Study On The Characterization Method Of Corrosion Degree Of 45 Steel Based On Ultrasonic Nonlinear Technology

Corrosion changes the structure and composition of metal materials,and the mechanical properties are seriously degraded.It is very important to test the corrosion degree of workpieces to ensure their safe use.At present,there are many traditional detection methods to characterize the corrosion degree of materials,but they have their own limitations.Ultrasonic nonlinearity is sensitive to surface defects,and the corrosion products of workpiece surfaces caused by corrosion may produce an ultrasonic nonlinear effect.This paper will try to find the correlation between the ultrasonic nonlinear coefficient and the degree of corrosion,study the feasibility of the ultrasonic nonlinear detection method to characterize the degree of corrosion and explore the ultrasonic nonlinear characterization of the degree of corrosion.The ultrasonic nonlinear detection of corrosion was carried out by taking the common industrial material 45 steel as the research object.45 steel specimens with different corrosion degrees were prepared by changing the corrosion conditions.The micromorphology of the specimens with different corrosion degrees was observed,the surface hardness of the specimens was measured,and the quality loss data of the specimens with different corrosion degrees were measured.The corrosion degree of the specimens was calibrated according to the quality loss caused by corrosion and the degree of micromorphology change.Four detection models of penetrating longitudinal wave,critical refraction longitudinal(Lcr)wave,Rayleigh wave,and collinear mixing of Lcr wave were constructed to carry out ultrasonic nonlinear detection of 45 steel specimens with different corrosion degrees.The experimental results show that except for the Rayleigh wave detection model,the nonlinear coefficients of the other three models are closely related to the corrosion degree,which indicates that the ultrasonic nonlinear technique is feasible to characterize the corrosion degree of 45 steel,and the Lcr wave detection model has the highest sensitivity to the change of the corrosion degree.According to the theory of ultrasonic nonlinear characterization and the corrosion degree of materials,the relationship between the corrosion degree,the microscopic morphology characteristics,and the ultrasonic nonlinear coefficient is explored.The results show that the variation of the ultrasonic nonlinear coefficient is mainly related to the number of corrosion products and the microcracks and holes in the corrosion products,and the variation of the number of corrosion products in the specimens with different corrosion degrees is the main reason for the variation of the nonlinear coefficient.In order to study the feasibility of ultrasonic nonlinear testing method to characterize the surface hardness of specimens with different corrosion degrees,the surface hardness of45 steel specimens with different corrosion degrees was measured,and the correlation between the surface hardness of specimens and the nonlinear coefficient was studied.The results show that there is a good fitting relationship between the surface hardness of specimens and the nonlinear coefficient,but the matrix structure of the specimen is different,and the fitting relationship between the surface hardness and the nonlinear coefficient of the specimen with different corrosion degree is also different.In practical application,specific testing standards should be established according to the tested material.