High - strength hexagon socket head cap screws are common mechanical fasteners. Here is a brief introduction:
- Definition and Grade: According to Chinese standards, they usually refer to hexagon socket head cap screws with a strength grade of 8.8 or above, including 10.9 - grade and 12.9 - grade ones. The performance grades of hexagon socket head cap screws for steel structure connections include more than 10 grades such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, and 12.9. Bolts with a grade of 8.8 and above are made of low - carbon alloy steel or medium - carbon steel and undergo heat treatment (quenching and tempering), which are generally called high - strength bolts.
- Appearance and Structure: The head is in the shape of an inner hexagon, which is convenient for tightening and loosening with a hexagonal wrench. It is usually cylindrical, and the inner hole depth is about half of the nominal thread diameter. The size range is wide, and the thread diameter can range from very small to 75 mm or more, and the length can be up to 3600 mm.
- Material and Manufacturing: They are usually made of high - strength alloy steel, such as 35VB, 20MnTiB, etc. After heat treatment processes such as quenching and tempering, their strength and toughness are improved to meet the requirements of high - strength applications.
- Application Fields: Widely used in industrial machine tools, tooling molds, construction machinery, mining machinery, and other industrial and engineering fields. They are also commonly used in key connection nodes of vehicles and steel structures, and play a key role in ensuring the firmness and stability of the connection.
- Standards: The Chinese standard is GB/T 70.1 - 2008, and the corresponding international standard is ISO 4762:2004. The American standard is ANSI/ASME B18.3.
- Surface Treatment: In order to improve corrosion resistance and other properties, surface treatments such as cadmium plating, zinc plating, tin plating, chemical blackening, phosphating, coating, and organic coating are often carried out.
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