The Effect Of Varying Al,Ti Contents And Solid Solution Treatment On The Microstructure And Property Of Incoloy800H Alloy

Incoloy800H alloy,invented by the Special Metals Corporation Group of Companies,is a kind of nickel-base austenite corrosion resistant alloy,which contents of 21 % Cr.Owing to its excellent corrosion resistance,high strength,good metallurgical stability and excellent machinery processing performance,more and more widely applied in petroleum,chemical industry,metallurgy,environmental protection,nuclear,aerospace and many other fields.Al,Ti is important alloy element in nickel base corrosion resistant alloy,has significant effect on the microstructure,corrosion resistance and mechanical properties of this alloy.In this work,the effect of varying Al and Ti contents of Incoloy800 H alloy on the phase transformations that might occur in the material was simulated using a thermodynamic modelling tool.Employ optical microscope(OM),scanning electron microscope(SEM),energy dispersive spectrum(EDS)to observe the microstructure as well as the corrosion morphology of tested alloy.Employ hardness testing,impact testing and tensile testing methods to analyze the mechanical properties of the tested alloy at room and high temperature.Potentiodynamic polarization curves,electrochemical impedance spectroscopy and the corrosion rate of the alloys were investigated by electrochemical workstation and static weight-loss method in different corrosive solutions.The results suggest that the microstructure of as-forged Incoloy800 H is composed of ? substrate,granular TiC,blocky Ti(C,N)and dendritic grain boundary precipitate Cr23C6.With the increase of Al and Ti contents,grain boundary precipitate phase Cr23C6 reduced gradually,Ti(C,N)precipitation was increased,grain size was reduced.From Alloy? to Alloy?,the yield strength and tensile strength of the tested alloy were increased from 438 MPa,621 MPa to 542 MPa,673 MPa respectively;the elongation and percentage reduction of area of the tested alloy were decreased from 43 %,67 % to 30.5 %,59 % respectively,at room temperature.With the increase of temperature,the yield strength and tensile strength of the alloy were decreased.When testing at 500 and 600?,the strength of the tested alloy is proportional to Al and Ti contents,and the fracture form is microporous gathered shaped.When testing temperature is increased to 700?,the strength of the tested alloy is inversely proportional to Al and Ti contents,shown that equal strength temperature of Incoloy800 H alloy is between 600 and 700?.Compared with the as-forged Incoloy800 H alloy,the microstructure of the tested alloy after solid solution treatment was became more uniform,grain size level of Alloy?,Alloy?,Alloy? were decreased from 5,6,6.5 to 4,4.5,5 respectively.And grain boundary precipitates Cr23C6 completely dissolved into the matrix.After solid solution treatment,hardness value of the tested alloy was decreased by 8 % 14 %,13.5 % and impact energy was improved by 67 %,75.5 %,72 %,respectively.At room temperature,500 and 600?,the strength of the tested alloy was proportional to Al and Ti contents,the plasticity appeared to reverse tendency.At 700?,the strength and the plasticity of the tested alloy were inversely proportional to Al and Ti contents,the fracture mode transformed from lower temperature transgranular fracture to intergranular fracture.With the increase of Al and Ti contents,corrosion potential Ecorr and linear polarization resistance Rp were decreased,corrosion current density Icorr was increased,corrosion resistance is decreased as well;capacitive and impedance arc radius,charge transfer reaction resistance Rt,inductive reactance RL were decreased,the tendency to pitting was increased.Large,faceted Ti(C,N)particles in Incoloy800 H provide preferred sites for pitting initiation in the chloride environments.As the extension of soaking time,the corrosion of experimental alloys developed from pitting to intergranular and intragranular corrosion.With the increase of Al and Ti contents,the number and size of crack on the corrosion product layer are increased,corrosion product layer tightness with the substrate is decreased.With the increase of HCl solution concentration,the corrosion resistance of experimental alloys dropped rapidly.The polarization curve of solution-annealed Incoloy800 H alloy was more stable in H2SO4 solution than in HCl solution.With the increase of Al and Ti contents,corrosion potential Ecorr and linear polarization resistance Rp were decreased,corrosion current density Icorr was increased,corrosion resistance is decreased as well;capacitive and impedance arc radius,the value of n were decreased,the tendency to pitting and Y0 were increased.Large,faceted Ti(C,N)particles in Incoloy800 H provide preferred sites for pitting initiation in the chloride environments.As the extension of soaking time,the corrosion of the tested alloy developed from pitting to uniform corrosion.With the increase of HCl solution concentration,the corrosion resistance of experimental alloys dropped rapidly.The existence of Cl-in the solution accelerated passive film damage on the surface of solution-annealed alloy.