Explanation of the A.I.S.I. System of Identification

A system of symbols
is used to identify the grades of standard steel.  In those symbols a
capital letter prefix “B” is used to indicate acid Bessemer steel, and “L”
within the grade number is used to identify leaded steels.  Numbers are used
to indicate grades of steel by chemical composition as described below.

Numerical
Designations.  A four-numeral series designates carbon steel or alloy
steel specified to chemical composition ranges.  Five numerals are used to
designate certain types of alloy steels.

The last two digits
of four-numeral series are intended, so far as feasible, to indicate
approximate middle of the carbon range; for example, 35 represents a range
of 0.32 to 0.38 percent.  It is necessary however to deviate from this rule
and to interpolate numbers in the case of some carbon ranges; and for
variations in manganese, phosphorous, sulphur, chromium, or other elements.

The first two digits
of the four-numeral series for the various grades of steel and their meaning
are as follows:

SERIES DESIGNATION

TYPES AND CLASSES

10xx

Nonsulphurized
Carbon Steel Grades.

11xx

Resulphurized
Carbon Steel Grades.

12xx

Rephosphorized
and Resulphurized Carbon Steel Grades.

13xx

Manganese 1.60 to 1.90 Per
Cent.

*15xx

Manganese 1.00 to 1.35 Per
Cent, Sulphur .20 to .30 Per Cent.

23xx

Nickel 3.50 Per Cent.

25xx

Nickel 5.00 Per Cent.

31xx

Nickel 1.25 Per
Cent—Chromium 0.65 or 0.80 Per Cent.

33xx

Nickel 3.50 Per
Cent—Chromium 1.55 Per Cent.

40xx

Molybdenum 0.25 Per Cent.

41xx

Chromium 0.95 Per
Cent—Molybdenum 0.20 Per Cent.

43xx

Nickel 1.80 Per
Cent—Chromium 0.50 or 0.80 Per Cent—Molybdenum 0.25 Per Cent.

46xx

Nickel 1.80 Per
Cent—Molybdenum 0.25 Per Cent.

48xx

Nickel 3.50 Per
Cent—Molybdenum 0.25 Per Cent.

50xx

Chromium 0.30 or 0.60 Per
Cent.

51xx

Chromium 0.80, 0.95 or 1.05
Per Cent.

5xxxx

Carbon 1.00 Per
Cent—Chromium 0.50, 1.00 or 1.45 Per Cent

61xx

Chromium 0.80 or 0.95 Per
Cent—Vanadium 0.10 or 0.15 Per Cent.

86xx

Nickel 0.55 Per
Cent—Chromium 0.50 Per Cent—Molybdenum 0.20 Per Cent.

87xx

Nickel 0.55 Per
Cent—Chromium 0.50 Per Cent—Molybdenum 0.25 Per Cent.

92xx

Manganese 0.85 Per
Cent—Silicon 2.00 Per Cent.

93xx

Nickel 3.25 Per
Cent—Chromium 1.20 Per Cent—Molybdenum 0.12 Per Cent.

94xx

Manganese 1.00 Per
Cent—Nickel 0.45 Per Cent—Chromium 0.10 Per Cent—Molybdenum 0.12 Per Cent.

97xx

Nickel 0.55 Per
Cent—Molybdenum 0.20 Per Cent—Chromium 0.17 Per Cent.

98xx

Nickel 1.00 Per
Cent—Chromium 0.80 Per Cent—Molybdenum 0.25 Per Cent.