Decarburization is generally avoided as it is reckoned to be a process detrimental to material surface properties. Based on the idea of duplex surface engineering, i.e., nitriding the case-hardened or through-hardened bearing steels for enhanced surface performance, this work deliberately applied decarburization prior to plasma nitriding to cancel the softening effect of decarburizing with nitriding and at the same time to significantly promote the nitriding kinetics. To manifest the applicability of this innovative duplex process, low-carbon M50NiL and high-carbon M50 bearing steels were adopted in this work. The influence of decarburization on microstructures and growth kinetics of the nitrided layer over the decarburized layer is investigated. The metallographic analysis of the nitrided layer thickness indicates that high carbon content can hinder the growth of the nitrided layer, but if a short decarburization is applied prior to nitriding, the thickness of the nitrided layer can be significantly promoted. The analysis of nitriding kinetics shows that decarburization reduces the activation energy for nitrogen diffusion and enhances nitrogen diffusivity. Moreover, the effect of decarburization in air can promote surface microstructure refinement via spinodal decomposition during plasma nitriding.

中文翻译：

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渗碳/淬火轴承钢的新型脱碳渗氮处理，以提高渗氮动力学和细化组织

通常认为脱碳是有害的，因为它被认为是不利于材料表面性能的过程。基于双重表面工程的思想，即对表面硬化或贯通淬火的轴承钢进行渗氮处理以提高表面性能，这项工作在等离子渗氮之前有意应用了脱碳，以消除渗氮的渗碳软化效果，同时显着促进氮化动力学。为了体现这种创新的双相工艺的适用性，这项工作采用了低碳M50NiL和高碳M50轴承钢。研究了脱碳对脱碳层上方氮化层的微观结构和生长动力学的影响。渗氮层厚度的金相分析表明，高碳含量可能会阻碍渗氮层的生长，但是如果在渗氮之前进行短时间的脱碳，则渗氮层的厚度会大大提高。氮化动力学分析表明，脱碳减少了氮扩散的活化能并增强了氮的扩散性。此外，空气中的脱碳作用可通过等离子氮化过程中的旋节线分解促进表面微观结构的细化。氮化动力学分析表明，脱碳减少了氮扩散的活化能并增强了氮的扩散性。此外，空气中的脱碳作用可通过等离子氮化过程中的旋节线分解促进表面微观结构的细化。氮化动力学分析表明，脱碳减少了氮扩散的活化能并增强了氮的扩散性。此外，空气中的脱碳作用可通过等离子氮化过程中的旋节线分解促进表面微观结构的细化。