Steel Deep Surface Defect Detection Method Based On Alternating Current Field Measurement

As the raw material of steel processing,steel plate is widely used in various fields,such as pipeline transportation,road and bridge,petrochemical industry and other industries.But in the steel plate production and other products processing and application process,it is easy to make the steel plate surface or deep surface cracks and other defects because of human factors and other external factors,which will seriously affect the performance of the steel plate and its processing products.If it can not be timely and effective detection,it may cause irreparable economic losses,and even affect the safety of people's lives,so the quality of steel plate and its processed products has become a concern of various industries.Aiming at the problem of detecting crack defects in any direction on the surface of the steel plate,a U-shaped probe-based alternating electromagnetic field detection method is proposed.This paper studies the mechanism of alternating electromagnetic field detection,establishes a mathematical model of the electromagnetic field distribution of the U-shaped detection probe on the surface of the steel plate through Maxwell's equations,and calculates the magnetic induction intensity inside the detection probe through the Biot-Savart law,using Faraday's law of induction Established a mathematical model of the distorted magnetic field and the induced voltage signal of the detection probe;Based on the principle and theoretical model of alternating electromagnetic field detection,a physical simulation model of the U-shaped probe was established using COMSOL simulation software to optimize the detection probe core structure,core size,lift-off value,excitation coil current and frequency and other parameters.Analyzed the electromagnetic field distribution on the surface of the steel plate to be inspected with or without defects,studied the influence of crack defects on the induced electromagnetic field distribution,and studied the formation mechanism of the detection signal caused by the defects by changing the conditions of the size of the defects on the surface of the steel plate;a U-shaped probe detection experimental platform was built to analyze the detection signals of steel plate cracks at different depths and perform data fitting.The experimental results and simulation are consistent with the theory.The results show that when there is no defect on the surface of the steel plate based on the alternating electromagnetic field detection technology of U-shaped detection probe,the electromagnetic field under the detection probe is uniformly distributed and in the state of electromagnetic equilibrium,and the probe has no detection signal.The detection technology can effectively detect cracks in arbitrary direction on the surface of the steel plate.For two cracks that are orthogonal to each other,the signal characteristics of the Z-axis component of the detection signal(perpendicular to the surface of the steel plate to be detected and pointing to the air)are reversed,and the deep surface cracks of the steel plate can be effectively detected with the detection depth up to 10 mm.This method effectively breaks through the limitation of the single direction of traditional alternating electromagnetic technology and provides a research basis for the detection of deeper crack defects.