(description)
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. Title of the Invention
BRAKE DISC WITH NICKEL-FREE STEEL LAYER AND MANUFACTURING METHOD
2. Applicant(s)
Name Nationality Address
BREMBO S.P.A. ITALIAN Via Brembo, 25 I-24035 Curno, Bergamo,
Italy
3. Preamble to the description
The following specification particularly describes the invention and the manner in which it is to be performed
2
DESCRIPTION
FIELD OF APPLICATION
[0001] The present invention relates to a method for making a brake disc and to a brake
disc for disc brakes.
5 PRIOR ART
[0002] A brake disc of a vehicle disc brake system comprises an annular structure, or
braking band, and a central fixing element, known as a bell, by which the disc is
attached to the rotating part of a vehicle suspension, for example a hub. The braking
band is provided with opposed braking surfaces suitable for cooperating with friction
10 elements (brake pads), housed in at least one gripper body placed astride of said braking
band and integral with a non-rotating component of the vehicle suspension. The
controlled interaction between the opposed brake pads and the opposed braking surfaces
of the braking band determine by friction a braking action which allows the deceleration
or stopping of the vehicle.
15 [0003] Generally, the brake disc is made of gray cast iron or steel. In fact, this material
allows good braking performance (especially in terms of limited wear) to be obtained at
relatively low costs. Discs made of carbon or carbon-ceramic materials offer much
higher performance, but at a much higher cost.
[0004] The limits of traditional discs of cast iron or steel are linked to excessive wear.
20 As far as gray cast iron discs are concerned, another very negative aspect is linked to
excessive surface oxidation, with the consequent formation of rust. This aspect affects
both the performance of the brake disc and its appearance, as the rust on the brake disc
is aesthetically unacceptable to the user. An attempt was made to address these
problems by making the discs in gray cast iron or steel with a protective coating. The
3
protective coating serves on the one hand to reduce the wear of the disc, and on the
other hand to protect the gray cast iron base from surface oxidation, thus avoiding the
formation of a layer of rust. The protective coatings available today and applied on
discs, although offering resistance to wear, are however subject to flaking that causes
5 the detachment thereof from the disc itself.
[0005] A protective coating of this type is described for example in patent US4715486,
relating to a low-wear disc brake. The disc, made in particular of cast iron, has a coating
made with a particle material deposited on the disc with an impact technique with high
kinetic energy. According to a first embodiment, the coating contains from 20% to 30%
10 of tungsten carbide, 5% of nickel and the balance of a mixture of chromium and
tungsten carbides.
[0006] In the case of application of the coating with flame spray techniques, a cause of
the detachment of traditional protective coatings from aluminum or aluminum alloy
discs is the presence of free carbon in the protective coating. This phenomenon also
15 affects gray cast iron or steel discs.
[0007] A solution to the aforesaid problems has been proposed by the same applicant in
international application WO2014/097187 as regards discs made of gray cast iron or
steel. It consists in creating a protective coating on the braking surfaces of a brake disc
obtained by depositing a material in particle form composed of 70 to 95% by weight of
20 tungsten carbide, 5% to 15% by weight of cobalt and 1% to 10% by weight of
chromium. The deposition of the material in particle form is obtained by the HVOF
(High Velocity Oxygen Fuel) technique, or by the HVAF (High Velocity Air Fuel)
technique or by the KM (Kinetic Metallization) technique.
[0008] More in detail, according to the solution offered in WO2014/097187, the
4
combination of the HVOF, HVAF or KM deposition technique and the chemical
components used for the formation of the coating allows a protective coating with high
bond strength to be obtained, which guarantees a high degree of anchoring on gray cast
iron or steel. The above solution allows the flaking phenomena of the protective coating
5 recorded in the prior art to be significantly reduced, but not to eliminate them
completely. In fact, even in discs provided with a protective coating made according to
WO2014/097186, peeling and sagging of the protective coating continue to occur -
albeit less frequently than in the prior art.
[0009] The aforementioned flaking and sagging may contribute in particular to the
10 release by rubbing of nickel particles, a metal which contributes significantly to
sensitization phenomena in the population.
[0010] However, in the specific field of steel production for brake discs, to date, the
presence of nickel is considered essential as it increases the strength of the steel and
toughness. Furthermore, nickel increases the resistance of steel to oxidation and
15 corrosion, but, above all, nickel increases the abrasive resistance of the steel and the
heat resistance of that steel, aspects which are extremely relevant for the stresses they
are subjected to in brake discs. Therefore, to date, the presence of nickel is considered
an essential element for the production of a cast iron or steel brake disc.
[0011] Taking into account the advantages in terms of wear resistance guaranteed by the
20 protective coatings and the simultaneous need to maintain the presence of nickel in the
composition of the brake disc, the need to solve the drawbacks mentioned in reference
to the prior art is very much felt in the field.
[0012] In particular, the need is felt to have gray cast iron or steel discs capable of
reducing the release of nickel particles, but at the same time capable of guaranteeing
5
adequate or equivalent thermal and mechanical performance typical of the prior art
brake discs, including high wear resistance of the disc and reliability over time.
[0013] According to a further aspect, the need is also felt to make steel discs with less
consumption of resources necessary for production (and therefore also of costs), while
5 maintaining an adequate hardness of the coating and at the same time a reduced (or even
absent) release of nickel particles.
[0014]
DISCLOSURE OF THE INVENTION
[0015] The need for brake discs capable of reducing the release of nickel particles, but
10 at the same time capable of guaranteeing adequate or equivalent thermal and mechanical
performance, is met by a brake disc and by a method for making a brake disc according
to the appended independent claims.
DESCRIPTION OF THE DRAWINGS
[0016] Further features and advantages of the present invention will become more
15 apparent from the following description of preferred and non-limiting embodiments
thereof, in which:
- Figure 1 shows a top plan view of a disc brake according to an embodiment of the
present invention;
- Figure 2 shows a sectional view of the disc of Figure 1 according to the section line II20 II indicated therein, according to an embodiment of the present invention;
- Figure 3 shows a sectional view of the disc of Figure 1 according to the section line IIII indicated therein, according to a further embodiment of the present invention;
- Figure 4 shows a sectional view of a half portion of a braking band according to an
embodiment of the present invention;
25 - Figure 5 shows a sectional view of a half portion of a braking band according to a
6
second embodiment of the present invention;
- Figure 6 shows a sectional view of a half portion of a braking band according to a third
embodiment of the present invention;
- Figure 7 shows a sectional view of a half portion of a braking band according to a
5 fourth embodiment of the present invention;
- Figure 8 shows a sectional view of a half portion of a braking band according to a fifth
embodiment of the present invention;
- Figure 9 shows a sectional view of a half portion of a braking band according to a sixth
embodiment of the present invention;
10 - Figure 10 shows a sectional view of a half portion of a braking band according to a
seventh embodiment of the present invention.
[0017] Elements or parts of elements common to the embodiments described hereinafter
will be indicated with the same reference numerals.
DETAILED DESCRIPTION
15 [0018] With reference to the above figures, reference numeral 1 globally denotes a
brake disc according to the present invention.
[0019] In the present discussion, where numerical percentage intervals are indicated, the
extremes of these intervals are always understood to be included, unless otherwise
specified.
20 [0020] According to a general embodiment of the invention, illustrated in the
accompanying figures, the brake disc 1 comprises a braking band 2, provided with two
opposite braking surfaces 2a and 2b, each of which at least partially defines one of the
two main faces of the disc.
[0021] The braking band 2 is made of gray cast iron or steel.
7
[0022] Preferably, the braking band 2 is made of gray cast iron. In particular, the entire
disc is made of gray cast iron. In the remainder of the description, reference will
therefore be made to a gray cast iron disc, without however excluding the possibility
that it is made of steel.
5 [0023] The disc 1 is provided with a base layer 30 which covers at least one of the two
braking surfaces 2a, 2b of the braking band and is preferably made in direct contact with
said braking surfaces 2a, 2b.
[0024] According to an aspect of the present invention, such base layer 30 is composed
of steel having a nickel content lower than or at most equal to 15%.
10 [0025] According to a further aspect of the present invention, such base layer 30 is
composed of steel having a nickel content lower than or at most equal to 7.5%, even
more preferably lower than or at most equal to 5%.
[0026] According to a further aspect of the present invention, such base layer 30 is
totally nickel-free. This makes it possible to limit, if not even avoid, the dispersion of
15 nickel particles during the life of the brake disc 1.
[0027] In general, in the present discussion, when reference is made to phrases such as
“nickel free” or “without nickel” or the like, it is meant exactly the total absence of
nickel but also an absence of nickel less than a small amount of nickel which may be
present due to traces or residual impurities due to the manufacturing process, but in any
20 case amounts of nickel lower than 1% or possibly at the most strictly lower than 5%, for
any layer.
[0028] It is clear that, to those skilled in the art, it is known what is meant when
referring to percentages of content of nickel or of any other component of the steel or
cast iron alloy. For example, reference is generally made to the percentage content by
8
mass with respect to the total content of the alloy. Therefore, in the continuation of the
present discussion, particular percentage calculations will be specified only where they
deviate from the aforementioned definition; where not specified, the percentages
indicated should be considered as understandable by those skilled in the art.
5 [0029] According to an embodiment of the invention, the steel of the base layer 30 is
composed of 10% to 15% chromium Cr, at most 1% silicon Si, at most 4% manganese
Mn, between 0.16% and 0.5% of carbon C and for the balance of iron Fe, i.e., for the
remaining percentage by weight of iron. This makes it possible to obtain a martensitic
steel, without nickel content.
10 [0030] Preferably, the content of carbon C of the steel of the base layer is comprised
between 0.16 and 0.25%.
[0031] Advantageously, the aforesaid composition allows a reduced percentage of any
carbides included in the steel to be used, without reducing the hardness of any coating
(described in more detail later in the text).
15 [0032] According to a preferred embodiment variant, the chromium (Cr) content in the
steel of the base layer 30 is comprised between 11% and 14%, extremes included.
[0033] According to an embodiment variant of the invention, for example shown in
Figure 5, the base layer 30 also is composed of one or more carbides included in the
nickel-free steel. Such inclusion is obtained by means of techniques known to those
20 skilled in the art of inclusion of carbides in steel, for example the carbides are dissolved
in the alloy.
[0034] Preferably, the one or more carbides included comprise at least one carbide
selected from the group comprising: tungsten carbide (WC), chromium carbide
9
(preferably, but not limited to, Cr3C2), Niobium carbide (NbC), titanium carbide (TiC).
It is clear that more than one carbide selected from the aforementioned group or all the
carbides present in the present group may also be present.
[0035] The one or more carbides included comprise at least one carbide selected from
5 the group comprising: tungsten carbide (WC), chromium carbide (e.g., Cr3C2),
Niobium carbide (NbC), titanium carbide (TiC).
[0036] According to an advantageous embodiment, for example shown in Figure 6, the
brake disc 1 comprises a protective surface coating 3 which covers the base layer 30 at
least on the side of one of the two braking surfaces 2a, 2b of the braking band. Such
10 protective surface coating 3 is arranged on one side of the base layer 30 which does not
face towards the braking surface 2a, 2b. Furthermore, the surface protective coating 3 is
composed of at least one carbide or more carbides in particle form which may be
deposited by the Thermal Spray deposition technique, for example by the HVOF (High
Velocity Oxy-Fuel) technique, or by the HVAF (High Velocity Air Fuel) technique or
15 by the APS (Atmosphere plasma spray) technique or by the Cold Spray deposition
technique, for example by the KM (Kinetic Metallization) technique, or by the
deposition technique using a laser beam, for example by the LMD (Laser Metal
Deposition) technique, or by HSLC - high speed laser cladding technique, or by EHLA -
Extreme High Speed Laser Application technique, or by TSC - Top Speed Cladding
20 technique.
[0037] The surface protective coating 3 is therefore obtained by depositing directly on
the disc 1 one or more carbides in particle form also by the HVOF technique, or by the
HVAF (High Velocity Air Fuel) technique or by the KM (Kinetic Metallization)
technique, preferably tungsten carbide (WC) or chromium carbide (for example, Cr3C2)
10
or niobium carbide (NbC) or titanium carbide (TiC).
[0038] According to a further embodiment variant, the surface protective coating 3 is
composed of steel having a nickel content lower than or at most equal to 15% or lower
or at most equal to 7.5%, or lower or at most equal at 5%, or even more preferably
5 totally free from nickel, and of one or more carbides included in the steel. In this variant,
in other words, the base layer 30 in nickel-free steel and above a protective surface
coating 3 composed of the aforementioned steel and one or more carbides included in
the steel are joined above the cast iron band in the order indicated.
[0039] The presence of carbides deposited on the surface or included in the steel
10 substantially or totally without nickel makes it possible to impart mechanical strength
and wear resistance, so as to compensate for the scarcity or total lack of nickel inside the
steel.
[0040] According to a variant, the surface protective coating 3 is composed of one or
more of the following carbides: tungsten carbide (WC), niobium carbide (NbC),
15 chromium carbide (for example, Cr3C2), titanium carbide (TiC). Preferably, such
protective surface coating 3 is obtained by depositing on the base layer 30 one or more
of the aforementioned carbides in particle form by the Thermal Spray deposition
technique, for example by the HVOF (High Velocity Oxy-Fuel) technique, or by the
HVAF (High Velocity Air Fuel) technique or by the APS (Atmosphere plasma spray)
20 technique or by the Cold Spray deposition technique, for example by the KM (Kinetic
Metallization) technique, or by the deposition technique using a laser beam, for example
by the LMD (Laser Metal Deposition) technique, or by HSLC - high speed laser
cladding technique, or by EHLA - Extreme High Speed Laser Application technique, or
by TSC - Top Speed Cladding technique. It is therefore clear that more than one carbide
11
selected from the aforementioned group or all the carbides present in the present group
may also be present.
[0041] According to an advantageous embodiment, the surface protective coating 3 is
composed of chromium carbide (for example, Cr3C2) and titanium carbide (TiC).
5 [0042] According to a variant, the surface protective coating 3 is composed of at least
one metal oxide or a mixture of metal oxides or a mixture of metals and ceramic
materials, preferably a mixture of aluminum oxides Al2O3, or a mixture of Al2O3 and
intermetallic matrix Fe-Cr, for example Fe28Cr.
[0043] According to an advantageous embodiment variant, the surface protective
10 coating 3 is composed of one or more of the following carbides: tungsten carbide (WC),
niobium carbide (NbC), chromium carbide (for example, Cr3C2), titanium (TiC), mixed
with a mixture of metal oxides or mixed with a mixture of metals and ceramic materials,
preferably with a mixture of aluminum oxides Al2O3, or a mixture of Al2O3 and
intermetallic matrix Fe-Cr, for example Fe28Cr.
15 [0044] It is clear that the oxides or mixtures of oxides, or the metals or mixtures of
metals and ceramic materials, or the mixtures of carbides and metal oxides described
above are preferably deposited by the same deposition techniques of the carbides in
particle form described above and in the present discussion.
[0045] Preferably, the surface protective coating 3 has a thickness comprised between
20 30 μm and 150 μm, and preferably between 50 μm and 90 μm.
[0046] According to an embodiment of the present invention, the steel of the base layer
30 comprises between 10% and 20% of chromium (Cr).
[0047] According to an embodiment of the present invention, the steel of the base layer
30 comprises at least 15% chromium (Cr), even more preferably between 16% and 18%
12
chromium.
[0048] According to an embodiment, the steel of the base layer 30 comprises at most
5% manganese (Mn), even more preferably, the manganese content is between 0.5% and
5%, extremes included, so as to at least partially compensate for the lack of the
5 properties of the steel alloy generally imparted by the presence of nickel, increasing the
mechanical strength.
[0049] In particular, according to an embodiment , in order to compensate for the scarce
quantity or complete absence of nickel and to obtain adequate performances for a brake
disc, the steel of the base layer 30 is composed of 10 to 20% of Chromium (Cr) by
10 weight, preferably between 16% to 18% of chromium (Cr) by weight, at most 1.5% by
weight of silicon (Si), at most 2% by weight of manganese (Mn), at most 0.03% by
weight of carbon (C) and for the balance iron (Fe), i.e. for the remaining percentage by
weight of iron.
[0050] Preferably, the base layer 30 has a thickness comprised between 20 μm and 300
15 μm, and preferably equal to 90 μm.
[0051] According to a variant of the invention, in order to compensate for the low
quantity or complete absence of nickel and to obtain adequate performance for a brake
disc, the steel of the base layer 30 has a molybdenum content between 0.5% and 10%,
even more preferably between 0.5% and 4.5%, extremes included and a manganese
20 content between 0.5% and 5%. The presence of molybdenum and manganese in the
above percentages allows adequate resistance to corrosion and at the same time
adequate mechanical resistance to be obtained.
[0052] According to an embodiment, between the base layer 30 and at least one of the
two braking surfaces 2a, 2b of the braking band 2 there is interposed an intermediate
13
layer 300 of steel comprising nickel, preferably with a nickel content higher than 5% in
the case in which the base layer 30 is totally free from nickel, or, even more preferably
with a nickel content of at least 5%, and even more preferably with a nickel content of at
least 5% and less than 15%.
5 [0053] According to an embodiment, the intermediate layer 300 comprises a steel with a
nickel content of at most 15% or equal to 15%.
[0054] According to an embodiment, the intermediate layer 300 comprises a steel with a
nickel content of at most 7.5% or equal to 7.5%.
[0055] According to a further embodiment, an intermediate layer 300 of nickel- free
10 steel is interposed between the base layer 30 and at least one of the two braking surfaces
2a, 2b of the braking band.
[0056] According to an embodiment, the intermediate layer 300 comprises a nickel-free
steel composed of 10% to 15% of chromium (Cr), at most 1% of silicon (Si), at most
4% of manganese (Mn), from 0.16% to 0.5% of carbon (C) and for the balance iron
15 (Fe). Preferably, the carbon (C) content is comprised between 0.16% and 0.25%.
[0057] The presence of the intermediate layer 300 allows a disc with adequate
mechanical features to be obtained, but at the same time with a reduced environmental
impact, by virtue of the presence of the base layer 30.
[0058] According to an embodiment, the intermediate layer 300 comprises steel
20 composed of 10% to 15% of chromium (Cr), at most 1% of silicon (Si), at most 4% of
manganese (Mn), from 0.16% to 0.5% of carbon (C) and for the balance iron (Fe).
Preferably, the carbon (C) content of the steel of the intermediate layer 300 is comprised
between 0.16% and 0.25%, extremes included.
[0059] According to an embodiment, the surface protective coating 3 comprises steel
25 composed of 10% to 15% of chromium (Cr), at most 1% of silicon (Si), at most 4% of
14
manganese (Mn), between 0.16% and 0.5% of carbon (C) and for the balance iron (Fe),
preferably without nickel.
[0060] Preferably, the carbon (C) content of the steel of the surface protective coating is
comprised between 0.16% and 0.25%, extremes included.
5 [0061] According to an embodiment, an auxiliary layer of ferritic-nitrocarburization or
an auxiliary ferroalumination layer is interposed between one of the two braking
surfaces 2a, 2b of the braking band and the base layer 30, or between one of the two
braking surfaces 2a, 2b of the braking band and the intermediate layer 300, or between
the base layer 30 and the surface protective coating 3, or between the intermediate layer
10 300 and the base layer 30.
[0062] According to an embodiment, an auxiliary layer of ferritic-nitrocarburization and
an auxiliary ferroalumination layer is interposed between one of the two braking
surfaces 2a, 2b of the braking band and the base layer 30, or between one of the two
braking surfaces 2a, 2b of the braking band and the intermediate layer 300, or between
15 the base layer 30 and the surface protective coating 3, or between the intermediate layer
300 and the base layer 30.
[0063] For simplicity of discussion, the brake disc 1 will now be described contextually
to the method according to the present invention. The brake disc 1 is preferably, but not
necessarily, made by the method according to the invention which will now be
20 described.
[0064] According to a first aspect of the present invention, a general embodiment of the
method according to the invention comprises the following operating steps:
a) preparing a brake disc, comprising a braking band and provided with two opposite
braking surfaces 2a, 2b, each of which defines at least partially one of the two main
25 faces of the disc, the braking band being made of gray cast iron or steel;
15
b) depositing a steel layer comprising at most 15% of nickel, preferably by laser
deposition technique, for example Laser Metal Deposition or Extreme High-Speed
Laser Material Deposition or by Thermal Spray deposition technique, or by Cold Spray
deposition technique, to form the base layer 30;
5 c) optionally depositing over said base layer 30 a material in particle form composed of
tungsten carbide (WC) or niobium carbide (NbC) or titanium carbide (TiC) or possibly
chromium carbide by a Thermal Spray deposition technique, e.g. by the HVOF (HighVelocity Oxy-Fuel) technique, the HVAF (High-Velocity Air Fuel) technique, the APS
(Atmosphere Plasma Spray) technique or a Cold Spray deposition technique, e.g. by the
10 KM (Kinetic Metallization) technique, or by a laser beam deposition technique, e.g. by
the LMD (Laser Metal Deposition) technique, or by the HSLC (High-Speed Laser
Cladding) technique, or by the EHLA (Extreme High-Speed Laser Application)
technique, or by the TSC (Top Speed Cladding) technique, forming a protective surface
coating 3 which covers at least one of the two braking surfaces of the braking band, for
15 example which covers the base layer 30, preferably at least for the entire surface of one
of the two braking surfaces 2a, 2b of the braking band.
[0065] According to a second aspect of the present invention, in a further general
embodiment of the method according to the invention comprises the following operating
steps:
20 a) preparing a brake disc, comprising a braking band and provided with two opposite
braking surfaces 2a, 2b, each of which defines at least partially one of the two main
faces of the disc, the braking band being made of gray cast iron or steel;
b) depositing a steel layer completely free from nickel, preferably by laser deposition
technique, for example Laser Metal Deposition or Extreme High-Speed Laser Material
16
Deposition or by Thermal Spray deposition technique, or by Cold Spray deposition
technique, to form the base layer 30;
c) optionally depositing over said base layer 30 a material in particle form composed of
tungsten carbide (WC) or niobium carbide (NbC) or titanium carbide (TiC) or possibly
5 chromium carbide by a Thermal Spray deposition technique, e.g. by the HVOF (HighVelocity Oxy-Fuel) technique, the HVAF (High-Velocity Air Fuel) technique, the APS
(Atmosphere Plasma Spray) technique or a Cold Spray deposition technique, e.g. by the
KM (Kinetic Metallization) technique, or by a laser beam deposition technique, e.g. by
the LMD (Laser Metal Deposition) technique, or by the HSLC (High-Speed Laser
10 Cladding) technique, or by the EHLA (Extreme High-Speed Laser Application)
technique, or by the TSC (Top Speed Cladding) technique, forming a protective surface
coating 3 which covers at least one of the two braking surfaces of the braking band, for
example which covers the base layer 30, preferably at least for the entire surface of one
of the two braking surfaces 2a, 2b of the braking band.
15 [0066] According to a third aspect of the present invention, in a further general
embodiment of the method according to the invention comprises the following operating
steps:
a) preparing a brake disc, comprising a braking band and provided with two opposite
braking surfaces 2a, 2b, each of which defines at least partially one of the two main
20 faces of the disc, the braking band being made of gray cast iron or steel;
a1) after step a), depositing on at least one of the two opposite braking surfaces 2a, 2b,
an intermediate layer 300 composed of nickel-free steel;
b) after step a1), depositing a steel layer completely free from nickel, preferably by laser
deposition technique, for example Laser Metal Deposition or Extreme High-Speed
17
Laser Material Deposition or by Thermal Spray deposition technique, or by Cold Spray
deposition technique, to form the base layer 30;
c) optionally depositing over said base layer 30 a material in particle form composed of
tungsten carbide (WC) or niobium carbide (NbC) or titanium carbide (TiC) or possibly
5 chromium carbide by a Thermal Spray deposition technique, e.g. by the HVOF (HighVelocity Oxy-Fuel) technique, the HVAF (High-Velocity Air Fuel) technique, the APS
(Atmosphere Plasma Spray) technique or a Cold Spray deposition technique, e.g. by the
KM (Kinetic Metallization) technique, or by a laser beam deposition technique, e.g. by
the LMD (Laser Metal Deposition) technique, or by the HSLC (High-Speed Laser
10 Cladding) technique, or by the EHLA (Extreme High-Speed Laser Application)
technique, or by the TSC (Top Speed Cladding) technique, forming a protective surface
coating 3 which covers at least one of the two braking surfaces of the braking band, for
example which covers the base layer 30, preferably at least for the entire surface of one
of the two braking surfaces 2a, 2b of the braking band.
15 According to an advantageous embodiment, step a1) provides for depositing an
intermediate layer 300 composed of nickel-free steel and from 10% to 15% of
chromium (Cr), at most 1% of silicon (Si), at most 4% of manganese (Mn), from 0.16%
to 0.5% of carbon (C), preferably from 0.16% to 0.25% of carbon (C), extremes
included, and for the balance of iron (Fe). According to a further aspect of the present
20 invention, in a further general embodiment of the method according to the invention
comprises the following operating steps:
a) preparing a brake disc 1, comprising a braking band 2 provided with two opposite
braking surfaces 2a, 2b, each of which defines at least partially one of the two main
faces of the disc, the braking band being made of gray cast iron or steel;
18
b) depositing a base layer 30 composed of steel totally free from nickel and from 10% to
15% of chromium (Cr), at most 1% of silicon (Si), at most 4% of manganese (Mn),
from 0.16% to 0.5% of carbon (C), preferably from 0.16% to 0.25%, and for the balance
iron (Fe).
5 According to a further aspect of the present invention, a general embodiment of the
method according to the invention comprises the following operating steps:
a) preparing a brake disc, comprising a braking band and provided with two opposite
braking surfaces 2a, 2b, each of which defines at least partially one of the two main
faces of the disc, the braking band being made of gray cast iron or steel;
10 a1) after step a), depositing on at least one of the two opposite braking surfaces 2a, 2b,
an intermediate layer 300 composed of steel comprising nickel, preferably according to
the features described in the previous paragraphs of the present discussion;
b) after step a1), depositing a steel layer completely free from nickel, preferably by laser
deposition technique, for example Laser Metal Deposition or Extreme High-Speed
15 Laser Material Deposition or by Thermal Spray deposition technique, or by Cold Spray
deposition technique, to form the base layer 30;
c) optionally depositing over said base layer 30 a material in particle form composed of
tungsten carbide (WC) or niobium carbide (NbC) or titanium carbide (TiC) or possibly
chromium carbide by a Thermal Spray deposition technique, e.g. by the HVOF (High20 Velocity Oxy-Fuel) technique, the HVAF (High Velocity Oxy-Fuel) technique, the APS
(Atmosphere Plasma Spray) technique or a Cold Spray deposition technique, e.g. by the
KM (Kinetic Metallization) technique, or by a laser beam deposition technique, e.g. by
the LMD (Laser Metal Deposition) technique, or by the HSLC (High-Speed Laser
Cladding) technique, or by the EHLA (Extreme High-Speed Laser Application)
25 technique, or by the TSC (Top Speed Cladding) technique, forming a protective surface
19
coating 3 which covers at least one of the two braking surfaces of the braking band, for
example which covers the base layer 30, preferably at least for the entire surface of one
of the two braking surfaces 2a, 2b of the braking band.
[0067] In addition to the aforementioned general embodiment variants of the method
5 according to the present invention, the method preferably provides for the further steps
which will be described below.
[0068] Preferably, in step c) the tungsten carbide (WC) or the niobium carbide (NbC) or
the titanium carbide (TiC) or possibly the chromium carbide is dispersed in a metal
matrix.
10 [0069] According to a preferred embodiment, in step c), the material in particle form is
composed of chromium carbide and titanium carbide.
[0070] Advantageously, the brake disc is arranged with a portion suitable for fixing the
disc to a vehicle, consisting of an annular portion 4 arranged centrally to the disc 1 and
concentric to the braking band 2. The fixing portion 4 supports the connecting element 5
15 to the wheel hub (i.e. the bell). The bell may be made in one piece with the annular
fixing portion (as illustrated in the accompanying figures) or it may be made separately
and, therefore, fixed through suitable connecting elements to the fixing portion.
[0071] The annular fixing portion 4 may be made of the same material as the braking
band, that is, of gray cast iron, or of another suitable material. The bell 5 may also be
20 made of gray cast iron or of another suitable material. In particular, the whole disc (i.e.
braking band, fixing portion and bell) may be made of gray cast iron.
[0072] Preferably, the braking band 2 is made by casting. Similarly, when made of gray
cast iron, the fixing portion and/or the bell may be made by casting.
[0073] The annular fixing portion may be made in a single body with the braking band
25 (as illustrated in the accompanying figures) or be made as a separate body, mechanically
20
connected to the braking band.
[0074] As regards the HVOF, HVAF or KM, or LMD or HSLC techniques, these are
three deposition techniques which are known to those skilled in the art and will
therefore not be described in detail.
5 [0075] HVOF (High Velocity Oxygen Fuel) is a powder spray deposition technique
which uses a spray device provided with a mixing and combustion chamber and a spray
nozzle. The chamber is supplied with oxygen and fuel. The hot combustion gas which
forms at pressures close to 1 MPA passes through the converging-diverging nozzle into
the powdered material reaching hypersonic speeds (i.e. higher than MACH 1). The
10 powder material to be deposited is injected into the hot gas stream, where it melts
rapidly and is accelerated to speeds of the order of 1000 m/s. Once impacted on the
deposition surface, the molten material cools rapidly and due to the impact with high
kinetic energy it forms a very dense and compact structure.
[0076] The High Velocity Air Fuel (HVAF) deposition technique is similar to the
15 HVOF technique. The difference is that in the HVAF technique the combustion
chamber is fed with air instead of oxygen. The temperatures involved are therefore
lower than those of the HVOF. This allows for greater control of the thermal alteration
of the coating.
[0077] The KM (Kinetic Metallization) deposition technique is a solid-state deposition
20 process in which metal powders are sprayed through a two-phase sonic deposition
nozzle which accelerates and triboelectrically charges metal particles within an inert gas
stream. Thermal energy is expected to be supplied to the transport stream. The process
transforms the potential energy of the compressed inert gas stream and the thermal
energy supplied into the kinetic energy of the powders. Once accelerated to high speed
21
and electrically charged, the particles are directed against the deposition surface. The
high-speed collision of the metal particles with this surface causes a large deformation
of the particles (approximately 80% in the direction normal to impact). This
deformation results in a huge increase in the surface area of the particles. Upon impact,
5 the effect is therefore intimate contact between the particles and the deposition surface,
which leads to the formation of metal bonds and a coating having a very dense and
compact structure.
[0078] Advantageously, as an alternative to the three deposition techniques listed above,
which share the fact that they are high kinetic energy impact deposition techniques,
10 other techniques may also be used which exploit different deposition methods, but
which are able to generate coatings having a very dense and compact structure.
[0079] The combination of the HVOF or HVAF or KM or LMD or HSLC deposition
technique and the chemical components used for the formation of the base layer 30 and
the surface protective coating 3, allows both high bond strength on the lower material on
15 which they are deposited and the deposition of powders with high carbide content to be
obtained.
[0080] As already mentioned above, the base layer 30 and the protective surface coating
3 cover at least one of the two braking surfaces of the braking band.
[0081] Hereinafter, the term “coating” will refer to both the set given by the base layer
20 30 and the protective surface coating 3, and to the base layer 30 alone, in the variant
which does not provide for the surface protective coating 3, but which provides for the
inclusion of carbides in the base layer 3.
[0082] Preferably, as illustrated in Figure 2 and Figure 3, the disc 1 is provided with a
coating 3, 30 which covers both the braking surfaces 2a and 2b of the braking band 2.
22
[0083] In particular, the coating 3, 30 may cover only the braking band, on a single
braking surface or on both.
[0084] According to embodiments not illustrated in the appended figures, the coating 3,
30 may also extend to other parts of the disc 1 such as the annular fixing portion 4 and
5 the bell 5, up to cover the entire surface of the disc 1. In particular, the coating 3, 30
may cover - in addition to the braking band - only the fixing portion or only the bell.
The choice is dictated by essentially aesthetic reasons, in order to have a homogeneous
coloring and/or finish on the whole disc or between some portions thereof.
[0085] Advantageously, the deposition of the particulate material for the formation of
10 the coating 3, 30 may be carried out in a differentiated manner on the surface of the disc
at least in terms of thickness of the coating.
[0086] At the braking band, the coating 3, 30 may be made with the same thickness in
the two opposite braking surfaces. Alternative solutions may be provided in which the
coating 3, 30 is made by differentiating the different thicknesses between the two
15 braking surfaces of the braking band.
[0087] According to an embodiment of the method, the step b) of depositing the base
layer 30 provides for depositing a composition in particle form composed of steel
having a nickel content of at most 15% or at most 7,5% or at most 5% or totally nickelfree steel, by laser deposition technique, preferably LMD (Laser Metal Deposition) or
20 EHLA (Extreme High-Speed Laser Material Deposition), or by Thermal Spray
deposition technique, or by the Cold Spray deposition technique.
[0088] In an advantageous embodiment, in step b) the composition in particle form
further comprises carbides mixed in a percentage not exceeding 50% by weight of the
total particule composition.
23
[0089] In an advantageous embodiment, in step b) the composition in particle form, in
addition to steel, also includes metal oxides or a mixture of metals and ceramic
materials, preferably a mixture of aluminum oxides Al2O3, or a mixture of Al2O3 and
intermetallic matrix Fe-Cr, for example Fe28Cr.
5 [0090] According to an embodiment, in step b) the composition in particle form, in
addition to steel, also includes metal oxides or a mixture of metals and ceramic
materials, preferably a mixture of aluminum oxides Al2O3, or a mixture of Al2O3 and
intermetallic matrix Fe-Cr, for example Fe28Cr, and also one or more carbides selected
from the group comprising: tungsten carbide (WC), niobium carbide (NbC), titanium
10 carbide (TiC), chromium carbide.
[0091] It is therefore clear that, by virtue of the aforementioned variants of the method,
it is possible to obtain a braking band 2 in which the base layer 30 comprises a mixture
of steel and metal oxides described above, or, in another variant, a mixture of steel and
metal oxides and carbides described above.
15 [0092] The preferred embodiment variants of the braking band and the arrangement
order of the base layer 30, of the intermediate layer 300 and of the surface coating layer
3, are also more understandable with reference to the appended figures.
[0093] Preferably, the step a1) of depositing the intermediate layer 300 provides for
depositing a composition in particle form composed of steel having a nickel content
20 between 5% and 15%, by means of a laser deposition technique, preferably LMD (Laser
Metal Deposition) or EHLA (Extreme High-Speed Laser Material Deposition), or by the
Thermal Spray deposition technique, or by the Cold Spray deposition technique.
[0094] According to an advantageous embodiment variant of the method, the step e1) is
provided of depositing an auxiliary layer of ferritic-nitrocarburization between one of
24
the two braking surfaces 2a, 2b of the braking band and the base layer 30, and/or
between one of the two braking surfaces 2a, 2b of the braking band and the intermediate
layer 300, and/or between the base layer 30 and the protective surface coating 3, and/or
between the intermediate layer 300 and the base layer 30.
5 [0095] According to an advantageous embodiment, the method comprises the step e2)
of depositing an auxiliary ferroalumination layer between one of the two braking
surfaces 2a, 2b of the braking band and the base layer 30, and/or between one of the two
braking surfaces 2a, 2b of the braking band and the intermediate layer 300, and/or
between the base layer 30 and the protective surface coating 3, and/or between the
10 intermediate layer 300 and the base layer 30.
[0096] Preferably, the ferroalumination step e2) comprises the steps of:
e21) immersing at least partially said braking band 2 into molten aluminum maintained
at a predetermined temperature so that the molten aluminum covers at least a
predetermined surface region of said braking band 2, said immersion being protracted
15 for a predetermined period of time to allow the diffusion of aluminum atoms into the
surface microstructure of said cast iron or steel with the consequent formation of
ferroaluminum intermetallic compounds in a surface layer of said braking band 2, thus
generating a layer comprising of ferroaluminum intermetallic compounds in said
predetermined surface region of said braking band 2;
20 e22) removing said braking band 2 from the molten aluminum;
e23) removing the aluminum remaining on said braking band 2 after extraction, so as
to expose said layer of ferroaluminum intermetallic compounds on the surface.
[0097] The layer of ferroaluminum intermetallic compounds exposed on the surface
imparts a superior resistance to corrosion and wear at said predetermined surface region
25
to the braking band 2 made of cast iron or steel.
[0098] Preferably, the layer of ferroaluminum intermetallic compounds comprises
FeAl3 as the prevailing phase of the ferroaluminum intermetallic compounds.
[0099] According to an advantageous embodiment, the predefined temperature at which
5 the molten aluminum is maintained is not higher than 750 °C, and is preferably between
690 °C and 710 °C, and even more preferably equal to 700 °C.
[00100] According to an advantageous aspect of the method, the predefined
period of immersion time is determined according to the thickness to be obtained for
said layer of intermetallic compounds, at the same temperature of the molten aluminum
10 said thickness increasing as the immersion time increases, with the same immersion
time, said thickness increasing as the temperature of the molten aluminum increases,
preferably said predefined immersion time being between 5 and 60 min, and even more
preferably equal to 30 min.
[00101] According to an advantageous aspect, before the immersion step e21),
15 the method comprises a step f) of decarburizing said predefined surface region of said
braking band 2 up to a predefined depth.
[00102] It has been experimentally verified that the presence of carbon in the
surface layer of the braking band subject to penetration by diffusion of aluminum atoms
(induced by aluminization) also leads to the formation of iron carbide as well as
20 intermetallic compounds. The presence of iron carbide creates points of discontinuity in
the layer of intermetallic compounds, points which may trigger both corrosive
phenomena and cracks. Advantageously, the surface decarburization therefore makes it
possible to avoid (or at least significantly reduce) the formation of iron carbide, leading
to the formation of a layer of intermetallic compounds more resistant to corrosion and
26
less subject to cracking.
[00103] Preferably, in said step f) the decarburization of said at least one
predefined surface region is carried out by means of an electrolytic process.
[00104] More in detail, said electrolytic process is carried out by immersing the
5 predefined surface region of said braking band in a bath of molten salts and applying an
electric potential difference between the bath and the braking band.
[00105] In applying the electric potential difference, the braking band is
connected to a positive pole (cathode), while the aforementioned bath of molten salts is
connected to a negative pole (anode). Carbon, particularly in the form of graphite flakes,
10 is oxidized to carbon dioxide by the release of electrons and atomic oxygen released at
the anode. Carbon reacts primarily with oxygen and is eventually bound as carbon
dioxide.
[00106] The oxidation of the surface of the braking band induced by the
electrolytic process is not limited to the carbon present therein, but also extends to the
15 metal matrix of the cast iron (iron), causing the formation of a surface film of metal
oxide. Reversing the polarity causes the reduction of the surface film of metal oxide
which is thus returned to the original metallic state.
[00107] Preferably, the aforementioned electrolytic process may therefore provide
that, after a predefined period of time in which the surface of the braking band has been
20 connected to the cathode to oxidize the carbon, the polarity is reversed so as to return
the metal oxide film to its original metallic state.
[00108] Operationally, the decarburization depth is controlled by adjusting the
duration of the electrolytic process, possibly divided into different polarity inversion
cycles. By increasing the duration of the decarburization process (oxidation phase of the
27
braking band; connection to the cathode), the decarburization depth increases, all other
conditions being equal.
[00109] The decarburization may be carried out with alternative processes to the
electrolytic process described above, for example by means of a laser treatment or a
5 chemical treatment.
[00110] Decarburization by electrolytic process is however preferred because:
- compared to a laser treatment it is much more efficient and rapid, ensuring a more
complete and uniform carbon removal in less time;
- compared to a chemical treatment (for example with potassium permanganate) it is
10 much more efficient (ensuring a more complete and uniform carbon removal in less
time) and does not leave oxidation areas of the metal matrix of the cast iron on the
treated portion.
[00111] More in detail, it has been observed that at the oxidized areas on the
metal matrix of the cast iron the wettability of the molten aluminum is very low and this
15 negatively affects the aluminization process and the features of the layer of intermetallic
compounds. Also for this reason, the electrolytic decarburization process is preferred
over the alternative processes indicated above.
[00112] As has already been pointed out above, the growth thickness of the
intermetallic compound layer is mainly influenced by the temperature of the molten
20 aluminum and the immersion time in the molten aluminum. However, it has been found
that a further factor affecting the thickness of the intermetallic compound layer is the
silicon content in the molten aluminum. The higher the weight content of silicon in the
molten aluminum, the lower the thickness of the intermetallic compound layer under the
same conditions. Preferably, the molten aluminum has a silicon content lower than 1%
28
by weight.
[00113] Preferably, the molten aluminum has an impurity content not higher than
1% by weight. In particular, aluminum with a maximum purity of 99.7% by weight may
be used, with the following impurities (% by weight): Si ≤ 0.30%; Fe ≤0.18%; Sr
5 ≤0.0010%; Na ≤0.0025%; Li ≤0.0005%; Ca ≤0.0020%; P ≤0.0020; Sn ≤0.020 %.
[00114] In some cases it has occurred that, despite having subjected the braking
band to decarburization and therefore eliminated the graphite flakes from a surface layer
at which the layer of intermetallic compounds would have formed, the resulting layer of
intermetallic compounds still included graphite flakes, as if they had never been
10 eliminated. This phenomenon may be explained by the fact that the dissolution of the
iron in the aluminum is so rapid that the decarburized layer is rapidly consumed and
consequently the metal compounds are formed in the layer below the decarburized layer,
i.e. where there are graphite flakes.
[00115] In other words, the excessive solubility of iron in molten aluminum may
15 totally or partially cancel the beneficial effects of the surface decarburization of the
braking surface.
[00116] Advantageously, in order to slow down the dissolution of the iron in the
aluminum bath, the step b1) of immersion in a bath of molten aluminum in which iron
has been dissolved may be carried out. In this way, by inhibiting the dissolution of the
20 iron in the aluminum, the formation of FeAl3 is kinematically promoted, so as to allow
the intermetallic compounds to form at the decarburized layer.
[00117] Preferably, the iron content in solution in the aluminum bath is not
higher than 5% by weight, and even more preferably it is comprised between 3% and
5%, and most preferably equal to 4% by weight to ensure a significant effect of slowing
29
of the melting process of the iron of the cast iron in the aluminum.
[00118] For example, an aluminum bath having the following composition (% by
weight) may be used: Al ≤ 97%; Fe 3-5%; with the following impurities: Si ≤ 0.30%; Fe
≤0.18%; Sr ≤0.0010%; Na ≤0.0025%; Li ≤0.0005%; Ca ≤0.0020%; P ≤0.0020; Sn
5 ≤0.020 %.
[00119] It has been experimentally observed that by carrying out aluminization
with an aluminum bath with iron in solution, especially if the iron content is close to the
solubility limit, more porous layers of intermetallic compounds are obtained. This may
be explained by a higher viscosity of the molten aluminum bath containing iron and a
10 consequent reduction of its wettability with respect to cast iron.
[00120] Advantageously, in order to form a layer of intermetallic compounds that
is compact and uniform and therefore not very porous, while avoiding at the same time
that this layer develops below the decarburized layer and incorporates the graphite
flakes present therein, the aforementioned step b1) of immersion is carried out in two
15 sub-steps:
- a first sub-step b11) of immersion in a first bath of molten aluminum, substantially
free of iron in solution (or at least present at most as an impurity; for example with an
iron content lower than 0.20% by weight), to obtain on said predefined surface region an
initial layer composed of ferroaluminum intermetallic compounds; and
20 - a second sub-step b12) of immersion in a second bath of molten aluminum, containing
iron in solution, to increase said initial layer until a final layer is obtained on said
predefined surface region composed of ferroaluminum intermetallic compounds having
a predefined thickness.
[00121] The immersion time of said braking band in said first bath is less than the
30
immersion time of said braking band in said second bath.
[00122] Preferably, the immersion of said braking band in said first bath is
continued for a period of time as short as possible, but sufficient to obtain on said
predefined surface region an initial layer composed of ferroaluminum intermetallic
5 compounds having a thickness not exceeding at 10 µm. In particular, the immersion
time in said first bath is between 3 and 5 minutes if the first bath is at a temperature of
about 700 °C. As the bath temperature increases, the immersion time must decrease.
[00123] More in detail, for the same temperature of the second bath, said
thickness increases as the immersion time increases and for the same immersion time,
10 said thickness increases as the temperature of the second bath increases.
[00124] Advantageously, both said first bath of molten aluminum and said second
bath have an impurity content not higher than 1% by weight. In particular, said two
molten aluminum baths have a silicon content lower than 1% by weight.
[00125] Preferably, the iron content in solution in the second aluminum bath is
15 not higher than 5% by weight (at 700 °C the solubility limit of iron in aluminum is 4%
by weight; aluminum saturated with iron), and even more preferably it is comprised
between 3% and 5%, and most preferably it is equal to 4% by weight. The iron content
should not be less than 3% to ensure a significant slowing effect of the melting process
of the iron of the cast iron in the aluminum.
20 [00126] Advantageously, both said first bath and said second bath are maintained
at a temperature lower than 680 °C, preferably not higher than 750 °C, more preferably
between 690 °C and 710 °C, and even more preferably equal to 700 °C.
[00127] Advantageously, the method may comprise a step of surface pretreatment
of the braking band which is carried out before said immersion step e21) at least at said
31
predefined surface region. Preferably, said surface pretreatment step comprises lapping,
degreasing, sandblasting and/or chemical removal of the surface oxides.
[00128] Preferably, the method comprises a step of removing a surface layer of
oxides from the molten aluminum bath before said immersion step e21). This step of
5 removal of the surface oxides is carried out both in the case in which immersion in a
single bath is contemplated, and in the case in which immersion is contemplated in two
successive steps in a first and in a second bath.
[00129] According to a preferred embodiment of the invention, the step of
removing the aluminum remaining adhered to said braking band after the extraction is
10 carried out in two sub-steps:
[00130] a first sub-step of removal is carried out on the braking band just
extracted from the molten aluminum to remove the molten aluminum still remaining
adhered to the braking band; and
[00131] a second removal sub-step is carried out on the braking band extracted
15 from the molten aluminum and cooled to remove the solidified residual aluminum
remaining after said first removal sub-step.
[00132] Preferably, the method comprises a quenching step of said braking band
carried out between said first removal sub-step and said second removal sub-step.
[00133] Advantageously, said first removal sub-step may be carried out by
20 mechanical shaving of the still liquid aluminum.
[00134] Advantageously, said second removal sub-step may be carried out by
chemical removal of the solidified aluminum not removed mechanically.
[00135] Preferably, the aforementioned chemical removal is carried out by
exposing the aluminum to ferric chloride for at least 4 minutes so as to cause the
32
following reaction:
Al+ FeCl3 -> AlCl3 + Fe
[00136] Chemical removal by ferric chloride should necessarily take place after
the solidification of the aluminum. Ferric chloride boils at 315 °C and therefore may not
5 be brought into contact with molten aluminum. Preferably, said chemical removal is
then carried out after said quenching step.
[00137] The aforementioned steps of the method referred to ferroalumination
therefore allow a braking band, and therefore a brake disc, to be obtained with increased
resistance to wear and corrosion.
10 [00138] It should be noted that the layer of ferroaluminum intermetallic
compounds may comprise a plurality of intermetallic compounds between iron and
aluminum, in particular Fe3Al, FeAl, FeAl2, FeAl3, Fe2Al5. The prevailing
intermetallic phase is FeAl3 as it is thermodynamically more stable.
[00139] According to an embodiment, the method provides for depositing an
15 auxiliary ferritic-nitrocarburization and an auxiliary ferroalumination layer between one
of the two braking surfaces 2a, 2b of the braking band and the base layer 30, and/or
between one of the two braking surfaces 2a, 2b of the braking band and the intermediate
layer 300, and/or between the base layer 30 and the protective surface coating 3, and/or
between the intermediate layer 300 and the base layer 30.
20 [00140] As may be appreciated from the above description, the brake disc
according to the invention allows the drawbacks of the prior art to be overcome.
[00141] By virtue of the combination of a steel base layer with reduced nickel
content or even totally nickel-free with a cast iron band, the brake disc 1 according to
the invention is substantially not subject to the production and release of nickel particles
33
during operation.
[00142] Not only that, according to particularly advantageous variants, the
addition of a protective surface coating 3 which includes or is coated with carbides,
allows both the wear resistance properties to be improved, also compensating for the
5 lack of nickel in the steel of the base layer, and adequate and increased mechanical
strength to be provided.
[00143] Particularly advantageously, the base layer 30 composed of totally
nickel-free steel and 10% to 15% chromium (Cr), at most 1% of silicon (Si), at most 4%
of manganese (Mn), from 0.16% to 0.5% of carbon (C), preferably from 0.16% to
10 0.25% of carbon (C), and for the balance of iron (Fe), allows a martensitic steel without
nickel to be made with less brittleness during use at high temperatures and at the same
time an adequate anticorrosive coating. These advantageous aspects are also
synergistically combined with the possibility of using a reduced percentage of any
carbides included in the steel, thus reducing the resources necessary for production,
15 while maintaining an adequate hardness of the coating.
[00144] Advantageously, the base layer 30, preferably nickel-free, also performs
a mechanical “cushioning” function for the protective surface coating 3 (anti-wear). The
base layer 30, in fact, assumes an elastic behavior which allows the stresses imparted to
the disc to be attenuated at least in part when in use. The base layer 30 therefore
20 operates as a sort of shock absorber or cushion between the disc and the protective
surface coating 3. In this way, a direct transmission of stresses between the two parts is
avoided, thus also reducing the risk of initiation of cracks in the protective surface
coating 3.
34
WE CLAIM:
1. A brake disc (1) for disc brake, comprising a braking band (2) provided with two
opposite braking surfaces (2a, 2b), each of which defines at least partially one of the two
5 main faces of the disc (1), the braking band (2) being made of gray cast iron or steel;
said disc being provided with a base layer (30), which covers at least one of the two
braking surfaces (2a, 2b) of the braking band, said base layer (30) being composed of
steel totally free from nickel.
2. Brake disc (1) for disc brake according to claim 1, wherein the base layer (30) is
10 further composed of one or more carbides included in the nickel-free steel.
3. Brake disc (1) for disc brake according to claim 2, wherein in the base layer (30) the
one or more carbides included comprise at least one carbide selected from the group
comprising: tungsten carbide (WC), chromium carbide, niobium carbide (NbC),
titanium carbide (TiC).
15 4. Brake disc (1) for disc brake according to any one of the preceding claims, wherein an
intermediate layer (300) of steel comprising nickel is interposed between the base layer
(30) and at least one of the two braking surfaces (2a, 2b) of the braking band (2).
5. Brake disc (1) for disc brake according to any one of claims 1 to 3, wherein an
intermediate layer (300) of nickel-free steel is interposed between the base layer (30)
20 and at least one of the two braking surfaces (2a, 2b) of the braking band (2).
6. Brake disc (1) for disc brake according to any one of the preceding claims,
comprising a protective surface coating (3) which covers the base layer (30) at least on
the side of one of the two braking surfaces (2a, 2b) of the braking band, said protective
surface coating (3) being arranged on a side of the base layer (30) which does not face
25 towards one of the two braking surfaces (2a, 2b), said protective surface coating (3)
35
being composed of one or more carbides in particle form deposited by a Thermal Spray
deposition technique, e.g. by the HVOF (High-Velocity Oxy-Fuel) technique, or by the
HVAF (High-Velocity Air Fuel) technique, or by the APS (Atmosphere Plasma Spray)
technique, or by a Cold Spray deposition technique, e.g. by the KM (Kinetic
5 Metallization) technique, or by a laser beam deposition technique, e.g. the LMD (Laser
Metal Deposition), or the HSLC (High-Speed Laser Cladding) technique, or the EHLA
(Extreme High-Speed Laser Application) technique, or the TSC (Top Speed Cladding)
technique.
7. Brake disc (1) for disc brake according to claim 6, wherein the one or more carbides
10 in particle form comprise tungsten carbide (WC) or chromium carbide or niobium
carbide (NbC) or titanium carbide (TiC).
8. Disc according to any one of the preceding claims, wherein the steel of the base layer
(30) comprises at least 15% of chromium (Cr).
9. Disc according to any one of the preceding claims, wherein the steel of the base layer
15 (30) is composed of 10% to 20% of chromium (Cr), at most of 1.5% of silicon (Si), at
most of 2% of manganese (Mn), at most of 0.03% carbon (C) and for the balance of iron
(Fe).
10. Disc according to any one of the preceding claims, wherein an auxiliary ferriticnitrocarburized layer or an auxiliary ferroalumination layer is interposed between one of
20 the two braking surfaces (2a, 2b) of the braking band and the base layer (30), and/or
between one of the two braking surfaces (2a, 2b) of the braking band and the
intermediate layer (300), and/or between the base layer (30) and the protective surface
coating, and/or between the intermediate layer (300) and the base layer (30).
11. Brake disc (1) for disc brake according to any one of claims 4 or from 6 to 9,
36
wherein the intermediate layer (300) comprises steel with a nickel content at most equal
to 15 %.
12. Brake disc (1) for disc brake according to claim 11, wherein the intermediate layer
(300) comprises steel with a nickel content at most equal to 7.5 %.
5 13. A method for making a brake disc comprising the following operating steps:
a) preparing a brake disc (1), comprising a braking band (2) provided with two opposite
braking surfaces (2a, 2b), each of which defines at least partially one of the two main
faces of the disc, the braking band being made of gray cast iron or steel;
b) depositing a base layer (30) composed of steel totally free from nickel.
10 14. Method according to claim 13, wherein the step b) of depositing the base layer (30)
provides depositing a composition in particle form composed of nickel-free steel, by
means of a laser deposition technique, preferably Laser Metal Deposition or Extreme
High-Speed Laser Material Deposition, or by means of a Thermal Spray deposition
technique, or by means of a Cold Spray deposition technique.
15 15. Method according to claim 13 or 14, further comprising the step c) of depositing
over said base layer (30) a material in particle form composed of tungsten carbide (WC)
or by niobium carbide (NbC) or titanium carbide (Tic) or chromium carbide by a
Thermal Spray deposition technique, e.g. by the HVOF (High-Velocity Oxy-Fuel)
technique, the HVAF (High-Velocity Air Fuel) technique, the APS (Atmosphere Plasma
20 Spray) technique or a Cold Spray deposition technique, e.g. by the KM (Kinetic
Metallization) technique, or by a laser beam deposition technique, e.g. by the LMD
(Laser Metal Deposition) technique, or by the HSLC (High-Speed Laser Cladding)
technique, or by the EHLA (Extreme High-Speed Laser Application) technique, or by
the TSC (Top Speed Cladding) technique, forming a protective surface coating (3)
37
which covers the base layer (30), preferably at least for the entire surface of one of the
two braking surfaces (2a, 2b) of the braking band.
16. A method according to any one of claims from 13 to 15, wherein after step a)
and before step b) the method comprises the step of:
5 a1) depositing on at least one of the two opposite braking surfaces (2a, 2b), an
intermediate layer (300) composed of nickel-free steel.
Dated this 23rd day of June, 2023