Eglin steel
Eglin steel is a high-strength, high-performance, low-alloy, low-cost steel, developed for a new generation of bunker buster type bombs, e.g. the Massive Ordnance Penetrator and the improved version of the GBU-28 bomb known as EGBU-28. It was developed by the US Air Force and the Ellwood National Forge Company.
The Air Force sought a low-cost replacement for strong and tough but expensive superalloy steels such as AF-1410, Aermet-100, HY-180, and HP9-4-20/30. A high-performance casing 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.
The material can be less expensive because it can be ladle-refined. It does not require vacuum processing. Unlike some other high-performance alloys, Eglin steel can be welded easily, broadening the range of its application. Also, it uses roughly half as much nickel as other superalloys, substituting silicon to help with toughness and particles of vanadium carbide and tungsten carbide for additional hardness and high-temperature strength. The material also involves chromium, tungsten, and low to medium amounts of carbon, which contribute to the material's strength and hardness.
Properties
At room temperature, ES-1's yield is, and its ultimate strength is. At, its yield is, and its ultimate strength is. Rockwell C hardness is 45.6. For toughness, the Charpy notch impact is at room temperature, and at.ES-1 is a balance of cost, tensile strength, high temperature tensile strength and toughness. By varying the heat treatment to include water or liquid nitrogen quenching, or omitting the normalization heat-treat to permit work hardening, properties can be improved. ES-5, with an economical air and water quench, provides of high-rate yield strength, and high-rate ultimate strength. Low-rate yield strength is, and low-rate ultimate strength is.
By comparison, ordinary structural steel has a yield strength of, and 4150 "ordnance" steel has a yield strength of.
Details
The material composition by weight is:- Iron
- Carbon
- Manganese
- Silicon, stabilizes the austenite phase, enhances toughness
- Chromium, increases strength and hardenability
- Molybdenum, increases hardenability
- Nickel, increases toughness
- Tungsten, increases strength and wear resistance
- Vanadium, increases toughness
- Copper
- Phosphorus
- Sulfur
- Calcium, sulfur control agent
- Nitrogen
- Aluminium
The material has to undergo heat treatment involving normalization, quenching and tempering to develop the required austenitic microstructure, with subsequent tempering. Test plates were. First they were normalized. They were charged in a furnace at, heated at per hour to, held at for an hour per inch of section size, and then air-cooled to room temperature. Next the samples were austenized by repeating the process up to, and held for an hour per inch of section size, then oil quenched to below. Finally, they were tempered in an oven that started below, increased at per hour per inch of section size, and allowed to air-cool to room temperature.