Requirements for the chemical composition of metal materials by cold heading machines

The chemical components of commonly used metal materials for cold heading machines include carbon, manganese, silicon, sulfur, phosphorus and other alloy elements.

1. Carbon content, carbon is the main element that affects the cold plastic deformation of steel. The higher the carbon content, the higher the strength of steel, and the lower the plasticity. For every 0.1 percentage increase in carbon content, its yield strength Re increases by 27.4MPa, the tensile strength Rm increases (58.8-78.4MPa), while elongation A decreases by 4.3 percentage, and cross-section shrinkage Z decreases by 7.3 percentage. When the carbon content of steel is less than 0.5 percentage, manganese content is less than 1.2 percentage, and cross-section shrinkage Z=80 percentage, the approximate relationship between unit cold deformation force P and the amount of C and Mn of steel is as follows: P=1950C plus 500Mn plus 1860 (MPa).

It can be seen that the carbon content in the steel of the cold heading machine has a great impact on the cold plastic deformation properties of the steel. In the actual process, when the carbon content of the steel for the extrusion of the cold heading machine is greater than 0.25%, the steel is required to anneale to a good plastic structure - spherical pearlite structure. For cold heading machines with a deformation degree of 65%-85% without going through the middle, the carbon content should not exceed 0.4%. When the carbon content of carbon steel exceeds 0.3%-0.5% is upset, the intermediate complete annealing process or warm upsetting is used.

2. The content of manganese, the effect of manganese on iron oxide (Mn plus FeO plus MnO plus Fe) in steel smelting is mainly added to deoxidize steel. Manganese acts on iron sulfide (Mn plus FeS plus MnS plus Fe) in steel, which can reduce the harmfulness of sulfur to steel. The formed manganese sulfide can improve the cutting performance of steel. Manganese improves the strength of steel and reduces the plasticity, which is unfavorable for the cold plastic deformation performance of steel, but the impact of manganese on deformation force is only about one-fourth of carbon. Due to the special performance requirements of the finished product, the manganese content is allowed to be 5 times that of sulfur. Except for the special requirements of the finished product, it should not exceed 0.9 percentage.

3. The content of silicon, silicon is the residue of the deoxidant in steel during smelting. When the silicon content in steel increases by 0.1 percentage, it will increase by 13.7mpa. Experience shows that when the silicon content exceeds 0.17 percentage and the carbon content is large, it will have a great impact on the reduction of steel's plasticity. Appropriately increasing the silicon content in steel is beneficial to the comprehensive mechanical properties of the steel, especially the elastic limit, and can also enhance the corrosion resistance of the steel. However, when the silicon content in steel exceeds 0.15 percentage, the steel will rapidly form non-metallic inclusions, and the high-silicon steel will not soften even if annealed, which will significantly reduce the cold plastic deformation performance of the steel. If silicon exists in the steel in the form of silicalic acid, the fine particles dispersed in the steel will wear the mold too quickly. Therefore, in addition to the high-strength performance requirements of the product, the steel used in cold heading machines always minimizes the silicon content.

4. Sulfur (S), sulfur is a harmful impurity. The sulfur in steel will separate the crystalline particles of metal from each other during cold heading machine, causing cracks. The existence of sulfur also causes the steel to become hot brittle and rust. Therefore, the sulfur content should be less than 0.06 percentage. When forging high-strength fasteners, it should be controlled below 0.04 percentage. Since sulfur, phosphorus and manganese compounds can improve cutting performance, the sulfur content of steel for cold heading machine nuts can be relaxed to 0.08 percentage-0.12 percentage to facilitate tapping.