Selection Of High-strength Bolt Materials

The correct selection of fastener materials in fastener manufacturing is an important part because the performance of fasteners is closely related to their materials. Cold heading steel is a steel for fasteners with high interchangeability produced by cold heading forming process. Because it is formed by metal plastic processing at room temperature, the deformation of each part is large, and the deformation speed is high. Therefore, the performance requirements for cold heading steel raw materials are very strict.

(1) If the carbon content is too high, the cold forming performance will decrease, and if the carbon content is too low, the mechanical performance requirements of the parts cannot be met.

(2) Manganese can improve the permeability of steel, but adding too much will strengthen the matrix structure and affect the cold forming performance.

(3) Silicon can strengthen ferrite to reduce cold forming performance and material elongation.

(4) Although boron has the effect of significantly improving the permeability of steel, it will also increase the brittleness of steel. Excessive boron content is very detrimental to workpieces such as bolts, screws and studs that require good comprehensive mechanical properties.

(5) Other impurity elements, their presence will segregate along the grain boundary and cause grain boundary embrittlement, and damage the mechanical properties of the steel should be reduced as much as possible.