High strength, high impact toughness steels are required in large quantities for many Air Force (AF) applications.
Often crucial material properties include initial impact/shock-up survival, resistance to bending, and abrasive material losses, such as for high performance penetrating weapons, colloquially referred to as “Bunker Busters.” Many high strength alloys suffer from low toughness – particularly low temperature toughness – which leads to a reduction of initial shock/early impact survivability. Low temperature qualities are critical because bombs loaded on airplanes flying at high altitudes become cold-soaked in the subzero stratosphere.
Alloys containing relatively high amounts of nickel and cobalt are traditionally used in these applications as they provide an ideal balance of strength and toughness.
However, these alloys are very expensive, and cost-prohibitive to make in large quantities. As an example, Eglin Steel (ES-1) was developed in the early 2000’s by industry paired with the US Air Force to provide a low-cost replacement for more expensive HP9-4-20, Aermet™, and AF-1410 alloys.
In 2012 AF96 steel development commenced to find a lower cost alternative to ES-1 that would exhibit the same superior properties in high strength and high impact toughness even with sections up to 4” thick. ES-1 contained tungsten alloy, but at 1% of the weight, the tungsten comprised 25% of the total cost of the steel components. AF96 steel contains little in the way of expensive alloy content and relies on special processing techniques/mechanisms to develop a high strength/toughness level even at low temperatures (-40F to -65F). AF96 steel is amenable to both sand/investment casting and forging processes, increasing production capability and lowering cost for the Air Force.