Avaliação do teor de martensita nos aços carbono A36 e AISI 1045 utilizando ensaio não destrutivo magnético

Abstract

Carbon steels are widely used in structural and mechanical applications due to their favorable balance between cost and mechanical properties. These properties are directly related to the material microstructure, which can be significantly modified through heat treatments. In this context, methods capable of evaluating microstructural changes in a non-destructive manner have become increasingly relevant. Magnetic testing techniques have been widely investigated as non-destructive methods for the microstructural characterization of carbon steels, since the magnetic properties of these materials are strongly influenced by phase transformations induced by heat treatments. In this context, the present study aimed to evaluate the influence of different heat treatments on the microstructure of ASTM A36 and AISI 1045 steels, with emphasis on martensite formation, through the analysis of magnetic parameters extracted from hysteresis curves and correlated with hardness test results. The samples were analyzed in the as-received condition, oil quenching, saline solution quenching, and quenching followed by tempering. Magnetic tests were performed using a magnetic probe based on a coil system, allowing the acquisition of B–H hysteresis loops in a single orientation relative to the applied magnetic field. The acquired electrical signals were processed using the GNU Octave environment, enabling the extraction of parameters such as coercive field, remanent induction, and saturation magnetization. Rockwell hardness tests were conducted to provide mechanical support for the analysis of the magnetic results. The results showed a positive correlation between coercive field and hardness for both steels analyzed, with a more pronounced relationship observed for AISI 1045 steel due to its higher hardenability and greater fraction of martensite formed after heat treatments. For ASTM A36 steel, due to its low carbon content, the observed variations were more limited, becoming more evident only in the saline solution quenching condition. Therefore, the results demonstrate that magnetic testing constitutes an effective and nondestructive tool for the indirect evaluation of microstructural changes and mechanical properties in carbon steels.