Editorial Feature

Overview of Surface Coating Technologies for Tool Steels

Surface coating technologies for tool steels are numerous some of which are summarised below, these type of surface coatings find use in drills, reamers, bore cutters, shank cutters, taps, milling tools and dies some of which are shown in Figure 1.

Example of drills, reamers, shank cutters and taps that have undergone surface treatments.

Figure 1 Example of drills, reamers, shank cutters and taps that have undergone surface treatments.

Steam Tempering

Steam tempering gives a strongly adhering blue oxide surface, which acts to retain cutting fluid and prevent chip to tool welding and thereby counteract the formation of built up edge.  Steam tempering can be applied to any bright tool but finds application mainly on drills and taps.

Bronze Finish

A bronze finish is a thin oxide layer formed on the tool surface and it is applied principally to cobalt high-speed steels.

Nitriding

Nitriding is a process, which is used to increase the hardness and wear resistance of the surface of a tool.  Particularly suitable for taps that are used on abrasive materials such as castings, bakelite, and the like.  Nitriding is used on twist drills when it is desirable to increase the strength and wear resistance of the cylindrical lands.

Hard Chromium Plating

Hard chromium plating under specific condition increases the surface hardness significantly, achieving values of up to 68Rc.  It is especially suitable when tapping structural grade steels, carbon steels, copper, brass, etc.

Titanium Nitride Coating (TiN)

Titanium nitride is a gold coloured ceramic coating applied by physical vapour deposition (PVD).  High hardness combined with low friction properties ensure considerably longer service life or alternatively better cutting performance from tools, which have been coated.  TiN coatings are used mainly for drills and taps.

Titanium Carbo Nitride Coating (TiCN)

Titanium carbo nitride is a ceramic coating applied by PVD coating technology.  TiCN is harder than TiN and has a lower coefficient of friction.  Its hardness and toughness in combination with good wear resistance ensure that it finds its principal application in the field of milling to enhance the performance of milling cutters.

Titanium Aluminium Nitride Coating (TiAlN)

Titanium aluminium nitride coatings, also called aluminium titanium nitride consist of a multi layer ceramic coating applied by PVD coating technology, which exhibits high toughness and oxidation stability.  These properties make it ideal for higher speeds and feeds whilst at the same time improving tool life. TiAlN is suitable for drilling and tapping. It is recommended to use TiAlN when machining dry.

TiAlN – X

TiAlN - X is a Titanium aluminium nitride coating, which incorporates the latest developments in surface coating technology. The high aluminium content of the coating combined with nanometer layering techniques ensures a unique blend of high temperature resistance, hardness and toughness.  This coating finds application on milling cutters which are intended to run without coolant and when milling materials with high hardness.

Chromium Nitride Coating (CrN)

CrN is an excellent coating for aluminium alloys and low-alloyed steel materials. CrN can also be used as an alternative on titanium and Nickel alloys. This coating has a low tendency for built up edges. Hardness values of 1750HV are common.

Super-R Coating

Super R is a coating specific to the milling operation. It exhibits low internal stress, high toughness and wear resistance, whilst demonstrating excellent oxidation resistance, thanks to the high oxidation temperature of the coating.

Zirconium Nitride Coating (ZrN)

Zirconium Nitride is a ceramic coating applied by PVD coating technology. It exhibits a combination of properties, which make it attractive when tapping aluminium and aluminium alloys.

Dialub (Diamond Like Coating)

Dialub is an amorphous diamond coating with extremely low coefficient of friction and high hardness. This coating is specially developed for tapping aluminium alloys with low Si-content.

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