Heat Transfer Coefficients During Quenching of Inconel and AISI 304 Stainless Steel Cylinders In NaNO2 Aqueous Solutions

In order to reduce distortion and cracking when quenching in water, uniform cooling should be promoted by avoiding full film boiling, if possible. The formation of a vapor blanket may be prevented either by imposing severe agitation or by quenching in water-based salt solutions. Furthermore, with the addition of optimum salt concentrations, the cooling rate may be favorably increased. In this work, the cooling characteristics of round bar - probes of Inconel 600 (ø12.6 mm) and AISI 304 stainless steel (ø8 mm) heated to 900°C and quenched by immersion in 1, 2, 3, 4 and 9% sodium nitrite (NANO2) aqueous mixtures are studied. Cooling curves were acquired using embedded thermocouples within the probes and the heat transfer coefficients and cooling rates were calculated for each quenching condition. It was found that an increase of NaNO2 concentration beyond 4% did not result in a corresponding increase in the cooling ability of the quenchant.