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High-speed steel ( HSS or HS) is a subset of , commonly used as cutting tool material.
Compared to high-carbon steel tools, high-speed steels can withstand higher temperatures without losing their temper (hardness), allowing use of faster cutting speeds. At room temperature, in their generally recommended heat treatment, HSS grades generally display high hardness (above 60 Rockwell C) and abrasion resistance compared with common carbon steel and . There are several different types of high speed steel, such as M42 and M2.
In 1899 and 1900, Frederick Winslow Taylor and Maunsel White ( A.K.A Maunsel White III; 1856–1912; grandson of Maunsel White; 1783–1863), working with a team of assistants at the Bethlehem Steel 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. Their experiments were characterised by a scientific empiricism in that many different combinations were made and tested, with no regard for conventional wisdom, 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 cutting speed to be tripled from 30 surface feet per minute to 90. A demonstration of cutting tools made from the new steel caused a sensation at the 1900 Paris Exhibition.
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-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
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. High Speed Steel (HSS) , Retrieved 17 May 2010.
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.
| + A sample of alloying compositions of common high speed steel grades (by %wt) (impurity limits are not included) |
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 steel kitchen knife and pocket knife.
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.
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