The rapid development of China's auto industry has increased the demand for steel materials. Although China has been the world's largest steel producer for many years, the steel for automobile engines and key components is mainly imported products due to the strength limitation. At the same time, the development trend of high performance and light weight of automobiles puts higher demands on the design stress and light weight of automobile fasteners. The high strength of steel for fasteners is the most effective way to solve this requirement. Performance requirements for steel for automotive fasteners Characteristics of steel smelting and rolling for automotive fasteners Current Status and Development of Steel for Automotive Fasteners Economical high strength bolt steel Ordinary hot-rolled steels often need to be spheroidized to meet the requirements of cold-form forming. The purpose is to make the flakes in the microstructure of the steel spherical by spheroidizing annealing, thus obtaining low deformation resistance. And excellent plastic materials. In the case of annealed medium carbon steel or medium carbon alloy steel, the spherical cementite is directly precipitated from the supercooled austenite under certain conditions. Our LED Emergency Twin Spot Lights are a cost effective replacement for old fashioned halogen emergency twin spot fittings. Due to the low power consumption of the LED lamps, only one battery is required, reducing option during charging. The super bright adjustable heads make this twin spot ideal for commercial and industrial applications. with a self test feature every 90 days to ensure correct operation. The Led Emergency Lights design makes it quick and simple to install. Twin Spot Emergency Light,Emergency Twin Spot,Led Twin Spot Emergency Lights,Led Emergency Twin Spot Light Foshan Nai An Lighting Electric Co.,ltd , https://www.emballast.com
Depth analysis of steel for automotive fasteners!
Good surface quality, high dimensional accuracy and low grade non-metallic inclusions and segregation;
Has high tensile strength and good cold heading performance;
Has high fatigue resistance and multiple impact tensile resistance;
It has a sufficiently low delayed fracture sensitivity and a low tough-brittle transition temperature.
Smelting technology
It adopts refining outside the furnace and continuous casting process with electromagnetic mixing. 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, 0, 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 heading performance of steel and improve the surface quality of steel.
Rolling technology
The high-speed and high-precision rolling process with controlled milk and controlled cooling functions is used to obtain the rolled heat treated wire with good dimensional accuracy and as few surface defects as possible.
Clean bolt steel
In terms of improving the coldness of steel and improving 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 the grain boundary embrittlement and improve the delayed fracture resistance of steel. Reducing the 0 content in steel can effectively reduce oxide inclusions and improve the cold working deformation ability of steel.
1. Microalloyed non-tempered steel
The bolts are made of microalloyed non-tempered steel, which can omit the spheroidizing annealing before bolt cold drawing and the quenching and tempering after bolt forming. It can also reduce the decarburization tendency of thread thread and improve the yield of bolts. The economic benefits are very obvious. .
Microalloyed non-tempered steel is mainly used to process 8.8 high strength bolts. For higher strength grades, such as the 12.9 grade é«™ strength bolts, there are no examples of microalloyed non-tempered steels.
2, free of annealing medium carbon steel or medium carbon alloy steel
3. Boron steel
The basic principle of boron steel composition design is to reduce the carbon content and improve the cold deformation ability of steel; add a trace amount of boron with a mass fraction of 0.0005% ~ 0.003 5% to compensate for the loss of strength and hardenability due to carbon reduction. Further, alloying elements such as Cr, Mn, and TI may be added as needed to further improve hardenability. However, due to the low tempering softening resistance of boron steel, the tempering temperature is 60-80 lower than that of SCM435 and ML40Cr. Therefore, the 10.9 grade high-strength bolt made of boron steel has high sensitivity to delayed fracture.
4. High-strength steel resistant to delayed fracture
The development of high-strength bolt steel with delayed fracture resistance is one of the hotspots of research work at home and abroad in recent years.
Most of the é«™ strength bolts are made of tempered martensite. The appropriate isothermal treatment process can be used to obtain the lower bainite and the appropriate multi-phase structure of martensite and retained austenite. The high strength of the martensite structure is utilized. The bainite and austenite structure have good delayed fracture resistance to achieve good delayed fracture resistance at the strength of the crucible. Or obtaining a fine martensite structure having no grain boundary or less grain boundary carbide by a suitable heat treatment process, and also having good delayed fracture resistance.
The rapid development of China's auto industry has brought huge market opportunities for domestic automotive fastener steel, and the high strength of automotive fastener steel has become an inevitable trend in the market development. Chinese steel enterprises with conditions should accelerate their cars. The research and development and production of steel for fasteners, drawing on the advanced production technology at home and abroad and the achievements already made, improve the localization rate of steel for automotive fasteners.