Development Of ER90S-G Matching Welding Wire For High-Strength Steel Sheet For Nuclear Power Containment And Study On Its Microstructure And Properties

In response to the large-scale development needs of the third-generation nuclear power in China,this subject researched and developed the high-strength steel supporting welding wire ER90S-G for the containment of CAP1700 nuclear power plants.According to the requirements of AMSE BPVC Volume II,Section C,SFA-5.28,the alloy system of ER90S-G welding wire is designed to be Mn-Cr-Ni-Mo.Through composition optimization and manufacturing process research,ER90S-G welding wire has been successfully prepared and studied structure and properties of deposited metal are analyzed,and the influence of welding current and post-weld heat treatment process on the properties of deposited metal is analyzed.Theφ1.2mm ER90S-G welding wire was used to weld high-strength steel AG728plates for containment of nuclear power,and the structure and properties of the welded joints were studied.The deposited metal test results show that the deposited metal structure of the four designed welding wires is mainly acicular ferrite,and the mechanical properties of the deposited metal meet the development indicators of the welding wire.The yield strength ranges from 656 to 703 MPa,the tensile strength ranges from 740 to 793 MPa,the impact absorption energy ranges from 74 to 140 J,and the elongation rate ranges from 23%to 27%.Among them,2#welding wire has the best comprehensive mechanical properties.The effect of welding process and post-weld heat treatment on the properties of deposited metal of 2#welding wire was studied.The results showed that with the increase of welding current,the tensile properties of deposited metal at room temperature and high temperature（150℃）showed an increase in strength first and then decrease trend.The impact absorption energy of-45℃decreases with the increase of welding current;the post-weld heat treatment of 610℃is performed on the deposited metal.As the heat treatment time increases,the strength of the deposited metal decreases slightly.The ductile-brittle transition temperature of the 2#welding wire deposited metal is-52.1℃,and the ductile-brittle transition temperature of the deposited metal after 610℃×10h heat treatment is-53.0℃,indicating that heat treatment has little effect on the ductile-brittle transition temperature.In the test range of this article,the deposited metal obtained by using180～190 A welding current and 610℃×10h heat treatment process has the best comprehensive mechanical properties.Theφ1.2mm ER90S-G welding wire is used for butt welding of high-strength steel AG728 plates,and the joints are subjected to post-weld heat treatment.The research results show that the weld structure is mainly composed of acicular ferrite and a small amount of granular bainite.The inclusion of MnSiO₃promotes the formation of acicular ferrite and is the main core for acicular ferrite nucleation.Its size is about 0.5μm.The coarse-grained zone in the heat-affected zone is dominated by martensite.After heat treatment at 610℃×10h,the acicular ferrite in the weld structure grows up and tempered sorbite and massive ferrite appear.The martensite in the coarse-grained zone of the heat-affected zone transforms into tempered martensite and tempered sorbite,the number of large-angle grain boundaries decreases,and the M-A component gradually disappears.The post-weld heat treatment slightly reduces the normal temperature strength,high temperature strength,and impact toughness of the joint.The microhardness of the weld and heat-affected zone decreases significantly,the microhardness of the base material decreases slightly,and the bending performance is significantly improved.The microscopic analysis results of the fracture of the-45℃impact test of the welded joints show that the impact fracture morphology with the notch located in the coarse-grained zone of the heat-affected zone has a river pattern characteristic of brittle cleavage fracture.Through heat treatment,it can be transformed into a quasi-cleavage feature that the river becomes shorter and shorter,and the microscopic morphology of the fracture in the base metal and the weld is basically dimples.The fracture morphology of welded joints in normal temperature and high temperature tensile tests are basically composed of dimples.In the dimples,inclusions or precipitated particles can be clearly seen.The fracture mechanism is a typical microporous aggregation fracture.