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 steel.
B. 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:
If a B shows up between the second and third digits of an AISI number, it means that this grade is a Boron steel; Sometimes a suffix H is attached to a AISI number to indicate that the steel has been produced to prescribed hardenability limits.
Up : XXX :x.xx% average carbon content
Down : 51100
13 | xx:1.75Mn | Manganese |
23 | xx:3.50Ni | Nickle |
31 | xx:1.25Ni, 0.65-0.80Cr | Nickle - Chromium |
40 | xx:0.20-0.25Mo | Molybdenum |
44 | xx:0.40-0.52Mo | |
41 | xx:0.50-0.95Cr, 0.12-0.30Mo | Chromium - Molybdenum |
46 | xx:0.85-1.82Ni, 0.20-0.25Mo | Nickle - Molybdenum |
48 | xx:3.5Ni, 0.25Mo | |
50 | xx:0.27-0.65Cr | Chromium |
51 | xx:0.80-1.05Cr | |
50 | xxx:0.50Cr, 1.00C | |
51 | xxx:1.02Cr, 1.00C | |
52 | xxx:1.45Cr, 1.00C | |
61 | xx:0.60-0.95Cr, 0.10-0.15V | Chromium - Vanadium |
92 | xx:1.4-2Si, 0.65-0.85Mn, <0.65cr | Silicon - Manganese |
43 | xx:1.82Ni, 0.50-0.80Cr, 0.25Mo | Nickle - Chromium - Molybdenum |
47 | xx:1.05Ni, 0.45Cr, 0.20-0.35Mo | |
81 | xx:0.30Ni, 0.40Cr, 0.12Mo | |
86 | xx:0.55Ni, 0.50Cr, 0.25Mo | |
87 | xx:0.55Ni, 0.50Cr, 0.25Mo | |
88 | xx:0.55Ni, 0.50Cr, 0.20-0.35Mo | |
93 | xx:3.25Ni, 1.20Cr, 0.12Mo | |
94 | xx:0.45Ni, 0.40Cr, 0.12Mo |
If a B shows up between the second and third digits of an AISI number, it means that this grade is a Boron steel; Sometimes a suffix H is attached to a AISI number to indicate that the steel has been produced to prescribed hardenability limits.
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