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Beryllium oxide: beryllium oxide not only loses a lot of steel, but also reduces the surface quality of forgings and the service life of forging dies. If pressed into the metal, forgings will be scrapped. Failure to remove beryllium oxide will affect machining.
Decarburization: decarburization refers to the phenomenon that all or part of the carbon on the steel surface is burned. Decarburization causes soft spots on the surface of the workpiece and reduces the hardness, wear resistance and fatigue strength of the surface.
Overheating and overburning: overheating refers to the coarseness of grain length after the steel exceeds the allowable temperature during heating. Overheating is not conducive to heat treatment, making the steel brittle and reducing the mechanical properties, but it can be eliminated by normalizing or annealing after forging. Overburning refers to the phenomenon of oxide or local melting of metal due to too long heating time and too high temperature. Over burning cannot be remedied.
Stress: due to the difference of internal and external heating of metal, the expansion is uneven, resulting in internal stress, which is called thermal stress. The successive changes of metallographic structure caused by heating also cause stress, which is called structural stress. This will cause cracks in the workpiece during heating, resulting in cracks and scrapping of the workpiece after machining.
Fracture in the cross section: this defect destroys the chemical composition and structural uniformity of the steel, reduces the quenching hardness and deteriorates the mechanical properties. If the temperature is too high during annealing to cause graphite section, it will not be easy to cut and cause overheating and deformation during quenching. However, if the annealing is under heated or the temperature is low, the pearlite cannot be completely * *, which is not conducive to cutting and subsequent heat treatment.
Hard and brittle network carbide: it weakens the bonding force between grains, significantly deteriorates the mechanical properties, especially reduces the impact toughness, but can be improved or eliminated by normalizing. If banded carbides appear, the hardness and structure after quenching and tempering will be uneven and easy to deform, which is also a defect of banded structure of pearlite and ferrite along the processing deformation direction. At the same time, it will also reduce the plasticity and toughness of steel, make the machining size unstable and the cutting tools wear rapidly.
Decarburization: decarburization refers to the phenomenon that all or part of the carbon on the steel surface is burned. Decarburization causes soft spots on the surface of the workpiece and reduces the hardness, wear resistance and fatigue strength of the surface.
Overheating and overburning: overheating refers to the coarseness of grain length after the steel exceeds the allowable temperature during heating. Overheating is not conducive to heat treatment, making the steel brittle and reducing the mechanical properties, but it can be eliminated by normalizing or annealing after forging. Overburning refers to the phenomenon of oxide or local melting of metal due to too long heating time and too high temperature. Over burning cannot be remedied.
Stress: due to the difference of internal and external heating of metal, the expansion is uneven, resulting in internal stress, which is called thermal stress. The successive changes of metallographic structure caused by heating also cause stress, which is called structural stress. This will cause cracks in the workpiece during heating, resulting in cracks and scrapping of the workpiece after machining.
Fracture in the cross section: this defect destroys the chemical composition and structural uniformity of the steel, reduces the quenching hardness and deteriorates the mechanical properties. If the temperature is too high during annealing to cause graphite section, it will not be easy to cut and cause overheating and deformation during quenching. However, if the annealing is under heated or the temperature is low, the pearlite cannot be completely * *, which is not conducive to cutting and subsequent heat treatment.
Hard and brittle network carbide: it weakens the bonding force between grains, significantly deteriorates the mechanical properties, especially reduces the impact toughness, but can be improved or eliminated by normalizing. If banded carbides appear, the hardness and structure after quenching and tempering will be uneven and easy to deform, which is also a defect of banded structure of pearlite and ferrite along the processing deformation direction. At the same time, it will also reduce the plasticity and toughness of steel, make the machining size unstable and the cutting tools wear rapidly.
