DBPapers
DOI: 10.5593/sgem2017/61/S24.024

INFLUENCE OF THE ULTRASOUNDS ON THE VOLUME FRACTION OF MARTENSITE IN THE MICROSTRUCTURE OF A DUAL-PHASE STEEL

C. Dulucheanu, T. Severin, M. Baesu
Tuesday 12 September 2017 by Libadmin2017

References: 17th International Multidisciplinary Scientific GeoConference SGEM 2017, www.sgem.org, SGEM2017 Conference Proceedings, ISBN 978-619-7408-12-6 / ISSN 1314-2704, 29 June - 5 July, 2017, Vol. 17, Issue 61, 179-186 pp, DOI: 10.5593/sgem2017/61/S24.024

ABSTRACT

In this article, the authors have analysed the influence of ultrasound, used in the quenching from the intercritical range (α + γ), on the volume fraction of martensite in the microstructure of a dual-phase steel with 0.087% C and 0.511% Mn. The ultrasonic oscillations, applied to the medium in which the quenching takes place, under the action of pressure and cavitation phenomenon, destroys and prevents the formation of vapor and gas films, thereby ensuring a more prolonged contact between the workpiece and the cooling medium; in this way the cooling rate is increased, which leads to a cooling more vigorous, the quenching with ultrasounds being more efficient than the classical. The ferrite-martensite microstructures, characteristic of dual-phase steels, were obtained by intercritical quenching that consisted of heating at 760 ⁰C (for 30 minutes) and cooling in water without mechanical agitation, water in ultrasonic field with frequency of 40 kHz and water in ultrasonic field with frequency of 59 kHz. After heat treatments, metallographic analyses were performed and determined the volume fraction of martensite; using of ultrasounds, and raising their frequency from 40 at 59 kHz, led to increase in the volume fraction of martensite in microstructures, increase contained between 5.70 and 17.58%.

Keywords: dual-phase steel, ultrasounds, intercritical quenching, volume fraction of martensite