多相复合协同提升纳米贝氏体轴承钢性能的路径及机理研究

Bearing is the key part for nearly all machineries. The material used for manufacturing bearing is crucial factor that determines the quality of bearing. Nanostructured bainitic bearing steel is the newly developed material that possesses excellent properties, which has displayed a great potential for industry application. Introducing a certain amount of martensite into the nanostructured bainitic microstructure, not only shortens the duration for heat treatment, solving the key problem that restrict the application of the nanostructured bainitic bearing steel, but also improves the comprehensive properties of bearing. However, there still are some fundamental questions that have not been answered, such as the effect of preformed martensite on the orientation of bainitic ferrite and its variation select; the evaluation on stability of retained austenite and the controlling path on the stability of retained austenite; and also the fatigue mechanism for the bearing with different microstructures. A kind of high carbon nanostructured bainitic bearing steel will be taken as the research object of the present project. The heat treatment process will be controlled to obtain the multi-phase microstructure with different volume fraction of nanostructured bainitic ferrite, retained austenite and martensite. A series of technologies for microstructure characterization, such as FIB, HRTEM and 3DAP, will be carried out to analyses the orientation relationship between phases and the difference on the chemical composition and structure among each phase. In-situ XRD and high resolution dilatometer test will be introduced to analyses the effect of martensite on the followed bainite phase transformation and on the microstructural evolution. The process study on the fatigue and wear will also be done to reveal the fatigue mechanism, stability of retained austenite and its basic effect. Finally, the cooperation mechanism among phases will be revealed, which will provide the theory supporting and technic supporting for the microstructure controlling of multiphase nanostructured bainitic bearing steel.

轴承是几乎所有设备的关节，其材料至关重要。纳米贝氏体轴承钢是近年来发展的一类高端材料，已展现出巨大的应用潜力。在纳米贝氏体组织中引入马氏体不仅可缩短热处理时间，解决制约其应用的瓶颈难题，还可提升轴承综合性能。然而，多相复合的纳米贝氏体轴承钢中仍有一些关键科学问题尚未解答，如：预生成马氏体对贝氏体取向、变体选择等微结构的影响规律，复合组织中残余奥氏体的稳定性评价及调控路径，疲劳失效机制差异等。本项目拟以一类高碳纳米贝氏体轴承钢为研究对象，通过工艺调控获得不同纳米贝氏体、马氏体、残余奥氏体含量的复合组织，通过FIB、HRTEM和3DAP技术，分析各相成分差异，通过TKD和TEM表征各相取向关系和结构差异；利用原位XRD和高分辨膨胀仪分析预马氏体对相变及微结构演变的影响；通过过程研究分析失效机制及各相的演变、残余奥氏体的稳定性及作用；最终阐明各相协同作用机制，为微结构调控提供理论支持和技术支撑。

本项目针对当前我国高端装备对高性能轴承的迫切需求，开展纳米贝氏体轴承钢性能调控路径基础研究。项目组完成了以下内容的研究工作：1）预先生成马氏体、后生成马氏体、渗碳体尺寸、第一阶段贝氏体含量、预先冷变形等系列组织和前处理工艺对高碳纳米贝氏体轴承钢相变动力学、微观结构、强韧性、耐磨性以及滚动接触疲劳性能的影响规律，分析了残余奥氏体的稳定性及其对耐磨性及滚动接触疲劳性能的影响机制；2）奥氏体化温度、等温时间等热处理参数对渗碳纳米贝氏体轴承钢表层组织中贝氏体、马氏体、残余奥氏体等各相含量的影响，以及对各项性能的影响机制；3）纳米贝氏体组织控制路径，以及贝氏体铁素体、残余奥氏体、新鲜马氏体对纳米贝氏体钢宏观强度和塑性的影响规律及作用机制。.研究发现预生成马氏体可显著细化贝氏体组织、提高钢的耐磨性能但会降低冲击韧性，优化出10%-15%为较为合理的预生成马氏体含量。发现残余奥氏体含量最高时，具有贝氏体-马氏体-奥氏体复合组织轴承钢的韧性最高，但全纳米贝氏体组织具有最佳的滚动接触疲劳性能。渗碳体尺寸从0.49μm细化0.20μm，可使轴承钢的耐磨性提高23%，滚动接触疲劳寿命提高2.5倍，但降低冲击韧性。引入少量预冷变形，可以将纳米贝氏体轴承钢的韧性提高1倍，耐磨性提高40%以上。建立了贝氏体组织尺寸控制模型，开发了基于过冷奥氏体强度控制和贝氏体尺寸控制的贝氏体轴承钢双阶段热加工工艺，可使轴承钢的热处理时间缩短90%以上。.研究成果加深了对纳米贝氏体轴承钢复相结构的认识，建立了轴承钢短周期热加工路径，为推动纳米贝氏体轴承钢的工业应用提供了理论支撑和技术支撑。发表学术论文17篇，出版专著1部、译著1部，授权发明专利4项，获省部级二等奖1项，培养博士研究生2名，硕士研究生5名。