1.3. Alloy Steels

In 1988 the United States produced 10.9 million tons of alloy steel, or 10.9% of total steel production (Ref 7, p.147). It was much less than carbon steel (86.9%), but when hardness, strength, and wear resistance of the machined parts are a necessity, the use of alloy steel is the right choice.

Alloy steels constitute a category of ferrous materials that exhibit mechanical properties superior to carbon steels as the result of additions of such alloying elements as nickel, chromium, and molybdenum. Total alloy content can range from 2.0% up to levels just below that of stainless steels. For many alloy steels, the primary function of the alloying elements is to increase hardenability in order to optimize mechanical properties and toughness after heat treatment (Ref 7, p. 149).

Steel is considered an alloy steel when the maximum content range of alloying elements exceeds one or more of the following limits: 1.65% manganese, 0.60% silicon, or 0.60% copper. Also included in the recognized field of alloy steels are steels with a specified or required range or minimum quantity of the following elements: aluminum, boron, chromium, cobalt, niobium, molybdenum, nickel, titanium, tungsten, vanadium, zirconium, or any other element added to obtain a desired alloying effect (Ref 8, p. 73) .

AISI SAE system of designations for alloy steels is similar to carbon steels. With four digits in the designation, the last two digits indicate carbon content in hundredths of a percent. In the chromium steels with...