Using WAAM to Locally Enhance Fatigue and Corrosion Resistance of Cast Steel Parts

Every year, thousands of cast-steel railcar couplers suffer from corrosion-initiated fatigue cracking in high-stress areas of the coupler knuckle. Between 2015 and 2018, 90,000 knuckles were replaced that may have been at risk of failure from unpredictable corrosion-fatigue. This coupler geometry has been in use as early as 1916, hence a countermeasure for fatigue cracking that does not involve altering the geometry or casting process is desired. Wire arc additive manufacturing (WAAM) is an emerging technology which enables production of complex near-net-shape components; however, less attention has been paid to WAAM’s potential for local enhancements in typical failure zones. By replacing the cast steel in the high-stress region of the knuckle with fatigue and corrosion resistant WAAM deposits, the whole knuckle will have a longer service life while maintaining its mechanical properties and overall geometry. The efficacy of this procedure relies on the ability to produce WAAM deposits with fewer defects than the base steel while introducing alloying elements (nickel, chromium, molybdenum) to strengthen and prevent corrosion. This WAAM procedure is accomplished utilizing gas tungsten arc welding (GTAW) with commercially available low-alloy filler wire prior to the knuckle’s heat treat schedule. The components performance will be validated by fatigue and corrosion testing. Selective use of WAAM technology to aid in the high-volume production of parts through local enhancements could be a step to efficiently utilize its capabilities in industry.