Dear Readers,
In construction engineering, bolts are frequently used. The grades of bolts typically range from 4.6 to 12.9. These are also referred to as Ordinary bolts (Commercial Grade), HT bolts (High Tension), and HSFG bolts (High Strength Friction Grip).
The bolt designation system consists of two numbers. The first number indicates the bolt's ultimate tensile strength, which can be 400 MPa, 800 MPa, or 1200 MPa. The second number signifies the point at which the bolt will permanently stretch. Specifically, a grade 4.6 bolt will permanently stretch at 60% of its ultimate tensile strength, a grade 8.8 bolt at 80%, and a grade 12.9 bolt at 90%.
Technically, it can be quoted that the first number is the tensile strength of the bolt material (N2 )/100. The second number is = 1/100. (the ratio of the Proof (or Yield ) stress and the Tensile strength expressed as a percentage = 100.[Yield (Proof stress) /Tensile strength] /100
For example, the tensile and proof strength of the steel for an 8.8 bolt is therefore calculated as follows
Tensile strength = 8 X 100 N/mm2 = 800 N/mm2 and Proof strength = 0.8*800 * 100 /100 = 640 N/mm2 (generally speaking 80% of 800N/mm2)
The lowest grade is 4.6, commonly known as commercial grade. Next comes grade 8.8, known as structural grade, and finally, the highest grade is 12.9, known as HT / HSFG bolt.
Available grades of bolts are 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9 & 12.9
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