Nuts 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., and the nuts of grade 8.8 and above are low carbon alloy steel or medium carbon steel and heat treated (Quenching, tempering), commonly known as high-strength nuts, the rest are generally known as ordinary nuts. The nut performance level label is composed of two parts of numbers, which respectively represent the nominal tensile strength value and yield strength value of the nut material
For example, a nut with a performance rating of 4.6 has the following meanings:
1. The nominal tensile strength of the nut material reaches 400MPa;
2. The yield ratio of the nut material is 0.6;
3. The nominal yield strength of the nut material reaches 400 × 0.6 = 240MPa.
Performance grade 10.9 high-strength nut, after heat treatment, the material can achieve:
1. The nominal tensile strength of the nut material reaches 1000MPa;
2. The yield ratio of the nut material is 0.9;
3. The nominal yield strength of the nut material is 1000 × 0.9 = 900MPa. The meaning of the performance level of the nut is an international standard. Nuts of the same performance level have the same performance regardless of the difference in material and place of origin, and are only selected for design. Performance level is sufficient.
The so-called strength grades of 8.8 and 10.9 refer to the nut's shear stress levels of 8.8GPa and 10.9Gpa. 8.8 Nominal tensile strength 800N / MM2 Nominal yield strength 640N / MM2 The general nut uses "XY" to indicate strength, X * 100 = tensile strength of this nut, X * 100 * (Y / 10) = yield strength of this nut (due to the sign: yield strength / tensile strength = Y / 10)
If grade 4.8, the tensile strength of this nut is: 400MPa, the yield strength is: 400 * 8/10 = 320MPa
In addition: stainless steel nuts are usually marked as A4-70, A2-70, the grade of stainless steel nuts is divided into 45, 50, 60, 70, 80, the material is mainly divided into austenite A1, A2, A4, martensite and iron Element body C1, C2, C4, its representation method such as A2-70, before and after "-" respectively indicate the nut material and strength level: "A2-70" is the performance mark of stainless steel nuts, screws, studs and nuts, "- "A2" before "" indicates the material group, namely the second group A2 of austenitic steel, the number part "70" after "-" indicates the performance level of the product, the number is 1/10 of the nominal tensile strength , That is, the performance tensile strength of this product is 700 N / mm2.