Finite Element Simulation Of Quenching Cracking Of Heavy Forgings

Wind power spindle is the key component of wind power generation,which has high requirements for mechanical properties.When the wind turbine spindle is designed as the center hole to enhance weight reduction,it also increases the failure probability in the quenching process.As a typical heavy forging,forged wind turbine spindle is easy to produce local stress concentration in the heat treatment process,which can reduce the mechanical properties of the spindle and even crack.The production cost of heavy forgings is high,once scrapped,the loss is huge,so it is very important to predict the failure risk in the production process to reduce the production cost.In the past,the stress judgment of heavy forgings mainly depends on experience or a small amount of simulation,and the data prediction is not accurate enough.Therefore,it is of great significance to improve the material database and establish the material model.In this paper,based on the production situation of cracking in the quenching process of large-scale forging wind turbine hollow spindle,the macro scale simulation and the micro scale crack initiation in the stress concentration area are studied.In this paper,the isothermal cooling process at different temperatures is studied by using GLEEBLE-3500 thermal simulator,and the relationship curve between phase change expansion and temperature is obtained.The austenite transformation temperature AC1=728℃,AC3=813℃.The relationship curve between martensite volume fraction and temperature was obtained by tangent method,and the koistinen Marburger equation was used for linear fitting.The distribution fitting equation was proposed for the inaccuracy of fitting curve at the initial stage of transformation.By fitting the change of expansion during isothermal process,it is determined that bainite and pearlite conform to Avrami crystallization kinetics equation.Drawing the isothermal transformation curve of 42CrMo,it is found that the bainite part of the isothermal transformation curve has "double nose"phenomenon.It is found that the transformation of bainite is incomplete with the increase of isothermal temperature.By calculating the unit expansion ratio and expansion coefficient of bainite and observing the metallographic diagram,the time curve of the maximum transformation of bainite is quantitatively analyzed.The phenomenon of incomplete bainite transformation was analyzed by coupling solute drag effect to explain the "double nose" phenomenon in TTT curve.Complete the secondary development of temperature field,stress field and tissue field subroutine.In view of the inaccuracy of the existing software transformation model,the microstructure field subroutine is compiled,and the distribution functions of bainite incomplete transformation,martensite transformation and the actual introduction of the dynamic equations are considered.The thermodynamic and kinetic subroutines are programmed to import the constitutive model of the simulation process.By comparing the experimental results with the simulation results,the verification of the subroutine is realized,and the gap between the mechanical and thermal constitutive models of the secondary development subroutine and the actual is small.The results show that the microstructure field can well reflect the actual phase transformation process.The distribution of temperature field,stress field and microstructure field of small shaft end of wind turbine spindle is simulated in macro scale.Aiming at the cracking phenomenon of small shaft end of Wind Turbine Spindle in production process,the simulation model of small shaft end is established.By analyzing the stress distribution of the small shaft end of the wind turbine spindle,it is judged that the axial crack is the main failure risk,and there is the possibility of circumferential crack propagation at the end face of the small shaft end of the spindle,which is consistent with the crack distribution in the actual production.The failure simulation with XFEM module was carried out in the stress concentration area at the micro scale,and the crack source was observed.