USAF-96 is a high-

strength Strength may refer to: Physical strength *Physical strength, as in people or animals * Hysterical strength, extreme strength occurring when people are in life-and-death situations *Superhuman strength, great physical strength far above human c ...

, 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-resistant ty ...

, developed for new generation of

bunker buster A bunker buster is a type of munition that is designed to penetrate hardened targets or targets buried deep underground, such as military bunkers. Armor piercing shells Germany Röchling shells were bunker-busting artillery shells, developed by ...

type bombs, e.g. the

Massive Ordnance Penetrator The GBU-57A/B Massive Ordnance Penetrator (MOP) is a precision-guided, " bunker buster" bomb used by the United States Air Force. This is substantially larger than the deepest-penetrating bunker busters previously available, the GBU-28 and ...

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 by 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 Signal ...

at the Eglin Air Force Munitions Directorate. It uses only materials domestic to the USA. In particular it requires no

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 isolat ...

. The development of this steel was directed 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, g ...

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 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 i ...

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 engin ...

bodies to machine parts. An earlier material,

Eglin steel Eglin steel (ES-1) 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 ...

, ES-1, resolved these issues but the

used in it was expensive, difficult to melt, and the resulting tungsten carbide particles made the material difficult to process in thick sections. However, the tungsten also gave ES-1 excellent high-temperature strength. These materials can be less expensive because they can be ladle-refined. They do not require vacuum processing. Unlike some other high-performance alloys, they can be

welded Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as braz ...

easily, broadening the range of applications. Also, these formulas use 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 to ...

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 tab ...

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 Vanadium carbide is the inorganic compound with the formula V C. It is an extremely hard refractory ceramic material. With a hardness of 9-9.5 Mohs, it is possibly the hardest metal-carbide known. It is of interest because it is prevalent in v ...

(and for ES-1, tungsten carbide) for additional hardness and high-temperature strength. The materials also use

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 hardne ...

, some

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 lea ...

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 In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

, which contribute to the materials'

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, USAF-96

USAF-96 is a balance of cost, 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. With an economical water quench, the yield at room temperature (

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 t ...

before deformation) is 194,600

psi Psi, PSI or Ψ may refer to: Alphabetic letters * Psi (Greek) (Ψ, ψ), the 23rd letter of the Greek alphabet * Psi (Cyrillic) (Ѱ, ѱ), letter of the early Cyrillic alphabet, adopted from Greek Arts and entertainment * "Psi" as an abbreviatio ...

(1341.7 MPa), ultimate strength (breaking point) is 250,100 psi (1724.3 MPa). Rockwell hardness is 48.7. For toughness, the Charpy V-notch result is 29.0 ft.-lb (39.3 J) at -40F (-40 °C). By comparison, ordinary A36 structural steel yields at , and 4150 "ordnance" steel (used in high-quality military gun barrels) at . The material is not expected to be corrosion resistant. Also, a hydrogen bake-out might be required to assure high-quality welds.

Details

USAF-96's composition by weight is: *

Carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

(0.24 to 0.32%) The upper limit prevents quench-cracking and defects. *

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 hardne ...

(2.00 to 3.00%), 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 lea ...

(0.50 to 1.50%), enhances hardenability, and the upper limit prevents segregation and stabilization of

bainite Bainite is a plate-like microstructure that forms in steels at temperatures of 125–550 °C (depending on alloy content). First described by E. S. Davenport and Edgar Bain, it is one of the products that may form when austenite (the face- ...

. *

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 ( pas ...

(0.05 to 0.35%), increases toughness, and prevents grain boundaries from growing at high temperatures. *

Manganese Manganese is a chemical element with the 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 industrial alloy use ...

(1.00% or less) This optionally can increase strength and toughness, but it is not required. The upper limit prevents secondary phases that reduce strength. *

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 to ...

(3.00% or less), increases toughness at low temperatures (<-40C). However, it increases cost. *

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 tab ...

(1.50% or less), 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 1000 K ...

phase, enhances toughness. The upper limit prevents softening of the steel and stabilization of the

phase. *

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 f ...

(balance of composition) Permitted impurities: *

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 pinkis ...

(maximum of 0.20%) *

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 Ear ...

(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 formula ...

(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 to ...

(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 ...

(max. 0.15%) *

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. I ...

(max. 0.025%) USAF-96 has an unusually wide range of production methods for a superalloy: 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 materials have to undergo

heat treatment Heat treating (or heat treatment) is a group of industrial, thermal 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 ...

involving

normalization Normalization or normalisation refers to a process that makes something more normal or regular. Most commonly it refers to: * Normalization (sociology) or social normalization, the process through which ideas and behaviors that may fall outside of ...

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 pha ...

and tempering to develop the required

austenitic 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 1000 ...

microstructure Microstructure is the very small scale structure of a material, defined as the structure of a prepared surface of material as revealed by an optical microscope above 25× magnification. The microstructure of a material (such as metals, polymers ...

, with subsequent tempering. Test plates (on example 1) were 1.5 inches, produced by a vacuum ladle. First they were normalized. They were charged in a furnace at 500F (260C). Heated at 300F (149C) per hour to 1875F (1024C). Held at 1850F for 30 minutes per inch of section size, and then water-quenched to below 125F (52C). Next the samples were tempered within 24 hours of quenching by heating them at 300F (149C) per hour and holding them for at least 60 minutes per inch at about 400F ((204C) or at least 3 hours, then cooled to room temperature.

Credit

The patent application for USAF-96 credits (Dr.) Rachel Ann Abrahams as inventor. USAF-96 was inspired by

; the inventor thinks of it as Eglin steel adjusted to work without tungsten.Northwest Florida Daily News
Accessed May 30, 2019. U.S. Patent 10450621 was issued to Dr. Abrahams on October 22, 2019.

References

{{Reflist, 2

External links

AFRL Munitions Directorate - Low-Alloy Steel

Techlink - Low Alloy, High-Impact-toughness Steel

ASM Journal - High strength with no Tungsten or Cobalt
Steels

Properties, USAF-96

Details

Credit

See also

References

External links