Category: HIGH-SPEED STEEL
The selection of a standard analysis by the manufacturer is the
result of a series of compromises between various properties imparted
to the steel by the addition of different elements and there is a
wide range of chemical analyses of various brands. The steel, to
be within the range of generally accepted analysis, should contain
over 16 per cent and under 20 per cent tungsten; if of lower tungsten
content it should carry proportionately more chromium and vanadium.
The combined action of tungsten and chromium in steel gives to it the
remarkable property of maintaining its cutting edge at relatively high
temperature. This property is commonly spoken of as red-hardness.
The percentages of tungsten and chromium present should bear a
definite relationship to each other. Chromium imparts to steel
a hardening property similar to that given by carbon, although
to a less degree. The hardness imparted to steel by chromium is
accompanied by brittleness. The chromium content should be between
3.5 and 5 per cent.
Vanadium was first introduced in high-speed steel as a scavenger,
thereby producing a more homogeneous product, of greater density
and physical strength. It soon became evident that vanadium used
in larger quantities than necessary as a scavenger imparted to
the steel a much greater cutting efficiency. Recently, no less an
authority than Prof. J. O. Arnold, of the University of Sheffield,
England, stated that high-speed steels containing vanadium have
a mean efficiency of 108.9, as against a mean efficiency of 61.9
obtained from those without vanadium content. A wide range of
vanadium content in steel, from 0.5 to 1.5 per cent, is permissible.
An ideal analysis for high-speed steel containing 18 per cent tungsten
is a chromium content of approximately 3.85 per cent; vanadium, 0.85
to 1.10 per cent, and carbon, between 0.62 and 0.77 per cent.
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