Brief introduction of high-strength bolt material and processing technology

High-strength bolts are made of high-strength materials, generally alloy steel. Of course there are stainless steel, carbon steel, etc. The material of high-strength bolts has a great influence on its properties. The following introduces the material of high-strength bolts in detail.

　　 Alloy steel in high-strength bolt materials is generally 30CRMOA, 35CRMOA, 40CRMOA and B7, B7M in the American Standard, etc. These are chromium-molybdenum steels, stainless steel such as B8M, A4-80, etc., and carbon steel is A325.

　　 In addition, the screws, nuts and washers of high-strength bolts are made of high-strength steel, commonly used 45 steel, 40 boron steel, 20 manganese titanium boron steel. Ordinary bolts are usually made of Q235 steel.

　　 According to GB/T1231-91, the recommended material for 10.9S bolts is 20MnTiB (applicable specification

The maximum tensile strength of the material used for high-strength bolts is closely related to the quenching treatment. After 40Cr quenching treatment, it is generally difficult to meet the material requirements of 10.9S-level high-strength bolts. The surface hardness is used to judge the maximum tensile strength of the material. (Guide: Briefly describe the method of anti-corrosion of stainless steel screws)

　　 In addition to the different properties in the treatment process, high-strength bolts of different materials have different delayed fracture properties under high stress.

　　40Cr high-strength bolts are mainly used in bolted spherical joint grids, and their design strength is generally 390MPa (d>u003d30mm) or 430MPa (d<30mm), and there is no high pretension in use. When used in a situation where a high pretension is to be applied, attention should be paid to understanding and ensuring its delayed fracture performance. The delayed fracture performance of 20MnTiB high-strength bolts is better than that of 40B.

　　 high-strength bolts with performance grade 10.9, after heat treatment, the material can reach:

　　1. The nominal tensile strength of the bolt material reaches 1000MPa;

　　2, the yield ratio of the bolt material is 0.9;

　　3, the nominal yield strength of the bolt material reaches 10000.9u003d900MPa

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

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