Dissertations / Theses on the topic 'Hot galvanized steel wire'

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.

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

Galvanized steel is one of the most common materials used in the construction industry for its relatively low cost paired with an acceptable corrosion resistance. Nevertheless, the early failure of a number of structures around the world that use galvanized steel has raised some controversy on the understanding of the corrosion behavior of zinc. This dissertation presents the results of several electrochemical studies and mathematical models done on zinc and galvanized steel as an attempt to fill in the gaps of current knowledge. Results indicate an increase on the corrosion rate with increasing amounts of Na₂SO₄, as well as a potential difference between samples in oxygen saturated, aerated, and de-aerated conditions is large enough to promote macrocell formation under aggresive conditions. The presence of sulphate in the soil significantly increased the corrosion rates and, thus, it is important to consider the effect of sulphate in determining the type of de-icing salt. In sulphate-free solutions, potassium acetate appeared to be the best option; while in the presence of sulphate, MgCl₂ and CaCl₂ had the lowest corrosion rate. The improved performance was attributed to the formation of a more evenly distributed corrosion product with better protective properties. Furthermore, when measuring corrosion at temperatures ranging from -5°C to 25°C, the rate observed at sub-zero temperatures is still higher than the rate acceptable for galvanized steel reinforced structures. SEM pictures show that the corrosion products grows preferentially in the vicinity of zinc grain boundaries and that it is apt to cracking with increasing thickness. A numerical model was developed to calculate the corrosion rate of galvanized steel in soil at three different stages of corrosion by considering key soil corrosion parameters. This thesis focuses on the effect of field conditions relevant to the Canadian climate on the corrosion performance of Mechanically Stabelized Earth (MSE) wall soil reinforcement and facings. Results indicate that the proposed model is suitable to be used for the service-life design and risk assessment of MSE walls and to determine the optimum zinc cover thickness.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

Zinc is used widely as a corrosion resistant coating on steel. However, in Europe, zinc is considered an environmental pollutant. Zinc-aluminum alloy coatings may be able to minimize the leaching of zinc into the environment. There are a number of thermodynamic and chemical variables that make the zinc-aluminum coating on steel more durable, in terms of thickness, hardness, corrosion rate, and roughness, thus minimizing zinc pollution and enhancing the durability of the galvanized product. Among these variables are the galvanizing bath temperature and chemical composition, and item immersion time and withdrawal rate. One way to investigate the interaction of these variables is via the use of neural networks. Neural networks are especially useful in mapping independent variables (such as temperature, percentage of alloying metals) to dependent variables (such as zinc layer hardness and thickness) that may be related to each other in a nonlinear fashion. Neural networks learn to recognize patterns, and subsequently store their knowledge after being exposed to a set of sample patterns. This stored knowledge can be used for prediction given a different set of input patterns. The ability of neural networks to predict output after the learning process has been completed makes them very useful in the study of galvanizing. Instead of having to use a great number of experiments to determine the characteristics of the galvanized zinc layer, a neural network can be used to model the galvanizing process, and can predict the properties of the galvanized layer, again, without having to resort to endless experiments - "a Virtual Galvanizing Laboratory." Actual laboratory experiments using zinc-aluminum alloy galvanizing baths were conducted in Rhesca Laboratories, Helsinki, Finland, using a Hot Dip Galvanizing Simulator. A total of thirty six samples were used in the study, thirty for training, and six for testing. A feedforward neural network was successfully trained using Neurodimension's Neurosolutions software. The results of the training and testing of the network exhibited correlation between the bath composition, dipping time, temperature and the sample thickness, roughness, corrosion resistance and hardness. These results indicate that it is possible to construct a "Virtual Galvanizing Laboratory" in which "virtual experiments" can be performed to predict the thickness, roughness, corrosion resistance and hardness properties of zinc-aluminum galvanized steel.

Includes bibliographical references.
The use of galvanised coatings on steel for structural ropes, bundles and wires has become standard practice as unprotected steel is prone to corrosion degradation. Galvanised coatings increase the service lifespan of steel by providing barrier and cathodic corrosion protection. Zinc (Zn) and zinc-aluminium (Zn-Al) alloys are the most commonly used metallic coatings on steel wire. Zn-Al coatings outperform Zn coatings, most notably in marine environments, as they combine the highly insulating oxide film associated with Al corrosion and the cathodic protection of Zn to the underlying steel.

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In this work the causes of rejection of lots of artifacts from the company Produto para Linhas Preformados, PLP, were analyzed which are made of steel SAE 1010 and SAE 1020 and zinc coated by hot-dip galvanizing. Lots of samples from different manufacturers were selected, with different chemical composition and geometry, but belonging to rejected lots and approved lots in accordance with usual market standards. The rejections are due to problems related to the adhesion of the layer of zinc. The samples were submitted to optical microscopy test, scanning electron microscopy and X-ray diffractions for comparative checking of between the structures of zinc formed layers by hot -dip galvanizing. To verify the corrosion in coating failure, corrosion tests were performed in three different environments: urban environment considered to be low-polluted; environment simulating sea water, salt spray. There is no failure evidence between the zinc coating and the substrate structure; irregular coatings and not very well defined phases were found in the rejected parts. In regions with failures, the results show a behavior similar to the literature with the rapid formation of rust at the beginning of the exposure followed by a show oxidation.
Neste trabalho foram analisadas as causas da rejeição de lotes de artefatos da empresa Produto para Linhas Preformados, PLP, fabricados com aços SAE 1010 e SAE 1020 e zincados por imersão a quente. Foram selecionadas amostras de lotes de fabricantes diferentes, com composição química e geometrias distintas, pertencentes a lotes rejeitados e a lotes aprovados de acordo com normas usuais de mercado. As rejeições se devem a problemas relacionados a aderência da camada de zinco. As amostras foram submetidas a exames por microscopia óptica, microscopia de varredura e análises por difração de raio-X para verificação comparativa entre as estruturas das camadas de zinco formadas no processo zincagem por imersão a quente. Para verificar a corrosão nas falhas de revestimento de zinco, foram realizados ensaios de corrosão em três ambientes diferentes: ambiente considerado urbano de baixa poluição; ambiente simulando água do mar; câmara de névoa salina. Não há indício de relação entre a falha nos revestimentos de zinco e a estrutura do substrato; revestimentos irregulares e com fases não muito bem definidas foram encontrados nas peças rejeitadas. Nas regiões com falha, os resultados evidenciam um comportamento semelhante ao da literatura, com formação rápida de ferrugem no início da exposição das peças seguida por uma oxidação lenta.

Afin de maitriser la qualité d'eau dans les réseaux d'eau chaude sanitaire, des traitements de désinfection thermiques et chimiques sont utilisés. Ces traitements de désinfection peuvent avoir un impact sur la dégradation des canalisations. L'influence de l'addition d'hypochlorite de sodium et de l'augmentation de la température sur la vitesse et le mode de dégradation des canalisations en cuivre, acier galvanisé, PERT/Al/PERT et PVCc a été étudiée. Pour ceci, des essais de vieillissement accéléré ont été réalisés en conditions statiques et dynamiques. Afin de réaliser les essais en conditions dynamiques, un banc d'essais à échelle 1 a été conçu et construit.La chimie des solutions d'hypochlorite de sodium à des températures élevées (>50°C) est complexe, ceci a motivé la réalisation d'une étude complémentaire sur les espèces présentes en fonction du pH et la cinétique de décomposition des solutions d'hypochlorite de sodium. Cette étude a révélé que l'augmentation de la température de 50°C à 70°C à une valeur de pH donnée produit une diminution significative de la concentration en acide hypochloreux. De plus, la décomposition de l'hypochlorite de sodium en chlorates est accélérée par la présence de cuivre et elle peut devenir significative à partir de 50°C.Les essais de vieillissement réalisés sur les canalisations ont révélé que l'addition d'hypochlorite de sodium est pénalisante par rapport à la vitesse de dégradation du cuivre, acier galvanisé et PERT/Al/PERT. Cependant, la dégradation du PVCc ne semble pas se voir affectée par l'addition d'hypochlorite de sodium. L'élévation de la température de 50°C à 70°C paraît accélérer légèrement la dégradation du PERT/Al/PERT et du PVCc. En revanche, avec une chloration de 25 ppm en hypochlorite de sodium, le mode de corrosion du cuivre est uniforme à 70°C tandis qu'il est localisé à 50°C.Les conclusions de ces résultats peuvent être d'utilité pour la conception et la maintenance des réseaux d'eau chaude sanitaire.

O processo industrial não-contínuo de zincagem por imersão a quente (ZIQ) pode ocasionar a contaminação superficial do aço-carbono zincado por imersão a quente (AZIQ) com resíduos de cloreto. Estes resíduos, se não forem efetivamente eliminados, podem influenciar negativamente no desempenho dos esquemas de pintura dos sistemas dúplex (zincagem mais pintura). Sabe-se que no processo de ZIQ, a cromatização é amplamente utilizada, entretanto, o efeito que este pós-tratamento exerce no desempenho dos esquemas de pintura ainda não é bem estabelecido. Neste contexto, este trabalho teve como objetivos: I - verificar o grau de contaminação no AZIQ com sal de cloreto devido ao próprio processo de ZIQ; II - verificar os efeitos da contaminação com sal de cloreto e da cromatização do processo ZIQ no desempenho de tintas aplicadas sobre o AZIQ; e III – determinar pré-tratamentos para pintura adequados para o bom desempenho das tintas aplicadas sobre o AZIQ. A metodologia adotada para alcançar o objetivo I envolveu a zincagem de chapas de aço-carbono em diferentes prestadores de serviço de ZIQ, em diferentes condições. Estas chapas zincadas foram analisadas por microanálise química qualitativa por espectrometria de dispersão de energia (EDS) em microscópio eletrônico de varredura (MEV) e pela determinação dos teores de cloreto superficiais, por método de extração com água em ebulição. A partir dos resultados obtidos para se alcançar o objetivo I, foi possível definir as condições no processo de ZIQ que potencialmente causam maior contaminação da superfície do AZIQ com sal de cloreto. Assim, para se alcançar os objetivos II e III, chapas de aço-carbono foram zincadas naquelas condições de máxima contaminação com sal de cloreto e parte delas foi submetida ao pós-tratamento de cromatização. Em seguida, uma grande parte destas chapas zincadas (cromatizadas ou não) foi submetida aos pré-tratamentos para pintura de desengraxe com solvente orgânico, de hidrojateamento a alta pressão, de jateamento abrasivo ligeiro e de ação mecânica com esponja abrasiva e água quente. Finalmente, as chapas zincadas, incluindo as não submetidas aos pré-tratamentos, foram pintadas com uma demão de tinta de aderência mais uma demão de tinta de acabamento. As chapas zincadas e pintadas foram submetidas a ensaios acelerados (imersão em água destilada e exposição em câmara de umidade saturada) e não-acelerados de corrosão (exposição em estação de corrosão atmosférica) e avaliadas por meio dos ensaios tradicionais de acompanhamento de desempenho (grau de empolamento e ensaios de aderência de tinta) e eletroquímicos (medida de potencial de circuito aberto, curva de polarização e espectroscopia de impedância eletroquímica – E.I.E.). Algumas chapas zincadas, antes da pintura, foram submetidas aos ensaios de caracterização física (exame microestrutural e morfológico em MEV e rugosidade superficial), química microanálise por EDS, difração de raios X e teor de cloreto superficial pelo método de extração com água em ebulição) e eletroquímica. Os resultados obtidos, neste estudo, permitiram verificar que a aplicação adicional de sal cloreto de amônio sólido durante o processo de ZIQ tende a aumentar o grau de contaminação superficial do AZIQ com cloreto e, as etapas de resfriamento e/ou de cromatização do processo também contribuem para esta contaminação. No geral, o desempenho do AZIQ cromatizado teve desempenho inferior em relação ao não-cromatizados. O hidrojateamento a alta pressão e a lavagem com água e ação mecânica foram os prétratamentos que proporcionaram os melhores desempenhos dos esquemas de pintura.
The batch galvanizing process (BGP) can lead to surface contamination of hot-dip galvanized steel (HDGS) with chloride residues. If these residues are not effectively eliminated, they can influence negatively on the performance of duplex systems (galvanizing plus painting). It is known that the chromate quenching is widely used in the BGP, however the effect of this post-treatment on the performance of duplex systems is not well established yet. In this sense, this work aimed: I – to verify the contamination degree of HDGS with chloride salt due to the BGP itself; II – to verify the effects of the chloride salt contamination and chromate quenching on the performance of paints applied on HDGS; and III – to determine the suitable surface preparation for painting in order for obtaining a good paint performance applied on HDGS. The adopted methodology to achieve goal I involved the galvanizing of steel plates in different service renderings with BGP, in different conditions. These HDGS plates were submitted to the qualitative energy dispersive microanalyses (EDS) in scanning electron microscopy (SEM) and to the determination of superficial chloride contents by the boiling water extraction method. From the obtained results, the conditions in the BGP that potentially lead to greater surface contamination of HDGS with chloride salt were determined. Thus, to achieve goals II and III, steel plates were galvanized under the maximum chloride salt contamination condition and part of them were submitted to chromate quenching. After that, a great part of these HDGS plates (chromated or non chromated quenching) was submitted to the surface preparations for painting through organic solvent cleaning, high pressure hydroblasting, sweep blasting and handled scrub cleaning with an abrasive sponge and hot distilled water. Finally, the HDGS plates, including those not submitted to the surface preparations for painting, were painted with one coat of primer plus one coat of finishing paint. The HDGS painted plates were submitted to accelerated (distilled water immersion and humidity chamber exposure) and non accelerated (atmospheric exposure) corrosion tests and their performance were verified by means of traditional tests (degree of blistering and paint adhesion) and electrochemical measurements (open circuit potential, polarization curve and electrochemical impedance spectroscopy – E.I.S.). Before painting, some HDGS plates were submitted to tests for physical (microstructural and morphological analyses in MEV and surface roughness), chemical (EDS, X-ray diffraction and superficial chloride contents by the boiling water extraction method) and electrochemical characterization. The obtained results allowed verifying that the additional application of solid ammonium chloride salt during the BGP tends to increase the degree of superficial chloride contamination of the HDGS and, the water and/or chromate quenching also contribute for this contamination. In general, the chromated HDGS presented worst performances. The high pressure hydroblasting and the handled scrub cleaning with an abrasive sponge and hot distilled water were the surface preparations for painting that provided the best performances of paint systems.

碩士
義守大學
材料科學與工程學系碩士班
94
The effects of zinc coating thicknesses, steel sheet substrates, baking treatment and prepainting process on the crack resistance capability of hot-dip galvanized steel sheets in deformation were studied. The relationship between zinc cracking modes and the deformation mechanisms of the zinc coatins were also discussed. These zinc coatings obtained from a continuous hot-dip galvanizing line consisted of δ, ζ and η-Zn phase. The hot-dip galvanized coatings showed a strong preferred orientation on the basal plane. 180∘0T bending deformation tests and tensile deformation tests were performed on the galvanized steel sheet samples to understand the deformation mechanisms and cracking behaviors. Microstructural observations indicated that the thicker zinc coatings exhibited worse cracking resistance in the 180∘0T bending deformation tests. Zinc coatings on annealed steel substrates showed better crack resistance than those on full hard steel substrates. Grain boundary separation and transgranular cleavage were responsible for the dominated cracking modes in the uniaxial tensile deformation and 180∘0T bending deformation, respectively. Mechanical twinning plays an important role in the deformation of zinc coatings. Peelings at the interface between the steel substrate and zinc coating were also observed at the rupture point after tensile tests. 300℃ baking treatment and commercial prepainting process showed helpful to improve the crack resistance capability of hot-dip zinc coatings. Recrystallization of zinc layer was found to be the root cause of the crack resistance improvement after prepainting or baking treatment.

博士
國立臺灣大學
材料科學與工程學研究所
99
Hot-dip galvanized steel (GI steel) is widely applied to automobile, electrical appliance and construction fields. To protect Zn coating against corrosion during transportation and storage, hexavalent Cr treatment is generally adopted. Hexavalent Cr coating provides superior barrier layer protection and self-healing protection. However, a strict restriction was imposed on the use of chromate passivation because of the toxicity of hexavalent Cr. Therefore, non-chromate treatments have received an ever-increasing attention. The purpose of this study is to develop a roll coating non-chromate passivation treatment for GI steel (commercial roll chromate passive coating as comparison). This study prior investigated the phosphate treatment for GI steel by immersion coating process. Then, the composite phosphate, molybdate and vanadate treatment for GI steel conducted by two-step and one-step roll coating process were explored. Results showed that the presence of Mg2+ in the phosphate solution, the phosphate coating prepared by immersion coating process was composed of mixed Zn phosphate hydrate and (Zn, Mg) phosphate hydrate with high degree of crystallinity. Elevating Mg2+ in the solution markedly reduced the phosphate grain size and increased the population density of the phosphate grains. As a result, the porosity of the phosphate coating was reduced with increasing solution Mg2+, which, in turn, improved the corrosion resistance of the coating. The one-step roll phosphate coating was porous, amorphous and was composed of mixed Zn phosphate/(Zn, Mg) phosphate and Zn(OH)2. The one-step roll phosphate coating underwent the molybdate or vanadate post treatment, the defects of the phosphate coating were mainly repaired and the incorporation of (H2PO4-, HPO42-) and (MoO2, MoO42-) or [V2O4 , V10O27(OH)5−, V10O286− …] was also detected. As a result, the corrosion resistance and self-healing ability of the coating were both improved. Compared to the two-step roll phosphate/molybdate coating, the two-step roll phosphate/vanadate coating had a better corrosion resistance and self-healing ability was owing to a less amount of the defects (more spherical particles) present in the coating, higher content of low-valent oxide with lower solubility (V2O4) and high-valent anion with greater oxidizing power [V10O27(OH)5−, V10O286− …] incorporated into the coating. The one-step roll phosphate(molybdate) coating and phosphate(vanadate) coating are both porous, amorphous and were composed of mixed Zn phosphate/(Zn, Mg) phosphate, Zn(OH)2, (H2PO4-, HPO42-) and (MoO2, MoO42-,) or [V2O4 , V10O26(OH)24-, V10O27(OH)5-...] and they showed a better corrosion resistance and self-healing ability than those of the one-step roll phosphate coating. Compared to the one-step roll phosphate(molybdate) coating, the one-step roll phosphate(vanadate) coating displayed a better corrosion resistance and self-healing ability was owing to a higher content of low-valent oxide with lower solubility (V2O4) and high-valent anion with greater oxidizing power [V10O26(OH)24-, V10O27(OH)5-...] incorporated in the relatively-thick coating. Compared with the molybdate post treatment or additives, vanadate post treatment or additives rendered a better corrosion resistance and self-healing ability of the phosphate coating, vanadate post treatment especially. Among the roll coating non-chromate passivation treatment (the two-step roll phosphate/vanadate, the one-step roll phosphate(vanadate), the two-step roll phosphate/molybdate, the one-step roll phosphate(molybdate), the two-step roll phosphate/vanadate demonstrated the best corrosion resistance was due to a less amount of the defects (more spherical particles) present in the coating. Besides, a higher content of high-valent anion with greater oxidizing power [V10O27(OH)5−, V10O286− …] incorporated into the coating contributed the best self-healing ability of the two-step roll phosphate/vanadate coating. Morover, elevating the concentration of [V10O27(OH)5−, V10O286− …] in the post solution rendered a similar corrosion protection and self-healing ability of the two-step roll phosphate/2vanadate coating as compared to those of commercial roll chromate coating.

碩士
義守大學
機械與自動化工程學系
107
Zinc is a light gray metal with a specific gravity of 7.14 and an atomic weight of 65.37. Zinc is a divalent metal in the compound. The standard potential of zinc is -0.76 volts, the electrochemical equivalent is 1.22 g/ampere-hour, and the melting point is 419 ° C. Zinc-plated, with surface shape and thickness controllable, maintenance-free, low cost, strong corrosion resistance of the coating, etc., and the surface roughness of the steel is produced according to the different manufacturing methods. Take the general processing unit as an example, each manufacturing process in a mechanical plant, different machining precisions and high-frequency vibrations during machining would result in various tolenrence. The machining parts will have a certain surface friction with the tool, resulting in the machining materials having different roughness on the machined surface. Due to the mechanical processing of the parts, the blueprint and the specification need to be hot-dip coated, so the adhesion and surface roughness of the coating are particularly important. Therefore, this study is aimed at the different surface roughness of the steel after mechanical processing. Mechanical properties related variations were studied.

碩士
國立臺灣大學
材料科學與工程學研究所
96
Hot-dip galvanized and galvanealed steel sheets have excellent corrosion resistance, and can be found in body panels and related components in the automobile industry. Large amounts of hot-dip galvanized steel plates are also used in structure, home appliances, and tool applications. To optimize the hot-hot dip galvanize process, it is essential to develop a quick and effective microstructural evaluation method. In this study, an effective technique to determine the effect of aluminum content in the zinc bath, bath temperature, strip entry temperature, and dip-time on the interface microstructure has been established. Results showed that Fe-Zn intermetallic compound can be observed in chemically color etched cross-sectional OM samples: ζ and δ were observed from the zinc coating towards the steel substrate. However, Γ and Fe-Al phases were not observed under OM due to its limited resolving power. In contrast, via cross-sectional TEM, selected area diffraction, EDAX, and GA-XRD analyses, higher aluminum content can be found at the zinc-steel interface in the form of granular and lamellar Fe2Al5 intermetallics. Also, open circuit potential can be a time-saving technique to analyze the presence of Fe-Al phase. Furthermore, the non-uniform corrosion behavior can be observed in the open circuit potential curve. Selective layer on the coating can be removed while performing open circuit potential in 4wt% HCl to observe each layer morphology and crystallinity in SEM and GA-XRD. In summary, when bath temperature, strip entry temperature, and hot-dip time increase, the extent of transformation from Fe-Al to Fe-Zn phases increases, in low aluminum content zinc bath (0.12 wt%). In mid-to-high aluminum content zinc bath (0.16 wt%, 0.20 wt%), in the condition that Fe-Al inhibition layer have not transformed to Fe-Zn intermetallics, the higher the bath or strip entry temperature, the higher thickness in the Fe-Al inhibition layer.

碩士
國立高雄應用科技大學
機械工程系
106
In this study of the salt spray test (SST:Salt Spray Test),exposure test, electrochemical and humidity resistance tests were used to study the corrosion resistance of hot dip galvanized (galvalume)steel sheets and prepainted steel sheets of different coatings. Salt spraying test of different coating amount of hot dip galvanized steel sheets observed that the amount of coating Z12 began to produce red rust in 200 hours and the rest of the coating amount did not occur red rust. The amount of coating Z18 started to produce red rust in 500 hours and Z22 started to produce red rust in 1000 hours, but there was still no red rust in Z27 to 1500 hours. The thickness of hot-dip galvanized steel sheets (SGCC-Z27) and the hot dip galvalume steel sheets (SGLC-AZ150) are equivalent to those of the two specifications that hot-dip galvanized steel sheets is 0.040mm/hot-dip galvalume steel sheets is 0.043mm.However,the corrosion current density is 1.199X10-7A compared to SGCC-Z27 and SGLC-AZ150 is 8.532X10-8A.Obviously,the corrosion resistance of hot-dip galvalume steel sheets will be better than that of hot-dip galvanized steel sheets with the same thickness as the coating.Hot dip galvalume steel sheets 20% deformation corrosion current density 32.4x10-7A is 4.56 times of the deformation current 0% corrosion current density 7.1 x10-7A.In addition, the corrosion current density of the hot-dip galvalume steel sheets increases as the deformation increases, which means that the corrosion rate increases.The smaller the radius of curvature of the ribs of the corrugated steel sheets will have an adverse effect on the corrosion resistance of the steel sheets. 55% Al-Zn Alloy-Coated steel sheet (55%Al-43.4%Zn-1.6%Si) polyester resin prepainted steel sheets(AZ150-PE) is immersed in 3.5% NaCl solution for 25 days after different tensile deformations (0%-20%). The polarization curve test was first conducted from the cathode to the anode with a potential scan rate of 0.5 mV/sec. The corrosion current density of prepainted polyester steel sheets increases sharply at 15% deformation from 1.77x〖10〗^(-6) A to 3.24x〖10〗^(-6) A.The deformation of 20% of the corrosion current density 860.3x10−10A is a 99.77% increase in the corrosion current density of 1.939x10−10A without deformation.The corrosion current density of the polyester resin prepainted steel sheets increases linearly with the increase of the deformation amount, and rises sharply at 15%.The polarization curve of the polyester resin (PE) /poiyvinylidene floride(PVDF)/siliconeized modify polyester (SMP) immersed for 20/25/30 days fit data that corrosion current density order is AZ150-PE> AZ150-SMP> AZ150-PVDF.

碩士
國立海洋大學
材料工程學系
83
Hot-dip galvanizing process is widely used for steel to prevent corrosion. Galvanized steel is also suggested to use in marine environment. To prolong the life of galvanized steel, various corrosion inhibitors were chosen to evaluate their inhibition efficiencies. Immerson test, potentiodynamic polarization technique and applied galvanostatic constant current method were combined to investigate corrosion inhibition efficiencies for various chemical additives in galvanized layer and steel respectively. Chemical additives include Na2CrO4‧4H2O、CaO、 Al2(SO4)3‧13H2O、Na2SiO3‧9H2O、Na2MoO4‧2H2O、 Na2CO、NaNO2、ZnSO4‧7H2O and Na3PO4‧12H2O. Results show that sodium chromate, sodium silicate and zinc sulfate are excellent corrosion inhbitors for both zinc coating and steel, and exbit good corrosion inhibition effect in 3.5% NaCl solution. The amount of aluminum sulfate and sodium phosphate added in 3.5% NaCl solution should be maintained below 2g/l, otherwise, corrosion rate will be increased. Galvanizing coating sacrificially protects steel, combines with addition of inhibitor, will be mostly improved.

碩士
長榮大學
職業安全與衛生學系碩士班
97
Hot-dip galvanizing is the technique widely used for steel corrosion protection in developed countries. Currently a majority of steel roll manufacturing factories are using the technique in their manufacturing processes. Metal fume is produced from the molten metals in the manufacturing processes. The metal fume can have the elements or their oxides of zinc, nickel, lead, chromium, manganese etc. The workers in the workplace can have adverse health effects due to exposure to these metals. Few studies were conducted on the exploration of whether the workers of hot-dip galvanizing manufacturing processes were exposed to the exceeding levels of the permissible exposure limits of the metals. More studies are needed for this topic. In this study the workers in a hot-dip galvanized steel roll manufacturing factory were recruited for personal breathing-zone exposure measurements of metal fumes and urine sample collection. Area samples of metal fumes were also taken when the personal exposure measurements were conducted. Each personal exposure sample was taken by using an IOM with a 25 mm mixed cellulose ester (MCE) filter. The area sample was taken by using a cassette with a 37 mm MCE filter. Urine samples of the workers were collected during the work time of a normal 8-hour workday. The metal contents of zinc, nickel, chromium lead and manganese of the collected samples were analyzed by atomic absorption spectrometry (Varian AAS 220FS, Australia) with a flame or graphite tube atomizer. During the period of exposure sampling, the characteristics of manufacturing processes, work activity and environmental setting were observed and recorded for exposure assessment modeling. The mean (±standard deviation) concentrations of zinc, nickel, lead, chromium, and manganese measured by the area samples were 5.36±2.74, 0.10±0.06, 0.25±0.12, 0.61±0.33 and 0.081±0.034 mg/m3, respectively. The mean (±standard deviation) concentrations of zinc, nickel, lead, chromium, and manganese measured from the personal samples were 7.90±9.54、0.11±0.13、0.28±0.29、0.28±0.32 mg/m3 respectively. The results indicated that the workers’ exposure to the metals exceeded the threshold limit values suggested by the ACGIH. The mean (±standard deviation) concentrations of chromium in the urine samples were 11.397(±8.25) g/dL which far exceeded the ACGIH’s biological exposure indices. Effective exposure control strategies are required to reduce the metal exposure of the workers in the manufacturing processes.

碩士
逢甲大學
交通工程與管理所
95
Bridges play a crucial role to communicate with two places and extend traffic scope of human. Thus, It''s an important subject for concerned agency to maintain bridges'' function and safety following its construction. As we know, Steel bridges show the characteristics of the lightweight, high strength and high ductility. However, the corrosion problem caused by aging of the coating system of steel bridges will affect the structural safety and increase the cost of maintenance at operation stage. Nowadays, many bridges did not meet its design life yet, and had demolished to pay huge cost for repair and replenishment. This is owing to lack of technique or quality as its beginning. This paper describes a hot dip galvanized steel bridge performing as a free maintenance and also discusses how to prevent the deformation of the galvanized fabrications during the period of the planning, design and maintenance of the galvanizing steel bridge. Moreover, offering a comfortable driving environment in the phase of maintenance. In the past, the bridge design unit only concerned what alternative is economic but neglected the after-cost in the bridge life cycle. As mentioned above, Steel Bridges expected to apply life cycle concept in bridge engineering aiming to minimum bridges'' life cycle cost. Therefore, it''s a major subject to decrease bridges'' cost in its life cycle.

Hot-dip galvanizing is widely used for corrosion protection of steel structures. However, there has been a plethora of recent reports on premature cracking in galvanized steel structures, which have resulted in some early decommissions or even hazardous collapses. This research focuses on cold-formed Rectangular Hollow Sections (RHS). A total of 108 tensile coupons were tested to investigate the effects of galvanizing as well as different pre-galvanizing treatments on the material properties around the cross sections of the specimens. For the first time, this thesis reports a comprehensive measurement of residual stresses in different directions at the member ends which are directly relevant to the cracking issue. The results were also compared to the residual stresses far away from the member ends, which are relevant to structural stability research. In all, the research provides a better understanding of the characteristics and structural performance of galvanized RHS to facilitate its application. The recommendations can help engineers, fabricators, and galvanizers mitigate the risk of cracking in RHS during galvanizing.
Graduate

碩士
中華大學
機械與航太工程研究所
89
SKD11-steel and SS41-steel are used as the substrates of die materials which were coated with TiN , CrN and DLC materials. The hot dip galvanized steel sheet was applied to evaluate the galling effect during press processes. According to the results of the surface roughness measurements and the hardness of the coating , surface roughness and hardness of die with coating materials are superior to which without coating materials. On the other hand, in terms of formability and coefficient of friction, die with coating materials also performs better than that without coating materials. Moreover, it was found that DLC coated materials have the best performance of formability, coefficient of friction and galling comparing with CrN and TiN materials. In addition, if considering SS41-steel and SKD11-steel plated with DLC material, SS41-steel is more competitive than SKD11-steel when expense is taken into account.

碩士
義守大學
材料科學與工程學系碩士班
96
In this research we made a comparison between the zinc cracking behavior of hot-dip 5% aluminium zinc steel sheets (Galfan Steel Sheets, GF) and that of hot-dip galvanized steel sheets (Galvanized Steel Sheets, GI), and discussed the baking treatment effect on the crack resistance. The specimens were acquired from a continuous hot-dip galvanized line. We analyzed the cracking resistance of coatings by using bending deformation tests and tensile deformation tests. We also performed the baking treatment to simulate the prepainting process. The thermal effect of prepainting process on the cracking resistance of coatings was discussed. The microstructure changes, and the cracking models after 180° 0T bending deformation and tensile test were studied using OM, SEM, EDS, GDS and XRD. The results showed that GI was superior in cracking resistance to GF. XRD analysis results showed that preferred orientation of GI changed from plane (002) to plane (100) or plane (101) during tensile deformation. During deformation process, a large amount of mechanical twins was generated in the hexagonal-closed-packed zinc solid phase in GI coating. Even though mechanical twinning occurs in GI was helpful to relax partial deformation strain and contribute more slip systems in the tensile deformation. However, mechanical twinning in GI changed the preferred orientation significantly and made the transgranular cleavage developing easier alone the basal plane of zinc. In contrast with GI, the eutectic structure of GF coating suppressed the occurrence of mechanical twinning suppressed. The cracking of GF prefered the mode of grain boundary separation after tensile test. The cracking of thicker coating prefers the mode of transgranular cleavage after bending test, Both grain boundary separation and transgranular cleavage could be observed in thinner coating after bending test. The experimental results also indicate that the coatings on the annealed steel substrate were superior in cracking resistance to the coatings on the full hard steel substrate. Zinc cracking resistance was found to decay after cyclic baking treatment. The porosity generation inside the Zn layers during cyclic baking treatment, which could be explained on the basis of the Kirkendall effect, was believed detrimental to the cracking resistance of Zn coatings.

The use of laser welding in the automotive industry in the past few decades has facilitated joining of hot-dip galvanized (HDG) steel sheets at high production rates and low cost. The recent development of tailor welded blanks (TWB) using laser welding allowed combinations of sheet grades and thicknesses to “tailor” the vehicle part for optimized design, structural integrity and crash performance but more importantly, reductions in weight. Welded blanks are further subjected to stamping or stretch forming prior to final assembly. Unfortunately, both welding and stretch forming cause the galvanized coating to deteriorate, and thereby, undermine the long term corrosion protection. Despite existing publications on zinc coated steel and advances in processing techniques, there is a lack of understanding on the influence of laser welding and stretch forming on the corrosion performance of HDG steel. Hence, the purpose of this study was to determine how welding speed and biaxial strain affect interstitial-free (IF) and high strength low allow (HSLA) steel coupons when they are subjected to continuous immersion and accelerated corrosion tests. The corrosion rates of the coupons were evaluated using electrochemical techniques and gravimetry. Changes in the galvanized coating were characterized using scanning electron metallography. It was observed that, the original zinc layer transformed into the delta and gamma Fe-Zn intermetallic phases locally in the heat affected zone (HAZ) after laser welding. The resulting microstructure was similar to that of a commercially galvannealed coating and exhibited superior corrosion resistance than that of pure zinc. Linear polarization resistance (LPR) measurements revealed that the zinc coating was able to protect a chemically exposed region of steel in 0.1 M NaCl solution. While the Nd:YAG laser welded coupons with narrow HAZs performed equally well as the non-welded ones, diode laser welded coupons, with a wide locally annealed coating in the HAZ, exhibited a decrease in the peak corrosion rate of zinc. Moreover, minimal amounts of rust were observed on the surface of the HAZ after testing. With biaxial strain, welded and deformed coupons generally demonstrated higher peak corrosion rates than that of undeformed welded ones. When subjected to cyclic corrosion testing according to SAE J2334, rust formed in the exposed region after one 24 hour test cycle due to wet-dry conditions. However, zinc corrosion products on the surface provided substantial corrosion resistance to the remaining zinc coating and to the steel substrate. Gravimetric measurements of welded coupons showed a linear increase in weight gain with increased exposed widths of the steel after 30 cycles but biaxial strain further increased the weight gain on deformed coupons. After 60 cycles, the trend became exponential for both welded and deformed coupons. There was a negligible difference between the corrosion performance of IF and HSLA steel. Using X-Ray diffraction and Raman spectroscopy, species of both iron and zinc corrosion products were identified. Without the application of paint coatings, zinc oxide (ZnO), zinc hydroxy chloride (ZnCl2[Zn(OH)2]4), and hydrozincite ([ZnCO3]2[Zn(OH)2]3) were responsible for passivating the surface and reducing the overall corrosion rate of the galvanized coating.

碩士
義守大學
材料科學與工程學系碩士班
94
The purpose of this study is to investigate the properties of Anti-Fingerprinted Coatings（AFP）and the subsequential properties of the AFP Galvanize and Galvalume coated steel sheets by various tests including thermal analysis, AFP electrical resistance measurement, AFP alkaline and acid resistance dipping tests, AFP Galvanize and Galvalume coated steel sheet electrical resistance measurements, AFP Galvanize coated steel sheet salt spray test（SST）, and Galvalume coated steel sheet alkaline resistance dipping tests. Meanwhile, alkaline and acid resistance dipping tests and SST for Galvanize, Galvalume, and Galfan coated steel sheets without AFP coating were conducted as well. Glow discharge spectrometer（GDS）, scanning electron microscope/energy dispersive spectrometer（SEM/EDS）and electron probe microanalyzer（EPMA） were utilized to explore the differences among various AFP coatings, corrosion mechanism and application of GI, GL, and GF coated steel sheet under various PH conditions. It was found that the measured surface electrical resistance of the AFP Galvanize coated steel sheet is essentially the resistance of the Galvanize coated steel sheet itself. Results of AFP alkaline and acid resistance dipping test show some difference among four types of AFP. On he other hand, no significant difference between chromium and non-chromium AFP Galvanize coated sheet sheet was found for the results of the salt spray test. From the SEM observation and the EDS element analysis, it was revealed that corrosion of the GI, GL and GF coatings all started from the zinc-rich area under acid condition, and GL coated steel sheets preformed the beat acid corrosion resistance among three coated steel sheets. On the other hand, it was aluminum-rich area first to corroded under alkaline condition, and GF coated steel sheets performed the best among them. Furthermore, the results of the salt spray tests has shown that corrosion started also from the zinc-rich area while GF coated steel sheet preformed the best among there.

碩士
義守大學
材料科學與工程學系碩士在職專班
100
The purpose of this study is to observe the effects of different cooling condi-tions on the formation of the spike-like spangles, with the conditions set and samples obtained directly in the production process. The main operation parameter of this study is the volume of cooling air in No.1 and No.2 up-leg coolers. When the volume of cooling air increased from 179m3/min to 288m3/min, the length of the spike-like spangles on both sides of the steel sheet shortened, with their frequency of appearance reduced accordingly. Observations under optical micro-scope revealed that the long, rectangular parts of a spike-like spangle showed an equiaxed grain structure, while the slender, needle-like ones on the sides showed a columnar grain structure. The grain sizes of the equiaxed and columnar crystals were found to be unaffected by different cooling rates, with no significant difference in their respective elemental compositions. Micro hardness tests showed that areas of spike-like spangles were harder than those of normal ones. The main factor con-tributing to a higher hardness is the much smaller grain size of the spike-like spangle. Results from salt spray tests showed no significant difference in corrosion re-sistance between spike-like spangles and normal ones.

碩士
國立高雄應用科技大學
模具工程系碩士班
96
This thesis focuses on the die design of non-offset punch profile for the cold-rolled zig-zag sheet blank bending in order to solve the wrinkling and fracturing problems occurred in the conventional offset punch profile design. The coated blank is cold roll-formed to create zig-zag edges to strengthen the plate in stead of plain sheet produced in rolling process. A special punch profile design called “golden finger” is proposed to cope with the roll-formed zig-zag edges on the blank and avoid the folding and wrinkling defects. The criterion of paint scratching has been established to evaluate the die design. The cutting profile designs are proposed to obtain a more uniform bent edge in the vertical wall of product. The design of experiments (DOE) method is adopted to study the effects of different die and process design factors. CAE analysis is adopted to predict the sheet material flow, stress, strain, and pressure induced after forming for different designs. The intuitive rules of non-offset punch profile design are proposed to create “golden fingers” on the punch to control material flow smoothly. The control point updating algorithm of a Bezier curve is proposed to design the profile of cutting edge effectively. The analysis results of the optimum design show a sound product was obtained without folding defect and less irregularity at the edge of vertical bent wall. The experimental results of bending are in good agreement with the edge profile prediction of simulations. The scratching of paint on the coated surface of blank is decreased using the optimum punch profile design.

碩士
中華大學
機械與航太工程研究所
90
In this study，SKD11 and SS41 are used as the substrates of die materials which were coated with TiN , CrN and DLC materials. The hot-dip galvanized steel sheet that were sprayed with 6917、6917 with graphite 、AC200、AC200 with graphite、AC240、AC240 with graphite、PU、PU with graphite、SS150、SS150 with graphite and Teflon（PTFE） was applied to evaluate the formability during press processes. According to the results，the formability of hot-dip galvanized steel using the die with coating materials is better than that using die without coating materials . Specimens Added of solid lubricants were found also improving the formability of the specimens. It was found that PU and PU with graphite are the two solid lubricants that can improve the formability of materials with or without using die coating materials. However， the use of these two lubricants will increase the coefficient of friction. The SKD11 die material with the use of solid lubricant AC200 had been measured with the least of coefficient of friction，but its improvement of formability is insignificant. According to the results ，the use of solid lubricant SS150 with all die materials is the best choice not only for improving formability but also achieving good coefficient of friction.

M. Tech. Metalurgical Engineering.
A research project was launched to produce zinc/ nickel, zinc/ tin and zinc/aluminium alloys at different concentrations and to test zinc pick-up with the typical steels used in South Africa. Results show that the addition of 0.023% Al and 0.06% Ni in the zinc bath can be successfully used to reduce the zinc pick up of commercial grades of steel. Tin improved quality of coating as compared to pure zinc.

碩士
國立中正大學
企業管理所
97
The steel industry is the foundation of all industries, it is the basic industry of the national construction and the national defense industry, and it has also being called the mother of industries. Due to the consideration of economic development and security reason of the national defence, the governments of most countries often taking high tariff, quota to limit or classifying as the specific project of importing etc., in order to protect the development of the national steel industry. The production facilities, equipments, raw materials and energy consumptions are all more costly than the general industries. Thus, the steel industries are highly capital and skill intensive. The steel industry in Taiwan has been through and strived for half a century. Nowadays, the complete foundation of the steel industry in Taiwan has been established and proceeds to grow up. However, the breakout of the global financial crisis last year causes the sudden stagnation for the demand of the steel-made products, and brings the severe crisis ever for the steel industry. In addition, the drastic fluctuation of the international petroleum price also causes the production costs to go up as well as the prices of a variety of energy and raw materials. Under the severe environment today, the profits in the steel industries have being shrinked. That forces the managers in this industry to take steps to deal with this situation. In addition to making great efforts to develop the new products, to increase the profit margins, and to maintain basic and smooth operations of produciton lines and the prerequisite in the scale of economy, managers can’t help but make more cost-effective decisions. Among these decision problems, the optimal productin planning problem and product mix problem are two of the most crucial problems to the steel industry. Thus, the objective of this research is to develop the mathematical programming models to cope with these two decision problems. By considering the hot-rolled line of wire rods and reforming bars material for real industry production, we take various kinds of limiting conditions under the realistic environment into the mathematical programming models, and obtain the best production planning and the optimal product mix for the case steel firm so that the corporate''s minimum total production costs and the best profit-making level can be achieved.

碩士
致遠管理學院
金屬材料工程與管理產業研發碩士專班
98
Of the wire coil surface quality defects in the rod mill plant, the highest failure rate of the rod mill materials has become the serious problem that want to solve. This study is to investigate the coil surface defects of X steel wire rod rolling processes, and statistical analysis, experimental observation and analysis, planning and implementation of the improvement and benefit evaluation methods are discussed. This study, combining with X steel ERP system data analysis, finds that in 2007, the lap and seam failure goods weight up to 941.4 tons. It accounts 44.22% of total defects, and 0.385% of the annual production. With actual observation and analysis, it is concluded the leading factors of causing rolling seam and lap surface defects includes the roller exception, adjustment, equipment, guide and other issues. Furthermore, after analyzing the cause-effect figures, the material size control, billet heating, guides, rollers, billet factors can be controlled. With the seam and lap surface defect formation mechanism analysis, it is found that the key factor is whether the formation of steel materials in rolling process can form a concave edge of the flange or poor conditions or defects. As for effects on flange in IM, roll groove fill rate up to more than 95% will result in the rolling steel flange phenomenon, of the materials which leads to complete formation of surface defects of final rolling wire.