Mangalloy
Encyclopedia
Mangalloy, also called manganese steel or Hadfield steel, is a steel alloy containing an average of around 13% manganese. Mangalloy is known for its high impact strength and resistance to abrasion.
Mangalloy is made by alloying steel, containing 0.8 to 1.25% carbon, with 11 to 15% manganese
. Mangalloy is a unique non-magnetic steel
with extreme anti-wear properties. The material is very resistant to abrasion
and will achieve up to three times its surface hardness during conditions of impact
, without any increase in brittleness which is usually associated with hardness. This allows mangalloy to retain its toughness
.
Most steels contain 0.15 to 0.8% manganese. High strength alloys often contain 1 to 1.8% manganese. At about 1.5% manganese content, the steel becomes brittle, and this trait increases until about 4 to 5% manganese content is reached. At this point, the steel will pulverize at the strike of a hammer. Further increase in the manganese content will increase both hardness and ductility
. At around 10% manganese content the steel will remain in its austenite
form at room temperature. Both hardness and ductility reach their highest points around 12%, depending on other alloying agents.
Mangalloy has been used in the mining
industry, cement mixer
s, rock crushers, railroad frogs, crawler treads for tractors and other high impact and abrasive environments. These alloys are finding new uses as cryogenic steels, due to their high strength at very low temperatures. Mangalloy is heat treatable, but the manganese lowers the temperature at which austenite transforms into ferrite
. Most grades are ready for use after annealing
and then quenching from a yellow heat, with no further need of tempering
, and usually have a normal Brinell hardness of around 200 HB, (roughly the same as 304 stainless steel), but, due to its unique properties, this number has very little effect on determining the abrasion and impact resistance of the metal.
Many of mangalloy's uses are often limited by its difficulty in machining
. The metal cannot be softened by annealing, and usually requires special tooling to machine. The material can be drilled with extreme difficulty using diamond or carbide. Although it can be forged from a yellow heat, it may crumble if hammered when white-hot, and is much tougher than carbon steel when heated. It can be cut with an oxy-acetylene torch, but plasma or laser cutting
is the preferred method. Despite its extreme hardness and tensile strength, the material may not always be rigid. It can be formed by cold rolling or cold bending.
would increase its hardness without affecting its malleability and toughness, but the mix was not homogeneous and the results of the experiment were not considered to be reliable. The abundance of manganese in the iron ore used by the Spartans helped to produce a sword tougher than those of their military opponents. In 1860, Sir Henry Bessemer, trying to perfect his Bessemer process
of steel making, found that adding manganese and carbon
to the steel after it was blown helped to remove excess sulfur
and oxygen
. Sulfur combines with iron to form a sulfide
that has a lower melting point
than steel, causing weak spots, which prevented hot rolling. Manganese is usually alloyed with most modern steels because of its powerful ability to remove sulfur, phosphorus
and oxygen, which are all common impurities in steel. Mangalloy was the first alloy created from carbon steel, also called Hadfield steel after its British inventor, Sir Robert Hadfield, in 1882.
Hadfield was in search of a steel that could be used for casting
which would exhibit both hardness and toughness, since ordinary carbon steels do not combine those properties. Steel can be hardened by rapid cooling, but loses its toughness, becoming brittle. Steel castings can not usually be cooled rapidly, for irregular shapes can warp or crack. Mangalloy proved to be extremely suitable for casting, as it did not form gas pockets called "blow-holes", and did not display the extreme brittleness of other castings.
Upon creating mangalloy, Hadfield tested the material, thinking that the results must have been erroneous. After performing several hundred tests, he realized that they must be accurate, although the reason for the combination of hardness and toughness defied any explanation at the time. Hadfield wrote, "Is there any case similar to this among other alloys of iron, if the term alloy may be used? No metallurgical treatise refers to them;...Possibly when the nature of the laws governing alloys is better understood, this will be found to be only one of other cases,..."
Material properties
Manganese
Manganese 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...
. Mangalloy is a unique non-magnetic 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...
with extreme anti-wear properties. The material is very resistant to abrasion
Abrasion (mechanical)
Abrasion is the process of scuffing, scratching, wearing down, marring, or rubbing away. It can be intentionally imposed in a controlled process using an abrasive...
and will achieve up to three times its surface hardness during conditions of impact
Impact force
In mechanics, an impact is a high force or shock applied over a short time period when two or more bodies collide. Such a force or acceleration usually has a greater effect than a lower force applied over a proportionally longer time period of time...
, without any increase in brittleness which is usually associated with hardness. This allows mangalloy to retain its 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...
.
Most steels contain 0.15 to 0.8% manganese. High strength alloys often contain 1 to 1.8% manganese. At about 1.5% manganese content, the steel becomes brittle, and this trait increases until about 4 to 5% manganese content is reached. At this point, the steel will pulverize at the strike of a hammer. Further increase in the manganese content will increase both hardness and ductility
Ductility
In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized...
. At around 10% manganese content the steel will remain in its austenite
Austenite
Austenite, 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...
form at room temperature. Both hardness and ductility reach their highest points around 12%, depending on other alloying agents.
Mangalloy has been used in the mining
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
industry, cement mixer
Concrete mixer
A concrete mixer is a device that homogeneously combines cement, aggregate such as sand or gravel, and water to form concrete. A typical concrete mixer uses a revolving drum to mix the components...
s, rock crushers, railroad frogs, crawler treads for tractors and other high impact and abrasive environments. These alloys are finding new uses as cryogenic steels, due to their high strength at very low temperatures. Mangalloy is heat treatable, but the manganese lowers the temperature at which austenite transforms into ferrite
Ferrite (iron)
Ferrite or alpha iron is a materials science term for iron, or a solid solution with iron as the main constituent, with a body centred cubic crystal structure. It is the component which gives steel and cast iron their magnetic properties, and is the classic example of a ferromagnetic material...
. Most grades are ready for use after annealing
Annealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
and then quenching from a yellow heat, with no further need of 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...
, and usually have a normal Brinell hardness of around 200 HB, (roughly the same as 304 stainless steel), but, due to its unique properties, this number has very little effect on determining the abrasion and impact resistance of the metal.
Many of mangalloy's uses are often limited by its difficulty in machining
Machining
Conventional machining is a form of subtractive manufacturing, in which a collection of material-working processes utilizing power-driven machine tools, such as saws, lathes, milling machines, and drill presses, are used with a sharp cutting tool to physical remove material to achieve a desired...
. The metal cannot be softened by annealing, and usually requires special tooling to machine. The material can be drilled with extreme difficulty using diamond or carbide. Although it can be forged from a yellow heat, it may crumble if hammered when white-hot, and is much tougher than carbon steel when heated. It can be cut with an oxy-acetylene torch, but plasma or laser cutting
Laser cutting
Laser cutting is a technology that uses a laser to cut materials, and is typically used for industrial manufacturing applications, but is also starting to be used by schools, small businesses and hobbyists. Laser cutting works by directing the output of a high-power laser, by computer, at the...
is the preferred method. Despite its extreme hardness and tensile strength, the material may not always be rigid. It can be formed by cold rolling or cold bending.
History
In 1816, a German researcher noted that adding fairly large amounts of manganese to ironIron
Iron 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...
would increase its hardness without affecting its malleability and toughness, but the mix was not homogeneous and the results of the experiment were not considered to be reliable. The abundance of manganese in the iron ore used by the Spartans helped to produce a sword tougher than those of their military opponents. In 1860, Sir Henry Bessemer, trying to perfect his Bessemer process
Bessemer process
The Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron. The process is named after its inventor, Henry Bessemer, who took out a patent on the process in 1855. The process was independently discovered in 1851 by William Kelly...
of steel making, found that adding manganese and 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...
to the steel after it was blown helped to remove excess sulfur
Sulfur
Sulfur 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...
and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. Sulfur combines with iron to form a sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
that has a lower melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
than steel, causing weak spots, which prevented hot rolling. Manganese is usually alloyed with most modern steels because of its powerful ability to remove sulfur, phosphorus
Phosphorus
Phosphorus 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...
and oxygen, which are all common impurities in steel. Mangalloy was the first alloy created from carbon steel, also called Hadfield steel after its British inventor, Sir Robert Hadfield, in 1882.
Hadfield was in search of a steel that could be used for casting
Casting
In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...
which would exhibit both hardness and toughness, since ordinary carbon steels do not combine those properties. Steel can be hardened by rapid cooling, but loses its toughness, becoming brittle. Steel castings can not usually be cooled rapidly, for irregular shapes can warp or crack. Mangalloy proved to be extremely suitable for casting, as it did not form gas pockets called "blow-holes", and did not display the extreme brittleness of other castings.
Upon creating mangalloy, Hadfield tested the material, thinking that the results must have been erroneous. After performing several hundred tests, he realized that they must be accurate, although the reason for the combination of hardness and toughness defied any explanation at the time. Hadfield wrote, "Is there any case similar to this among other alloys of iron, if the term alloy may be used? No metallurgical treatise refers to them;...Possibly when the nature of the laws governing alloys is better understood, this will be found to be only one of other cases,..."