Determination of the cooling rate of different heat extraction media and the influence on the hardness of ABNT 8620 steel

Abstract

Cooling rate of steel from its austenitic temperature influences the microstructure and resulting mechanical properties. The study on cooling media rates is still poor in the literature, making it necessary to study it. In the present work, heat extractions were carried out on SAE 8620 steel from its austenitization temperature, in moderately and severely agitated water, brine and air media. From the cooling curves, it was verified that the agitation of the heat extraction medium has an influence on their severity, and that the stirred brine and water severely extracted heat in the same time interval, with different cooling rates, being water the largest one, with a maximum cooling rate of 221,25 ° C/s at a temperature of approximately 180 °C. On the other hand, the hardness obtained for the most severe media, despite being close, the severely stirred brine made it possible to obtain a higher average hardness, which was 60,2 HRC. The present work was therefore possible to obtain satisfactorily the cooling curves and rates for air, water and brine when subjected to conditions of moderate and severe agitation, to be used in heat treatments by continuous cooling.