The common defects of steel valve castings in ultrasonic testing mainly include the following:

1、 Stomata

Definition: Pores are voids formed by residual gas inside a casting, usually spherical, ellipsoidal, or irregular in shape.

Cause: Gas fails to escape during the solidification process of metal, leaving behind small voids inside the metal.

Characteristics: The inner wall is smooth, contains gas, and has a high reflectivity for ultrasonic waves. However, due to its point like defects, it may affect the amplitude of the reflected waves.

2、 Inclusion

Definition: Inclusions refer to non-metallic substances such as oxides, sulfides, etc. that are mixed into the metal melt during the melting process.

Cause: During the smelting process, the reaction products or refractory materials on the furnace body peel off and enter the liquid metal, which is then rolled into the casting or steel ingot body during pouring.

Characteristics: Slag inclusions usually do not exist singly, but rather in a dense state or dispersed at different depths, similar to volumetric defects but with a certain degree of linearity.

3、 Shrinkage and looseness

Definition: Shrinkage is an internal cavity formed during the solidification process of a casting due to volume shrinkage, usually located in the hot center or thick part of the casting; Shrinkage refers to small and dispersed gaps.

Cause: When the casting cools and solidifies, its volume shrinks, resulting in hollow defects in the later solidified parts due to the lack of liquid metal replenishment.

Characteristics: Large and concentrated shrinkage, rough inner wall, surrounded by many impurities and small pores; Shrinkage is small and scattered.

4、 Crack

Definition: Cracks are linear defects inside or on the surface of castings, including hot cracks, cold cracks, stress cracks, etc.

Cause: The shrinkage stress during metal cooling and solidification exceeds the ultimate strength of the material, or is related to the shape design and casting process of the casting, as well as the cracking sensitivity caused by high impurity content in the metal material (such as thermal brittleness when sulfur content is high, cold brittleness when phosphorus content is high, etc.).

Characteristic: Cracks may appear in any part of the casting, which has a serious impact on the mechanical properties and service life of the casting.

5、 Incomplete fusion and incomplete penetration

Definition: Non fusion refers to the defect formed by incomplete fusion of metal melts from different parts of a casting; Incomplete penetration is a defect formed during the welding process where the weld metal has not fully melted through the base metal.

Cause: Improper casting or welding processes result in incomplete fusion of the metal melt or incomplete penetration of the weld through the base metal.

Characteristics: These defects may cause a decrease in the mechanical properties of castings or welds, and even lead to fracture.

6、 Other issues in ultrasonic testing

In addition to the common casting defects mentioned above, other problems may also be encountered during ultrasonic testing, such as delayed ultrasonic propagation, abnormal echo reception, signal interference, and probe wear. These issues may affect the accuracy of the detection results, so when conducting ultrasonic testing, it is necessary to optimize the detection environment, regularly maintain the probe, select suitable materials, record data, and take comparative measures to ensure the reliability of the detection results.

In summary, common defects in ultrasonic testing of steel valve castings include porosity, inclusions, shrinkage and porosity, cracks, and lack of fusion and penetration. To ensure product quality and safe operation, it is necessary to promptly detect and address these defects.