Strength grade classification and classification of stainless steel bolts

TIME：

2021-11-12

Different grades of bolts have different hardness ranges. Generally speaking, the higher the grade of the bolt, the higher the hardness range. Speaking of hardness, let's first popularize the knowledge of hardness. Hardness is an indicator of bolt performance and can be measured with a hardness tester.

There are three commonly used methods to express hardness:

1. Vickers hardness (HV) - press the material surface with a load of less than 120kg and a diamond square cone indenter with a vertex angle of 136°, and divide the load value by the surface area of the material indentation pit to get the Vickers hardness value (HV).

2. Brinell Hardness - The measurement principle is to use a certain test force F (N) (the unit of force is usually kilogram force kgf, note: 1kgf=9.8N, kgf means one kilogram of force) to press a hardened steel ball or carbide ball with a diameter of D (mm) into the surface of the metal to be tested, keep it for a specified time, remove the test force, measure the average diameter of the indentation d (mm) with a reading microscope, and then calculate the Brinell hardness HB value according to the formula, or find the HB value from the prepared Brinell hardness table based on d.

3. Rockwell Hardness - The hardness value is determined by the plastic deformation depth of the indentation, with 0.002 mm as a hardness unit. Using different indenters and different test forces in the Rockwell hardness test will produce different combinations, corresponding to different Rockwell hardness scales (HRA, HRB, HRC).

The hardness range of bolts of different grades is as follows:

According to the above table, for example: the Vickers hardness range of 6.8-grade bolts is 190 - 250 HV

The Rockwell hardness range of 8.8-grade M12 bolts is 22 -32 HRC

The Brinell hardness range of 12.9-grade bolts is 380 - 429 HBW

The above is the hardness range represented by different grades of bolts

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