Application of Ultrasonic Testing Technology on Large Ductile Iron Castings

Ultrasonic waves are widely used for the detection of the intrinsic quality of metal products due to their characteristic acoustic characteristics such as self-reflection, refraction, and diffraction. The graphite in the ductile iron is distributed in the matrix in a spherical shape. Due to the difference in the spheroidization of the graphite balls, different ultrasonic characteristics are exhibited when the intrinsic quality of the ductile iron parts is detected by ultrasonic technology, so that the ductile iron parts, especially the large ductile irons. Ultrasonic testing technology has become a difficult problem in current nondestructive testing technology.

In view of the ultrasonic testing technology of large ductile iron castings, the author summarizes the indirect evaluation method of spheroidization rate and the typical waveform characteristics of defects such as looseness, shrinkage, shrinkage and inclusions, and realizes the ductile iron castings. The determination of the intrinsic quality condition.

I. Indirect evaluation of spheroidization rate and waveform characteristics of typical defects

1. Indirect assessment of spheroidization rate

Due to the difference in spheroidization process and casting sequence, the spheroidization effect of the molten iron is different, so that the spheroidization rate of the ductile iron castings is different, thereby directly affecting the reflection waveform of the ultrasonic waves. Under normal circumstances, when the spheroidization rate is low, the ultrasonic shape is displayed in a coarse crystal waveform, and there is no obvious bottom surface reflection wave.

In the actual test, the spheroidization of the ductile iron casting can be roughly determined according to the attenuation coefficient of the acoustic wave in the ductile iron casting and the acoustic wave propagation velocity. The smaller the attenuation coefficient value is, the higher the acoustic wave velocity is, the higher the spheroidization rate is. On the contrary, the larger the attenuation coefficient value is, the lower the spheroidization rate is.

2. Waveform characteristics of typical defects

Please refer to the attachment for more details: