Investigation On Microstructure Property And Crack Resistance Of690 Nickel-based Weld Matel

Recently,environmental pollution and energy shortage are two factors that limit the development of the world,clean energy is a crucial tool for solving those issues.As so many clean energies for selecting,nuclear power due to the distinct advantages(mature and stable power supply for the large scale development),makes development and utilization of nuclear power become one of the important choice to solve the energy shortage in our country.With the rapid development of China's nuclear power industry,690 nickel-based alloys have been widely used in the manufacture of nuclear power equipment.It is necessary to research the welding materials of 690 nickel-based alloys.Solidification crack is one of the most common ceacks in weld matel of 690 nickel-based alloys,find out the causes of solidification crack can provide reference for the development,production and weldability of nickel-based alloy welding materials.The experimental focus on microstructure,mechanical properties and resistence of solidification cracks,two welding materials of 690 alloy were welding on low alloy steel with same welding parameters and method to make two weld metals.Adopting optical microscope,scanning electron microscope,X-ray diffraction,transmission electron microscope to analyse the microstructure and precipitates of weld metal.The mechanical properties of deposited metal were analyzed by hard test,tension test,impact test,bending test and intergranular corrosion test.Recording the length,number and location of crack in weld metal are and furtherly finding causes of cracks.The results show that microstructure of two weld metals are columnar crystals and consisit of ?-Ni(Cr,Fe)phase and less Nb-rich phase.Type-II boundaries and transition areas appear on the fusion line in two weld metal due to the composition difference between welding materials and base materials.Two desposited matels show well mechanical properties and resistence of intergranular corrosion,the tensile strength is 641 MPa and 639 MPa,the impact power is 100 J and 106 J respectively.The solidification cracks of two weld metals mainly appear in the top half of buffering layer which adjacent to the base material.The average length of cracks in 1#weld matel and 2# weld matel is 598 ?m and 781 ?m,the maximum length is 1089?m and 1683 ?m,the number of cracks in 1# weld matel is about 50% lower than that of 2# weld matel.Much Mn and less Nb of welding material will increase the resistance of solidification cracks of weld matels.Buffering layer acquire too much Fe from base matel because of the higher dilution rate,Fe can cause low dissolved Nb levels in weld matel,precipitated Nb react with S to form low melting sulfide which induced solidification cracks during solidification stage of weld matels.