Industry knowledge :What are the main characteristics and causes of common forging defects?

Release time:

09 Mar,2023

1The main features: improper processing of die forging will cause surface roughness and scale scar. When forging austenitic and martensitic stainless steel, it is easy to produce such rough scale scar. Reasons as followsUneven lubrication or improper selection of lubricating oil types and poor quality of lubricating oil can cause local mucous membranes.

2. Error defect

Main features: The upper part of the die forging is dislocated along the parting surface relative to the lower part.

Cause: There is no balance dislocation lock on the forging die, or the die forging is installed incorrectly, or the gap between the hammer head and the rail is too large.

3, insufficient forging defects

Main features: The size of the die forging increases in the direction perpendicular to the parting surface. When the size exceeds the size specified in the drawing, there will be insufficient die forging.

Reasons: large size, low forging temperature, excessive wear of the mold cavity, etc., will lead to insufficient pressure or excessive resistance of the flash bridge, insufficient equipment tonnage, and excessive billet volume.

4. Local filling is insufficient

Main features: mainly occurs in the rib of the die forging, convex dead Angle, etc., and the top of the filling part or the edge of the forging is not filled enough, so that the forging outline is not clear

Reasons: Unreasonable design of preforming cavity and billet cavity, small tonnage of equipment, insufficient heating of billet and poor metal flow may lead to the defect.

5, casting structure residue

Main features: If there is residual casting structure, the elongation and fatigue strength of the forgings are often unqualified. Because on the low-rate specimen, the flow line of the blocked part of the residual casting is not obvious, and even dendritic products can be seen, which mainly appear in the forgings using steel ingot as billet.

Reason: Due to insufficient forging ratio or improper forging method. This defect reduces the performance of forgings, especially impact toughness and fatigue properties.

6, grain inhomogeneity

Main features: Some parts of the forging grain is particularly coarse, while other parts of the grain is small, forming an uneven grain. Superalloys and heat-resistant steels are particularly sensitive to grain inhomogeneity.

Cause: Low final forging temperature leads to local work hardening of the superalloy blanks. In the process of quenching and heating, some grains grow seriously or the initial forging temperature is too high, and the deformation amount is insufficient, so that the deformation degree of the local area falls into critical deformation. The inhomogeneity of grain can easily lead to the decline of fatigue and durability.

7. Folding defects

Main features: The flow line at the fold of the low-magnification specimen is bent, and the appearance of the fold and crack is similar. If it's a crack, the flow line will be cut twice. On the high-magnification specimens, unlike the crack bottom, the oxidation on both sides is serious, and the folded bottom is blunt.

Reasons: mainly due to the rod forgings and crankshaft forgings in the drawing process is too small, the amount of pressure is too large or the anvil corner radius is too small caused. Folding defects cause oxidized surface metals to fuse together during forging.

8. Improper distribution of forging flow line

Main features: low power forging flow line reflux, eddy current, disconnection, convection and other flow line disorders.

Reasons: improper mold design, improper choice of forging method, unreasonable shape and blank size.

9. Ribbon organization

Main features: A structure in which other structures or ferrite phases in the forging are distributed in bands. It is mainly found in austenitic ferritic stainless steel, semi-martensitic steel and eutectoid steel.

Reason: This is caused by forging deformation when two groups of parts coexist. It reduces the transverse plasticity index of the material and is prone to cracking along the ferrite region or two-phase boundary.