1. Bolts, studs, screws:
Carbon steel is generally used for grades 3.6, 4.6, 4.8, 5.6, 5.8, and 6.8, and no heat treatment is required;
Grades 8.8 and 9.8 are generally selected from low carbon alloy steel or medium carbon steel, quenching + tempering;
10.9 grades generally use low or medium carbon alloy steel or alloy steel, quenching + tempering;
Grade 12.9 is generally selected from alloy steel, quenching + tempering.
2. Nuts:
Carbon steel is generally used for grades 4, 5, and 6 without heat treatment, and medium carbon steel is generally used for grades 8 and 9, quenching and tempering; alloy grades, quenching and tempering are added for grades 10 and 12 to improve mechanical properties.
3. Material:
1. Carbon (C): improve the strength of steel parts, especially heat treatment performance; but with the increase of carbon content, plasticity and toughness decrease, which will affect the cold heading performance and welding performance of steel parts;
2. Manganese (Mn): to improve the strength of steel parts and to improve the hardenability to a certain extent, that is, the strength of hardened penetration is increased during quenching, and manganese can also improve the surface quality, but too much manganese has a significant impact on ductility and The bad solderability also affects the control of the coating during electroplating;
3. Nickel (Ni): improve the strength of steel parts, improve the toughness at low temperature, improve the resistance to atmospheric corrosion, and ensure a stable heat treatment effect to reduce the effect of hydrogen embrittlement;
4. Chromium (Cr): improve hardenability, improve wear resistance, improve corrosion resistance, and help maintain strength at high temperatures;
5. Molybdenum (Mo): It can help control the hardenability, reduce the sensitivity of steel to temper brittleness, and improve the tensile strength at high temperature;
6. Boron (B): It can improve the hardenability and help make the low carbon steel produce the expected response to heat treatment;
7. Alum (V): refines austenite grains and improves toughness
8. Silicon (Si): To ensure the strength of steel parts, proper content can improve the plasticity and toughness of steel parts.
9. Sulfur (S) improves machinability, produces hot embrittlement, deteriorates the quality of steel, and the increase in S content will also have a bad effect on weldability.
10. Phosphorus (P) has a solid solution strengthening and cold work hardening effect. Used in combination with steel to improve the atmospheric corrosion resistance of low-alloy high-strength steel, but reducing its impact performance. Used in combination with S and Mn to improve machinability , Increase tempering brittleness and cold brittleness sensitivity
