Effect Of Hot Working Process On Microstructure Of GH4698

GH4698 alloy has good comprehensive properties such as high temperature strength,fatigue resistance,fracture toughness and plasticity,and its structure also maintains good stability and reliability at high temperatures.Therefore,GH4698 alloy is widely used in extra large turbine disks for aeroengine.With the development trend of high performance,long service life and large scale of aero engines,the gas temperature in front of the turbine increases significantly,the load of parts increases constantly,and the working condition becomes worse and worse.The performance requirements of the turbine disc become more demanding,which greatly increases the manufacturing difficulty of the turbine disc.As a common material of turbine disk,the microstructure of GH4698 alloy is very important in the thermal processing.This article focuses on the influence of hot working process on the microstructure of GH4698 alloy,in order to provide important theoretical support for solving the problems of turbine disk manufacturing.In this paper,the GH4698 alloy is used as the research object,and the Thermoecmastor-z thermal simulation test machine was used to study the rheological behavior of the alloy under different deformation temperature(950~1200℃),strain rate(0.01~10s-1)and strain level via thermal compression simulation experiment,the constitutive equation based on the rheological curve and its hot working diagram were established,and the critical strain of dynamic recrystallization of GH4698 alloy was determined.The microstructure evolution of GH4698 alloy during hot deformation was studied using EBSD technology.The effects of deformation conditions(strain level,deformation temperature,strain rate)on the percentage of dynamic recrystallization,the nucleation mechanism of dynamic recrystallization and the percentage of special grain boundary of GH4698 alloy were analyzed,The distribution of the percentage of dynamic recrystallization and the Σ3 grain boundary of GH4698 alloy after hot deformation were established.It was found that the region with high strain and low ln Z(45~50)is more conducive to the occurrence of dynamic recrystallization and the formation of the ∑3 grain boundary,while the region with high ln Z(50~62)is not conducive to the occurrence of dynamic recrystallization and the formation of the ∑3 grain boundary.Scanning electron microscopy,EBSD and other technical methods were used to study the evolution of the microstructure of GH4698 alloy after heat treatment.The influence of different deformation conditions(strain level,deformation temperature,strain rate)on the grain size of GH4698 alloy after solid solution,∑3 grain boundary and γ′ phase precipitation behavior after aging were analyzed.Based on the existing test data,the distribution diagram of the grain size and the formation of the ∑3 grain boundary of the GH4698 alloy under the "1120℃ + 8h + quenching" solution process was established.According to microstructure analysis and experimental data,it was concluded that the strain level has a weak influence on the distribution of γ′ phase and particle size precipitated after aging.Under the combination of high temperature and low strain rate,the γ′ phase is uniformly distributed and the particles size is larger.