Technology Digests / Analysis of Electric Flash Butt Weld Vertical Failures

TD24-004

July 17, 2024
Authors
  • Kerry Jones
  • Ananyo Banerjee
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Key Findings

  • Three vertical weld fractures were caused by a longitudinal tensile stress overload. The fracture initiation sites were along the thinnest part of the rail web; an area that does not see severe bending or contact stresses.
  • Brittle carbon-rich phase was found mostly concentrated at the concave sides of all three fracture initiation sites.
  • All three fractured welds had untempered and brittle martensite stringers with manganese sulfide inclusions close to each fracture initiation location.
  • Excessive heat from welding, along with the presence of carbon content higher than eutectoid amounts (0.77–0.79) in the parent rails, may have caused the formation of the brittle carbon-rich phases.

Analysis of Electric Flash Butt Weld Vertical Failures

Three electric flash butt (EFB) welds failed on MxV Rail’s new High Speed Loop (HSL) during the early stages of train operations. All three welds failed due to vertical fractures that initiated near the neutral axis in the web. The welds failed after accumulating very little tonnage during several successive nights of temperatures below 15°F — the coldest temperatures experienced since the welds were made. One side of the fracture initiation point showed a convex protrusion, while the other side contained a concave indentation. A macro acid etch revealed both flow lines caused by the weld heat input and the subsequent solidification during the EFB process and alloy element segregation along the centerline of the web. Microscopic examinations revealed brittle carbon-rich cementite at the fracture initiation locations along with untempered brittle martensite along some of the flow lines and manganese sulfide (MnS) inclusions near the martensite. The martensite formed during…