Quality Classification Rating Of Welded Defects And Its Effect To The Property Of Welded Joint

The bogie is an important part of high speed train,which affects the train operation and the traffic safety.Bogie frame is always welded structure,which is complex with dense welded joints.The welding defects make welded joint the weak link of the whole bogie frame.SMA490BW steel is a kind of high strength weathering steel which has good strength,toughness and excellent atmospheric corrosion resistance,so it is the preferred material for high-speed train bogie.In recent decades,evaluation standard of the welded joint defects based on fracture mechanic has developed and widely applied to engineering practice.The bogie of high speed train is carefully studied and the work is as follows:According to GB/T228-2002 standard,tension testing of SMA490BW steel at room temperature was carried out.According to GB/T21143-2007 standard,the fracture toughness Kc of SMA490BW steel was test by the crack tip opening displacement?CTOD?using three-point bend specimens.Stress simulation of each part of the bogie frame was test by the software ANSYS.The welding defects of the welded joints were measured and analyzed.According to BS7910-2005,quality classification rating and residual fatigue life estimation of the bogie gearbox hanging seat welding defects in welding joint were carried out.The results showed that SMA490BW steel has good toughness with the fracture toughness Kc is 2120.75MPa·mm^1/2.The fracture surface of the three-point bending specimen is a pure plane strain brittle fracture with the smooth fracture surface,and the brittle fracture zone is symmetrical micro-granular.The welding defects of the lack of penetration,porosity and incomplete fusion were found in welded joints;In order to guarantee the welding defects could not extend to the critical size after 2×10⁶ cycle,the positive and facade welded joints of gearbox hung must reach the level Q3.Fatigue experiment results showed that there was no crack in the gearbox hanging seat when the welded joints reached level Q3 after 10⁷ cycles by using magnetic particle inspection.Weld anatomy was carried out after,and the initiation of fatigue crack on the heat affected zone of reverse side and facade weld,while the positive weld is intact.The welding joints of the gearbox hanging seat were sampling dissected after fatigue test.The micro fatigue cracks were found in the opposite and fa?ade welded joints,while there was no defect in the positive welded joints.