AMS 6409 is a sub-type specification of Steel 4340, an alloy with excellent toughness, very good abrasion resistance, very good shock and impact resistance, and good atmospheric corrosion resistance. The alloy has medium concentrations of nickel, chromium, and molybdenum and medium carbon content.
Thanks to its favorable properties, AMS 6409 finds use in many fields, including the heavy machinery industry, automotive industry, commercial and military aircraft, military ground vehicles, rocket motor cases, pressure vessels, etc.
Tech Steel & Materials offers AMS 6409 in a bar, forging, and tubing form. AMS 6409 comes in the normalized and tempered condition. As a result, the material possesses higher toughness and strength than in the annealed condition, but it’s also not readily machinable.
Thus, we recommend a spheroidized structure or a coarse lamellar pearlitic structure to improve machinability. Similar care should be applied when welding, or otherwise cracking can occur. If necessary, the material should be preheated from 400-580 °F to (≈200-300 °C), followed by after-welding stress relief at 1020-1200 °F (≈550-650 °F). Then, the stress relief should be 60 °F (15 °C) lower than the tempering temperature.
For additional surface hardness, AMS 6409 can be treated with flame or induction hardening (Rc 50) or nitriding (Rc 60).