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Structural fillet weld cracks - FCAW process, High Carbon Equivalent (CEq)

By Materials & Welding




  • presence of crack at weld root towards the beam side / section. This crack was observed along the weld toe area (beam side) as seen from the outer surface

  • CE for beam material was found to be higher than maximum permissible value as per ASTM A992
  • The beam side HAZ crack was observed to be initiated from weld root side. Crack was not observed to propagate in the parent metal instead it remained inside the HAZ area.
  • HV10 hardness at the HAZ area (beam side) was observed to be more (334-436) in both the examined cross sectional samples. Higher beam side hardness could be due to presence of needle shape widmanstatten ferrite and pockets of untempered martensite in the HAZ structure. High Carbon Equivalent (0.47) of beam section combined with insufficient pre-heat temperature during welding can increase the critical cooling rate and cause un-desirable high hardness microstructure in the HAZ area. Further if any diffusible hydrogen is present in the weld joint, it may increase the high hardness HAZ cracking propensity.
  • Further this high HAZ hardness (susceptible to cracking) combined with possible hydrogen level in the weld joint might have caused this HAZ crack starting from the weakest zone of incomplete weld root fusion in the fillet weld.
Recommendations:
Re qualify the welding procedure using high heat input, higher preheat (200 °C), and post heat at 200 °C for 2-4 hrs


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