ANNEALING.
Annealing has for its object: (1) Completely undoing the effect of hardening, leaving the steel soft and ductile (2) refining the grain, in which case the crystals are allowed to re-arrange and re-adjust themselves, usually growing to a rather large size (3) and removing strains and stresses caused by too rapid cooling. Such cooling strains are particularly likely to exist where the rate of cooling is different in different parts of the bar, but the process of annealing ought to remedy any such condition, leaving the steel soft, ductile and of refined and uniform crystalline structure throughout.
The process of annealing is easier to explain than it is to actually put into practice. The steel is first packed in lime, charcoal, fine dry ashes or sand, and then sealed in long air-tight tubes or boxes.
The whole receptacle is next slowly brought up to a dull red heat, of about 1500 degrees Fahrenheit.
It is very important to heat the material uniformly all the way through, and then hold it in this condition from three to eight hours. Thus, allowing the slipping of one allotropic condition into another.
The receptacle must be cooled equally slowly, either allowing the packed steel to cool slowly down with the furnace, or by placing the same in a soaking or cooling pit, which also accomplishes the desired result.
After the receptacle has become entirely cooled it is opened and the steel unpacked and removed. The steel is then ready for its final inspection before shipping to the tool maker.