412 APPLIED SCIENCE 



consists in taking an iron box and placing a quantity of hot 

 ashes in the bottom. A board is laid on them and the articles 

 to be annealed are placed on the board after having been 

 heated to a uniform low red heat. They are then covered 

 with another piece of board and the whole is buried. The 

 wood absorbs heat from the steel fast enough to insure good 

 annealing, while the wood in turn is heated and holds the 

 steel just below a red heat long enough to soften it properly. 

 Steel intended for dies, the surface of which is to be engraved, 

 should be annealed by this method. 



473. Water Annealing. When it is necessary to anneal 

 a piece of steel quickly, the process may be accomplished 

 by heating it to a uniform red heat and then allowing it to 

 cool in the air. A current of air should not be allowed to 

 strike it until the red disappears. The instant the red dis- 

 appears, the steel should be plunged in water and left until 

 cool. Soapsuds or oil give better results than water. While 

 water annealing is not to be advocated for general use, in an 

 emergency it is extremely useful. 



While annealing is intended primarily to soften steel, 

 it has another use, which is to do away in a great measure 

 with the tendency which steel has to spring when hardened. 

 This tendency arises from the internal stresses which are 

 caused by the various operations through which the steel 

 passes in the steelmill or forgeshop. 



When steel is to be annealed to remove stresses, the skin, 

 i.e., the outer surface, is first cut away. The remaining 

 piece must be large enough to be machined to size without 

 straightening after annealing, as the operation of straighten- 

 ing steel when cold tends to set up strains that show them- 

 selves when the steel is hardened. 



