采用OM, EPMA, XRD和IXRD等手段, 研究了低温超饱和渗碳(low temperature colossal carburization, LTCC)工艺中CO气体浓度对316L 不锈钢表面渗碳层的微观组织、C浓度分布、表面相结构以及残余应力的影响. 基于热动力学理论建立了LTCC传质和扩散模型, 利用DICTRA软件计算了渗碳层的C浓度和活度分布, 并与实验结果进行比较. 结果表明, 经LTCC工艺处理后的316L 不锈钢表面会形成高硬度的S相, 并产生压缩残余应力. 另外, 增加渗碳工艺中CO 浓度可以显著提高不锈钢表面渗碳层中的C浓度, 进而提高其硬度和压缩残余应力. 在C浓度较低时, 计算的C浓度和活度分布与实验结果吻合很好, 当C浓度较高时, 由于陷阱阵点的减少以及较大压缩残余应力的作用导致计算结果偏低.

Because of excellent corrosion resistance, good toughness and machinability, austenitic stainless steels are widely used in many industries. In order to improve the corrosion resistance, the carbon content of austenitic stainless steel is ultra-low, resulting in low surface hardness, poor wear and fatigue resistance properties which limit its application. Low temperature colossal carburization (LTCC) is a kind of novel surface strengthening technology for significantly increasing the surface hardness of austenitic stainless steels, while keeping their original excellent corrosion resistance because of no formation of carbides. The wear, fatigue and corrosion resistance of austenitic stainless steel of low temperature carburized layer have been investigated in recent years. However, the researches on key technical parameters, especially the carburizing atmosphere and the alloying element, have been rarely reported due to intellectual property protection limits. In this work, OM, EPMA, XRD and IXRD are used to investigate the effects of CO concentration on the microstructure, carbon concentration distribution, phase constitution and residual stress of the carburized layer on 316L austenitic stainless steel surface. Based on thermodynamic theory, the model of carbon transfer and diffusion was also built by software DICTRA to calculate the distribution of carbon concentration and activity of low temperature carburized layer. The results reveal that S phase is detected on 316L austenitic stainless steel surface treated by LTCC, and the compressive residual stress is formed at the same time. The increment of CO concentration can significantly increase the carbon concentration of carburized layer, which improve the hardness and compressive residual stress. The simulated carbon concentration and activity distributions are in accordance with the experimental results when the carbon concentration is lower, but when the carbon concentration is higher, the simulated carbon concentration is lower than experimental results due to the decrease of trapping sites and high compressive residual stress.