Bolt Performance Grade

Bolt performance grade is an internationally recognized grading standard for measuring the mechanical properties of bolts used in steel structural connections. It covers over ten grades, ranging from 3.6 to 12.9, with grade 8.8 and above being high-strength bolts. The grade designation consists of two digits: the nominal tensile strength (in MPa) and the yield strength ratio. For example, grade 4.6 corresponds to a tensile strength of 400 MPa and a yield strength ratio of 0.6, resulting in a yield strength of 240 MPa. High-strength bolts are made from low-carbon alloy steel or medium-carbon steel and undergo heat treatment (quenching and tempering). For example, grade 10.9 has a tensile strength of 1000 MPa and a yield strength of 900 MPa. Bolt performance grade designations consist of two digits, representing the nominal tensile strength and yield strength ratio of the bolt material. For example, a bolt with a performance grade of 4.6 means:

　　1. The bolt material has a nominal tensile strength of 400 MPa;

　　2. The bolt material has a yield strength ratio of 0.6;

　　3. The bolt material has a nominal yield strength of 400 × 0.6 = 240 MPa. A high-strength bolt with a performance grade of 10.9, after heat treatment, can achieve the following:

　　1. The bolt material has a nominal tensile strength of 1000 MPa;

　　2. The bolt material has a yield strength ratio of 0.9;

　　3. The bolt material has a nominal yield strength of 1000 × 0.9 = 900 MPa.