【作者】 杨俊；

【导师】 钱东升；

【作者基本信息】 武汉理工大学 ， 材料科学与工程， 2019， 硕士

【摘要】 轴承是最广泛应用的零件。在轴承制造工艺中球化退火是必不可少的一道工序,便于材料后续的切削加工。本文针对GCr15轴承材料的套圈,提出一种新型温成形技术,以实现短时间成形和球化过程。并针对这种新型温成形技术的可行性、球化机理、调控方法及工业上的具体实践开展系统研究。通过多道次变形和单道次变形及以珠光体离异共析相变和以共析相变为基础的温压缩实验,对温轧环过程形变相变协同控制实现组织球化的可行性进行分析探究,得出原珠光体团的形态、温变形参数和珠光体相变形式均对GCr15轴承钢碳化物球化效果产生重要影响。通过Jeziorny方法和珠光体扩散形核相变理论分别建立小应力和大变形条件下的珠光体相变过程的球化模型,探究了温变形过程中的组织球化机理。发现在GCr15轴承钢温变形过程中,存在珠光体离异共析相变和共析相变的竞争及相变球化和形变球化的竞争。认为这种新型温成形技术中,其球化本质是通过温变形控制离异共析相变占珠光体相变的比例。同时建立大变形条件下的球化模型,对形变球化过程进行了研究和讨论。通过珠光体离异共析相变前变形和相变后的变形实验,并用变形织构,铁素体晶粒尺寸,碳化物析出位置,亚晶分布,极图,残余应力分布,应力应变关系等手段对形变相变协同控制温成形过程组织演变规律及动态再结晶和铁素体回复状况进行分析。通过淬火和回火实验分析退火后的铁素体晶粒与淬火后的马氏体晶粒之间的遗传关系。通过硬度及宏观形貌分析,发现形变会促使形核位置发生改变,相变能消除变形引起的组织不均匀性。最后,通过在成都天马铁路轴承有限公司热轧环生产线上对轧制前保温,升温,两相区域轧制,预先热轧等不同温轧方案不同区域的组织形貌进行分析,根据结果设计了一种两次相变两次变形的温轧工艺。发现通过精确调控轧制过程中形变和相变参数能在130min内获得圆度高,不规则碳化物极少的球状渗碳体组织,淬火和回火后马氏体晶粒尺寸也符合标准。更多还原

【Abstract】 GCr15 bearing steel is the most widely used bearing material.In the bearing forming process,whether it is cold ring rolling or hot ring rolling,spheroidizing annealing is an indispensable process for the subsequent cutting of the material.However,the conventional spheroidizing annealing process usually requires an isothermal temperature of more than 10 hours,which is extremely wasteful of energy.In this paper,a new type of warm forming technology is proposed.By controlling the pearlite divorced eutectoid transformation and deformation parameters during the warm rolling process,it is possible to obtain a fine and fine round carbide structure with good uniformity in a short time.The forming effect is a new energy-efficient process.This paper will systematically study the feasibility,spheroidization mechanism,control methods and industrial specific practices of this new warm forming technology.In this study,the multi-pass deformation and single-pass deformation and the warm compression experiments with divorced eutectoid transformation and eutectoid transformation are used to realize the feasibility of tissue spheroidization in the process of deformation and transformation during warm ring rolling.The analysis of the properties revealed that the morphology,warm deformation parameters and pearlite transformation of the original pearlite group had an important effect on the spheroidization effect of the carbide.Subsequently,the spheroidization model of pearlite transformation process under small stress and large deformation conditions was established by Jeziorny method and pearlite diffusion nucleation phase transition theory respectively,and the mechanism of tissue spheroidization during warm deformation was explored.It is found that in the process of warm deformation of bearing steel,there is competition for pearlite divorced eutectoid transformation and eutectoid transformation,and competition for phase spheroidization and deformation spheroidization.It is believed that in this new type of warm forming technology,the spheroidization essence is to control the proportion of divorced eutectoid transformation to pearlite transformation by warm deformation,and at the same time to mechanically break the layered carbide structure to achieve rapid spheroidization.In order to specifically study the interaction mechanism between the deformation and transformation of the warm forming spheroidization process and control it,the deformation experiment before the transformation and phase transformation of pearlite divorce eutectoid transformation was designed.Through the deformation texture,ferrite grain size,carbide precipitation position,subgrain distribution,pole figure,residual stress distribution,stress-strain relationship,etc.,the deformation evolution and the structural evolution and dynamic recrystallization of the thermoforming process are controlled.The ferrite recovery status was analyzed.It indicates that the deformation can promote the transformation,and the transformation can improve the warm forming effect.The precise regulation of deformation and transformation is the necessary means to realize the short-flow warm ring rolling forming process.Finally,an attempt was made to industrial warm ring rolling on the hot ring rolling production line of Chengdu Tianma Railway Bearing Co.,Ltd.The microstructures of different regions of different warm rolling schemes such as pre-rolling,temperature rise,two-phase rolling,pre-hot rolling,etc.were analyzed.According to the results,a two-phase and two-deformation warm ring rolling process was designed.It is found that by precisely controlling the deformation and transformation parameters during the ring rolling process,the spherical cementite structure with extremely high roundness and few irregular carbides can be obtained within 130 min.The martensite grain size after quenching and tempering also meets the standard.更多还原