1.Porosity
This is a small cavity formed by the gas that does not escape during the solidification process of the metal, which has a smooth inner wall, contains a gas, and has a high reflectance to the ultrasonic wave, but because it is substantially spherical or ellipsoidal, It is also a point defect that affects its reflection amplitude. The pores in the ingot are crushed into area-type defects after forging or rolling to facilitate the detection by ultrasonic testing.
2. Shrinkage and looseness
When the casting or the ingot is cooled and solidified, the volume is contracted, and a void-like defect is formed in the final solidified portion because the liquid metal is not replenished. Large and concentrated cavities are called shrinkage cavities, and small and scattered cavities are called loose. They are generally located in the last solidified part of the ingot or casting center. The inner wall is rough and surrounded by many impurities and fine pores. Due to the law of thermal expansion and contraction, shrinkage cavities are inevitable, but have different shapes, sizes and positions depending on the processing method, and become defects when they extend to the casting or ingot body. If the steel ingot is cut into the forging after the blank forging, it will become a residual shrinkage hole (recession of the shrinkage hole, residual shrinkage pipe).
3. Slag inclusion
The slag in the smelting process or the refractory material on the furnace body is peeled off into the liquid metal, and is entangled in the casting or the steel ingot body during casting to form a slag inclusion defect. The slag inclusions usually do not exist singly, tend to be dense or dispersed at different depths, and they are similar to volumetric defects but tend to have a certain degree of linearity.
