What are the bolt grades and the corresponding materials?

The performance grades of bolts used 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 of grade 8.8 and above are made of low-carbon alloy or medium-carbon steel and have undergone heat treatment (quenching and tempering); they are commonly referred to as high-strength bolts, while the rest are known as ordinary bolts. The bolt performance grade designation consists of two digits, which represent the nominal tensile strength value of the bolt material and the yield strength ratio, respectively. For example, a bolt with a performance grade of 4.6 means that the nominal tensile strength of the bolt material is at the 400 MPa level ； The yield strength ratio of the bolt material is 0.6. The corresponding material can be identified based on the tensile strength and yield strength ratio.