OUTIL DE COUPE

CUTTING TOOL

Abrégé français

Un outil de coupe pour un produit ligneux aux caractéristiques de performance améliorées est divulgué. Il est caractérisé par une résistance du matériau de plus de 100 J mesurée dans le sens longitudinal en tant qu'énergie d'impact AV (SBP) conformément à la fiche de test acier-fer 1314 (SEP), par une dureté du matériau supérieure à 60 HRC et par une résistance accrue à la corrosion ainsi qu'à l'usure Il est constitué d'un alliage ayant la composition chimique suivante en pourcentage massique : C = 0,7 à 0,9, Si = < 0,8, Mn = 0,35 à 0,45, S = < 0,005, Cr = 7,5 à 8,5, Mo = 1,4 à 1,8, Ni < 0,4, V = 0,5 à 0,7, W = < 0,3, Al = 0,003 à 1,0, Fe = le reste, avec des impuretés provenant de la production. Le matériau pour outil de coupe traité thermiquement a une teneur totale en carbure de plus de 3 % en volume, dont au moins 0,35 % en volume de monocarbures, et sa matrice est constituée de martensite recuite.

Abrégé anglais

A cutting tool for a wood material having improved performance characteristics is provided. The cutting tool is characterized by a material toughness of more than 100J measured in longitudinal direction as impact energy AV (SBP) pursuant to steel-iron test sheet (SEP) 1314, with a material hardness of more than 60 HRC and increased corrosion resistance as well as wear resistance thereof consisting of an alloy with a chemical composition in % by weight of: C = 0.7 to 0.9 Si = .ltoreq. 0.8 Mn = 0.35 to 0.45 S = < 0.005 Cr = 7.5 to 8.5 Mo = 1.4 to 1.8 Ni = < 0.4 V = 0.5 to 0.7 W = < 0.3 Al = 0.003 to 1.0 Fe = remainder and production-related contaminations. The thermally treated material of the cutting tool has a total carbide content of more than 3% by volume, of which at least 0.35% by volume are monocarbides and the matrix consists of annealed martensite.

Revendications

Claims
1. A cutting tool, in particular knives for machining wood as
well as for products with wood, such as chipboards and the
like, having a material toughness of more than 100J
measured in longitudinal direction as impact energy AV
(SBP) pursuant to Stahl-Eisen-Prüfblatt [steel-iron test
sheet] (SEP) 1314, with a material hardness of more than 60
HRC and increased corrosion resistance as well as wear
resistance thereof consisting of an alloy with a chemical
composition in % by weight of:
C = 0.7 to 0.9
Si = .ltoreq. 0.8
Mn = 0.35 to 0.45
S = < 0.005
Cr = 7.5 to 8.5
Mo = 1.4 to 1.8
Ni = < 0.4
V = 0.5 to 0.7
W = < 0.3
Al = 0.003 to 1.0
Fe = remainder as well as production-related
contaminations,
wherein the thermally treated material of the cutting tool
has a total carbide content of more than 3% by volume, of
which at least 0.35% by volume are monocarbides and the
matrix consists of annealed martensite.
2. The cutting tool according to claim 1, wherein the alloy
has an A1 content of 0.15 to 0.25% by weight.
3. The cutting tool according to claim 1 or 2, whose surface
zone has an increased nitrogen content.
4. The cutting tool according to any one of the claims 1 to 3,
-7-

which has a coating which is preferably formed as a
compound with carbon and/or nitrogen and/or oxygen.
5. The cutting tool according to claim 4, in which the coating
contains a chromium compound.
-8-

Description

CA 02537018 2006-02-20
Cutting Tool
The invention relates to a cutting tool, in particular, for
cutting wood.
In the woodworking industry, knives or cutting strips which are
simultaneously subjected to wear due to adhesive and abrasive
stresses, to deflection and to pressure in the cutting edge
region, largely abruptly, are used for cutting wood, in
particular logs, i.e. for so-called "chipper applications". The
material of tools or knives of this type should therefore also
be resistant to stress due to tannin from a corrosion-chemical
point of view and should, at the same time, obtain or have both
maximum toughness and maximum wear resistance as well as a high
degree of hardness by means of a thermal tempering treatment.
The demands for continuously increasing performance with maximum
safety in operation of the woodworking facilities can ultimately
only be met by cutting tools with an appropriately adapted
performance profile. In other words: Wear, peripheral damages
due to plastic deformations on the one hand, and conchoidal or
lenticular breaks of the edges primarily due to impact stresses
on the other hand, as well as a premature knife breakage due to
material properties adapted to one another are to be prevented,
in particular in the cutting region of the knife, .
It is known to use steels with the material No. 1.2362 according
to DIN for "chipper applications". Knives made of this steel
have a high material toughness in the thermally hardened state,
however, their wear resistance, the inherent stability of the
cutting region and the corrosion resistance is, for the most
part, too low. To improve the inherent stability of the cutting
edge, knives or cutting strips are often made of steel according
to material No. 1.2363, said cutting tools usually not having a
sufficient resistance to wear. Attempts have already been made
to use an alloy according to AT 393 387 as cutting tool material,
- 1 -

CA 02537018 2006-02-20
whereby the best results with respect to the wear performance
could be obtained, though errors occasionally occurred which
indicate a material toughness which is too low.
The object of the invention is to overcome the respective
disadvantages of the prior art and to create a cutting tool, in
particular a knife, of the aforementioned type which exhibits
synergetically improved performance characteristics during
processing, in particular when cutting wood with sporadic
stresses or interrupted cuts, as a result of a limited selection
of the concentration of the respective elements in the steel or
of the chemical composition as well as the thermal tempering and
the microstructure of the material.
This object is obtained with a cutting tool of the aforementioned
type having a material toughness of greater than 100,7, measured
in longitudinal direction, as impact energy AV (SBP) pursuant to
Stah1-Eisen-Priifblatt [steel-iron test sheet] (SEP) 1314; with
a material hardness of more than 60 HRC and increased corrosion
resistance as well as wear resistance thereof consists of an
alloy having a chemical composition of % by weight:
C - 0.7 to 0.9
Si - < 0.8
Mn - 0.35 to 0.45
S - < 0.005
Cr - 7.5 to 8.5
Mo - 1.4 to 1.8
Ni - < 0.4
V - 0.5 to 0.7
W - < 0.3
A1 - 0.003 to 1.0
Fe - remainder as well as production-related contaminations,
wherein the thermally treated material of the cutting tool has
a total carbide content of more than 3% by volume, of which at
least 0.35% by volume are monocarbides and the matrix consists
of annealed martensite.
- 2 -

CA 02537018 2006-02-20
The advantages obtained with the invention can essentially be
seen therein that the required or the desired individual
properties are simultaneously maximized by the limited selection
of the respective contents of the alloying components, adjusted
to one another, and a conventional thermal treatment of the steel
with a hardening, with a cooling of about 1030°C followed by a
triple annealing at a temperature of about 550°C and creating a
desired microstructure.
A high toughness of the tool material is, as was found, necessary
because breakages at the cutting edges and even knife breakages
can occur at a value of less than 100J for the impact energy
measured on an impact bending test in longitudinal direction.
At the same time, according to the invention, high material
hardness values which ensure an extensive inherent stability of
the entire cutting region during high sudden stresses are
necessary. A hardness of less than 60 HRC enables plastic
deformations of the tool material which can lead to an adverse
affect of the tool function in the cutting operation.
According to the invention, the concentration of the respective
alloying components is important for a chemical stability and for
the profile of the mechanical properties of the tool material,
because they determine the separation and conversion kinetics and
the structure during a thermal treatment.
By relating the alloying components, one can see, in particular,
the contents of carbon simultaneously with the contents or the
activity of the respective carbide-forming components to carbon.
In a limited range of 0.7 to 0.9% by weight carbon, monocarbides
are produced by 0.5 to 0.7 % by weight vanadium, said
monocarbides have a small diameter, are distributed homogeneously
and deliver a substantial contribution to the wear resistance of
the material with a content of at least 0.35% by volume without
negatively affecting its toughness. High contents of carbon and
vanadium can disadvantageously affect the interaction of the
- 3 -

CA 02537018 2006-02-20
alloying components and usually lead to a coarser carbide
structure, as a result of which the material toughness
deteriorates. Low concentrations of these components of less
than 0.7% by weight carbon and 0.5% by weight vanadium
overproportionally reduce the wear resistance of the material.
According to the invention, the carbon content of the alloy is
set in the range of 0.7 to 0.9% by weight also with respect to
forming M~C3 and Mz3C6 carbides with the further carbide-forming
components of the steel, the desired properties of the matrix
which consists of annealed martensite are also obtained with said
content. In this case, the respective concentration of chromium
and molybdenum in the range of 7.5 to 8.5 or 1.4 to 1.8 are
essential for a desired total carbide content of more than 3.0%
by volume, however, the tungsten content is restricted to a value
of less than 0.3% by weight due to the material embrittling
effect.
Manganese promotes the hardenability of the steel in contents of
0.35 to 0.45 and binds the sulphur which should exhibit a
concentration value of less than 0.005% by weight to manganese
sulf ide .
Nickel acts in a disturbing manner on the separating and
converting kinetics of this cutting steel during a hardening
treatment, so that a Ni content of less than 0.4% by weight is
essential for the desired tool quality.
The content of aluminum in the steel in the limits of 0.003 to
1.0% by weight, provided according to the invention, has an
especially advantageous effect on the one hand on the hardening
and annealing behaviour or on the annealed structure and the
mechanical properties of the material; on the other hand, the
quality of a surface layer, e.g. a nitride layer, or the adhesion
of a coating, e.g. a nitride, carbon nitride or oxide carbon
nitride layer of metals, in particular of titanium and/or
- 4 -

CA 02537018 2006-02-20
chromium, is also promoted by aluminum. Aluminum increases the
activity and the diffusion coefficients of carbon in austenite.
The diffusion coefficients of chromium, molybdenum and vanadium
are lowered in the austenite and in the ferrite by aluminum.
This means a reduction in the solubility of carbon in the
austenite, so that the stability of the austenite is lowered and,
as a result, the martensite starting point increased, as a result
of which the residual austenite content is in turn greatly
lowered in the hardened structure. Aluminum is mainly dissolved
in the matrix and delivers a contribution to the mixed crystal
hardness. The high affinity of aluminum to nitrogen increases
the hardness of the diffusion layer of nitrified steels.
An aluminum content of 0.15 to 0.25% by weight in the alloy is
preferred.
The invention will be described in greater detail with reference
to an example:
A molten mass having a composition, in % by weight, of C = 0.81,
Si = 0.68, Mn = 0.39, P = 0.015, S = 0.003, Cr = 8.06, Mo = 1.59,
Ni = 0.26, V = 0.61, W = 0.19,. A1 = 0.17, Fe remainder was poured
to form blocks after a ladle-metallurgical treatment. After a
reheating and annealing time of 31 hours, it was rolled to form
flat stock from which "chipper knives" were produced by
machining.
After heating and thoroughly warming the knives or the cutting
strips to 1030°C, they were forcibly cooled to a temperature of
about 50°C which was followed by a triple annealing at a
temperature of between 545°C and 560°C. After this thermal
treatment, the hardness of the material from a sample tool was
61 HRC free of residual austenite. Impact bending samples with
the following dimensions were removed from the concrete tool:
length 55 mm, width 10 mm and height 7 mm. A toughness test of
the material on these samples resulted in an impact bending
energy of essentially 115J. Metallographic and residual tests
- 5 -

CA 02537018 2006-02-20
showed that the material in a matrix consisting of annealed
martensite had a total amount of carbides of 3.21% by volume, of
which carbides 0.43% by volume were monocarbides of the MC type
and the remainder carbides of the formation M7C3 and M~C6. It
should thereby be remembered that no residual austenites were
present in the structure.
A "chipper knife" according to the invention, made parallel to
the test tool, was inserted in a device for cutting logs under
more difficult conditions due to adhering soil particles and
resulted in a tool life improvement of 120% in comparison to a
high-performance knife from the market compared to it.
- 6 -