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Quenched and tempered AISI 5115 steel was plasma nitrided and nitrocarburized at 550¢ªC for 5 hours in atmospheres of 80%N2 balanced with various amounts of H2 and CO2 gases. The amount of CO2 varied from zero to 10%. Optical microscopy, XRD and microhardness testing were carried out to characterize surface layers of the treated specimens. The results showed that increasing of CO2 in the gas mixture up to 7% increases the thickness of compound layer and enhances the formation of ¥å phase in the layer. Microhardness testing did not show any change in the hardness profiles of the diffusion layers by addition of CO2 to the treating atmosphere. |