300M-HS 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. Vacuum arc remelting (VAR) is used to provide optimium cleanliness and preferred ingot structure
This variant has been developed for applications requiring 287 ksi (1979 MPa) minimum tensile strength through stringent control of chemistry and processing parameters. The enhanced properties of 300M-HS permit the design of lighter aircraft components that exhibit equivalent load carrying capacities compared to standard 300M components.