Take the 10.9 level as an example: 10 represents the nominal tensile strength (1000MPa), and 9 represents the yield strength ratio (0.9). The rest can be deduced by analogy.
No other grades are currently seen, and grade 12.9 is relatively rare.
The materials used for grade 8.8 and 10.9 are 42CrMo, 42CrMoA, 35CrMo, 42CrNiMo, 40Cr steel.
The occasions used at all levels should be determined by calculation, mainly calculating their shear stress, frictional force, and compressive stress.
The performance level of bolts is divided into 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 10.9, 12.9 from small to large.
This marking method means taking 10.9 as an example
10 indicates 1/100 of the tensile strength of the bolt, which means that the tensile strength of this grade of bolt must reach 1000MPa, which may actually be higher than 1000MPa.
GB/T3098.1 stipulates that the minimum tensile strength of this grade of bolts must be greater than 1040MPa.
The indicated yield ratio after the decimal point is the bolt's (yield strength/tensile strength) = 0.9
That is, the yield strength=1000*0.9=900MPa, the yield strength of this grade of bolt must be higher than 900MPa to be qualified.
Usually we call the three grades of bolts 8.8, 10.9, and 12.9 as high-strength bolts.
It should be noted that GB/T3098.1 does not give specific values of yield strength for these three grades of bolts, because for high-strength bolts 0.8 and 0.9 are the minimum yield strength ratios specified by this grade. Because high-strength bolts are used for very important links, there is no spot on the market and must be ordered with the bolt manufacturer. Therefore, the specific yield ratio is generally produced by the buyer’s specific value.