Research On 500MPa Class High Performance Steel (Q500qE) Using In Railway Steel Bridges

High-performance steel is the higher cost-effective bridges steel with integrated optimization of the mechanical properties, easy processing, suitable for low temperature and corrosive environment. It not only maintained higher yield strength, but also increased and improved significantly in weathering resistance, weldability and resistance performance to brittle fracture than traditional bridges steel. High-performance steel represents the development trend of bridge steel in a considerable extent.The mechanical properties of a new 500MPa grade high-performance steel (Q500qE) made by China was researched systemic and tested comprehensive in this paper. It is try to solve the technical problems of high-performance steel using in large-span railway steel bridges.With the testing and research of Q500qE high-performance steel of the material and plate specimens tensile and low-cycles fatigue, low temperature impact ,fatigue crack growth, fracture toughness (CTOD), the typical construction details of railway steel bridge fatigue, wide plate tension and full-scale model beam static tests and Finite Element Analysis, etc., the main research results are as following:①Yield ratio has few relationship with the plasticity, fatigue crack growth rate, low-cycles performance and fracture toughness (CTOD). The percentage elongation of Q500qE base metal is more than 20% although the yield ratio of material is different. Q500qE has good plasticity, better ability to crack and the redistribution of stress concentration ability. Also, the brittle transition temperature of Q500qE base metal reduced greatly than the Q370qE and Q345qD bridge steel, with good low temperature impact toughness. The brittle transition temperature of Q500qE weld metal is equal to Q370qE bridge steel.②With decreasing temperature, the fracture toughness (CTOD) of 44mm thickness Q500qE base metal changed little, but the fracture toughness (CTOD) of 60mm thickness Q500qE base metal decreased obviously when temperatures down to -40℃. The fracture toughness (CTOD) of various thickness of Q500qE weld is lower than the base metal.③Combined with BS7910: 2005, the fracture toughness (CTOD) value of bridge steel and welded joints is evaluated in this paper. The evaluation method provides a basis for evaluation the fracture toughness of bridge steel and welded joints use the fracture toughness (CTOD).④The fatigue test of five typical structural details of railway steel bridge was carried out. The results indicated that Q500qE high-performance steel has slightly higher fatigue strength in the typical structural details than Q370qE bridge steel which is now used railway steel bridge widely. The fatigue properties of Q500qE high-performance steel meet the requirements of railway bridges.⑤As the strength increased and the grain refinement, the fracture toughness Kc of Q500qE high-performance steel base metal is generally better than Q370qE and Q345qD bridge steel, and is higher than Q500qE high-performance steel welded joints. At low temperatures, the fracture toughness Kc of Q500qE welded joints decreased significantly, but in general, the anti-fracture properties of Q500qE welded joints is equal to Q370qE welded joints roughly.⑥Although with high yield ratio, but in practice Q500qE can form a plastic hinge as the same component of Q345qD. And Q500qE is better than Q345qD in recovery capacity of displacement with the characteristics of components in the same section. The security test on the model beam and the material showed that: Q500qE high-performance steel meet the normal requirements of railway bridge in the strength of security reserves and deformation reserves in accordance with design by yield strength of 500MPa.In conclusion, Q500qE high-performance steel with the yield ratio of 0.86 satisfy the basic requirements of railway steel bridges in the anti-fracture, fatigue and safety, and can be used in the construction of railway steel bridges.There are innovations in this paper:①For the first time, the yield ratio and plastic of high performance steel was researched and tested comprehensive use of materials, full-size thickness plates and the full-scale model beams. It is solved of safety problems of Q500qE high-performance steel using in railway steel bridges.②For fracture toughness (CTOD) values assessment, the paper suggests that taking the single edge fatigue precrack of CTOD specimen as a flaw, combined with the failure assessment curve of FAD and the 2B-level evaluation method in BS 7910:2005 " Guide on Methods for Assessing the Acceptability of Flaws in Metallic Structures ", the CTOD value of the bridge steel can be evaluated. The evaluation method provides a basis for evaluation the fracture toughness of bridge steel and welded joints use the fracture toughness (CTOD).③In the wide plate tensile test, the low-temperature environment box is researched and development firstly which combination of the EVA board, automatic temperature control system, automatic liquid nitrogen irrigation system and temperature measure sensor of the sample surface. It is more accurate of test temperature control and higher degree of automation compared to the existing similar low-temperature environment test equipment of wide plate tensile.