T.O. 1-1A-9
SECTION II
FERROUS (STEEL) ALLOYS
2-1. CLASSIFICATION.
2-2. SAE NUMBERING SYSTEM. A numeral index system is used to identify the compositions of the SAE steels, which
makes it possible to use 'numerals that are partially descriptive of the composition of material covered by such numbers.
The first digit indicates the type to which the steel belongs; for example "1" indicates a carbon steel; "2" a nickel steel;
and "3" a nickel chromium steel. In the case of the simple alloy steels, the second digit generally indicates the
approximate percentage of the predominant alloying element. Usually the last two or three digits indicate the
approximate average carbon content in "points" or hundredths of 1 percent. Thus "2340" indicates a nickel steel of
approximately 3 percent nickel (3.25 to 3.75) and 0.40 percent carbon (0.38 to 0.43). In some instances, in order to
avoid confusion, it has been found necessary to depart from this system of identifying the approximate alloy composition
of a steel by varying the second and third digits of the number. An instance of such departure is the steel numbers
selected for several of the corrosion--and heat resisting alloys.
2-3. The basic numerals for the various types of SAE steel are:
2-4. CARBON STEELS, Steel containing carbon in percentages rant from 0.10 to 0.30 percent is classed as low carbon
steel. The equivalent SAE numbers range from 1010 to 1030. Steels of this grade are used for the manufacture of
articles such as safety wire, certain nuts, cable bushing, etc. This steel in sheet form is used for secondary structural
parts and clamps and in tubular form for moderately stressed structural parts.
2-1
