What materials are used for high strength bolts
Writer： admin Time：2019-10-12 21:56
The maximum tensile strength of materials used for high-strength bolts has a great relationship with quenching treatment. Generally, it is difficult to meet the material requirements of class 10.9s high-strength bolts after 40Cr quenching treatment.In addition to the different properties in the treatment process, the delayed fracture properties of high-strength bolts with different materials under high stress are also different.
2. The 40Cr high-strength bolt is mainly used in the bolt ball node network frame, and its design strength is generally 390MPa(d>=30mm) or 430MPa (d <30mm), without high pre-tensile stress in use.Attention should be paid to understanding and ensuring the delayed fracture performance when applying high pretension.The delayed fracture performance of 20MnTiB high strength bolt is better than that of 40B.
3. According to GB/ t1231-91, the recommended materials of 10.9S bolt are 20MnTiB (applicable specification <=M24) and 35VB(applicable specification <=M30).In quenching, large-diameter high-strength bolts are not easy to be fully quenched, so generally do not use large-diameter high-strength bolts, if you want to use, you should reduce its working stress.
Mechanical properties of bolts, screws and studs of carbon steel and alloy steel - marking:
(1) carbon steel and alloy steel bolts, screws and studs (screw diameter of 1.6-39mm, operating temperature of -50 ° c -- 300 ° c) have a total of 10 performance grade marking codes, namely 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 are heat-treated (quenching and tempering), generally called high-strength bolts, and the rest are commonly called ordinary bolts.
(2) bolt performance grade label is composed of two parts, which respectively represent the nominal tensile strength value and bending strength ratio of bolt materials.
For example, a bolt with performance grade 4.6 means:
A. the nominal tensile strength of bolt material reaches 400MPa;
B. The bending strength ratio of bolt material is 0.6;
C. Nominal yield strength of bolt material reaches 400×0.6=240MPa class
Performance grade 10.9 high strength bolt, its material after heat treatment, can achieve:
A. The nominal tensile strength of bolt material reaches 1000MPa;
B. The bending strength ratio of bolt material is 0.9;
C. Nominal yield strength of bolt material reaches 1000×0.9=900MPa class.