The majority of the American Iron and Steel Institute (AISI) grade steel available in the UK is Carbon or alloy steel, which has a four digit reference number. The first two digits indicate the alloying element and the last two indicate the amount of carbon in the specification.
Often AISI and SAE grades have the same identification number. The AISI range of steel specifications also includes stainless steels which are 3 digit numbers starting with 2, 3, 4 or 5. The most popular of these are the 300 series austenitic stainless grades, followed by the 400 series martensitic grades.
Carbon Steel
10XX Plain carbon steel, Mn 1.00% max
11XX Resulphurised free cutting
12XX Resulphurised – Rephosphorised free cutting
15XX Plain carbon steel, Mn 1.00-1.65%
Manganese Steel
13XX Mn 1.75%
Nickel Steel
23XX Ni 3.50%
25XX Ni. 5.00%
Nickel Chromium Steel
31XX Ni 1.25%, Cr 0.65-0.80%
32XX Ni 1.75%, Cr 1.07%
33XX Ni 3.50%, Cr 1.50-1.57%
34XX Ni 3.00%, Cr 0.77%
Molybdenum Steel
40XX Mo 0.20-0.25%
44XX Mo 0.40-0.52%
Chromium Molybdenum Steel
41XX Cr 0.50-0.95%, Mo 0.12-0.30%
Nickel Chromium Molybdenum Steel
43XX Ni 1.82%, Cr 0.50-0.80%, Mo 0.25%
47XX Ni 1.82%, Cr 0.50-0.80%, Mo 0.25%
Nickel Molybdenum Steel
46XX Ni 1.05%, Cr 0.45%, Mo 0.20-0.35%
48XX Ni 0.85-1.82%, Mo 0.20-0.25%
Chromium Steel
50XX Ni 3.50%, Mo 0.25%
51XX Cr 0.27-0.65%
50XXX Cr 0.80-1.05%
51XXX Cr 0.50% C 1.00% min
52XXX Cr 1.02%, C 1.00% minCr 1.45%, C 1.00%
Chromium Vanadium Steel
61XX Cr 0.60-0.95%, V 0.10-0.15%
Tungsten Chromium Steel
72XX W 1.75%, Cr 0.75%
Nickel Chromium Molybdenum Steel
81XX Ni 0.30%, Cr 0.40%, Mo 0.12%
86XX Ni 0.55%, Cr 0.50%, Mo 0.20%
87XX Ni 0.55%, Cr 0.50%, Mo 0.25%
88XX Ni 0.55% Cr 0.50% Mo 0.35%
Silicon Manganese Steel
92XX Si 1.40-2.00%, Mn 0.65-0.85% Cr 0.65%
Nickel Chromium Molybdenum Steel
93XX Ni 3.25%, Cr 1.20%, Mo 0.12%
94XX Ni 0.45%, Cr 0.40%, Mo 0.12%
97XX Ni 0.55%, Cr 0.20%, Mo 0.20%
98XX Ni 1.00%, Cr 0.80%, Mo 0.25%