Achievement of ultrafast cooling rate in a hot steel plate by air-atomized spray with different surfactant additives

Ultrafast cooling of a 6 mm thick hot stainless steel plate (AISI 304) has been achieved by high flow conditions of air and water, which is needed at the runout table of a hot strip mill to develop advanced high strength steels. The present study primarily focuses on the effect of adding different types of surfactants at various concentration levels to air atomized water spray for enhancement of ultrafast cooling rate. The anionic, cationic and non-ionic surfactants used have been characterized by measuring their surface tension, contact angle and viscosity. The surfactant enhanced heat transfer experiments have been conducted with a full cone atomizer at a fixed nozzle to surface distance using constant air and water flow rates optimized earlier. The initial surface temperature of the test plate has been maintained at 900 degrees C in each case. The experimental measurements have been applied to a commercial inverse heat conduction solver (INTEMP) to estimate local surface heat flux as well as surface temperature histories. The concentration of all the surfactants has been optimized based on the highest cooling rate. Depending on their spreadability, wetting characteristics and ability to foam formation, the cationic and non-ionic surfactants are found to produce better cooling effects than the anionic surfactant. These enhanced ultrafast cooling rates can be useful to produce advanced high strength steels in the steel industries. (c) 2013 Elsevier Inc. All rights reserved.