3,063 aisi 4140 carbon alloy steel round bars products are offered for sale by suppliers on , of which steel round bars accounts for 70%, stainless steel bars accounts for 1%, and steel wire accounts for 1%. A wide variety of aisi 4140 carbon alloy steel round bars options are available to you, such as aisi, astm, and jis.4140 Round Bars, SAE AISI 4140 Alloy Steel Bars AISI 4140 round bars steel is an engineering alloy steel containing molybdenum and chromium. 4140 steel round bars falls in a class of low alloy steel. It has high fatigue strength, toughness, abrasion and impact resistance, and torsional strength. It can be heat treated in a number of ways to give it a combination of properties.