From the perspective of the development of the entire manufacturing industry, fasteners are called "the rice of industry". Fasteners usually only occupy a small part of the entire product structure, but as an organic part of the product, they play an important role. From the perspective of the application of standard fasteners in the world, the industries mainly include electronics industry, maintenance and construction industry, and automobile industry are the three major users of fasteners. For example, there are many types of automotive fasteners, which are mainly divided into four categories, including standard fasteners, non-standard fasteners, standard mechanical components and non-standard mechanical components; among them, non-standard fasteners have high quality requirements. Among the non-standard fasteners, engine connecting rod bolts, flywheel bolts, wheel bolts, suspension bolts, etc., due to their high quality and good stability, our country has not yet met the localization requirements, and a small part relies on imports.
Due to the lack of attention paid to fasteners in the automotive industry, the development of automotive fasteners lags far behind the development of the automotive industry. Fasteners account for a small proportion of finished automobiles, but the damage to the whole vehicle is very large. The reasons for the fracture of fasteners can be analyzed from the following three aspects. The strength of the materials used for fasteners is not enough. Fracture occurs under the action of external load; because the material used in the fastener is unreasonable during the heat treatment process, there are defects such as surface cracks; due to the fatigue fracture of the fastener under the action of external long-term load.
In order to produce high-quality fastener standard products, in the process of selecting the steel used for fasteners, the chemical composition of the steel used must be strictly controlled, the content of harm