Study On Hot Deformation Behavior And Thermomechanical Treatment Process Of AerMet100 Steel

AerMet100 steel is a secondary hardening ultra-high strength steel. This paper mainly deals with the microstructure evolution and mechanical properties of hot deformation and tempering process of the steel. The new technology such as deforming aging, pre aging, double aging were introduced in order to optimize its microstructure and mechanical properties. The proper pre aging + double aging technology produced better strength and toughness properties of the steel.The dynamic recrystallization（DRX） behavior of ultrahigh strength AerMet100 steel during hot compression test were studied in the temperature ranges of 850-1150 ℃ and the strain rate ranges of 0.01 – 10 s- 1 on a Gleeble-3500 thermo-mechanical simulator. The results shows that the raise of temperature and the decrease of strain rate is benefit to DRX. The hot deformation activation energy Q=402kJ/mol, constitutive equations, DRX critical strain model, DRX kinetics model and recrystallizing grain size model have been obtained by the regression analysis of the experimental data. The DRX kinetics model predicted that the decrease of temperature and the increase of strain rate will postpone the occurrence of DRX which consistent with the experiment results.The effect of deforming aging after hot compression on microstructure and hardness of AerMet100 steel were investigated. The results shows that with the raise of isothermal temperature, the size martensite lath increased, the hardness decreased. The microstructure is finer and the rebound hardness when aging at 510 ℃ because of the deformation induced precipitation, the dispersion precipitates nail the dislocation and hinder the growth of the martensite structure. During the deforming aging process precipitation will be occurred in the vicinity of 510 ℃ and the holding time should not be longer than the 180 s.The effect of temper process on microstructure and mechanical properties of forged AerMet100 steel were investigated by variety aging technology. When normal aging in the range of 460⁵10 ℃ with the raise of aging temperature,the size of martensite lath increase first then decreased, the hardness and strength are decrease first then increased and the impact toughness increases continuously. The martensite structure is smallest along with the hardness and tensile strength are reach the peak when aging at 480℃. pre aging + normal aging（510℃×30min, OQ+482℃×5h, AC） process can obtain excellent strength and toughness（ σ104J=AK; 1946MPa=b）. The improving of strength and toughness was attribute to the pre aging at a high temperature of 510℃ which promoted the C atom diffusion that added the amount of membrane reversed austenite and enhanced its stability. And the M₂ C precipitate maintained a good lattice relationship with the matrix because of the short isothermal time（≤30min） of pre aging, the precipitation strengthening effect improved the strength.