Study On The Relationship Between Microstructure And Acoustic Parameters Of Metal Materials

Martensite stainless steel, which is mainly constituted by iron, chromium and carbon, has corrosion resistance and can enhanced by heat treatment. Because of its good mechanical properties (high strength, hardness and wear resistance) and corrosion resistance, it is widely used in industrial machinery. However, the grain continues growing in high temperature, resulting in creep damage and reducing strength. Additionally, corrosive media leads to corrosion of parts and reduces its strength in corrosive environment. Therefore, In order to ensure normal operation of equipment, the mierostructure of equipment has to be inspected periodic. Metallographic method is the most common method of Nondestructive testing. Because the method has complicated destructive process, long test cycle, the workpiece is not suitable for in-service testing. On the basis of link between the martensitic stainless steel microstructure and ultrasonic parameter, ultrasonic velocity and attenuation coefficient are measured, and the relationship between the martensitic stainless steel microstructure and the ultrasonic parameter is obtained.First we select the specimen material and design specimen size in view of materials science and ultrasonic. Secondly we try to obtain the required organization through heat treatment. Then grain size and special ferrite content is analyzed through metallographic analysis software. At last the ultrasonic evaluation of tissue samples is researched with ultrasonic velocity method and ultrasonic attenuation method. Relationship of martensitic stainless steel microstructure between ultrasound evaluation is obtained. The results show:(1) Ultrasonic velocity and acoustic attenuation coefficient of variation are mainly influenced by the heat treatment temperature, sound velocity and attenuation coefficient are variable at different heat treatment temperature.(2) If the heat treatment temperature does not reach the phase transition temperature, which means that stainless steel is no stress, velocity magnitude is mainly depended on ferrite content changes. If the heat treatment temperature is reached, that is, stainless steel has internal stress, velocity size mainly is depended on to material iron ferrite content, internal stress size and grain size.(3) When the heat treatment temperature is low, the main reason that attenuation coefficients are different is the second phase particle density. When the heat treatment temperature is high, the main reason that attenuation coefficients are different is impedance matrix viscosity, the density of second phase particles, and average grain size.The research results in this paper are achieving ultrasonic nondestructive evaluation of martensitic stainless steel microstructure and it is theoretical basis for ultrasound identification martensitic stainless steel. The result has practical value of meaturing martensitic stainless steel line detection device.