For a rough classification it is safe for us to divide the steel world into four general divisions as follows:
1. The harder, high carbon steels used for tools, dies, etc.
2. The mild and medium steels of which wire, rod, bar, plate, pipe and structural shapes for bridges, ships and “sky scrapers” are made.
Hardening a Piece of Tool Steel. Ready to Quench
3. Alloy steels, to which some metal such as nickel, manganese or chromium gives definite properties and the name.
4. Those other modern materials which are known as “self-hardening” and “high-speed steels.”
Bowknot Made from Piece of Steel Pipe
The two classes last named are not simple iron-carbon alloys and their properties are less directly derived from and do not so plainly depend upon carbon. Metallurgically, then, they are not steels in the exact former sense of the word; but as they do require carbon—though perhaps in lesser amount, are made by regular steel processes, have most of the characteristics of steel and are used for the same general purposes, they are undoubtedly entitled to the appellation “steel.” However, to distinguish, they are usually termed “alloy steels.”