Non-destructive evaluation of formability of zinc-coated steel sheets using electromagnetic acoustic transducer

Abstract An ultrasonic technique for evaluation of the formability of zinc-coated steel sheets has been developed. The technique is based on the dispersion relation, which correlates the velocity anisotropy of the S 0 -mode Lamb wave to the texture defined by orientation distribution coefficients. In cold rolled steel sheets, we have already developed the evaluation system and installed it on two continuous annealing production lines. In this paper, we describe how to remove the effect of the zinc-coated layer from the measured velocity and the evaluation results of the formability for zinc-coated steel sheets. The coating induced a decrease in the S 0 -mode Lamb wave velocity. The change in ultrasonic velocity due to the zinc-coated layer has been shown to be compensated by using a simple correction curve, which enables the correction for the effect of zinc coating from the known coating/substrate thickness ratio. The test results indicate that the monitoring of the formability for zinc-coated steel sheets as well as for cold rolled steel sheets is quite feasible.