Minas Gerais, Brazil
Minas Gerais, Brazil

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Jia Z.,University of Louisiana at Lafayette | Misra R.D.K.,University of Louisiana at Lafayette | O'Malley R.,Nucor Steel Decatur LLC | Jansto S.J.,CBMM Co.
Materials Science and Engineering A | Year: 2011

We describe here the precipitation behavior and mechanical properties of 560MPa Ti-Nb and 770MPa Ti-Nb-Mo-V steels. The precipitation characteristics were analyzed in terms of chemistry and size distribution of precipitates, with particular focus on the crystallography of precipitates through an analysis of electron diffraction patterns. In addition to pure carbides (NbC, TiC, Mo2C, and VC), Nb containing titanium-rich carbides were also observed. These precipitates were of a size range of 4-20nm. The mechanism of formation of these Ti-rich niobium containing carbides is postulated to involve epitaxial nucleation of NbC on previously precipitated TiC. Interface precipitation of NbC was an interesting observation in compact strip processing which is characterized by an orientation relationship of [001]NbC//[001]α-Fe, implying that the precipitation of NbC occurred during austenite-ferrite transformation. © 2011 Elsevier B.V.


Misra R.D.K.,University of Louisiana at Lafayette | Jia Z.,University of Louisiana at Lafayette | O'Malley R.,LLC Sheet Mill | Jansto S.J.,CBMM Co.
Materials Science and Engineering A | Year: 2011

We describe here the precipitation behavior of copper and fine-scale carbides during thermo-mechanical processing and isothermal aging of copper-bearing niobium-microalloyed high strength steels. During thermo-mechanical processing, precipitation of e{open}-copper occurs in polygonal ferrite and at the austenite-ferrite interface. In contrast, during isothermal aging, nucleation of e{open}-copper precipitation occurs at dislocations. In the three different chemistries investigated, the increase in strength associated with copper during aging results only in a small decrease in impact toughness, implying that copper precipitates do not seriously impair toughness, and can be considered as a viable strengthening element in microalloyed steels. Precipitation of fine-scale niobium carbides occurs extensively at dislocations and within ferrite matrix together with vanadium carbides. In the presence of titanium, titanium carbides act as a nucleus for niobium carbide formation. Irrespective of the nature of carbides, copper precipitates and carbides are mutually exclusive. © 2011 Elsevier B.V.


Santos A.P.,Associacao Salgado de Oliveira | Santos A.P.,Institutos Superiores Of Ensino Do Censa | Guimaraes R.C.,CBMM Co. | Carvalho E.M.,Federal University of Uberlandia | Gastaldi A.C.,Hospital Das Clinicas Of Ribeirao Preto
Respiratory Care | Year: 2013

BACKGROUND: Flutter VRP1, Shaker, and Acapella are devices that combine positive expiratory pressure (PEP) and oscillations. OBJECTIVES: To compare the mechanical performance of the Flutter VRP1, Shaker, and Acapella devices. METHODS: An experimental platform and a ventilator, used a flow generator at 5, 10, 15, 20, 26, and 32 L/min, were employed at angles of -30°, 0°, and +30° to evaluate Flutter VRP1 and Shaker, whereas Acapella was adjusted at intermediate, higher, and lower levels of resistance, including positive expiratory pressures (PEP) along with air outflow rates and oscillation frequencies. RESULTS: When the relationships between pressure amplitudes of all air flows were analyzed for the 3 devices at low and intermediate pressures levels, no statistically significant differences were observed in mean pressure amplitudes between Flutter VRP1 and Shaker devices. However, both devices had different values from Acapella, with their pressure amplitude values being higher than that of Acapella (P = .04). There were no statistically significant differences in PEP for the 3 angles or marks regarding all air flows. The expected relationships between variables were observed, with increases in PEP, compared to those of air flows and resistance. Nevertheless, there was a statistically significant difference in frequency of oscillation between these devices and Acapella, whose value was higher than those of Flutter VRP1 and Shaker devices (P = .002). At intermediate pressure levels, the patterns were the same, in comparison to low pressures, although the Acapella device showed frequencies of oscillation values lower than those of Flutter VRP1 and Shaker (P < .001). At high pressures, there were no statistically significant differences among the 3 devices for frequency of oscillations. CONCLUSIONS: The Flutter VRP1 and Shaker devices had a similar performance to that of Acapella in many aspects, except for PEP. © 2013 Daedalus Enterprises.


Jansto S.G.,CBMM Co.
Materials Science and Technology Conference and Exhibition 2010, MS and T'10 | Year: 2010

Value-added applications of niobium (Nb) microalloyed steels continue to be developed meeting the increasing material demands within the automotive, pipeline and structural carbon steel segments. High quality production of these value-added Nb-bearing steels is realized through the synergistic balance of the process and physical metallurgy. Process metallurgy practices presented include development of the steel chemistries, proper melting and alloy additions, secondary refining, slab and billet reheat furnace operation, and alternative hot rolling considerations to successfully obtain a fine grain, homogeneous microstructure within production environments. Case examples of the necessary process metallurgy practices to meet the physical metallurgy objectives are discussed incorporating current niobium-bearing steel product applications. A sustainability structural steel study recently completed presents the positive environmental impact of Nb-microalloyed steel applications as it relates to more effective product design, reduced steelmaking emissions and reduced energy consumption. Copyright © 2010 MS&T'10®.


Jansto S.G.,CBMM Co.
AIST Steel Properties and Applications Conference Proceedings - Combined with MS and T'11, Materials Science and Technology 2011 | Year: 2011

The application of niobium (Nb) in high carbon steels enhances both the metallurgical properties and processability products such as steel bar, sheet and plate. Such process and product metallurgical improvements relate to the Nb-pinning effect of the austenite grain boundaries in microalloyed 0.25 to 0.95%C steels during the reheat furnace process prior to rolling. Consequently, Nb microalloyed high carbon automotive and long product steel applications have been developed. The Micro-Niobium Alloy Approach© is described and correlated to a variety of high carbon steel grades and applications. Metallurgical Operational Implementation (MOI©)) links the product requirements to the mill capability and resultant process metallurgical implementation. This integrative approach connects the Nb process and physical metallurgy necessary to achieve the desired ultra-fine grain, homogeneous high carbon steel microstructures that exhibit superior toughness, strength, fatigue performance and weldability.


Jansto S.G.,CBMM Co.
SEAISI Quarterly (South East Asia Iron and Steel Institute) | Year: 2012

The MicroNiobium® Alloy Approach has been applied in carbon steels exceeding 0.20% carbon such as AISI1050 grade automotive and AISI1080 long product steel applications. Developed applications involve automotive fasteners, seismic resistant rebar and pre-stressed concrete wire rod. The MicroNiobium Alloy Approach mechanism is described and correlated to a variety of medium and high carbon steel grades and applications. The application of the MicroNiobium Alloy Approach in over 0.20% carbon steels enhances the metallurgical properties, consistency and processability of the hot rolled product. Such process and product metallurgical improvements relate to the Nb-pinning effect of the austenite grain boundaries in Nb-microalloyed steels exceeding 0.20%C steels. The key operational attribute is the micro-addition of Nb in higher carbon steels which mechanistically pins the austenite grain boundary during the reheat furnace process, thereby minimizing abnormal grain growth in the billet or slab prior to rolling. Typically abnormal grain growth occurs when thermal fluctuations and furnace abnormalities exist in actual reheat furnace operations. This abnormal grain growth leads to inhomogeneous ferrite grains in the final hot rolled product and subsequent variations and reductions in mechanical property performance such as fatigue, fracture toughness and yield-to-tensile properties. Additional evolving development opportunities and applications span pressure vessels, automotive coil springs, eutectoid rail steels, alloy tool and die steels, and tyre rod.


Jansto S.G.,CBMM Co.
METAL 2013 - 22nd International Conference on Metallurgy and Materials, Conference Proceedings | Year: 2013

Over 200 million tons of Nb-bearing steels were continuously cast and hot rolled globally in 2012. These Nb-bearing plate, bar and sheet products are manufactured throughout the world. Numerous publications discuss the traditional ductility trough for carbon steels with and without microalloy additions of Nb, V and/or Ti. The steelmaking and process metallurgy parameters under actual mill conditions are rarely correlated to the hot ductility behavior. The hot ductility troughs associated with simple carbon-manganese steels can also result in surface and internal quality issues if certain steelmaking and casting parameters are not followed. Although higher carbon equivalent steels generally exhibit inherently lower hot ductility behavior, as measured by percent reduction in area at elevated temperature, these steels still exhibit sufficient ductility to satisfactorily meet the unbending stress and strain gradients existing in the straightening section of most casters. The relationship between the steelmaking and caster operation and the resultant slab quality is related through the hot ductility behavior. This global Nb-bearing continuous casting steel research study concludes that the incidence of slab cracking during casting is related more to the steelmaking and caster process parameters. These parameters include the superheat variation, transfer ladle temperature stratification, mould flux incompatibility, casting speed fluctuation, elemental residual chemistry level and excessive secondary cooling. This paper defines these operational root causes supported by physical metallurgy hot ductility data from industrial samples. © 2013 TANGER Ltd., Ostrava.


Jansto S.G.,CBMM Co.
Materials Science and Technology Conference and Exhibition 2011, MS and T'11 | Year: 2011

The application of niobium (Nb) in high carbon steels enhances both the metallurgical properties and processability products such as steel bar, sheet and plate. Such process and product metallurgical improvements relate to the Nb-pinning effect of the austenite grain boundaries in microalloyed 0.25 to 0.95%C steels during the reheat furnace process prior to rolling. Consequently, Nb microalloyed high carbon automotive and long product steel applications have been developed. The Micro-Niobium Alloy Approach© is described and correlated to a variety of high carbon steel grades and applications. Metallurgical Operational Implementation (MOI©) links the product requirements to the mill capability and resultant process metallurgical implementation. This integrative approach connects the Nb process and physical metallurgy necessary to achieve the desired ultra-fine grain, homogeneous high carbon steel microstructures that exhibit superior toughness, strength, fatigue performance and weldability.


Processes for producing low-nitrogen metallic chromium or chromium-containing alloys, which prevent the nitrogen in the surrounding atmosphere from being carried into the melt and being absorbed by the metallic chromium or chromium-containing alloy during the metallothermic reaction, include vacuum-degassing a thermite mixture comprising metal compounds and metallic reducing powders contained within a vacuum vessel, igniting the thermite mixture to effect reduction of the metal compounds within the vessel under reduced pressure i.e., below 1 bar, and conducting the entire reduction reaction in said vessel under reduced pressure, including solidification and cooling, to produce a final product with a nitrogen content below 10 ppm. The final products obtained, in addition to low-nitrogen metallic chromium in combination with other elements, can be used as raw materials in the manufacture of superalloys, stainless steel and other specialty steels whose final content of nitrogen is below 10 ppm.


Processes for producing low nitrogen, essentially nitride-free chromium or chromium plus niobium-containing nickel-based alloys include charging elements or compounds which do not dissolve appreciable amounts of nitrogen in the molten state to a refractory crucible within a vacuum induction furnace, melting said elements or compounds therein under reduced pressure, and effecting heterogeneous carbon-based bubble nucleation in a controlled manner. The processes also include, upon cessation of bubble formation, adding low nitrogen chromium or a low nitrogen chromium-containing master alloy with a nitrogen content of below 10 ppm to the melt, melting and distributing said added chromium or chromium-containing master alloy throughout the melt, bringing the resulting combined melt to a temperature and surrounding pressure to permit tapping, and tapping the resulting melt, directly or indirectly, to a metallic mold and allowing the melt to solidify and cool under reduced pressure.

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