The performance grades of bolts for steel structure connection are divided into more than 10 grades such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, among which bolts of grade 8.8 and above are made of low-carbon alloy steel or medium-carbon steel and are heat-treated (Quenching, tempering), commonly known as high-strength bolts, and the rest are commonly known as ordinary bolts. The large hex head bolt performance grade label consists of two numbers, which respectively represent the nominal tensile strength value and the yield ratio of the bolt material.
For example, the big hex head bolt performance grade 4.6 bolt, its meaning is:
1. The nominal tensile strength of the large hex head bolt material reaches 400MPa.
2. The yield ratio of the large hex head bolt material is 0.6.
3. The nominal yield strength of the large hex head bolt material can reach 400×0.6=240MPa performance grade 10.9 high-strength bolts.
After heat treatment of large hex head bolt material, it can reach:
1. The nominal tensile strength of the large hex head bolt material reaches 1000MPa.
2. The yield ratio of the large hex head bolt material is 0.9.
3. The nominal yield strength of the large hex head bolt material is 1000×0.9=900MPa. The meaning of the bolt performance grade is the international standard. The bolts of the same performance grade have the same performance regardless of the difference between the material and the place of production. The design Only select the performance level above.