A Novel LiNO3-Based Eutectic Salt Mixture for Industrial Heat Treatment

Abstract

A potassium nitrate-lithium nitrate-sodium nitrate (KNO<inf>3</inf>-LiNO<inf>3</inf>-NaNO<inf>3</inf>) eutectic mixture having a low melting point has been proposed as an alternative high-temperature quench medium. Inconel and steel probes were used to compare the quench performance of a conventional sodium nitrite (NaNO<inf>2</inf>) eutectic mixture and the proposed alternative medium at different bath temperatures. For the Inconel probe, the heat extraction rate was higher in the eutectic LiNO<inf>3</inf> mixture maintained at 150°C. At elevated bath temperatures of 200°C, 250°C, and 300°C, the heat extraction rate was higher in the eutectic NaNO<inf>2</inf> mixture. AISI 52100 steel probes quenched in eutectic LiNO<inf>3</inf> quench medium at 150°C and 200°C showed higher hardness. At bath temperatures of 250°C and 300°C, the hardness of AISI 4140 steel probes quenched in both media was comparable. Wettability studies on Inconel and steel surfaces revealed the occurrence of nonuniform dilation of a LiNO<inf>3</inf> eutectic mixture droplet. On the steel surface, the phenomenon occurred at lower temperatures, which resulted in an extended boiling stage and increased hardness. © 2022 by ASTM International