What are the general materials of high strength bolts?

1。 The maximum tensile strength of high strength bolt materials is closely related to quenching treatment. After 40Cr quenching treatment, it is difficult to meet the material requirements of 10.9s grade high strength bolts. In less stringent inspection, the maximum tensile strength of the material can be determined according to the surface hardness after quenching treatment. Different materials of high-strength bolts in high stress state, in addition to the performance in the treatment process, their delayed fracture performance is also different.
        2。 40Cr high-strength bolts are mainly used in space truss with bolt ball joints. The design strength is 390 MPa (d > = 30mm) or 430 MPa (d < 30mm), and there is no high prestress in use. In the case of high pretension, attention should be paid to understand and ensure its delayed fracture performance. The delayed fracture property of 20MnTiB high strength bolt is better than that of 40B.
       3。 According to GB / t1231-91, the recommended materials for 10.9s bolts are 20MnTiB (applicable code < = M24) and 35VB (applicable code < = M30). In quenching treatment, the large diameter high strength bolt is not easy to harden, so the large diameter high strength bolt should not be used generally. If it is to be used, its working stress should be reduced. (gb799, L-bolt, etc., thread diameter 6-120mm, length unlimited, material: Q235, 45 × Q, Q345B, 40Cr, 35CrMoA, etc. anchor bolts can be divided into straight hook type, arc hook type, anchor melon type, stiffening anchor plate type, Q235 type, 35 × steel foot, including 24000 sets of high-strength bolts, 40 materials, 210 "high-strength bolts, etc.) 0 sets, composed of two open channels of Tongjiezi project, and concrete construction stack The steel girder of the bridge has been installed and put into use. 1。 The steel structure is connected by high strength bolts

The friction coefficient of 10.9 grade friction type high strength bolt is 045. The bolt material is 20MnTiB and the nut material is 15mnvb. What national standard is adopted for the bolt? How to put forward requirements to manufacturers when purchasing steel structures in GB / T 3632-2008
Mechanical property marking of carbon steel and alloy steel bolts, screws and studs:
(1) carbon steel and alloy steel bolts, screws and studs have 10 performance grade codes (thread diameter 1.6-39mm, working temperature - 50 ℃ - 300 ℃), including 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9 and 12.9 (the working temperature of free cutting steel bolts, screws and studs shall not exceed 250 ℃). Among them, the bolts of grade 8.8 and above are made of low-carbon alloy steel or medium carbon steel. After heat treatment (quenching and tempering), they are generally called high-strength bolts, and other bolts are generally called ordinary bolts.
(2) the nominal strength ratio of the bolt material is represented by two parts of the yield strength.
For example, a bolt with a performance class of 4.6 represents:
1. The nominal tensile strength of bolt material reaches 400MPa;
2. The yield strength ratio of bolt material is 0.6;
3. The nominal yield strength of bolt material is 400 × 0.6 = 240mpa
The bolt has high performance grade of 10.9
4. The nominal tensile strength of bolt material can reach 1000MPa
5. The yield strength ratio of bolt material is 0.9;
6. The nominal yield strength of bolt material is 1000 × 0.9 = 900MPa.
The meaning of bolt performance grade is international standard. For bolts of the same performance level, the performance is the same regardless of the material and origin, so the performance grade can only be selected in the design
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