1. The stomata
This is a small cavity formed by the gas that the metal solidification process does not escape inside the metal. Its inner wall is smooth and contains gas, which has a high reflectivity to the ultrasonic wave, but because it is basically spherical or ellipsoid, it is a point defect, which affects its reflection amplitude. The air hole in the ingot is flattened into an area defect after forging or rolling, which is beneficial to be found by ultrasonic detection.
2. Clip slag
The slag in the smelting process or the refractory on the furnace body peels into the liquid metal, and is involved into the casting or steel ingot when pouring, forming the slag clamp defect. Slag usually does not exist alone, often in a dense state or scattered at different depths, it is similar to volume defects but often has a certain linearity.
3. Casting cracks
The crack in the casting is mainly caused by the shrinkage stress of the metal cooling solidification exceeds the ultimate strength of the material, it is related to the shape of the casting design and casting process, and also related to the cracking sensitivity of some impurities in the metal materials (such as high sulfur content, cold brittleness, high phosphorus content, etc.). In the spindle, there will also be cracks in the shaft crystal, and in the subsequent billet forging, it will remain in the forging as the internal crack of the forging.
4. Turn over the skin
This is steelmaking from the ladle to the ingot casting ingot, because of pouring interruption, pause, poured into the liquid metal surface in the air rapid cooling form oxide film, new pouring into the liquid metal will break into the ingot body and form a hierarchical (area) defects, it in the subsequent ingot billet forging is not forging.
5. Anisotropy
When the casting or ingot is cooled and solidified, the cooling speed from the surface to the center is different, so different crystallization tissue will be formed, which shows the anisotropy of mechanical properties, and also leads to the anisotropy of acoustic properties, that is, there is different sound velocity and sound attenuation from the center to the surface. The presence of this anisotropy can have an adverse effect on the size and position of the assessed defects during ultrasonic detection.
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Post time: Jun-27-2024