AISI/SAE Steel Numbering System

TechTipsMachining knowledge, made practicalAISI / SAE Steel Numbering SystemHow to read a 4-digit steel designation: the first digits identify the alloy family, the last two give the carbon content in hundredths of a percent (e.g. 1045 = plain carbon steel, 0.45% C).

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Reading the code: in 10XX, "10" is the series (alloy family) and "XX" is the nominal carbon content in hundredths of a percent. Example: 4140 → series 41 (chromium-molybdenum steel) with ~0.40% carbon. A letter "L" inside the code (e.g. 12L14) indicates added lead for free machining; "B" indicates boron.

Steel Series by Alloy Family

Family Series Composition
Carbon Steels 10XX Plain carbon, mn 1.00% max
11XX Resulfurized free machining
12XX Resulfurized/rephosphorized free machining
15XX Plain carbon, mn 1.00-1.65%
Manganese Steel 13XX MN 1.75%
Nickel Steels 23XX NI 3.50%
25XX NI 5.00%
Nickel-Chromium Steels 31XX NI 1.25%, CR .65-.80%
32XX NI 1.75%, CR 1.07%
33XX NI 3.50%, CR 1.50-1.57%
34XX NI 3.00%, CR .77%
Molybdenum Steels 40XX MO .20-.25%
44XX MO .40-.52%
Chromium-Molybdenum Steels 41XX CR .50-.95%, MO .12-.30%
Nickel-Chromium-Molybdenum Steels 43XX NI 1.82%, Cr .50-.80%, MO .25%
47XX NI 1.05%, Cr .45%, MO .20-.35%
Nickel-Molybdenum Steels 46XX NI .85-1.82%, MO .20-.25%
48XX NI 3.50%, MO .25%
Chromium Steels 50XX CR .27-.65%
51XX CR .80-1.05%
50XXX CR .50%, C 1.00% MIN
51XXX CR 1.02%, C 1.00% MIN
52XXX CR 1.45%, C 1.00% MIN
Chromium-Vanadium Steels 61XX CR .60-.95%, V .10-.15%
Tungsten-Chromium Steels 72XX W 1.75%, CR .75%
Nickel-Chromium-Molybdenum Steels 81XX NI .30%, Cr .40%, MO .12%
86XX NI .55%, Cr .50%, MO .20%
87XX NI .55%, CR .50%, MO .25%
88XX NI .55%, CR .50%, MO .35%
Silicon-Manganese Steels 92XX SI 1.40-2.00%, MN .65-.85%, CR 0-.65%
Nickel-Chromium-Molybdenum Steels 93XX NI 3.25%, CR 1.20%, MO .12%
94XX Ni .45%, Cr .40%, Mo .12%
97XX NI .55%, CR .20%, MO .20%
98XX NI 1.00%, CR .80%, MO .25%
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