300m Alloy Steel

300M is a low alloy, vacuum melted, highly strength steel that is an improved version of the AISI 4340 steel, where the percentage of silicon, vanadium and carbon and molybdenum are increased. In accordance with AMS 6257, AMS 6417 and AMS 6419, 300M provides tensile strength up to 1900-2100 MPa as a result of final heat treatment – the highest tensile strength of through hardening alloy steel available.

The main difference between 300M and ordinary 4340 is a high strength coupled with the properties of toughness and fatigue resistance. Silicon content increases strength and prevents steel from softening under tempering process, whereas the increase in the content of vanadium leads to finer grain structure and prevents grain growth during the heat treatment. The combination of these two results in significantly increased fracture toughness of 300M as compared to other steels with similar strength values.

300M is a vacuum melted steel used in aerospace industry. The manufacturing process helps to reduce the number of non-metallic inclusions and to provide the purity of material. It is a through hardening alloy with uniform properties through thicknesses needed for landing gear. Austenitizing temperature is about 871°С; further oil quenching and double tempering at 315°С are performed.

Main applications of 300M include aircraft landing gear – the dominating material in this sphere for decades now, as well as rocket motor casings, driveshafts, high strength fasteners and structural airframe parts.