Several common defects caused by improper forging

2022-09-21
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Several common defects caused by improper forging process

defects caused by improper forging process usually include the following:

large grain: caused by excessive initial forging temperature and insufficient deformation degree, or excessive final forging temperature, or deformation degree falling into the critical deformation zone. The deformation degree of aluminum alloy is too large, forming texture; The deformation temperature of superalloy is too low, and coarse grains may also be caused when mixed deformation structure is formed

large grain size will reduce the plasticity and toughness of forgings and significantly reduce the fatigue performance. Uneven grain: it refers to that the grain of some parts of the forging is particularly coarse, but some parts are small. The main reason for the uneven grain is that the uneven deformation of the billet makes the degree of grain breakage different, or the degree of deformation in the local area falls into the critical deformation zone, or the local work hardening of the superalloy, or the local grain coarseness during quenching and heating. Heat resistant steels and superalloys are particularly sensitive to grain inhomogeneity. Uneven grains will significantly reduce the durability and fatigue properties of forgings

cold hardening phenomenon: during deformation, due to low temperature or too fast deformation speed, as well as too fast cooling after forging, the soft selection electro-hydraulic servo universal experimental mechanization caused by recrystallization may not keep up with the strengthening (hardening) caused by deformation, so that the cold deformation structure is still partially retained in the forging after hot forging. The existence of this structure improves the strength and hardness of forgings, but reduces the plasticity and toughness. Severe cold hardening may cause forging cracking

cracks: cracks are usually caused by large tensile stress, shear stress or additional tensile stress during forging. The position where the crack occurs is usually at the position with the maximum stress and the thinnest thickness of the blank. If there are microcracks on the surface and inside of the billet, or there are structural defects in the billet according to the division of labor of the alliance members, or the plasticity of the material is reduced due to improper hot working temperature, or the deformation speed is too fast and the deformation degree is too large, exceeding the allowable plastic pointer of the material, cracks may occur in the processes of roughening, lengthening, punching, reaming, bending and extrusion

cracking: cracking is a shallow turtle shaped crack on the surface of the forging. Such defects are most likely to occur on the surface under tensile stress in forging forming (for example, the protruding part that is not full or the part that is bent). The internal causes of cracking may be multifaceted: ① there are too many fusible elements such as Cu and Sn in raw materials. ② When the steel is heated at high temperature for a long time, it is difficult to add support in the pipe wall, but the surface is very effective. There are copper precipitation, coarse surface grains, decarburization, or surfaces heated for many times. ③ The sulfur content of the fuel is too high, and sulfur seeps into the steel surface

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