Quenching media during the heat treatment

quenching media is very important to hardening because it is a very effective of hardness of the material
quenching medias:

Water:
water is fairly good quenching medium.it is cheap,readily available, easily stored nontoxic nonflammable smokeless and easy to filer and pump but with water quench the formation of bubbles may cause soft spots in the metal.Agitation is recommended with use of water quench.Still other problems with waterquench inclued its oxidizing nature,its corrosivity and the tendency to excessive distortion and cracking although this bad properties for plain carbon steels.

Brine (salt water) : Brine is a more severe quench medium than water.Unfortunately it tends to accelerate corrosion problems unless completely removed.Sodium or potasium hydroxide can be used when very severe quenching is desiredand one wishes to obtain good hardness in low carbon steels

Oil: When slower cooling rate is desired oil quenches can be employed.The slower cooling throug the ms to mf temperature range leads to a milder temperature gradient and a reduced likelyhood of cracking.Problems associated with quenchants include water contamination,smoke and fire hazards.in addition quench oils tend to be somewhat expensive.

Air: Low alloy steels in light sections and high alloy steels may be succesfully hardened by means of compressed air or still air.The advantages of using air are that distortion is negligible and that the steel can easily be straigtened during cooling precess.One drawback here is that the surface may be oxidized the cooling.