Defects Arising When Forging Is Heated

1. Beryllium oxide:

Beryllium oxide not only loses a lot of steel, but also reduces the surface quality of the forging and the service life of the forging die. If pressed into the metal, it will cause the forging to be scrapped. Failure to remove beryllium oxide will affect machining.

2. Decarbonization:

Decarbonization refers to the phenomenon that all or part of the carbon on the surface of the steel is burned off. Decarbonization makes the surface of the workpiece appear soft points, reduce the surface hardness, wear resistance and fatigue strength.

3. Overheating and overburning:

Overheating refers to the coarse grain growth after the steel exceeds the allowable temperature in heating. Overheating is not conducive to heat treatment, making the steel brittle and mechanical properties reduced, but can be eliminated by normalizing or annealing after forging. Overburning refers to the phenomenon of oxide or local melting of metal due to the heating time is too long and the temperature is too high. Overburn cannot be remedied.

4. Stress:

Due to the difference in heat inside and outside the metal, the expansion is uneven, resulting in internal stress, called thermal stress. The successive changes in the metallographic structure caused by heating also cause stress, which is called organizational stress. This will cause the workpiece to crack in the heating, causing the workpiece to crack and scrap after machining.

5. Cross section fracture:

This defect destroys the chemical composition and organizational uniformity of the steel, reduces the quenching hardness, and deteriorates the mechanical properties. If the annealing temperature is too high and the graphite section is caused, it will not be easy to cut and cause overheating and deformation during quenching. However, if the annealing is underheated or the temperature is low, the pearlite can not be fully globalized, and it is not conducive to cutting and later heat treatment.

6. Hard and brittle network carbide:

It weakens the binding force between the crystals, making the mechanical properties significantly worse, especially the impact toughness is reduced, but it can be improved or eliminated by normalizing. If banded carbides appear, the hardness and organization after quenching and tempering will be uneven, and it is easy to deformation, which is also a defect of pearlite and ferrite banded organization along the direction of processing deformation. At the same time, it will also reduce the plasticity and toughness of the steel, so that the processing size is unstable, and the tool is rapidly worn.