Structural characterization of nitrided 34CrAlNi7 steel

Abstract

The nitriding behaviour of 34CrAlNi7 alloy steel was investigated under three different nitriding processes. One of them is salt-bath nitriding that was carried out at a temperature of 525 degrees C for treatment time of 1, 2 and 3 h. The others are ion nitriding and fluidized bed nitriding that were conducted at 500 degrees C and 540 degrees C, respectively, in treatment time of 6, 12 and 18 h. The thickness of compound layer, measured by means of a digital thickness instrument attached to optical microscope, ranged from 3 mu m to 16 mu m depending on nitriding technique and treatment time. The presence of gamma'-Fe4N and epsilon-Fe2-3N phases formed in the compound layer was confirmed by XRD analysis. Kinetics studies showed that the effective diffusion coefficients are 453 x 10(-14), 77.8 X 10(-14) and 278 X 10(-14) m(2) s(-1) for salt bath, plasma and fluidized bed processes, respectively.