Category: HEAT TREATMENT OF STEEL
With the exception of several of the higher types
of alloy steels, where the percentages of special elements run quite
high, which causes a slight air-hardening action, the carburizing
steels are soft enough for machining when air cooled from any
temperature, including the finishing temperature at the hammer.
This condition has led many drop-forge and manufacturing concerns
to consider annealing as an unnecessary operation and expense.
In many cases the drop forging has only been heated to a low
temperature, often just until the piece showed color, to relieve
the so-called hammer strains. While this has been only a compromise
it has been better than no reheating at all, although it has not
properly refined the grain, which is necessary for good machining
Annealing is heating to a temperature slightly above the highest
critical point and cooling slowly either in the air or in the furnace.
Annealing is done to accomplish two purposes: (1) to relieve mechanical
strains and (2) to soften and produce a maximum refinement of grain.
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