Prediction of Phase Composition and Nitrogen Concentration During the Nitriding Process in Low-Alloy Steel

Abstract

A diffusion/transformation coupled model has been developed which combines finite difference (FD) model with a phenomenological model. The composition of the different iron-nitrogen(Fe-N) hardening phase can be regard as a function of nitriding time and nitrogen concentration. The diffusion model and transformation model are linked by the limiting nitrogen solubilities and the effective diffusion coefficients. The effect of alloy elements (Cr, Mo, Mn, V, Ni etc.) is considered by introducing an alloy coefficient for limiting nitrogen solubilities and diffusion coefficient. The diffusion/transformation model can predict nitrogen concentration, phase composition and hardness distribution. The model is employed to simulate the nitriding process of SCr420H low-alloy steels. The simulated nitrogen concentration and hardness profiles are consistent with the measured ones. In addition, the predicted depth distributions of iron-nitrogen phase agree well with the available experimental results. Therefore, the comparison shows the reliability of the coupled model. It can be applied to improve the nitriding process parameters.

Improving Surface Hardness of AISI H13 Steel by Pack Nitriding

“…Fig 7 is the XRD pattern of cross section of N6Z2 sample nitrided at 600 o C. The results show the presence of nitride compounds, Fe3N and Fe2N. The formation of nitride compounds in XRD analysis shows that the phase formed in the white layer is mostly the Fe2N or ε-phase [13,14]. This can also be proven from Fig.…”

“…From the results of the analysis, the phase formed from the white layer is the α-Fe2N phase based on the number of dissolved nitrogen atoms in the sample, which is more than 12%[12].Fig7is the XRD pattern of cross section of N6Z2 sample nitrided at 600 o C. The results show the presence of nitride compounds, Fe3N and Fe2N. The formation of nitride compounds in XRD analysis shows that the phase formed in the white layer is mostly the Fe2N or ε-phase[13,14]. This can also be proven from Fig.6with 13.39% dissolved nitrogen atoms.…”

“…Diffusion coefficient value (D) of 0.3 and 0.4 d.o.a was obtained from the regression slope of the curve which yield: 1.17 x 10 -2 cm 2 /s and 1.47 x 10 -2 cm 2 /s, respectively. Based on the slope value, the activation energy (Q) can be calculated using the Arrhenius plot of 1/T (nitriding temperature) against ln D [13]. From the calculation, Q of 0.…”

Finite Element Modeling and Experimental Verification of Nitriding Process in S30C Steel

“…The detail of introducing heat conduction and diffusion equations is already presented in the previous articles [8][9][10] . Here, improved equations are summarized in the following.…”