Research On Ultrasonic Testing Of Porous Defects In The Center Of Steel Ingots Based On Pore Features

As an upstream industry in the production of large forgings,the quality of steel ingots directly affects the subsequent production forging process and even the quality of finished steel products.For a long time,due to the difficulty of detection technology and other reasons,steel ingots have been entering the follow-up production link under the condition of unknown internal defects.Due to the lack of complete quality standards for steel ingots,the forging process is almost entirely based on the accumulation of experience or data from relevant literature,there is no exact basis for the removal of steel ingot risers and nozzles,and the utilization rate of steel ingots is low.Therefore,it is of great significance to detect internal defects of steel ingots by means of ultrasonic non-destructive testing,so as to realize the positioning,quantification and qualitativeness of defects.Using A-type ultrasonic testing technology pulse reflection method combined with direct contact method,defect detection of 42 Cr Mo die-casting ingot,ultrasonic detection waveforms at different height positions are obtained,and three-dimensional reconstruction of internal defects of steel ingots is completed by contour imaging method.The results show that there is a large amount of scattered noise in the echo signal,and the defect echo has different shapes,manifested in multiple aspects such as amplitude,root width,symmetry,and whether there are sharp peaks.The defects are distributed in a volume in the space,and the basic position is the axis.It is close to the riser end and radially close to the center.By constructing the echo model of ultrasonic detection,the traditional EMD noise reduction method and the improved EMD noise reduction method are used to simulate and analyze the noise reduction of the echo model.The simulation results show that the combination of EMD and db3 wavelet is adopted,the wavelet decomposition level is 4layers,and the maximum and minimum criterion threshold is selected as the threshold to obtain the optimal noise reduction effect.The simulation results are applied to the noise reduction of the echo signal of steel ingot defects,and the noise reduction effect is obvious.Obtain the actual defect distribution inside the steel ingot through low-power inspection.The internal defects of the steel ingot appear to be loose in the center,and the actual defect length and width range are larger than the ultrasonic detectable area.The shape of defects presents two types: diffuse and aggregated strips.The echo signal of dispersive defects is greatly affected by porosity,and the echo signal of aggregate strip defects is greatly affected by its morphological characteristics.By extracting the characteristic parameters of the defect echo,the relationship between the signal and the center porosity is analyzed.It reveals that the mean amplitude and kurtosis coefficient of the clustered strip center porosity in the time domain are much higher than those of the diffuse type.The loose porosity of the dispersive center is linearly related to the four parameters of the bottom width of the defect echo,the duration of the falling edge,the high frequency component and the kurtosis coefficient.Finally,based on the experimental results,a quantitative evaluation process for ultrasonic testing of loose defects in the center of the steel ingot was established.