Steel billets of 40 Cr 4B grade, rejected on the basis of blue fracture test, were chosen for inclusion study. For grain size measurement, micro-alloyed steel plates (one with 0.03% Nb and the other with 0.08% Ti) were selected. Additionally, experiments were done on the plates to evolve a correlation between precipitates and the extent of attenuation. The plates were heat treated in order to induce different grain sizes and precipitates.

Ultrasonic transducer with 10 MHz was used for measuring the attenuation coefficient (), Correlation equations were evolved based on Rayleigh Scattering relationships, between and the mean grain size (), determined through quantitative metallography primarily. The equation correlating various metallographic features with ultrasonic attenuation parameters is given below:

where K₁ - Absorption constant, K₄ - Scattering constant and f - Frequency of ultrasound

The values of the scattering constant for the two grades were established using known grain sizes and frequency. The relationship thus developed can be utilized to predict the grain size. As regards the precipitation, a broad estimation of the total volume could be made using attenuation parameter. Extensive TEM work is however needed to refine such predictions. The paper shows a few of them.