Alloy Steel

 A steel which owes its distinctive properties to elements other than carbon. Steel is considered to be alloy steel when the maximum of the range given for the content of alloying elements exceeds one or more of the following limits2:
Manganese 1.65 percent
Silicon 0.60 percent
Copper 0.60 percent

or a definite range or a definite minimum quantity of any of the following elements is specified or required within the limits of the recognized field of constructional alloy steels:
Aluminum
Boron
Chromium (up to 3.99 percent) Cobalt
Columbium
Molybdenum
Nickel
Titanium
Tungsten
Vanadium
Zirconium
or any other alloying element added to obtain a desired alloying effect.

Small quantities of certain elements are unavoidably present in alloy steels. In many applications, these are not considered to be important and are not specified or required. When not specified or required, they should not exceed the following amounts:
Copper 0.35 percent
Chromium 0.20 percent
Nickel 0.25 percent
Molybdenum 0.06 percent