Study On Nondestructive Testing Method Of Hot Rolling Steel Plate By Eddy Current And Electromagnetic Ultrasound

In recent years,enterprises have higher and higher requirements for the quality of steel plates.It is the premise to improve the quality of steel plates to find the defects in hot rolled steel plates in time and adjust the process parameters timely.In the actual demand of defect detection,a single detection method is difficult to meet the requirements of large-scale,rapid and accurate judgment and analysis of specimen defects.Electromagnetic ultrasonic detection method can be a good solution to the detection of the internal defects of hot rolled steel plate,but due to the superposition of the echo signal and the transmitted wave caused the defects of the surface of steel plate detection purposes;The eddy current testing method can detect the defects on the surface and near the surface with high precision,but due to the limitation of skin depth,it cannot effectively detect the defects in the deeply buried parts.Therefore,by combining the eddy current detection method with the electromagnetic ultrasonic detection method,a composite detection probe is designed.This method can solve the problems of surface defects and internal defects detection of hot rolled steel plate well,and improve the production quality of hot rolled steel plate.In this paper,an electromagnetic ultrasonic and near-field eddy current composite probe is designed.A 30 mm thick Q235 steel plate is taken as the test object,and a time-division multiplexing two-dimensional composite detection simulation model is established by using COMSOL simulation software.First,the parameters of the spiral coil were determined.For the iron oxide inclusion defect located in the depth of the steel plate(15-30mm)and different from the air defect,the echo displacement vibration signal was used for quantitative analysis,and the particle dynamic electric field was used for qualitative analysis.Secondly,an eddy current coil was added to detect the defects within 5mm of the depth of the steel plate by using the near-field eddy current.The eddy current detection performance of the two composite structure probes was analyzed,and the defect parameters were retrieved by using the support vector machine algorithm.For the defects in the depth of 5-15 mm of steel plate,the near field eddy current measurement range is not up to,and the electromagnetic ultrasonic detection within this range is not accurate,so the defect detection within this range becomes a difficult problem.In order to solve this problem,a simulation model of electromagnetic ultrasonic and far-field composite detection sensor with shielding structure,time-division multiplexing and shared helical coils was designed,and analyzed and studied.The depth range of the steel plate is 5-15 mm,which is the area where the electromagnetic ultrasound and the far-field eddy current work together.The characteristic signal obtained by the electromagnetic ultrasound and the coil induced voltage and impedance parameters obtained by the far-field eddy current are fused by the support vector machine of the gray Wolf optimization algorithm,and the parameters of the defect are inverted.The simulation results show that the accuracy of the designed electromagnetic ultrasonic and far-field composite coil for defect detection reaches 96.14%,and the far-field eddy current can make up for the blind spot of electromagnetic ultrasonic detection very well.In order to verify the correctness of the simulation results,low temperature experiment and high temperature experiment are designed.In the low temperature experiment,the electromagnetic ultrasonic thickness measuring instrument was used to detect the defects in different positions,and the electromagnetic ultrasonic echo signal was obtained.For the defect at the depth of 5-15 mm,the signal generator is used to excise the spiral coil and collect the signal of the far-field eddy current detection coil.The two types of data characteristics are input into the SVM model to verify the correctness of the simulation model.In the high temperature experiment,the test block was tested at 300 ?,400 ? and 500? respectively,the influence of temperature on the electromagnetic ultrasonic detection signal was analyzed,and the compensation algorithm of echo time and amplitude was given.