High speed steel
Encyclopedia
High speed steelMost copyeditors today would tend to choose to style the unit adjective high-speed with a hyphen, rendering the full term as high-speed steel, and this styling is not uncommon (Kanigel 1997 is an example of a work edited thus). However, it is true that in the metalworking industries the styling high speed steel is long-established and is more commonly seen. Therefore, both can be considered acceptable variants. (HSS or HS) is a subset of tool steel
s, commonly used in tool bit
s and cutting tool
s. It is often used in power saw blades and drill bit
s. It is superior to the older high carbon steel
tools used extensively through the 1940s in that it can withstand higher temperatures without losing its temper (hardness). This property allows HSS to cut faster than high carbon steel, hence the name high speed steel. At room temperature, in their generally recommended heat treatment, HSS grades generally display high hardness (above HRC60) and a high abrasion resistance (generally linked to tungsten
content often used in HSS) compared to common carbon and tool steel
s.
manufactured in India around 350 BC and production of Damascus
and Japanese layered steel blades in years 540 AD and 900 AD.
In 1868 the English metallurgist Robert Forester Mushet
developed Mushet steel
, considered to be the forerunner of modern high speed steels. It consisted of 2% carbon
(C), 2.5% manganese
(Mn), and 7% tungsten
(W). The major advantage of this steel was that it hardened when air cooled from a temperature at which most steels had to be quenched for hardening. Over the next 30 years the most important change was the substitution of chromium
(Cr) for manganese
.
In 1899 and 1900, Frederick Winslow Taylor
and Maunsel White, working with a team of assistants at the Bethlehem Steel Company
at Bethlehem, Pennsylvania
, USA, performed a series of experiments with the heat treating of existing high-quality tool steels, such as Mushet steel; heating them to much higher temperatures than were typically considered desirable in the industry. Their experiments were characterized by a scientific empiricism in that many different combinations were made and tested, with no regard for conventional wisdom or alchemic recipes, and with detailed records kept of each batch. The end result was a heat treatment process that transformed existing alloys into a new kind of steel that could retain its hardness at higher temperatures, allowing much higher speeds, feeds, and depths of cut when machining.
The Taylor-White process was patented and created a revolution in the machining industries, in fact necessitating whole new, heavier machine tool designs so the new steel could be used to its full advantage. The patent was hotly contested and eventually nullified.
The first alloy that was formally classified as high speed steel is known by the AISI
designation T1, which was introduced in 1910. It was patented by Crucible Steel Co. at the beginning of the 20th century.
Although molybdenum rich high speed steels such as AISI M1 have been used since the 1930s, shortages and hence high costs of raw materials during World War II spurred the development of alloy designs with molybdenum being substituted for tungsten to produce cheaper steel. The developments in molybdenum-based high speed steel during this period made them on par with and in certain cases better than tungsten-based high speed steels. This started with the use of M2 steel (sulfurized version of M1) instead of T1 steel.
, milling cutter
s, tool bit
s, gear cutters, saw blades, etc., although usage for punches and dies is increasing.
High speed steels also found a market in fine hand tools where their relatively good toughness at high hardness, coupled with high abrasion resistance and fine, made them suitable for low speed applications requiring a durable keen (sharp) edge, such as files
, chisels, hand plane blades, and high quality kitchen
, pocket knives
, and swords
.
, tungsten
, molybdenum
, vanadium
, or cobalt
. Generally, the X component is present in excess of 7%, along with more than 0.60% carbon
. (However, their alloying element percentages do not alone bestow the hardness-retaining properties; they also require appropriate high-temperature heat treatment in order to become true HSS; see History above.)
In the unified numbering system
(UNS), tungsten-type grades (e.g. T1, T15) are assigned numbers in the T120xx series, while molybdenum (e.g. M2, M48) and intermediate types are T113xx. ASTM standards recognize 7 tungsten types and 17 molybdenum types.
The addition of about 10% of tungsten and molybdenum in total maximises efficiently the hardness and toughness of high speed steels and maintains these properties at the high temperatures generated when cutting metals.
. It is widely used in metal manufacturing because of its superior red-hardness as compared to more conventional high speed steels, allowing for shorter cycle times in production environments due to higher cutting speeds or from the increase in time between tool changes. M42 is also less prone to chipping when used for interrupted cuts and cost less when compared to the same tool made of carbide. Tools made from cobalt-bearing high speed steels can often be identified by the letters HSS-Co.
). Most coatings generally increase a tool's hardness and/or lubricity. A coating allows the cutting edge of a tool to cleanly pass through the material without having the material gall (stick) to it. The coating also helps to decrease the temperature associated with the cutting process and increase the life of the tool.
, remelting (glazing), and compositional modification. It is possible to achieve different molten pool shapes and temperatures. Cooling rates range from 103 – 106 K s-1. Beneficially, there is little or no cracking or porosity formation.
While the possibilities of heat treating at the surface should be readily apparent, the other applications beg some explanation. At cooling rates in excess of 106 K s-1 eutectic microconstituents disappear and there is extreme segregation of substitutional alloying elements. This has the effect of providing the benefits of a glazed part without the associated run in wear damage.
The alloy composition of a part or tool can also be changed to form a high speed steel on the surface of a lean alloy or to form an alloy or carbide enriched layer on the surface of a high speed steel part. Several methods can be used such as foils, pack boronising, plasma spray powders, powder cored strips, inert gas blow feeders, etc. Although this method has been reported to be both beneficial and stable, it has yet to see widespread commercial use.
Tool steel
Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion, their ability to hold a cutting edge, and/or their resistance to deformation at elevated temperatures...
s, commonly used in tool bit
Tool bit
The term tool bit generally refers to a non-rotary cutting tool used in metal lathes, shapers, and planers. Such cutters are also often referred to by the set-phrase name of single-point cutting tool. The cutting edge is ground to suit a particular machining operation and may be resharpened or...
s and cutting tool
Cutting tool
In the context of machining, a cutting tool is any tool that is used to remove material from the workpiece by means of shear deformation. Cutting may be accomplished by single-point or multipoint tools. Single-point tools are used in turning, shaping, plaining and similar operations, and remove...
s. It is often used in power saw blades and drill bit
Drill bit
Drill bits are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides torque and axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes....
s. It is superior to the older high carbon steel
Plain-carbon steel
Carbon steel, also called plain-carbon steel, is steel where the main interstitial alloying constituent is carbon. The American Iron and Steel Institute defines carbon steel as: "Steel is considered to be carbon steel when no minimum content is specified or required for chromium, cobalt,...
tools used extensively through the 1940s in that it can withstand higher temperatures without losing its temper (hardness). This property allows HSS to cut faster than high carbon steel, hence the name high speed steel. At room temperature, in their generally recommended heat treatment, HSS grades generally display high hardness (above HRC60) and a high abrasion resistance (generally linked to 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...
content often used in HSS) compared to common carbon and tool steel
Tool steel
Tool steel refers to a variety of carbon and alloy steels that are particularly well-suited to be made into tools. Their suitability comes from their distinctive hardness, resistance to abrasion, their ability to hold a cutting edge, and/or their resistance to deformation at elevated temperatures...
s.
History
Although development of modern high speed steel began in the second half of the 19th century, there is documented evidence of similar grades of steel produced earlier. These include hardened steels in China in 13th century BC, wootz steelWootz steel
Wootz steel is a steel characterized by a pattern of bands or sheets of micro carbides within a tempered martensite or pearlite matrix. It was developed in India around 300 BCE...
manufactured in India around 350 BC and production of Damascus
Damascus steel
Damascus steel was a term used by several Western cultures from the Medieval period onward to describe a type of steel used in swordmaking from about 300 BCE to 1700 CE. These swords are characterized by distinctive patterns of banding and mottling reminiscent of flowing water...
and Japanese layered steel blades in years 540 AD and 900 AD.
In 1868 the English metallurgist Robert Forester Mushet
Robert Forester Mushet
Robert Forester Mushet was a British metallurgist and businessman, born April 8, 1811, in Coleford, in the Forest of Dean, Gloucestershire, England. He was the youngest son of Scottish parents, Agnes Wilson and David Mushet; an ironmaster, formerly of the Clyde, Alfreton and Whitecliff...
developed Mushet steel
Mushet steel
Mushet steel, also known as Robert Mushet's Special Steel , self-hardening steel and air-hardening steel, is considered the first tool steel and air-hardening steel. It was invented in 1868 by Robert Forester Mushet. Prior to Mushet steel, steel had to be quenched to harden it...
, considered to be the forerunner of modern high speed steels. It consisted of 2% 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...
(C), 2.5% manganese
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...
(Mn), and 7% 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...
(W). The major advantage of this steel was that it hardened when air cooled from a temperature at which most steels had to be quenched for hardening. Over the next 30 years the most important change was the substitution of 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...
(Cr) for manganese
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...
.
In 1899 and 1900, Frederick Winslow Taylor
Frederick Winslow Taylor
Frederick Winslow Taylor was an American mechanical engineer who sought to improve industrial efficiency. He is regarded as the father of scientific management and was one of the first management consultants...
and Maunsel White, working with a team of assistants at the Bethlehem Steel Company
Bethlehem Steel
The Bethlehem Steel Corporation , based in Bethlehem, Pennsylvania, was once the second-largest steel producer in the United States, after Pittsburgh, Pennsylvania-based U.S. Steel. After a decline in the U.S...
at Bethlehem, Pennsylvania
Bethlehem, Pennsylvania
Bethlehem is a city in Lehigh and Northampton Counties in the Lehigh Valley region of eastern Pennsylvania, in the United States. As of the 2010 census, the city had a total population of 74,982, making it the seventh largest city in Pennsylvania, after Philadelphia, Pittsburgh, Allentown, Erie,...
, USA, performed a series of experiments with the heat treating of existing high-quality tool steels, such as Mushet steel; heating them to much higher temperatures than were typically considered desirable in the industry. Their experiments were characterized by a scientific empiricism in that many different combinations were made and tested, with no regard for conventional wisdom or alchemic recipes, and with detailed records kept of each batch. The end result was a heat treatment process that transformed existing alloys into a new kind of steel that could retain its hardness at higher temperatures, allowing much higher speeds, feeds, and depths of cut when machining.
The Taylor-White process was patented and created a revolution in the machining industries, in fact necessitating whole new, heavier machine tool designs so the new steel could be used to its full advantage. The patent was hotly contested and eventually nullified.
The first alloy that was formally classified as high speed steel is known by the AISI
American Iron and Steel Institute
The American Iron and Steel Institute is an association of North American steel producers. Its predecessor organizations date back to 1855 making it one of the oldest trade associations in the United States. AISI assumed its present form in 1908, with Elbert H...
designation T1, which was introduced in 1910. It was patented by Crucible Steel Co. at the beginning of the 20th century.
Although molybdenum rich high speed steels such as AISI M1 have been used since the 1930s, shortages and hence high costs of raw materials during World War II spurred the development of alloy designs with molybdenum being substituted for tungsten to produce cheaper steel. The developments in molybdenum-based high speed steel during this period made them on par with and in certain cases better than tungsten-based high speed steels. This started with the use of M2 steel (sulfurized version of M1) instead of T1 steel.
Applications
The main use of high speed steels continues to be in the manufacture of various cutting tools: drills, tapsTaps and dies
Taps and dies are cutting tools used to create screw threads, which is called threading. A tap is used to cut the female portion of the mating pair . A die is used to cut the male portion of the mating pair . The process of cutting threads using a tap is called tapping, whereas the process using a...
, milling cutter
Milling cutter
Milling cutters are cutting tools typically used in milling machines or machining centres . They remove material by their movement within the machine or directly from the cutter's shape .-Features of a milling cutter:Milling cutters come in several shapes and many sizes...
s, tool bit
Tool bit
The term tool bit generally refers to a non-rotary cutting tool used in metal lathes, shapers, and planers. Such cutters are also often referred to by the set-phrase name of single-point cutting tool. The cutting edge is ground to suit a particular machining operation and may be resharpened or...
s, gear cutters, saw blades, etc., although usage for punches and dies is increasing.
High speed steels also found a market in fine hand tools where their relatively good toughness at high hardness, coupled with high abrasion resistance and fine, made them suitable for low speed applications requiring a durable keen (sharp) edge, such as files
File (tool)
A file is a metalworking and woodworking tool used to cut fine amounts of material from a workpiece. It most commonly refers to the hand tool style, which takes the form of a steel bar with a case hardened surface and a series of sharp, parallel teeth. Most files have a narrow, pointed tang at one...
, chisels, hand plane blades, and high quality kitchen
Kitchen knife
A kitchen knife is any knife that is intended to be used in food preparation. While much of this work can be accomplished with a few general-purpose knives – notably a large chef's knife, a tough cleaver, and a small paring knife – there are also many specialized knives that are designed for...
, pocket knives
Pocket knife
A pocket knife is a folding knife with one or more blades that fit inside the handle that can still fit in a pocket. It is also known as a jackknife or jack-knife...
, and swords
Sword
A sword is a bladed weapon used primarily for cutting or thrusting. The precise definition of the term varies with the historical epoch or the geographical region under consideration...
.
Types
High speed steels belong to the Fe-C-X multi-component alloy system where X represents chromiumChromium
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...
, molybdenum
Molybdenum
Molybdenum , 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...
, vanadium
Vanadium
Vanadium 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...
, or cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
. Generally, the X component is present in excess of 7%, along with more than 0.60% 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...
. (However, their alloying element percentages do not alone bestow the hardness-retaining properties; they also require appropriate high-temperature heat treatment in order to become true HSS; see History above.)
In the unified numbering system
Unified numbering system
The unified numbering system is an alloy designation system widely accepted in North America. It consists of a prefix letter and five digits designating a material composition. A prefix of S indicates stainless steel alloys, C for copper, brass, or bronze alloys, T for tool steels, etc...
(UNS), tungsten-type grades (e.g. T1, T15) are assigned numbers in the T120xx series, while molybdenum (e.g. M2, M48) and intermediate types are T113xx. ASTM standards recognize 7 tungsten types and 17 molybdenum types.
The addition of about 10% of tungsten and molybdenum in total maximises efficiently the hardness and toughness of high speed steels and maintains these properties at the high temperatures generated when cutting metals.
| Grade | C 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... | Cr 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... | Mo Molybdenum Molybdenum , 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... | W 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... | V Vanadium Vanadium 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... | Co Cobalt Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.... | Mn 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... | Si 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... |
|---|---|---|---|---|---|---|---|---|
| T1 | 0.65–0.80 | 3.75–4.00 | ||||||
| 17.25–18.75 | 0.9–1.3 | |||||||
| 0.1–0.4 | 0.2–0.4 | |||||||
| M2 | 0.95 | 4.2 | 5.0 | 6.0 | 2.0 | |||
| M7 | 1.00 | 3.8 | 8.7 | 1.6 | 2.0 | |||
| M35 | 0.94 | 4.1 | 5.0 | 6.0 | 2.0 | 5.0 | ||
| M42 | 1.10 | 3.8 | 9.5 | 1.5 | 1.2 | 8.0 | ||
| Note that impurity limits are not included | ||||||||
M2
M2 is a high speed steel in tungsten-molybdenum series. The carbides in it are small and evenly distributed. It has high wear resistance. After heat treatment, its hardness is the same as T1, but its bending strength can reach 4700 MPa, and its toughness and thermoplasticity are higher than T1 by 50%. It is usually used to manufacture a variety of tools, such as drill bits, taps and reamers. Its decarbonization sensitivity is a little bit high.M35
M35 is similar to M2, but with 5% cobalt added. The addition of cobalt increases heat resistance.M42
M42 is a molybdenum-chromium-vanadium-tungsten high speed steel alloy with an additional 8% cobaltCobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
. It is widely used in metal manufacturing because of its superior red-hardness as compared to more conventional high speed steels, allowing for shorter cycle times in production environments due to higher cutting speeds or from the increase in time between tool changes. M42 is also less prone to chipping when used for interrupted cuts and cost less when compared to the same tool made of carbide. Tools made from cobalt-bearing high speed steels can often be identified by the letters HSS-Co.
Coatings
To increase the life of high speed steel, tools are sometimes coated. One such coating is TiN (titanium nitrideTitanium nitride
Titanium nitride is an extremely hard ceramic material, often used as a coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface properties....
). Most coatings generally increase a tool's hardness and/or lubricity. A coating allows the cutting edge of a tool to cleanly pass through the material without having the material gall (stick) to it. The coating also helps to decrease the temperature associated with the cutting process and increase the life of the tool.
Surface modification
Lasers and electron beams can be used as sources of intense heat at the surface for heat treatmentHeat 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...
, remelting (glazing), and compositional modification. It is possible to achieve different molten pool shapes and temperatures. Cooling rates range from 103 – 106 K s-1. Beneficially, there is little or no cracking or porosity formation.
While the possibilities of heat treating at the surface should be readily apparent, the other applications beg some explanation. At cooling rates in excess of 106 K s-1 eutectic microconstituents disappear and there is extreme segregation of substitutional alloying elements. This has the effect of providing the benefits of a glazed part without the associated run in wear damage.
The alloy composition of a part or tool can also be changed to form a high speed steel on the surface of a lean alloy or to form an alloy or carbide enriched layer on the surface of a high speed steel part. Several methods can be used such as foils, pack boronising, plasma spray powders, powder cored strips, inert gas blow feeders, etc. Although this method has been reported to be both beneficial and stable, it has yet to see widespread commercial use.