The only forging method for large forgings is free forging. However, free forging has many unavoidable defects in elongation. Let's discuss these defects below.

1. If small steel ingots are used for production, the length of the metal material is small, and the quality risk of elongating the small round billet is greater; if large steel ingots are used, the length of the metal material is increased, and the actual utilization rate of the raw materials is low.

The mass of the forging is about 2.1×104kg. If the free forging process uses a 3.2×104kg steel ingot, it is upset to a diameter of Φ2200mm, and the billet length is 780mm. The small round billet is distributed and pulled out. The distribution length L is only 400mm according to the card table, and the elongation is partially upset, that is, the aspect ratio of the elongated length (2200/400) reaches 5.5. According to the condition of elongated length L≥0.3D, the minimum distribution length should be ≥700mm. The minimum length of the metal material should be ≥700mm. At this time, the core of the billet cannot protrude, resulting in shrinkage folding defects; at the same time, the ingot water inlet deposits cannot be effectively squeezed, resulting in dense defects in the forgings. Defects exceeding the standard are equivalent to scrapping. Therefore, the free forging process must use larger ingots, and the raw material utilization rate is reduced to 40%-50%. The actual economic benefits are difficult to benefit the people who have escaped poverty.

2. A large number of blanks are discharged at the transition angle, causing the actual size of the forging to exceed the deviation in the process requirements.

Due to the step difference between the diameter of the flange and the shaft parts, the metal material is unevenly distributed after the free forging process is carded, the small circle of the forging is elongated, and the step transition is subjected to tensile stress. A large number of blanks are accumulated at the position where the flange transition angle is larger, and due to uneven deformation, the surface of the inner end of the flange is uneven, which affects the subsequent processing size and needs to increase the length processing allowance, resulting in the actual quality of the forging blank exceeding the process requirements by more than 20%, and the economic benefits are poor.

3. The shape of the forging is difficult to control.

If the free forging is improper, the small circle and the flange are prone to serious eccentricity, resulting in the need for multiple alignments in the diameter direction in subsequent processing, or even scrapping due to failure to meet the size requirements.

4. If the small circle cannot be forged during heating, it needs to be reheated in the furnace.

The diameter of the flange has no trimming margin, and repeated furnace heating causes the grains of the flange to coarsen. The ultrasonic flaw detection generates a large number of echo reflections at the grain boundary, which cannot meet the requirements of the initial sensitivity and the reduction of the bottom wave number of the ultrasonic flaw detection. The echo interference caused by the coarsening of the organization and grains makes it impossible to distinguish the defect wave.