Study On High-strength High-toughness Welding Wire For Nuclear Power

SA738Gr.B steel is the main material of nuclear power steel containment vessel,but its matching high-strength high-toughness solid wire is rarely studied and reported.This paper aims to develop the high-strength high-toughness solid wire for SA738Gr.B steel,and studies the development of welding wire,deposited metal properties,rolling process,performance of actual welded joint and weldability of the high-strength high-toughness steel.The main research results are as follows:(1)High quality 1#and 2#high-strength high-toughness welding wires with different compositions are obtained by vacuum refining,Zr-Ti element composite deoxidation and controlled rolling and drawing.The microstructure of both 1#and 2#deposited metal are composed of acicular ferrite and pro-eutectoid ferrite.The tensile and impact properties at room temperature are good,and the low temperature impact is up to the standard.For 1#and 2#deposited metal after 600°C×10 h post-weld heat treatment,the acicular ferrite structure become coarse,and the proportion of pro-eutectoid ferrite increase,and the tensile and impact properties decrease.(2)The static and dynamic recrystallization process of 1#and 2#steel are simulated through Gleeble3800 thermal simulator.The roughing rolling temperature of1#steel is more than 1050°C,at the same time the finishing rolling start temperature should be less than 900°C.Its dynamic recrystallization kinetics model is(5=?0)221.42×10~3/(8.31·).The roughing rolling temperature of 2#steel is more than 1050°C,the finishing rolling start temperature should be less than 950°C.Its dynamic recrystallization kinetics model is(5=?0)225.86×10~3/(8.31·).(3)1#and 2#high-strength high-toughness welding wires are used for the welding joint test of SA738Gr.B steel.The tensile properties of 1#and 2#welded joints are up to the standard,but the low temperature impact toughness is poor.The low temperature impact toughness of 2#welding joint is better than 1#welding wire.After 600°C×10 h post-weld heat treatment,the tensile and impact toughness of the welded seam and heat-affected zone of the two sets of welded joints decrease.The two sets of welded joints pass the 180°side bend test and the macroscopic cross section have no defects such as pores,impurities and cracks.The microstructure of 1#weld seam includes pro-eutectoid ferrite,side slab ferrite and granular bainite while 2#weld seam includes pro-eutectoid ferrite,side slab ferrite and acicular ferrite.The microstructure of both 1#and 2#heat-affected zone include lath bainite,a small amount martensite and part of acicular ferrite.Because there are fewer pro-eutectoid ferrite and side-plate ferrite and more columnar intra-crystalline acicular ferrite in the welded seam of 2#welding wire,moreover the bainite and martensite grains is finer in the heat-affected zone of 2#welding wire,so the 2#welding wire has better performance than 1#welding wire.(4)The weldability of steels for high-strength high-toughness welding wires is studied by Gleeble3800 thermal simulator.When the heat input of 1#and 2#steel are about 30kJ/cm and 60kJ/cm respectively,the microstructure of bainite,granular bainite and a small amount of acicular ferrite can be formed in the coarse-grained heat-affected zone,which has good comprehensive mechanical properties.