Bolts are common standard rooms commonly used in mechanical equipment. According to the latest national standards (equivalent to ISO international standards), the performance grades of general bolts include 9/4.8/5.6/5.8/6.8/8.8/9.8/10.9/12.9 and so on. The grade, that is to say the 3.6-class bolt has been eliminated according to the new standard.
What is the meaning of the performance level mark? The bolt performance level code is composed of two parts, and the two parts are separated by a dot.
One or two digits to the left of the dot indicate 1/100 of the nominal tensile strength in MPa.
The number to the right of the dot indicates 10 times the ratio of the nominal yield strength to the nominal tensile strength.
Note that the values mentioned here are all nominal values, not actual values.
Then the nominal value of the tensile strength of the 4.8 bolt is 400 MPa, but the minimum value should be 420 MPa, that is, in the test, the tensile strength of the bolt is not lower than 420 MPa, the nominal value of the yield strength is 320 MPa, but the minimum value is 340 MPa. If it is a simple estimate, it is ok to use the nominal value, but if it is a bolt performance test, it cannot be judged by the nominal value.
The following table shows the nominal and minimum requirements for the tensile strength and yield strength of common bolts of different performance grades. It can be seen that the nominal value of most cases is not equal to the minimum value.
In addition to the performance levels of the two digital identification bolts separated by dots, it is also possible to mark the performance level of the bolts in numbers and combinations of letters.
Stainless steel bolt marking
The stainless steel bolt marks are composed of two parts separated by short strokes. The first part indicates the type of stainless steel, and the second part indicates the performance level of the bolt. This part is generally composed of 2 or 3 digits, which represents 1/10 of the tensile strength. , expressed in MPa.
The letters in the first part,
A== austenitic steel
C is martensitic steel
F is ferritic steel
High strength bolts for steel structures
Sometimes we will see that the bolt is marked as 10.9S or 8.8S. What is the difference between the normal 10.9 and 8.8? In fact, the meanings of the previous numbers are the same. The steel structure with "S" indicates the high-strength hexagon. Bolts, bolt sizes of the same thread size will be larger than ordinary bolts.
Special bolt
In high-temperature or low-temperature applications, the two-part number separated by a dot is not used to indicate the performance level of the bolt. It needs to be expressed according to the group and grade of the material.
