Avaliação da influência da temperatura de tratamento térmico de um aço inoxidável AISI 430, laminado a quente e recozido, na dissolução de carbonetos de cromo e no ataque corrosivo à superfície

Abstract

Non-stabilized stainless steel AISI 430 presents chromium carbides in its microstructure that are dispersed in the ferritic matrix of the steel. Depending on the thermal cycle used in the steel, these carbides preferentially precipitate in grain boundaries, generating a region pour in chromium next to them, what is a sensitization process. These sensitized regions are more susceptible to corrosive attacks. This way, chromium carbides dissolution in AISI 430 had been evaluated after heat treatments in different temperatures as well as what was the influence on the material’s surface microstructure after corrosive attacks. After an initial characterization, hot rolled and annealed samples had been heat treated in an electrical furnace and using a dilatometer. Temperatures varied from 750 to 1050°C, in 80s cycles and with fast cooling. From 950°C on, there is a decrease in the amount of carbides as the temperature of heat treatment increases. From 1000°C on, there is an increase in material hardness and martensite is present in the microstructure. Phase transformation during cooling occurs around 200°C. Some heat treated samples had been electrolytically attacked; others, had been attacked with sulfuric acid. It was not observed any influence of heat treatment temperature in the electrolytic attack; otherwise, in the samples attacked by sulfuric acid, the higher the heat treatment temperature, the smaller was the corrosive attack.