Of Ti Content On The Microstructure And Mechanical Properties Of Inconel690

Inconel690 is an austenitic nickel-based corrosion resistant alloy with about 30% (wt%)chromium content.It's now considered as the most ideal steam generator tube in nuclear power plants because of its excellent corrosion resistance,high strength,good metallurgical stability and excellent processing characteristics.It's widely used at home and abroad.However Inconel690 can't be immune to stress corrosion cracking,corrosion resistance should get further enhanced and improvedIn this paper,for the purpose of improving corrosion resistance,three furnace alloys have been designed with different content of titanium;the effect of titanium and heat treatment process on microstructures and properties of Inconel690 has been studied in detail.Fist of all,the effect of titanium on precipitated amount of M₂₃C₆ in Inconel690 have been analyzed by thermo-calc software,the results showed that with the increase of titanium,the content of carbon in matrix dropped significantly,the precipitated amount of M₂₃C₆ could be lower after thermal treatment,so it's helpful to intergranular corrosion resistance.However phase analysis showed that the effect of titanium on dropping carbon content is not obvious,the reason is relate to the precipitated activity of Ti(CN)and smelting process.The variation of morphology,size,distribution of M₂₃C₆ carbides and the regulation of Chromium content near grain boundaries during thermal treatment in 4 to 100 hours are the emphasis of this study.The results showed that time of thermal treatment affected carbides in alloy with 0.35%Titanium obviously,there is no significant variation of M₂₃C₆ during thermal treatment in 25～100h;the lowest chromium content on grain boundaries was high when titanium content increased,and Cr-depleted zone was relatively narrow,so titanium is helpful to inhibiting chromium depleted on grain boundaries.With the extension of thermal treatment,chromium content on grain boundaries rebounded.The effect of titanium on precipitated phase and properties of alloy is analyzed in detail.The results showed that titanium content affected the types of precipitated phase. Cr-rich M₂₃C₆ and Ti(CN)carbides precipitated after thermal treatment at 715℃.γ' phase precipitated when titanium content was 1.1%,they dispersed in matrix.After 100h of thermal treatment,γ' phase also precipitated in alloy with 0.7%titanium,but not in alloy with 0.35%titanium.Titanium content affected strength in alloys after thermal treatment obviously.After 715℃×15h thermal treatment,alloy's strength increased obviously both at room temperature and 350℃when titanium content was 1.1%,because ofγ' phase strengthening matrix,while plasticity is still high.So it can make the thickness of pipes thinner,cost can be saved.The effect of solution temperature on recrystallization of Inconel690 has been studied in this paper,the recrystallization temperature was between 1020 to 1075℃,carbides were dissolved completely during 1120 to 1170℃,With the increase of titanium,alloy's strength in solution state either at room temperature or 350℃was increased.