针对316L奥氏体不锈钢表面强化, 进行了低温表面渗碳实验并测量了渗后试样渗碳层内C浓度沿深度方向的分布. 建立了以“陷阱-去陷阱”质量传递机制为基础的动力学模型, 认为Cr原子在C的扩散过程中对C原子具有陷阱作用, 利用该模型计算出渗后试样中C浓度沿渗层深度方向的分布, 并与实验结果进行比较. 结果表明, 实验测得的C浓度沿渗层深度方向的分布形状呈现凸状, 与简单Fick定律得出来的结果不同, 而基于“陷阱-去陷阱”模型得到的计算结果与实验结果符合较好, 表明陷阱作用在C扩散过程中起重要作用. Cr原子通过对C原子陷阱作用, 降低C的扩散系数, 对实验数据拟合得到C的去陷阱激活能为165 kJ/mol. 所提出模型仅适用于未发生碳化物析出的低温渗碳, 且并未考虑扩散应力的影响.

Low-temperature surface carburization has proven to be one of the most effective techniques for improving the mechanical properties of 316-type austenitic stainless steel (Fe-Cr-Ni alloy), including surface hardness, fatigue resistance and wear resistance. It is well known that carbon diffusion in austenitic stainless steel is a very complicated process and still not fully understood. So it is of great importance to figure out the carbon diffusion mechanism in steel and establish a model that can predict the carbon concentration along the depth direction in any given carburization conditions. Studies in recent years reveal that trapping effect should be considered in carbon diffusion in austenitic steels at low temperature. In this work, low-temperature surface carburization treatment was carried out with 316L austenitic stainless steel, and the carbon concentration along the depth direction was measured. A kinetic model based on the "trapping-detrapping" mass transport mechanism for simulating the carbon fraction-depth profile was developed. This model considered that the diffusion of carbon under the influence of trap sites formed by local chromium atoms. Then the calculated carbon concentration was compared to the experimental results in order to check the validity of the model. The results show as follow: (1) in low-temperature-carburized 316L austenitic stainless steel, the carbon fraction-depth profile exhibits plateau-type shape which is not consistent with the standard analytic solution of the diffusion equation (Fick's law of diffusion); (2) carbon fraction-depth profile based on "trapping-detrapping" model is in good agreement with experimental carbon fraction-depth profile, which indicates the trapping effect plays an important role in carbon diffusion; (3) carbon diffusivity decreases by the trapping effect of Cr atoms, and the detrapping energy of carbon deduced from fitting experimental data is 165 kJ/mol; (4) the proposed model can only be used to describe the carbon diffusion in austenitic stainless steel during low-temperature surface carburization without chromium carbide precipitation. In addition, the influence of stresses induced by incorporating the carbon into austenite lattice on the carbon transport mechanism is not included in the trapping-detrapping model.