As the water boils, it forms a vapor jacket around the steel and unless it is circulated or flushed rapidly from the surface, this jacket will inhibit cooling. In thin cross sections this is not as much of a problem as it would be in thicker sections, but if not taken into consideration results can be spotty. I like to use rainwater for my water quenches because the mineral content of municipal or well water can affect the results of the quench. Brine A faster quench than water is brine . In some steels that have a low hardenability it may be necessary to go to a brine quench.
Brine solution is made by adding salt, sodium chloride, to water.
The effect of brine on the quench is to make the water more efficient by precipitating on the steel and then blowing off very rapidly creating rapid agitation and disrupting the vapor jacket. Polymer quenchants Polymer quenchants use a polymer additive to water. There are many kinds of polymer, POG, PAG etc, and each have particular attributes. The effect of the polymer is that you fairly precisely control the speed of the quench by varying the amount of concentration. Polymer quenchants are used in industry where the temperature of the quench and concentrations are tightly controlled and are most effective when used with induction or atmosphere controlled furnaces.