Nitretação a plasma do aço AISI 4140 com fluxo pulsado de nitrogênio: influência do potencial de nitrogênio e da temperatura na formação da camada nitretada

Abstract

AISI 4140 is low-alloy steel that has wide use in industry and vast employment in materials research, as it is a material that combines durability, economic viability and a good response to treatments for improved mechanical properties. One way to achieve this is through plasma nitriding, a surface hardening process that uses glow discharge to force the diffusion of nitrogen into the material. This process generally produces two areas in the material, the composite layer and the diffusion layer, which are greatly influenced by the parameters of time, temperature, gas composition of the atmosphere and nitrogen flow rate of the treatment. There are many studies regarding the formation of the composite layer, which can bring advantages or disadvantages to the material depending on the application. For this project, we used the plasma nitriding treatment with a D.C. (Direct Current) source, with temperatures of 400 ºC, 450 ºC and 500 ºC, time of 2 hours, with pulsed nitrogen flow of P0218, 2 minutes with the nitrogen flow on and 18 minutes with it off during the 2 hours of process, and variation in the gaseous atmosphere of 45%N2 + 35%H2 + 20%Ar, 70%N2 + 10%H2 + 20%Ar and 95%N2 + 5%H2. For the parameters used, it was found that temperature has the greatest effect on the thickness of the diffusion layer, and in addition, the 500 ºC treatments were the only ones not to present a composite layer. However, the 500 ºC samples showed residual tensile stress, which can be detrimental to the working life of the material, depending on its application.