Stoma
This is the metal solidification process can not escape the gas left in the metal to form a small cavity, the inner wall is smooth, containing gas, the ultrasound has a high reflectivity, but because of its basically spherical or ellipsoidal, That is, point defects, affecting the reflection amplitude. The pores in the steel ingot are forged or rolled and then flattened into area defects to facilitate the ultrasonic testing.
2. shrinkage and loose
Casting or ingot cooling and solidification, the volume to shrink, in the final part of the solidification because there is no liquid metal to be added to the formation of hollow defects. Large and concentrated hollow cavity is called shrinkage, small and scattered gaps are called loose, they are usually located in the ingot or casting center of the final solidified part of its coarse inner wall, accompanied by many around many impurities and small pores. Due to the law of thermal expansion and contraction, shrinkage is inevitable, but with different processing methods and processing methods have different shapes, sizes and locations, as it extends to the casting or ingot body becomes a defect. In the billet forging billet if not cut clean and into the forging into the residual shrinkage cavity (shrinkage cavity residual shrink tube).
3 slag
During the melting process, the refractory on the slag or the furnace body flakes into the liquid metal and is caught in the body of the casting or ingot during casting to form a slag inclusion defect. Slag usually does not exist a single, often dense or scattered at different depths, it is similar to the volume of defects, however, tend to have a certain degree of linearity.
Inclusion
Reaction products (such as oxides, sulfides and the like) - non-metallic inclusions in the smelting process, or the addition of certain components in the metal components are incompletely melted and remain as metal inclusions, such as high-density and high-melting components , Molybdenum and so on.
5 segregation
Segregation in castings or ingots mainly refers to segregation of components formed during the smelting process or metal melting due to uneven distribution of components. The mechanical properties in segregated areas are different from the mechanical properties of the entire metal matrix, and the difference exceeds the allowable standard Range becomes a flaw.
7. Cold interval
This is a unique type of delamination defects in castings, mainly related to casting process design of castings. It is caused by splashing, overturning waves, pouring interruptions or pouring of two or more strands from different directions ) Metal flow encounter and other reasons, as the liquid metal surface cooling to form a semi-solid film to remain in the casting body to form a diaphragm-like area type defects.
8 over the skin
This is the steelmaking ingot ingot ingot ingot mold from the ladle, because pouring interrupted, pause and other reasons, the first pouring liquid metal surface rapidly cooled in the air to form an oxide film, the pouring liquid pouring the newly poured liquid Break through into the ingot body and the formation of a hierarchical (area type) defects, which in the subsequent ingot billet forging can not be forged to eliminate.
Anisotropy
Casting or ingot cooling and solidification, the surface to the center of the cooling rate is different, and thus the formation of different crystalline structure, showing the anisotropy of mechanical properties, but also led to the anisotropy of acoustic properties, that is, from the center to The surface has different sound velocity and sound attenuation. The existence of this anisotropy, castings ultrasonic testing to assess the size and location of defects will have a negative impact.
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