Ultrasonic attenuation and microstructural evolution throughout tension–compression fatigue of a low-carbon steel

We have studied the microstructural evolution in a wrought low-carbon steel (ASTM-A105), containing 0.21 mass% C and subjected to tension–compression cyclic loading, through in situ monitoring of the attenuation and velocity of a surface shear-wave with the electromagnetic acoustic resonance (EMAR) technique. This technique is a combination of the resonant technique and a non-contacting electromagnetic acoustic transducer (EMAT). The EMAT operates with a magnetostrictive mechanism and it is the key to establishing a non-contacting monitoring of microstructural change in a materialʹs surface region with high sensitivity. The attenuation coefficient is sensitive to the accumulated fatigue damage, showing two peaks around 2% and 90% of life. This novel phenomenon is interpreted in terms of dislocation mobility change and dislocation rearrangement. Transmission electron microscope (TEM) observation has supported this view. This technique has a potential to assess damage and predict the fatigue life of steels.