Ultrasonic Nondestructive Characterization Of Steel For D Grade Sucker Rod

Steel is an attractive and traditional engineering material, applied very extensively. And along with the steel and iron material production modernization, current steel production has developed already from pursuing mechanical property brought by single structure to making comprehensive mechanical properties brought by multi-phases compound structure, which is adapt to high-speed of the production and meet the need of industrial development also. As well know, steel can make radical changes in its properties by tailoring the microstructure. However, steel properties can change from charge to charge and even in the same charge or after deformation/heat treatment processes not all parts have the same mechanical properties. In addition, the material properties can be degraded during the service.For there is a close relationship between structures and properties of material, material structure testing and characterization become an important component of material science. Compared with the way of destructive testing, ultrasonic nondestructive characterization and evaluation (UNDC&E) has been concerned by material workers for its obvious superiority and the latent application prospects. As well know, ultrasonic wave transmitting in material structure decide its acoustic parameters (such as velocity and attenuation coefficient of sound), and there is a direct relationship between acoustic parameter and different states of microstructure of material. However, when UNDC&E for steel which has multi-phases mixing structure, it is rather difficult to detect the difference among structures by traditional ultrasonic methods (such as traditional attenuation coefficient absolute measurements and phase velocity measurements), because of few differences among microstructures, large attenuation for ultrasonic scattering brought by multi-phases mixing structure, and very harsh conditions for experiments. All these make it difficult to characterize structure and mechanical properties of materials by using ultrasonic parameter.In this paper, an experimental immersion beam focus technique is developed, and one testing and signal processing system of small diameter rod steel is set-up for characterization as-rolled and tempered 30Mn2SiV steel for D grade sucker rod with different mixed microstructures. The microstructures of 30Mn2SiV Steel's three kinds of specimens are mixed with lamellar pearlite, ferrite, globular pearlite, upper bainite with different compound and percentage. Some ultrasonic signal of samples which including the information of different microstructures are obtained by using the ultrasonic testing system. The signal'snormalized spectra of three kinds of specimens of 30Mn2SiV Steel are compared according to the principle of spectral analysis technique, and relationships between ultrasonic parameters (relative attenuation coefficient and relative phase velocity) which have been calculated by phase and magnitude spectrum and three kinds of multi-phases mixed microstructures are investigated. The results show that the mixed microstructures of 30Mn2SiV steel for D grade sucker rod can be identified by using ultrasonic relative phase velocity and relative attenuation coefficient methods.