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Category: FAQ's for
Tungsten Carbide
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What
is the difference between cemented and tungsten
carbide? |
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Cemented
carbides consist of hard grains of the carbides
of transition metals (Ti, V, Cr, Zr, Mo, Nb,
Hf, Ta, and/or W) cemented or bound together
by a softer metallic binder consisting of
Co, Ni, and/or Fe (or alloys of these metals).
Tungsten carbide (WC), on the other hand,
is a compound of W and C. Since most of the
commercially important cemented carbides are
based on WC as the hard phase, the terms "cemented
carbide" and "tungsten carbide" are often
used interchangeably. (close) |
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What
are the key properties of cemented carbides
I should be concerned with when selecting
a grade for my application? |
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The key
properties of cemented carbides that define
their performance level for different applications
include abrasion resistance (directly related
to the hardness of the grade), fracture strength,
and fracture toughness. In general, the abrasion
resistance or hardness of any grade is inversely
proportional to its fracture toughness. Very
often grade selection involves finding the
best compromise between abrasion resistance
and toughness. In some instances strength
and corrosion resistance can be important
factors in the grade selection process. (close) |
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Which
grade characteristics affect the properties
of cemented carbide? |
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The properties
of cemented carbides are affected by four
primary material characteristics, namely,
(i) the average grain size of the carbide
phase, (ii) the weight or volume percent of
the binder alloy present, (iii) the composition
of the carbide phases, and (iv) the composition
of the binder alloy. In general, hardness
increases (and fracture toughness decreases)
as the average hard phase grain size decreases
and/or the weight or volume fraction of the
binder decreases. The strength increases as
the average grain size of hard phase decreases
at any given binder fraction. Corrosion resistance
increases as Ni and/or Cr is substituted for
Co in the binder alloy. (close) |
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Which
properties are important in metalcutting applications?
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Depending
upon the type of metalcutting operation (turning,
milling, drilling, etc.), different combinations
of properties are needed in order to obtain
optimum results. For example, in turning and
drilling applications the cutting tool is
in continuous contact with the workpiece.
Hence, for these applications, abrasion resistance
and strength are the most important properties
to consider. However, in operations such as
milling, which invariably involve interrupted
cutting, and hence high impact forces, toughness
can be an important factor. Grades employed
for metalcutting applications are usually
based on fine to medium hard phase grain sizes
(0.5 to 1.5 m) and low to medium Co contents
(6 to 15 wt.%). (close) |
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Are
grades used for cutting nonferrous metals
different from those used for ferrous metals?
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Yes. Grades
used for cutting nonferrous metals are usually
based on WC as the hard phase and Co as the
binder phase. On the other hand, grades used
for cutting ferrous metals usually contain
other hard carbides (e.g., TiC, TaC, NbC,
etc.) besides WC. The presence of the TiC,
TaC, NbC, etc. is useful in preventing chemical
interactions between the ferrous metals and
the cutting tool (which can lead to cratering
on the surface of the tool). In addition,
carbides such as TiC, TaC, NbC, etc. can help
increase the hot hardness and strength of
cemented carbides. (close) |
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Which
grades are useful in metalforming applications?
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In contrast
to metalcutting (where abrasion resistance
and strength are of paramount importance),
cemented carbides used in metalforming applications
will invariably be subject to high impact
and shock forces. Hence, grades used for metalforming
applications must possess high toughness levels
with adequate abrasion resistance and strength.
Grades employed for metalforming applications
are typically based on coarse grain sizes
(3 to 8 m) and high binder contents (15 to
30 wt. %). (close) |
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Which
grades are useful in earth drilling or boring
applications? |
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In many
respects the characteristics of the grades
employed for earth drilling and boring represent
a compromise between the characteristics that
are important for metalcutting and those that
are important for metalforming applications.
Grades for earth drilling and boring must
possess the highest toughness levels for any
given abrasion resistance level, while simultaneously
possessing adequate strength levels. The best
compromise is usually arrived at by using
grades that are based on coarse grain sizes
(3 to 8 m) and relatively low Co levels (6
to 16 wt. %). (close) |
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