1. Large grains; Large grains are usually caused by high initial forging temperature transition and lack of deformation level, or high final forging temperature transition, or deformation level falling into critical deformation zone. The deformation level of aluminum alloy is too large, which constitutes texture; The deformation temperature transition of superalloy is too low, which may also cause coarse grains when it forms mixed deformation structure. Coarse grain size will reduce the plasticity and toughness of forgings, and the fatigue performance will drop obviously.

2. Uneven grains; Uneven grain size means that the grains in some parts of the forging are particularly coarse, but in some parts they are small. The main reason for uneven grain size is that uneven deformation in different parts of the blank leads to different levels of grain breakage, or the deformation level in some areas falls into the critical deformation zone, or the superalloy is partially work hardened, or some grains are coarse during quenching and heating. Heat-resistant steels and superalloys are particularly sensitive to uneven grain size. Uneven grains will obviously reduce the durability and fatigue properties of forgings.

3. Cold hardening phenomenon; Due to low temperature during deformation or too fast deformation speed, and too fast cooling after forging, the softening caused by recrystallization may not keep up with the strengthening (hardening) caused by deformation, so that the cold deformed structure is still preserved locally in the forgings 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 crack.

4. Cracks; Cracks are usually caused by large tensile stress, shear stress or additional tensile stress during forging. Cracks usually occur in the parts with the greatest stress and the thinnest thickness of the blank. If there are micro-cracks on the outside and inside of the blank, or there are structural defects in the blank, or improper hot working temperature reduces the plasticity of the data, or the deformation speed is too fast and the deformation level is too high, which exceeds the plastic index allowed by the data, cracks may occur in the processes of roughing, drawing, punching, reaming, bending and extrusion.

5. Cracking; Cracking is a shallow turtle crack on the surface of forging. This kind of defect is most likely to occur in the appearance of tensile stress in forging forming (for example, the protruding part that is not filled or the bent part). The internal causes of cracking may be various: ① There are too many fusible elements such as Cu and Sn in the original data. (2) When heated at high temperature for a long time, there is copper precipitation, coarse grains, decarburization or repeated heating on the steel surface. (3) the fuel sulfur content is too high, and sulfur permeates the surface of steel.

6. Flash crack; Flash crack is a crack that occurs at the parting surface during die forging and trimming. The causes of flash cracks may be as follows: (1) In die forging operation, the metal is violently moved by heavy blow, resulting in the phenomenon of rebar penetration. ② The trimming temperature transition of magnesium alloy die forgings is too low; The trimming temperature transition of copper alloy die forgings is too high.

7. Crack on parting surface; Cracks on parting surface refer to cracks along the parting surface of forgings. There are many nonmetallic inclusions in the original data, and the movement and concentration to the parting surface during die forging or the residual shrinkage tube often forms cracks on the parting surface after being crowded with flash during die forging.

8. folding; Folding is formed by bringing together oxidized surface metals during metal deformation. It can be composed of two (or more) metal convection sets; It can also be formed by the rapid and massive activity of a metal, which brings the surface metal near the local area with activity, and the two are assembled; It can also be formed by bending and backflow of deformed metal; It can also be formed by local metal deformation and being pressed into another local metal. Folding is related to the original data and the shape of the blank, the design of the die, the layout of the forming process, the smoothness and the practical operation of forging. Folding not only reduces the bearing area of parts, but also often becomes a source of fatigue due to stress concentration here.

9. cross-flow; Cross-flow is a way of improper streamline distribution. In the cross-flow area, the streamline originally scattered at a certain angle gathers together to form the cross-flow, which may make the grain size difference between the inside and outside of the cross-flow area quite different. The cause of the cross-flow is similar to that of folding, which is composed of two metals or one metal with the other, but the local metal of the cross-flow is still a whole; Cross-flow reduces the mechanical properties of forgings, especially when the grains on both sides of the cross-flow zone are quite different.

10. The forging streamline is not spread smoothly; Unfavorable streamline distribution of forgings refers to streamline disorder such as streamline cutting, backflow and eddy current at low magnification of forgings. If the die design is improper or the forging method is unreasonable, the flow line of the prefabricated blank will be disordered; Uneven movement of metal caused by improper operation of workers and wear of dies can make the streamline distribution of forgings not smooth. Poor streamline will reduce various mechanical properties, so there are requests for streamline dispersion for important forgings.

11. Residual casting structure; The residue of casting structure is mainly present in forgings with ingot as blank. As-cast structure mainly remains in the difficult deformation zone of forgings. Insufficient forging ratio and improper forging method are the main reasons for casting structure residue; The residual casting structure will reduce the properties of forgings, especially the impact toughness and fatigue performance.

12. The carbide segregation level does not meet the requirements; The request of non-conformity of carbide segregation grade is mainly presented in ledeburite die steel. The main reason is that the carbides in forgings are unevenly distributed, concentrated in large blocks or distributed in a network. The main reason for this defect is the poor carbide segregation grade in the original data, and the forging ratio is not enough or the forging method is improper. Forgings with this defect are prone to partial overheating and quenching crack during heat treatment quenching. The manufactured cutting tools and dies are easy to break when used.

13. banded organization; Banded structure is a kind of structure in which ferrite and pearlite, ferrite and austenite, ferrite and bainite, and ferrite and martensite are distributed in bands in forgings, which are mostly present in hypoeutectoid steel, austenitic steel and semi-martensitic steel. This kind of structure is a banded structure produced during forging deformation under the condition of coexistence of two phases, which can reduce the transverse plasticity index of data, especially the impact toughness. In forging or parts work, it is often easy to crack along the ferrite belt or the boundary between the two phases.

14. Lack of partial filling; The lack of partial filling mainly occurs in ribs, convex corners, corners and rounded corners, and the size does not meet the requirements of the drawing. The reasons may be as follows: ① low forging temperature and poor metal activity; ② Insufficient tonnage of equipment or lack of hammering force; (3) The design of blank mold is unreasonable, and the blank volume or section size is unqualified; (4) accumulation of oxide scale or welding deformed metal in the die cavity.

15. Undervoltage; Undervoltage refers to the general increase of the dimension perpendicular to the parting surface, which may be caused by: ① low forging temperature. ② Lack of equipment tonnage, hammering force or hammering times.

16. dislocation; Dislocation refers to the displacement of forgings along the upper half of the parting surface relative to the lower half. The reasons may be as follows: ① the gap between the slider (hammer head) and the guide rail is too large; (2) the design of forging die is unreasonable, and there is a shortage of lock or guide post to eliminate the dislocation force; ③ Bad mold device.

17. Axis bending; The axis of forging is bent, and there is an error with the geometric position of plane. The reasons may be as follows: (1) the forging is not paid attention to when it is ejected from the die; ② Uneven stress during trimming; (3) The cooling rate of each part is different when the forging is cooled; ④ Improper liquidation and thermal disposal.

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