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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. In addition, it is often used in bowl gouges and skew for woodturning. 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 Rockwell hardness 60) and abrasion resistance (generally linked to tungsten and vanadium content often used in HSS) compared with common carbon and tool steels. There are several different types of HS steel, such as M42 and M2. [1]
In 1868 English metallurgist Robert Forester Mushet developed Mushet steel, considered the forerunner of modern high-speed steels. It consisted of 2% carbon, 2.5% manganese, and 7% tungsten. 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 manganese with chromium. [2]
In 1899 and 1900, Frederick Winslow Taylor 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 at Bethlehem, Pennsylvania, 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. [3] [4] 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 [5] 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. [6]
The first alloy that was formally classified as high-speed steel is known by the AISI designation T1, which was introduced in 1910. [7] It was patented by Crucible Steel Co. at the beginning of the 20th century. [2]
Although molybdenum-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. [2] [8]
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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. [9] They belong to the Fe–C–X multi-component alloy system where X represents chromium, tungsten, molybdenum, vanadium, or cobalt. Generally, the X component is present in excess of 7%, along with more than 0.60% carbon.
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. [10]
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.
Grade | C | Cr | Mo | W | V | Co | Mn | Si |
---|---|---|---|---|---|---|---|---|
T1 | 0.65–0.80 | 4.00 | - | 18 | 1 | - | 0.1–0.4 | 0.2–0.4 |
M1 | 0.80 | 4 | 8 | 1.5 | 1.0 | - | - | - |
M2 | 0.85 | 4 | 5 | 6.0 | 2.0 | - | - | - |
M7 | 1.00 | 4 | 8.75 | 1.75 | 2.0 | - | - | - |
M35 | 0.92 | 4.3 | 5 | 6.4 | 1.8 | 5 | - | 0.35 |
M42 | 1.10 | 3.75 | 9.5 | 1.5 | 1.15 | 8.0 | - | - |
M50 | 0.85 | 4 | 4.25 | .10 | 1.0 | - | - | - |
Combining molybdenum, tungsten and chromium steel creates several alloys commonly called "HSS", measuring 63–65 Rockwell "C" hardness.
The addition of cobalt increases heat resistance, and can give a Rockwell hardness up to 70 Min. [13]
HSS drill bits formed by rolling are denoted HSS-R. Grinding is used to create HSS-G, cobalt and carbide drill bits. [15]
The main use of high-speed steels continues to be in the manufacture of various cutting tools: drills, taps, milling cutters, tool bits, 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, chisels, hand plane blades, and damascus kitchen knives and pocket knives.[ citation needed ]
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.[ citation needed ]
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, opacity, and luster, but may have properties that differ from those of the pure metals, such as increased strength or hardness. In some cases, an alloy may reduce the overall cost of the material while preserving important properties. In other cases, the mixture imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength.
"Stellite" is a registered trademark of Kennametal Inc. and is used in association with cobalt-chromium alloys.
A drill bit is a cutting tool 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 to create holes drill bits are usually attached to a drill, which powers them to cut through the workpiece, typically by rotation. The drill will grasp the upper end of a bit called the shank in the chuck.
Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definition of which elements belong to this group differs. The most common definition includes five elements: two of the fifth period and three of the sixth period. They all share some properties, including a melting point above 2000 °C and high hardness at room temperature. They are chemically inert and have a relatively high density. Their high melting points make powder metallurgy the method of choice for fabricating components from these metals. Some of their applications include tools to work metals at high temperatures, wire filaments, casting molds, and chemical reaction vessels in corrosive environments. Partly due to the high melting point, refractory metals are stable against creep deformation to very high temperatures.
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:
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 hardness, resistance to abrasion and deformation, and their ability to hold a cutting edge at elevated temperatures. As a result, tool steels are suited for use in the shaping of other materials, as for example in cutting, machining, stamping, or forging.
Tungsten carbide is a chemical compound containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into shapes through sintering for use in industrial machinery, cutting tools, chisels, abrasives, armor-piercing shells and jewelry.
Tempering is a process of heat treating, which is used to increase the toughness of iron-based alloys. Tempering is usually performed after hardening, to reduce some of the excess hardness, and is done by heating the metal to some temperature below the critical point for a certain period of time, then allowing it to cool in still air. The exact temperature determines the amount of hardness removed, and depends on both the specific composition of the alloy and on the desired properties in the finished product. For instance, very hard tools are often tempered at low temperatures, while springs are tempered at much higher temperatures.
In machining, 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 jet cutter. The cutting edge is ground to suit a particular machining operation and may be resharpened or reshaped as needed. The ground tool bit is held rigidly by a tool holder while it is cutting.
Chromium(II) carbide is a ceramic compound that exists in several chemical compositions: Cr3C2, Cr7C3, and Cr23C6. At standard conditions it exists as a gray solid. It is extremely hard and corrosion resistant. It is also a refractory compound, which means that it retains its strength at high temperatures as well. These properties make it useful as an additive to metal alloys. When chromium carbide crystals are integrated into the surface of a metal it improves the wear resistance and corrosion resistance of the metal, and maintains these properties at elevated temperatures. The hardest and most commonly used composition for this purpose is Cr3C2.
Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties.
A cold saw is a circular saw designed to cut metal which uses a toothed blade to transfer the heat generated by cutting to the chips created by the saw blade, allowing both the blade and material being cut to remain cool. This is in contrast to an abrasive saw, which abrades the metal and generates a great deal of heat absorbed by the material being cut and saw blade.
Cemented carbides are a class of hard materials used extensively for cutting tools, as well as in other industrial applications. It consists of fine particles of carbide cemented into a composite by a binder metal. Cemented carbides commonly use tungsten carbide (WC), titanium carbide (TiC), or tantalum carbide (TaC) as the aggregate. Mentions of "carbide" or "tungsten carbide" in industrial contexts usually refer to these cemented composites.
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 Forester Mushet. Prior to Mushet steel, steel had to be quenched to harden it. It later led to the discovery of high-speed steel.
Cobalt-chrome or cobalt-chromium (CoCr) is a metal alloy of cobalt and chromium. Cobalt-chrome has a very high specific strength and is commonly used in gas turbines, dental implants, and orthopedic implants.
An annular cutter is a form of core drill used to create holes in metal. An annular cutter, named after the annulus shape, cuts only a groove at the periphery of the hole and leaves a solid core or slug at the center.
USAF-96 is a high-strength, high-performance, low-alloy, low-cost steel, developed for 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 was developed by the US Air Force at the Eglin Air Force Munitions Directorate. It uses only materials domestic to the USA. In particular it requires no tungsten.
Shock resisting steels are a class of tool steels designed to resist breakage by shock. Under the AISI classification system there are seven types, labeled S1 to S7.
The famous patent suit of the Bethlehem Steel company against the Niles-Bement-Pond Company for infringement of two fundamental patents of F. W. Taylor and M. White (668,369 and 668,270, both of Feb. 19, 1907,) has been decided in favor of the defendant... The decision of the court emphasizes that there is no new composition of steel invented by Taylor and White...