A36 Mild Steel is a structural steel.
ASTM A36 steel is the most commonly available of the hot-rolled steels. It is generally available in round rod, square bar, rectangle bar, as well as steel shapes such as I-Beams, H-beams, angles, and channels. The hot roll process means that the surface on this steel will be somewhat rough. Note that its yield strength is also significantly less than 1018 - this means that it will bend much more quickly than will 1018. Finally, machining this material is noticeably more difficult than 1018 steel, but the cost is usually significantly lower.
http://www.onlinemetals.com/steelguide.cfm2 inch diameter
A36 One Ft. (12") Length - $21.47
1018 One Ft. (12") Length - $19.42
Stick with the 1018, its cheaper, stronger and more machineable.