Efeitos do tratamento térmico de solubilização sobre o crescimento de grão e o grau de sensitização dos aços inoxidáveis austeníticos AISI 321 e AISI 347

• Ano de defesa: 2007
• Autor(a) principal: Silva, Eden Santos
• Orientador(a): SOUSA, Regina Célia de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Maranhão
• Programa de Pós-Graduação: PROGRAMA DE PÓS-GRADUAÇÃO EM FÍSICA/CCET
• Departamento: FISICA
• País: BR
• Palavras-chave em Português: Aços inoxidáveis austeníticos; crescimento de grão anormal; sensitização e solubilidade
• Palavras-chave em Inglês: Austenitic stainless steel; abnormal grain growth; sensitization; solubility
• Área do conhecimento CNPq: CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::FISICO-QUIMICA
• Link de acesso: http://tedebc.ufma.br:8080/jspui/handle/tede/732

Austenitic stainless steels present high resistance to corrosion under some aggressive medium, being for this widely used in the industrial sector. These steels, when submitted to determined temperature intervals can be sensitized due to the precipitation of chromium carbides in the grain boundaries, becoming subject to intergranular corrosion. When alloy elements are added to the steel base, turning it stabilized, they can prevent sensitization, however modifying completely the behavior of the grain growth of these steels. This work investigates the behavior of the austenitic grain growth and the degree of sensitization of stainless steel austenitic AISI 321 and AISI 347, when submitted to annealing thermal treatments, between 800 and 1200° C, and to sensitization treatments at 600° C, for different times of exposition, respectively. The sensitization degree was determined qualitatively through electrochemical attack and quantitatively by the double cycle potentio-kinetics reactivation test (DLEPR). The grain growth behavior in function of the temperature disclosed that, for temperatures below the grain growth critical temperature, Tcg, due to the pinning of the grain boundaries by precipitated particles, the grain growth is completely annulled. For temperatures above Tcg, due to the dissolution and to the coarsening of particles, occurs abnormal grains growth. At high temperatures, the grains become coarse and the grain growth resembles the growth of normal grains. The Tcg varies with the austenitização time, due to the increased coarsening of precipitated particles, with the increase of time. The estimated values for the TiC and NbC particles critical ratio, on the order of, on around 10 nm, are in excellent accord with literature data. Previous annealing treatments, carried out for 800 and 900° C, had been efficient in preventing the sensitization of the steel AISI 321. AISI 347 has proved to be more efficient than AISI 321 in accomplishing this task when used at high temperatures.