Study On Stress Corrosion Charactoristics And Mechanical Properties Of Q420qD Steel

With the rapid development of civil engineering and infrastructure construction in China,the demand for high-performance steel is increasing day by day.In recent decade,Q420qD with high strength,high toughness and other excellent properties has become a very important steel in the construction of traffic civil engineering,which is favored by investors and designers.As Q420qD is more and more used in the complex environment of ocean,industrial atmosphere or groundwater erosion,the steel corrosion caused by this has caused the structural member sec tion loss,performance degradation and durability reduction and other issues,which makes the corrosion problem of steel structure in the service life become an important factor affecting its life-cycle durability design.At the same time,the steel struct ure works with stress due to the load in the normal use stage,especially the underground structure is also affected by the stray current in the surrounding environment,which will further aggravate the corrosion of the steel structure.In this paper,the stress corrosion characteristics and mechanical properties of Q420qD steel will be studied through experiments,and the bearing capacity of concrete-filled steel tubular columns in subway structure after corrosion is predicted by finite element analysis.In this paper,30 stressed and unstressed specimens were carried out accelerated corrosion of electricity test and tensile test.The stress-strain curves of the specimens with and without stress were obtained,and the variation law of the stress-strain curves under different corrosion degrees was analyzed.It is found that the mass loss rate of stressed and unstressed specimens increases nonlinearly with corrosion time,and the corrosion rate of specimens with stress is slightly faster than that of specimens without stress.In addition,the degradation model of nominal yield strength and nominal ultimate strength with mass loss rate and section loss rate calculated according to the original section area of specimens with and without stress is also established.It is found that the degradation rate of nominal yield strength and nominal ultimate strength of stressed specimens is faster than that of unstressed specimens when the data dispersion is small.At the same time,the degradation model of yield strength and ultimate strength with mass loss rate and section loss rate is also established.In the elongation degradation model of specimens with or without stress after corrosion,the elongation decreases linearly with the increase of mass loss rate and section loss rate.In addition,the fracture morphology of tensile specimens with and without stress was analyzed.For the specimens with or without stress corrosion,the surface morphology of some specimens was scanned by 3D topography scanner before tensile test.The development law of surface morphology of specimens with and without stress was analyzed,and the shape of pits was observed,and the distribution of pit depth and ratio of diameter to depth were explored.The surface morphology of all corrosion specimens was collected by Canon camera.The fractal dimension of all specimens was calculated by differential box dimension.The variation of fractal dimension with mass loss rate and corrosion time was explored.The finite element software is used to analyze the corrosion of concrete-filled steel tubular column after corrosion.According to the subway structure environmental factors and the chemical composition of steel,the corrosion rate of steel in subway environment is fitted.The results show that the bear ing capacity of concrete-filled steel tube column changes within about 5% after corrosion in subway structure.