Brake disc for motor vehicle and method for producing such brake disc

Abstract

The invention relates to a brake disc for a motor vehicle, the disc comprising at least one outer surface (2a, 3a) comprising a coating (6), the coating (6) having: a first layer (7) arranged at least partially on the outer surface (2a, 3a), the first layer (7) comprising steel having a chromium content of between 10 wt% and 20 wt% relative to the total weight of the steel; a second layer (8) arranged on the first layer (7), the second layer (8) comprising a steel matrix having a chromium content of between 10 wt% and 20 wt%, relative to the total weight of the steel, and a content of at least one carbide of between 15 vol% and 40 vol%, based on the total volume of the second layer, the carbide is selected from the following compounds: silicon carbide, chromium carbide, tungsten carbide, niobium carbide, titanium carbide or a mixture thereof, and preferably selected from niobium carbide, titanium carbide or a mixture thereof; the coating (6) is obtained according to a technique for depositing a material from a laser at very high velocities, referred to as EHLA.

Description

[0001] The present invention relates generally to the control of pollutant emissions from motor vehicles, and more specifically to the emission of fine particulate matter during the braking process of motor vehicles.

[0002] Specifically, the present invention relates to a brake disc for motor vehicles and a method for producing such a brake disc.

[0003] In motor vehicles, the wear of the brake discs during braking and the friction between the brake pads and the brake discs cause pollutant particles to be released into the atmosphere.

[0004] Emissions of particles smaller than 10 µm (PM10, also known as fine particulate matter) are particularly dangerous to the respiratory system of people.

[0005] Therefore, in the context of the future Euro 7 standard, the new European regulations aim to limit particulate emissions during the braking process of passenger and commercial motor vehicles.

[0006] There exists a device that allows released particles to be captured based on the operation of a suction turbine triggered during braking.

[0007] However, this device is bulky and only captures particles during braking.

[0008] Another solution is to integrate the particulate filter into the braking system.

[0009] However, these filters are particularly expensive.

[0010] There are also brake discs made of alloy cast iron, which contain additional elements such as vanadium.

[0011] Although the addition of cast iron can improve the wear resistance and thermal fatigue properties of brake discs and thus reduce particle release, this solution is insufficient for even the most powerful motor vehicles.

[0012] Therefore, the object of the present invention is to overcome these shortcomings and to propose a solution that aims to optimize the wear limit of brake discs, particularly the wear limit of brake discs in motor vehicles, and to reduce the release of fine particles.

[0013] Therefore, a brake disc for a motor vehicle is proposed, the brake disc including at least one outer surface having a coating, the coating comprising:

[0014] A first layer, disposed on all or part of the outer surface, the first layer comprising steel having a chromium content of between 10% and 20% by mass relative to the total mass of the steel;

[0015] A second layer disposed on the first layer comprises a steel matrix having a chromium content of between 10% and 20% by mass relative to the total mass of the steel, and a content of at least one carbide of between 15% and 40% by volume relative to the total volume of the second layer. The carbide is selected from the following compounds: silicon carbide, chromium carbide, tungsten carbide, niobium carbide, titanium carbide, or mixtures thereof, preferably selected from niobium carbide, titanium carbide, or mixtures thereof.

[0016] The coating was obtained using a technique called EHLA (Extreme High Speed ​​Laser Deposition of Materials).

[0017] Preferably, the coating is a two-layer coating consisting only of the first layer and the second layer.

[0018] Based on one characteristic, the steel in the first layer and / or the steel in the second layer can be ferritic steel.

[0019] Preferably, the ferritic steel is a steel comprising: chromium content between 16% and 18% by mass, silicon content less than or equal to 1% by mass, nickel content less than or equal to 0.6% by mass, manganese content less than or equal to 1% by mass, carbon content less than or equal to 0.08% by mass, molybdenum content less than or equal to 1% by mass, phosphorus content less than or equal to 0.045% by mass, sulfur content less than or equal to 0.03% by mass, titanium content less than or equal to 0.01% by mass, optional other added elements (such as copper, vanadium, niobium or tin), and the remainder being iron and unavoidable impurities.

[0020] In one embodiment, the second layer may include a titanium carbide content of between 15% and 25% by volume, preferably between 17% and 23% by volume, and more preferably between 19% and 21% by volume, relative to the total volume of the second layer.

[0021] In another embodiment, the second layer may include a niobium carbide content of between 25% and 35% by volume, preferably between 27% and 33% by volume, and more preferably between 29% and 31% by volume, relative to the total volume of the second layer.

[0022] In another embodiment, the second layer may comprise a mixture of carbides, wherein the content of each carbide in the mixture is between 5% and 20% by volume, preferably between 5% and 10% by volume, relative to the total volume of the second layer.

[0023] According to one feature, the second layer may comprise a mixture of niobium carbide and titanium carbide, wherein the niobium carbide content relative to the total volume of the second layer is between 5% and 20% by volume, preferably between 5% and 10% by volume, and the titanium carbide content relative to the total volume of the second layer is between 5% and 20% by volume, preferably between 5% and 10% by volume.

[0024] Advantageously, the material on which the brake disc with the coating is disposed can be cast iron, preferably layered graphite cast iron.

[0025] Preferably, the brake disc may include first and second opposite surfaces, each comprising first and second outer surfaces, each of the first and second outer surfaces including friction tracks designed to cooperate with the brake pads, the coating being disposed at least partially on these friction tracks, preferably only on these friction tracks.

[0026] The present invention also relates to a method for producing a brake disc as described above, the method comprising forming a first layer and a second layer of coating by means of a technique for depositing materials using ultra-high-speed laser (EHLA).

[0027] Preferably, the step of forming the second layer of the coating in this production method includes using a cermet.

[0028] The present invention also relates to a motor vehicle comprising at least one brake disc as described above.

[0029] Further objects, advantages, and features will become clear from the following description, given by way of example only and with reference to the accompanying drawings, in which:

[0030] [ Figure 1 [Illustration] is a schematic cross-sectional view of a brake disc for a motor vehicle according to an embodiment of the present invention.

[0031] [ Figure 2 ]yes Figure 1 The image shows a detailed view of the friction track of the brake disc.

[0032] [ Figure 3 This illustrates the operating mode of EHLA technology.

[0033] In the following text, and unless otherwise specified, the limits of the range of values ​​are included within the range, especially in the expression “included in”.

[0034] Furthermore, the expression "at least one" as used in this specification is equivalent to the expression "one or more".

[0035] Figure 1A brake disc 1 for a motor vehicle is shown, the brake disc including at least one outer surface.

[0036] In the example shown, the brake disc 1 is a ring structure, which includes a first surface 2 and a second surface 3 opposite to the first surface 2.

[0037] The first surface 2 has a first outer surface 2a, and the second surface 3 has a second outer surface 3a.

[0038] The first outer surface 2a and the second outer surface 3a each include friction tracks (first friction track 4 and second friction track 5, respectively) designed to cooperate with the brake pad (not shown).

[0039] Each friction track 4, 5 forms an area that contacts the brake pad, such that the friction of the fixed brake pad on the first friction track 4 and the second friction track 5 of the movable brake disc 1 causes the vehicle to brake.

[0040] The first outer surface 2a and the second outer surface 3a of the brake disc 1 are at least partially coated with a coating 6.

[0041] Advantageously, the coating 6 is formed on the friction tracks 4 and 5.

[0042] The coating 6 is preferably formed only on the friction tracks 4 and 5 in order to limit the cost of the brake disc 1.

[0043] The coating 6 can be formed on all or part of the friction tracks 4 and 5, preferably on all of the friction tracks 4 and 5.

[0044] The brake disc 1 on which the coating 6 is formed is preferably made of cast iron. Cast iron is a particularly economical material, and its high thermal conductivity allows it to store heat and dissipate heat generated by friction during braking.

[0045] Advantageously, the material of the brake disc 1 on which the coating 6 is formed can be layered graphite cast iron (such as GJL 150 cast iron).

[0046] GJL 150 cast iron consists of the following components by mass: 3.7% carbon, 1.87% silicon, 0.61% manganese, less than 0.1% sulfur, less than 0.1% phosphorus, less than 0.1% copper, less than 0.1% nickel, less than 0.1% chromium, less than 0.1% molybdenum, less than or equal to 0.1% titanium, less than 0.1% vanadium, less than 0.1% niobium, and less than 0.1% selenium. The remainder is iron and unavoidable impurities.

[0047] The coating 6 includes a first layer 7 arranged to contact the first outer surface 2a and the second outer surface 3a.

[0048] The first layer 7 contains steel having a chromium content between 10% and 20% by mass relative to the total mass of the steel in the first layer 7.

[0049] Preferably, the steel in the first layer 7 is ferritic steel.

[0050] Ferritic steel refers to steel with a central cubic crystal structure and a chromium content between 10% and 20% by mass relative to the total mass of the steel.

[0051] Ferritic steels are particularly advantageous because they have a low tendency to form cracks, especially due to their low coefficient of thermal expansion, which is close to that of the cast iron used.

[0052] Preferably, the ferritic steel of the first layer can be a ferritic stainless steel comprising: chromium content between 16% and 18% by mass, silicon content less than or equal to 1% by mass, nickel content less than or equal to 0.6% by mass, manganese content less than or equal to 1% by mass, carbon content less than or equal to 0.08% by mass, molybdenum content less than or equal to 1% by mass, phosphorus content less than or equal to 0.045% by mass, sulfur content less than or equal to 0.03% by mass, titanium content less than or equal to 0.01% by mass, optional other added elements (such as copper, vanadium, niobium or tin), the remainder being iron and unavoidable impurities.

[0053] Preferably, all unavoidable impurities account for less than 0.15% by mass.

[0054] Preferably, each unavoidable impurity is present in less than 0.05% by mass.

[0055] According to one example, the first layer 7 of ferritic steel can be ferritic stainless steel commonly known as 430L steel or by its European name X2Cr17, which consists of the following: 16.29% chromium by mass, 0.94% silicon by mass, 0.53% nickel by mass, 0.28% manganese by mass, 0.08% carbon by mass, 0.06% molybdenum by mass, 0.031% phosphorus by mass, 0.02% sulfur by mass, 0.003% titanium by mass, with the remainder being iron and unavoidable impurities. These percentages are defined relative to the total mass of the steel.

[0056] The coefficient of thermal expansion of ferritic steel is close to or similar to that of cast iron.

[0057] Specifically, the coefficient of thermal expansion of 430L steel is 10.4 × 10⁻⁶. -6 K -1 Its coefficient of thermal expansion is very close to that of GJL 150 layered graphite cast iron (which is equal to 10.7 × 10⁻⁶). -6 K -1 This has a beneficial effect on limiting the number and depth of cracks.

[0058] The coating 6 further includes a second layer 8 disposed on the first layer 7.

[0059] The first layer 7 forms an adhesive layer between the first outer surface 2a and the second outer surface 3a of the brake disc 1 and the second layer 8.

[0060] The second layer 8 contains a steel matrix having a chromium content between 10% and 20% by mass relative to the total mass of the steel.

[0061] Preferably, the steel of the matrix of the second layer 8 is the same as that of the first layer 7, in order to increase affinity and thus increase the adhesion between the first layer 7 and the second layer 8.

[0062] In this way, the steel of the second layer 8 is preferably ferritic steel.

[0063] Preferably, the ferritic steel of the second layer 8 can be a ferritic stainless steel comprising: chromium content between 16% and 18% by mass, silicon content less than or equal to 1% by mass, nickel content less than or equal to 0.6% by mass, manganese content less than or equal to 1% by mass, carbon content less than or equal to 0.08% by mass, molybdenum content less than or equal to 1% by mass, phosphorus content less than or equal to 0.045% by mass, sulfur content less than or equal to 0.03% by mass, titanium content less than or equal to 0.01% by mass, optional other additive elements different from the foregoing elements (such as copper, vanadium, niobium or tin), the remainder being iron and unavoidable impurities.

[0064] Preferably, all unavoidable impurities account for less than 0.15% by mass.

[0065] Preferably, each unavoidable impurity is present in less than 0.05% by mass.

[0066] According to one example, the second layer 8 ferritic steel can be a ferritic stainless steel commonly known as 430L steel, which consists of the following by mass: 16.29% chromium, 0.94% silicon, 0.53% nickel, 0.28% manganese, 0.08% carbon, 0.06% molybdenum, 0.031% phosphorus, 0.02% sulfur, and 0.003% titanium, with the remainder being iron and unavoidable impurities. These percentages are defined relative to the total mass of the steel.

[0067] Furthermore, the second layer 8 includes a content of at least one carbide between 15% and 40% by volume relative to the total volume of the second layer.

[0068] The one or more carbides are selected from the following compounds: silicon carbide, chromium carbide, tungsten carbide, niobium carbide, titanium carbide, or mixtures thereof.

[0069] Silicon carbide, chromium carbide, tungsten carbide, niobium carbide and titanium carbide have the advantage of being readily available in powder form, which facilitates their deposition on brake disc 1 via thermal spraying.

[0070] Silicon carbide, chromium carbide, and titanium carbide are also particularly advantageous due to their moderate cost and high mechanical strength.

[0071] Preferably, one or more carbides are selected from niobium carbide and titanium carbide, or mixtures thereof, which exhibit very good mechanical strength properties.

[0072] Even more preferably, the selected carbide is titanium carbide, which has similar mechanical and thermal properties to niobium carbide but is cheaper.

[0073] In one embodiment, the second layer 8 may include a titanium carbide content that is between 15% and 25% by volume, preferably between 17% and 23% by volume, and more preferably between 19% and 21% by volume, relative to the total volume of the second layer 8.

[0074] According to one example, the second layer 8 may include a titanium carbide content equal to 20% by volume relative to the total volume of the second layer 8.

[0075] In another embodiment, the second layer 8 may include a niobium carbide content of between 25% and 35% by volume, preferably between 27% and 33% by volume, and more preferably between 29% and 31% by volume, relative to the total volume of the second layer.

[0076] According to one example, the second layer 8 may include a niobium carbide content of 30%.

[0077] In another embodiment, the second layer may comprise a mixture of carbides, wherein the content of each carbide in the mixture is between 5% and 20% by volume, preferably between 5% and 10% by volume, relative to the total volume of the second layer.

[0078] A more economical coating can be obtained by mixing multiple types of carbides in a lower proportion.

[0079] According to one embodiment, the second layer 8 may, for example, comprise a mixture of niobium carbide and titanium carbide, wherein the niobium carbide content relative to the total volume of the second layer is between 5% and 20% by volume, preferably between 5% and 10% by volume, and the titanium carbide content relative to the total volume of the second layer is between 5% and 20% by volume, preferably between 5% and 10% by volume.

[0080] According to one example, the second layer 8 may contain a mixture of niobium carbide and titanium carbide, wherein the niobium carbide content is 5% by volume and the titanium carbide content is 10% by volume relative to the total volume of the second layer 8.

[0081] The first layer 7 forms an adhesion layer between the first outer surface 2a, the second outer surface 3a, and the second layer 8.

[0082] The proximity of the substrate formed by the first outer surface 2a and the second outer surface 3a to the coefficient of thermal expansion of the first layer 7 helps to increase this adhesion.

[0083] The second layer 8 forms a first resistance barrier, which reduces the occurrence of cracks caused by friction between the coated brake disc 1 and the brake pads.

[0084] In addition to the second layer 8, the first layer 7 forms a second mechanical resistance barrier, which reduces the occurrence of cracks.

[0085] Preferably, coating 6 is a two-layer coating consisting only of the first layer and the second layer.

[0086] The bilayer structure of coating 6 allows for a limitation on the number of interfaces. Pores can exist at these interfaces and are the root cause of debonding in coating 6, making it brittle under mechanical stress. Therefore, the bilayer structure allows for a mechanically stronger coating 6 than structures with more than two interfaces.

[0087] The thickness of coating 6 is between 300 and 500 µm, preferably between 350 and 450 µm.

[0088] Preferably, the thickness of the first layer 7 is between 100 and 200 µm.

[0089] Preferably, the thickness of the second layer 8 is between 100 and 200 µm.

[0090] The coating 6 was obtained using a technique called EHLA (Extreme High Speed ​​Laser Deposition of Materials).

[0091] The phrase "material deposition via ultra-high-speed laser" in this invention should be understood to refer to thermal spraying technology, also known as "ultra-high-speed laser application process" and represented by the acronym EHLA.

[0092] refer to Figure 3 EHLA technology, like the laser cladding technology from which it is derived, is based on using a high-power industrial laser 9 to melt and / or weld metal powder. The powder, carried by a gas (such as argon), forms a powder stream 10 sprayed onto a substrate, thereby creating a metallurgical bond. This process allows for the formation of a heat-affected region 11 with the substrate, thus ensuring good adhesion to the substrate (such as the first outer surface 2a and the second outer surface 3a).

[0093] EHLA laser deposition technology enables deposition rates up to 200 m / min and depths up to 500 cm⁻¹. 2 The surface rate is 1 / min, which is 100 times faster than in conventional laser cladding technology. In fact, some parameters (such as laser power or powder flow rate) are even higher.

[0094] Unlike conventional laser cladding, in EHLA technology, the particles melt approximately 1 mm from the substrate before contacting it. The entire powder stream 10 converges toward region 12 at a distance from the substrate. The particles present in the thus molten powder stream 10 are then transported by gas and fall into the molten pool 13. Because the substrate has also been heated by the laser 9, the heat-affected region 11 (which corresponds to the molten area between the powder-coated portion and the substrate portion) is thinner than in a laser cladding process, and the substrate absorbs less energy.

[0095] The very thin or even non-existent heat-affected region 11 obtained by the EHLA technology allows the material (such as cast iron) on which the coating 6 is formed to be deformed during the formation of the coating 6, and does not change its properties, especially its resistance to deformation.

[0096] The coating 6 obtained through EHLA technology has optimized mechanical strength properties, particularly against thermomechanical stress and wear, thus enabling the brake disc 1 to limit the emission of polluting particles during and outside the braking phase of the motor vehicle.

[0097] The present invention also relates to a method for producing a brake disc as described above, the method comprising forming a first layer 7 and a second layer 8 of a coating 6 by means of a technique for depositing materials using ultra-high speed laser (referred to as EHLA).

[0098] Advantageously, the production method includes forming a coating 6 on a first friction track 4 and forming a coating 6 on a second friction track 5.

[0099] In this production method, the materials of the first layer 7 and the second layer 8 are sprayed in powder form.

[0100] The powder being sprayed to form the first layer 7 contains steel having a chromium content between 10% and 20% by weight relative to the total mass of the steel.

[0101] The powder being sprayed to form the second layer 8 contains steel, which is intended to form the matrix of the second layer 8 after spraying, and has a chromium content of between 10% and 20% by weight relative to the total mass of the steel.

[0102] The powder sprayed to form the second layer 8 also includes a content of at least one carbide relative to the total volume of the second layer, comprising between 15% and 40% by volume. The carbide intended to form a reinforcement in the steel matrix after spraying is selected from the following compounds: silicon carbide, chromium carbide, tungsten carbide, niobium carbide, titanium carbide, or mixtures thereof, preferably selected from niobium carbide, titanium carbide, or mixtures thereof.

[0103] The features described above for the first layer 7 apply to powder intended to form the first layer 7.

[0104] The features described above for the second layer 7 apply to powders intended to form the second layer 8.

[0105] Preferably, the particle size of the powder intended to form the first layer 7 and the particle size of the powder intended to form the second layer 8 are between 10 and 60 µm.

[0106] Preferably, the particles of powder intended to form the first layer 7 and the particles of powder intended to form the second layer 8 are primarily spherical in shape.

[0107] The second layer 8, which is in powder form, preferably incorporates one or more carbides in the form of cermet.

[0108] The term "cermet" should be understood to mean powder containing ceramic reinforcements incorporated into a metallic phase.

[0109] According to one example, cermets can include carbide particles inserted into a matrix containing iron and chromium, thus forming aggregates.

[0110] Preferably, the matrix of the cermet mainly contains iron and chromium.

[0111] The term "major" should be understood to mean a matrix in which the total content of iron and chromium accounts for 50% or more of the weight of the cermet.

[0112] Preferably, the step of forming the second layer 8 in the production method includes using cermet.

[0113] In other words, the powder used to form the second layer 8 of coating 6 is doped with one or more carbides in the form of cermet.

[0114] The use of cermets enables the regular deposition of materials with constant thickness.

[0115] Integrating carbides in the form of spherical cermets into steel facilitates their deposition via spraying.

[0116] Preferably, the production method includes machining steps performed after the formation of coating 6 to form a surface that may be irregular and uniform, and to adjust its thickness.

[0117] After machining, the thickness of coating 6 is between 300 and 500 µm, preferably between 350 and 450 µm.

[0118] What can be provided are brake discs intended for use in transport vehicles other than motor vehicles, and particularly brake discs for use in the aviation or railway sectors.

[0119] Example:

[0120] Example 1: 430L + 30 vol% NbC double coating applied via EHLA spraying

[0121] The coating of Example 1 was formed on a GJL 150 layered graphite cast iron brake disc. The coating comprises a first layer arranged in contact with the cast iron and composed of 430L stainless steel. A second layer disposed on the first layer consists of a 430L steel matrix and niobium carbide reinforcement. The niobium carbide content is 30% by volume relative to the total volume of the second layer.

[0122] The deposition of the first and second layers is carried out sequentially by spraying the first and second layer materials in powder form using EHLA technology.

[0123] Specifically, a second layer is formed by spraying a powder mixture containing 430L steel powder and niobium carbide powder. The niobium carbide powder is sprayed in a cermet form, meaning it contains niobium carbide particles intercalated into a matrix containing iron and chromium to form aggregates. The cermet-type powder used incorporates 80% niobium carbide and 20% FeCr by weight relative to the total weight of the cermet.

[0124] Machining steps are performed to achieve the thickness obtained after grinding and spraying. Taking into account the irregular surface of the first layer, the coating obtained after machining has a thickness ranging from 350 to 400 µm.

[0125] Adding niobium carbide to 430L steel increases the hardness of the second layer relative to the first layer. The resulting average hardness of the second layer is 485 HV1.

[0126] Testing for thermal damage and measuring particulate emissions during braking allows for the identification of the absence of cracks and a reduction in particulate emissions.

[0127] Therefore, brake discs coated with EHLA technology can achieve excellent performance in terms of resistance to thermal damage and particulate emissions during braking.

[0128] Example 2: 430L + 20 vol% TiC double-layer coating applied via EHLA spraying

[0129] The coating of Example 2 was also formed on a GJL 150 layered graphite cast iron brake disc. This coating comprises a first layer arranged in contact with the GJL cast iron and composed of 430L stainless steel. A second layer disposed on the first layer consists of a 430L steel matrix and titanium carbide reinforcement. The titanium carbide content is 20% by volume relative to the total volume of the second layer.

[0130] The deposition of the first and second layers was carried out sequentially by spraying powder using EHLA technology.

[0131] Specifically, a second layer is formed by spraying a powder mixture containing 430L steel powder and titanium carbide powder. The titanium carbide powder is sprayed in a cermet form, that is, containing titanium carbide particles intercalated into a matrix containing iron and chromium to form aggregates. The cermet-type powder used incorporates 70% titanium carbide and 30% FeCr by mass relative to the total mass of the cermet.

[0132] Similar to Example 1, machining steps are performed to achieve the thickness obtained after grinding and spraying. The coating obtained after machining has a thickness ranging from 440 to 470 µm.

[0133] Testing for thermal damage and measuring particulate emissions during braking allows for the identification of the absence of cracks and a reduction in particulate emissions.

[0134] Therefore, brake discs coated with EHLA technology can achieve excellent performance in terms of resistance to thermal damage and particulate emissions during braking.

Claims

1. Brake disc for a motor vehicle, comprising at least one outer face (2a, 3a) having a coating (6) comprising: - a first layer (7) arranged at least partially on the outer face (2a, 3a), the first layer (7) comprising a steel having a chromium content comprised between 10% and 20% by mass with respect to the total mass of the steel; - a second layer (8) arranged on the first layer (7), the second layer (8) comprising a steel matrix having a chromium content comprised between 10% and 20% by mass with respect to the total mass of the steel, and a content of at least one carbide selected from the following compounds: silicon carbide, chromium carbide, tungsten carbide, niobium carbide, titanium carbide or mixtures thereof, comprised between 15% and 40% by volume with respect to the total volume of the second layer, preferably selected from niobium carbide, titanium carbide or mixtures thereof; - the coating (6) being obtained using a technique called EHLA, which consists in depositing material at ultra-high speed by laser.

2. The brake disc of claim 1, wherein, - the steel of the first layer (7) and / or the steel of the second layer (8) being a ferritic steel, preferably consisting of: a chromium content comprised between 16% and 18% by mass, a silicon content less than or equal to 1% by mass, a nickel content less than or equal to 0.6% by mass, a manganese content less than or equal to 1% by mass, a carbon content less than or equal to 0.08% by mass, a molybdenum content less than or equal to 1% by mass, a phosphorus content less than or equal to 0.045% by mass, a sulphur content less than or equal to 0.03% by mass, a titanium content less than or equal to 0.01% by mass, optionally other additive elements such as copper, vanadium, niobium or tin, the remainder being iron and unavoidable impurities.

3. The brake disc of claim 1 or 2, wherein, - the second layer (8) comprising a titanium carbide content comprised between 15% and 25% by volume, preferably comprised between 17% and 23% by volume, more preferably comprised between 19% and 21% by volume with respect to the total volume of the second layer (8).

4. The brake disc of claim 1 or 2, wherein, - the second layer (8) comprising a niobium carbide content comprised between 25% and 35% by volume, preferably comprised between 27% and 33% by volume, more preferably comprised between 29% and 31% by volume with respect to the total volume of the second layer (8).

5. The brake disc of claim 1 or 2, wherein, - the second layer (8) comprising a mixture of carbides, the content of each carbide being comprised between 5% and 20% by volume, preferably between 5% and 10% by volume with respect to the total volume of the second layer (8).

6. The brake disc of claim 5, wherein, - the second layer (8) comprising a mixture of niobium carbide and titanium carbide, the niobium carbide content being comprised between 5% and 20% by volume, preferably comprised between 5% and 10% by volume with respect to the total volume of the second layer, and the titanium carbide content being comprised between 5% and 20% by volume, preferably comprised between 5% and 10% by volume with respect to the total volume of the second layer (8).

7. The brake disc of any one of the preceding claims, wherein, - the material of the brake disc (1) on which the coating (6) is arranged being made of cast iron, preferably of lamellar graphite cast iron.

8. Brake disc according to any one of the preceding claims, comprising first and second opposite faces (2, 3) having first and second outer surfaces (2a, 3a) respectively, each of the first and second outer surfaces (2a, 3a) comprising a friction track (4, 5) intended to cooperate with a brake pad, the coating (6) being arranged at least partially, preferably only, on the friction tracks (4, 5).

9. Method for producing a brake disc according to any one of the preceding claims, comprising forming the first and second layers (7, 8) of the coating (6) by a technique of deposition of material at ultra-high speed, called EHLA.

10. The production method as claimed in claim 9, wherein, The step of forming the second layer (8) of the production method comprises the use of a cermet.

11. Motor vehicle comprising at least one brake disc (1) according to any one of Claims 1 to 8.

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