Efeito do acabamento superficial na resistência à corrosão de aços inoxidáveis coloridos.
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2010
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Uma tecnologia para coloração de aços inoxidáveis por eletrodeposição foi desenvolvida e patenteada pelo CETEC junto ao INPI 9703991-8. Esta tecnologia foi transferida para uma empresa mineira que produz e comercializa o produto no Mercado nacional e internacional. A coloração pode ser realizada em chapas de aço inoxidável com diferentes texturas e acabamentos. No entanto, tem sido constatado que a coloração de aço em alguns dos acabamentos mecânicos espelhados, dependendo do lote de produção da chapa de aço inoxidável, revela manchas que comprometem a aparência do produto. Acredita-se que tais manchas possam estar sendo originadas por deformações mecânicas superficiais induzidas no polimento mecânico e que estas poderiam ser removidas pelo processo de polimento eletroquímico. Com o propósito de equacionar este problema, no presente trabalho, foram avaliados os efeitos do polimento eletroquímico de um aço ABNT 304 com acabamento mecânico industrial tipo bright buffing (BB), com o objetivo de melhorar a qualidade dos aços inoxidáveis coloridos no que diz respeito à aparência e a resistência à corrosão. Foi avaliada a influência da temperatura no processo de polimento eletroquímico; Estudou-se o comportamento do aço inoxidável polido em diferentes correntes; Determinou-se a perda de massa do aço e a possível remoção das fases provenientes de camadas de deformação e tensões residuais induzidas nos processos de polimento mecânico e também riscos e outros danos mecânicos superficiais, que comprometem a homogeneidade da coloração das chapas de aço inoxidável; Verificou-se a refletividade do aço polido eletroliticamente para uma posterior coloração; Constatou-se que é possível realizar o polimento eletroquímico, nos aços inoxidáveis ABNT 304BB, utilizando uma solução concentração de 250g/L de CrO3 + 500g/L H2SO4. A densidade de corrente, a temperatura e o tempo de polimento são parâmetros críticos no polimento eletroquímico. Foi possível efetuar o polimento em diferentes corrente (1,0, 3,5 e 4,5A) de polimento. O processo de polimento eletroquímico o aço apresenta perda de massa. As medidas de refletância indicam que as amostras polidas quando comparadas as amostras na condição como recebida aumentaram sua refletividade após o processo de polimento. As imagens obtidas pela técnica de Microscopia de Força Magnética e os Difratogramas de Raio-X comprovam que o processo de polimento eletroquímico foi eficiente para remover a martensita dos aços inoxidáveis austeniticos. A rugosidade das amostras polidas na temperatura de 85°C é menor quando comparados a das amostras que foram polidas na temperatura de 25°C e com as amostras como recebida. O polimento eletroquímico influencia o comportamento mecânico das chapas de aço inoxidável ABNT 304BB, diminuindo a dureza e aumentando o módulo de elasticidade. O processo de polimento eletroquímico parece provocar o desaparecimento da camada de passivação do aço, mas após a coloração eletroquímica esta é recuperada. ___________________________________________________________________
ABSTRACT: A technology for coloring stainless steel by electroplating was developed and patented by CETEC INPI 9703991-8. This technology was transferred to a mining company that produces and sells the product on the nationally and internationally market. Staining can be performed on stainless steel plates with different textures and finishes. However, it has been found that the color of steel in some of the mechanical machining mirrored, depending on the batch production of stainless steel plate, patches shows that compromise the appearance of the product. It is believed that such spots may be being caused by mechanical deformations induced in the surface mechanical polishing and that these could be removed by electrochemical polishing process. In order to address this issue in the present study evaluated the effects of electrochemical polishing of an AISI 304-finish industrial mechanic type bright buffing (BB), in order to improve the quality of stainless steel colored with respect the appearance and corrosion resistance. The influence of temperature on electrochemical polishing; studied the behavior of polished stainless steel at different currents, determined the mass loss of steel and the possible removal of the phases from layers of distortion and residual stresses induced in the process mechanical polishing as well as risks and other mechanical damage surface, thereby affecting the uniformity of the color of stainless steel plates, was found the reflectivity of polished steel electroplated for later staining, found that it is possible to realize the electrochemical polishing in stainless steel ABNT 304BB, using a solution concentration of 250 g / L CrO3 + 500 g / L H2SO4. The current density, temperature and time of polishing are critical parameters in the electrochemical polishing. It was possible to perform polishing at different current (1.0, 3.5 and 4.5 A) polishing. The process of electrochemical polishing the steel is weight loss. Reflectance measurements show that the samples polished when compared to the samples provided as received increased its reflectivity after polishing process. The images obtained by the technique of Magnetic Force Microscopy and diffraction of X-rays show that the electrochemical polishing process was efficient to remove the martensite in austenitic stainless steels. The roughness of polished samples at a temperature of 85 ° C is lower when compared to the samples that were polished at 25 ° C and the samples as received. The electrochemical polishing influences the mechanical behavior of stainless steel sheets ABNT 304BB, decreasing the hardness and increasing the modulus of elasticity. The electrochemical polishing does not alter the electrochemical corrosion resistance of AISI 304 stainless steel, however, the growth of color film by interference in the stainless steel surface after polishing gives greater protection to the surface of stainless steel studied in this work.
ABSTRACT: A technology for coloring stainless steel by electroplating was developed and patented by CETEC INPI 9703991-8. This technology was transferred to a mining company that produces and sells the product on the nationally and internationally market. Staining can be performed on stainless steel plates with different textures and finishes. However, it has been found that the color of steel in some of the mechanical machining mirrored, depending on the batch production of stainless steel plate, patches shows that compromise the appearance of the product. It is believed that such spots may be being caused by mechanical deformations induced in the surface mechanical polishing and that these could be removed by electrochemical polishing process. In order to address this issue in the present study evaluated the effects of electrochemical polishing of an AISI 304-finish industrial mechanic type bright buffing (BB), in order to improve the quality of stainless steel colored with respect the appearance and corrosion resistance. The influence of temperature on electrochemical polishing; studied the behavior of polished stainless steel at different currents, determined the mass loss of steel and the possible removal of the phases from layers of distortion and residual stresses induced in the process mechanical polishing as well as risks and other mechanical damage surface, thereby affecting the uniformity of the color of stainless steel plates, was found the reflectivity of polished steel electroplated for later staining, found that it is possible to realize the electrochemical polishing in stainless steel ABNT 304BB, using a solution concentration of 250 g / L CrO3 + 500 g / L H2SO4. The current density, temperature and time of polishing are critical parameters in the electrochemical polishing. It was possible to perform polishing at different current (1.0, 3.5 and 4.5 A) polishing. The process of electrochemical polishing the steel is weight loss. Reflectance measurements show that the samples polished when compared to the samples provided as received increased its reflectivity after polishing process. The images obtained by the technique of Magnetic Force Microscopy and diffraction of X-rays show that the electrochemical polishing process was efficient to remove the martensite in austenitic stainless steels. The roughness of polished samples at a temperature of 85 ° C is lower when compared to the samples that were polished at 25 ° C and the samples as received. The electrochemical polishing influences the mechanical behavior of stainless steel sheets ABNT 304BB, decreasing the hardness and increasing the modulus of elasticity. The electrochemical polishing does not alter the electrochemical corrosion resistance of AISI 304 stainless steel, however, the growth of color film by interference in the stainless steel surface after polishing gives greater protection to the surface of stainless steel studied in this work.
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Programa de Pós-Graduação em Engenharia de Materiais. Rede Temática em Engenharia de Materiais, Pró-Reitoria de Pesquisa e Pós-Graduação, Universidade Federal de Ouro Preto.
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Citation
DUARTE, M. C. da S. Efeito do acabamento superficial na resistência à corrosão de aços inoxidáveis coloridos. 2010. 85f. Dissertação (Mestrado em Engenharia de Materiais) – Universidade Federal de Ouro Preto, Ouro Preto, 2010.