Quenching: Brine and Caustic

The addition of salts (brine) and caustic soda (NaOH) to water is employed to increase its cooling capacity.
Small additions of salts decrease the vapor film duration (inherent of water quenching), and at optimal
concentrations, it might be eliminated. The vapor film stage is not desirable on steel quenching due to the
low heat transfer and nonuniform cooling that leads to distortion and cracking, mainly because of the uneven
thermal and transformational stresses generated through the quenched part. These aqueous solutions can
increase the heat transfer coefficient from two to five times while promoting a more uniform cooling and are
commonly employed when low-hardenability steels are quenched. For interrupted quenching where high
cooling rates are required to produce a shell–core-type microstructure, these solutions could also be used.
The effect of various aqueous solutions (NaCl, NaOH, LiCl, KCl, NaNO2, NaNO3, CaCl2, NaSO4, and
MgSO4) on the heat transfer mechanisms as well as on the heat flux during quenching is reviewed.