This article outlines the drawbacks and problems of the traditional flange forging process, and conducts an in-depth study on the process control, forming method, process implementation, forging inspection and post-forging heat treatment of flange forgings in combination with specific cases. The article proposes an optimization plan for the flange forging process and evaluates the comprehensive benefits of this plan. The article has certain reference value.

The drawbacks and problems of traditional flange forging process

For most of the forging enterprises, the main focus in the process of flange forging is on the investment and improvement of forging equipment, while the raw material discharging process is often ignored. According to the survey, most of the factories usually use sawing machines when they are used, and most of them use semi-automatic and automatic band saws. This phenomenon not only greatly reduces the efficiency of the lower material, but also has a large space occupation problems and saw cutting fluid pollution phenomenon. In the traditional flange forging process is usually used in the conventional open die forging process, the forging accuracy of this process is relatively low, the wear and tear of the die is large, prone to low life of forgings and a series of bad phenomena such as wrong die.

Process optimization of flange forgings

FORGING PROCESS CONTROL

(1) The control of organizational characteristics. Flange forging is often martensitic stainless steel and austenitic stainless steel as raw materials, this paper selected 1Cr18Ni9Ti austenitic stainless steel for flange forging. This stainless steel does not exist isotropic heterocrystalline transformation, if it is heated up to about 1000 ℃, it is possible to obtain a relatively uniform austenitic organization. Thereafter, if the heated stainless steel is cooled rapidly, then the austenitic organization obtained can be maintained to room temperature. If the organization is slow-cooled, then it is easy to appear alpha phase, which makes the hot state of stainless steel plasticity is greatly reduced. Stainless steel is also an important reason for the destruction of intergranular corrosion, the phenomenon is mainly due to the generation of chromium carbide in the grain edge. For this reason, the phenomenon of carburization must be avoided as far as possible.
(2) Strictly adhere to the heating specifications, and effective control of forging temperature. When heating 1Cr18Ni9Ti austenitic stainless steel in the furnace, the surface of the material is very prone to carburization. In order to minimize the occurrence of this phenomenon, should
Avoid contact between stainless steel and carbon-containing substances. Because of the poor thermal conductivity of 1Cr18Ni9Ti austenitic stainless steel in low temperature environment, it needs to be heated slowly. The specific heating temperature control should be carried out in strict compliance with the curve in Figure 1.

Figure.1 1Cr18Ni9Ti austenitic stainless steel heating temperature control
(3) flange forging operation process control. First of all, the specific process requirements must be strictly followed to reasonably select the raw material for the material. Before heating the material should be a comprehensive inspection of the material surface, to avoid cracks, folding and inclusions in the raw material and other problems. Then, when forging, it should be insisted to lightly beat the material with less deformation first, and then hit hard when the plasticity of the material increases. When upsetting, the upper and lower ends should be chamfered or crimped, and then the part should be flattened and struck again.

FORMING METHOD AND DIE DESIGN

When the diameter does not exceed 150mm, the butt weld flange can be formed by open header forming method with a set of dies. As shown in Figure 2, in the open die set method, it should be noted that the height of the upsetting blank and the ratio of the pad die aperture d is best controlled at 1.5 – 3.0, the radius of the die hole fillet R is best 0.05d – 0.15d, and the height of the die H is 2mm – 3mm lower than the height of the forging is appropriate.

Fig. 2 Open die set method
When the diameter exceeds 150mm, it is advisable to choose the flange butt welding method of flat ring flanging and extrusion. As shown in Fig. 3, the height of blank H0 should be 0.65(H+h) – 0.8(H+h) in the flat ring flanging method. The specific heating temperature control should be carried out in strict compliance with the curve in Figure 1.

Fig. 3 Flat ring turning and extrusion method

PROCESS IMPLEMENTATION AND FORGING INSPECTION

In this paper, the stainless steel bar shearing method is used and combined with the use of constrained shearing process to ensure the quality of the product cross-section. Instead of using the conventional open die forging forging process, the closed precision forging method is adopted. This method not only makes the forging
This method not only improves the accuracy of forging, but also eliminates the possibility of wrong die and reduces the process of edge cutting. This method not only eliminates the consumption of scrap edge, but also eliminates the need for edge cutting equipment, edge cutting dies, and the associated edge cutting personnel. Therefore, the closed precision forging process is of great significance to save costs and improve production efficiency. According to the relevant requirements, the tensile strength of deep hole forgings of this product should not be less than 570MPa and the elongation should not be less than 20%. By taking samples in the deep hole wall thickness part to make test bar and conducting tensile test test, we can get that the tensile strength of the forging is 720MPa, yield strength is 430MPa, elongation is 21.4%, and the sectional shrinkage is 37%. It can be seen that the product meets the requirements.

POST-FORGING HEAT TREATMENT

1Cr18Ni9Ti austenitic stainless steel flange after forging, pay special attention to the appearance of intergranular corrosion phenomenon, and to improve the plasticity of the material as much as possible, to reduce or even eliminate the problem of work hardening. In order to obtain good corrosion resistance, the forging flange should be effective heat treatment, for this purpose, the forgings need to be solid solution treatment. Based on the above analysis, the forgings should be heated so that all carbides are dissolved into austenite when the temperature is in the range of 1050°C – 1070°C. Immediately afterwards, the resulting product is cooled rapidly to obtain a single-phase austenite structure. As a result, the stress corrosion resistance and the resistance to crystalline corrosion of the forgings are greatly improved. In this case, the heat treatment of the forgings was chosen to be carried out by using forging waste heat quenching. Since forging waste heat quenching is a high-temperature deformation quenching, its compared with conventional tempering, not only does not require the heating requirements of quenching and quenching equipment and related operator configuration requirements, but also the performance of forgings produced using this process is much higher quality.

Comprehensive benefit analysis

The use of the optimized process to produce flange forgings effectively reduces the machining allowance and die slope of the forgings, saving raw materials to a certain extent. The use of saw blade and cutting fluid decreases in the process of forging, which greatly reduces the consumption of materials. With the introduction of forging waste heat tempering method, eliminating the energy required for thermal quenching.

Conclusion

In the process of producing flange forgings, the specific process requirements should be taken as the starting point, combined with modern science and technology to improve the traditional forging method and optimize the production plan.