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28 HAND-FORGING
The carbon being extracted makes the metal malleable and soft and so that it cannot be hardened by heating and cooling in water as steel can.
Mild Steel.—The structure of mild steel is similar to wrought iron. In steel the grain is bright and crystalline in appearance, while in iron it is fibrous. Soft steel contains a little more carbon than iron, making it a little harder to weld, and it must not be heated so hot. It will readily bend in any shape while hot without danger of breaking. Mild steel should be used when there is considerable bending or forging to be done.
Tool Steel is used to make the various tools used in the shop, such as chisels, drills, punches, etc. It varies in hardness according to the amount of carbon it contains. The more carbon it contains, the harder fire and water will make it. It should never be heated as hot as iron or soft steel, as it will burn in the fire, or, if struck a blow with a hammer, it would fly to pieces. It can be welded if it does not contain too much carbon, and most tool steel may be welded, if handled carefully, by using a flux, such as borax, or some other welding compound. It is hardened or tempered by heating it to a dull red and quenching it in water or oil. As an example, to temper a cold chisel, heat it with a slow heat to a dark red, say for 1^/2 in. on the cutting end; then cool it in water by dipping it for an inch, remove it, and with a piece of
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Hand Forging by Thomas F. Googerty