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Hartner
tool materials

Carbide

Carbide, similar to steel, is a less than precise and indeed a very ge- Hardness K IC
neral term for an entire material group. Carbide can be produced in an 1750 13
infinite number of variations with different characteristics through the 1750 13
combination of at least two basic constituents. 1700
1700
12
12
1650
1650
Carbide production 11
Carbide consists of a hardness carrier – tungsten carbide plus may- 1600 11
1600
be one or more carbides – and an extremely tough component: Co- Hardness HV50
balt (Co). Cobalt basically serves as a cementing or binding agent in 1550 10 Toughness KIC MP am 0,5
1550
10
which the carbide particles are distributed. 1500
In order to satisfy the diverse demands that, dependent on the indivi- 1500
dual application task, are placed on carbide, Hartner offers a choice 1450 9 9
of more than 20 different standard carbide types. Some are especially 1450
hard, others possess a very high toughness, some are ultra fine grain 1400 8
and others are coarse. Furthermore, on the request of the customer, 1400 0,2 0,4 0,6 0,8 1,0 1,2 1,48
1,2
1,0
0,8
0,2
1,4
0,6
0,4
any conceivable carbide grade can be developed and produced as a Grain size in µm
special carbide, so-to-speak.
Toughness
Toughness is defined as the resistance the material offers against the
Our carbide division has a state-of-the-art laboratory at its disposal to growth of a fissure. A high fissure resistance is an indication of “good-
ensure our carbide always corresponds with customer requirements. natured” carbide, possessing high impact resistance. Unfortunately,
From the raw material to the finished product, samples are continuo- hardness and toughness are opposing attributes.
usly examined in order to guarantee and document the highest quality High cobalt content and/or coarse hard material grains are an indica-
and process reliability in accordance with the certification. tion of tough carbide. High toughness is required when a sudden or
high cutting load occurs during the machining process. A high cutting
Basic characteristics of carbide load arises when there is a high friction coefficient between tool and
workpiece. The coefficient of friction is determined by the surface
For drilling applications the following characteristics are of im- roughness of the tool and by the chemical relationship between the
portance: tool surface and the workpiece.
Please note, toughness is not synonymous with high bending
Rigidity strength. An important and specific characteristic for determining the
Rigidity is a measure of the energy that is required to force a material bending strength is the cutting edge stability.
to deform. With carbide it is determined by the cobalt content. The
higher the cobalt content, the lower the rigidity of the material.
Cutting edge stability
The rigidity of conventional carbide is more than double compared to Cutting edge stability is defined as the resistance of the cutting edge
that of steel. Subsequently, holes of considerably greater straightness against the breakaway of individual hard material grains or larger
can be produced with carbide drills than with steel drills. However, grain formations. The bending strength provides a rough measure of
this positive effect of the rigidity is limited because of deformation the cutting edge stability. In addition to toughness, the size of the
forced upon the drill – for example through offset or imbalance – re- longest grain boundary within the structure of the material is also of
sult in a heavy increase in load on the material. Therefore, more rigid importance for the bending strength. Subsequently, high toughness
materials are also more prone to breakage. increases the bending strength, however, longer grain boundaries (=
coarser grains) lowers it.
Hardness
Hardness is described as the resistance of a material against penetra- Reaction
tion of another. It is clear, that the tool material must be considerably Although today most carbide tools are coated, the reaction tendency
harder than that of the workpiece, in order to not be exposed to ex- between carbide and workpiece must be taken into consideration.
cessive wear. Because of rapid wear of the coating at the cutting edge, a reaction
between tool and workpiece is indeed a possibility.
There are several possibilities to adjust the hardness of carbide: on
the one hand by modifying the cobalt content and on the other hand Similar to pitting in the corrosion process, a localised attack can have
by varying the carbide grain size. If the cobalt content is increased a considerably longer lasting effect than any damage over a large
whilst retaining the same grain size, the hardness of the carbide is re- area. Due to the high temperature development at the cutting edge,
duced. However, if the grain size is reduced whilst retaining the same cobalt in particular reacts very quickly with ferrous metals. Other me-
cobalt content, the hardness is increased. tals, such as titanium or silicon are prone to react with tungsten car-
bide. For these reasons, the cobalt content is of interest regarding the
reaction of the tool.

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