ALLOY STEELS.
What is an alloy steel? The general definition of an alloy steel is, "a solidified solution of two or more metallic substances". The International Committee upon the nomenclature of iron and steel defines alloy steels as "those steels which owe their properties chiefly to the presence of an element (or elements) other than carbon".
This latter definition more nearly applies to our case, but it must be born in mind that the distinction between an element added merely to produce a slight benefit to ordinary carbon steel, and the very same element added to produce an alloy steel itself, is sometimes a very delicate one. For example: Manganese is added in amounts usually less than 1.50% to all Bessemer and Open-Hearth Steels, for the purpose of getting rid of oxygen, and neutralizing the effect of the sulphur. But this does not produce an Alloy Steel. When we make "manganese steel" containing 10 to 20% manganese, the material then has properties quite different from the same steel without the manganese, and we then have a Manganese Alloy Steel.
Thus, for our purpose, we may consider an alloy steel as being one to which some element other than carbon has been added in sufficient amount to materially affect the physical properties which the steel will have when hard.