Connecting rod is one of the important components in the engine. Its quality directly affects the safe use and driving of the engine and even the whole vehicle. The quality of connecting rod is directly related to its mechanical properties and service life. Forging automobile connecting rod can produce plastic deformation of metal materials, improve the structure and obtain high mechanical properties. It has the advantages of easy processing, good surface quality, short production cycle and stable production process. It has been widely used in industrial production.

The production status of connecting rod at home and abroad has been introduced. The main defects of heat treatment of quenched and tempered steel connecting rod are:

1. After quenching and tempering, the surface hardness of connecting rod is higher or lower.
2. Deformation occurs after heat treatment, sometimes directly leading to scrapping of parts; Although some products can meet the requirements through correction, the operation is complex and may produce residual stress, resulting in the decline of product performance; More often, large machining allowance is reserved, which leads to the increase of raw materials and processing costs.
3. After heat treatment, overheating, oxidation and decarburization of connecting rod parts occur.
4. Quenching crack or even crack is the most important form of heat treatment defects. As a fatal heat treatment defect, quenching crack cannot be repaired. After quenching crack occurs, the parts are only scrapped.

By analyzing the defects of heat treatment of quenched and tempered steel connecting rod, the problems of heat treatment of the above quenched and tempered steel connecting rod forgings were solved. The defects of quenching and tempering treatment are difficult to avoid and control. Therefore, the connecting rod is made of non quenching and tempering steel, which saves the heat treatment process of quenching and tempering steel, avoids the defects of heat treatment, reduces the cost and avoids environmental pollution. In order to analyze the quality, microstructure and mechanical properties of forgings, the contents of connecting rod microstructure analysis and nondestructive testing of connecting rod defects are introduced, which provides technical data for the establishment of nondestructive testing laboratory.