The parking ratchet is an important safety component of the car. Cracking occurs in the grinding surface during quenching and grinding processes after carburizing; thus, the goal of this research is to clarify the key cracking cause of the parking ratchet. Optical microscopy (OM), scan electronic microscope (SEM), energy dispersive spectroscopy (EDS), X-ray stress analyzer, etc., were used to systematically test and analyze the cracking cause. The results show that the microstructure of the parking ratchet with cracks after carburizing and quenching is normal, the residual stress of the surface is normal, with no oxide and decarburized layer within the crack areas, without burning during grinding, while it was found that oxide inclusions existed on the area of the crack, which is different from the normal specimens. Hence, a conclusion can be drawn that the cracking cause on the surface of the parking ratchet results from the oxide inclusions in the raw material. This study provides a feasible direction for the failure analysis and control of the cracks on parking ratchets during the manufacturing process.
Keywords: carburizing and quenching; compressive stress; cracking; grinding; oxide inclusion; parking ratchet.