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Automotive bolts
2025-12-12
The strength level and type of steel used for automotive bolts. The standard bolts used by various automobile manufacturers are 8.8 grade bolts, mostly made of boron steel. The reason for the lower price of boron steel bolts is that the content of boron is very low, which can make the carbon equivalent of the steel very low, thus eliminating the need for the prior spheroidizing annealing before processing.
The 10.9 grade bolts are made of alloy steel and boron steel. The difference from the 8.8 grade boron steel bolts is that the content of harmful elements such as P and S, which cause delayed fracture, has been reduced, and a phosphorus-free lubricating coating is used during drawing.
The 12.9-grade automotive bolts are made of alloy steel, while the 14.9-grade automotive bolts are made of special alloy steel. The steel contains low impurity content and also contains elements such as V that cause the formation of carbides, which trap hydrogen in the steel and enhance its resistance to delayed fracture.
The highest strength level bolts used in mass production of automobiles are 16T. Their material is hypereutectoid steel processed by drawing, and vanadium carbide in the steel traps hydrogen, making it harmless. The tightening capacity of the bolts is further enhanced, so they can also be used to manufacture 16.9-grade ultra-high strength bolts.
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