Research On Utrasonic Nondestructive Testing Methodology Of Hydrogen Damage Materials

Hydrogen corrosion of metal material caused by hydrogen damage will lead to"lagging damage" such as brittle fracture, in which, delayed fracture occurs under theinfluence of static stress below the yield strengths of material. Due to that it happenssuddenly and unpredictably, such failure mode is extremely dangerous and will causevery serious consequences. Research on non-destructive evaluation method forhydrogen damage of material in the initial period is of great value.This article aims on nondestructive testing of material suffered from hydrogendamage by using ultrasonic microscopy technique. The main contents are as follows:(1) According to the characteristics of the hydrogen concentration distributioninside the hydrogen damage material, an automatic measurement software programbased on acoustic microscopy for measuring the surface wave velocity distribution ofthe cross-section of hydrogen samples has been developed. It can automaticlymeasure the surface wave velocity on the cross-section of samples at equal intervalsand calculate the surface wave velocity by time-resolved analysis method.(2) Transducers with small area of PVDF film are designed and fabricatedindependently. These transducers have high center frequency, good noise ratio andsmall test area.Morever, the resolution of these transducers have been improved.(3) In order to obtain dispersion curves, samples which were charged hydrogenin high temperature and pressure for18hours,24hours and36hours are measured byV(f,z) analysis methods. The hydrogen damage inside the material can be evaluated bydispersion curves. The programme and transducers with small area of PVDF film areused to measure the surface wave velocity of20#steel and16MnR steel withhydrogen charged for36hours. The wave velocity distribution on the cross-section ofsamples are in accordance with the experiment result of hardness testing and theobservation of metallographic microstructure. The experiment results show that thesurface wave velocity can be used to evaluate the degree of hydrogen damage.(4) High speed steels are prepared by dipping in H2S solution under differentdensities and different time. The surface wave velocity and longitudinal wave velocityof samples after soaking are measured. Therefore, the parameters of mechanicalproperties of samples can be determined.The effect of storage time on mechanicalproperties were researched. In short, this paper through measuring surface wave velocity, achieved onevaluating the degree of corrosion and revealling correlation between ultrasonicparameters and hydrogen corrosion, solved evaluation issues of hydrogen damage ofmaterials, which has important implications for prediction and evaluation life ofmaterial suffered hyrogen damage.