Tratamento térmico em aço carbono ASTM A36 e sua influência na resistência à corrosão

Abstract

ASTM A36 steel is a low alloy structural steel with wide use in construction and common applications. The chemical composition directly influences the metallurgical properties of metals, as in the case of steel, in which the carbon content and other alloying elements (manganese, silicon, sulfur) are verified to relate to the strengths. Although corrosion resistance is relatively limited, carbon steel is widely used in marine applications, petroleum production and refining, for example. It is possible to modify some properties of steel with the use of heat treatments, such as full annealing, normalizing, quench hardening, which improve them due to the microstructure change. Steel full annealing is the heat treatment in which it involves austenitizing, in which austenite nucleus prefer to form on the grain boundaries of the ferrite and subsequently perlite transformation. This nucleation will tend to homogenize the existing perlite in the microstructure, in addition to the slow cooling that will provide the grain growth. The purpose of this work is to present how this phase transformation, caused by high exposed temperature and after slow cooling, will influence the microstructure and corrosion resistance properties in saline environments, besides analyzing the minimization of a phenomenon called banding, which is when the perlite has shapes towards the lamination. From the results, it was found that the full annealing heat treatment directly influenced the grain size and the organization of fine perlite as the austenitizing temperature was increased. In addition, it was observed that the grain size and corrosion resistance is not a linear relationship and, because it is a hypoeutectoid steel, it did not obtain significant results, but in general, the sample treated at 950 ºC obtained better results.