*1040 alloy :
Carbon : 0.37 - 0.44 %
1040 steel has a higher (0.40%) carbon content for greater strength than the lower carbon alloys. It is hardenable by heat treatment, quench and tempering to develop 150 to 250 ksi tensile strength.
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*The American Iron and Steel Institute, which inaugurated this system, uses a very clear, defined method of explanation for this nomenclature. In their 4-digit system for classifying all Carbon Steel alloys, which are most commonly used to make forged irons, the number 1 means the metal is a carbon steel. The second digit of 0 or 1 refers to the processing method for making the carbon steel alloy, which is not important for this explanation. The last two digits confirm the percentage of the element Carbon in the alloy, such that 1040 means the alloy contains between 0.37% to 0.44% Carbon in the mix.