Experimental And Numerical Investigation On Microstructure Evolution Of TRIP Steel Seamless Tube In Hydroforming Process

The light weight of transport machinery has been receiving an increasing attention as the concept of low-carbon,energy-saving and environment-friendly was advocated in recent years.Using the hollow structures take place the solid ones has been one of main ways to reduce transport machinery weight.As an advanced technology characterized by light weight and integrity,which can be used to manufacture hollow structural components and variable cross-section parts,obtained more attention.On the other hand,in the field of material research The TRIP(Transformation induced plasticity)steel has high strength as well as good obdurability,which has been widely used in transport machinery.Introducing TRIP steel technology into the steel tube manufacturing field,the seamless tube which is making out of TRIP steel owns good comprehensive mechanical properties.The thesis was carried out integrating with the major item of The National Seed Foundation of China(N130403013),"Microstructure Evolution Mechanism of TRIP Steel Seamless Tube in Hydroforming".Based on the experimental and finite element simulation of high pressure forming in seamless tube of TRIP steel,the deformation behavior during deformation and the microstructure evolution law of TRIP steel seamless tube were investigated,and the process of hydroforming of TRIP steel seamless tube was simulated.The main works involved in the thesis are listed as follows:(1)There is an overview on the hydroforming of TRIP steel seamless tube,the characteristic of TRIP steel and the principle and features of hydroforming were explained,and their research and practical applications status were analyzed.(2)The microstructures of different parts of sample under different experimental conditions in TRIP steel seamless tube hydroforming were observed by using the metallurgical microscope,SEM and EBSD,and the volume fraction of retained austenite was measured by XRD.The microstructure evolution law of TRIP steel seamless tube was investigated.(3)The finite element analysis software-LS-DYNA is used for modeling TRIP steel seamless tube analyzing the hydroforming process.The reliability of the finite element model was verified according to experimental data.(4)The influence rules of deformation conditions on the microstructure evolution of TRIP steel seamless tubes were analyzed by using the finite element model combined with the experimental results under the same conditions.The optimal load path of TRIP steel seamless tube was presented by combining the experiment result and simulation result.(5)In order to study the forming law of TRIP steel seamless tube of hydroforming process in complex stress-strain condition,T-shaped tube hydroforming process was studied.Through the establishment of thirteen groups of high pressure forming models,the stress,strain and wall thickness distribution of steel pipes in the process were analyzed,as well as the influence of axial feeding,maximum internal pressure and friction coefficient on TRIP seamless steel deformation behavior in hydroforming process.