The concentration of commonly used NaOH aqueous solution is 5% ~ 15% (mass fraction), which is suitable for quenching carbon structural steel and carbon tool steel. The concentration of 30% ~ 50% NaOH aqueous solution is suitable for easy distortion, cracking of the workpiece and the mold, the use of temperature control in not more than 60 ℃.

　　The surface of the workpiece is smooth after quenching in NaOH aqueous solution, and has a certain bluing effect (when the concentration is high), but this aqueous solution has a stimulating smell due to the escape of gas, so attention should be paid to it.

table Quenching Distortion of Ring Workpiece in Aqueous Solution of Water, Salt and Alkali

Note: The distortion is measured according to the deflection difference of the notched ring. The outer diameter of the ring is 57mm and there is an eccentric hole with a diameter of 30mm.