What is a high strength bolt? What is the high strength bolt material?

For those who do not understand the purchase of high-strength bolts, or the sales staff, the company does not specialize in producing high-strength bolts. Therefore, they do not know much about what kind of screw material is used for high-strength bolts. It is not clear what high-strength bolt materials are all? The person who might sell the screw only knows that the high-strength bolts are stainless steel and iron, that is, carbon steel. But what are the details of the materials, they are not very clear. Faced with this problem, Shenzhen Chuanggu Screw Manager Zhu elaborated on it.

Some low-carbon steel screws, such as ISO Class 4.8 SAE Grade 1-2, which have no mechanical performance requirements, are sufficient for Q235A SAE 1015 DIN C15. There is no heat treatment at all, directly cold-worked, and fasteners of a slightly higher grade. : ISO Class 6.8 SAE Grade 3-4 requires steel with a carbon content of 0.2% or more, such as C1020 C1022 Ml20 ML35, etc. These bolts do not require any heat treatment, and the cold work strength can fully meet the requirements. In fact, the higher the carbon content, the more difficult it is for cold forming, and it is not necessary to use the 6.8-level bolts as a material. The special case is another matter.



The most commonly used screws are ISO Class 8.8 SAE Grade 5 screws. Generally used medium carbon steel, ML35 SAE 1035 DIN 35 JIS SWRCH35K After heat treatment (quenching + tempering), SAE5140 40Cr, etc., addition of alloying elements to heat treatment Hardenability is of great help, so the bolts with large gauges can be alloyed without the use of medium carbon steel, which leads to the phenomenon that we often say that the central part is “hardened”.

ISO Class 9.8 10.9 SAE Grade 8 uses low to medium alloy steel materials, after heat treatment (quenching + tempering), alloy materials have a good combination of mechanical properties. The commonly used materials are 40Cr 35CrMo SAE5140 SCM435 SAE4135 SAE4137 JIS SCr440 (H) DIN 41Cr4, etc., in fact, 45# can also achieve the required mechanical properties, but in terms of comprehensive mechanical properties is slightly inferior to alloy steel.

ISO Class 12.9 SATM A574 is a high-strength bolt with high mechanical properties. It should be heat treated (quenched + tempered) with medium carbon alloy steel, such as SCM435 35CrMo SAE 4137 SAE4135 DIN 34CrMo4. When the surface treatment is subjected to the pickling process, hydrogen embrittlement occurs, so there must be a process of dehydrogenation (especially a fastener with sharp corners), or it will die very badly.



1. The maximum tensile strength of the material used for high-strength bolts has a great relationship with the quenching treatment. After 40Cr quenching treatment, it is generally difficult to achieve the material requirements of 10.9S high-strength bolts. In the less stringent inspection, the surface hardness after quenching treatment can be used. To determine the maximum tensile strength of the material. In addition to the different properties in the process, high-strength bolts with different materials have different retardation properties under high stress conditions.

2. 40Cr high-strength bolts are mainly used in bolt-and-ball joint grids, and their design strength is generally 390MPa (d>=30mm) or 430MPa (d
3. According to GB/T1231-91, the recommended material for 10.9S bolts is 20MnTiB (applicable specifications (GB799, L-bolt, etc., can be used to produce anchor bolts with a thread diameter of 6-120mm, the length is not limited, the materials are: Q235, 45#, Q345B 40Cr, 35CrMoA, etc., the anchor bolts can be straight hook type, arc hook type, anchor melon type and stiffening anchor plate type, Q235 material foot, 35# steel foot, 24000 sets of high-strength bolt material is 40, There are 210") 0 sets of high-strength bolts. The materials for the construction of the open channel of the two copper street sub-projects and the steel beams of the construction trestle have been installed and put into operation. The layout of the two bridges is as follows (Figure 1): Bolted connections are used for steel construction.

Torsional shear type high strength bolt 109 grade friction type connection friction coefficient 045 bolt material 20 manganese titanium boron (20MnTiB) nut material 15 manganese vanadium (15MnVB) What kind of national standard for this bolt, how to ask the manufacturer when purchasing GB/T3632 -2008 Steel structure.

Marking of the mechanical properties of carbon steel and alloy steel bolts, screws and studs:

(1) There are 10 performance grade marking codes for carbon steel and alloy steel bolts, screws and studs (thread diameter 1.6-39mm, working temperature -50°C-300°C), which are 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9 and 12.9 (Bolts, screws and studs made of free-cutting steel shall not exceed 250 °C). Among them, the bolts of grade 8.8 and above are made of low carbon alloy steel or medium carbon steel and heat treated (quenched and tempered). They are commonly referred to as high-strength bolts, and the rest are commonly referred to as ordinary bolts.

(2) The bolt performance grade label is composed of two parts, which represent the nominal tensile strength value and the yield ratio of the bolt material.

For example, a bolt with a performance class of 4.6 means:

a, the bolt material has a nominal tensile strength of 400MPa;
b, the bolt material has a yield ratio of 0.6;
c. The nominal yield strength of bolt material is up to 400×0.6=240MPa grade performance grade 10.9 high strength bolt. After heat treatment, the material can reach:
a, the bolt material has a nominal tensile strength of 1000 MPa;
b, the bolt material has a yield ratio of 0.9;
c. The nominal yield strength of the bolt material is 1000×0.9=900MPa.

The meaning of the bolt performance grade is the international standard. The bolts of the same performance grade have the same performance regardless of the difference between the material and the place of origin. Only the performance grade can be selected in the design.

The above details the material used for high-strength bolts, and what is the high-strength bolt material. The introduction is clearer. I believe that it is very helpful for everyone to understand the basic knowledge of high-strength bolts.

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