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High-speed steel (HSS or HS) is a subset of tool steels, commonly used in tool bits and cutting tools. 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 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 abrasion resistance (generally linked to tungsten and vanadium content often used in HSS) compared with common carbon and tool steels. == History == Although development of modern high speed steel began in the second half of the 19th century, there is documented evidence of similar levels of steel produced earlier. These include hardened steels in China in 13th century BC, wootz steel manufactured in India around 350 BC and production of Damascus and Japanese layered steel blades in years 540 AD and 900 AD.〔Roberts, George (1998) ''Tool Steels'', 5th edition, ASM International, ISBN 1615032010〕 High speed properties of those steels would be mostly coincidental, and the result of local iron ores containing natural traces of tungsten or other favorable alloying components. 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 significant change was the replacement of manganese (Mn) with chromium (Cr).〔 In 1899 and 1900, Frederick Winslow Taylor and Maunsel White, working with a team of assistants at the Bethlehem Steel Company at Bethlehem, Pennsylvania, US, 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 characterised 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, and rate of cutting 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, material shortages and high costs caused by World War II 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〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「High-speed steel」の詳細全文を読む スポンサード リンク
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