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Eglin Steel
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Eglin Steel (ES-1) is a high-strength, high-performance, low-alloy, low-cost steel, developed for new generation of bunker buster type bombs, eg. the Massive Ordnance Penetrator and the improved version of the GBU-28 bomb known as EGBU-28. It was developed in collaboration between the US Air Force and the Ellwood National Forge Company.
The development of Eglin Steel was commissioned in order to find a low-cost replacement for strong and tough but expensive AF-1410, Aermet-100, HY-180, and HP9-4-20/30 steels. Such high-performance material is required so the weapon survives the high impact speeds required for deep penetration. The material has a wide range of other applications, from missile parts and tank bodies to machine parts. Unlike some other high-performance alloys, Eglin Steel can be welded easily, further broadening the range of its applications.
The composition of the material involves chromium, tungsten, and low to medium amount of carbon, which contribute to the material's strength and hardness, nickel (in a relatively low amount) and silicon which help with toughness, and vanadium and tungsten carbide particles which contribute additional hardness and high-temperature strength.
The material composition is: [1]
- Iron (remaining balance to 100%)
- Carbon (0.16-0.35%)
- Manganese (0.85%)
- Silicon (max. 1.25%), stabilizes the austenite phase, enhances toughness
- Chromium (max. 1.50-3.25%), enhances strength and hardenability
- Molybdenum (max. 0.55%), enhances hardenability
- Nickel (5.00%), increases toughness
- Tungsten (0.70-3.25%), enhances strength and wear resistance
- Vanadium (0.05-0.3%), increases toughness
- Copper (0.50%)
- Phosphorus (impurity, max. 0.015%)
- Sulfur (impurity, max. 0.012%)
- Calcium (max. 0.02%), sulfur control agent
- Nitrogen (impurity, max. 0.14%)
- Aluminium (max. 0.05%)
The material has to undergo heat treatment involving quenching, in order to develop the required austenitic microstructure, with subsequent tempering.