Fatigue Fracture of Steel Wheels for a Coke-Oven Car

A double-flange trailer wheel, in service on a coke-oven pusher car for about five years, broke. Specifications called for rolled steel track wheels conforming to ASTM A 186 (since reclassified as A 504). Chemical analysis showed the metal in the wheel to be medium-carbon steel within the ranges given in ASTM A 186. Visual examination of the broken wheel revealed that cracks ran parallel with the base of the lower row of numbers stamped with heavy indentation on the web section. Microscopic examination showed the metal in the web, rim, and tread to be in the normalized condition. Evidence found supports the conclusions that fatigue failure of the wheel was the result of heavy stamp marks that acted as stress raisers in the weaker web section. Because this was a double-flange wheel, considerable side thrust was applied to the wheel, causing stress concentration at the web. Recommendations included following the ASTM specification A 504 regarding location of stamped identification numbers (marks identifying the wheels must be stamped on the back face of the rim not less than 3.2 mm from the inner edge of the rim).