Eglin steel (ES-1) is a high- strength, high-performance, low-alloy, low-cost

steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...

, developed for a new generation of bunker buster type bombs, e.g. the Massive Ordnance Penetrator and the improved version of the

GBU-28 The GBU-28 is a 5,000-pound (2,268 kg) class laser-guided " bunker busting" bomb produced originally by the Watervliet Arsenal, Watervliet, New York. It was designed, manufactured, and deployed in less than three weeks due to an urgent need ...

bomb known as EGBU-28. It was developed in collaboration between the

US Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Sig ...

and the Ellwood National Forge Company. The development of Eglin steel was commissioned to find a low-cost replacement for strong and tough but expensive

superalloy A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, ...

steels such as AF-1410,

Aermet-100 AerMet alloy is an ultra-high strength type of martensitic alloy steel. The main alloying elements are cobalt and nickel, but chromium, molybdenum and carbon are also added. Its exceptional properties are hardness, tensile strength, fracture to ...

, 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 In military terminology, a missile is a guided airborne ranged weapon capable of self-propelled flight usually by a jet engine or rocket motor. Missiles are thus also called guided missiles or guided rockets (when a previously unguided rocket ...

parts and

tank A tank is an armoured fighting vehicle intended as a primary offensive weapon in front-line ground combat. Tank designs are a balance of heavy firepower, strong armour, and good battlefield mobility provided by tracks and a powerful ...

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 Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...

as other

s, substituting

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

to help with

toughness In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.vanadium carbide and

tungsten carbide Tungsten carbide (chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into ...

for additional hardness and high-temperature strength. The material also involves

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hard ...

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...

, and low to medium amounts of

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...

, which contribute to the material's strength and

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...

Properties

At room temperature, ES-1's yield (

tensile strength Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials ...

before deformation) is 193 900 psi (1 337 MPa), ultimate strength (breaking point) is 246 700 psi (1 701 MPa). At 900°F (482°C), yield is 191 400 psi (1 320 MPa), and ultimate strength is 215 700 psi (1 487 MPa). Rockwell C hardness is 45.6 (448 HV₁₀). For toughness, the Charpy notch impact is 56.2 foot-pounds (76 J) at room temperature, and 42.7 ft-lbs (58 J) at -40F (-40°C). 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 In materials science, work hardening, also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. Work hardening may be desirable, undesirable, or inconsequential, depending on the context. This strengt ...

, properties can be improved. ES-5, with an economical air and water quench, provides 244 800 psi (1 688 MPa) of high-rate yield strength, and 291 900 psi (2 013 MPa) high-rate ultimate strength. Low-rate yield strength is 216 000 psi (1 489 MPa), and low-rate ultimate strength is 270 200 psi (1 863 MPa). By comparison, ordinary

structural steel Structural steel is a category of steel used for making construction materials in a variety of shapes. Many structural steel shapes take the form of an elongated beam having a profile of a specific cross section. Structural steel shapes, si ...

yields at 36,000 PSI, 4150 "ordnance" steel (used in high-quality military gun barrels) at 75,000.

Details

The material composition by weight is: *

Iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...

(84.463–90%) *

Carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...

(0.16–0.35%) *

Manganese Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...

(0.85%) *

Silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

(max. 1.25%), stabilizes the

austenite Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 100 ...

phase, enhances toughness *

Chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hard ...

(max. 1.50–3.25%), enhances strength and hardenability *

Molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lead ...

(max. 0.55%), enhances hardenability *

Nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...

(5.00%), increases toughness *

Tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...

(0.70–3.25%), enhances strength and

wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in ...

resistance *

Vanadium Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an oxide layer ( pass ...

(0.05–0.3%), increases toughness *

Copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...

(0.50%) *

Phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...

(impurity, max. 0.015%) *

Sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

(impurity, max. 0.012%) *

Calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...

(max. 0.02%), sulfur control agent *

Nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

(impurity, max. 0.14%) *

Aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...

(max. 0.05%) The material has an unusually wide range of production methods for a superalloy: electric arc, ladle refined with vacuum treatment; vacuum induction melting; vacuum arc remelting, and even electro slag remelting. Vacuum treatments are recommended for best strength and premium uses. The material has to undergo heat treatment involving normalization,

quenching In materials science, quenching is the rapid cooling of a workpiece in water, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as ...

and tempering to develop the required austenitic microstructure, with subsequent tempering. Test plates were 1 inch. First they were normalized. They were charged in a furnace at 500F. Heated at 125F per hour to 1625–1725F. Held at 1750F 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 1700F, and held for an hour per inch of section size, then oil quenched to below 125F. Finally, they were tempered by in an oven that started below 500F, increased at 100F per hour per inch of section size, and allowed to air-cool to room temperature.U.S. Patent No. 7,537,727 B2, Accessed July 16, 2009, column 4, line 35

Credit

The patent credits Morris Dilmore and James Ruhlman as inventors.

References

{{Reflist, 2

External links

AFRL Horizons - Eglin steel

Ellwood National Forge Company
Steels

Properties

Details

Credit

See also

References

External links