Research On The Ultrasonic Testing Of Nodularity Of Big Gear Section Of Austempered Ductile Iron

Austempered Ductile Iron (ADI) has a good and comprehensive mechanic characteristics ofhigh intensity, high extensibility, high resilience. It also has a high flexural strength and a goodquality of abrasion resistance. Therefore, ADI is being emphasized by the field of engineersdomestic and abroad. With the increasing output of ADI cast, its quality testing and control isbeing paid attention to and emphasized by engineers.Under certain circumstances, the linear relation between spheroidization rate of ADI andlongitudinal wave sound velocity is proved correctly. However, when used in the processing, theultrasonic testing of spheroidization rate still stays at the level of specimen (test block) testing.And because of the peculiarity of constitution structure and chemical composition of ADI,various raw material, melting equipment and the difference of processing in different factoriescause the application of ultrasonic testing of ADI spheroidization rate to be still in the elementarystage.This dissertation shows that the transmission of ultrasonic wave in ductile iron cast meetsdifferent shapes of graphite. Different sound velocity and density of graphite and matrix causedifferent acoustic impedance. So it causes a part of sound waves reflected, thus the energy oftransmission wave reduces, and decaying wave increases. Because the sound velocity anddecaying waves constitute inverse proportion, so the velocity reduces. Under certain volume ofgraphite, the higher the spheroidization rate is, the smaller its surface area is. The smaller thegraphite scatters the sound wave, the lethargy becomes smaller and the sound velocity ofultrasonic waves also becomes smaller. Because the phase components of the matrix is different,under the same circumstance of spheroidization rate, the sound velocity has obvious differenceunder different cast constitution and austempered constitution. When there is more ferrite andless cementite, the decaying wave of ultrasonic wave becomes smaller and the sound velocitybecomes higher; when there is less ferrite and more cementite, because of the reflection by cementite to ultrasonic wave strengthens, decaying wave becomes bigger and the sound velocitybecomes lower. Through research, by building the linear relation between ADI spheroidizationrate and ultrasonic velocity, one can get fitting equation, and compare and analyze the results ofontology ultrasonic testing and Ontology anatomical metallographic evaluation. The researchshow that the fitting equation is effective and it can meet the demand of production.