Reasons Analysis on Magnetic Powders Aggregation of Hook-head Flange of Coupler on Subway Train

Magnetic powders aggregation phenomenon was found at the hook-head flange of the coupler for subway train when magnetic powders inspection. Cross-section of magnetic powders aggregation area was analyzed by means of macro analysis, metallographic examination, SEM morphology analysis and energy spectrum analysis to find the magnetic powders aggregation reasons. The results show that welding character and lots of defects were found at the magnetic powder aggregation area. Welding defects such as holes and slag inclusions were found at the weld, and cast porosity defect was found at the heat-affected zone near the weld bond. These above defects would form leakage magnetic field, make the magnetic powders aggregate here, and produce magnetic powders aggregation phenomenon when magnetic powders inspection.