The air compressor-grade impeller blades used by a feed company break during use. The installation time of the air compressor is 2 years and 3 months. The impeller is operated in a sealed factory with normal temperature. The medium inside the impeller is air. The working pressure is 0.254 net, the number of revolutions is 29650, and the flow rate is 24.1. The blade material is redundant. There was no obvious anomaly before the accident in Yucheng. In order to find out the cause of the blade fracture, the author analyzed the failure.
1 physical and chemical inspection 1.1 macroscopic inspection of the fracture failure of the macroscopic morphology of the impeller 4.
The middle arrow is the broken blade, the blade falls off along the outer edge, and there is no obvious plastic deformation at the edge of the falling part. 2 There are 8 blades in the right-hand direction of the fractured blade. The total number of blades is 17 pieces. The grinding wear is severe, the outer edge has been deformed and curled, and there are obvious grinding marks on the disk side of the impeller. 2 arrows in the middle, the other leaves are lightly damaged. The inlet surface of the fractured blade may have a plurality of point-like pits with small fires, and the distribution is irregular. 3. The gas outlet surface is not pitted. The maximum size of the pit is about the observation by a stereo microscope. The edge of the pit is clear and tidy. There are rust layers and attachments in the pit, but there is no corrosion.
In the other blades, only a pit was found in the inlet surface of the sheet.
1.2 The macroscopic inspection of the fracture is made of 5, and the fracture of the fractured impeller blade is more serious and there is no macroscopic plastic deformation. There are two sources of fracture in the fractured blade, such as the arrow as the main source of fracture, and the inlet surface of the fracture source has exactly the pit defect. In the 1st area, the fracture at the outer edge of the blade and the corner of the 3rd area is slightly rough, which is the final fracture zone; the fracture extension area is smooth and fine with the main fracture in the 2nd zone, and the pattern of the bead line is clear, with fatigue fracture characteristics=1.
1.3 Fracture microscopic examination Scanning electron microscopy was used to observe the microscopic morphology of the 5 interrupted regions. 6 is the main fault source morphology, which can be fractured and generated on the outer edge of the inlet surface of the blade and extends along the thickness of the blade wall; 7 is the shape of the extended zone, the fatigue fringing is obvious, and the fatigue fracture characteristics of the station; 8 is the fracture source morphology. The position is also at the outer edge of the blade, ie the inlet face when the impeller rotates. 9 is the final fracture zone, and the appearance of the dimple is 2.
1.4 Chemical composition analysis The chemical composition analysis was carried out on the fractured leaves. The chemical composition of the fractured leaves was consistent with the requirements of 8 butyl 2007 for 017, 44 cans.
1.5 Hardness analysis Rockwell hardness test was carried out on the fractured blade. The result was 32.0 rulers, 32.5, only 33.0 rulers, and converted to Brinell hardness of 298, 3, 3023, 306. 1. Within the technical requirements.
1.6 Metallographic examination Sampling on the fractured blade, grinding and polishing, and observing with an optical microscope. According to Ding 15612005 standard, the inclusions were evaluated as follows, the result is class 2.5, 03 microstructure is tempering chemical composition analysis result mass fraction item detection value martensite + 3 ferrite, 3 ferrite area is about 12 , mostly in the form of strips, local area density is large, there are also 8 ferrites distributed in the network state, 12.13 is the microstructure of the side of the main fault source area, 8 ferrite content is relatively, and the crack propagation direction and 8 iron The orientation of the body is distributed.
2 Comprehensive analysis of the chemical composition and hardness of the fractured blade are in line with the technical requirements of the standard 0017, 40 steel, indicating that the blade material is qualified. The macroscopic non-uniform distribution of the inlet surface of the fractured blade can be unevenly distributed. There are no signs of corrosion. According to its size and shape and only the presence of the inlet surface, it can be judged that the pit is not a corrosion hole and should be damaged. Pit, hard particles entrained in the foot gas, such as sand, hit the pit formed by the blade surface under high-speed operation and vibration state of the blade; there is no macroscopic plastic deformation at the edge of the broken door = the main fracture source is generated from the inlet surface of the blade In the injured area, the fracture is dominated by the fracture extension area. The area of ​​the termination zone is small, showing a low stress fatigue cracking feature. When the blade is subjected to external stress, its surface is subjected to large stress, and the injured pit becomes a stress concentration point, which causes the generation of fatigue crack source. In addition, the content of 8 ferrite in the microstructure of the blade accounts for about 12, and there is a requirement that the most severe field of view of the 8 ferrite content in the relatively dense area or the network of distributed steel should not exceed, and the content of 5 ferrite in the leaf. Excessive. The distribution of ferrite in the source region of the fracture is also concentrated, so it is easy to produce local microscopic plastic deformation and synergistic deformation of martensite structure in the 8 ferrite concentration zone, and promote the crack propagation.
In summary, the blade fracture is a fatigue fracture under low stress state. Therefore, the blades of the falling piece are broken first, and the remaining blades are worn and worn later.
3 Conclusion The source of blade fracture is located in the injury pit of the inlet surface. When the blade is subjected to complex alternating external stress, the blade surface is subjected to large stress, and the damage pit becomes a stress concentration zone, resulting in a higher fatigue fracture source. It will reduce the hardness and strength of the local area of ​​the blade and promote the expansion of fatigue crack.
Zhang Dong, Zhong Peidao, Tao Chunhu, and so on. Failure analysis M. Beijing defense Guo Guoqiang. Material Quality Detection and Analysis Technology 1. Beijing China
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