【摘要】 随着工业对高性能低碳钢要求不断提高，传统渗碳工艺常受到工件表面粗糙度大、晶粒尺寸不均等问题的影响，导致渗碳层厚度和硬度分布不均匀，限制了20CrMnTi等材料在关键工程中的应用。为此，旨在探讨滚压预处理对20CrMnTi渗碳行为的影响，重点分析滚压预处理如何改善材料表面质量、细化晶粒、增多晶界，从而加速碳原子吸附和扩散，提高渗碳效率及层深，并最终改善渗碳层的硬度和均匀性。通过调控滚压下压量和刀具进给速度获得不同预处理条件的样品。样品经过正火、固体渗碳、淬火和回火等热处理工艺，同时利用光学显微镜、扫描电子显微镜(SEM)、电子背散射衍射(EBSD)以及显微维氏硬度测试对材料表面、断面和渗碳层的微观组织、晶粒尺寸、晶界分布、碳浓度及硬度进行系统表征。此外，基于实验数据，还建立了碳原子吸附和扩散的动力学模型，分别从吸附等温线和多通道扩散两个方面定量描述滚压预处理对渗碳行为的影响，其模型结果与实验现象基本吻合。研究结果表明，滚压预处理显著改善了试样的表面平整度和表层材料的均匀性，并通过细化晶粒和增加晶界密度，有效提高了材料的整体有效扩散系数，从而使碳原子能够以更高速率均匀扩散，促使渗碳层硬度和深度均有明显提高。该研究不仅深化了对滚压预处理机制的认识，而且为低碳钢渗碳工艺优化提供了科学的理论支持和实践依据，对拓展高性能工程结构材料的应用具有重要意义。更多还原

【Abstract】 A systematic investigation was conducted to examine the effect of rolling pretreatment on the carburizing behavior of low-carbon steel 20CrMnTi. The study is motivated by the increasing demand for high-performance materials in engineering applications and the limitations of traditional carburizing processes. Conventional methods often result in uneven surface roughness and coarse grain structures, leading to nonuniform carburized layer depths and hardness distributions, which restrict material performance in critical applications. To address these deficiencies, rolling pretreatment was applied to improve surface quality and refine grain structure, thereby increasing the density of fast diffusion channels, such as grain boundaries. This study investigates the influence of rolling pretreatment on the microstructure, surface quality, and diffusion kinetics during carburizing, and it provides a theoretical basis for optimizing carburizing processes. In this work, 20 CrMnTi cold-drawn bars were normalized at 850 ℃ for 20 min and subsequently machined into cylindrical specimens with reduced diameters. The specimens then underwent rolling pretreatment using a specially designed tool mounted on a CNC lathe. The tool, equipped with a 7 mm diameter tungsten carbide ball, applied controlled compressive forces through varying feed rates and displacements. Rolling parameters were systematically adjusted, with particular emphasis on rolling displacement（Δ）, identified as the key parameter influencing surface deformation, grain refinement, and microstructural evolution. Following pretreatment, all specimens were subjected to a carburizing cycle consisting of heat treatment at 930 ℃ for 120 min using a solid carburizing method（90% carbon powder and 10% barium carbonate）, quenching at 850 ℃, and tempering at 180 ℃. The experiments were performed under carefully controlled conditions in a box-type electric furnace to ensure isothermal treatment. A series of characterization methods was employed to analyze the effects of rolling pretreatment on the carburized layers. Optical microscopy and scanning electron microscopy were used to observe microstructural changes, while electron backscatter diffraction quantified grain orientation and boundary distributions. Micro Vickers hardness testing and laser confocal microscopy were utilized to measure surface hardness and roughness, respectively. In addition, energy-dispersive X-ray spectroscopy was employed to assess carbon concentration profiles in the carburized layers. Results showed that rolling pretreatment significantly enhanced surface microhardness, with maximum values reaching 250 HV_0.05—approximately 51.5% higher than that of conventionally turned specimens. Surface quality also improved markedly, with arithmetic mean height（Sa） reduced from approximately 6.711 μm to 1.943 μm, corresponding to a 70.89% improvement. The depth of the carburized layer increased from 500 μm to 750 μm（a 50% rise）, while its overall hardness improved by 11.76% compared with the control group. To elucidate the mechanisms governing carbon absorption and diffusion during carburizing, two kinetic models were developed. First, a modified Langmuir adsorption isotherm was proposed to account for changes in surface characteristics brought about by rolling pretreatment. The maximum adsorption capacity was adjusted by a correction factor that incorporates the variations in grain boundary density and surface roughness. Second, a diffusion kinetics model was established based on Fick’s second law for one-dimensional diffusion, combined with a dual-channel diffusion mechanism that considers both lattice and grain-boundary diffusion. In conclusion, rolling pretreatment effectively refines grain structure and improves surface smoothness in 20CrMnTi steel, thereby enhancing carbon diffusion and adsorption kinetics during carburizing. The resulting improvements in carburized layer depth and microhardness provide valuable insights into process optimization. The proposed kinetic models offer a quantitative framework that links rolling parameters with diffusion behavior and interfacial reactions during carburizing. The findings of this research are of significant importance, as they provide a new theoretical foundation and a practical approach for optimizing carburizing processes, enabling the production of high-performance low-carbon steels with enhanced surface properties suitable for demanding engineering applications.更多还原