possible: global coefficient of pig-iron/refractory heat transfer h pig−iron/lining g−i and nodal temperature Ti . Starting from these nodal properties, the wear of the lining or the growth of scabs may be controlled, independently of the mechanisms responsible for them. In the same way, the properties and influence zone of the dead man in the hearth of the blast furnace may be calculated, along with those regions where the fluid is allowed to move without any other restrictions than the ones of the corresponding viscous flow (raceway hearth region).

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Wear in ultrafine hardmetal mills manufactured by sinter + HIP

2006-12-01 , Ordóñez, Alejandro , Gonzalez-Ojeda, Roberto , Sánchez-Moreno, José Manuel

Ultrafine WC-Co milling tools were wear-tested in finishing machining conditions. Mills manufactured in the laboratory followed the powder metallurgy route for ultrafine grades. Total density in hardmetal grades of 0.2 and 0.4 μm was achieved through the Sinter + HIP technique. Wear in laboratory mills was compared with wear in coarse and ultrafine grade commercial mills. All mills cutting edges suffered wear mainly in the abrasive and chipping form. Chipping was excessive and peculiar in form in the laboratory mills; a slight presence of the fragile η phase was discovered. Laboratory mills showed similar wear to the commercial coarse grades, and much more than that of commercial ultrafine grades. A lack of toughness is suggested due to a small difference in the WC mean grain size, in the Co mean free path (λ) and in its distribution: homogeneous in laboratory mills and heterogeneous in the commercial ones. ©Metal Powder Industries Federation (MPIF)

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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 Grained HSLA Steels for Cold Forming

2010 , Gonzalez-Ojeda, Roberto , García García, José Ovidio , Barbés Fernández, Miguel Ángel , Quintana, María José , Verdeja González, Luis Felipe , Verdeja González, José Ignacio

The industrial level production of ultrafine grained (or ultrafine ferrite) ferrous alloys was investigated through three examples of steels that complied with the EN 10149-2 Euronorm and were produced by advanced controlled hot rolling techniques. The steel samples were tension tested and chemically analyzed, and the microstructure was evaluated through quantitative metallographic techniques to determine parameters such as yield stress, amount of microalloying elements, strain hardening coefficient, grain size, and grain size distribution. These steels were micro-alloyed with Ti, Nb, and Mn with ASTM grain sizes of approximately 13–15. The careful control of chemical composition and deformation during production, giving a specific attention to the deformation sequences, austenite non-recrystallization temperatures and allotropic transformations during cooling, are indispensable to obtain steels with an adequate strain hardening coefficient that allows cold working operations such as bending, stretching or drawing.

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Effect of Mo on high entropy Ti-Nb-Zr-Ta alloy: Phase equilibria, microstructure and mechanical properties

2023 , Aranda, Víctor A. , Figueroa, I. A. , Amigó-Borrás, V. , Gonzalez-Ojeda, Roberto , Lozada Flores, Octavio , Vidilli, André Luiz , Barcelos Otani, Lucas , González, Gonzalo

Thermal and mechanical properties of Ti-Nb-Ta-Zr high entropy alloys are often influenced by element content and manufacturing routes, producing significant differences between mechanical properties and microstructure. This work presents a Ti-Nb-Ta-Zr alloy in which Mo is added by adjusting the composition with phase equilibria simulation, improving the mechanical properties based on a mixture of two chemically different solid solutions (BCC1 and BCC2). The materials were produced by arc-melting suction casting. Characterization of the dendritic and interdendritic zones was carried out by means of X-ray spectroscopy, indicating the segregation of Ta and Nb in BCC1 and Zr and Ti in BCC2 phases. The dislocation density increased preferentially in the interdendritic Zr-Ti rich zones. The mechanical properties results were related to the chemical differences between the BCC1 and BCC2 lattice parameters induced by the Mo addition. With Mo segregating between both BCC cells, the resulting microstructure increased the yield strength, being confirmed with the kernel average maps, which showed that, after compression tests, the interdendritic zone accumulated a high density of dislocations, resulting in the segregation of Ti and Zr, affecting the mechanical response of Mo containing alloy. © 2023 Elsevier B.V.

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Dual-phase ultrafine grained steels produced by controlled rolling processes

2011 , Quintana, María José , Gonzalez-Ojeda, Roberto , Verdeja González, Luis Felipe , Verdeja González, José Ignacio

Double-phase steels are an excellent alternative in the production of automotive parts that require high mechanical resistance, high impact strength and elevated elongation. These materials are produced using low-alloy steels as a basis, reducing costs and resulting in a combination of martensite and ferrite structures with ultrafine grain sizes. These characteristics are accomplished through a strict control of rolling conditions: strain rate, cooling rate and direct quenching. This work presents the results of tension testing of two types of double phased steels, along with microstructural characterization, in order to understand the effect of the advanced thermomechanical controlled rolling processes on the formation of the microstructure and the resulting mechanical properties.

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Influence of strain rate and heat treatments on tensile and creep properties of Zn-0.15Cu-0.07Ti alloys

2016 , Quintana, María José , García, José Ovidio , Gonzalez-Ojeda, Roberto , Verdeja, José Ignacio

The use of Cu and Ti in Zn alloys improves mechanical properties as solid solution and dispersoid particles (grain refiners) may harden the material and reduce creep deformation. This is one of the main design problems for parts made with Zn alloys, even at room temperature. In this work the mechanical behavior of a Zn-Cu-Ti low alloy is presented using tensile tests at different strain rates, as well as creep tests at different loads to obtain the value of the strain rate coefficient m in samples parallel and perpendicular to the rolling direction of the Zn strip. The microstructure of the alloy in its raw state, as well as heat treated at 250°C, is also analyzed, as the banded structure produced by rolling influences the strengthening mechanisms that can be achieved through the treatment parameters. © The author; licensee Universidad Nacional de Colombia.