The defects caused by improper titanium forging process are usually as follows
1. The large grain size
Large grains are usually caused by high initial forging temperature and insufficient deformation degree, or high final forging temperature, or deformation degree falling into critical deformation zone. The deformation degree of aluminum alloy is too large and the texture is formed. If the deformation temperature of superalloy is too low, the formation of mixed deformation structure may also lead to the formation of coarse grains, which will reduce the plasticity and toughness of the forgings and the fatigue performance.
2. Uneven grain size
Grain inhomogeneity means that some parts of the forgings have extremely large grains, while others have small grains. The main reasons for the non-uniform grains are that the uneven deformation of the billet makes the grain breakage degree different, or the deformation degree of the local area falls into the critical deformation zone, or the local work hardening of the superalloy, or the local coarse grains during quenching and heating. Heat resistant steel and superalloys are particularly sensitive to grain inhomogeneity. The durability and fatigue property of the forgings will be decreased obviously due to the inhomogeneous grain.
3. Cold hardening
During deformation, due to low temperature 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 some cold deformed structures are still retained inside the forging after hot forging. The presence of this tissue improves the strength and hardness of the forgings, but reduces the plasticity and toughness. Severe coldness may result in forging.
Crack in 4.
Cracks are usually caused by tensile stress, shear stress or tensile stress during forging. The crack usually occurs in the area with the greatest stress and thinnest thickness of the billet. If there are microcracks on the surface and inside of the blank, or microstructure defects in the blank, or improper thermal processing temperature reduces the plasticity of the material, or the deformation speed is too fast, the deformation degree is too large, exceeding the allowable plastic pointer of the material, etc., then cracks may occur in the procedures such as coarse, drawing, punching, reaming, bending and extrusion.
Cracks in 5.
The crack is a shallow turtle crack on the forging surface. Such defects are most likely to occur on surfaces that are subjected to tensile stresses during forging formation (for example, unfilled projections or bent parts). The internal causes of cracking may be various: the raw materials combined with Cu, Sn and other fusible elements are too much. (2) high temperature for a long time heating, steel surface copper precipitation, surface grain coarse, decarburization, or after many heating surface. (3) too high fuel sulfur content, sulfur permeate the surface of steel.
6. Flying edge crack
Flying-edge crack is a crack that occurs at the parting surface during die forging and cutting. The causes of flying-edge cracks may be as follows: (1) In the die forging operation, the metal flows strongly due to the impact of the phenomenon of perforation. Too low cutting temperature of magnesium alloy die forgings; The cutting temperature of copper alloy die forging is too high.
7. Crack on parting surface
The crack of parting surface is the crack along the parting surface of forging. There are many non-metallic inclusions in raw materials, and the parting surface cracks are often formed when the flow to the parting surface and the concentrated or shrinkage tube remains are squeezed into the flying edge during die forging.
Folding is the confluence of surface metals that have been oxidized during metal deformation. It may be formed by the convergence of two (or more) strands of metal convection; It can also be formed by the confluence of a large and rapid flow of a metal to the adjacent part of the surface metal with the flow; It can also be caused by bending and backflow of the deformed metal; It can also be caused by partial metal deformation and being pressed into another part of the metal. Folding is related to the shape of the raw material and blank, the design of the die, the arrangement of the forming process, the lubrication condition and the actual operation of forging. Folding not only reduces the bearing area of the part, but also tends to be a source of fatigue due to the stress concentration here.
Cross - current is a form of improper distribution of streamlines. In the cross - flow area, the streamlines which originally distributed at certain Angle converge to form the cross - flow, and the grain size outside the cross - flow area may differ greatly. The reason of cross flow is similar to folding. It is formed by the confluence of two metals or one metal with the other, but the metal in the cross flow part is still a whole. Cross flow reduces the mechanical properties of the forging, especially when the grains on both sides of the cross flow zone are significantly different.
10. Forging streamline distribution is not correct
Improper distribution of flow line of forging means that flow line disruption, reflux, eddy and other flow line disorders occur at low times of forging. If the die design is improper or the forging method is not reasonable, the flow line of the prefabricated blank is disordered; Improper operation by workers and uneven flow of metal due to die wear can make the flow line distribution of forging unfavourable. The non - streamline will reduce the mechanical properties, so the important forgings have the requirement of streamline distribution.
11. Casting tissue residue
The residual casting structure is mainly found in forgings made of ingots as billets. The as-cast structure mainly remains in the difficult deformation area of forgings. Inadequate forging ratio and improper forging method are the main causes of casting tissue residue. Casting tissue residue will degrade the performance of forging, especially the impact toughness and fatigue performance.
12. Carbide segregation grades do not meet requirements
The discrepancy of carbide segregation grade is mainly found in Lyxtonian mold steel. The main reason is that the distribution of carbide in forgings is not uniform, and it is distributed in large masses or in network. The main reasons for this defect are poor grade of carbide segregation of raw materials, insufficient forging ratio or improper forging method during forging. Forgings with this defect are prone to local overheating and cracking during heat treatment and quenching, and the made cutting tools and molds are prone to collapse when used.
13. Banded structure
The banded structure is a kind of structure with banded distribution in forgings of ferrite and pearlite, ferrite and austenite, ferrite and bainite, ferrite and Martensite, which are mostly found in subeutectic steel, austenite steel and semi-martensite steel. This kind of structure is the banded structure produced when forging deformation under the condition of two-phase coexistence, which can reduce the transverse plastic pointer of the material, especially the impact toughness. It is easy to crack along the ferrite belt or the junction of two phases in forging or part work.
14. Insufficient partial filling
Local filling shortage mainly occurs in rib rib, convex corner, corner and rounded corner, and the size does not meet the requirements of the drawing. The reasons may be: Low forging temperature, poor metal fluidity; (2) insufficient tonnage of equipment or insufficient hammer force; (3) The billet die design is not reasonable, billet volume or section size is not qualified; The oxide scale or welded deformed metal is piled up in the mold chamber.
15. Under voltage
Under pressure refers to the direction perpendicular to the parting surface of the size generally increased, the cause may be: low forging temperature. (2) Insufficient equipment tonnage, insufficient hammer force or hammer times.
16. Wrong move
Dislocation is the displacement of the forging along the upper part of the parting surface relative to the lower part. The reasons may be: (1) the clearance between the slider (hammer head) and the guide rail is too large; (2) Unreasonable design of forging die, lack of lock or guide post to eliminate the wrong shifting force; (3) Poor mold installation.