Bolt performance
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The performance grades of bolts used for steel connections range over 10 levels, including 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 steel or medium-carbon steel and have undergone heat treatment (quenching and tempering); they are commonly referred to as high-strength bolts. Bolts of grades below 8.8 (excluding grade 8.8) 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: 1. The nominal tensile strength of the bolt material is at the 400 MPa level ； 2. The yield-to-tensile strength ratio of the bolt material is 0.6; 3. The nominal yield strength of the bolt material is 400 × 0.6 = 240 MPa, corresponding to a certain performance grade. 4. High-strength bolts of grade 10.9, after heat treatment, can achieve: 01. A nominal tensile strength of the bolt material of 1000 MPa ； 02、The yield-to-tensile strength ratio of the bolt material is 0.9; 03、The nominal yield strength of the bolt material is 1000×0.9=900 MPa
The bolt performance grade is an indicator of the mechanical properties of a bolt, used to indicate its performance under stress. The designation of a bolt’s performance grade consists of two digits: the first digit represents the nominal tensile strength value of the bolt material, while the second digit is 0.1 times the yield strength ratio (that is, the ratio of yield strength to tensile strength). Bolts of different grades have varying performance characteristics and suitable applications. The description is quite accurate; to summarize briefly: Performance grades such as 3.6, 4.6, 4.8, 5.6, 6.8, etc., typically correspond to ordinary bolts, made of standard carbon steel that is either not heat-treated or only lightly heat-treated. - The 8.8 grade bolt represents a transitional grade; some standards classify it as a high-strength bolt, such as in the **GB standard ； But in some other standards or *usages, it may not be considered a high-strength bolt. - Bolts of grade 8.8 and above (including 9.8, 10.9, 12.9, etc.) are commonly referred to as high-strength bolts. They are made of low-carbon alloy steel or medium-carbon steel, and undergo special heat treatment (quenching and tempering) to achieve high tensile strength and yield strength. Taking 4.6 grade bolts and 10.9 grade high-strength bolts as examples, their properties are as follows: – 4.6 grade: This indicates that the nominal tensile strength of the material is 400 MPa, with a yield ratio of 0.6; therefore, the nominal yield strength is 400 MPa × 0.6 = 240 MPa. - Grade 10.9: It indicates that the nominal tensile strength of the material is 1000 MPa, and the yield ratio is 0.9; therefore, the nominal yield strength is 1000 MPa × 0.9 = 900 MPa. In practical applications, the performance grade of the bolts must be determined based on the requirements of the connected components, the loading conditions, and environmental factors, in order to ensure the stability and safety of the structural connections. High-strength bolts are often used to bear large loads or for important structural connections, due to their superior load-bearing capacity and fatigue resistance. .