Air Force

Low alloy, high impact toughness steel

Strength and toughness without expensive alloys. Superb material properties at -40 Celsius, even in thick sections.

Materials

Dr. Rachel Abrahams of the U.S. Air Force Research Laboratory’s Munitions Directorate has invented a new alloy for manufacturing bunker-buster munitions. The patented formula is available via license agreement to companies that would make, use, or sell it commercially.

The US Air Force Seeks to commercialize a tungsten free, low alloy steel with the strength, ductility and impact toughness at sub-zero temperatures equivalent to steels that cost several times more.

Typical Composition of USAF-96 Steel

The low alloy steel, known as USAF-96, when thermally processed with the Air Force’s patented method has an ultimate tensile strength of 245 KSI; yield strength at 0.2% offset of 187 KSI; elongation to failure of 13%; and an impact toughness as measured with a Charpy V-notch test at -40°C of 30 ft-lb.

Of particular benefit is the through hardenability and toughness, which has demonstrated strength and toughness at -40°C even with sections up to 4-inches in thickness.

Steel with this combination of performance usually contains significant amounts of tungsten, cobalt, or nickel, which are amongst the most expensive alloying elements.

Moreover, tungsten is difficult to process and complicates the waste streams; most high-performance nickel-cobalt alloys require expensive vacuum-induction-melting/vacuum-air-remelting (VIM-VAR) techniques.

USAF-96 Steel contains no tungsten or cobalt and is a low carbon, low nickel-alloy steel composition. In addition to its material cost advantage, USAF-96 Steel can be produced using standard air-melt production processes, at a substantially lower cost than prior methods.

USAF-96’s material composition along with specific thermal processing conditions leads to the growth of beneficial nano-scaled carbides in a martensitic matrix that allows the steel to possess its high-performance characteristics even in heavier sections while using reduced quantities of expensive alloying elements.

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