High-speed steel (HSS or HS) is a subset of

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 h ...

s, commonly used as cutting tool material. It is often used in power-saw blades and

drill bit Drill bits are cutting tools used in a drill to remove material to create holes, almost always of circular cross-section. Drill bits come in many sizes and shapes and can create different kinds of holes in many different materials. In order ...

s. It is superior to the older high-

carbon 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, coba ...

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 Rockwell hardness 60) and abrasion resistance (generally linked to

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 ...

and

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 ( pass ...

content often used in HSS) compared with common

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 makes ...

and

History

In 1868 English metallurgist

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 ...

developed

Mushet steel 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 and the first air-hardening steel.. It was invented in 1868 by Robert ...

, considered the forerunner of modern high-speed steels. It consisted of 2%

, 2.5%

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 u ...

, and 7%

. 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 significant change was the replacement of

with

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 h ...

. In 1899 and 1900,

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 h ...

and Maunsel White (''né'' Maunsel White III; 1856–1912; grandson of Maunsel White; 1783–1863), working with a team of assistants at the

Bethlehem Steel Company The Bethlehem Steel Corporation was an American steelmaking company headquartered in Bethlehem, Pennsylvania. For most of the 20th century, it was one of the world's largest steel producing and shipbuilding companies. At the height of its succe ...

Bethlehem, Pennsylvania Bethlehem is a city in Northampton and Lehigh Counties in the Lehigh Valley region of eastern Pennsylvania, United States. As of the 2020 census, Bethlehem had a total population of 75,781. Of this, 55,639 were in Northampton County and 19,3 ...

, US, performed a series of experiments with heat treating 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 characterised by a scientific empiricism in that many different combinations were made and tested, with no regard for conventional wisdom or alchemic recipes, and detailed records kept of each batch. The 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 and rate of cutting when machining. The Taylor-White process was patented and created a revolution in machining industries. Heavier machine tools with higher rigidity were needed to use the new steel to its full advantage, prompting redesigns and replacement of installed plant machinery. The patent was 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.Roberts, George (1998) ''Tool Steels'', 5th edition, ASM International, It was patented by Crucible Steel Co. at the beginning of the 20th century. Although

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 le ...

-rich high-speed steels such as AISI M1 had seen some use since the 1930s, it was the material shortages and high costs caused by WWII that spurred development of less expensive alloys substituting molybdenum for tungsten. The advances in molybdenum-based high speed steel during this period put them on par with, and in certain cases better, than tungsten-based high speed steels. This started with the use of M2 steel instead of T1 steel.The Metals Society, London, "Tools and dies for industry", 1977

Types

High speed steels are alloys that gain their properties from a variety of alloying metals added to carbon steel, typically including tungsten and molybdenum, or a combination of the two, often with other alloys as well. They belong to the Fe–C–X multi-component alloy system where X represents

, or

cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, ...

. Generally, the X component is present in excess of 7%, along with more than 0.60%

. In the

unified numbering system The unified numbering system (UNS) is an alloy designation system widely accepted in North America. Each UNS number relates to a specific metal or alloy and defines its specific chemical composition, or in some cases a specific mechanical or physi ...

(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 ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, a ...

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 those properties at the high temperatures generated when cutting metals.

Molybdenum High Speed Steels (HSS)

Combining molybdenum, tungsten and chromium steel creates several alloys commonly called "HSS", measuring 63–65 Rockwell "C" hardness. ; M1: M1 lacks some of the red-hardness properties of M2, but is less susceptible to shock and will flex more. ; M2: M2 is the "standard" and most widely used industrial HSS. It has small and evenly distributed carbides giving high wear resistance, though its decarburization sensitivity is a little bit high. After heat treatment, its hardness is the same as T1, but its bending strength can reach 4700 MPa, and its toughness and thermo-plasticity are higher than T1 by 50%. It is usually used to manufacture a variety of tools, such as drill bits, taps and reamers. 1.3343 is the equivalent numeric designation for M2 material identified in ISO 4957. ; M7: M7 is used for making heavier construction drills where flexibility and extended drill life are equally important. ; M50: M50 does not have the red-hardness of other grades of tungsten HSS, but is very good for drills where breakage is a problem due to flexing the drill. Generally favored for hardware stores and contractor use. It is also used in high-temperature

ball bearing A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this ...

s. These steels are obtained by alloying tungsten, chromium, vanadium, cobalt and molybdenum with steel.

Cobalt High Speed Steels (HSS)

The addition of

increases heat resistance, and can give a Rockwell hardness up to 70 Min. ; M35: M35 is similar to M2, but with 5% cobalt added. M35 is also known as Cobalt Steel, HSSE or HSS-E. It will cut faster and last longer than M2. ; M42: M42 is a molybdenum-series high-speed steel alloy with an additional 8% cobalt. It is widely used in metal manufacturing industries 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.

Surface modification

Lasers and electron beams can be used as sources of intense heat at the surface for

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 al ...

, remelting ( glazing), and compositional modification. It is possible to achieve different molten pool shapes and temperatures, as well as cooling rates ranging from 10³ to 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.

Forming

HSS

drill bits Drill bits are cutting tools used in a drill to remove material to create holes, almost always of circular cross-section. Drill bits come in many sizes and shapes and can create different kinds of holes in many different materials. In order ...

formed by

rolling Rolling is a type of motion that combines rotation (commonly, of an axially symmetric object) and translation of that object with respect to a surface (either one or the other moves), such that, if ideal conditions exist, the two are in contact ...

are denoted HSS-R. Grinding is used to create HSS-G, cobalt and carbide drill bits.

Applications

The main use of high-speed steels continues to be in the manufacture of various cutting tools: drills, taps,

milling cutter Milling cutters are cutting tools typically used in milling machines or machining centres to perform milling operations (and occasionally in other machine tools). They remove material by their movement within the machine (e.g., a ball nose mill) ...

tool bit A tool bit is 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, as distinguished from other cutting tools such as a saw or water je ...

s, hobbing (gear) cutters, saw blades, planer and jointer blades, router bits, 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, made them suitable for low speed applications requiring a durable keen (sharp) edge, such as

files File or filing may refer to: Mechanical tools and processes * File (tool), a tool used to ''remove'' fine amounts of material from a workpiece **Filing (metalworking), a material removal process in manufacturing ** Nail file, a tool used to gent ...

chisels A chisel is a tool with a characteristically shaped cutting edge (such that wood chisels have lent part of their name to a particular Grind#Typical grinds, grind) of blade on its end, for carving or cutting a hard material such as wood, Rock (g ...

hand plane A hand plane is a tool for shaping wood using muscle power to force the cutting blade over the wood surface. Some rotary power planers are motorized power tools used for the same types of larger tasks, but are unsuitable for fine-scale planing, ...

blades, and damascus

kitchen knives 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, a small paring knife and some sort ...

and pocket knives. High speed steel tools are the most popular for use in woodturning, as the speed of movement of the work past the edge is relatively high for handheld tools, and HSS holds its edge far longer than high carbon steel tools can. High speed steel is used for cast iron cutting as well in CNC machines.

References

{{DEFAULTSORT:High Speed Steel Steels Metalworking cutting tools