The bolt performance is divided into 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9 and other more than 10 grades.
Among them, the bolts of 8.8 and above grade are made of low carbon alloy steel or medium carbon steel
and have been hardened and tempered, and are generally referred to as high-strength bolts,
while the rest are generally referred to as ordinary bolts.The bolt performance grade is composed of two parts,
which respectively represent the nominal tensile strength value and the flexural strength ratio of the bolt material.
The nominal yield strength of the bolt is up to 400×0.6=240MPa, and the nominal tensile strength of the bolt is up to 1000MPa after heat treatment.The bending strength ratio of bolt material is 0.9;
The nominal yield strength of the bolt is 1000×0.9=900MPa.