Coatings for cutting tools
Examples of drills, reamers, shank cutters and taps that have undergone surface treatments (taken
from an article at http://www.azom.com overviewing surface coating technologies for tool steels).
Reasons for coatings:
? Improvement of wear resistance
? Increase of tool life
? They enable cutting tools to be used at higher cutting speeds
Improved wear resistance arises from the high hardness, low ? and chemical inertness of the
coatings.
The first coating to be developed commercially, and still used today, was titanium nitride, TiN,
deposited by PVD or CVD, e.g., on high-speed steels (HSS).
High-speed steels are high-alloy steels containing ~ 0.8–1.0 wt% carbon.
General purpose HSS contain W, Mo, V and Cr as alloying elements. Typical carbides occurring in
these steels through secondary hardening are W2C, WC, Mo2C, VC, Cr23C6 and Fe3W3C.
‘T’ grades such as T1 steels contain high levels of tungsten, while ‘M’ grades such as M2 either
have molybdenum with limited tungsten or similar levels of tungsten and molybdenum.
Cobalt-containing HSS contain W, Mo, V, Cr and Co as alloying elements. These more expensive
HSS are more brittle than non-cobalt types, but give better cutting performance on hard, scaly,
materials that are machined with deep cuts at high speed (Roberts et al., p. 289).
Cobalt is present in solid solution in the austenite and tempered martensite rather than being
introduced as a carbide former. Although it can produce Co3C and Co2C, it is at best a weak carbide
former. Instead, it helps to raise the solidus temperature of the HSS which is useful for high
temperature operation of these high-speed steels (Roberts et al., p. 283).
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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