Ultrasonic modelling of coarse grained austenitic steel

摘要

Railway crossings are subject to repetitive explosive impact collisions from rolling stock. Such repetitive action acts as a catalyst for fatigue cracking, which compromises the structural integrity of these safety critical components. For this reason, crossings are manufactured from high manganese steel, which is highly resistant to fatigue cracking due to its work hardening properties. Due to the inherent coarse grained structure and anisotropic material properties, in-service inspection of crossings using conventional ultrasonic techniques is ineffective. Consequently inspection is limited to surface techniques such as visual and dye-penetrant. A solution has been developed which enables reliable volumetric inspection of crossings. The technique known as Synthetic Aperture Focusing Technique (SAFT), offers enhanced flaw resolution and signal to noise ratio (SNR), due to its ability to reduce grain noise through spatial averaging. This paper presents the development of a procedure to accurately model the effect of coarse grained, austenitic steel on ultrasonic inspection. The coarse grains and anisotropy result in high levels of beam scattering, energy absorption and poor SNR. These effects were simulated using the CIVA software and compared with experimental results. This study led to the design of an annular phased array transducer capable of full volume inspection of the manganese steel crossings.