Property class of bolts
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, etc. Among them, the 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, the rest are commonly known as ordinary bolts.
The bolt performance grade label consists of two parts of numbers, which respectively represent the nominal tensile strength value and yield ratio of the bolt material.
For example, a bolt of property class 4.6 means:
- The nominal tensile strength of the bolt material reaches 400MPa;
- The yield-strength ratio of the bolt material is 0.6;
- The nominal yield strength of the bolt material reaches 400×0.6=240MPa
High-strength bolts with a performance class of 10.9, after heat treatment, can achieve:
- The nominal tensile strength of the bolt material reaches 1000MPa;
- The yield-strength ratio of the bolt material is 0.9;
- The nominal yield strength of the bolt material is 1000×0.9=900MPa
The meaning of bolt performance grade is an international standard. Bolts of the same performance grade, regardless of the difference in material and origin, have the same performance, and only the performance grade can be selected in the design. The strength classes are called 8.8 and 10.9 Refers to the shear stress level of the bolt is 8.8GPa and 10.9Gpa 8.8 Nominal tensile strength 800N/MM2 Nominal yield strength 640N/MM2 The general bolts use “X.Y” to indicate the strength, X100=tensile strength of this bolt, X100*(Y/10)=yield strength of this bolt (Because it is stipulated by the logo: yield strength/tensile strength=Y/10) =============== Such as level 4.8 Then the tensile strength of this bolt is: 400MPa, and the yield strength is: 400*8/10=320MPa