基于环件铸辗复合成形的42CrMo钢组织演变机理研究

The new casting-rolling compound process has many merits such as shortening process flow, saving materials and energy. Wether the cast structure can be transformed into fine and homogenied forged structure during the new process is the key problem of the new process. Now researches on the hot deformation behavior and structure evolution mechanism of the as-cast steel are few. The development of the new process is lacking theory basis. The project is based on the new casting-rolling compound process. As-cast 42CrMo steel will be researched in the project. The thermal mechanical simulation test, numerical simulation and reduced-scale test will be used to research the plastic deformation behavior and microstructure evolution mechanism of the casting billet during thermal-mechanical coupling forming process. The thermaldynamic condition make the as-cast strucrue transform to forged structure and influence rule of the deformation parameters such as deformation temperature, strain rate and deformation degree on the microstructure evolution will be found out. The method to refine grain during the hot deformation process with multi-pass, unsteady, non-uniform and thermal-mechanical coupling will be obtained. The research results will provide basis for optimizing process parameters,predicting and controlling the forming quality during the ring rolling process. A solid theoretical foundation will be provided for the short casting-rolling compound forming process produced big rings.

铸辗复合成形新工艺具有流程短、节材节能等优点，而铸态组织是否能在辗扩中转变为细匀化的锻态组织成为新工艺能否成功的关键。目前关于铸态钢的热塑性变形行为及组织演变机理研究较少，新工艺的发展缺乏理论支撑。本项目基于环件短流程铸辗复合精确成形新工艺理论，以铸态42CrMo钢为研究对象，利用热力模拟实验、数值模拟及缩比实验，研究铸坯在热力耦合变形过程中的塑性变形行为和组织演变机理，研究42CrMo钢铸态组织向锻态组织转变的热力学条件以及变形参数（如变形温度、变形速度、变形量等）对组织演变的影响规律，获得多道次、非稳态、非均匀、热力耦合作用下变形过程中晶粒细化的方法和途径，为后续辗环工艺参数的优化、成形件质量预测与控制提供依据，为大形环件短流程铸辗复合成形新工艺的开发奠定坚实的理论基础。

本项目基于环件短流程铸辗复合精确成形新工艺，以铸态42CrMo 钢为研究对象，利用单道次、双道次和多道次（五道次）热力模拟压缩实验，研究了热变形行为及组织演变规律；建立了自动元胞机（CA）有限元模型，实现了42CrMo钢环件铸辗复合成形的跨尺度模拟；通过热力模拟压缩实验获得了变形参数对组织演变的影响规律，获得了变形温度（850℃-1150℃）和终锻温度（850℃-1000℃）、应变速率（0.01S-1-10S-1）、变形量（5%-72%）、道次间隔时间（5S-60S）对微观组织演变的影响规律。得出结论变形温度在1050℃-1100℃可以获得较为均匀细小的微观组织，而终锻温度在930℃和970℃附近时得到更好的组织；高的应变速率（大于1S-1）由于对晶粒的破碎作用使晶粒细化，微观组织更为细化；变形量是决定变形后微观组织的重要因素，变形量越大，变形后的微观组织越均匀细小；因此在铸辗复合成形中，大的辗扩比是决定铸态组织是否能在热辗扩中转变为锻态组织的关键因素。在多道次变形中，道次间隔时间对变形后材料的组织也有影响，在5S-60S范围内，随着道次间隔时间的增长，组织变得粗大。研究结果为铸辗复合成形的辗扩工艺参数的优化、成形件质量预测与控制提供了依据。