Steel industry is the base of economic development. Its relevant industries are quite wide and it may drive the whole development of its upper/down streams, especially coated steel products with excellent character of corrosion resistance to lead the market requests from traditional construction industry to home appliance, automobiles, and further extending to information and electronic industries. The local capacity of galvanized steel products had been sharply one time increased in 2000. Problems of how to digest the products keenly exist and the local environment in coated industry faces to be re-organized. Meanwhile under the impact of Asian financial storm, suppliers of hot rolled coils had been altered from the originally three companies to the exclusive one monopolized by China Steel, after An Feng¡¦s bankruptcy and Yieh Loong¡¦s emergence by China Steel. In addition, due to being attracted by the excellent environments and offered conditions from the cross-strait, the corporations of upper/down streams have been moving out. Thus the rolling/coating manufacturers of middle steam locally are forced to face the problems of raw materials being monopolized, capacity excess and local customers moving out. The study takes Sheng Yu Steel Co., Ltd. as the example to research how the coating steel manufacturer using the resources in hand to make the appropriate strategies in view of the great change of steel industry. Facing the internal and external influences, local coating steel manufacturers have to make efforts together to breakthrough the current barriers and pursue the future developments. Government should also push hard on economic development and speed up public construction to stimulate the consumption and lead the growth of economic prosperity. The suggestions to the leader of steel industry, China Steel, --- being the only national integrated steel refinery, under the condition of exclusively monopolizing raw materials, China Steel should regard itself as the national steel mill and consider the rises or falls of the whole steel industry in Taiwan, in addition to pursue its own benefits, but also to consider the existing space and international competition for the down-steam customers, in order to avoid the customers¡¦ bankruptcies or moving out due to the poor operation surrounding. The suggestions to the steel industry and the studied company are ¡V 1. To control the supply sources of raw materials, to avoid being controlled by the only supplier. 2. To emerge or make alliance with the local dealers of the same line, to extend business scope and lower the competitive pressure. 3. To develop high-added value products and practical application of new products, to replace imported products. 4. To strengthen R&D, to promote the abilities of manufacture process and products application.

Made available in DSpace on 2014-06-11T19:28:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2003Bitstream added on 2014-06-13T20:58:35Z : No. of bitstreams: 1 aguiar_fec_me_guara.pdf: 2530188 bytes, checksum: 16dfca08c4ceaff67e483005f4ffffa9 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Neste trabalho estudou-se o comportamento eletroquímico e as características microestruturais de chapas de aço eletrozincado e zincado sem e com revestimentos de fosfatos, oriundos de diferentes banhos fosfatizantes, aplicados pelo processo industrial coil-coating utilizado pela TEKNO S.A. Este trabalho também traz contribuições referentes ao estudo da chapa revestida com Galvalumeâ que é um revestimento composto de uma liga constituída de 55% de alumínio, 43% de zinco e 2% de outros constituintes, entre eles o Silício. Com o estudo desse material pode-se comprovar e determinar qual revestimento com e/ou sem fosfatos tem maior resistência à corrosão. A análise metalográfica superficial das chapas e revestimentos foi realizada por Microscopia Óptica, Microscopia Eletrônica de Varredura e EDS. Ensaios normalizados de rugosidade e de dureza Vickers também foram realizados. A resistência à corrosão proporcionada pelos diferentes revestimentos de zinco e fosfatos foi avaliada por ensaios eletroquímicos como potencial vs tempo em circuito aberto e em corrente controlada, polarização potenciodinâmica, voltametria cíclica e espectroscopia de impedância eletroquímica em solução de cloreto de sódio 3,5% e pH ~ 8,1, equivalente à água marinha. Todo este trabalho teve como objetivo principal, comparar quanto à resistência a corrosão, três diferentes banhos fosfatizantes aplicados nas chapas zincadas, com o intuito de propor ajustes no processo vigente da TEKNO que forneceu todo suporte necessário para realização deste estudo. / In this work it was studied the electrochemical behavior and the microstructure characteristics of zinc coated steel plates with and without phosphate coatings originating from different baths applied for the coil-coating industrial process used by TEKNO S.A. This work also brings referring contributions to the study of Galvalumeâ coating, that is a coating composed of 55% of aluminum, 43% of zinc and 2% of other constituent league, among them the silicon. With this material study it was possible to estimate and determinate which coating has larger resistance to the corrosion. The surface metallographic analysis of all the coatings were accomplished by Optical Microscopy, Scanning Electron Microscopy and Energy Dispersive Spectrography techniques. Normalized methods of rugosity and hardness Vickers were also accomplished. The corrosion resistance for the different coatings was evaluated by electrochemical techniques as potential x time in open circuit , potenciodynamic polarization curves, cyclic voltammetric curves, galvanostatic curves and Electrochemical Impedance Spectroscopy in sodium chloride solution of 3,5% to the pH ~ 8,1 equivalent to the sea water. The main objective, in this work, was to compare the corrosion resistance of three different phosphates baths applied in the galvanized steel sheets, in order improve the effective process of TEKNO that supplied every necessary support for accomplishment of this study.

Galvanized sheet is produced commercially by hot dipping steel sheet in a galvanizing bath to produce a thin zinc rich protective coating on the steel. This investigation is concerned with the solidification of the galvanized layer with particular reference to the growth of large "spangles" in the galvanized layer. The manner in which the galvanized layer solidifies was found to be dependent on a number of factors including melt supercooling, nucleation rate, dendritic growth, bath composition, bath impurities, and cooling rate. The present results show that the supercooling necessary to activate nucleating sites in a typical galvanizing bath is less than 1°C. The supercooling which occurs in the galvanized layer as it solidifies is also generally less than 1°C, contrary to results reported in the literature. This suggests that grains nucleate in the bulk of the galvanized layer, and not necessarily at the air or iron surfaces of the melt as has been reported. No clear evidence was obtained which shows that spangles, with large dendrite spikes, are associated with large melt supercooling. Accordingly, spangle formation cannot be attributed to higher dendritic velocities resulting from large thermal supercooling. The surface topography of the galvanized layer is a property of major consideration in industrial applications of the galvanized product. Present measurements show that the surface topography is strongly dependent on the solidification structure of the galvanized layer. Large spangles solidify dendritically with large variations in the surface topography. The spangles have shiny and frosty sectors, which are relatively smooth and rough respectively, and inclined to the steel sheet surface. Large depressions are present at the boundaries between adjacent spangles, termed "pulldown", which can markedly reduce the effective thickness of the galvanized layer, and cannot be removed by subsequent treatment of the galvanized sheet. Increasing the concentration of lead in the bath increased the pulldown. The mechanism of pulldown formation is not clear. Volume shrinkage during solidification cannot account for the large depressions observed. The hot dipped galvanized samples prepared in this investigation used galvanized sheets as starting material. Observation of the distribution of bath alloy additions in the samples, using microprobe analysis and radioactive tracers, clearly showed that the original galvanized layer was replaced by the metal from the bath. Solute segregation in a galvanized layer containing spangles is directly associated with the dendritic growth of the spangles. Solute is depleted in the dendrite spikes and concentrated between the spikes. No solute concentration was observed at the grain boundaries between adjacent spangles. Some preferential surface segregation, associated with shiny and frosty sectors of a spangle, was observed. The growth of large spangles in the galvanized layer is directly related to the galvanizing bath composition. Large spangles are obtained with alloying additions which have very limited solid solubility in zinc and relatively low liquid surface tensions. The diameter of the spangles decrease as the surface tension of the alloy addition increases. Spangle growth is associated with dendritic growth. Dendritic growth occurs as a result of constitutional supercooling at the dendrite tip due to solute segregation during growth at the solid/liquid interface. It is proposed that the presence of a thin layer of highly concentrated solute at the dendrite tip changes the curvature of the tip. The change is related to the liquid surface tension of the solute. Solutes with lower values of surface tension decrease the tip curvature which results in an increase in dendrite velocity and larger spangles. The orientation of the spangles is shown to vary appreciably. The basal plane of a spangle is observed to be inclined to the surface of the steel sheet at angles between 8 and 80 degrees. This differs from reports which indicate that the basal plane is nearly parallel to the steel sheet. The growth of a spangle is primarily associated with dendritic growth. Small (0001) platelets of solid form at heterogeneous nucleating sites in the melt from which <1010> spikes grow. Each spangle forms from a single nucleating source which is randomly oriented with respect to the surface of the steel sheet. As the dendrite spikes grow they shortly encounter the melt/air interface or the melt/steel interface. The spikes will continue to grow along the surfaces at a high velocity in a direction defined by the initial <1010> direction of the growing spikes. As the primary spike grows, secondary and tertiary spikes form, generally inclined to the melt surface and in <10l0> directions when possible. The secondary branches of a primary stalk which grow along the melt/air interface form shiny spangle segments. The secondary branches on the opposite side of the primary spike grow along the melt/steel surface and form frosty sectors. The difference is not due to an orientation difference between the spangles as reported in the literature. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Orientador : Roberto Zenhei Nakazato / Banca: Tomaz Manabu Hashimoto / Banca: Maria Auxiliadora Silva de Oliveira / Resumo: Neste trabalho estudou-se o comportamento eletroquímico e as características microestruturais de chapas de aço eletrozincado e zincado sem e com revestimentos de fosfatos, oriundos de diferentes banhos fosfatizantes, aplicados pelo processo industrial coil-coating utilizado pela TEKNO S.A. Este trabalho também traz contribuições referentes ao estudo da chapa revestida com Galvalumeâ que é um revestimento composto de uma liga constituída de 55% de alumínio, 43% de zinco e 2% de outros constituintes, entre eles o Silício. Com o estudo desse material pode-se comprovar e determinar qual revestimento com e/ou sem fosfatos tem maior resistência à corrosão. A análise metalográfica superficial das chapas e revestimentos foi realizada por Microscopia Óptica, Microscopia Eletrônica de Varredura e EDS. Ensaios normalizados de rugosidade e de dureza Vickers também foram realizados. A resistência à corrosão proporcionada pelos diferentes revestimentos de zinco e fosfatos foi avaliada por ensaios eletroquímicos como potencial vs tempo em circuito aberto e em corrente controlada, polarização potenciodinâmica, voltametria cíclica e espectroscopia de impedância eletroquímica em solução de cloreto de sódio 3,5% e pH ~ 8,1, equivalente à água marinha. Todo este trabalho teve como objetivo principal, comparar quanto à resistência a corrosão, três diferentes banhos fosfatizantes aplicados nas chapas zincadas, com o intuito de propor ajustes no processo vigente da TEKNO que forneceu todo suporte necessário para realização deste estudo. / Abstract: In this work it was studied the electrochemical behavior and the microstructure characteristics of zinc coated steel plates with and without phosphate coatings originating from different baths applied for the coil-coating industrial process used by TEKNO S.A. This work also brings referring contributions to the study of Galvalumeâ coating, that is a coating composed of 55% of aluminum, 43% of zinc and 2% of other constituent league, among them the silicon. With this material study it was possible to estimate and determinate which coating has larger resistance to the corrosion. The surface metallographic analysis of all the coatings were accomplished by Optical Microscopy, Scanning Electron Microscopy and Energy Dispersive Spectrography techniques. Normalized methods of rugosity and hardness Vickers were also accomplished. The corrosion resistance for the different coatings was evaluated by electrochemical techniques as potential x time in open circuit , potenciodynamic polarization curves, cyclic voltammetric curves, galvanostatic curves and Electrochemical Impedance Spectroscopy in sodium chloride solution of 3,5% to the pH ~ 8,1 equivalent to the sea water. The main objective, in this work, was to compare the corrosion resistance of three different phosphates baths applied in the galvanized steel sheets, in order improve the effective process of TEKNO that supplied every necessary support for accomplishment of this study. / Mestre

No description available.

Thesis (Ph. D.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains xi, 106 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 101-106).

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains vii, 83 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 80-82).

A proteção contra a corrosão do aço galvanizado com um tratamento via cromatização, apesar de apresentar desempenho superior à outras alternativas, gera efluentes tóxicos ao meio ambiente e em especial aos seres humanos. Dentre as alternativas apresentadas até o presente momento, que incluem diversos tipos de tratamentos para esse substrato, um deles é o revestimento com silanos. Apesar desse revestimento ter um satisfatório desempenho, vem se utilizando incorporações em seu preparo, para se potencializar seu desempenho. A incorporação escolhida nesse trabalho foi a do tanino, um inibidor de corrosão natural, extraído de vegetais. O objetivo desse trabalho é avaliar um revestimento do silano Ortossilicato de tetraetila (TEOS) junto de um tanino para o aço galvanizado destinado a aplicações onde não há pintura. Essa sinergia deve proteger a superfície até que o zinco consiga de forma natural desenvolver sua pátina protetora, formando uma barreira entre substrato e eletrólito. Foram revestidas chapas de aço galvanizado com períodos de imersão que variaram entre 2 e 10 minutos, com soluções na concentração de tanino de 2g/L e 10g/L com diferentes valores de pH, em uma solução previamente preparada de TEOS em concentração de 2%, água 49% e etanol 49%. Realizou-se análise comparativa entre os diferentes parâmetros de tratamento proposto neste trabalho com aço galvanizado somente desengraxado e aço galvanizado cromatizado nas seguintes técnicas: espectroscopia de impedância eletroquímica, polarização potenciodinâmica, microscopia eletrônica de varredura acoplada a espectroscopia de energia dispersiva, e ensaios de corrosão acelerada em câmara úmida e névoa salina. Os resultados apresentados indicam que diferentes concentrações de tanino e tempos de imersão não são significativos para causar diferenças relevantes entre os desempenhos e que os substratos tratados demonstraram um desempenho superior comparado às amostras que não tinham nenhum tipo de tratamento e inferiores às amostras cromatizadas. / The corrosion protection of galvanized steel with a chromatized treatment, despite superior performance to other alternatives, generates effluents toxic to the environment and especially to humans. Among the alternatives presented to date, which include several types of treatments for this substrate, one of them is the coating with silanes. Although this coating has a satisfactory performance, it has been using incorporations in its preparation, to enhance its performance. The incorporation chosen in this work was that of tannin, a natural corrosion inhibitor, extracted from plants. The objective of this work is to evaluate a coating of silane tetraethyl orthosilicate (TEOS) with tannin for galvanized steel, for applications where there is no paint. This synergy should protect the surface until zinc can naturally develop its protective patina, forming a barrier between substrate and electrolyte. Galvanized steel plates were coated with immersion times ranging from 2 to 10 minutes, with solutions at tannin concentration of 2 g/L and 10 g/L with different pH values, in a previously prepared solution of TEOS at a concentration of 2% , 49% of water and 49% of ethanol. A comparative analysis was performed between the different treatment parameters proposed in this work with galvanized steel only degreased and galvanized steel chromatized in the following techniques: electrochemical impedance spectroscopy (EIE), potentiodynamic polarization, scanning electron microscopy coupled to dispersive energy spectroscopy, and corrosion tests accelerated in humid chamber and saline mist. The results indicated that different concentrations of tannin and immersion times are not significant to cause relevant differences between the performances and that the substrates demonstrated superior performance compared to the samples that had no type of treatment, and inferior to the samples chromatized.

The major concern regarding the use of hot-dip galvanized (HDG) steel as reinforcement in concrete has been the high rate of corrosion experienced by the zinc during the first hours in the fresh, wet, and highly alkaline concrete. The present work was aimed at clarifying three issues associated with these concerns. The first involves the metallurgical phases at the surface of the zinc coating. The concentration of zinc at the surface is a function of processing procedures, surface treatment, and exposure to weathering. Differences in the coating surface composition influence the corrosion behaviour of HDG steel reinforcing bars when they are embedded in concrete. The second issue involves the increasing use of supplementary cementing materials in concrete, which change the chemistry of the concrete pore fluid, and also influence the corrosion. The third issue is that the initial corrosion is accompanied by hydrogen evolution, which could increase the pore volume of adjacent cement and thereby, decrease the bond stress between the concrete and the steel. In order to limit the hydrogen evolution, a chromate layer is applied after galvanizing. The results of the project have demonstrated that, during zinc corrosion in ordinary Portland cement (OPC) concrete, calcium hydroxyzincate formed on untreated HDG steel provided sufficient protection against corrosion. Therefore, it is concluded that treating HDG rebar with dilute chromic acid is unnecessary as a method of passivating zinc. A layer of zinc oxide and zinc carbonate formed through weathering on HDG bars slightly increased the initial corrosion rate and passivation time compared with the non-weathered rebars. HDG steel with an alloyed coating, i.e. consisting of Fe-Zn intermetallic phases, required a longer time to passivate than those with a pure zinc surface layer. The lower zinc content of the surface limited the rate of CHZ formation and, hence, delayed passivation. However, regardless of the surface condition, the coating depth loss after two days of embedment in OPC concrete was insignificant. In concretes containing 8% cement replacement with silica fume, or 25% cement replacement with slag, the initial corrosion rates were higher than those in OPC due to higher pH and lower calcium contents of the concrete pore solution. The higher corrosion rates lead to initial depth losses which are considered significant. However, in these concretes, chromate treatment was also shown to be unnecessary. Through porosity assessment of cements adjacent to HDG bars, it was found that hydrogen evolution accompanying zinc corrosion did not have an impact on the pore volume of cements: any additional pores created by hydrogen gas are filled by the zinc corrosion products. The negligible difference in pore volume between cements adjacent to chromated and non-chromated bars further confirmed that chromated treatment was unnecessary.

The major concern regarding the use of hot-dip galvanized (HDG) steel as reinforcement in concrete has been the high rate of corrosion experienced by the zinc during the first hours in the fresh, wet, and highly alkaline concrete. The present work was aimed at clarifying three issues associated with these concerns. The first involves the metallurgical phases at the surface of the zinc coating. The concentration of zinc at the surface is a function of processing procedures, surface treatment, and exposure to weathering. Differences in the coating surface composition influence the corrosion behaviour of HDG steel reinforcing bars when they are embedded in concrete. The second issue involves the increasing use of supplementary cementing materials in concrete, which change the chemistry of the concrete pore fluid, and also influence the corrosion. The third issue is that the initial corrosion is accompanied by hydrogen evolution, which could increase the pore volume of adjacent cement and thereby, decrease the bond stress between the concrete and the steel. In order to limit the hydrogen evolution, a chromate layer is applied after galvanizing. The results of the project have demonstrated that, during zinc corrosion in ordinary Portland cement (OPC) concrete, calcium hydroxyzincate formed on untreated HDG steel provided sufficient protection against corrosion. Therefore, it is concluded that treating HDG rebar with dilute chromic acid is unnecessary as a method of passivating zinc. A layer of zinc oxide and zinc carbonate formed through weathering on HDG bars slightly increased the initial corrosion rate and passivation time compared with the non-weathered rebars. HDG steel with an alloyed coating, i.e. consisting of Fe-Zn intermetallic phases, required a longer time to passivate than those with a pure zinc surface layer. The lower zinc content of the surface limited the rate of CHZ formation and, hence, delayed passivation. However, regardless of the surface condition, the coating depth loss after two days of embedment in OPC concrete was insignificant. In concretes containing 8% cement replacement with silica fume, or 25% cement replacement with slag, the initial corrosion rates were higher than those in OPC due to higher pH and lower calcium contents of the concrete pore solution. The higher corrosion rates lead to initial depth losses which are considered significant. However, in these concretes, chromate treatment was also shown to be unnecessary. Through porosity assessment of cements adjacent to HDG bars, it was found that hydrogen evolution accompanying zinc corrosion did not have an impact on the pore volume of cements: any additional pores created by hydrogen gas are filled by the zinc corrosion products. The negligible difference in pore volume between cements adjacent to chromated and non-chromated bars further confirmed that chromated treatment was unnecessary.