Acoustic Measurements as a Nonconventional Alternative for Metallurgical Characterization of a Low-Carbon Mechanical Construction Steel

Steels are susceptible to changes in their properties due to thermal effects; characterizing these changes in real time is one of the most pressing needs in the industry. The industrial ultrasound method is presented as a nondestructive technological alternative for mechanical characterization through direct correlation with acoustic properties. Therefore, the objective of the research was to correlate acoustic properties with hardness measurements in a mechanical construction steel induced to small microstructural changes by heat treatments. For this purpose, nine experimental tests were planned through the factorial interaction of the heating temperature in the austenitic region of 870, 920 and 970°C, and the cooling medium, inside the furnace, still air and oil. Each sample was characterized by Vickers hardness tests, optical metallography and ultrasound using the pulse-echo technique with longitudinal waves. The results and statistical tests showed significant changes in hardness and acoustic attenuation coefficient due to the effect of the microstructural change produced in the samples according to the imposed thermal cycle. The experimental data, arranged in a contour plot, show that hardness exhibits a negative correlation with respect to the velocity and attenuation coefficient; both acoustic parameters show a tendency to decrease and hardness to increase as the martensitic structures in the steel increase. The correlation obtained is presented as an alternative to non-destructive testing aimed at mechanical characterization using ultrasonic acoustic measurements.