Eglin Steel
Encyclopedia
Eglin steel 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 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 superalloy
s, 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.
before deformation) is 224,500 PSI
(1547 MPa), ultimate yield (breaking point) is 263,700 PSI (1818 MPa). At 900°C, yield is 193,900 PSI (1337 MPa), and ultimate yield is 246,700 (1701 MPa). Rockwell hardness is 45.6 (455 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
, properties can be improved.
ES-5, with an economical air and water quench,
provides 244,800 PSI of yield, and 291,900 PSI ultimate yield.
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 and tempering
in order 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.
Strength of materials
In materials science, the strength of a material is its ability to withstand an applied stress without failure. The applied stress may be tensile, compressive, or shear. Strength of materials is a subject which deals with loads, deformations and the forces acting on a material. A load applied to a...
, high-performance, low-alloy, low-cost steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
, developed for new generation of bunker buster
Bunker buster
A bunker buster is a bomb designed to penetrate hardened targets or targets buried deep underground.-Germany:Röchling shells were bunker-busting artillery shells, developed by German engineer August Cönders, based on the theory of increasing sectional density to improve penetration.They were tested...
type bombs, eg. the Massive Ordnance Penetrator
Massive Ordnance Penetrator
The Massive Ordnance Penetrator GBU-57A/B is a project by the U.S. Air Force to develop a massive, precision-guided, "bunker buster" bomb...
and the improved version of the GBU-28
GBU-28
The Guided Bomb Unit 28 is a 5,000 pound laser-guided "bunker busting" bomb nicknamed "Deep Throat" 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 during Operation Desert Storm to...
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 superalloy
Superalloy
A superalloy, or high-performance alloy, is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. Superalloys typically have a matrix with an austenitic face-centered cubic crystal structure. ...
steels such as AF-1410, Aermet-100
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 toughness, and ductility. Aermet is weldable with no...
, 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
Missile
Though a missile may be any thrown or launched object, it colloquially almost always refers to a self-propelled guided weapon system.-Etymology:The word missile comes from the Latin verb mittere, meaning "to send"...
parts and tank
Tank
A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...
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
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
easily, broadening the range of its application. Also, it uses roughly half as much nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
as other superalloy
Superalloy
A superalloy, or high-performance alloy, is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. Superalloys typically have a matrix with an austenitic face-centered cubic crystal structure. ...
s, substituting silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
to help with toughness
Toughness
In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing; Material toughness is defined as the amount of energy per volume that a material can absorb before rupturing...
and particles of vanadium carbide
Vanadium carbide
Vanadium carbide, VC, is an extremely hard refractory ceramic material. It is commercially used in tool bits cutting tools. It has the appearance of gray metallic powder with cubic crystal structure....
and tungsten carbide
Tungsten carbide
Tungsten carbide is an inorganic chemical compound containing equal parts of tungsten and carbon atoms. Colloquially, tungsten carbide is often simply called carbide. In its most basic form, it is a fine gray powder, but it can be pressed and formed into shapes for use in industrial machinery,...
for additional hardness and high-temperature strength. The material also involves chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
, tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
, and low to medium amounts of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
, which contribute to the material's strength
Strength of materials
In materials science, the strength of a material is its ability to withstand an applied stress without failure. The applied stress may be tensile, compressive, or shear. Strength of materials is a subject which deals with loads, deformations and the forces acting on a material. A load applied to a...
and hardness.
Properties
At room temperature, ES-1's yield (tensile strengthTensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...
before deformation) is 224,500 PSI
Pounds per square inch
The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...
(1547 MPa), ultimate yield (breaking point) is 263,700 PSI (1818 MPa). At 900°C, yield is 193,900 PSI (1337 MPa), and ultimate yield is 246,700 (1701 MPa). Rockwell hardness is 45.6 (455 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
Work hardening
Work hardening, also known as strain hardening or cold working, is the strengthening of a metal by plastic deformation. This strengthening occurs because of dislocation movements within the crystal structure of the material. Any material with a reasonably high melting point such as metals and...
, properties can be improved.
ES-5, with an economical air and water quench,
provides 244,800 PSI of yield, and 291,900 PSI ultimate yield.
Details
The material composition by weight is:- IronIronIron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
(remaining balance to 100%) - CarbonCarbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
(0.16-0.35%) - ManganeseManganeseManganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
(0.85%) - SiliconSiliconSilicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
(max. 1.25%), stabilizes the austeniteAusteniteAustenite, also known as gamma phase iron, 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 ; other alloys of steel have different eutectoid temperatures...
phase, enhances toughness - ChromiumChromiumChromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
(max. 1.50-3.25%), enhances strength and hardenability - MolybdenumMolybdenumMolybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
(max. 0.55%), enhances hardenability - NickelNickelNickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
(5.00%), increases toughness - TungstenTungstenTungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
(0.70-3.25%), enhances strength and wearWearIn materials science, wear is erosion or sideways displacement of material from its "derivative" and original position on a solid surface performed by the action of another surface....
resistance - VanadiumVanadiumVanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...
(0.05-0.3%), increases toughness - CopperCopperCopper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
(0.50%) - PhosphorusPhosphorusPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
(impurity, max. 0.015%) - SulfurSulfurSulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
(impurity, max. 0.012%) - CalciumCalciumCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
(max. 0.02%), sulfur control agent - NitrogenNitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
(impurity, max. 0.14%) - AluminiumAluminiumAluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
(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
Heat treatment
Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass...
involving normalization, quenching and tempering
Tempering
Tempering is a heat treatment technique for metals, alloys and glass. In steels, tempering is done to "toughen" the metal by transforming brittle martensite or bainite into a combination of ferrite and cementite or sometimes Tempered martensite...
in order to develop the required austenitic microstructure
Microstructure
Microstructure is defined as the structure of a prepared surface or thin foil of material as revealed by a microscope above 25× magnification...
, with subsequent tempering
Tempering
Tempering is a heat treatment technique for metals, alloys and glass. In steels, tempering is done to "toughen" the metal by transforming brittle martensite or bainite into a combination of ferrite and cementite or sometimes Tempered martensite...
. 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.