Acoustic Birefringence and Poisson's Ratio Determined by Ultrasound: Tools to Follow-Up Deformation by Cold Rolling and Recrystallization

Abstract

Poisson's ratio and birefringence, both measured by ultrasound, are used to follow the evolution of the anisotropy in ASTM A-36 steel plates cold-rolled between 5 and 50% deformation, and then subjected to recrystallization at 900 and 1000 °C. Times of flight of longitudinal and shear waves along the thickness of the plates were measured. As orthotropy increases, both birefringence and the difference between Poisson's ratios measured using a shear wave polarized along the length and another wave polarized along the width of the plate, are linearly related to the degree of deformation and cold-rolled hardness. In addition, the ultrasonic methods used clearly detected the complex changes in anisotropy produced by the austenization and recrystallization heat treatments. Thus, Birefringence or Poisson's ratio, measured by ultrasound, can be used to follow-up nondestructively changes in the anisotropy of rolled plates as a function of both, degree of deformation and recrystallization heat treatment.

Ultrasonic Assessment of the Influence of Cold Rolling and Recrystallization Annealing on the Elastic Constants in a TWIP Steel

“…In fact, as the reduction increased to 52%, the velocity decreased by 411 ms −1 , or 13.4%. A qualitatively similar behavior was observed in a low-alloy steel [ 17 ]; there, however, only decreased 2.7% at a 52% reduction, so, for the TWIP steel, the twin-lamellar structure that follows the rolling direction, as described above, must play a role in such a prominent effect. Ultimately, at a 70% reduction, with the presence of profuse shear bands, the velocity decreased even further, totaling 471 ms −1 ; that is a fall of more than 22 GPa or 28% in .…”

“…These three values correspond to the phase velocities of three nondispersive ultrasonic waves with mutually perpendicular polarization vectors. Thus, if the elastic constants are known, wave velocities in a material can be predicted by solving the Christoffel equation or, inversely, the elastic constants can be assessed from experimentally measured wave velocities [ 17 ].…”

“…Since and differ in an orthotropic solid, unlike in an isotropic solid, there is no unique value for Poisson’s ratio. Nonetheless, by extrapolating Equation (5) to the orthotropic case, two values for Poisson’s ratio are determined from ultrasound measurements with incidence from the rolling plane; their difference, , can be used to assess the departure from isotropy [ 17 ]: …”

“…The ultrasonic method described in Section 2 was effectively used in a previous work [ 17 ] to monitor the structural evolution of a cold-rolled and recrystallized low-alloy steel. A linear relationship was found between deformation and both birefringence and Poisson’s ratio, and the complex changes in anisotropy produced by the austenization and recrystallization heat treatments were clearly detected.…”

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

“…To define relationships between microstructure-sensitive parameters and material response to damage, it is available to use engineering techniques of nondestructive testing. The acoustic birefringence technique is widely used for assessing damage and monitoring the material state [1][2][3][4][5][6]. This technique has several advantages: it is applicable for industrial use due to its simplicity and reliability; there is no need to know the thickness of the structural element; noncontact electromagnetic acoustic transducers can be used; acoustic birefringence is independent of temperature [7][8][9].…”