TABLE 7-5. FORGING., NORMALIZING AND ANNEALING TREATMENTS OF TOOL AND DIE STEELS (CONTD)
a. The temperature at which to start forging is given as a range, the higher aide of which should be used for large sections and heavy or rapid reductions, and
the lower aide for smaller sections and lighter reductions,, as the alloy content of the steel ,, the time of soaking at forging temperature increases proportionately..
Likewise, as the alloy content increases, it becomes more necessary to cool slowly from the forging temperature.. With the very high alloy steels,, such as high
speed or air hardening steels,, this slow cooling is imperative in order to prevent cracking and to leave the steel in a semi-soft condition. Either furnace cooling
or burying in an insulating medium such as lime, mica, or silocel la satisfactory.
b. The length of time the steel is held after being uniformly heated through at the normalizing temperature,, varies from about 15 minutes for a small section to
about 1 hour for larger sizes,, Cooling from the normalizing temperatures is done in still air. The purpose of normalizing after forging is to refine the grain
structure and to produce a uniform structure throughout the forging. Normalizing should not be confused with low temperature(about 1200F)) annealing used for
the relief of residual stresses resulting from heavy -machining, bonding and forming.
c. The annealing temperature is given as a range,, the upper limit of which should be used for cargo sections,, and the lower limit for smaller sections., The
temperature varies from about 1 hour for light sections and small furnace charges of carbon or low alloy steel, to about 4 hours for heavy sections and large
furnace charges of high alloy steel.