Estudo dos efeitos de tratamentos térmicos em aço de baixa liga e alta resistência DOMEX 700

Abstract

DOMEX 700 is a low alloy steel with high mechanical strength. It is widely used in the automotive industry, for example, due to its high mechanical properties of hardness and resistance. However, when subjected to the welding process, its mechanical characteristics are reduced in the thermally affected zone. In this work, the effects of heat treatments on DOMEX 700 are investigated after exposure to temperatures of 850, 900 and 950°C for 30 minutes and also after manual autogenous TIG welding process. Twelve combinations of quenching and tempering heat treatments were evaluated. The hardness and the resulting microstructure were analyzed for each case, and were compared to the characteristics of the DOMEX 700 as received, without heat treatment. Quenching carried out at 950°C with subsequent tempering at 450°C proved to be an adequate heat treatment to restore the microstructure and hardness of the steel after exposure to high temperature. After welding, the heat treatment itself was not able to restore the microstructure in a similar way to the material as received, showing a reduction in hardness both in the region of the weld bead and in the base material due to grain growth. The severe oxidation of the welded surface that occurred during the heat treatment indicated that the material was also more susceptible to oxidation after the welding process.