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In this article,the crack found on the beam of the heavy truck produced by a specific company is investigated.Fracture topography indicates the crack origins from the center of shearing plane and the failure mode should be attributed to low-circle fatigue crack.The tensile-compressive stress on the beam induced by acceleration and braking during driving is the main alternating stress source.The analysis of metallographic structure of crack origin region proves the correspondence between the M/A constituents of the segregation band and the micro-cracks on the shearing plane due to poor shearing quality.On the other hand,TiN inclusions accelerate the process of fatigue crack concurrently.Inspection and polishing on the shearing plane after plate slitting should be the effective method to eliminate the fatigue core.