Numerical Simulation Research On Hot Forging Process Of GH738 Superalloy Bolt

High temperature alloy is an important structural material in aerospace and nuclear industry.It is widely used in the manufacture of various parts of aeroengine for its excellent high temperature mechanical properties.The forming of high temperature alloy bolt fastener is mainly divided into two parts: the hot upsetting forming of bolt head and the rolling processing of thread part.Hot upsetting is a kind of processing method that the blank is heated to a certain temperature and then upsetting.After hot upsetting,the fastener has excellent mechanical properties,complete metal streamline and distribution along the product shape,good comprehensive performance and high fatigue strength.Rolling thread belongs to the near net forming process,which makes the workpiece plastic deformation under the pressure of the rolling wheel,forming the corresponding specifications of thread.Compared with cutting,it has the advantages of high processing efficiency and high utilization rate of raw materials.GH738 alloy is a typical hard to deform superalloy.Its mechanical properties are very sensitive to the processing technology.Improper control of the processing process will produce coarse-grained and mixed crystal phenomena,which will affect the fatigue performance,durability,notch sensitivity and impact toughness of alloy products.Therefore,the development of hot deformation process and the control of microstructure and properties of GH738 alloy have been the focus of research.During the heating process of hot deformation,the grain structure will grow or coarsen to a certain extent,which will affect the control of the structure and properties of the subsequent hot deformation.Therefore,it is necessary to control the grain size of GH738 alloy strictly and reasonably,which is also the key to make the hot deformation process.In this paper,The hot compressing experiments of GH738 superalloy were carried out at a temperature range of 1000-1160? and a strain rate range of 0.01-10s-1 to figure out the impact of the process parameters on the flow stress.A typical dynamic recrystallization model is established by introducing the work hardening index.The effect of temperature and strain rate on the mechanical properties was studied.The results show that the increase in temperature and decrease in strain rate caused a decrease in peak stress.Finite element method was applied to analyze the effect of process parameters on the stress,strain,temperature distribution and damage values.This article has also discussed the difference between single-step forming and multi-step forming by finite element analysis.The conclusion is that single-step forming is more suitable than multi-step forming on GH738 superalloy upsetting.This paper provides a basis for predicting defects and optimizing process on bolt upsetting forming of GH738 superalloy.