In one of the earlier chapters we saw that annealing refines (make finer) the grain of a steel casting and improves its physical properties. Annealing for refining purposes is practiced with other steel products also, and with just as effective results.
However, the mechanical shaping of steel while at cherry-red or at a white heat much more materially refines the grain while helping the strength and greatly increasing the ductility of the alloy. Steel which has been hot-forged or rolled is said to have been “hot worked.” Steel usually is “hot worked,” for “cold-working” methods are not so generally applicable and the product is more liable to suffer under the more drastic treatment. The amount of “hot-work,” at proper temperatures, that low and medium carbon steels will stand with improvement of the grain and physical properties is considerable.
As we must anyway shape the metal into useful implements and other products, it is fortunate that the quality of the metal is benefited by the process.
No. 69a. Photomicrograph of Cold-Drawn Steel Wire Showing Distortion of the Crystals from Cold Working
Hot Working does not produce distortion
but makes the grain finer. Annealing relieves
this distortion to a great extent.
(Magnification 70 Diameters.)
Forging
Undoubtedly the earliest shaping of ferrous (iron) metals was by hammering the small balls of metal into bars, spears or swords. Presumably it was done with stone hammers which later had to give way to hammers made of iron. These had sufficient hardness to serve the purpose well.
For hundreds of centuries the shaping of iron, steel and the other metals into tools and weapons must have been done by such forging methods. It is not difficult for us to picture the early smiths at their work, laboriously and yet very skillfully hammering into spear-heads and sword-blades the lumps of iron or Wootz Steel which they had made in their crude furnaces.
