1. Large grain size; Large grain size is usually caused by high initial forging temperature transition and lack of deformation level, or high final forging temperature transition, or deformation level falling into the critical deformation zone. Aluminum alloy deformation level is too large, forming texture; When the deformation temperature of high-temperature alloys is too low, it may also cause coarse grains when forming a mixed deformation structure; Coarse grain size will reduce the plasticity and toughness of forgings, and significantly decrease their fatigue performance.
2. Uneven grain size; Uneven grain size refers to the fact that the grains in certain parts of a forging are particularly coarse, while in other parts they are smaller. The main reason for uneven grain size is the uneven deformation of the billet, which results in varying levels of grain breakage, or the deformation level in some areas falling into the critical deformation zone, or the partial work hardening of high-temperature alloys, or the coarsening of some grains during quenching and heating. Heat resistant steel and high-temperature alloys are particularly sensitive to uneven grain size. Uneven grain size will significantly reduce the durability and fatigue performance of forgings.
3. Cold hardening phenomenon; Due to low temperature or too fast deformation speed during deformation, as well as rapid cooling after forging, the softening caused by recrystallization may not keep up with the strengthening (hardening) caused by deformation, resulting in local preservation of cold deformation structure inside the forged part after hot forging. The existence of this organization improves the strength and hardness of forgings, but reduces plasticity and toughness. Severe cold hardening phenomenon may cause forging cracking.
4. Cracks; Cracks are usually caused by significant tensile stress, shear stress, or additional tensile stress during forging. The location where cracks occur is usually in the area where the stress Z of the billet is high and the thickness Z is thin. If there are microcracks on the surface and inside of the billet, or if there are structural defects inside the billet, or if the plasticity of the material is reduced due to improper hot processing temperature, or if the deformation speed is too fast, the deformation level is too large, and exceeds the allowable plasticity pointer of the material, cracks may occur in processes such as roughing, lengthening, punching, expanding, bending, and extrusion.
5. Cracking; Cracking is a shallow turtle shaped crack on the surface of forgings. The surface subjected to tensile stress during forging forming (such as unfilled protruding areas or bent areas) is prone to such defects. The internal causes of cracking may be multifaceted: ① There are too many melting elements such as Cu and Sn in the original material. ② When heated at high temperatures for a long time, the surface of the steel material may have copper precipitation, coarse grains, decarburization, or a surface that has been repeatedly heated. ③ The sulfur content of the fuel is too high, causing sulfur to seep into the surface of the steel material.
6. Flying edge cracks; Flying edge cracks are cracks that occur at the parting surface during forging and trimming. The reason for the occurrence of flying edge cracks may be: ① During the forging operation, the metal undergoes intense movement due to heavy impact, resulting in the phenomenon of piercing ribs. ② The cutting edge temperature transition of magnesium alloy die forgings is too low; The cutting edge temperature of copper alloy die forgings is too high.
7. Cracks on the parting surface; Splitting surface crack refers to the crack generated along the splitting surface of the forging. The original data shows that there are many non-metallic inclusions, and during die forging, they tend to move towards the parting surface and concentrate or shrink, resulting in the formation of cracks on the parting surface after being squeezed into the flying edge.
8. Folding; Folding is the process by which oxidized surface metals come together 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 activity to the nearby surface metal, and the combination of the two; It can also be formed by the bending or reflow of deformed metals; It can also be formed by the deformation of a local metal part and being pressed into another local metal. Folding is related to the shape of the raw materials and blanks, the design of the mold, the arrangement of the forming process, the smoothness condition, and the practical operation of forging; Folding not only reduces the load-bearing area of the parts, but also often becomes a source of fatigue during operation due to stress concentration in this area.
9. Flow through; Flow through is a way of improper dispersion of flow lines. In the flow-through region, streamlines that were originally scattered at a certain angle gather together to form a flow-through, which may result in a significant difference in grain size between the inside and outside of the flow-through region. The reason for the occurrence of overcurrent is similar to folding, which is composed of two strands of metal or one strand of metal carrying another strand of metal converging, but the metal in the local area of overcurrent is still a whole; Flow through reduces the mechanical properties of forgings, especially when there is a significant difference in grain size between the two sides of the flow through zone.
10. Improper dispersion of forging flow lines; The uneven distribution of forging flow lines refers to the occurrence of flow line disruptions such as cutting, backflow, and eddy currents at low magnification of the forging. If the mold design is improper or the forging method selection is unreasonable, the flow of prefabricated blanks will be disrupted; Improper operation by workers and uneven movement of metal caused by mold wear can result in uneven distribution of forging flow lines. Irregular flow lines can reduce various mechanical properties, so there is a request for flow line dispersion for important forgings.
11. Residual structure in casting; The residual structure of casting is mainly present in forgings made from ingots as raw materials. The as cast microstructure mainly remains in the difficult deformation zone of the forging. Insufficient forging ratio and improper forging methods are the main reasons for residual casting structure; The residual structure in casting can cause a decrease in the performance of forgings, especially in terms of impact toughness and fatigue performance.
12. The carbide segregation level does not meet the request; The non-compliance of carbide segregation levels is mainly manifested in the use of martensitic die steel. The main reason is the uneven distribution of carbides in forgings, which are concentrated in large blocks or distributed in a network like pattern. The main reason for the formation of this defect is the poor segregation level of carbides in the original material, coupled with insufficient forging ratio or improper forging methods during the forging process Forgings with such defects are prone to partial overheating and quenching cracking during heat treatment quenching. The cutting tools and molds made are prone to breakage during use.
13. Banded tissue; Banded structure is a type of structure in which ferrite and pearlite, ferrite and austenite, ferrite and bainite, and ferrite and martensite are dispersed in a banded manner in forgings. They are mostly present in hypoeutectoid steels, austenitic steels, and semi martensitic steels. This type of organization is a banded structure produced during forging deformation in the presence of two phases, which can reduce the lateral plasticity index of the material, especially the impact toughness. It is often prone to cracking along the ferrite band or at the junction of two phases during forging or component work.
14. Lack of partial filling; The lack of partial filling mainly occurs in the ribs, convex corners, corners, and rounded corners, and the dimensions do not meet the requirements of the drawing. The possible reasons for this may be: ① low forging temperature and poor metal mobility; ② Insufficient equipment tonnage or lack of hammering force; ③ Unreasonable design of the blank mold, resulting in non-conforming volume or cross-sectional dimensions of the blank; ④ Accumulation of oxide scale or welding deformation metal in the mold cavity.
15. Undervoltage; Underpressure refers to the general increase in size perpendicular to the parting surface direction, which may be caused by: ① low forging temperature. ② Lack of equipment tonnage, insufficient hammering force, or insufficient hammering frequency
16. Misalignment; Misalignment refers to the displacement of the upper half of the forging along the parting surface relative to the lower half. The possible reasons for this may be: ① The gap between the slider (hammer) and the guide rail is too large; ② The design of the forging die is unreasonable, and there is a shortage of locking ports or guide columns to eliminate the displacement force; ③ Poor mold device
17. Axis bending; The axis of the forging is bent and there is an error in the geometric position of the plane. The possible reasons for this may be: ① Not paying attention when forging out of the mold; ② Uneven force during edge cutting; ③ The cooling rate of each local area during forging cooling varies; ④ Improper liquidation and heat treatment.
