Tempered Bainite and Martensite Embrittlement in Microalloyed Steel for Forged Railroad Wheel to Heavy Haul Application

This research shows two new microalloyed steels with niobium (Nb) for railroad wheels (Nb1 and Nb2) applied on heavy haul transportation (load over 30 tons/axle). The have mixed microstructure composed of pearlite bainite (finished wheel rim section), another one martensite (black section removed machining) obtained by continuous cooling quenching heat treatment followed tempering. bainitic martensitic are sensitive to the temper embrittlement phenomenon; therefore, knowing temperature range these is mandatory in order avoid such an event tempering process. Charpy specimens were extracted from wheels, austenitized (860 ºC), quenched water four minutes, tempered at different temperatures obtain curve. Three materials compared: AAR (Association American Railroads) Class C steel pearlitic (not embrittlement), Nb1, Nb2 martensitic, bainitic, microstructures. (Nb), molybdenum (Mo), silicon (Si) addition. effect Si content (analyzed Scanning Electronic Microscope (SEM)), regarding phenomenon, was also studied. analyzed Transmission (TEM) improving its characterization.