Terminology
- Iron is a naturally occurring metallic element. It is almost never found in its native form (pure iron) in nature. It is usually found as an oxide or sulfide, with many other impurity elements mixed in.
- Wrought iron is the purest form of iron generally encountered or produced in quantity. It may contain as little as 0.04% Carbon (by weight). From its traditional method of manufacture, wrought iron has a fibrous internal texture. Quality wrought-iron blacksmithing takes the direction of these fibers into account during forging, since the strength of the material is stronger in line with the grain, than across the grain. Most of the remaining impurities from the initial smelting become concentrated in silicate slag trapped between the iron fibers. This slag produces a lucky side effect during forge-welding. When the silicate melts, it makes wrought-iron self-fluxing. The slag becomes a liquid glass that covers the exposed surfaces of the wrought-iron, preventing oxidation which would otherwise interfere with the successful welding process.
- Steel is a mixture of Iron and between 0.3% to 1.7% Carbon by weight. The presence of carbon allows steel to assume one of several different crystalline configurations. Macroscopically, this is seen as the ability to "turn the hardness of a piece of steel on and off" through various processes of heat-treatment. If the concentration of carbon is held constant, this is a reversible process. Steel with a higher carbon percentage may be brought to a higher state of maximum hardness.
- Cast iron is iron that contains between 2.0% to 6% Carbon by weight. There is so much carbon present, that the hardness cannot be switched off. Hence, cast iron is a brittle metal, which can break like glass. Cast iron cannot be forged without special heat treatment to convert it to malleable iron.
Steel with below 0.6% Carbon content cannot be hardened by simple heat-treatment enough to make useful hardened-steel tools. Hence, in what follows, wrought-iron, low-carbon-steel, and other soft unhardenable iron varieties will be referred to indiscriminately as just iron.
Read more about this topic: Blacksmith