Forged Steel's Ultrasonic Water Immersion Flaw Detection And Three-Dimensional Imaging Technology Research

Ultrasonic flaw detection is an important method in nondestructive testing. Water immersion ultrasonic flaw detection uses water as coupling agent and the probe which does not contact the steel parts sends out ultrasonic going through the water to the steel parts to carry out detection. Based on the technology of water immersion ultrasonic flaw detection, this paper studies the water immersion vertical detection technology, the water immersion oblique incidence detection technology and the water immersion ultrasonic scanning three-dimensional imaging technology. Main contents are:(1)Discuss the selection of probe from three aspects, namely, type, size and frequency. Water immersion probes include unfocusing and focusing probe according to whether the probe focuses or not. Use these two types of probes to test two blocks,one contains three inclined flat bottom holes of different angles and the other contains multiple internal defects, results show that, unfocusing probe covers a larger space when scanning, focusing probe's sound energy concentrates better and it is not sensitive to the direction of defects. Analyze the effect of probe's size and frequency on flaw detection and find that the size and frequency chosen according to the steel thickness, defects and testing requirements must ensure the detection of minimum defects required and smaller ultrasonic attenuation. The calculation formula of focusing column's position in steel parts is obtained by theoretical analysis and calculation of the water layer thickness and its influence on focusing column in water immersion detection. By implementing water immersion vertical detection on a forged steel parts, combined with macroscopic examination, metallographic examination and scanning electron microscope test, find that using water immersion flaw detection imaging analysis function can obtain projection images and layer changes of steel internal defects in different perspective. Water immersion ultrasonic flaw detection plays a very important role in mastering defects' morphology and prejudging defects' property.(2)The defects' orientation affects the water immersion ultrasonic vertical detection and this influence is sometimes great. Use water immersion small angle longitudinal wave incidence detection method to tilt the probe a small angle to scan the block of three inclined flat bottom holes of different angles and results show that small angle longitudinal wave incidence detection reflects defects' actual morphology and equivalent size, and scanning results are less affected by defects' orientation.Adjust the probe's tilt angle between 15.4° and 22.4° and use transverse wave obtained by wave type conversion principle to scan a thin plane steel parts containing multiple deep artificial flat bottom holes, results show that detection sensitivity is the highest at this time and detection result is good. Water immersion oblique incidence detection can make up for the shortcomings of conventional vertical detection in theinspection of plane forged steel parts.(3)Develop three-dimensional imaging program of the original ultrasonic scanning software using MATLAB, import water immersion ultrasonic scanning result file into the imaging program and then it can realize imaging display, layer display in different perspective and 3D imaging. This program makes up for the deficiency of the original scanning system and it plays an important role in the analysis of the defects' morphology, position, change and so on. Fit ultrasonic DAC curve using steel parts' multiple bottom echo heights obtained by actual measurement,use this curve to carry out transmission correction of water immersion ultrasonic scanning results and it can compensate the ultrasonic attenuation and obtain more realistic defect's morphology.