大型GH4738合金开坯工艺研究方法及设计依据

Research Methods and Design Basis for Cogging Process of Large-Scale GH4738 Superalloy

摘要:

通过有限元模型结合二次开发的方法，基于工艺串联性和组织遗传性探究了大尺寸GH4738合金在复杂连续变形的开坯工艺中坯料内部晶粒组织分布及演化情况，给出了一种工艺设计、结果预测的通用性方法。根据Ф660 mm级GH4738合金实际开坯工艺进行了有限元模拟计算，将模拟结果与实际坯料对应位置的晶粒度进行了对比，验证了所建立模型的可靠性及准确性。依托该模型，以典型的镦粗和拔长过程为例，分析并给出了工艺参数对坯料在多火次变形过程中的组织演变规律及工艺制定方法：在镦粗过程中，随着压下速度的增大、变形温度降低、压下量减小，坯料内部动态再结晶程度下降；在拔长过程中，随着压下速度的减小、拔长温度升高、进给量减小，坯料内部动态再结晶程度升高。此外，结合具体分析，在镦粗过程中建议压下速度控制在5~12 mm/s，第1次镦粗温度为1160 ℃，单火次压下量控制在25%~35%之间；而拔长过程相较于镦粗过程更为复杂，在综合考虑坯料内部晶粒细化、拔长过程中坯料表面温降、出现“凹心”现象等因素后建议：单火次拔长压下速度控制在60~90 mm/s之间，第2次拔长温度选择1120~1130 ℃之间，单火次拔长进给量控制在200~350 mm之间。

Abstract:

The distribution and evolution of the internal grain structure of large-scale GH4738 alloy during the complex continuous deformation cogging process, based on the process sequentiality and organizational heredity, were investigated by employing a finite element model combined with secondary development methods, providing a general approach for process design and outcome prediction. Finite element simulation calculations were conducted based on the actual billet preparation process of GH4738 superalloy with Ф660 mm grade, comparing the simulation results with the grain size at corresponding positions of the actual billets to verify the reliability and accuracy of the established model. Utilizing this model, typical upsetting and cogging processes were analyzed, and the effects of process parameters on the microstructural evolution of the billet during multiple deformation passes were discussed, along with methods for process formulation. Results show that during the upsetting process, as the upsetting speed increases, the deformation temperature decreases, the reduction amount decreases, and the degree of dynamic recrystallization within the billet decreases. In the cogging process, as the upsetting speed decreases, the cogging temperature increases, the feed amount decreases, and the degree of dynamic recrystallization within the billet increases. Furthermore, based on the specific analysis, it is recommended to control the upsetting speed during the upsetting process between 5 and 12 mm/s; the initial upsetting temperature should be 1160 °C; the single-pass reduction amount should be controlled between 25% and 35%. The cogging process is more complex than the upsetting process. Taking into account the factors such as grain refinement within the billet, surface temperature drop during the cogging process, and the occurrence of the "concave center" phenomenon, the upsetting speed is controlled between 60 and 90 mm/s; the second cogging temperature is chosen between 1120 and 1130 °C; the feed amount is controlled between 200 and 350 mm.