Research On Hot Deformation Behavior And Microstructure Of AF1410 Steel

AF1410 steel has been widely used in aerospace field because of its high strength,high toughness,good fatigue resistance and corrosion resistance.Most of AF1410 steel aerostructures are produced by the hot die forging.However,there are few studies on the plastic deformation mechanism and microstructure evolution of AF1410 steel during hot deformation.In addition,the lack of AF1410 steel material data in the existing numerical simulation software has greatly limited the finite element simulation of this material's thermoforming process.Therefore,the thermal deformation behavior of AF1410 steel at different deformation temperatures,multi-range strain rates is investigated in this paper.The constitutive equations,dynamic recrystallization models and thermal processing maps of AF1410 steel were constructed.In addition,this paper established a finite element simulation material model based on the constitutive model and dynamic recrystallization model of AF1410 steel.The finite element simulation software DEFORM was used as a platform to numerically simulate the thermal compression process of AF1410 steel double-cone specimens.The results of strain field,temperature field and grain size of the double-cone thermocompression specimen were obtained by simulation.And the accuracy of the finite element model was verified by physical experiments.The main research contents and results of the paper are as follows:?1?The hot deformation behavior and the microstructure evolution of AF1410 steel were studied by the single-pass isothermal compression experiment of cylindrical specimens.The corresponding constitutive equations,thermal processing maps,and dynamic recrystallization models were established.The microstructure was analyzed in conjunction with the thermal processing maps.An optimum processing parameters of hot deformation for this steel can also be obtained by the maps,in which the hot temperature is 1050¹150?and the strain rate is0.007⁰.36s^-1.?2?The microstructure of the hot simulated compressive specimens was studied and the effect of different deformation parameters on the grain size of the microstructure was analyzed.The results showed that the grain size of AF1410 steel hot-compressed specimen increases with the increase of deformation temperature and the decrease of deformation rate.The dynamic recovery tends to occur under the deformation conditions of high temperature and low strain rate,and the grain is easy to coarsen.It is prone to incomplete dynamic recrystallization at low deformation temperatures and high strain rates,which leads to the presence of mixed crystals including deformed grains and recrystallized grains.?3?Thermally simulated compression specimens were heat treated?900?/1h+680?/6h?.The evolution of grain structure in thermal deformation and heat treatment of the specimens was analyzed,and the precipitates of the heat treated specimens were analyzed in detail.The results show that the uneven grains of the thermal compression samples with different parameters become basically uniform and the grains size range from 14 to 23?m.However,the effect of coarse heat treatment on the microstructure is not obvious.The martensite gradually transform into ferrite and carbide after high temperature tempered.The coarse precipitates mainly include needle-shaped M₂C with Mo-rich and square-shaped M₂₃C₆carbide with Cr-rich and there are not coherent relationship between the carbides and the martensite matrix.?4?The accuracy of the AF1410 steel numerical simulation material model was verified by the hot compression test of AF1410 steel double-cone samples.The microstructure of the typical region of the double-cone thermal compression specimen was analyzed and the thermal deformation process was simulated using DEFORM software.The results show that the double-cone specimens have different degrees of dynamic recrystallization in different regions.As the strain amount increases,the dynamic recrystallization volume fraction gradually increases,and an“S”type curve is obtained for the relationship between DRX fraction and strain values.Dynamic recrystallization first nucleates at the grain boundaries,and it expands into the grains as the amount of strain increases.The comparison between the experiment results and the simulation results shows that the finite element simulation based on the AF1410 steel constitutive model and the dynamic recrystallization model at high temperature deformation has a good predictability for the thermal deformation process.