Effect of Tempering Temperature on Microstructure and Mechanical Properties of Bainitic Railway Wheel Steel with Thermal Damage Resistance by Alloy Design

Thermal damage is one of the principle modes of wagon railway wheels. A new bainitic railway wheel steel with high thermal damage resistance and good combination of strength, plasticity, and toughness was developed. Microstructure and mechanical properties of the new steels in a tempered condition at different temperatures were examined. Microstructures were observed using scanning electron microscope and transmission electron microscope. Mechanical properties were evaluated by tensile, hardness, and Charpy impact tests with a simultaneous comparison to pearlitic railway wheel steel. The characteristic of retain austenite and V(C,N) were measured through X-ray diffractometry and energy disperse spectroscopy. The results indicate that this new bainitic wheel steel presents a submicron-sized carbide-free bainite morphology and preferable integrated mechanical properties when tempered at 280-360 degrees C. Precipitation strengthening plays an important role for the high strength, since a two-time-strengthening mechanism of the yield strength led by precipitation has been found at 280-360 and 480-560 degrees C, respectively. Compared with a pearlitic railway wheel steel, bainitic wheel steel tempered at 320 degrees C has a 10% higher yield strength, five times higher impact toughness, and much better thermal damage resistance, which is a promising railway wheel material for higher speed or heavier axle-load service conditions.