Engenharia de Materiais

Agora exibindo 1 - 5 de 5

Pit morphology and its microstructure relation in 850°C aged UNS S31803 (SAP 2205) duplex stainless steel
(2003-07-24) Rodrigo Magnabosco; ALONSO-FALLEIROS, N.
This work described the relationship between microstructure of UNS S 31803 (SAP 2205) aged at 850°C and pitting morphology after cyclic polarization in chloride aqueous solution. The initial material, solution treated for 30 minutes at 1120°C and water quenched, was aged at 850°C for periods up to 100 hours. Cyclic polarization in 3,5% NaCl aqueous solution was conducted on #600 grounded sample surfaces. After polarization, the samples were sectioned transversal and perpendicular to polarized surface to allow the inner view of pitting corrosion using scanning electron microscope. It was found that sigma phase formation after 850°C aging treatment reduced pitting potential, and pitting corrosion occurred as selective corrosion of chromium and molybdenum impoverished regions, like interfaces between sigma phase and metallic matrix.
Pitting corrosion of UNS S41000 and UNS S42000 stainless steels
(2009-09-06) BORGES, A. O.; ALONSO-FALLEIROS, N.; Rodrigo Magnabosco
The aim of this work is to evaluate the pitting corrosion resistance, through potentiodynamic polarization tests, in two commercial martensitic stainless steels, named UNS S41000 and UNS S42000, by using four electrolytes of 0.10M Na2SO4, with different concentration of chloride: 0.01M NaCl; 0.05M NaCl; 0.10M NaCl; 0.60M NaCl (3.5%). The received samples showed a ferritic microstructure with spheroidized carbides (annealed), whereas it was observed a microstructure of tempered martensite after heat treatment. Considering the same condition - annealed or quenched and tempered - the hardness of steel UNS S42000 was always higher than steel UNS S41000. In potentiodynamic tests, the potential scan rate was defined as 1mV/s after exploratory tests which showed this parameter influence on the curve shape. From then on, it was possible to obtain polarization curves with scanning rate of 1mV/s, starting at open-circuit potential after a five minute immersion and 600 grit surface finish. The results showed that the higher chloride ion concentration, the lower the pitting potential. For a given electrolyte, pitting potential measured for annealed steel UNS S41000 is slightly higher than the same steel on quenched and tempered condition. The intense chromium carbide precipitation at the grain boundaries of former prior austenite, a phenomenon that can lead to sensitization, may be a reason for it. Through immersion tests, it was found out that pitting potential of UNS S41000, after heat treatment, is lower than corrosion potential in the electrolyte composed of (3.5% NaCl + 0.10M Na2SO4). Otherwise, steel UNS S42000 presented higher pitting potential after heat treatment. In this case, intergranular carbide precipitation was not observed and the quench and temper treatment, at first, generates a higher content of chromium in solid solution if compared with the annealing treatment, leading to a greater corrosion resistance. Pitting density and their sizes are chloride concentration dependent: the higher ion chloride concentration, the lower is pit density and the larger is pit width. According to the studied conditions, the most suitable electrolyte for pitting potential determination is composed of (0.10M NaCl + 0.10M Na2SO4). The shape of the obtained potentiodynamic polarization curves with this electrolyte allowed the identification and accurate determination of the pitting potential.
Investigation of the effect of the interstitial content on the degree of sensitization at 600°C in ferritic stainless steels Investigação do efeito do teor de intersticiais sobre o grau de sensitização em aços inoxidáveis ferríticos a 600°C
(2007-01-05) SERNA-GIRALDO, C. A.; IDE, C. R.; Rodrigo Magnabosco; KUNIOSHI, C. T.; ALONSO-FALLEIROS, N.
The purpose of this work was to investigate the effect of carbon and nitrogen in 17%Cr ferritic stainless steels (16%Cr-0.04%C-0.032%N; 17.2%Cr-0.02%C-0.0062%N; 18.5%Cr-0.008%C-0.0213%N) on the degree of sensitization (DOS). These steels were solution annealed at 1200°C and quenched in water. Isothermal treatments were carried out at 600°C between 5 minutes and 16 hours. The Double Loop Electrochemical Potentiokinetic Reactivation test (DL-EPR) was carried out in a 0.5M H2SO4 solution at (25 ± 2)°C. The DOS was evaluated using a ratio between maximum anodic current density in reversion, ir and activation, ia. The microstructural examination of specimens was carried out using optical and scanning electron microscopy after metallographic etching with Vilella's reagent. The results showed a DOS variation with time. Maximum values of DOS were obtained for each steel, followed by its reduction. The intensity of DOS and its kinetics vary in function of the carbon and nitrogen content in steels.
Investigação do efeito do teor de intersticiais sobre o grau de sensitização em aços inoxidáveis ferríticos a 600ºC
(2007-05-22) SERNA-GIRARDO, CARLOS AUGUSTO; IDE, CRISTIANE REIS; Rodrigo Magnabosco; KUNIOSHI, CLARICE TERUI; ALONSO-FALLEIROS, NEUSA
O objetivo do presente trabalho foi investigar o efeito do teor de carbono e nitrogênio em aços inoxidáveis ferríticos com 17%Cr (16%Cr-0,04%C-0,032%N; 17,2%Cr-0,02%C-0,0062%N; 18,5%Cr-0,008%C-0,0213%N) sobre o grau de sensitização (GS). Os aços foram solubilizados a 1200°C e resfriados em água. Tratamentos isotérmicos foram realizados a 600°C entre 5 minutos e 16 horas. Foi realizado o ensaio de reativação eletroquímica potenciodinâmica de ciclo duplo (DL-EPR) em solução 0,5M H2SO4 a (25 ± 2)°C. O GS foi medido através da relação entre as densidades de correntes anódicas máximas nas etapas de reversão, i r, e ativação, i a. O exame microestrutural dos corpos-de-prova foi realizado nos microscópios óptico e eletrônico de varredura após ataque metalográfico com reagente Vilella. Os resultados mostram variação do GS com o tempo. Um máximo de GS foi obtido para cada aço e, posteriormente, foi observada diminuição do GS. A intensidade do GS e o tempo de ocorrência variaram em função dos teores de carbono e nitrogênio nos aços.
VIDA EM FADIGA DE AÇOS CARBONO COM ESTRUTURA BIFÁSICA FERRITA-MARTENSITA
(2001-10-31) Rodrigo Magnabosco; BOTTON, T.

Engenharia de Materiais

Navegar

Filtros

Configurações

Ordenar por

Resultados por página

Resultados da Pesquisa