1. The performance of steel for automotive fasteners

Steel for automotive fasteners:

Excellent surface quality, superior dimensional accuracy and advanced other non-metallic inclusions and segregation;

High tensile strength and excellent cold performance;

Has a high burnout resistance and multiple offensive tensile resistance;

It has a low enough delayed fracture sensitivity and a low tough-brittle transition temperature.

2. Smelting and rolling characteristics of steel for automotive fasteners

2.1, smelting technology

Adopting refining outside the furnace and continuous casting process with electromagnetic mixing. The first is to bundle the primary elements such as C, Si, Mn, Cr, Mo in the steel in a small range, and even if the content of impurities such as P, S, 0, N in the low steel reaches high purity, Non-metallic inclusions have low index and low segregation level, which improves the cold performance of steel and improves the surface quality of steel.

2.2, rolling technology

The high-speed and high-precision rolling process with the functions of tube bundle and tube bundle cold is adopted, and the rolled cold-treated wire is obtained, and it has excellent dimensional accuracy and even a small surface flaw.

3. Current status and development deviation of steel for automotive fasteners

3.1, clean bolt steel

In terms of improving the coldness of steel and improving steel, it is necessary to control the content of impurity elements even in low steel. Low S content can improve the deformation ability of steel, reduce non-metallic inclusions in steel, improve toughness and plasticity; low P content can reduce the deformation resistance of steel, while low P, S content can reduce its segregation at grain boundaries. It will intensify grain boundary embrittlement and improve the delayed fracture resistance of steel. The 0 content in low-sink steel can be used to reduce the inclusion of oxides, thus improving the cold processing deformation ability of steel.

The Research Institute of Iron and Steel Research on the stress corrosion cracking threshold of the ML42CrMo steel with high cleanliness, the KISCC suppression study, the KISCC of the cleanliness steel is much better than the commercial steel, so the steel is still guaranteed after the high strength With a high overall performance, the P and S content of high-strength bolt steel should be further lowered.