1: 4140 steel introduction
    AISI SAE 4140 alloy steel is a chromium molybdenum alloy steel specification widely used in general purpose high tensile steel for components, like axles, shafts, bolts, gears and other applications. Similar to alloy grade AISI 4130 chrome moly alloy steel but with a slightly higher carbon content. The higher carbon content of AISI 4140 steel gives greater strength and heat treatment capabilities in comparison to AISI / ASTM 4130 alloy steels, however it does have inferior weldability characteristics..

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2: 4140 Steel equivalent