GCr15轴承铸坯径向热辗扩微观变形与孔洞缺陷基础研究

发布时间：2018-06-18 12:02

本文选题：GCr15铸坯 + 径向热辗扩　；参考：《武汉理工大学》2015年硕士论文

【摘要】：中小型轴承环件(套圈)作为中小型轴承的基体组件,广泛应用于各类机械设备领域。中小型轴承环件的传统塑性加工工艺主要包括锻造制坯工序(下料、镦粗、冲孔等)和径向辗扩工序。而轴承铸坯径向热辗扩成形工艺,是铸辗复合新工艺中针对中小型轴承环件成形的一种低碳高效成形的新工艺。新工艺将传统中小型环件成形工艺中冗长复杂的锻造制坯改进为铸造制坯,大幅度缩短了工艺流程,提高了材料利用率,降低了废气排放,具有很高的经济效益和环境效益。但目前,铸坯径向热辗扩新工艺的研究还处于起步阶段,国内外研究基本处于空白,相应的指导理论不足,还难以得到应用与推广。针对此现状,本研究对GCr15轴承铸坯径向热辗扩工艺进行了相关基础研究。研究重点围绕GCr15轴承铸坯热辗扩过程中铸态组织转变和铸造缺陷改善两大关键问题开展,以期为新工艺的进一步研究与应用提供一定的理论指导和科学依据。对于铸态组织转变方面,通过数值模拟技术建立了GCr15铸坯径向热辗扩微观组织有限元模型,研究了铸坯热辗扩过程中微观组织的演变行为。首次提出了晶粒细化极限的概念,并对晶粒细化极限进行了理论探究,从应变和Z-H系数两个方面对晶粒细化极限进行了讨论。晶粒细化极限的提出对于铸态环件热辗扩过程中晶粒尺寸的控制具有非常重要的作用。开展了GCr15铸坯径向热辗扩工艺实验,对成形后环件进行了金相测试,探究了不同变形量下环件晶粒尺寸的演变规律。研究结果对于铸坯热辗扩过程中晶粒尺寸的控制具有重要意义。对于铸造缺陷改善方面,以球形孔洞为研究对象,通过数值模拟技术建立了GCr15铸坯球形孔洞有限元模型。通过建立球形孔洞局部坐标系,研究了球形孔洞的基本演变行为,并探究了影响球形孔洞演变的主要因素,揭示了工艺参数对球形孔洞演变的影响。通过比较球形孔洞和柱形通孔的演化行为,提出了球形孔洞演变的理论假设,并对假设进行了验证,以此建立了球形孔洞的形状变化预测模型。设计并开展了孔洞演变实验,进一步探究了铸坯孔洞缺陷在热辗扩过程中的演变规律。
[Abstract]:As the base assembly of medium and small bearing, small bearing ring (ring) is widely used in various fields of machinery and equipment. The traditional plastic processing technology of small and medium bearing ring mainly includes forging process (blanking, upsetting, punching etc.) and radial rolling process. The radial hot rolling forming process of bearing billet is a new low carbon high efficiency forming process for small and medium bearing ring forming in the new casting rolling compound process. The new process improves the long and complicated forging billets in the traditional forming process of small and medium-sized ring parts into casting billets, greatly shortens the process flow, improves the utilization ratio of materials, reduces the exhaust gas emissions, and has high economic and environmental benefits. However, at present, the research on the new technology of radial hot rolling is still in its infancy, the research at home and abroad is basically blank, the corresponding guiding theory is insufficient, and it is difficult to be applied and popularized. In view of this situation, this research has carried on the correlation basic research to the GCr15 bearing billet radial hot rolling technology. The research focuses on the two key problems of as cast structure transformation and casting defect improvement during hot rolling of GCr15 bearing billet in order to provide certain theoretical guidance and scientific basis for the further study and application of the new technology. For the transformation of as-cast structure, the finite element model of the microstructure of GCr15 billet was established by numerical simulation, and the evolution of microstructure during hot rolling was studied. The concept of grain refinement limit is put forward for the first time, and the grain refinement limit is studied theoretically. The grain refinement limit is discussed from two aspects: strain and Z-H coefficient. The grain refinement limit is very important for the control of grain size in the hot rolling process of as-cast ring. The experiment of GCr15 billet radial hot rolling process was carried out. The metallographic test of the formed ring was carried out, and the evolution law of the ring grain size under different deformation quantities was investigated. The results are of great significance to the control of grain size during hot rolling of billet. For the improvement of casting defects, the finite element model of spherical cavity in GCr15 billet was established by numerical simulation. The basic evolution behavior of spherical voids was studied by establishing local coordinate system of spherical voids, and the main factors affecting the evolution of spherical voids were explored, and the influence of technological parameters on the evolution of spherical voids was revealed. By comparing the evolution behavior of spherical cavity and cylindrical through hole, the theoretical hypothesis of spherical hole evolution is proposed, and the hypothesis is verified, and a prediction model of spherical cavity shape change is established. The hole evolution experiment was designed and carried out, and the evolution law of cavity defect in hot rolling process was further explored.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TH133.3;TG306

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