According to the statistics of the China Association of Automobile Manufacturers in January 2010, the production and sales of Chinese cars in 2 years were 13.79 million and 13 respectively. 480,000 vehicles, an increase of 48% and 46% respectively. The rapid development of the automotive industry has increased the demand for steel materials. Although China has been the world's largest steel producer for many years, the steel for engine and key component fasteners is mainly based on imported products. The trend of high performance and light weight of automobiles puts higher demands on the design stress and light weight of automotive fasteners. The high strength of fastener steel is the most effective way to solve this requirement.

1. Performance requirements for steel for automotive fasteners Steel requirements for automotive fasteners: (l) Good surface quality, high dimensional accuracy and low grade non-metallic inclusions and segregation; (2) High Tensile strength and good coldness; (3) high fatigue resistance and multiple impact tensile resistance; (4) low enough delayed fracture sensitivity and low tough-brittle transition temperature.

2. Characteristics of smelting and rolling of steel for automotive fasteners 2.1 Smelting technology uses refining outside the furnace and continuous casting process with electromagnetic stirring. Mainly to control the main elemental components such as C, Si, Mn, Cr, MO in steel to a small range, and to reduce the content of impurities such as P, S, O, N in steel to achieve high purity of steel. The purpose of low non-metallic inclusions and low segregation level is to improve the cold pier properties of steel and improve the surface quality of steel. 2.2 Rolling technology adopts high-speed and high-precision rolling process with controlled rolling and controlled cooling functions to obtain rolled heat treated wire (non-tempered or no-anneal) and has good dimensional accuracy (no need for drawing. And as little surface defects as possible (no need to peel).

3. Current status and development direction of steel for automotive fasteners 3.1 Clean bolt steel In order to improve the cold piercing property of steel and improve steel, it is necessary to reduce the content of impurity elements in steel as much as possible. Reducing the S content can improve the deformability of the steel, reduce the non-metallic inclusions in the steel, and improve the ductile plasticity; lowering the P content can reduce the deformation resistance of the steel, while reducing the P, S content can also reduce the segregation at the grain boundary. It can reduce grain boundary embrittlement and improve the delayed fracture resistance of steel. Reducing the O content in steel can effectively reduce oxide inclusions and improve the cold working deformation ability of steel.