Forging process of barrel forgings

Barrel parts are an important type in the forging industry. With the development of China’s heavy equipment manufacturing industry, the application of large barrel parts is increasing, which provides rare business opportunities for the large free forging industry. However, due to the large weight of large barrel parts, complex process, forging process, easy to have quality problems, also brings great difficulty to forging.

Our company ordered a large barrel type part, the material is 20SiMn, the weight of the forging is 52,890kg, which needs to use 83t ingot production, the utilization rate is 63.7%. The equipment is 80MN hydraulic press with forging ratio of 3.4. The forging diagram is shown in Figure 1:

  • (1) Hardness ≥ 140HBW;
  • (2) Room temperature mechanical properties: Rm ≥ 470MPa, Rp0.2 ≥ 260MPa, A5 ≥ 16%, Z ≥ 30%, AKV ≥ 24J;
  • (3) Ultrasonic testing in accordance with ASTM A388 05.

20220505092002 15767 - Forging process of barrel forgings
Figure.1 Forging diagram

Preparation

Chemical composition

In order to better control the quality of forgings and reduce the inclusions such as S and P as much as possible within the cost allowed. The internal control chemical composition requirements are shown in Table 1.
Table.1 Chemical composition of forgings (mass fraction, %)

C Si Mn P S Cu
Standard value 0.16 – 0.22 0.60 – 0.80 1.00 – 1.30 ≤0.025 ≤0.025 ≤0.20
Internal control value 0.18 – 0.20 0.65 -0.75 1.00 – 1.20 ≤0.020 ≤0.010 ≤0.20

Smelting and process route

In order to ensure the smooth production of qualified forgings, the ingots are smelted by vacuum, vacuum pouring method to improve the purity of the steel and reduce the defects such as segregation and shrinkage of the ingots.
The process route is: electric furnace (vacuum smelting) → ingot (vacuum pouring) → hot forging plant → forging → post-forging heat treatment → inspection → non-destructive testing → mechanical properties test → rough machining → delivery.

Forging process

Analysis of the forging process

The outer diameter of forging is 2480mm, height H=1995mm. 83t ingot in our factory is actually: eight-edged, small head 1625mm, large head 1880mm, ingot body height 3155mm, ingot body weight 64830kg.
The following two process options can be used:
Option 1, according to the forging of the circle, only upsetting to the height of the forging, and then after the reaming process can be completed.
Fire 1: Pressing jaws, chamfering, drawing length to 1650mm, length about 3780mm, undercutting 1650mm×3450mm, and water spout removal 150mm.
The 2nd fire:upsetting ingot to H=2300mm, 2000mm or so, punching 850mm hole, flat end face. The 3rd to 4th fire: reaming to forging size, finishing out the finished product.
The upsetting ratio of option 1 is 1.4, and the reaming ratio is 1.2. The forging ratio is too small to meet the needs of forging performance. The forging height is too high during the second punching, so it is easy to punch off and cause scrap.
Option 2, according to the barrel forging, it is necessary to upsetting to a certain height, and then after the drawing and reaming process can be completed.
Fire 1: Pressing jaws, chamfering, drawing length to 1650mm, length about 3780mm, undercutting 1650mm×3400mm, water spout removal 200mm.
The 2nd fire:upsetting ingot to H=1000mm, 2990mm or so, punching 850mm hole, flat end face.
The 3rd to 4th fire: drawing length to about 2000mm, reaming to forging size, finishing out the finished product.
Option 2 has an upsetting ratio of 3.4 and a length-drawing ratio of 1.5, using a hollow punch to remove the bad quality of the center of the ingot, which can meet the needs of the forging performance.
Through comprehensive analysis of the above two options, it is decided to adopt the second option. In order to ensure the mechanical properties and non-destructive testing requirements of forgings, forging together the holes and looseness inside the ingot, breaking the as-cast tissue in the ingot, and obtaining good performance forgings, a large upsetting ratio and hollow punch are used.

Post-forging normal tempering process

Normal tempering is used after forging, and the process is shown in Figure 2. Through forging
The post-forging normal tempering process is used to refine the grain, eliminate the tissue stress and achieve the required mechanical properties.
Mechanical properties required.
20220505093253 91445 - Forging process of barrel forgings
Figure.2 Heat treatment process

Inspection

After normal tempering, the forgings are inspected. The length dimension is slightly oversize, the outer diameter is qualified, and the inner diameter end is cracked, but it does not affect the dimension of the part. The test is performed according to ASTM A388 05 and the result meets the requirements of the part. Scribe, rough machining, and take samples according to the drawing requirements (Figure 3). Take tangential specimens:two groups of tensile specimens (each group of one pull and three punches), two groups of axial specimens (each group of one pull and three punches). After the test, the mechanical properties meet the requirements.
20220505093512 44007 - Forging process of barrel forgings
Figure.3 Mechanical properties sampling chart

Forging defects and preventive measures

Unevenness of the end face

Uneven end face of forging is a common problem of barrel type parts, which causes waste of raw materials and increase in machining, so it is flattened as much as possible after punching and reaming.

End Cracking

There are many reasons for end cracks, such as heat conduction of the mandrel during forging and contact between the end face and air, which causes the end face temperature to decrease, and when the forging is turned back and forth, cracks will be produced under the action of stress. Therefore, forging as much as possible to forge both ends first, and then the middle part of the forging, which can reduce the degree of cracking to a certain extent [1].

Internal surface cracking

The surface of the punch or mandrel is not smooth, and small cracks are produced on the inner surface when punching, and the cracks keep expanding when the mandrel is drawn long. Therefore, we should pay attention to the smoothness of the outer diameter of the punch to reduce the generation of cracks.

Uneven wall thickness

Uneven punching, uneven heating temperature, uneven forging force and uneven operation level of workers can cause uneven wall thickness when punching. Therefore, avoid punching deviation, to ensure uniform heating temperature, forging force tends to be consistent will reduce the degree of uneven wall thickness [2].

Conclusion

By controlling the original defects of ingots through double vacuum smelting of ingots and using a reasonable process scheme, the internal quality of forgings was improved and forgings with mechanical properties and nondestructive testing were manufactured to meet the requirements.

Authors: Tingwei Ma, Nijia Ye, Yuhong Wang, Zhihua Liu, Qian Ma, Wei Liu

Source: Network Arrangement – China Forged Flanges Manufacturer – Yaang Pipe Industry Co., Limited (www.metallicsteel.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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References:

  • [1] Yong-Hong Liu. Experience of forging large long cylinders [J]. Large castings and forgings, 1998, 2:25-26.
  • [2] Ji Yong. Common quality problems and solutions of long cylinder forgings [J]. Large castings and forgings, 2008, 4:46-47.

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