Perhaps, many people don’t understand the German standard. What is the difference between the bolts produced by the national standard?
1. The maximum tensile strength of the material used in German standard bolts is closely related to the quenching treatment. After quenching with 40Cr, it is generally difficult to meet the material requirements of 10.9S grade high-strength bolts. In less stringent inspections, the maximum tensile strength of the material can be judged according to the surface hardness after quenching. In addition to the different properties during processing, high-strength bolts of different materials have different delayed fracture properties under high stress.
2. 40Cr high-strength bolts are mainly used for space trusses with bolted spherical joints. Their design strength is usually 390MPa (d> 30mm) or 430MPa (d <30mm), and there is no high pre-tensioning stress in use. When applied to situations that require high pretension, attention should be paid to understanding and ensuring delayed fracture performance. The delayed fracture performance of 20MnTiB high-strength bolts is better than 40B.
3. According to GB/T1231-91, the recommended material for 10.9S bolts is 20MnTiB (applicable specification <= M24) and 35VB (applicable specification <= M30). In the quenching process, large-diameter high-strength bolts are not easy to harden. Therefore, in general, do not use too large-diameter high-strength bolts. If you want to use it, you should reduce its working stress. (GB799, L-shaped bolts, etc., can produce bolts with a thread diameter of 6-120 mm. The length is unlimited. The material is Q235, 45, Q345B, 40Cr, 35CrMoA, etc.. The bolts can be straight hook type, arc hook type, and anchor Type and reinforced anchor plate type, Q235 material feet, 35 steel feet, including 24,000 sets of high-strength bolts, 40 sets of high-strength bolts, 210"). The material 20 high-strength bolt set is the open channel for the construction of the 2 Tongtongzi project. The layout of the steel beams of the trestle bridge and concrete construction has been installed and put into use as follows: high-strength bolt connection for steel structure. Torsion-shear type high-strength bolt 109 friction type connection friction coefficient 045 bolt material 20 MnTiB nut material 15 MnVB this National standards for bolts, how to ask the manufacturer's GB/T3632-2008 when purchasing
Mechanical properties of carbon steel and alloy steel bolts, bolts and studs of German standard bolts for steel structures:
(1) Carbon steel and alloy steel bolts, bolts and studs have 10 performance grade labels (thread diameter is 1.6-39 mm, working temperature is -50-300℃). They are 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9 and 12.9 respectively (the working temperature of bolts, bolts and studs made of free-cutting steel cannot exceed 250°C). Bolts of grade 8.8 and above are made of low-carbon alloy steel or medium-carbon steel, and are heat treated (quenched and tempered). They are usually called high-strength bolts, while other bolts are usually called ordinary bolts.
(2) The bolt performance grade label consists of two parts, representing the ratio of the nominal tensile strength to the yield strength of the bolt material.
For example, a bolt with performance class 4.6 means:
A. The nominal tensile strength of the bolt material is 400 MPa.
B. The yield strength ratio of the bolt material is 0.6.
C. The nominal yield strength of the bolt material reaches 400×0.6 = 240MPa.
After heat treatment, the 10.9 grade high-strength bolt material can reach:
A. The nominal tensile strength of the bolt material reaches 1000MPa.
B. The yield strength ratio of the bolt material is 0.9.
C. The nominal yield strength of the bolt material is 1000×0.9 = 900MPa.
The meaning of bolt performance grade is an international standard. Regardless of the material and source, bolts of the same performance class have the same performance. Only the performance level can be selected in the design.