| NCF3015 alloy is an iron-nickel-based,age-enhanced valve alloy.The alloy strictly controls the Ni content in the alloy from the perspective of cost saving and environmental protection,adjusts the Ti/Al ratio and other element ratios,and increases the strengthening phase in the alloy.The precipitation of ?' to achieve higher performance requirements,the alloy will be considered as an alternative to the expensive nickel-based alloys Nimonic 80A and Inconel 751,used in engine air valves.At present,NCF3015 alloy has been listed in Europe and the United States,and the reaction is good.Therefore,China considers to localize it.In this paper,Thermo-Calc thermodynamic calculation software is used to optimize the alloy composition,and nine different element ratios are designed to obtain the influence of alloying elements on the equilibrium precipitation phase,and finally determine the reasonable alloying element range.The best hot working process of the alloy was obtained by Gleeble-3800 thermal simulator.SEM,TEM,EBSD,XRD and other mechanical properties were used to obtain the micro structure evolution and performance changes of the alloy in different heat treatment systems and long-term aging.It is found that the main precipitates in NCF3015 alloy are Laves phase,?" phase,?' phase,? phase MC phase,and each element should be controlled at:Cr 13.5%?14.5%,Ni+Al+Ti 32%+1.9%+2.6%nearby.Control Mo element 0.4?0.7%,Nb element 0.6%,calculated are the precipitation phase in equilibrium state,the precipitation phase in the actual material will be based on the experimentally verified precipitation phase.The research proves that The strain rate is 0.1s-1.When the temperature exceeds 1000?,the softening process of the material is greater than the hardening behavior when the true strain is less than 0.7.When the true strain is greater than 0.7,the hardening behavior of the material is dominant;the strain rate is 1s-1 and 10s-1,the material undergoes a dynamic softening process dominated by dynamic recrystallization.NCF3015 is suitable for hot working temperature range of 1050?1150?,strain rate is 0.1s-1?0.39s-1.Based on Arrhennius equation,NCF3015 valve is obtained.The thermal deformation activation energy of the alloy isQ=242.785KJ·mol-1.When the deformation rate is 1s-1,the small-angle grain boundary is reduced after 1200? deformation at 950?.34%,the high angle grain boundary increased by 66%.As the solution temperature of NCF3015 alloy increases,the lamellar precipitation at the grain boundary appears partially dissolved.At the same time,the strength of the alloy decreases,the hardness decreases slightly,and the toughness increases first and then decreases.As the aging temperature increases,the intragranular ?' phase coarsens and the lamellar precipitation at the grain boundary increases.When the temperature is increased,the strength first increases and then decreases,the plasticity and toughness continue to decrease,and the hardness increases slightly.With the increase of aging time,the strengthening phase ?' phase is stably precipitated in the crystal,the strength increases,the plasticity and toughness decrease,and the hardness increases slightly.There are two forms of ?' in NCF3015 alloy.The ?' phase in the crystal is spherical and stable,and the ?' phase at the grain boundary is clustered and extended into the crystal.The ?' phase and the ? matrix satisfy.The lattice relationship is(100)? ||(100)?'&[022]? ||[022]?',the number of ?' phases is not aging at 100h 3.7 times in the sample,aging to 2000h,the number of ?' phase changes little,only 0.24%,at this time ?' phase change is mainly concentrated in the nucleus growth.At 700? aging to 500h,the ? phase begins to precipitate in the NCF3015 alloy,causing the toughness to drop sharply.The mass fraction of aging 2000h can reach 0.305%,which is 2.4 times that at 500h.During the aging process,the plasticity of NCF3015 alloy continued to decrease,and the strength increased first and then decreased.The tensile strength at 1000 h was the highest at 1361 MPa. |
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