Dry Quenching

the bottom of the tank and crack as a result of the more rapid cooling. Nonferrous metals are not routinely quenched in oil unless specifications call for oil quenching. Caustic Soda A solution of water and caustic soda, containing 10 percent caustic soda by weight, has a higher cooling rate than water. Caustic soda is used only for those types of steel that require extremely rapid cooling and is NEVER used as a quench for nonferrous metals. WARNING CAUSTIC SODA REQUIRES SPECIAL HANDLING BECAUSE OF ITS HARMFUL EFFECTS ON SKIN AND CLOTHING. DRY QUENCHING This type of quenching uses materials other than liquids. Inmost cases, this method is used only to slow the rate of cooling to prevent warping or cracking. Air quenching is used for cooling some highly alloyed steels. When you use still air, each tool or part should be placed on a suitable rack so the air can reach all sections of the piece. Parts cooled with circulated air are placed in the same manner and arranged for uniform cooling. Compressed air is used to concentrate the cool- ing on specific areas of a part. The airlines must be free of moisture to prevent cracking of the metal. Although nonferrous metals are usually quenched in water, pieces that are too large to fit into the quench tank can be cooled with forced-air drafts; however, an air quench should be used for nonferrous metal only when the part will not be subjected to severe corrosion conditions and the required strength and other physical properties can be developed by a mild quench. Solids The solids used for cooling steel parts include cast- iron chips, lime, sand, and ashes. Solids are generally used to slow the rate of cooling; for example, a cast-iron part can be placed in a lime box after welding to prevent cracking and warping. All solids must be free of mois- ture to prevent uneven cooling. 2-11