Research on flange forging technology

This article outlines the drawbacks and problems of the traditional flange forging process, and conducts an in-depth research 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.

20220322093955 61871 - Research on flange forging technology

1. The disadvantages 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 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 the forgings and a series of bad phenomena such as wrong die.

2. Process optimization of flange forgings

2.1 Forging process control

  • (1) The control of organizational characteristics. Flange forging 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 to about 1000 ℃, you can get a more uniform austenite 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, contact between stainless steel and carbon-containing substances should be avoided. Because of the poor thermal conductivity of 1Cr18Ni9Ti austenitic stainless steel in low-temperature environment, so it needs to be heated slowly. 
  • (3) Flange forging operation process control. First of all, the specific process requirements must be strictly in accordance with the reasonable selection of raw materials for the material. Before the material is heated, the surface of the material should be thoroughly inspected to avoid cracks, folding and inclusions in the raw material. 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.

2.2 Forming method and die design

When the through diameter does not exceed 150mm, the butt weld flange can be formed by open header method. In the open die set method need to pay attention to is the height of the upsetting blank and pad die aperture d ratio is best controlled at 1.5-3.0, die hole fillet radius R is best for 0.05d-0.15d, while the height of the die H to lower than the height of the forging 2mm-3mm is appropriate. When the through diameter exceeds 150mm, it is appropriate to choose the flat ring flip extrusion forming method for flange butt welding. In the flat ring flip extrusion method need to pay attention to the height of the blank H0 should be 0.65 (H + h) – 0.8 (H + h).

2.3 Process implementation and forging inspection

This paper adopts the bar shear method and combines the use of constrained shear process to ensure the quality of the product section. Forging no longer choose the conventional open die forging forging process, but take the closed precision forging method. This method not only makes the accuracy of forging greatly improved, 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 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.

2.4 Heat treatment after forging

1Cr18Ni9Ti austenitic stainless steel flanges 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 forged 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 should be cooled rapidly to obtain a single-phase austenite structure. In this way, the stress corrosion resistance and the resistance to crystalline corrosion of the forgings will be 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 the forgings produced using this process is much higher quality.

3. Comprehensive benefit analysis

The optimized process is used to produce flange forgings, which effectively reduces the machining allowance and die slope of the forgings and saves 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 the forging waste heat tempering method, the energy required for thermal quenching is dispensed with.

4. 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 methods and optimize the production program.

Source: China Flange Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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