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Microstructure and Fracture Splitting Properties of a Fracture Splitting Notch Produced in a Connecting Rod (C70S6) Using Pulsed Laser Grooving
S-Q. Kou, J-W. Wang and Y. Gao

A high carbon steel (C70S6) connecting rod used by the 71C truck has been notched with a Nd:YAG laser pulse and then tested with a fracture splitting experiment. First, the key factors that determine the quality of fracture splitting, including microstructure, micro-hardness and hardened layer depth that are in the vicinity of the fracture splitting notch were studied. Then, based on the analysis results on the properties of the fracture splitting notch, qualitative analysis was carried out on the fracture surfaces. The experimental results showed that with appropriate processing parameters, an ideal fracture splitting notch could be obtained with a small bell mouth, a cylindrical central part, small root radius, high sharpness and moderate depth at the entrance. Also, laser grooving was found to be superior to the other possible processing methods like broaching, etc. for producing the fracture splitting notch. The area in the vicinity of the fracture splitting notch was divided into three parts: the melting zone; the solid-state phase transition zone and the base metal. The texture in the heat affected zone (HAZ) was refined significantly, with brittle martensite being largely generated to ensure the occurrence of a brittle fracture. Microhardness was measured to be as high as 790 HV, which is higher than the base metal and manifested as an obvious hardening effect as the type of fracture was found to be a brittle fracture.

Keywords: Nd:YAG laser, high carbon steel, connecting rod (C70S6), fracture splitting notch, microstructure, brittle fracture

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