Hino Fuso Universal Rear Bolt

1、Spheroidizing annealing of high-strength bolts

When the hexagon socket head bolts are produced by the cold heading process, the original structure of the steel will directly affect the forming ability during cold heading processing. Therefore, the steel must have good plasticity. When the chemical composition of the steel is constant, the metallographic structure is the key factor determining the plasticity. It is generally believed that the coarse flaky pearlite is not conducive to cold heading forming, while the fine spherical pearlite can significantly improve the plastic deformation ability of the steel.
For medium carbon steel and medium carbon alloy steel with a large amount of high-strength fasteners, spheroidizing annealing is performed before cold heading, so as to obtain uniform and fine spheroidized pearlite to better meet the actual production needs.

2、 Shelling and descaling of high-strength bolts

The process of removing iron oxide plate from cold heading steel wire rod is stripping and descaling. There are two methods: mechanical descaling and chemical pickling. Replacing the chemical pickling process of wire rod with mechanical descaling improves productivity and reduces environmental pollution. This descaling process includes bending method, spraying method, etc. The descaling effect is good, but the residual iron scale cannot be removed. Especially when the scale of the iron oxide scale is very strong, so the mechanical descaling is affected by the thickness of the iron scale, the structure and the stress state, and is used in carbon steel wire rods for low-strength fasteners. After mechanical descaling, the wire rod for high-strength fasteners undergoes a chemical pickling process to remove all the iron oxide scales, that is, compound descaling. For low carbon steel wire rods, the iron sheet left by mechanical descaling is likely to cause uneven wear of grain drafting. When the grain draft hole adheres to the iron sheet due to the friction of the wire rod and the external temperature, the surface of the wire rod produces longitudinal grain marks.