Acoustic Birefringence Changes in the Base Metal and Heat Affected Zone of ASTM 1020 Steel under Plastic Deformation and Fatigue

This paper deals with metallographic studies and ultrasonic investigations of acoustic birefringence in the base metal and heat affected zone of welded specimens of ASTM 1020 steel under uniaxial tension and low-cycle fatigue. We examined microstructural changes on the surface using optical microscope. It was found that development of slip bands differs in the base metal and heat affected zone. The ultrasonic pulse echo method was used for the determination of acoustic birefringence and velocities of ultrasonic shear waves. The differences in the change in velocities in the base metal and in heat affected zone were revealed. Acoustic birefringence was found to change monotonously in the base metal under fatigue as well as in the base metal and heat affected zone under uniaxial tension. For heat affected zone, during fatigue, acoustic birefringence was found to change non-monotonously up to cycle ratio of 0.3 and decrease monotonously after cycle ratio of 0.3. Based on the relationship between relative number of loading cycles, or plasticity resource, and acoustic birefringence, ultrasonic techniques were proposed for assessing damage

Thermo-ultrasound method for determining the damage of structural material

The effect of plastic strain and temperature on the longitudinal and shear waves velocity of austenitic stainless steel 12Kh18N10T (analogue AISI 321) is investigated. Cryogenic corrosion-resistant austenitic steel 12Kh18N10T is interesting due to the fact, that during plastic deformation a martensitic phase is formed. The martensitic phase significantly changes the electromagnetic, elastic and strength properties of the entire material. The formation of a new phase in conjunction with the process of plastic deformation has a significant effect on the temperature dependence of the elastic wave velocity. As a result of the studies, numerical values of the temperature-velocity factor for longitudinal and shear ultrasonic waves in steel 12Kh18N10T were obtained. The relationship between changes of the magnetic phase and temperature-velocity factor is suggested; it can be used for determining the material damage by the ultrasound method