Revestimentos de zinco obtidos por imersão a quente têm sido amplamente utilizados em estruturas expostas em solos, águas naturais e atmosfericamente, devido a excelente resistência em meios de baixa agressividade. Nessas aplicações, as arestas de corte ficam expostas e estão mais susceptíveis à corrosão. Objetivando relacionar a microestrutura dos revestimentos com técnicas de microssondas eletroquímicas, para melhor entender os processos corrosivos de aços galvanizados, buscou-se uma nova metodologia para ampliar as fases e obter uma estrutura em camadas. Para a caracterização da morfologia dos revestimentos obtidos pelo processo de galvanização por imersão a quente (galvanized, galvannealed e galvalume) utilizou-se microscopia óptica e eletrônica de varredura com microanálise. Para verificar e analisar os mecanismos de corrosão das fases presentes nos revestimentos de zinco de forma localizada empregou-se a técnica de varredura por eletrodo vibratório (SVET) e microcélula capilar (MEC), e de forma complementar, para identificar os produtos de corrosão formados utilizou-se micro difração de raios X (μ-DRX). Os resultados demonstraram que a metodologia empregada neste estudo é adequada para avaliar as fases de forma individual ou conectadas galvanicamente, e assim identificar as fases mais ativas durante os processos corrosivos. Os resultados obtidos por microcélula complementam os mapeamentos de densidade de corrente obtidos por eletrodo vibratório, mostrando que os intermetálicos permanecem estáveis após os ensaios e a região mais ativa é o revestimento não intemperizado (polido) próximo à interface aço/revestimento. O revestimento que apresentou melhor resistência à corrosão em soluções contendo cloreto foi o Zn55Al. O espectro μ-XRD para o revestimento galvanized, indica a presença das fases zincita e Fe-α sobre o aço IF (interstitial free), mostrando que sob condições de OCP a superfície de aço IF foi protegida pelo revestimento apesar da sua grande área. Esta precipitação pode ainda proteger áreas de aço expostas aonde o revestimento foi danificado por arranhões ou na aresta de corte. / Hot-dip zinc coatings have been widely used in structures exposed to soils, natural water and atmosphere due to their excellent resistance in low aggressive media. In such applications, the cutting edges are exposed and more susceptible to corrosion. In order to correlate the microstructure of the coating with electrochemical microprobe techniques, a new methodology was developed to amplify the size of the phases and to obtain a layered structure. Optical microscopy and scanning electron microscopy were used to characterize the morphology of the coatings obtained by the hot dip galvanization process (galvanized, galvannealed e galvalume). Scanning vibrating electrode technique (SVET) and capillary microcell (MEC) were used to identify and study the corrosion mechanisms of the phases present in zinc coatings. The corrosion products were identified by X-ray micro-diffraction (μ-XRD). The results demonstrated that the methodology employed in this study is adequate to evaluate the phases individually or galvanically connected, thus identifying the most active phases during the corrosive processes. The results obtained by microcell complement the current density mappings obtained by vibrating electrode, showing that the intermetallics remain stable after the analysis and the most active region is the not wedered coating near the steel/coating interface. The coating that showed the best corrosion resistance in solutions containing chloride was the Zn55Al. The μ-XRD spectrum for the galvanized coating indicates the presence of zincite and Fe-α on the IF steel (interstitial free), showing that under OCP conditions the IF steel surface was protected by the coating despite its large area. This precipitation can further protect exposed steel areas where the coating has been damaged by scratches or at the cutting edge.

Este trabalho apresenta um estudo do processo de cromatização de arames galvanizados da Linha de Galvanização 2 da Gerdau Riograndense através do entendimento das variáveis de processo que podem ser alteradas com o intuito de proporcionar uma resistência à oxidação branca maior do que a fornecida com os parâmetros de processo utilizados atualmente. Amostras de arames foram coletadas diretamente da linha de galvanização e submetidas a ensaios acelerados de corrosão em câmaras de umidade saturada (NBR 8095 e ISO 6270-2)16 e de névoa salina (NBR 8094 e ASTM B 117)15. Com base nos resultados obtidos destes ensaios são propostas alterações nas variáveis de processo, como por exemplo, tempo de imersão no tanque de cromatizante, avaliando o aumento ou não do poder protetivo. Os resultados obtidos até agora mostraram que as configurações operacionais da Linha de Galvanização 2 não oferecem uma condição para a formação de uma camada protetora eficiente. Espera-se com este trabalho justificar junto à Empresa a necessidade de alteração de parâmetros de processo para que se consiga obter significativo aumento no poder protetivo conferido pelo cromatizante ao arame galvanizado, e assim, ter condições de disponibilizar ao mercado um produto com qualidade superior no que tange a resistência à oxidação branca. / This work presents a study about the chromatization process for galvanized steel wires in the Galvanizing Line 2 of the Gerdau Riograndense through the understanding of variables of the process that can be modified to provide a superior white corrosion resistance than the one which is provided actually. Samples of wires were collected directly from the galvanizing line and submitted to accelerated corrosion tests in the saturated humidity chamber (NBR 8095 and ISO 6270-2)16 and the salt spray chamber (NBR 8094 and ASTM B 117)15. Based in the results from this tests changes in the process variables are proposed like immersion time in the chromatizating bath to evaluate the increase or decrease of the protective action. The results obtained so far showed that the operational configurations of the Galvanizing Line 2 do not offer a good condition to create an efficient protective layer on the wire. The expectation of this work is to justify to the company that changes in the parameters process are necessaries to get a significant increasing of the protective chromatizating action on the galvanized wire and this way to have conditions to offer to costumers a product with superior quality about white corrosion resistance.

O comportamento eletroquímico do aço-carbono 1005, do aço galvanizado e do zinco foi estudado em meios aerados de ácido sulfúrico 0,5 mol.L-1 (aço-carbono) e cloreto de sódio 0,01 mol.L-1 na ausência e presença do inibidor de corrosão benzotriazol (BTAH), a 25 ºC. Foram empregadas como técnicas ensaios gravimétricos, medidas de transitórios de potencial de circuito aberto, voltametria linear, espectroscopia de impedância eletroquímica (EIE), varredura com eletrodo vibratório (SVET), microscopia eletrônica de varredura (MEV), espectroscopia por dispersão de energia (EDS), espectroscopia eletrônica de raio X (XPS), espectroscopia Raman. O BTAH se mostrou inibidor para os três materiais metálicos nos meios estudados, comportando-se como inibidor misto. A sua ação inibidora decresce na ordem Zn>aço carbono>aço galvanizado em meio de cloreto de sódio. Para o aço-carbono em meio de ácido sulfúrico a adição de íons Cu(II) eleva a eficiência do BTAH, mas em tempos mais elevados de imersão há formação de cobre metálico que promove corrosão galvânica. Em meio de cloreto de sódio os filmes formados sobre aço e sobre zinco correspondem aos respectivos complexos Fe(III) e Fe(II) e de Zn(II) com BTAH. A ação sobre o zinco do BTAH, no caso do aço galvanizado reduz a eficiência na proteção catódica conferida pelo zinco ao aço. A eficiência inibidora sobre aço-carbono depende da composição da liga e da natureza das inclusões presentes no material. Estudos sobre a secção transversal do aço galvanizado em meio de cloreto de sódio mostraram que o BTAH inibe a oxidação do zinco, com formação do complexo, e a redução do oxigênio sobre o aço, com adsorção da molécula de BTAH. O filme formado sobre zinco, ensaiado separadamente, obedece à isoterma de Langmuir, com valores de energia livre padrão de adsorção que evidenciam a natureza química da adsorção, apontando para um complexo com BTAH. / The electrochemical behavior of carbon steel, galvanized steel and zinc has been studied in aerated 0.5 mol.L-1 sulfuric acid and 0.01 mol.L-1 sodium chloride solutions in the absence and presence of benzotriazole (BTAH) at 25ºC. Weight loss experiments, open circuit potential, transient measurements, linear voltammetry, electrochemical impedance spectroscopy (EIS), scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), canning vibrating electrode technique (SVET), X-ray photoelectron spectroscopy and Raman spectroscopy used as techniques. BTAH has shown inhibition for the three materials in the media studied and acted as a mixed inhibitor. Its inhibitive effect decreases in the sequence Zn>carbon steel>galvanized steel in chloride medium. In sulfuric medium the BTAH efficiency is improved with the presence of Cu(II) ions but this effect is suppressed at long times immersion when metallic copper is formed promoting galvanic corrosion. The films formed on zinc and carbon steel in chloride medium correspond, respectively to a Fe(II), Fe(III) mixed complex and to Zn(II) complex with BTAH. Studies on the cross section of galvanized steel (cut edge) have shown that the high effect of BTAH as inhibitor for zinc tends to decrease the efficiency of cathodic protection of this metal on carbon steel. For carbon steel in sulfuric medium the composition and the nature of inclusions have an important role on the inhibitor efficiency. On the cut edge the inhibitor promotes the formation of a zinc complex on this metal and it is adsorbed on carbon steel as a molecule inhibiting the oxygen reduction. The film formed on zinc when separately studied obeys to a Langmuir isotherm with standard adsorption free energy values denoting the presence of chemical adsorption as an indicative of the presence of a complex

Este trabalho apresenta um estudo do processo de cromatização de arames galvanizados da Linha de Galvanização 2 da Gerdau Riograndense através do entendimento das variáveis de processo que podem ser alteradas com o intuito de proporcionar uma resistência à oxidação branca maior do que a fornecida com os parâmetros de processo utilizados atualmente. Amostras de arames foram coletadas diretamente da linha de galvanização e submetidas a ensaios acelerados de corrosão em câmaras de umidade saturada (NBR 8095 e ISO 6270-2)16 e de névoa salina (NBR 8094 e ASTM B 117)15. Com base nos resultados obtidos destes ensaios são propostas alterações nas variáveis de processo, como por exemplo, tempo de imersão no tanque de cromatizante, avaliando o aumento ou não do poder protetivo. Os resultados obtidos até agora mostraram que as configurações operacionais da Linha de Galvanização 2 não oferecem uma condição para a formação de uma camada protetora eficiente. Espera-se com este trabalho justificar junto à Empresa a necessidade de alteração de parâmetros de processo para que se consiga obter significativo aumento no poder protetivo conferido pelo cromatizante ao arame galvanizado, e assim, ter condições de disponibilizar ao mercado um produto com qualidade superior no que tange a resistência à oxidação branca. / This work presents a study about the chromatization process for galvanized steel wires in the Galvanizing Line 2 of the Gerdau Riograndense through the understanding of variables of the process that can be modified to provide a superior white corrosion resistance than the one which is provided actually. Samples of wires were collected directly from the galvanizing line and submitted to accelerated corrosion tests in the saturated humidity chamber (NBR 8095 and ISO 6270-2)16 and the salt spray chamber (NBR 8094 and ASTM B 117)15. Based in the results from this tests changes in the process variables are proposed like immersion time in the chromatizating bath to evaluate the increase or decrease of the protective action. The results obtained so far showed that the operational configurations of the Galvanizing Line 2 do not offer a good condition to create an efficient protective layer on the wire. The expectation of this work is to justify to the company that changes in the parameters process are necessaries to get a significant increasing of the protective chromatizating action on the galvanized wire and this way to have conditions to offer to costumers a product with superior quality about white corrosion resistance.

Orientador: Celia Marina de Alvarenga Freire / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia mecanica / Made available in DSpace on 2018-08-04T09:48:54Z (GMT). No. of bitstreams: 1 Santos_MarciaCristinaGoncalvesdos_M.pdf: 7174846 bytes, checksum: 71b57284d8926f02702b824e265c956a (MD5) Previous issue date: 2005 / Resumo: A excelente resistência do Zinco em diferentes ambientes corrosivos e sua habilidade em proteger o aço, fazem do aço galvanizado e eletrodepósitos, materiais comuns na indústria automotiva e de construção civil. Os substratos de aço galvanizado e eletrodepósitos de Zinco necessitam, no entanto, ser protegidos em ambientes altamente corrosivos por revestimentos orgânicos (pinturas).A má aderência do sistema Zinco/pintura faz com que a superfície do substrato de Zinco receba um pré-tratamento contendo Cromo relativamente barato e efetivo porém, tóxico ao homem e ao meio ambiente. Filmes poliméricos contendo silanos organofuncionais surgem como alternativa à substituição de pré-tratamento livre de Cromo hexavalente 'CR POT. +6¿, pois são moléculas que podem atuar como agente de acoplamento, promotores de adesão e como protetoras de superfície. A principal vantagem da sua utilização é a promoção da adesão entre materiais orgânicos (pinturas) e inorgânicos (metais). Os sistemas Galvanizado/Silano e Ligas eletrodepositadas/Silano, foram estudados nesta dissertação. Para tanto, técnicas como EIE (Espectroscopia de Impedância Eletroquímica), XPS (Espectrometria Fotoelétrica de Emissão de Raios-X), Ângulo de Contato e análises microscópicas foram utilizadas. A avaliação da resistência por barreira foi feita através da Espectroscopia de Impedância Eletroquímica em solução de 0,1 M de NaCI, comparando-se os desempenhos dos revestimentos. A cura induziu uma modificação importante nos diagramas de impedância, além de outras variáveis, como a concentração, o tempo de hidrólise, os tipos de silano e os substratos diferentes. Os resultados indicaram o Zn/Co revestido por VS e Zn/Fe revestido por 'gama¿-UPS como os sistemas mais promissores / Abstract: The Zinc' s excellent resistance, as used in differents corrosive environments, and its hability to protect steel, make galvanized steel (HDG) and Zinc electrodepositions very usual materiaIs in the automotive and construction industries. Galvanized steel and Zinc electrodepositions substrates need, however, to be protected from strongly corrosive environments by organic coatings (painting). Zinc/paint system weak adhesion results in a relatively cheap and effective zinc substrate pretreatment, however toxic to humam being, and also to the environment. Organofunctional silanes appear as an altemative to substitute this pretreatment, without making use of hexavalent chromium 'CR POT. +6¿), because they are bifuncional molecules that can act as adhesion promoters and surface protectors. The main benefit to employ them is to promote adhesion between organic (painting) and inorganic (metals) materiaIs. The GalvanizedlSilane and Electrodeposition Alloys/Silane systems had been studied in this essay. Techniques like EIS (Electrochemical Impedance Spectroscopy), XPS (X-Ray Emission Photoeletric Spectrometry), Contact Angle and microscopical analyses were used in this work. The barrier for resistance was evaluated through Electrochemical Impedance Spectroscopy in a 0,1M NaCI solution comparing coatings performances. Curing caused as importante modification in the impedance diagrams, as well as other variables like concentration, hydrolysis time, silane types and different substrates. The results indicate the Zn/Co alloy coated for VS and Zn/Fe alloy coated for 'gama¿-UPS as the systems most promising / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Le travail présenté essaie de comprendre les mécanismes de l’action d’un inhibiteur de corrosion présent dans un revêtement hybride sous forme de pigments intercalés dans les hydroxydes double lamellaires (HDL) pour la protection de l’acier galvanisé. Trois étapes clés ont été choisies pour ce travail : (1) l’identification d’un inhibiteur de corrosion hydrosoluble pour l’acier galvanisé avec une compréhension de sa réactivité, (2) la détermination des facteurs et des mécanismes contrôlant la libération de l’inhibiteur à partir d’HDL et (3) la compréhension des mécanismes de protection dans un système modèle avec le revêtement hybride contrôlé par la libération de l’inhibiteur et la réactivité d’inhibiteur. MoO42- a montré la meilleure efficacité d'inhibition comparable à CrO42- dans des solutions alcalines et neutres. L’effet inhibiteur de MoO42- a été associé à la formation d’un film riche en Mo(V). L'effet de cet anion sur la dissolution de l'acier à bas carbone a été également vérifié pour exclure la possibilité d'un effet d'accélération des espèces choisies. Les tests de lixiviation ont montré que la libération de MoO42- à partir d’HDL a été contrôlée par la nature des ions échangés à partir du support par un mécanisme d'échange d'ions à un pH neutre et par la dissolution du cadre de la LDH à un pH alcalin. La présence de seulement Cl- conduit à moins de 40% de libération de MoO42- après 24 h d'immersion alors que les additions des carbonates ont abouti à libération de 100% après 1 h. Les tests d'immersion ont montré léger effet d'inhibition du système de revêtement dans Cl- et une augmentation dans CO32- en accords avec le niveau plus élevé de MoO42- libéré. / The current work was dedicated to the investigation of the fundamental mechanisms of the action of a layered double hydroxide (LDH) inhibitor hybrid coated systems for the corrosion protection of galvanized steel. The objective of the work was achieved by the realization of three milestones: (1) the identification of the effective water soluble inhibitor on Zn and steel substrates and the understanding the mechanisms of its action, (2) the revealing the factors and mechanisms controlling the release of the selected inhibitor from Zn2Al/-LDH hosts and (3) the understanding the mechanisms of coated system controlled by inhibitor release and its action. MoO42- showed the best inhibition efficiency comparable to CrO42- in alkaline and neutral solutions. The protective properties of MoO42- were assigned to the fast formation of Mo(V) film. The effect of MoO42- on the dissolution of low carbon steel was also verified to exclude the possible accelerating effect of chosen species. The leaching tests showed that MoO42- release from LDH was controlled by the nature of the exchanged ions from the media by ion-exchange mechanism at neutral pH and by the dissolution of the LDH framework at alkaline pH. The presence of only Cl- resulted in less than 40 % of MoO42- release after 24 hours of the immersion while the additions of the carbonates resulted in 100 % release after 1 hour. The immersion tests showed slight inhibiting effect of coated system in Cl and high in CO32- medias coherent with higher level of MoO¬42- released. The ways to control the inhibitor release and hence, the inhibition performance of coated systems were discussed in the vein of environment composition.

O uso de chapas finas de aço, revestidas ou não, tem sido crescente nos últimos anos, principalmente aquelas que tem revestimento à base de zinco. Isto ocorre tanto na indústria automobilística e mecânica como na construção civil, que geralmente fabricam suas peças e estruturas utilizando um procedimento de soldagem. O objetivo deste trabalho é estabelecer procedimentos de soldagem à arco elétrico com proteção gasosa - GMAW - com transferência por curto circuito, para elementos de chapa fina de aço carbono não revestido e aço zincado, de modo a se obter junções de qualidade aceitável e diminuição das distorções decorrentes dos ciclos térmicos presentes durante a soldagem e, consequentemente a redução das tensões residuais. Em termos de qualidade da solda, propões-se uma combinação de consumíveis disponíveis no mercado, de modo a reduzir os defeitos como: porosidade, respingos, trincas e perda de revestimento. No caso das chapas finas de aço zincado, a melhor combinação de consumíveis encontrada foi: arame com baixo teor de desoxidantes, ER70S-3, e como gás de proteção a mistura 8% CO2 + 92% Ar. Quanto à redução e controle das distorções, três técnicas são utilizadas. A técnica que utiliza em escoadouro dinâmico de calor, formado por um jato de gás refrigerador aplicado logo após o arco de solda durante a soldagem, apresentou maior eficiência na redução das distorções, provenientes do ciclo térmico. / The thin sheet steels, coated or not, has been widely used nowadays, mainly the hot dip galvanized steel sheets. It\'s observed as in the mechanic and automobilist industry as in the civil construction that in manufacturing of pieces and structures employ welding procedures. The aim of this work is to establish procedures to gas metal are welding with short circuit transfer of thin sheet steel elements, not coated and zinc-coated steel, in order to get junctions of acceptance quality and reduction of welding stress and distortion. This distortion arise of the thermal cycles that occur during the welding. In terms of the weld quality is defined the best consumables combination available in the market, in such a way to reduce the weld defects like porosities, spatters, cracks and loss of covering. To galvanized steel sheets, the combination: wire ER70S-3 and mixture 8%CO2 + 92% Ar showed the best performance. Three techniques were employed for control and reduce the welding distortion. One that using a spot heat sink following the arc, in this case the cooling jet, was more efficient that others techniques.

Mechanically stabilized earth (MSE) walls are a more advanced form of a retaining wall, often larger and able to hold back more backfill. This is achieved by reinforcing strips or meshes (most often galvanized steel) placed into the soil, which are held in place by friction. The strips mechanically stabilize the earth while undergoing tension. The wall is covered with concrete medallions that connect to the reinforcements. The medallions have only a secondary structural role in holding up the wall but provide cover that protects the soil from washing away. MSE walls are structures expected to have very long service lives (e.g. 100 years). Confirmation is needed that such durability can be achieved, especially to show that the progression of corrosion of the reinforcement is slow enough. Ten MSE walls around Florida were instrumented (electrical connections were made through the concrete covers to the buried elements) between 1996- 1998 and used to survey corrosion rates of galvanized strip or mesh soil reinforcements. Initial estimates of corrosion-related durability were obtained at that time, indicating a good prognosis for long term durability. The objective of the research in this thesis was to obtain additional indications of the durability of reinforcements in MSE walls in Florida so as to perform a more reliable projection of future performance. Corrosion behavior was measured at the same locations as the initial survey by electrochemical nondestructive tests and by destructive tests. The nondestructive testing consisted of half-cell potentials, polarization resistance measurements, and electrochemical impedance spectroscopy. Corrosion rates reported in this thesis are based upon polarization resistance measurements. The destructive testing consisted of soil extraction and hardware extraction. Hardware extraction enabled independent verification of estimates of electrochemical corrosion rate. Analysis of extracted soil verified that soil composition was within construction specifications. The data from the current survey were also used to further improve prediction of corrosion. The present series of evaluations confirm that the structures are performing as desired based upon the updated model projection of future corrosion.

In recent years, the automotive industry has turned to press hardened steels (PHS) to improve passenger safety while enabling vehicle weight reduction. To form the complex shapes required for this purpose, they are often direct hot press formed. It is possible to provide corrosion resistance to these parts by galvanizing the PHS sheets prior to direct hot press forming (DHPF). However, the austenitization of the galvanized steel causes the Zn-based coating to transform into two intermetallic phases. These are iron-rich α-Fe(Zn) and zinc-rich Г-Fe3Zn10. The Г-Fe3Zn10 is liquid during traditional DHPF, and the applied stress can result in liquid metal embrittlement (LME). Recently, two new grades of PHS have been developed, which allow for DHPF at 600-700°C, below the Fe-Zn peritectic temperature at 782°C, thus avoiding LME. These prototype PHS grades are designated 2%Mn (0.2C-2Mn-0.25Si-0.005B (wt%)) and 2.5%Mn (0.2C-2.5Mn-0.25Si-0.005B (wt%)). The objective of this work is to determine the effect of DHPF on the ability of a Zn-based coating to provide robust cathodic protection to the two prototype PHS. Galvanized panels of both the 2%Mn and 2.5%Mn steel were DHPF with a U-shape die at 700°C. The surface and cross-section of the coating were examined to determine the effects of DHPF on the coating surface. Die friction during DHPF resulted in die wiping on the wall of the part, leading to removal of surface Г-Fe3Zn10. In cross-section, coating cracks were present at the wall and corner of the U-shape part due to the deformation during DHPF. Potentiodynamic polarization scans were used to determine the corrosion potential of the coating, and this was used to calculate the driving force for cathodic protection using the difference in corrosion potential between the coating phases and the substrate. It was found that only Γ-Fe3Zn10 provided robust cathodic protection to both steel substrates, and the driving force for cathodic protection was lower for the coated DHPF 2.5%Mn steel. Galvanostatic scans were used to evaluate dissolution kinetics of coating phases. Robust cathodic protection was provided by the galvanized coating for austenitization times of 30 - 120 s for the 2%Mn substrate and 30 - 60 s for the 2.5%Mn substrate. The duration that robust cathodic protection was provided was shortest at the wall of the U-shape part. This result was attributed to die wiping caused by DHPF, where the surface is smoothed by die friction. When there is less Г-Fe3Zn10 in the coating, such as at longer austenization times, surface Г-Fe3Zn10 was removed and an increased amount of α-Fe(Zn) is exposed, which does not provide robust cathodic protection. In addition, coating cracks form along α-Fe(Zn) grain boundaries after austenitization for 180 s on all examined regions of the U-shape part, allowing a greater surface area of the coating exposed to electrolyte, further increasing dissolution of the coating. / Thesis / Master of Applied Science (MASc)

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