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Volta Redonda, Brazil

Silva Dias J.,Federal University of Rio de Janeiro | Costa H.R.M.,Federal University of Rio de Janeiro | de Aguiar R.A.A.,Federal University of Rio de Janeiro | de Araujo Alves Lima R.,Federal University of Rio de Janeiro | And 2 more authors.
Materials Science Forum | Year: 2013

The main objective of this work is to optimise welding parameters for the process of resistance spot welding applied to Interstitial Free (IF) steel sheets, in order to increase the life of conventional copper electrodes. The methodology consisted of using a weld tester to ensure the accuracy of the results. The main parameters selected through a weldability survey were force, time and welding current. To evaluate the resistance of the weld and the electrode wear mechanical tests were performed, such as tensile-shear, cross-tension and peel test. A microstructural evaluation by optical microscopy (OM) and scanning electron microscopy (SEM) was carried out. The results show a reduction in the thickness of the coating in the steel shetts, and macro and microstructures were observed in the weld region. The tensile-shear and cross-tension tests were verified using electrode caps of up to 1250 points with acceptable welds. The methodology used for parameter selection has highlighted an optimal combination of 200kgf electrodes force, 9 cy welding time (cycles) and 7.8 kA welding current, in overlapped 0.75mm thick IF steel sheets, thereby increasing the lifetime of the electrode and ensuring a better quality of weld and consequent reduction in the energy applied in the welding process. © (2013) Trans Tech Publications, Switzerland.

Da Silva Dias F.M.,Federal University of Fluminense | Da Costa e Silva A.L.V.,Federal University of Fluminense | Fonseca F.A.V.,Companhia Siderurgica Nacional CSN | De Campos M.F.,Federal University of Fluminense
65th ABM International Congress, 18th IFHTSE Congress and 1st TMS/ABM International Materials Congress 2010 | Year: 2010

It is described the methodology employed in the development of a new IF (Interstitial Free) galvanized steel produced by CSN with excellent forming, designed for the automotive industry. It was found need of improvement to fulfill the EDDQ grade (yield point ≤180 MPa), with application for extra deep drawing. A new galvanized Ti-stabilized IF steel was developed, with extra low carbon content, for both external and internal components. The mechanical properties were analyzed to evaluate the forming of the materials and to check if the new steel presents superior behavior. Tensile tests and the statistical software MINITAB 15.1 were employed for the evaluation of the results and process capability analysis.

Silva S.N.,Companhia Siderurgica Nacional CSN | Vernilli F.,University of Sao Paulo | Justus S.M.,Sao Paulo State University | Longo E.,Sao Paulo State University | And 3 more authors.
Materials and Corrosion | Year: 2013

In this work it is presented a methodology applied by Companhia Siderúrgica Nacional (CSN, Brazil) in order to assess its blast furnace 3 carbon refractory hearth lining conditions. The aim of the investigation was the gathering of critical data base for blast furnace refractories life cycle follow up and eventual repair decision taking. The sample drilling locations were chosen around the tap holes and hearth bottom areas. The advancing drilling depths were based on local temperature profiles. The isotherm limit of 500 °C was elected as a control parameter to assess the critical carbon refractory condition. The guidelines for sampling and testing as well as the results obtained through the physical and chemical characterizations of the cored samples are presented. The condition of the refractory lining is discussed under the light of the different known wear mechanisms of blast furnace hearth carbon refractories. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Santos N.A.,Eriez Flotation Division Brazil | Duarte F.,Eriez Flotation Division Brazil | Fan M.,Eriez Flotation Division | Honaker R.,University of Kentucky | And 2 more authors.
6th Int. Congress on the Science and Technology of Ironmaking 2012, ICSTI 2012 - Including Proceedings from the 42nd Ironmaking and Raw Materials Seminar, and the 13th Brazilian Symp. on Iron Ore | Year: 2012

Cavitation is a process of formation, growth and subsequent collapse of gas and/or vapor-filled cavities, or microbubbles, in a fluid. Several fundamental studies about this phenomenon have shown that microbubbles generated on mineral surfaces facilitate bubble-particle attachment, and ultimately improves flotation performance. This work presents the Feed Air Jet, a feed pre-aeration cavitation sparger system developed by Eriez. Using coal, cavitation was applied to a flotation feed stock studied in laboratory setting in the USA. This feed pretreatment technique resulted in a significant increase in recovery and flotation kinetics. The Feed Air Jet was also installed at an industrial plant in Brazil and enhanced the overall metallurgy by increasing the mass recovery of the iron (Fe) values while reducing the amount of entrained iron in the tailings stream.

Silva S.N.,Companhia Siderurgica Nacional CSN | Vernilli F.,University of Sao Paulo | Justus S.M.,Sao Paulo State University | Araujo C.M.D.S.,Companhia Siderurgica Nacional CSN | And 4 more authors.
Steel Research International | Year: 2013

The growing demand for steels with tighter compositional specifications led the Companhia Siderúrgica Nacional (CSN) to develop more efficient processes. To solve this problem this paper aims to identify the operational variables more impacting in the desulfurization process, specifically in torpedo car, as well as its causes and solutions. Then select and test, with laboratorial and industrial tests, desulfurizing agents based of CaC 2, CaO, CaCO3, and Mg to assess the cost per quantity of product desulfurized. The mixture with best results was not that one with highest content of CaC2. It is believed that this mixture showed better efficiency because of the increased agitation of the bath, produced by the releasing of gas from compound CaCO3 present in this mixture. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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