Research On Nondestructive Testing Of Hot Stamping Steel With Dual Phase On Magnetic Barkhausen Effect

With the development of automobile industry,the resource and environmental problems caused by automobiles are becoming more and more urgent.As an important means of automobile energy saving and emission reduction,automobile lightweight is valued by the majority of automobile manufacturers.Hot-stamping high-strength steel,as a kind of steel with good lightweight effect and low cost,has been widely used in many cars.At the same time,some areas of the automobile need better toughness,so toughened hot stamping steel with a multiphase structure is required.Multipahse structure has a more urgent need for rapid detection.Traditional detection methods often take a long time and cause irreversible damage to parts,making it difficult to adapt to the detection requirements.In this article,a non-destructive testing method based on the Magnetic Barkhausen Effect is used to detect the dual-phase microstructure of hot stamping high-strength steel.Magnetic Barkhausen effect is a complex phenomenon produced in the process of irreversible magnetization of ferromagnetic materials.When a magnetic field is applied,the magnetic domains of the ferromagnetic material will flip toward the direction of the applied magnetic field.During the inversion process,the magnetic domain encounters the pinning inside the material to generate a magnetic noise signal,namely,Magnetic Barkhausen Noise(MBN).The MBN signal is closely related to the microstructure,stress state,and grinding damage of the material.This article mainly explores the relationship between MBN signal and the microstructure and stress state of dual-phase high-strength steel.The second chapter introduces the MBN testing instrument independently developed by the laboratory.Designed and manufactured the detection sensor,purchased other components,and developed the signal processing program,including signal denoising,time domain processing,frequency domain analysis,time-frequency analysis,etc.The third chapter studies the relationship between the martensite/bainite dual-phase structure and the MBN signal,and verifies the accuracy of MBN in detecting the martensite/bainite dual-phase specimen.The heat treatment experiment was designed and the martensite/bainite dual-phase samples of different phase ratios were produced using the Gleeble 3500-GTC.As the bainite ratio increases,the MBN signal first weakens and then increases.When the bainite content is greater than 29.97%,there is a linear relationship between the peak value,the root mean square of the MBN signal and the bainite ratio.Comparing the results of MBN detection with the the phase content obtained from the SEM photo,tensile strength and yield strength obtained from the tensile experiment,it is found that the accuracy of using MBN to detect the horse/shell dual-phase specimens is high.The fourth chapter studies the relationship between the martensite/ferrite dual-phase structure and the MBN signal,and distinguishes the effects of phase content and tensile strain on the MBN signal.Through the subcritical quenching process,martensite/ferrite dual-phase structure specimens of different phase ratios were manufactured,and the specimens were cut into equal-strength beams,and strains were applied to the equal-strength beams.It is found that both the decrease of martensite ratio and the increase of tensile strain will lead to the increase of the time-domain characteristic value of MBN signal.However,the influence of martensite ratio and tensile strain on the frequency domain is different.The tensile strain uniformly affects the entire frequency range,while the change of martensite ratio more affects the signal in the middle and low frequency bands.