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 bolt performance grade label consists of two numbers, which respectively indicate the nominal tensile strength value and the yield ratio of the bolt material.
For example, a bolt with a large hex bolt performance grade of 4.6, its meaning is:
1. The nominal tensile strength of the large hex bolt material reaches 400MPa; 2. The yield ratio of the large hex bolt material is 0.6; 3. The nominal yield strength of the large hex bolt material reaches 400×0.6=240MPa, performance level 10.9, high strength bolt.
After heat treatment, the large hex bolt material can reach: 1. The nominal tensile strength of the large hex bolt material is 1000MPa; 2. The yield strength ratio of the large hex bolt material is 0.9; 3. The nominal yield strength of the large hex bolt material is 1000 The meaning of the performance level of ×0.9=900MPa grade bolts is an international standard. For bolts of the same performance level, regardless of the difference in material and origin, the performance is the same. Only the performance level can be selected in the design.