300M VAC-ARC steel is a modified 4340 steel with added silicon allowing for use of a higher tempering temperature. The steel has high hardenability and strength with good ductility and toughness in heavy sections. It is used primarily in the 270/300ksi (1862/2068) tensile strength range for structrual aircraft applications. Vacuum arc remelting (VAR) is used to provide optimium cleanliness and preferred ingot structure.
