Research On The Microstructure And Properties Of Nuclear Valve Alloys

Seawater is the cooling water of nuclear power plant.Nuclear valves used in the seawater will be subject to severe corrosion,thereby affecting its service life and safety.In this paper,a variety of modern materials analysis and testing methods were used to study microstructure,mechanical properties and corrosion resistance of cast 2507 duplex stainless steel,forged 2507 duplex stainless steel and Inconel718 nickel base alloy after different heat treatment.And provide theoretical reference for the actual production of nuclear valve alloys.The cast 2507 duplex stainless steel is subjected to solution treatment in the temperature range of 1050??1150?,and the microstructure include light austenite and dark ferrite.With the increase of the solution temperature,the ferrite content increased,the degree of austenite Wei Wei degree decreased,the two-phase structure was coarsened.After 1125? solution treatment,the tensile strength reached the highest value of 709.8MPa.The full immersion weightlessness test in 6%FeCl3 solution shows that the corrosion rate of cast 2507 duplex stainless steel is gradually accelerated with the increase of solution temperature.From the potential polarization curve and electrochemical impedance analysis shows that,Electrochemical potential polarization curves and electrochemical impedance analysis show that.With the increase of the solution temperature,the breaking potential Eb and the passivation film resistance R3 of the 2507 duplex stainless steel in 3.5%NaCl solution are reduced,the stability of the passivation film is reduced and the corrosion resistance is decreased.After 1050?solution treatment,the passivation film resistance R3 up to 76009?,corrosion resistance is good;after 1150? solution treatment,R3 is only 16931?.The untreated forged 2507 duplex stainless steel tissue contains a hard brittle phase.After treatment at 1050??1150?,the microstructure of the microstructure is composed of austenite and ferrite.When the solution temperature is 1050??1075?,the two phases are close to 1:1.The tensile strength of stainless steel after solution treatment is maintained at 730MPa?760MPa.The full immersion weightlessness test in 6%FeCl3 solution shows that the corrosion rate of forged 2507 duplex stainless steel is gradually accelerated with the increase of solution temperature.From the electrochemical corrosion test,forged 2507 duplex stainless steel at 1050??1150? solution treatment,with the solution temperature rise corrosion resistance decreased gradually.Increased solution temperature,ferrite content increased,ferrite forming elements Mo and Cr concentration decreased,Mo and Cr is the main anti-pitting elements of stainless steel,so the corrosion resistance of stainless steel will decline.Inconel718 nickel-based superalloy as-cast microstructures exist dendrite segregation,need to be homogenized.After the direct aging treatment,due to the pinning effect of the ?phase,the grain size of the alloy is fine,the mechanical properties are better,the tensile strength is as high as 13 45.81 MPa.After 1050? solution and aging treatment,the ? phase is completely dissolved,the pinning effect disappears,the grain size of the alloy is coarse,the mechanical properties are poor,and the tensile strength is only 1294.79MPa.From the electrochemical corrosion test,direct aging treatment of the alloy,the second phase content(such as ?,?',?")is more,and easy to form a large number of micro-corrosion of the battery,corrosion resistance is poor;the second phase of the alloy treated with the solution and aging treatment was dissolved and the corrosion resistance was improved.After 1050? solution and aging treatment,the alloy passivation film resistance up to 3029?,the corrosion resistance is better.