1. Grade: The strength grades of metric bolts mainly include: 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9, 12.9, a total of 10 performance grades.
The distinction and meaning of high-strength bolts: bolts of grade 8.8 and above are collectively called high-strength bolts, and other grades of bolts are called ordinary-strength bolts.
2. The meaning of the bolt performance grade label: The bolt performance grade label consists of two numbers, which represent the nominal tensile strength and yield ratio of the bolt. For example, a high-strength bolt with a performance grade of 4.8 means:
1: The nominal tensile strength of the bolt material is 400MPa
2: The yield ratio of the bolt material is 0.8
3: The nominal yield strength of the bolt material is 400x0.8 = 320MPa
3. The mechanical performance level of bolts mainly has the following four indicators:
a. Strength index (tensile strength, yield point, yield strength, guaranteed stress);
b. Hardness index (Vickers hardness, Brinell hardness, Rockwell hardness, surface hardness);
C. Plasticity and toughness indicators (elongation, wedge load strength, impact absorption, head firmness);
d. Decarburization layer index (minimum height of undecarburized layer of thread, maximum depth of fully decarburized layer).