The SAE classification system uses numerical codes to designate steel compositions. The first digit indicates the class of steel (e.g. 1 for carbon steel). The second digit usually represents the percentage of the main alloying element. The last two digits indicate the carbon content as a percentage. For example, SAE 1070 designates a carbon steel with approximately 0.70% carbon. SAE 4130 is an exception, as chromium is the main alloy rather than molybdenum, even though it is classified as a group 4 steel. The second digit of 1% indicates the chromium content of around 1%.

1. A/C MATERIALS DATE :
SAE CLASSIFICATION OF STEELS NAME :
GENERAL
A standardized numerical index system, originally developed by the Society of Automotive Engineers
(SAE), is used to designate the steel used in aircraft and automotive construction with this system, it is
possible to use numerical on the shop drawings and blueprints to describle in part the quality of material
covered by such numbers. For instance, high-carbon steel is designated as 1070.
NUMERICAL INDEX SYSTEM
The first figure (digit) of the classification number indicates to which class the steel belongs : thus, the
figure (1) in the number 1070 indicates a carbon steel ; if figure were (2), a would indicate a nickel
steel, and, if (3), a nickel-chromium steel. The second figure in the SAE number 1070 is zero. This
indicates that there is no alloying element; which is the case in plain carbon steels. In the case of alloy
steels, the second figure generally indicates the approximate percentage % of the principle alloying
element.
Carbon steels 1
Nickel steels 2
Nickel-Chromium steels 3
Molybdenum steels 4
Chromium steels 5
Chromium-vanadium steels 6
Tungsten steels 7
Manganese-Molybdenum and nickel-Chromium-Molybdenum steels 8
Silicon-Manganese steels 9
SAE 1 0 70
First figure (1), carbon steel
Second figure (0), no alloy
Last two figures (70), approximately
0.70 % carbon
SAE 2 3 30
First figure (2), nickel steel
Second figure (3), approximately
3 % nickel
Last two figures (30), approximately
0.40 % carbon
Usually, the last two or three figures (digits) indicate the average carbon content in points or
hundredths of 1 %.
The last two figures in SAE 1070 being 70 tells us that the steel contains 0.70 % carbon, which is less
than 1 %. Thus, the number 2340 indicates a nickel steel of approximately 3 % nickel (3.25 to 3.75 %)

2. and 0.40 % carbon (0.35 to 0.45 %) ; and the number 71360 indicates, a tungsten steel of about 13 %
tungsten (12 to 15 %) and 0.60 % carbon (0.50 to 0.70 %). The basic numerals of the various qualities
of steels specified are as follows :
SAE 7 13 50
First figure (7), tungsten steel
second figure (13), approximately
13 % tungsten
Last two figures (50), approximately
0.60 % carbon
In determining the approximated composition of steel from the SAE number, it should be noted that the
class or basic alloying element is indicated by the first figure. That the percentage of the basic alloying
element is indicated by the second figure in the most classes; and the carbon content in hundredths of
one per cent is indicated by the last two figures.
SAE 4130 is in exception to the general rules previously mentioned. Because the SAE code was set up
in, or about the year 1906, there was no provision made for 4130, a chrome molybdenum steel,
introduced later in about the year 1918. Actually, chromium is the predominating alloy in 4130 steel,
and not molybdenum, even through it is classed as a group (4) steel. The second figure (1) in 4130 steel
indicates approximately 1 % chromium. The molybdenum content, being lower than the chromium, is
not given. This is show in the following analysis and example :
SAE 4 1 30
(Contains)
Carbon 0.28%-0.33%
Chromium 0.80%-1.10%
Manganese 0.40%
Molybdenum 0.15%-0.25%
Phosphorus (max) 0.40%
Sulphur (max) 0.40%
Silicon 0.20%-0.35%
SAE Chrome Moly 4 1 30
First figure (4), molybdenum steel
Second figure (1), approximately
1 % chromium
Last two figures (30), approximately
0.30 % carbon