The following defects are usually caused by improper forging process: 

1. The large grain size is usually caused by high initial forging temperature and insufficient deformation degree, or high final forging temperature, or deformation degree falling into critical deformation zone. When the deformation temperature of high temperature alloy is too low, the mixed deformation structure may be formed with coarse grains, which will reduce the ductility and toughness of the forgings and fatigue property. 

2. Grain inhomogeneous grain inhomogeneous means that the grain in some parts of the forgings is very coarse, but in some parts it is small. The main reason for the non-uniformity of grain is that the non-uniformity of deformation in different parts of the billet causes the non-uniform degree of grain breakage, or the degree of local deformation falls into the critical deformation zone, or the local work hardening of the superalloy, or quenching heating when the local grain size coarse. Heat-resistant steels and superalloys are particularly sensitive to grain inhomogeneity. The non-uniformity of grain will obviously reduce the endurance and fatigue properties of the forgings.

 3. The softening due to recrystallization may not keep up with the hardening due to deformation due to low temperature or too fast deformation speed, and too fast cooling after forging, thus, the cold deformation microstructure is still retained in the hot forging part. The presence of this microstructure increases the strength and hardness of the forgings, but decreases the plasticity and toughness. Severe cold hardening may cause cracking.

 4. The crack is usually caused by the existence of large tensile stress, shear stress or additional tensile stress during forging. The cracks usually occur at the position with the highest stress and the thinnest thickness of the billet. If there are micro-cracks on the surface and inside of the billet, or if there are defects in the structure of the billet, or if the improper hot-working temperature reduces the plasticity of the material, or if the deformation speed is too fast or the degree of deformation is too large, exceeding the allowable plastic pointer of the material, etc. , then in the removal of thick, elongate, punching, expanding, bending and extrusion processes may produce cracks. 

5. The crazing is a shallow crazing on the surface of the forgings. Such defects are most likely to occur on surfaces subject to tensile stress in the forging process (e. g. , non-filled projections or bending) . The internal causes of cracking may be various: (1) there are too many fusible elements such as Cu and Sn in the raw materials. 2 when the steel is heated for a long time at high temperature, the surface of the steel has copper precipitation, coarse grain, decarburization, or the surface which has been heated several times. The sulfur content of the fuel is too high, and the surface of the steel material is sulphurized.

 6. Flash crack Flash crack is a kind of crack on parting surface during die forging and trimming. The reason of Flash CRACK MAY BE AS FOLLOWS: (1) in die forging operation, the metal flow is so strong as to produce the phenomenon of rib piercing. Magnesium alloy die forging edge cutting temperature is too low, copper alloy die forging edge cutting temperature is too high. Kill. Parting surface crack is the crack along the parting surface of forgings. There are many non-metallic inclusions in the raw materials, and the die surface cracks are often formed when the die forging flows toward the parting surface and remains of the concentrated or shrunk pipe are squeezed and flanged during the die forging. 

8. Folding is the process of metal deformation has been oxidation of the surface of the metal together to form the convergence. It can be formed by the confluence of two (or more) metal convection, or by the rapid mass flow of a metal with adjacent parts of the surface metal flow, the combination of the two formed; It can also be caused by the bending and backflow of the deformed metal, or by the partial deformation of one part of the metal being pressed into another. Folding is related to the shape of raw material and blank, the design of die, the arrangement of forming process, lubrication and the actual operation of forging. The folding not only reduces the bearing area of the part, but also becomes the fatigue source because of the stress concentration. 

9. Through-and-through flow is a form of improper distribution of streamline. In the cross-flow region, the streamline originally distributed at a certain angle join together to form the cross-flow, and the grain sizes inside and outside the cross-flow region may be quite different. The cause of cross-flow is similar to that of folding. It is formed by the confluence of two metals or one metal with another, but the metal of the cross-flow part is still a whole. The mechanical properties of the forgings are reduced by cross-flow, especially when the grain difference between the two sides of the cross-flow zone is very large. 

10. The irregularity of streamline distribution of forgings refers to the phenomena of streamline cutting off, reflow, eddy current and so on. If the die design is improper or the forging method is not reasonable, the preform blank streamline is disordered, and the metal flow is uneven due to the improper operation of the workers and the wear of the die, the streamline distribution of the forgings is not smooth. 

The flow line is not smooth will make all kinds of mechanical properties reduced, so for important forgings, there are requirements of flow line distribution. Kill. The residual casting structure mainly occurs in the forgings using ingots as billets. As-cast microstructure mainly remains in the difficult deformation zone of forgings. Insufficient forging ratio and improper forging method are the main reasons for the formation of residual casting structure. The retained structure in casting can degrade the properties of forgings, especially the impact toughness and fatigue properties. 

12. Carbide segregation grade not conforming to requirements carbide segregation grade not conforming to requirements mainly occurs in ledeburite tool and die steels. The main reason is the uneven distribution of carbides in the forgings. The main reason for this defect is that the carbide segregation of raw material is poor, and the forging with this defect is easy to overheat and crack when heat treatment is quenched. Made of cutting tools and mold easy to use, and so on.

 13. The banded structure the banded structure is a kind of structure in which the ferrite and pearlite, ferrite and Austenite, ferrite and Bainite, ferrite and martensite are distributed in a banded form in the forgings, they are mostly found in sub-co-folded steels, austenitic steels and semi-martensite steels. The banded structure produced by forging deformation in the case of two-phase coexistence can reduce the transverse plasticity index, especially the impact toughness. It is easy to crack along the ferrite zone or the junction of two phases when forging or parts are working.

 14. Local inadequate filling local inadequate filling mainly occurred in rib, convex corner, corner, fillet parts, size does not meet the drawing requirements. The causes may be: 1 low forging temperature, poor metal fluidity, 2 insufficient equipment tonnage or hammer force, 3 unreasonable design of blank die, blank volume or section size unqualified; 4 Die bore to deposit oxide scale or weld deformed metal. 

15. Under-pressure and under-pressure refers to the general increase in size perpendicular to the parting direction, the reason may be: 1 forging temperature is low. 2 The equipment tonnage is insufficient, the hammering force is insufficient or the hammering frequency is insufficient. 16. Offset offset offset is the displacement of the upper part of the die face of the forging relative to the lower part. The causes may be: 1 The clearance between the slider (Hammer) and the guide rail is too large; 2 the forging die design is not reasonable, the lack of offset force of the locking or guide pillar; 3 the die installation is not good. Kill. Axis bending forgings axis bending, and plane geometric position error. The reasons may be as follows: 1 The forging is not careful when it leaves the die, 2 the stress is not even when it cuts the edge, 3 the cooling speed of each part of the forging is different when it cools, 4 the cleaning and heat treatment are not proper. 

Source: Learn a little heat treatment every day