General Information about Alloy Steel

The workers pouring a molten alloy steel into mold

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. Most of the pipe that operate in harsh environment is made of alloy steel materials 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 51 100 13 xx:1.75Mn  Manganese 23 xx:3.50Ni  Nickel 31 xx:1.25Ni, 0.65-0.80Cr  Nickel-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  Nickel-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  Nickel-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.