Overheating and overburning of the elastic pin coupling

　　Overheating and overburning of the elastic pin coupling: Overheating refers to the growth of coarse grains after the steel exceeds the allowable temperature during heating.Stress: due to the difference in heat between the inside and outside of the metal, the expansion is uneven, and internal stress is generated, which is called thermal stress.If the temperature is too high during annealing to cause graphite cross-section, it will not be easy to cut and cause overheating and deformation during quenching.Decarburization causes soft spots on the surface of the workpiece, reducing the hardness, wear resistance and fatigue strength of the surface.

　　Fracture appears in the cross section of the elastic pin coupling: This defect destroys the chemical composition and uniformity of the structure of the steel, reduces the quenching hardness, and deteriorates the mechanical properties.At the same time, it will also reduce the plasticity and toughness of the steel, making the turning size unstable, and the tool wears quickly.The successive changes of metallographic structure caused by heating also cause stress, which is called tissue stress. 

　　Banded carbides appear on the surface of the elastic pin coupling, which will cause uneven hardness and structure after quenching and tempering, and easy to deform. This is also a kind of banded structure of pearlite and ferrite along the processing deformation direction. defect.However, if the annealing is underheated or the temperature is too low, the pearlite will not be spheroidized, which is not conducive to cutting and subsequent heat treatment.Overburning cannot be remedied: Flexible pin coupling 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 it is pressed into the metal, it will cause the forging to be scrapped.

　　The hard and brittle mesh carbide of the elastic pin coupling: it weakens the bonding force between the crystals and significantly deteriorates the mechanical properties, especially the impact toughness, but it can be improved or eliminated by normalizing.Decarburization: Decarburization refers to the phenomenon that all or part of the carbon on the steel surface is burned off.