Microstructure And Properties Of SP2215 Heat Resistant Steel Transient Liquid Phase Bonded Joints

SP2215 heat-resistant steel has high temperature resistance,corrosion resistance and good comprehensive mechanical properties.SP2215 heat-resistant steel is currently used in the world for ultra-supercritical generator steel with good performance and good development prospects.When the traditional fusion welding method is used,the heat input is large,the residual stress generated by the joint is high,and creep failure occurs during high temperature operation.Transient liquid phase diffusion welding has the advantages of low welding temperature,short welding time,small joint deformation and high welding quality.It has high application value in the welding of SP2215 heat-resistant steel.In this paper,Fe-based,Ni-based,Fe-based + Ni-based,Fe-based + Ni-based + Fe-based,four forms of amorphous alloy foil as the intermediate layer.In an open environment,industrial argon is used for protection.SP2215 heat resistant steel is subjected to transient liquid phase diffusion bonding.The distribution,microstructure,mechanical properties and micro-fracture morphology of the welded joints were analyzed by means of metallographic microscope,scanning electron microscope,microhardness tester and electronic universal testing machine.The research shows that the Fe-based,Ni-based,Fe-based + Ni-based three forms of amorphous alloy foils are used as the intermediate layer,and TLP diffusion welding is carried out under different process parameters.Through the microstructure analysis and mechanical properties of the joint,the tensile strength of the joint is 673 MPa,594 MPa,470 MPa,which is far lower than the tensile strength of the base metal(780 MPa),There are inclusions in the joint weld,which causes the joint to break easily at the weld seam,failing to meet the requirements for use.The Fe-based + Ni-based + Fe-based composite amorphous alloy foil was used as the intermediate layer.TLP diffusion welding was carried out under different process parameters,and the tensile strength of the joint was significantly improved.The best welding process is: welding temperature 1245 ?,welding time 240 s,welding pressure 6 MPa.Under this process,the joint is welded without weld,and the main elements of the middle layer are evenly distributed on the joint,and the tensile strength(781 MPa)? microhardness(185 HV)are consistent with the base metal.The bending test is qualified,and the TLP diffusion connection of SP2215 austenitic heat-resistant steel is realized.By comparing the microstructure and mechanical properties of the welded joints under different intermediate layers,it can be seen that when the intermediate layer is not suitable,the joint welding quality can not meet the requirements no matter how the welding process parameters are adjusted.Only when the intermediate layer is suitable,the joints that meet the welding requirements can be obtained by adjusting the welding process parameters.Therefore,the selection of the intermediate layer material plays a key role in TLP diffusion welding.There are many factors affecting the quality of joint welding,but the influence of each factor is different.First,the pre-weld preparation has the greatest impact,followed by the selection of the intermediate layer material,and finally the welding process parameters.The influence of welding process parameters on joint welding quality is: welding temperature> welding pressure> welding time.In order to obtain the joint with the best welding quality and avoid defects such as porosity,inclusions,brittle phase and misalignment of the weld,it is necessary to strictly control the various influencing factors.