Mushet steel, also known as Robert Mushet's Special Steel and, at the time of its use, self-hardening steel and air-hardening steel,
[.] is considered to be both the first
tool steel
Tool steel is any of various carbon steels and alloy steels that are particularly well-suited to be made into tools and tooling, including cutting tools, dies, hand tools, knives, and others. Their suitability comes from their distinctive har ...
and the first
air-hardening steel.
[.] It was invented in 1868 by
Robert Forester Mushet
Robert Forester Mushet (8 April 1811 – 29 January 1891) was a British metallurgist and businessman, born on 8 April 1811, in Coleford, in the Forest of Dean, Gloucestershire, England. He was the youngest son of Scottish parents, Agnes Wilson ...
. Prior to Mushet steel, steel had to be
quenched
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 ph ...
to harden it.
It later led to the discovery of
high-speed steel
High-speed steel (HSS or HS) is a subset of tool steels, commonly used as cutting tool material.
It is often used in power-saw blades and drill bits. It is superior to the older high-carbon steel tools used extensively through the 1940s in tha ...
.
Properties
The
chemical composition
A chemical composition specifies the identity, arrangement, and ratio of the elements making up a compound.
Chemical formulas can be used to describe the relative amounts of elements present in a compound. For example, the chemical formula for ...
of Mushet steel varied;
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 ...
was the main alloying constituent, which ranged between 4 and 12%, while
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 ...
(2–4%) and
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 ...
(1.5–2.5%) were the secondary alloying constituents. Typical samples contain 9% tungsten, 2.5% manganese, and 1.85% carbon.
Mushet steel was harder than standard water quenched steel. It was found that Mushet steel could be best hardened by submitting it to an air blast after
forging
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which ...
.
Mushet steel is non-magnetic.
Use
Mushet steel was primarily used in
machine tools
A machine tool is a machine for handling or machining metal or other rigid materials, usually by cutting, boring, grinding, shearing, or other forms of deformations. Machine tools employ some sort of tool that does the cutting or shaping. Al ...
due to its ability to retain its hardness at high temperatures. In 1894,
Frederick Winslow Taylor
Frederick Winslow Taylor (March 20, 1856 – March 21, 1915) was an American mechanical engineer. He was widely known for his methods to improve industrial efficiency. He was one of the first management consultants. In 1909, Taylor summed up ...
conducted machining comparison tests between Mushet steel and
high carbon tool steel. He found that it could cut 41 to 47% faster on hard
tire steel forgings and approximately 90% faster on
mild steel
Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:
* no minimum content is specified or required for chromium, cobal ...
s. He also found that if a stream of water was used as a
cutting fluid
Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists) ...
the
cutting speed could be increased by 30%. After Taylor's tests results were published Mushet and other self-hardening steels became popular in machine tools.
[.] Prior to Taylor's tests Mushet steel was often just used to increase the time between regrinds, take larger cuts, or machine harder materials.
In 1899 and 1900,
[.] Taylor and Maunsel White were experimenting with hardening processes for Mushet steel and other self-hardening steels. They discovered if the steel is heated to near its melting point it creates a more durable metal. The metal will retain its hardness up to a
red heat
The practice of using colours to determine the temperature of a piece of (usually) ferrous metal comes from blacksmithing. Long before thermometers were widely available it was necessary to know what state the metal was in for heat treating it a ...
. This type of hardened self-hardening steel was the first high speed steel.
References
Bibliography
*.
*
*.
*{{Citation , last = Stoughton , first = Bradley , title = The Metallurgy of Iron and Steel , publisher = McGraw-Hill , year = 1908 , edition = 1st (third impression) , url = https://books.google.com/books?id=Rh5KAAAAMAAJ.
Steels