Ultrasonic Attenuation in Steel and Cast Iron

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Ultrasonic attenuation in steel and cast iron with various kinds of texture were measured in the frequency range from 0.5 to 25 megacycles per second making use of pulsed longitudinal ultrasonic waves. For this purpose, several processes of heat treatments were applied successively to the same specimens and at every stage of such treatments the attenuation measurements were carried out. The chromium-molybdenum steel and carbon steel specimens were normalized, hardened by quenching, and tempered to make the structure of troostite and sorbite, and the differences among attenuations at each stage were determined. For determining the effect of austenite grain size on the ultrasonic attenuation, the measurements were made for the carbon steel specimens heat-treated above transformation point. The white cast iron was prepared, then tempered successively till the spheroid graphite structures were reached, and the attenuations were studied at every stage of tempering. The attenuation measurements were also made both for flake graphite cast iron with various sizes of flake graphite distributing in wide range and for spheroid graphite cast iron, and the effects of the shape and size of crystallized graphite on the attenuation were studied. The results of measurements are summarized as follows : (1) In the case of steel ultrasonic attenuation varies remarkably with the change of the texture. In the specimens with pearlite structure, a large attenuation value was observed and the value rose steeply with frequency, so that the sound wave hardly penetrated through this medium at frequencies higher than about 10 Mc/sec. The predominant factor causing such a high attenuation is the grain size of austenite phase. In quenched specimens of martensite structure the ultrasonic attenuation was fairly low at high frequencies as 20 Mc/sec. In tempered specimens of troostite or sorbite structure, the lower attenuation values were observed. And these low attenuations are considered to be caused by the elastically anisotropic character of each grain. (2) In cast iron the ultrasonic attenuation shows complicated dependence upon the texture. The form and size of crystallized graphite in cast iron have remarkable effect on the attenuation. White cast iron without crystallized graphite has low attenuation value. In flake graphite cast iron, very high attenuation was observed and the value increased steeply with frequency. These characters are determined directly by the size of flake graphite. The cast iron of intermediate structure, including spheroid graphite cast iron, has medium value. (3) The most predominant factor determining the magnitude of ultrasonic attenuation is the Rayleigh scattering of ultrasound by grains. The rate of energy loss by scattering depends upon the size and elastically anisotropic character of the crystal grains.
東北大学の論文

著者

Kamigaki Kazuo
The Research Institute For Iron Steel And Other Metals

Ultrasonic Attenuation in Steel and Cast Iron

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