AMS 6359 is a sub-type specification of Steel 4340, nickel-chromium-molybdenum steel with medium carbon content. The alloy is deep-hardening, meaning it possesses excellent tensile strength in the hardened and tempered form. Furthermore, AMS 6359 parts can have excellent surface hardness after flame hardening or nitriding.
Tech Steel & Materials offers this specification in plate, sheet, and strip in the annealed form. Thus, the material is readily machinable using standard methods, including sawing, turning, drilling, cutting, boring, etc. However, if machining after hardening and tempering is necessary, it’s recommended to follow specific guidelines.
Similar rules apply for welding. AMS 6359 can be readily welded using most methods, but only in the annealed condition. When welded in the hardened condition, there is a danger of quench cracking. Nonetheless, if necessary, a good weld can be achieved by preheating the area from 400-580 °F to (≈200-300 °C), followed by after-welding stress relief at 1020-1200 °F (≈550-650 °F).
AMS 6359 possesses multiple positive properties, including excellent toughness, good abrasion resistance, very good shock, and impact resistance, and good atmospheric corrosion resistance. As a result, it’s mostly used in the heavy machinery industry for manufacturing transmission components, including shafts, gears, and axles.