Grade 4.8 and Grade 8.8 refer to the grade of performance bolts that have nothing to do with the material of the bolts. The standard values of 4.8 and 8.8 are based on the characteristics of the data, the better the performance.

Class 4.8 is defined as: 4 means 4 * 100 = 400mpa, which means the tensile strength of the bolt is 400mpa, the yield strength ratio is 0.8, and the nominal yield strength is 400×0.8 = 320mpa. The properties of 8.8 grade bolts are: tensile strength = 800mpa, yield strength = 800 * 0.8 = 640mpa.

The difference as below:
1. Grade 4.8 bolts are made of unprocessed round steel, the specifications and models are not accurate enough, and the deformation is large during bending resistance, but the installation is convenient, the production cost is low, and it is mostly used for tensile connection or temporary fixing during installation; Grade 8.8 The shank of the bolt is processed by numerical control with smooth surface, precise specifications and models, complicated manufacturing and installation, high price, and rarely used.
2.4.8 or 8.8 is usually written on the hex head of the bolt. Class 4.8 is generally called ordinary bolts, and class 8.8 is called high-strength bolts.

General bolts can be divided into three grades: A, B, and C according to the manufacturing precision. Grades A and B are specially manufactured bolts, and Grade C is for random bolts. For the connecting bolts used in steel frame structures, unless otherwise specified, they are generally made of ordinary C-grade bolts. There are differences in the processing methods of different grades. Generally, the corresponding processing methods are as follows: ①The bolts of A and B grade bolts are processed by numerical control, with smooth surfaces, accurate specifications, and the grades of raw and auxiliary materials. It is grade 8.8, the manufacture and installation are complicated, the price is high, and it is rarely used; ② Grade C bolts are made of unprocessed round steel, the specifications and models are not accurate enough, and the characteristic grades of the raw and auxiliary materials are grade 4.6 or grade 4.8. The deformation is large during the bending connection, but the installation is convenient and the production cost is low. It is mostly used for tensile connection or temporary fixation during installation.

Grade contains meaning: According to relevant standards, bolt performance grades are divided into more than 10 grades such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, among which bolts above grade 8.8 are made of low carbon alloy steel or medium carbon After the steel is heat treated (quenched, tempered), it is usually called a high-strength bolt, and the rest is usually called an ordinary bolt. The bolt performance grade label consists of two numbers representing the nominal tensile strength value and yield ratio of the bolt material.

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