The present paper investigates the microstructure and mechanical properties’ aspects of AISI 4140 steel front axle beams developed by roll and hot-die forging processes. Microstructure of the processed beams exhibited tempered martensite, and nonmartensitic products, such as retained austenite and ferrite at the case and core, respectively. Fatigue testing results indicate that roll forged beams have demonstrated 37% higher fatigue lives (Weibull B50 life) compared to hot-die forged beams, despite similar quasi-static tensile properties. The improved fatigue performance of the roll forged beams over hot-die forged beams is attributed to the fine, close texture and rationalized material flow in the beams processed by the roll forging process. Finite element analysis and experimental strain measurements of subject component indicate that the stress levels due to fatigue loads are well below the static yield strength and endurance limit of AISI 4140 steel; however, the notches present in the form of flash or partition lines of the forged beams have initiated the fatigue failures of the beams.

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