Bolt strength level

Updated:09-10-2019
Summary:

Bolt: Mechanical parts, cylindrical threaded fasteners […]

Bolt: Mechanical parts, cylindrical threaded fasteners with nuts. A type of fastener consisting of a head and a screw (a cylinder with an external thread) is required to be fitted with a nut for fastening the two parts with through holes.

The strength level is based on the mechanical properties.

Mechanical properties: The ability of a material to resist deformation and fracture under certain temperature conditions and external forces is called the mechanical properties of the material. Conventional mechanical properties mainly include: strength, hardness, ductility and toughness.

a. Strength refers to the resistance of a metal material to deformation or fracture under the action of an external force.

b. Plasticity refers to the ability of a metal material to plastically deform before fracture.

c. Toughness refers to the ability of metallic materials to withstand shock loads.

d. Hardness is a performance indicator that measures the hardness of a material.

According to the relevant standards, the bolt performance grade is divided into more than 10 grades of 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, among which the bolts of grade 8.8 and above are made of low carbon alloy steel or medium carbon steel and heat treated. (Quenching, tempering), commonly known as high-strength bolts, the rest are commonly referred to as ordinary bolts. 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, which means:
1. The nominal tensile strength of bolt material is up to 400MPa;
2. The yield ratio of the bolt material is 0.6;
3. The nominal yield strength of bolt material is up to 400×0.6=240MPa

Performance grade 10.9 high strength bolts, after heat treatment, can achieve:
1. The nominal tensile strength of bolt material is up to 1000MPa;
2. The yield ratio of the bolt material is 0.9;
3. The nominal yield strength of the bolt material is 1000×0.9=900MPa

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