The identification method of high strength national standard bolt mainly depends on five aspects:
Look at the mark. Generally, the packing box of bolts has identification. It can be divided into 8.8, 10.9 and 12.9 grades. In general, there is no grade mark on the hexagonal plane of hexagon bolt, which is a common grade, while high strength bolt generally has strength indication. For example: 8.8; but notice that there are too many fake and shoddy goods nowadays, we should also pay attention to the channel of purchasing goods and check and accept the goods.
Generally speaking, the grade of hexagon socket bolts is relatively high. The reason is that the hexagon hole of hexagon socket bolts can only be used after heat treatment. The materials that can improve the hardness after treatment are quenched and tempered steel, which has high mechanical strength after quenching and tempering;
High strength bolts without galvanizing are generally black. The black outer layer is an oxide layer formed by artificial processing, which is called blackening in industry. A strong alkali resistant layer can be formed on the surface of the metal to resist corrosion. There is also a process called hair blue, the role and principle of the same. Therefore, high strength bolts will not rust in general!
The simplest empirical judgment: throw it to the ground, listen to the sound, and the high-strength sound is brittle. If the sound is bright, it is strip steel. In the scratch test with saw blade and other hard tools, the surface hardness of high-strength bolts is larger than that of ordinary bolts.
The problem of quenching and tempering is that the general high-strength material is grade 8.8. Some merchants may not temper the high-strength materials when they are sold to customers at grade 12.9 or 10.9. The way to distinguish them is to see that in the sun, the hair that is not quenched and tempered is dark, and the one that has been tempered is colored. This is the most basic knowledge.
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