Research On Nonlinear Ultrasonic Testing Of Microscopic Damage Of P91 Steel

Along with the rapid development of society,the healthy economic system puts forward higher and higher requirements for the energy industry,especially for the electric power industry.P91 steel is a new generation of heat-resistant steel in China with its good performance,and is widely used in various types of power plant units.As we all know,the operation of the power plant unit environment is very harsh,and the safety demand is high.So a rapid nondestructive testing method for P91 steel micro damage is very important.Nonlinear ultrasonic testing technology is a kind of nondestructive testing technology which is very sensitive to the microscopic damage of materials.Thus,this paper uses the non-linear ultrasonic testing platform to detect the micro damage of P91 steel.The specific research contents are divided into three parts as follows:(1)The detection methods of material micro damage are summarized and compared,the shortcomings of traditional detection methods in the micro damage of P91 steel are analyzed,the advantages of non-linear ultrasonic detection method are introduced,and the research of non-linear ultrasonic detection at home and abroad is summarized in this paper.After that,the theoretical basis and expression formula of non-linear ultrasonic detection of micro damage of metal materials are deduced,and dislocation model and dislocation and precipitate model are introduced to explain the change of non-linear ultrasonic coefficient from the microstructure level.(2)According to the service environment and service characteristics of P91 steel,specific set of P91 steel thermal damage test block and P91 steel creep damage test block are established.Next,according to the theoretical requirements of nonlinear ultrasound,SNAP-5000 system is selected as the core system to build a nonlinear ultrasonic testing platform,and the hardness test and metallographic test of P91 steel micro damage test block are carried out to verify the accuracy of nonlinear ultrasonic testing.(3)Nonlinear ultrasonic testing was carried out on the microscopic damage test block of P91 steel by using the nonlinear ultrasonic testing platform.The results show that the nonlinear ultrasonic coefficient of P91 steel thermal damage test block changes in a double peak,with a maximum value at 4000 H and 14000 h,and the overall nonlinear coefficient changes greatly;The variation trend of the nonlinear coefficient of creep damage test block of P91 steel is monotonically increasing,and the nonlinear coefficient increases with the increase of creep time,and the growth rate of the heataffected area is the highest,followed by the weld area,and the base material area is the smallest.Comparing the metallographic test results with the nonlinear ultrasonic test results,it is found that the change of internal microstructure and the nonlinear coefficient of P91 steel can be verified by the dislocation and precipitate model,which also indicates the accuracy of the nonlinear ultrasonic test on the microscopic damage of P91 steel.