Materials Surface Treatment

HSS Surface Treatment:

Many surface treatments have been developed in an attempt to extend tool life, reduce power consumption, and to control other factors which affect operating conditions and costs. Some of these treatments have been used for many years and have proven to have some value. For example, the black oxide coatings which commonly appear on drills and taps are of value as a deterrent to build-up on the tool. The black oxide is basically a 'dirty' surface which discourages the build-up of work material One of the more recent developments in coatings for high speed steel is titanium nitride by the physical vapor deposition (PVD) method. Titanium nitride is deposited on the tool surface in one of several different types of furnace at relatively low temperature, which does not significantly affect the heat treatment (hardness) of the tool being coated This coating is known to extend the life of a cutting tool significantly or to allow the tool to be used at higher operating speeds. Tool life can be extended by as much as three times, or operating speeds can be increased up to fifty percent.

Cast Alloys:

The alloying elements in high speed steel, principally cobalt,chromium and tungsten, improve the cutting properties sufficiently, that metallurgical researchers developed the cast alloys, a family of these materials without iron Atypical composition for this class of tool material was 45 percent cobalt, 32 percent chromium, 21 percent tungsten,and 2 percent carbon. The purpose of such alloying was to obtain a cutting.
tool with hot hardness superior to high speed steel When applying cast alloy tools, their brittleness should be kept in mind and sufficient support should be provided at all times. Cast alloys provide high abrasion. resistance and are thus useful for cutting scaly materials or those with hard inclusions.