Experimental Study On Mechanical Properties And Toughness Of Q460C High-strength Steel And Its Weld

High strength steel has been gradually applied in large-scale bridge structures, long spanand space structures and tall buildings. As the strength of steel plate’s increases, fracturetoughness shall decrease due to adverse factors such as status of stress and strain and processtechnology etc., particularly in the case of low temperature applications. Besides, most of highstrength steel’s structure is welded structure, the left welding problems affecting itslow-temperature-toughness obviously, causing the reduction of the toughness performance, andresulting in low-temperature-brittle fracture. The main conclusions were made as following:(1) The Chinese steel structure design code and industry standards of steel were comparedwith that of Europe, U.S.A, UK, Australia, Hong Kong and Japan about the provisions forbrittle fracture of steel. Find out that these provisions were with local characteristics for eachone as well as basing upon the local temperature closely; Moreover two examples of fracturetoughness of high-strength steel through the J-integral fracture toughness and plane strainfracture toughness KⅠCwere calculated and compared.(2) Uniaxial tensile test of Q460C, the high-strength construction-structure steel has beencarried out at the low temperature to obtaining the intensity index (including yield strength f_y,tensile strength f_u), the plastic index (including elongation at break δ, reduction of area ψ), andthe rule of these index along the temperature changing, as well as calculating the Q460C steel’stemperature sensitive coefficient, which may be used to forecast the intensity index of Q460C atlow temperature. Furthermore analyze the scanning electronic microscope of the tensilespecimen fracture surfaces.(3) This paper carried out a tensile test study on the mechanical properties of Q460C buttwelded steel, the high-strength constructive steel, at low temperature, getting the yield strength,tensile strength, the elongation at rupture, reduction of area and yield ratio with the temperaturedescending. Meanwhile, the values were compared with that of mechanical properties ofnon-welded Q460C steel.Temperature sensitivity coefficients of the welded Q460C steel werecalculated and then the strengths at low temperature can be forecasted. Moreover, the scanningelectronic microscopes of the tensile specimen fracture surfaces were analyzed.(4) Impact toughness tests of Q460C steel at low temperature were performed, andanalyzed the scanning electronic microscopes of the charpy-type specimen fracture surfaceswith different temperature points to observe their toughness or brittle characteristics.Meanwhile, a Boltzmann function fit analysis was made on the charpy impact test results ofQ460C, in order to obtain the brittle ductile transition temperature.(5) Impact toughness test of high strength structural butt welded steel plate was conductedat low temperature, to obtain its notched bar impact strength AKvwhich changed with the descending low temperature; Specimen of weld zone as well as heat-affected zone of Q460Csteel the high strength steel were prepared. Moreover Boltzmann function was used to fit theregression analysis of experimental data. Furthermore the scanning electronic microscopes ofthe specimen fracture surfaces were analyzed.(6) Crack Tip Opening Displacement (CTOD) tests were carried out on Q460C structuralsteels, but also a microcosmic analysis of the fracture appearance. And the CTOD values ofQ460C were compared with that of Q235, Q345and Q390at low temperature. Moreover, aBoltzmann function fitting analysis was applied to the experimental data, and the ductile-brittletransition temperature and the changing law were obtained.(7) Three-point-bending fracture toughness tests of weld zone and that of heat affectedzone of Q460C constructional high-strength steel at distinct low temperature were determined.And the values of CTOD for weld zone and heat affected zone of Q460C steel were obtained.Then making use of a regression analysis with Boltzmann equation, the ductile-brittle transitiontemperature and variation with temperature are acquired. Furthermore analyze the scanningelectronic microscope of the TPB specimen fracture surfaces with five temperature points.(8) It was necessary to study on the elasto-plastic fracture performance of the standardthree point bend specimen of Q460C high strength construction steel, by ANSYS finite elementsoftware. The crack sensitivity of Q460C steel at room temperature was proved. The analysiswas made on displacements of notch, three-dimensional stresses as well as crack tip openingdisplacement by solid95elements.