Materials used for common fasteners
1、 At present, the standard parts on the market are mainly carbon steel (including the steel for easy cars), stainless steel (including the stainless steel for easy cars), copper (including the copper for quick cutting).
（1） Carbon steel. We distinguish low carbon steel, medium carbon steel, high carbon steel and alloy steel by carbon content in carbon steel.
1. Low carbon steel C% ≤ 0.25% is commonly referred to as A3 steel in China. Foreign countries are basically called 1008101510181022, etc. Mainly used for grade 4.8 bolts, grade 4 nuts, small screws and other products without hardness requirements. (Note: 1022 material is mainly used for drilling tail nail.)
2. Medium carbon steel 0.25% < C% < 0.45% is generally called No.35 and No.45 steel in China, and 1035, ch38f, 1039 and 40ACr in foreign countries. Mainly used for Grade 8 nuts, grade 8.8 bolts and grade 8.8 hexagon products.
3. High carbon steel C% > 0.45%. Not used in the market at present
4. Alloy steel: add alloy elements to ordinary carbon steel to increase some special properties of steel: such as 35, 40 chrome molybdenum, SCM435, 10b38. SCM435 chromium molybdenum alloy steel is mainly used for aromatic screws, and the main components are C, Si, Mn, P, s, Cr, mo.
（2） Stainless steel. Performance level: 45, 50, 60, 70, 80
It mainly consists of austenite (18% Cr, 8% Ni) with good heat resistance, corrosion resistance and weldability. A1, A2, A4
Martensite and 13% Cr have poor corrosion resistance, high strength and good wear resistance. C1, C2, C4 ferritic stainless steel. 18% Cr has better upsetting property and better corrosion resistance than martensite. At present, the imported materials are mainly Japanese products. It is mainly divided into SUS302, SUS304 and SUS316 by level.
（3） Copper. The common material is brass Zinc copper alloy. H62, H65 and H68 copper are mainly used as standard parts in the market
三、Influence of various elements in the material on the properties of steel:
1. Carbon (c): improve the strength of steel, especially its heat treatment performance, but with the increase of carbon content, plasticity and toughness will decline, and will affect the cold heading performance and welding performance of steel.
2. Manganese (MN): to improve the strength of steel parts, and to some extent improve the hardenability. That is to say, during quenching, the strength of hardening penetration is increased, and the surface quality of manganese can be improved, but too much manganese is not good for ductility and weldability. And it will affect the plating control.
3. Nickel (Ni): improve the strength of steel parts, improve the toughness at low temperature, improve the atmospheric corrosion resistance, and ensure stable heat treatment effect, reduce the role of hydrogen embrittlement.
4. Chromium (CR): it can improve hardenability, wear resistance, corrosion resistance, and maintain strength at high temperature.
5. Molybdenum (MO): it can help to control hardenability, reduce the sensitivity of steel to temper embrittlement, and has a great influence on improving the tensile strength at high temperature.
6. Boron (b): it can improve hardenability and help to make low carbon steel react with heat treatment as expected.
7. Alum (V): refine austenite grain and improve toughness.
8. Silicon (SI): to ensure the strength of steel parts, appropriate content can improve the plasticity and toughness of steel parts.
4、 A brief introduction to the characteristics of stainless steel (304, 316)
（1） The three materials are all 300 series austenitic stainless steel with the following chemical composition:
The relationship between the main chemical composition and the properties of stainless steel.
1. Carbon C can increase hardness and strength, and too high content will reduce its ductility and corrosion resistance
2. Chromium CR can increase the corrosion resistance and oxidation resistance, refine the particles, increase the strength, hardness and wear resistance
3. Ni can increase the strength and corrosion resistance at high temperature and reduce the rate of cold work hardening
4. Mo increases the strength and has excellent corrosion resistance to oxides and seawater
5. Copper and copper are good for cold forming and reduce magnetism