Eiji Isono1, Tatsuru Ueno1 and Tateshi Udagawa1
1Central Research Laboratories Fuji Iron and Steel Co., Ltd., Sagamihara
An extraordinary attenuation of ultrasonic Lamb waves in mild steel sheets up to 500°C was observed, and we confirmed that it is due to the Snoek damping of carbon and/or nitrogen dissolved in the steel.
The measurement of Lamb wave attenuation has been devised more quantitatively in order to confirm the relation between the aging index and other quality of steel sheets and the internal friction.
The results are as follows:
(1) The internal friction Q-1 max by pulsed Lamb waves at 2.25 MHz of a commercial ultrasonic flaw detector is roughly equal to the total concentration of solute carbon and nitrogen atoms in the specimen following Smit's relation.
(2) Group velocity of Lamb waves is found to be suitable as the velocity of waves to obtain Q-1.
(3) The solution of precipitated atoms, carbon and/or nitrogen, is observed when the specimen is heated above 325°C.
(4) The relation between the aging index and Q-1 max of specimens is found to be quite similar to that already reported.
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