Analysis on grinding crack of φ135 mm 48MnV steel crankshaft
During the grinding and inspection stage,some surface-initiated turtle-back cracks were observed on the con-necting rod neck of ø135 mm 48MnV steel crankshaft after surface induction hardening and tempering.These surface cracks were analyzed by optical microscope,scanning electron microscopy equipped with an energy dispersive spectrometer,and microhardness tester.The results indicated that the observed cracks were grinding cracks.The cracks only existed on the surface layer of the hardened layer,with a depth of about 340-510 μm.The surface layer of the hardened layer had the lowest hardness.Then it firstly increased and then leveled off,and gradually decreased to the hardness of connecting rod journal substrate.The microstructure of the connecting rod journal from the hardened layer to the substrate was:quenched martensite+residual austenite → tempered martensite+tempered troostite → tempered martensite → ferrite+pearlite.
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