Valve castings occur in 9 big flaws, do you know why?

1, the valve body pores

This is the metal solidification process can not escape the gas left in the metal inside the formation of small holes, the smooth wall, containing gas, the ultrasound has a high reflectivity, but also because it is basically spherical or ellipsoid, That is, point-like defects, affecting its reflection amplitude. The stomata in the ingot is crushed into an area defect by forging or rolling and is advantageous for detection by ultrasonic testing.

2, shrinkage and loose

Casting or ingot cooling solidification, the volume to shrink, in the final part of the solidification because of the lack of liquid metal can form a hollow-like defects. Large and concentrated voids are called shrinkage holes. Small and scattered voids are called loose, and they are usually located in the final 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 is inevitable, but with the processing process different methods have different shapes, sizes and locations, when it extends to the casting or ingot body becomes defective. In the case of billet forging, the ingot will become the residual shrinkage (shrinkage residual, residual shrinkage) if it is not removed from the forging.

3, slag

The slag in the smelting process or the refractory on the furnace furnace is exfoliated into the liquid metal and is entrained in the casting or ingot body during casting to form a slag defect. The slag is usually not present in a single state, often in a dense state or dispersed in different depths. It is similar to volume-type defects but tends to have a certain degree.

4, mixed with

 (Such as oxides, sulfides, etc.) in the smelting process - non-metallic inclusions or additives of certain components of the metal component are not completely melted and remain in the form of metal inclusions such as high density, high melting point components - tungsten , Molybdenum and so on.

5, casting segregation

The segregation in the casting or ingot mainly refers to the segregation of the components formed during the melting process or the melting of the metal due to the uneven distribution of the composition. The mechanical properties of the segregated areas are different from those of the whole metal matrix. The difference is beyond the allowable standard The scope becomes a defect.

6, casting cracks

Cracks in the casting are mainly due to the fact that the shrinkage stress of the solidification of the metal is more than the ultimate strength of the material. It is related to the shape design and casting process of the casting and the cracking of the metal material. (Such as hot brittleness when the sulfur content is high, cold brittleness when the phosphorus content is high, etc.). In the ingot will also produce axial intergranular cracks in the subsequent billet forging if not forging, will remain in the forging to become the internal crack forging.

7, cold separation

This is a unique delamination defect in the casting, mainly related to the casting process design of the casting, which is caused by splashing, tumbling, casting interruption, or two (or multiple) ) Metal flow and other reasons, because the liquid metal surface formed by the semi-solid film to stay in the casting body to form a diaphragm-like area-type defects.

8, turning skin

This is the steel from the ladle to the ingot casting ingot, because pouring interruption, pause and other reasons, the first pouring of liquid metal surface in the air quickly cooled to form an oxide film, in the continued pouring of new liquid metal into the Breaking through the ingot into the ingot and the formation of a layered (area type) defects, it is in the subsequent steel ingot billet forging can not be forced to eliminate.

9, anisotropy

When the casting or ingot is cooled and solidified, the cooling rate from the surface to the center is different, resulting in different crystal structures, exhibiting anisotropy of mechanical properties, and leading to anisotropy of acoustic properties, The surface has a different sound velocity and sound attenuation. The presence of this anisotropy will adversely affect the size and location of the defect when evaluating the ultrasonic inspection of the casting.

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