Aplicação de tratamento duplex em baixa temperatura no aço inoxidável AISI 316L: efeito na microdureza superficial e na resistência à corrosão

Abstract

Stainless steels have high resistance to corrosion due to the nickel and chromium content, however, for more demanding typological applications, improvements in mechanical properties, such as surface hardness and wear resistance, are required. To achieve these improvements, some alternatives are considered, such as duplex treatment, which is a technique that combines conventional nitriding that increases surface hardness and the deposition of thin films using the same equipment as plasma nitriding, ensuring greater film stability. However, treatments can negatively impact corrosion resistance, especially at high temperatures, leading to chromium depletion and degradation of anticorrosive properties. In this sense, this work proposes to investigate the application of a duplex treatment at low temperature, involving the conventional nitriding process followed by plasma deposition with a cathode cage, using a vanadium cage, with the objective of obtaining 316L steel with a better balance between mechanical properties and corrosion resistance. After treatments, the samples were subjected to the following characterizations: Vickers microhardness (HV); Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy Analysis (EDS); Daimler Benz VDI Rockwell C test; open circuit potential (OCP) measurements, electrochemical impedance spectroscopy (EIE) and potentiodynamic polarization. Images of the surface morphology of the films showed good uniformity with low presence of pores and voids and good distribution of Vanadium. The treatment carried out at 400° C showed a significant increase of 260% in the microhardness of the surface, on the other hand, the treatment carried out at 350° C did not have the same performance, with its microhardness value corresponding to the base material, although the untreated sample had showed better corrosion resistance behavior compared to the treated samples, the film obtained by treatment at 350° C showed the lowest loss of corrosion resistance compared to the sample treated at 400° C. However, these results cannot be analyzed in isolation, as the sample at 400 °C had a significant increase in microhardness, justifying the application of these treatment conditions to obtain a material with good mechanical properties without significant loss of corrosion resistance.