Study On Boundary Conditions And Influencing Factors Of Hot Forging Of 300m Steel

300M steel has the advantages of high strength,high fracture toughness,good fatigue resistance,etc.It is widely used in large aviation critical load-bearing structural parts such as aircraft landing gear.The forming process of large forgings is very complicated.The use of numerical simulation technology can effectively improve the forming efficiency,optimize the process flow and die structure,and improve the quality of forgings.The reliability of numerical simulation results depends largely on the accuracy of the thermal deformation boundary conditions,so it is of great significance to determine the boundary conditions of300M steel hot forging and study its influencing factors.In this paper,the heat transfer coefficient of 300M surface and interface contact heat transfer coefficient are first determined by the inverse problem of heat conduction,and then the friction coefficient of 300M steel under different conditions is determined by the ring upsetting method,and the heat transfer coefficient and friction coefficient of different factors Impact.On this basis,the method of combining Deform numerical simulation and on-site production was used to verify the accuracy of the boundary conditions,and it was successfully used to guide enterprises to produce large die forgings.The main research contents and results of the paper are as follows:(1)Furnace heating and air cooling experiments were carried out on forged 300M steel.Using the inverse heat conduction method combined with the reverse heat transfer module in Deform,the surface heat transfer coefficient-temperature relationship curve of 300M steel was solved.Between 0.005 N/(s·mm·?)?0.08 N/(s·mm·?),it first increases with the increase of temperature.When the temperature rises to 750?,it starts to decrease.(2)The interface heat transfer coefficient of 300M steel was determined,its influencing factors were explored,and the interface heat transfer model of 300M steel was constructed.The contact heat transfer experiment of forged 300M steel was carried out,and the inverse problem of transient heat conduction was combined with Deform numerical simulation to quantify the power function relationship between pressure and interface contact coefficient.Using SEM and XRD to observe the surface morphology,microstructure and phase of the oxide layer of 300M steel under different oxidation times,it was found that the surface oxidation has a significant hindrance to the interface heat transfer.It is a power function relationship.Comprehensive analysis of the effect of the coupling effect of pressure and oxidation on the interface contact heat transfer coefficient,and the overall fitting results in a functional relationshiph(28)18.850361(/d)^0.64001P^0.58634,indicating that the hindering effect of oxidation on heat exchange is less than the promoting effect of pressure on heat exchange.(3)The friction coefficient of 300M steel under different conditions was measured,and the influencing factors of friction coefficient were discussed.A ring upsetting experiment was carried out on forged 300M steel,and combined with finite element numerical simulation technology to solve the friction coefficient at different mold temperatures,lubricant types and oxidation time.The results show that:oxidation time affects the thermal deformation friction coefficient of 300M steel No significant effect;friction coefficient decreases with increasing mold temperature.The friction coefficient is the smallest when the mold temperature is 400?.The type of lubricant has a significant effect on the friction coefficient.The friction coefficient when using Condat 10 is the smallest,about 0.27?0.35.The friction coefficient changes dynamically during the hot forging process and increases with the amount of deformation.(4)On-site verification experiments on large forgings of forged 300M steel were carried out to further optimize the boundary conditions determined under laboratory conditions and apply them to actual die forging production.The forgings before and after die forging were compared with the final forgings obtained by numerical simulation Compared with the loading load,the dimensional agreement is good and the maximum load error is only 4%,indicating that the boundary conditions solved have high accuracy.