Bolt is a common mechanical part, which is often used in many places. It is a kind of fastener consisting of head and screw. It needs to be used together with nut to fasten and connect two parts with through holes. Maybe you don't know much about the grade and material of bolts. This article will introduce the knowledge about bolt material and grade, so that more people can learn to identify these small properties of bolts.
What are the grades and materials of bolts?
Bolt grade refers to bolt grade 4.8, 8.8 and 10.9.
Material refers to the material used for bolts, such as 45 # steel, 35CrMo steel and 304 stainless steel.
The grade and material of bolts have a certain relationship. Low carbon steel can only produce low strength bolts, carbon steel can produce medium strength bolts, and alloy steel can produce high strength bolts. Some bolt grades specify the corresponding chemical composition and mechanical properties, which also specify the materials.
Here is a list of the materials that can be used for bolts at common levels. 4.8 The grade can be A3 Q235, Q195 and other low-carbon steel materials. 5.8 All materials above grade Q235 can be used without heat treatment. 8.8 Grade thread diameter is below 16mm, 35 # is quenched and tempered, and above 16mm, 45 # and low-carbon alloy steel are quenched and tempered. 10.9 grade medium carbon alloy steel quenched and tempered heat treatment 35CRMO 40CR, etc.
Can high-strength bolts and ordinary bolts be distinguished by material?
Generally, it is classified according to the strength grade.
The performance grades of bolts for steel structure connection can be 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 them, bolts of grade 8.8 and above are made of low-carbon alloy steel or medium carbon steel and are generally referred to as high-strength bolts after heat treatment (quenching and tempering), and the rest are generally referred to as ordinary bolts. The bolt property grade designation consists of two parts of figures, representing the nominal tensile strength value and yield strength ratio of the bolt material.
For example, bolts of property class 8.8 mean:
1. The nominal tensile strength of bolt material reaches 800MPa;
2. The yield ratio of bolt material is 0.8;
3. The nominal yield strength of bolt material reaches 800 × 0.8=640MPa, the most commonly used high-strength bolts are 8.8 and 10.9, and the most commonly used ordinary bolts are 4.8.
In real life, how to distinguish whether the bolt on the hand is a high-strength bolt? If the bolt head is marked with 4.8 or 8.8, it can be directly determined whether it is a high-strength bolt. Secondly, it can also be classified from the color. If it is black, it can be estimated that it is high-strength screw. Moreover, from the sound of torture, the sound of high-strength bolts is relatively clear. You can also use a grinder to grind and judge by the sparks. In a word, there are many ways to judge whether a bolt is of high strength.
