To improper forging process generated defects usually are the following:
Large grains: the initial forging temperature and deformation degree, or final forging temperature is too high, or the fall critical deformation degree caused by the deformation zone. Aluminum deformation degree is too large, the texture is formed; distortion temperature of the high temperature alloy is too low, the formation of the mixed deformed microstructure may also cause coarse grains.
The grain coarsening will lower the ductility and toughness of the forgings, fatigue performance is significantly decreased. Grain uneven: means forging some parts of the grain, particularly coarse, certain parts are smaller. The main reason for the uneven grain billets throughout the deformation uneven so to the grain crushing varying degrees, or the degree of deformation of the local area drop the people critical deformation zone, or the local processing of high-temperature alloys hardening or quenching when the local grain thick. The heat-resistant steel and high temperature alloys are particularly sensitive to grain uneven. The grain will enable the forging lasting performance uneven fatigue noticeable performance degradation.
Chilled phenomenon: the deformation due to low temperature or the deformation speed is too fast, and cooling too quickly after forging, may render recrystallization caused by softening can not keep up the deformation caused by the hardening (hardening), thereby inside forging after hot forging is still part of the reservation cold deformation organizations. Such organizations exist to improve the strength and hardness of forgings, but reduces the ductility and toughness. The severe chill phenomenon may be caused by the forging cracks.
Cracks: cracks are usually forged when there is a large tensile stress, shear stress or tensile stress caused attached. The occurrence of cracks, usually on the blank maximum stress, the thickness of the thinnest part. If the blank surface and internal micro cracks, or blank memory improper organizational defects or thermal processing temperature of the material is plastic lower or deformed too fast, too large deformation degree, more than the plastic material allows pointer withdrawal in crude, stretching, punching, reaming, bending and extrusion processes are likely to crack.
Cracking: cracking show shallow turtle-shaped crack in the forging surface. Forging forming surface of the subject to tensile stress (for example, not filled with the projecting portion or the curved portion) most prone to such defects. The internal factors may cause cracking many the: ¢Ù raw materials together elements such as Cu, Sn fusible excessive. ¢Ú high temperature heating for a long time, the surface of the steel material has a copper deposition, the surface of the coarse grains, decarburization, or after repeated heating surface. The ¢Û fuel sulfur content is too high, and sulfur penetrate steel surface.
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