There are more than 10 grades, such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc., of which the bolts of grade 8.8 or above are made of low carbon alloy steel or medium carbon steel and after heat treatment (quenching and tempering), generally referred to as high-strength bolts, and the rest are commonly referred to as ordinary bolts.Bolt performance grade label consists of two parts, which respectively represent the nominal tensile strength value and bending strength ratio of bolt material.Such as:
Performance class 4.6 bolts, meaning:
1. The nominal tensile strength of bolt material reaches 400MPa;
2. The bending strength ratio of bolt material is 0.6;
3. The nominal yield strength of bolt material reaches 400×0.6=240MPa class
Performance grade 10.9 high strength bolt, its material after heat treatment, can achieve:
1. The nominal tensile strength of bolt material reaches 1000MPa;
2. The bending strength ratio of bolt material is 0.9;
3. The nominal yield strength of bolt material reaches 1000×0.9=900MPa class
The meaning of bolt performance grade is the international general standard, the bolt of the same performance grade, regardless of the difference of its material and origin, its performance is the same, the design can only choose the performance grade.
The strength grades of 8.8 and 10.9 refer to the shear stress grades of the bolts of 8.8GPa and 10.9GPa.