Application and requirement of high strength bolt

According to the performance grade of high strength bolt, it can be divided into 8.8 grade and 10.9 grade, and the torsion shear type is only used in grade 10.9. In the marking method, the number before the decimal point represents the tensile strength after heat treatment, and the number after the decimal point represents the yield ratio, that is, the ratio between the measured yield strength and the measured ultimate tensile strength. Grade 8.8 indicates that the tensile strength of the bolt rod is not less than 800MPa and the yield ratio is 0.8; grade 10.9 indicates that the tensile strength of the bolt rod is not less than 1000MPa and the yield ratio is 0.9. In structural design, the diameter of high-strength bolts is generally M16 / M20 / M22 / M24 / M27 / M30, but M22 / M27 is the second choice series, and under normal circumstances, M16 / M20 / M24 / M30 is the main choice.
When assembling high strength bolt connection pair, the side of nut with round table should face the side with chamfer of washer. The chamfered side of the washer under the bolt head should face the bolt head when assembling the large hexagon head high strength bolt connection pair. The large hexagon high strength bolt is pressure bearing type.

Grade strength
The performance grade of bolts for steel structure connection can be divided into 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. Among them, bolts of grade 8.8 and above are made of low-carbon alloy steel or medium carbon steel and heat treated (quenching and tempering), which are generally called high-strength bolts, and the rest are commonly referred to as ordinary bolts. The bolt performance grade label consists of two parts, which respectively represent the nominal tensile strength and yield strength ratio of bolt material. For example, the bolt of performance grade 4.6 means:
1. The nominal tensile strength of bolt material is 400MPa;
2. The yield strength ratio of bolt material is 0.6, and the nominal yield strength of bolt material is 400 × 0.6 = 240mpa.
After heat treatment, the material can reach 10
1. The nominal tensile strength of bolt material reaches 1000MPa;
2. The yield strength ratio of bolt material is 0.9, and the nominal yield strength of bolt material is 1000 × 0.9 = 900MPa.
The meaning of bolt performance grade is an international standard. The performance of bolts with the same performance level is the same regardless of the difference of material and origin, so only performance grade can be selected in design.
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