Enterprise Name: CHENGDA MODEL SET
Contact person: Business Department
Mobile phone: 198-5734-5006
Address: 39 Success Road, Jiashan Economic Development Zone, Zhejiang Province
Websit : en.chengda-mould.com
According to the statistics of China Automobile Industry Association in January 2010, China's automobile production and sales in 2009 were 13.79.1 million vehicles and 13.6448 million vehicles, an increase of 48% and 46% respectively over the same period of last year. The rapid development of automobile industry has increased the demand for iron and steel materials. Although China has been the world's largest steel producer for many years, steel for automobile engine and key parts fasteners is mainly imported products due to strength limitation. At the same time, the development trend of high performance and lightweight of automobile is also increasing. Die manufacturers have put forward higher design stress and lightweight of automobile fasteners. High strength steel for fasteners is an effective way to solve this requirement.
1. Performance requirements of steel for automotive fasteners
Steel requirements for automotive fasteners:
It has good surface quality, high dimensional accuracy and low grade non-metallic inclusions and segregation.
It has high tensile strength and good cold heading performance.
It has high fatigue resistance and multiple impact tensile resistance.
It has sufficiently low delayed fracture sensitivity and low ductile-brittle transition temperature.
2. Smelting and rolling characteristics of steel for automobile fasteners
2.1. Smelting Technology
The continuous casting process with out-of-furnace refining and electromagnetic mixing is adopted. It is mainly to control the main elements such as C, Si, Mn, Cr, Mo in the steel in a small range, and to reduce the impurity content of P, S, 0 and N in the steel as far as possible, so as to achieve the goal of high purity of steel, low non-metallic inclusions and low segregation grade, so as to improve the cold heading performance of steel and improve the surface quality of steel.
2.2. Rolling Technology
High-speed and high-precision rolling process with functions of controlling emulsification and cooling was adopted to obtain hot-rolled wire with good dimensional accuracy and as few surface defects as possible.
3. Present Situation and Development Direction of Steel for Automotive Fasteners
3.1. Clean bolt steel
In order to improve the cold heading and quality of steel, it is necessary to reduce the content of impurity elements in steel as much as possible. Reducing S content can improve the deformation ability of steel, reduce non-metallic inclusions in steel and improve toughness and plasticity; Reducing P content can reduce the deformation resistance of steel, and at the same time reduce P and S content can also reduce its segregation at grain boundary, reduce grain boundary embrittlement, and improve the delayed fracture resistance of steel; Reducing 0 content in steel can effectively reduce oxide inclusions and improve cold working deformation of steel. Ability.
The stress corrosion threshold stress intensity factor (KISCC) of ML42CrMo steel with high cleanliness was studied by the General Institute of Iron and Steel Research. The KISCC of the cleanliness steel is much higher than that of the commercial steel. Therefore, in order to ensure that the steel still has high comprehensive properties after high strength, the content of P and S of the high strength bolt steel should be further reduced.
3.2. Economical High Strength Bolt Steel
3.2.1. Microalloyed Non-quenched and Tempered Steel
Using microalloyed non-quenched and tempered steel to make bolts can omit spheroidizing annealing before cold drawing and quenching and tempering after bolt forming. It can also reduce decarburization tendency of threaded threads and improve the yield of bolts. The economic benefit is obvious.