Fatigue Testing of Microalloyed AAR Class C Wheel Steel

Abstract

Railroad wheels guide a freight car along the rails while supporting mechanical loads, and also serve as the brake drum in the air brake system of a freight car. Since a 36-inch diameter freight car wheel experiences approximately 560 revolutions per mile, and since many North American freight cars accrue 100,000 miles per year in service, fatigue properties of steel are very important. Further, elevated tread temperatures resulting from tread braking are known to significantly reduce the yield strength of the wheel steel at the tread surface. This paper describes fatigue testing of AAR rim quenched Class C wheel steel manufactured with microalloy additions. Small amounts of selected alloy elements were purposely added to develop a wheel steel with improved high temperature yield strength. Rotating bending fatigue tests, conducted at a well-known professional testing laboratory, were performed at ambient and elevated temperatures using complete stress reversal (R = -1) cycling. Stress-life (S-N) curves were constructed and the microalloy steel results were compared to existing fatigue data, and to results for typical Class C steel with no microalloy additions. Past research work is briefly reviewed. Test results are discussed with emphasis on the implications for service performance of wheel steel.