Experimental Research On Static And Fatigue Performance Of Corroded Steel Welded Joints

Q355(formerly Q345)steel and its welded joints are widely used in ordinary steel structures.Steel structures corrosion is deeply concerned.In this paper,I employed the neutral salt spray test to accelerate the corrosion and conducted the static and fatigue performance tests on the steel base materials and welded joints with the ER50-6 welding wire.This paper focuses on the welded joints' corrosion,static and fatigue performance based on the tests' statistics.The major work content and results are as followed:(1)The Artificial accelerated corrosion test: 52 specimens of two sizes were subjected to neutral salt spray corrosion with a maximum corrosion period of 80 days.By virtue of the high-strength matching welding process referred in the paper,I used the ER50-6 welding wire as the cladding metal and found that the corrosion morphology of it is smaller and denser than the Q355 steel base material.And its corrosion rate is also faster than the Q355 steel base material.By analyzing the microscopic metallographic composition of each section,I found that the material properties and metallographic differences after overheating are the major factors relative to the differences in corrosion rate and morphology.(2)Tensile tests of three types of 45 specimens with 5 different corrosion periods: These tests were performed to obtain the mechanical properties' degradation curves of various specimens.Then I analyzed the degradation rate and obtained the corresponding relationship between mechanical properties and corrosion rate.The study found that the degradation rate of the ultimate strength and the nominal yield strength of the welded joint is lower than that of its deformation,and the welded specimens with mild corrosion also show strong brittle failure during the tensile process.(3)Fatigue life tests for welded joints: I made comparative analyses of test pieces of different corrosion rates,stress ratios and loading stress amplitude.According to the tests,corrosion intensifies the brittle failure of welded joints,pits increase the structural stress at the weld toe,and the length of fatigue life drops with the increase of the corrosion rate.Welding height is an important factor influencing the fatigue strength of welded joints.Planing the welding height can increase the fatigue life to a certain extent.By the specific welding process referred in the paper,when the stress ratio is 0.1 and 0.2,there is no obvious differences in the fatigue life of welded joints after planed remaining height.I also used scanning electron microscope(SEM)to analyze the tensile fracture and fatigue fracture microscopically.According to my research,the damage of the weld joint starts from the source of crack initiation.Fatigue bands are generated during the tension-tension fatigue vibration,and the fatigue fracture of the weld joint is shown as the instantaneous brittle fracture.