4340 is a Standard grade Alloy Steel. It is commonly called AISI 4340 Nickel-chromium-molybdenum steel. It is composed of (in weight percentage) 0.38-0.43% Carbon (C), 0.60-0.80% Manganese (Mn), 0.035%(max) Phosphorus (P), 0.04%(max) Sulfur (S), 0.15-0.30% Silicon (Si), 0.70-0.90% Chromium (Cr), 1.65-2.00% Nickel (Ni), 0.20-0.30% Molybdenum (Mo), and the base metal Iron (Fe). Other designations of AISI 4340 alloy steel include UNS G43400 and AISI 4340.
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