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. In the case of the simple alloy steels, the second digit generally indicates the approximate percentage of the predominant alloying element.
The US designations for steels are those of the American Iron and Steel Institute (AISI) and the Society of Automotive Engineers (SAE). In both of them, the composition is denoted by a four digit number.
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; ‘‘3’’ a nickel chromium steel etc.
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 numbers selected for several of the corrosion and heat resisting alloys.
The last two digits stand for carbon content. For example, xx45 stands for 0.45%C. The first two digits denote the other alloying elements. For example, 1040 stands for a 0.40%C steel. AISI 4340 means a NI-Cr-Mo steel, with 1.8%Ni, 0.8%Cr, 0.25%Mo, and 0.4%C. The 9260 is a spring steel with 25%Si, 0.9%Mn and 0.6%C. The 52100 is a ball bearing steel with 1.45%Cr and 1.0%C.
Click on the link to see a list of SAE AMS standards covering the following material categories:
Group of standards for stainless steels: Part One
Group of standards for stainless steels: Part Two
Group of nickel alloys/heat resistant nickel alloys
Group of standards for iron and steel castings
Group of standards for forgings
Group of standards for coated steels & welding and filler materials