Study On Tensile Fracture Behavior Of 12%Cr Rotor Steel And Establishment Of Damage Model

Ultra-supercritical coal-fired power generation technology as a clean and efficient power generation technology,in recent years both at home and abroad have invested a lot of time and money to achieve significant progress.Of rotor as the entire unit ultra supercritical power generation units,one of the key components of its quality,length of service,the serious influence of the power of the whole unit,but this kind of forging in our country still cannot achieve completely independent research and development of production,its core design and manufacturing technology to our further research and development.We usually use 9%～12%Cr ferritic heat resistant steel to forge the rotor,but limited by smelting technology and forging technology,rotor forging in Our country compared with foreign countries in performance and quality is still a certain gap.Based on the above background,this paper takes the common rotor steel12%Cr rotor steel as the research object and combines numerical simulation with thermal simulation experiment to study the cracking problem of 12%Cr rotor steel during thermal deformation.The main research contents and achievements of this paper are as follows:The stress and strain curves under different deformation conditions were obtained by isothermal tensile test on Gleeble-1500D thermal simulation machine to study the effect of thermal deformation conditions on tensile fracture.With the increase of temperature and strain rate,the dynamic recrystallization occurs and the thermoplasticity of 12%Cr rotor steel becomes better.However,when the temperature exceeds 1150℃,overheating and overburning will make the plasticity of the material become worse.By observing the fracture morphology and microstructure of the sample,the tensile fracture of 12%Cr rotor steel at high temperature is a typical ductile fracture.There are a lot of dimples at the fracture surface,and there are heterogeneous particles at the bottom of the dimples.In the high temperature tensile process,there is a difference between the plastic deformation ability of precipitated particles and the matrix metal,which leads to the concentration of tensile stress in the vicinity of the two particles,and the boundary of the two particles is pulled apart or the dissimilar particles are fractured to produce micropores.The hyperbolic sinusoidal constitutive model was established on the basis of the experimental data of hot tension,and the hot working diagrams under different strains were drawn.According to the hot working diagrams,the most suitable hot working conditions for 12Cr%rotor steel were obtained,which were as follows:temperature 1000～1200℃,strain rate 0.005～0.05s^-1.Based on the experimental data of thermal tension,the damage values under different deformation conditions were obtained according to the ductile fracture criterion,and the damage evolution equations were obtained by fitting temperature and strain rate with critical damage value and critical fracture strain.The effect of initial damage threshold strain,temperature and strain rate is considered in this equation.The forging process of partial rotor was simulated in DEFORM-3D,and it was found that surface cracks were easily formed at the joint of two anvil.Choose different anvil forging,forging through the upper flat anvil v-shaped anvil forging,the surface is more smooth,the surface is not easy to crack,but the upper flat anvil v-shaped anvil forging process is more complicated than the upper flat anvil flat anvil,the need for longer time.