Technical conditions for large shaft forgings

The technical conditions of large shaft forgings, for conventional forging, the role of forging to be completed in stages.
The first stage: the casting tissue is mainly broken thoroughly, in order to meet the requirements of mechanical properties, especially Ak value, is very sensitive, so it is not allowed to retain the casting tissue. This stage is achieved by a single or two upset drawing.
The second stage: completely forging the internal pore defects, strictly preventing the initiation of new cracks inside, in order to meet the technical requirements of ultrasonic testing.
The third stage: the forging method (controlled forging) controlling the thermodynamic parameters is used to control the generation of mixed crystals.
The second stage has the functions of the first stage, but the first stage may not meet the requirements of the second stage; The third stage must have the effect of the first stage, the second stage cannot meet the requirements of the third stage at all.
In the whole forming process of shaft forgings, only the optimization and combination of new forging technology theory and technology can make the deformation mechanism of each stage get the best coordination. The main points are:
1) At every moment of forging deformation, the internal tensile stress should be avoided or reduced, and the occurrence of bi-directional tensile stress should be eliminated.
2) In the deformation stage dominated by breaking casting structure, conical plate forging and new FM forging method can be adopted (not only the anvil width ratio W/H is used to control the axial tensile stress in the center of the blank deformation zone, The material width ratio B/H is used to control the transverse tensile stress in the center of the blank deformation area, and the forging method of using ordinary flat anvil on the top and large platform on the bottom) or LZ forging method (flat anvil drawing process with material width ratio B/H and anvil width ratio W/H to control the internal quality of the forging).
3) In the deformation stage dominated by internal pores, it should be completed in one drawing. New FM forging method or LZ forging method can be adopted for drawing, and JTS method can be added in the middle, and it is not allowed to have flat coarse deformation after JTS compaction.
4) The drawing length method should first choose LZ forging method to check, such as the anvil width ratio W/H is too small to meet the requirements, then choose a new FM forging method. Whether LZ forging method is used or new FM forging method is used, the reasonable matching of width ratio W/H, width ratio B/H and reduction ratio △H/H should be strictly controlled. JTS forging process can be used in forging processes of 300 MW and above.
5) When the blank is heated in the main deformation stage, the initial forging temperature should reach 1250 ~ 1270℃, and enough holding time should be guaranteed to facilitate segregation diffusion and ensure the uniform temperature of bad material.
6) The square section blank is transformed into a round section blank, which is allowed to be pressed into octahedral body by flat anvil. The rest of the forming process should be completed by the upper and lower V-shaped anvil of 120° or 135°.
7) To eliminate mixed crystal controlled forging, high temperature stop forging or low temperature stop forging process can be adopted.
In the conventional forging process of large shaft forgings, the problem is that the role of the previous process may be eliminated or weakened by the subsequent process. Therefore, the conventional forging technology should be reformed according to the newly developed forging technology theory -- the function of forging should be completed in stages, that is, to solve the problems of different contents in different stages with clear objectives. In this way, time saving, labor saving and good quality can be achieved.
It is possible to make the deformation mechanism of each stage get the best coordination by using the newly developed technology such as cone upsetting, LZ forging or FM forging which controls the material width ratio B/H and anvil width ratio W/H simultaneously, and forging which controls the thermodynamic parameters.