Keywords: Quench, aqueous solution, alkali, solution, water, NaOH, cooling,

　　After the concentration of NaOH in the solution exceeds 15%, with the increase of the concentration, the maximum cooling rate decreases, the corresponding temperature moves to the high temperature, and the cooling rate below 300 ℃ is further reduced, and the cooling performance is more excellent.
　　As the solution temperature increases, the maximum cooling rate decreases, and the corresponding temperature moves to a low temperature, and the cooling rate below 300 ℃ decreases.
　　50% NaOH aqueous solution (mass fraction) has excellent cooling performance and is an ideal quenching medium. It is mostly used for quenching workpieces or tools that are easy to deform, crack or have complex shapes.

Fig. Hardenability of 25mm diameter cylindrical specimen quenched in aqueous solution of water, salt and alkali

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