1. 11/18/13 eFunda: General Information on AlloySteels
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General Information
Alloy steels comprise a wide variety of steels which have compositions that exceed the limitations of C, Mn,
Ni, Mo, Cr, Va, Si, and B which have been set for carbon steels. However, steels containing more than
3.99% chromium are classified differently as stainless and tool steels.
Alloy steels are always killed, but can use unique deoxidization or melting processes for specific applications.
Alloy steels are generally more responsive to heat and mechanical treatments than carbon steels.
AISI Designation
Typically, alloy steels are designated by distinct AISI (American Iron and Steel Institute) four-digit numbers.
The first two digits indicate the leading alloying elements, while the last two digits give the nominal carbon
content of the alloy in hundredths of a percent. Occasionally we see five-digit designations where the last
three digits tell that the carbon is actually over 1%. Here is an example:
XXX :x.xx% average carbon content
51100
13xx:1.75Mn Manganese
23xx:3.50Ni Nickel
31xx:1.25Ni, 0.65-0.80Cr Nickel-Chromium
40xx:0.20-0.25Mo
Molybdenum
44xx:0.40-0.52Mo
41xx:0.50-0.95Cr, 0.12-0.30Mo Chromium-Molybdenum
46xx:0.85-1.82Ni, 0.20-0.25Mo
Nickel-Molybdenum
48xx:3.5Ni, 0.25Mo
50xx:0.27-0.65Cr

2. 11/18/13 eFunda: General Information on AlloySteels
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