Avaliação de curvas de dureza de aços temperados por indução

Abstract

Surface heat treatment processes via induction heating has been widely used in industries when wear resistance is needed. This process is analyzed in the present work. Some process variables define the hardness layer to be reached in the part such as the frequency used in the electromagnet coil and the steel composition. The objective of this work was to develop a simple methodology to estimate the expected profile for hardness curves of induction hardened steels processed in a similar way. The definition of process parameters will be discussed, as in the case of power density, where tabulated values are verified according to frequency and penetration depth, using these data to calculate input and output power in the coil. Using the online software “Heat Treatment Guide” and materials found in the literature, analyzes of the cooling curves, the tempering temperature, and the behavior of the hardness curves along the thickness of the pieces were performed. Thus, it was shown that the SAE 1020 steel, which would present a surface hardness after heat treatment of approximately 350 Hv, is very inefficient in the surface quenching process due to its low content of alloying elements. It was found that the process is much more efficient for SAE 1045 steel, which due to a higher concentration of alloying elements (mainly carbon) favored the formation of a hardened surface layer, with a hardness of approximately 750 Hv, presenting a more ductile core (approximately 230 Hv) than other steels. SAE 4340 steel has high hardenability, with the surface layer reaching a hardness of approximately 680 Hv. The AISI S1 and AISI O1 steels would present surface hardness of 780 Hv and 880 Hv, and their cores with hardness close to that of the SAE 4340 steel (455 Hv and 335 Hv, respectively), and the hardenability between the two is different, due to the elements of alloy present in their compositions, which result in a better ability of the steel to form the martensitic phase.