Grain size correction of welding residual stress measurement in a carbon steel plate using the critical refraction of longitudinal waves

In this, a method to measure welding residual stress in butt-welded joints of carbon steel plates using longitudinal critically refracted wave (L_cr wave) is proposed. Cross-correlation was employed to calculate the difference in time of flight between L_cr wave, and the optimal step length for the measurements is discussed. To determine L_cr wave acoustoelastic coefficient of the heat affected zone (HAZ), the relationship between the L_cr wave acoustoelastic coefficient and the grain size is established. The results show that one cycle is the optimal step length for the difference in the time-of-flight calculation, and with increasing grain size increase, L_cr wave acoustoelastic coefficient decreases in the form of a power function. In addition, grain size can be determined by using amplitude of the L_cr wave, so that the measured value of welding residual stress in HAZ can be corrected. The welding residual stress in melted zone (MZ) is corrected by calibrating acoustoelastic coefficient of the MZ. The acoustoelastic coefficient of the MZ is larger than that of parent material (PM). At last, welding residual stress in the butt-weld joint is measured and corrected with the L_cr wave technique. The results are verified by the hole drilling method.