Forging of titanium and titanium alloy forging (bottom)
Forging of titanium and titanium alloy forging
There are several points worthy of our attention for the initial forging:
1. Selection of initial forging temperature: The initial forging temperature should be selected from 150 to 250 °C above the a+B/B transition temperature (phase transformation point), at which time the as-cast microstructure is the highest.
2. When starting to forge, you should first hit the hammer with a light hammer to change the ingot, and then increase the amount of deformation. The amount of reduction is large, so that the cast structure is not prone to cracks. If you start with a heavy hammer, it is easy to cause serious unevenness of the internal structure, which is prone to cracks. However, the amount of deformation of the blank is small, and in the repeated forging operation, cracks are generated due to a serious unevenness in the center portion of the material and the surface.
3. If it is free forging with a hammer, it is necessary to pay attention to the thermal effect temperature rise problem, because the internal deformation heat generated by the hammer impact causes the local temperature to rise, resulting in uneven tissue.
4. It is necessary to change the forging axis several times, change the facet and angle, and avoid the sharp angle generated during the forging process. Because the acute angle cooling speed is fast, the internal crack of the blank may occur.
5. According to the specified standard of the contract of supply, the number of extractions is reasonably selected. For example, ASM4928 is different from ASTM348. The ASM4928 standard requires that there should be no continuous mesh a organization, that is, the original grain boundary cannot be retained. Many times the drawing process, otherwise the grain boundary is difficult to eliminate.
6. The upper and lower anvils used in forging are preferably preheated to about 300 °C. When the upsetting is performed, the metal flows along the contact surface, and the deformation is relatively uniform, so that the deformation amount can be increased.
7. Since the temperature at which the titanium ingot is heated is very high, in order to avoid the adhesion of the blank to the anvil surface, it is timely to sprinkle some talcum powder on the anvil surface.
8. In order to completely break the mesh of the Wei's organization, in the case of production conditions, the forged billet will be quickly after the final forging of each fire in the blanking process or after the final fire forging. Put into cold water, through the chilling conditions, the mesh breakage is more complete, the structure is more uniform and fine, the principle is that the forged chill is forged by the forged crushed mesh and the tissue is less than recrystallization and polymerization, and the forging blank is not water-cooled. At a high temperature, the energy provided by the internal heat of the Weissite grain boundary will also grow and reduce the effect of forging the broken grain boundary. Water cooling can also effectively eliminate the segregation of some metal elements, so water cooling is a good method. Many places of forging use this process, the purpose is to get a better organizational shape. Of course, in the chilling process, it is necessary to prepare a larger container, and at the same time, it is also necessary to pay attention to production safety and prevent burns.
In the selection of forging equipment, of course, the press is preferred, especially the blank forging press has the advantage that the forging hammer is incomparable. (1) The forgeability is much stronger, because the tonnage of the press is often more than 1000 tons, The amount of reduction in each forging process is much greater than the depth of the forging hammer. Although the speed of the press is slow, the deformation is easier. (2) The temperature rise of forging is small, because the speed of the press is not fast, it will not cause the local temperature rise difference and cause serious imbalance of the structure, and also reduce the chance of internal cracks.
Compared with hydraulic forging, the forging hammer forging speed is much faster than that of the hydraulic press. In the forging process, the speed and weight of the forging must be controlled to ensure the proper temperature of the forging and high processing plasticity.
Forging of hydraulic presses, the temperature rise of forgings is very small, and the processing and recrystallization of metal can be mostly completed, but the speed of the hydraulic press is slower and slower. It is reasonable to grasp the amount of pressing each time, shorten the forging time as much as possible, and reduce the temperature drop.
In forging, we often alternate the upsetting and lengthening. The purpose is to change the axis of the blank during the forging process, so that the internal organization is as uniform as possible. What are the characteristics of the upsetting and lengthening? Let me talk about upsetting.
What is the upsetting, in the forging deformation, the process of increasing the height of the blank and increasing the cross section is upsetting.
The purpose of upsetting is:
a. Increasing the degree of destruction of the as-cast structure, that is, trying to destroy the coarse grain boundary of the as-cast structure, making it an intermittent state, and cannot be connected into a whole ring.
b. In order to make the elongation of the upset have a large deformation ratio, increase the forging ratio of the forging, in order to facilitate a more complete change of the internal metallographic structure.
c. In order to make the internal metallographic structure uniform, it is necessary to constantly change the axis of the blank. Each time it is roughed, it is to change the axis once.