Must the A325 bolt be a hexagonal head bolt? Throughout the entire ASTM A325-2009, in addition to the "Type3 heavy hex structural bolts" mentioned in Table 2, there is no indication that the hexagonal bolts must be described elsewhere. But when determining "Type 3 heavy hex structural bolts", you have to figure out what "Type 3" means? In the original ASTM A325-2009, Type 1 Bolts refers to carbon steel, boron-containing carbon steel, alloy steel, boron-containing alloy steel bolts; Type 2 was cancelled in 2002, no analysis here; then the focus is Type 3 Bolts refers to the bolts of weathering steel (weathering steel refers to a certain degree of corrosion resistance in the atmosphere, and its corrosion resistance is much lower than that of stainless steel). Instead of Table 2, it can be understood as a weathering steel material used to make heavy-duty hex head bolts. Table 1 - Carbon steel, boron-containing carbon steel, alloy steel, boron-containing alloy steel chemical elements, Table 2 - Heavy-duty high-strength hex head bolt weathering steel material
We note that the word Bolts is mentioned in various expressions, meaning bolts. Since the A325 is a standard in ASTM, let's talk about the bolts in the US. In the United States, the definition of bolts has been debated for many years. The final conclusion is: 1. The externally threaded fastener is not allowed to be implanted due to its head or other shape design, and can only be locked or disassembled by means of a nut, such as a round neck bolt, With bolts, etc.); 2. Externally threaded fasteners must be mated with nuts to achieve their intended function, such as bolts (such as steel bolts). Therefore, in the North American market, a 'bolt' is understood to be an externally threaded fastener that must be used with a nut and tightened on one side of the nut. So is the Bolts expressed by A325 necessarily a hexagonal bolt? Everyone needs to think about it.
Once the material is determined, it is necessary to obtain suitable mechanical properties through various treatments. Table 3 first specifies the hardness, as shown in the following table:
This table specifies the HBW hardness and HRC hardness. By comparing GB/T 3098.1-2010 as follows: Table4
We found that the hardness values ​​specified in A325 are similar to those specified in GB/T 3098.1-2010 Class 8.8 bolts. Finally, we use the A325 against the provisions of pull, yield, elongation, and contraction (see Table 5), and GB/T 3098.1-2010 (Table 4 and Table 6):
Tensile strength and yield strength are exactly the same, the elongation of 8.8 bolts is slightly smaller, and the shrinkage rate of 8.8 is much larger than A325.
in conclusion:
From the above comparison, the A325 is mechanically similar to the 8.8 grade bolts that are commonly referred to.As we walked through the park, we saw the picture below (photographed at the base of the streetlight in Kaohsiung Central Park)
It is not difficult to understand why it is used here.
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