Brake disc and process for manufacturing thereof

Abstract

The application relates to the technical field of metal material hot processing, and discloses a brake disc and a preparation process thereof. The brake disc is composed of the following chemical components with mass percentages: iron 92.73-93.70%, carbon 3.70-3.90%, silicon 1.50-1.80%, manganese 0.65-0.75%, titanium 0.015-0.03%, boron 0.07-0.14%, copper 0.25-0.35%, tin 0.03-0.05%, phosphorus <=0.05% and sulfur <=0.08%. The application further provides a preparation process of the brake disc, which comprises the following steps: S1, smelting and component adjustment; S2, in-situ composite reaction; S3, composite inoculation treatment; S4, molding and pouring; S5, post-treatment; and S6, cooling of the casting. According to the technical scheme, the in-situ generated hard phase can significantly improve the high-temperature hardness, wear resistance and thermal cracking resistance of the brake disc.

Description

Technical Field

[0001] This invention relates to the field of hot working technology of metal materials, specifically to a brake disc and its manufacturing process. Background Technology

[0002] As a key component ensuring driving safety, the material properties of automotive brake discs directly determine the reliability and stability of the braking system. Currently, gray cast iron is widely used as the mainstream material for manufacturing automotive brake discs due to its good thermal conductivity, vibration damping, wear resistance, and low production cost, and it can meet the requirements under normal driving conditions.

[0003] However, with the continuous improvement of vehicle power performance and the increasing complexity of usage scenarios, the braking requirements of vehicles under harsh conditions such as high speed, high load, or long downhill slopes are becoming increasingly prominent. During continuous or high-intensity braking, the surface temperature of the brake disc can rise sharply to several hundred degrees Celsius, which gradually exposes the inherent defects of traditional gray cast iron materials. High temperatures cause the pearlitic matrix structure of cast iron to soften, and its hardness and strength decrease significantly. This performance degradation directly leads to the deterioration of wear resistance and accelerates the wear of the brake disc.

[0004] Repeated and drastic temperature changes subject brake discs to enormous thermal stress cycles, making them highly susceptible to thermal fatigue cracks in areas of material stress concentration. Once these micro-cracks form, they continue to propagate during subsequent braking cycles, potentially leading to macroscopic cracking or even breakage of the brake disc, posing a serious threat to driving safety. Therefore, effectively improving the mechanical stability and thermal crack resistance of gray cast iron brake discs under high-temperature conditions has become a pressing technical challenge in the field of vehicle braking systems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a brake disc and its manufacturing process, which solves the problem that existing gray cast iron brake discs suffer from severe mechanical property degradation and are prone to thermal cracking failure under high-temperature conditions.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a brake disc comprising the following chemical components by mass percentage;

[0007] Iron 92.73-93.70%, Carbon 3.70-3.90%, Silicon 1.50-1.80%, Manganese 0.65-0.75%, Titanium 0.015-0.03%, Boron 0.07-0.14%, Copper 0.25-0.35%, Tin 0.03-0.05%, Phosphorus ≤0.05%, and Sulfur ≤0.08%.

[0008] A specific ratio of titanium (Ti) and boron (B) elements was introduced into a gray cast iron matrix. These two elements underwent an in-situ chemical reaction in a high-temperature molten iron environment to generate dispersed titanium diboride (TiB). 2） Ceramic reinforcing phase. The mechanism of this reaction is as follows:

[0009] High thermodynamic stability: TiB2 is an intermetallic compound with a high melting point (about 3225℃), high hardness, high thermal stability and chemical inertness.

[0010] The generated TiB2 particles are dispersed in the cast iron matrix as hard particles. At room temperature, they can effectively pin dislocations and hinder matrix slip, thereby playing a significant dispersion strengthening role and improving the hardness and tensile strength of the material.

[0011] Under high-temperature conditions, when the cast iron matrix softens due to temperature rise, the TiB2 particles with extremely high thermal stability can continue to maintain their high hardness and strength, serving as a load-bearing skeleton, inhibiting the plastic deformation of the matrix, and acting as a wear-resistant phase to resist friction and wear, thus enabling the brake disc to exhibit excellent high-temperature hardness and high-temperature wear resistance as a whole.

[0012] During the intense temperature cycling of braking, this thermal expansion mismatch generates a microscopic compressive stress field at the interface between TiB2 particles and the matrix. This stress field effectively relaxes and counteracts macroscopic thermal stress, reducing the driving force for the initiation of hot cracks. Simultaneously, the dispersed hard particles deflect and pin the initiating microcracks, increasing the resistance to crack propagation and thus significantly improving the brake disc's resistance to thermal fatigue.

[0013] Copper and tin in the formula act as pearlite stabilizing elements, ensuring that the matrix structure is pearlite with good comprehensive mechanical properties. At the same time, the content of harmful impurities such as phosphorus and sulfur is strictly controlled to avoid the formation of low-melting-point brittle phases, thus guaranteeing the intrinsic quality of the material.

[0014] Preferably, the titanium and boron are dispersed in the cast iron matrix of the brake disc as in-situ generated titanium diboride reinforcing phases.

[0015] By adopting the above technical solution, it is clarified that the existence forms of Ti and B elements are the structural basis for achieving the technical effects of this invention. This allows the reinforcing phase to most effectively exert its functions of dispersion strengthening, high-temperature load bearing, and crack propagation inhibition.

[0016] Preferably, the cast iron matrix of the brake disc is pearlitic, and the graphite morphology is type A graphite.

[0017] This ensures that the brake disc substrate has high strength and high wear resistance. Type A graphite is the most ideal graphite form in gray cast iron. Its flake structure can give the material good thermal conductivity and vibration damping. At the same time, its tip is relatively blunt, and compared with other forms of graphite, the stress concentration effect is minimal, which is beneficial to improving the mechanical properties and fatigue life of the material.

[0018] A manufacturing process for a brake disc includes the following steps;

[0019] S1. Smelting and Composition Adjustment: Melt scrap steel and recycled materials to adjust the basic chemical composition;

[0020] S2, In-situ composite reaction: At a preset temperature, titanium-iron alloy is first added to molten iron and stirred, followed by the addition of boron-iron alloy and stirring, so as to generate a reinforcing phase in situ in molten iron;

[0021] S3. Composite Inoculation Treatment: The molten iron that has completed the in-situ composite reaction is subjected to primary inoculation, secondary inoculation and in-flow inoculation treatment in sequence;

[0022] S4. Shaping and Casting: Casting is performed using the prepared sand mold;

[0023] S5. Post-treatment: Cooling, cleaning, and low-temperature annealing of the casting.

[0024] Step 1: Pre-dissolution and homogenization of titanium. First, titanium-iron alloy is added to the molten iron at high temperature and stirred thoroughly. This step aims to ensure that the titanium element is fully dissolved and evenly distributed in the molten iron matrix, providing uniform reaction sites for subsequent reactions.

[0025] Step Two: Addition of Boron and Selective Reaction. Boron-iron alloy is added after the titanium atoms are evenly distributed. Due to the strong chemical affinity between titanium and boron, the newly added boron atoms will preferentially react with the already evenly distributed titanium atoms in situ.

[0026] Step 3: Suppression of Harmful Phases. The key function of this process sequence is that it utilizes the thermodynamic priority of the Ti-B reaction to effectively suppress the formation of coarse network or needle-like brittle borides (such as Fe2B) or carborane compounds by boron reacting with iron and carbon. If boron is added too early or simultaneously with titanium, such harmful phases are easily formed, severely disrupting the matrix and causing a sharp decrease in the material's toughness.

[0027] Step 4: Morphology control of the reinforcing phase. By controlling the reaction temperature and stirring intensity, TiB2 can be dispersedly nucleated and uniformly grown throughout the molten iron system, ultimately forming small, uniformly distributed reinforcing particles, thereby maximizing its reinforcing and toughening effect.

[0028] The composite inoculation treatment in step S3 works synergistically with the in-situ reaction step. Through three stages of inoculation—primary, secondary, and in-flow—especially the introduction of special inoculants containing bismuth and gadolinium, the eutectic nucleation cores can be increased to the maximum extent, the graphite morphology can be optimized, and the eutectic clusters can be refined. This ensures the acquisition of a microstructure with excellent type A graphite and pearlite matrix, allowing the in-situ generated TiB2 reinforcing phase to exert its full potential in a healthy matrix.

[0029] Preferably, the in-situ composite reaction in step S2 is carried out at a temperature of 1535℃-1545℃; after adding the titanium-iron alloy, it is electromagnetically stirred for 3-4 minutes; then the boron-iron alloy is added, and it is strongly electromagnetically stirred for 45-60 seconds.

[0030] The temperature range of 1535℃-1545℃ is the optimal range to ensure the full dissolution of titanium and boron and the optimal reaction kinetics. Specific stirring time and intensity precisely control the degree of element homogenization and the nucleation and growth process of the reaction product TiB2, which are key process parameters for obtaining fine, dispersed reinforcing phases.

[0031] Preferably, the composite incubation treatment in step S3 specifically includes:

[0032] First inoculation: A barium silicon inoculant, accounting for 0.3% of the total weight of the molten iron, is laid at the bottom of the ladle;

[0033] Secondary inoculation: After pouring out the hot metal, add 0.15% to 0.2% of bismuth oxysilane inoculant and 0.15% to 0.2% of gadolinium silane inoculant, which account for 0.15% to 0.2% of the total weight of the molten iron, to the ladle;

[0034] In-flow inoculation: During casting, add silicon-zirconium inoculant accounting for 0.1% of the total weight of molten iron.

[0035] A multi-layered inoculation system is employed. Initial coarse inoculation is performed using barium silicon inoculant, followed by efficient secondary inoculation using bismuth-silicon oxysilane and gadolinium silicon inoculants. Bismuth effectively prevents white cast iron formation and promotes type A graphite formation, while the rare earth element gadolinium (Gd) possesses powerful purifying and remodeling properties. Finally, in-flow inoculation with zirconium silicon effectively resists inoculation fading, ensuring the uniformity of the casting's microstructure at the end of the pouring process.

[0036] Preferably, the bismuth-silicon oxyacetylene inoculant used in the secondary inoculation has the following chemical composition by weight percentage: silicon 65.0%–72.0%, bismuth 1.0%–3.0%, calcium 0.5%–1.5%, with the balance being iron and trace oxides; the gadolinium-silicon inoculant has the following chemical composition by weight percentage: silicon 55.0%–65.0%, gadolinium 4.0%–6.0%, calcium 0.5%–1.5%, with the balance being iron.

[0037] Preferably, in step S1, the basic chemical composition of the molten iron is adjusted to: carbon 3.65%–3.75%, silicon 1.50%–1.80%, manganese 0.65%–0.75%, copper 0.25%–0.35%, tin 0.03%–0.05%, phosphorus ≤0.05%, sulfur ≤0.08%, with the balance being iron.

[0038] Preferably, the pouring in step S4 is carried out at a pouring temperature of 1450°C.

[0039] Preferably, the low-temperature annealing process in step S5 is as follows: the temperature is raised to 560℃-580℃ at a rate of 100℃ / h, held for 2.5 to 3 hours, and then cooled in the furnace at a rate of 40℃ / h to below 200℃ before being removed from the furnace.

[0040] The low-temperature annealing process aims to eliminate internal stress generated during casting, improve the dimensional stability and toughness of castings, and avoid adverse effects on the pearlite matrix and reinforcing phases.

[0041] This invention provides a brake disc and its manufacturing process. It has the following beneficial effects:

[0042] 1. This invention generates a dispersed titanium diboride (TiB2) ceramic phase in situ within a cast iron matrix. Utilizing the significant difference in thermal expansion coefficients between TiB2 and the iron matrix, a micro-stress field is formed at the particle / matrix interface during thermal cycling. This stress field effectively dissipates macroscopic thermal stress and inhibits the initiation of hot cracks. Simultaneously, the high-hardness TiB2 particles pin and deflect the propagation path of microcracks, significantly improving crack propagation resistance and thus systematically enhancing the thermal fatigue life of the brake disc.

[0043] 2. This invention employs an in-situ reaction sequence of titanium followed by boron, leveraging the stronger chemical affinity between titanium and boron to preferentially promote the Ti + 2B → TiB2 reaction. This effectively suppresses the formation of coarse, brittle, network-like borides (such as Fe2B) by the combination of boron with iron and carbon. This process design ensures that the final reinforcing phase consists of small, uniformly dispersed TiB2 particles, maximizing its dispersion strengthening effect and fundamentally eliminating microstructural defects that severely damage the toughness and integrity of the material.

[0044] 3. This invention employs an in-situ reaction sequence of titanium followed by boron, utilizing the stronger chemical affinity between titanium and boron to preferentially generate the target reinforcing phase TiB2. This successfully suppresses the formation of coarse network or needle-like brittle borides (such as Fe2B), eliminating potential crack initiation sites. Simultaneously, combined with an efficient three-stage composite inoculation treatment, it ensures the matrix structure is an ideal mix of type A graphite and pearlite, providing a high-quality microstructure carrier for the TiB2 reinforcing phase to exert its maximum effectiveness. Attached Figure Description

[0045] Figure 1 This is a flowchart of the preparation process of the present invention;

[0046] Figure 2 This is a schematic diagram of the in-situ recombination reaction steps of the present invention;

[0047] Figure 3 This is a schematic diagram of the composite incubation process of the present invention;

[0048] Figure 4 This is a schematic diagram of the post-processing steps of the present invention;

[0049] Figure 5 This is a graph showing the hardness comparison at different temperatures according to the present invention. Detailed Implementation

[0050] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] Please see the appendix Figure 1 -Appendix Figure 5 This invention provides a brake disc and its manufacturing process.

[0052] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0053] Scrap steel is low-carbon steel scrap, and its chemical composition contains no more than 0.045% phosphorus (P) and no more than 0.050% sulfur (S) by mass.

[0054] The recycled material refers to the gating system and scrapped parts of the same grade of castings produced by the process described in this invention, which have undergone shot peening cleaning before use.

[0055] The carbon raiser is a graphitized petroleum coke carbon raiser with a fixed carbon (C, CAS No.: 7440-44-0) content of not less than 98.5% by mass, a sulfur (S) content of not more than 0.05% by mass, and a particle size of 1-5 mm.

[0056] Ferrosilicon is a silicon-iron alloy, mainly composed of silicon and iron, with silicon accounting for 72.0% to 78.0% by mass.

[0057] Ferromanganese, a high-carbon form of ferromanganese, is mainly composed of manganese and iron, with manganese accounting for 75.0% to 82.0% by mass.

[0058] Titanium-iron alloy is mainly composed of titanium and iron, with titanium accounting for 68.0% to 72.0% of the mass percentage and having a particle size of 5 to 30 mm.

[0059] Boron-iron alloy is mainly composed of boron and iron, with boron content ranging from 17.0% to 20.0% by mass and a particle size of 5 to 30 mm.

[0060] Ferrochrome alloy, a high-carbon ferrochrome alloy, is mainly composed of chromium and iron, with chromium accounting for 60.0% to 68.0% by mass.

[0061] The primary inoculant is a silicon-barium inoculant, with the following chemical composition by weight percentage: silicon (Si) 68.0%–75.0%, barium (Ba, CAS No.: 7440-39-3) 2.0%–4.0%, calcium (Ca, CAS No.: 7440-70-2) 1.0%–2.0%, and the balance being iron (Fe), with a particle size of 1–5 mm.

[0062] Secondary inoculants, including:

[0063] The bismuth oxysilane inoculant, by weight percentage, has the following chemical composition: silicon (Si) 65.0%–72.0%, bismuth (Bi, CAS No.: 7440-69-9) 1.0%–3.0%, calcium (Ca) 0.5%–1.5%, with the balance being iron (Fe) and trace oxides;

[0064] The chemical composition of the silicon-gadolinium inoculant, by weight percentage, is: silicon (Si) 55.0%–65.0%, gadolinium (Gd, CAS No.: 7440-54-2) 4.0%–6.0%, calcium (Ca) 0.5%–1.5%, with the balance being iron (Fe).

[0065] The inoculant is a silicon-zirconium inoculant with the following chemical composition: silicon (Si) 70.0%–76.0%, zirconium (Zr, CAS No.: 7440-67-2) 1.0%–3.0%, calcium (Ca) 0.5%–1.5%, and the balance being iron (Fe), with a particle size of 0.2–0.8 mm.

[0066] Example 1:

[0067] This embodiment provides a manufacturing process for a brake disc, including the following steps:

[0068] Smelting and Composition Adjustment: 60% scrap steel and 40% recycled material by mass are added to a medium-frequency induction furnace for melting and then heated to 1580℃ for 10 minutes for overheating. After slag removal, samples are taken for spectral analysis. Subsequently, carbon raisers, ferrosilicon, and ferromanganese are added to adjust the basic chemical composition of the molten iron to: carbon 3.80%, silicon 1.50%, manganese 0.70%, copper 0.30%, tin 0.04%, phosphorus ≤0.05%, sulfur ≤0.08%, with the balance being iron and unavoidable impurities.

[0069] In-situ composite reaction: The temperature of molten iron is precisely stabilized at 1540℃. First, titanium-iron alloy is added to the furnace to achieve a final titanium content of 0.022% by mass in the molten iron; after addition, medium-power electromagnetic stirring is maintained for 3 minutes. Subsequently, boron-iron alloy is rapidly added to the furnace to achieve a final boron content of 0.10% by mass in the molten iron; after addition, strong electromagnetic stirring is performed for 45 seconds.

[0070] Composite inoculation treatment: The molten iron, after reaction, is heated to 1520℃ in preparation for tapping. A 0.3% (by weight) silicon-barium inoculant is spread at the bottom of the empty ladle as primary inoculation. After tapping, a 0.2% (by weight) silicon-bismuth oxide inoculant and a 0.2% (by weight) silicon-gadolinium inoculant are added to the surface of the molten iron in the ladle as secondary inoculation. During casting, a 0.1% (by weight) silicon-zirconium inoculant is added through a flow-inoculation device.

[0071] Sand mixing and core making: Resin sand is prepared using a continuous sand mixer. Using 50 / 100 mesh quartz sand as the base material, 1.0% furan resin (by weight of sand) and 40% sulfonic acid curing agent (by weight of resin) are added and mixed thoroughly. A cold core box core making machine is used to inject the mixed resin sand into the core box to prepare the air duct core and partition core required for the brake disc, ensuring that the sand core surface is smooth and defect-free.

[0072] Molding and Casting: Sand molds are made using a high-pressure static pressure molding line, and the sand cores prepared in the previous step are assembled into the mold cavity. The surface hardness of the mold cavity is 88Hc. Molten iron is transported to the casting station and cast at a casting temperature of 1450℃. The casting time for a single mold is controlled within 12 seconds.

[0073] Post-processing: After cooling in the sand mold for 30 minutes, the casting is removed from the sand, followed by shot blasting and grinding of the gating system and risers. The cleaned casting is then sent to an electric resistance furnace for low-temperature annealing. The process is as follows: the temperature is raised to 560℃ at a rate of 100℃ / h, held for 2.5 hours, and then cooled in the furnace at a rate of 40℃ / h to below 200℃ before being removed from the furnace.

[0074] Example 2:

[0075] This embodiment provides a manufacturing process for a brake disc, including the following steps:

[0076] Smelting and Composition Adjustment: 60% Q235 scrap steel and 40% recycled material by mass are added to a medium-frequency induction furnace for melting and then heated to 1580℃ for 10 minutes for overheating. After slag removal, samples are taken for spectral analysis. Subsequently, carbon raisers, ferrosilicon, and ferromanganese are added to adjust the basic chemical composition of the molten iron to: carbon 3.70%, silicon 1.70%, manganese 0.65%, copper 0.25%, tin 0.03%, phosphorus ≤0.05%, sulfur ≤0.08%, with the balance being iron and unavoidable impurities.

[0077] In-situ composite reaction: The temperature of molten iron is precisely stabilized at 1545℃. First, titanium-iron alloy is added to the furnace to achieve a final titanium content of 0.015% by mass in the molten iron; after addition, medium-power electromagnetic stirring is maintained for 3 minutes. Subsequently, boron-iron alloy is rapidly added to the furnace to achieve a final boron content of 0.07% by mass in the molten iron; after addition, strong electromagnetic stirring is performed for 45 seconds.

[0078] Composite inoculation treatment: The molten iron, after reaction, is heated to 1520℃ in preparation for tapping. A 0.3% (by weight) silicon-barium inoculant is spread at the bottom of the empty ladle as primary inoculation. After tapping, a 0.2% (by weight) silicon-bismuth oxide inoculant and a 0.2% (by weight) silicon-gadolinium inoculant are added to the surface of the molten iron in the ladle as secondary inoculation. During casting, a 0.1% (by weight) silicon-zirconium inoculant is added through a flow-inoculation device.

[0079] Sand mixing and core making: Resin sand is prepared using a continuous sand mixer. Using 50 / 100 mesh quartz sand as the base material, 1.0% furan resin (by weight of sand) and 40% sulfonic acid curing agent (by weight of resin) are added and mixed thoroughly. A cold core box core making machine is used to inject the mixed resin sand into the core box to prepare the air duct core and partition core required for the brake disc, ensuring that the sand core surface is smooth and defect-free.

[0080] Molding and Casting: Sand molds are made using a high-pressure static pressure molding line, and the sand cores prepared in the previous step are assembled into the mold cavity. The surface hardness of the mold cavity is 88Hc. Molten iron is transported to the casting station and cast at a casting temperature of 1450℃. The casting time for a single mold is controlled within 12 seconds.

[0081] Post-processing: After cooling in the sand mold for 30 minutes, the casting is removed from the sand, followed by shot blasting and grinding of the gating system and risers. The cleaned casting is then sent to an electric resistance furnace for low-temperature annealing. The process is as follows: the temperature is raised to 560℃ at a rate of 100℃ / h, held for 2.5 hours, and then cooled in the furnace at a rate of 40℃ / h to below 200℃ before being removed from the furnace.

[0082] Example 3:

[0083] This embodiment provides a manufacturing process for a brake disc, including the following steps:

[0084] Smelting and Composition Adjustment: 55% scrap steel and 45% recycled material by mass are added to a medium-frequency induction furnace for melting and then heated to 1590℃ for overheating treatment for 10 minutes. After slag removal, samples are taken for spectral analysis. Subsequently, carbon raisers, ferrosilicon, and ferromanganese are added to adjust the basic chemical composition of the molten iron to: carbon 3.90%, silicon 1.80%, manganese 0.75%, copper 0.35%, tin 0.05%, phosphorus ≤0.05%, sulfur ≤0.08%, with the balance being iron and unavoidable impurities.

[0085] In-situ composite reaction: The temperature of molten iron is precisely stabilized at 1535℃. First, titanium-iron alloy is added to the furnace to achieve a final titanium content of 0.030% by mass in the molten iron; after addition, medium-power electromagnetic stirring is maintained for 4 minutes. Subsequently, boron-iron alloy is rapidly added to the furnace to achieve a final boron content of 0.14% by mass in the molten iron; after addition, strong electromagnetic stirring is performed for 60 seconds.

[0086] Composite inoculation treatment: The molten iron, after reaction, is heated to 1525℃ in preparation for tapping. A 0.3% (by weight) silicon-barium inoculant is spread at the bottom of the empty ladle as primary inoculation. After tapping, a 0.2% (by weight) silicon-bismuth oxide inoculant and a 0.2% (by weight) silicon-gadolinium inoculant are added to the surface of the molten iron in the ladle as secondary inoculation. During casting, a 0.1% (by weight) silicon-zirconium inoculant is added through a flow-inoculation device.

[0087] Sand mixing and core making: Resin sand is prepared using a continuous sand mixer. Using 50 / 100 mesh quartz sand as the base material, 1.0% furan resin (by weight of sand) and 40% sulfonic acid curing agent (by weight of resin) are added and mixed thoroughly. A cold core box core making machine is used to inject the mixed resin sand into the core box to prepare the air duct core and partition core required for the brake disc, ensuring that the sand core surface is smooth and defect-free.

[0088] Molding and Casting: Sand molds are made using a high-pressure static pressure molding line, and the sand cores prepared in the previous step are assembled into the mold cavity. The surface hardness of the mold cavity is 88Hc. Molten iron is transported to the casting station and cast at a casting temperature of 1450℃. The casting time for a single mold is controlled within 12 seconds.

[0089] Post-processing: After cooling in the sand mold for 30 minutes, the casting is removed from the sand, followed by shot blasting and grinding of the gating system and risers. The cleaned casting is then sent to an electric resistance furnace for low-temperature annealing. The process is as follows: the temperature is raised to 560℃ at a rate of 100℃ / h, held for 2.5 hours, and then cooled in the furnace at a rate of 40℃ / h to below 200℃ before being removed from the furnace.

[0090] Example 4:

[0091] This embodiment provides a manufacturing process for a brake disc, including the following steps:

[0092] Smelting and Composition Adjustment: 60% scrap steel and 40% recycled material by mass are added to a medium-frequency induction furnace for melting and then heated to 1580℃ for 10 minutes for overheating. After slag removal, samples are taken for spectral analysis. Subsequently, carbon raisers, ferrosilicon, and ferromanganese are added to adjust the basic chemical composition of the molten iron to: carbon 3.80%, silicon 1.50%, manganese 0.70%, copper 0.30%, tin 0.04%, phosphorus ≤0.05%, sulfur ≤0.08%, with the balance being iron and unavoidable impurities.

[0093] In-situ composite reaction: The temperature of molten iron is precisely stabilized at 1540℃. First, titanium-iron alloy is added to the furnace to achieve a final titanium content of 0.022% by mass in the molten iron; after addition, medium-power electromagnetic stirring is maintained for 3 minutes. Subsequently, boron-iron alloy is rapidly added to the furnace to achieve a final boron content of 0.10% by mass in the molten iron; after addition, strong electromagnetic stirring is performed for 45 seconds.

[0094] Composite inoculation treatment: The molten iron, after reaction, is heated to 1520℃ in preparation for tapping. A 0.3% (by weight) silicon-barium inoculant is spread at the bottom of the empty ladle as primary inoculation. After tapping, a 0.15% (by weight) silicon-bismuth oxide inoculant and a 0.15% (by weight) silicon-gadolinium inoculant are added to the surface of the molten iron in the ladle as secondary inoculation. During casting, a 0.1% (by weight) silicon-zirconium inoculant is added through a flow-inoculation device.

[0095] Sand mixing and core making: Resin sand is prepared using a continuous sand mixer. Using 50 / 100 mesh quartz sand as the base material, 1.0% furan resin (by weight of sand) and 40% sulfonic acid curing agent (by weight of resin) are added and mixed thoroughly. A cold core box core making machine is used to inject the mixed resin sand into the core box to prepare the air duct core and partition core required for the brake disc, ensuring that the sand core surface is smooth and defect-free.

[0096] Molding and Casting: Sand molds are made using a high-pressure static pressure molding line, and the sand cores prepared in the previous step are assembled into the mold cavity. The surface hardness of the mold cavity is 88Hc. Molten iron is transported to the casting station and cast at a casting temperature of 1450℃. The casting time for a single mold is controlled within 12 seconds.

[0097] Post-processing: After cooling in the sand mold for 30 minutes, the casting is removed from the sand, followed by shot blasting and grinding of the gating system and risers. The cleaned casting is then sent to an electric resistance furnace for low-temperature annealing. The process is as follows: the temperature is raised to 580℃ at a rate of 100℃ / h, held for 3 hours, and then cooled in the furnace at a rate of 40℃ / h to below 200℃ before being removed from the furnace.

[0098] Comparative Example 1:

[0099] Compared with Example 1, the difference is that: no titanium-iron alloy and boron-iron alloy are added during the smelting process, and only one inoculation treatment is performed, without secondary inoculation and in-flow inoculation. The remaining steps are the same as in Example 1.

[0100] Comparative Example 2:

[0101] Compared with Example 1, the difference is that in the in-situ composite reaction step, titanium-iron alloy is not added, only boron-iron alloy is added to the molten iron, and the remaining steps are the same as in Example 1.

[0102] Comparative Example 3:

[0103] Compared with Example 1, the difference is that in the in-situ composite reaction step, no ferroborone alloy is added, only ferrotitanium alloy is added to the molten iron, and the remaining steps are the same as in Example 1.

[0104] Comparative Example 4:

[0105] Compared with Example 1, the difference is that the in-situ composite reaction step is not performed (i.e., titanium-iron alloy and boron-iron alloy are not added), and high-carbon ferrochrome alloy is added in the basic chemical composition adjustment step. The remaining steps are the same as in Example 1.

[0106] Comparative Example 5:

[0107] Compared with Example 1, the difference is that in the composite inoculation process, the secondary inoculation is not performed (i.e., after the soup is poured out, the bismuth oxysilane inoculant and gadolinium silane inoculant are not added to the pouring ladle), only the primary inoculation and in-flow inoculation are performed, and the remaining steps are the same as in Example 1.

[0108] Test example:

[0109] Test Example 1: Final Chemical Composition Analysis

[0110] Experimental description:

[0111] This test aims to accurately determine the final chemical composition of the brake disc castings prepared in each embodiment and comparative example, in order to verify the precision and effectiveness of the process described in this invention in controlling each chemical element, especially the core reactive elements titanium (Ti) and boron (B).

[0112] Sampling: Using a wire cutting machine, block samples with a size of not less than 30mm × 30mm × 10mm were cut from the hub or flange part (non-friction working surface) of the finished brake disc castings of each group (Examples 1-4, Comparative Examples 1-5).

[0113] Sample preparation: The surface of the sample to be analyzed was coarsely ground using a grinding wheel, and then finely ground using 80-grit and 120-grit sandpaper in sequence on an automatic polishing machine until the surface was smooth, clean, and free of defects such as oxide scale, pores, and sand holes. The prepared sample was then cleaned with anhydrous ethanol and dried.

[0114] Instrument Calibration and Analysis: Before analysis, the spectrometer is calibrated using cast iron standard materials that match the matrix of the sample being tested. The prepared sample is placed on the instrument's excitation stage, ensuring effective protection of the discharge region by the argon atmosphere. Excitation analysis is performed at three different locations for each sample, with each excitation lasting approximately 20 seconds. The instrument software automatically records and calculates the mass percentage content of each element, and the average of the three valid measurements is taken as the final analytical result.

[0115] The experimental data are shown in Table 1:

[0116] Table 1. Chemical composition analysis results (mass percentage, %) of the castings in each embodiment and comparative example:

[0117] sample carbon silicon manganese phosphorus sulfur titanium boron copper tin chromium Example 1 3.72 1.51 0.69 0.041 0.065 0.21 0.09 0.31 0.042 <0.01 Example 2 3.64 1.68 0.66 0.045 0.072 0.16 0.07 0.24 0.033 <0.01 Example 3 3.77 1.78 0.74 0.032 0.051 0.29 0.13 0.36 0.051 <0.01 Example 4 3.69 1.52 0.71 0.039 0.063 0.23 0.11 0.29 0.038 <0.01 Comparative Example 1 3.71 1.48 0.72 0.043 0.068 0.008 <0.001 0.30 0.041 <0.01 Comparative Example 2 3.73 1.53 0.68 0.040 0.066 0.009 0.09 0.32 0.039 <0.01 Comparative Example 3 3.68 1.49 0.70 0.044 0.069 0.22 <0.001 0.29 0.040 <0.01 Comparative Example 4 3.70 1.50 0.71 0.041 0.067 0.23 0.10 0.31 0.043 0.41 Comparative Example 5 3.74 1.49 0.69 0.042 0.064 0.21 0.09 0.30 0.042 <0.01

[0118] Summarize

[0119] The chemical composition analysis data in Table 1 provides a basic verification of the feasibility of this technical solution.

[0120] First, the data confirms that the preparation process of the present invention can precisely control the basic chemical composition (carbon, silicon, manganese, etc.) of cast iron. The basic composition of all embodiments and comparative examples is within the reasonable technical range of gray cast iron brake discs, ensuring that the material has a qualified matrix structure.

[0121] Secondly, and most importantly, the test results of Examples 1 to 4 show that the final actual content of the core reactive elements titanium and boron is highly consistent with the target addition amount set in the process steps, and the fluctuation range is within the normal tolerance of industrial production. This directly proves that the smelting addition process adopted in this invention is stable and effective, and can ensure that the two key precursor elements are successfully and sufficiently melted into the molten iron matrix and retained in the final casting.

[0122] In contrast, the data from Comparative Examples 1-4 also met the design expectations: in Comparative Example 1, the content of titanium and boron was at the residual level; Comparative Examples 2 and 3 contained only the target amounts of boron and titanium, respectively; and Comparative Example 4 contained the target amount of chromium. The compositional data from these comparative examples established a clear compositional benchmark for isolating variables, highlighting the synergistic effect of titanium-boron, and demonstrating the superiority of the process of this invention in subsequent performance tests.

[0123] Test Example 2: Quantitative Analysis of Residual Acid-Insoluble Matter

[0124] Experimental description:

[0125] The experiment selected samples from Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 for comparative analysis. The specific experimental steps are as follows:

[0126] Sample preparation: Samples were cut from the castings of each group, crushed using a crusher, and particles smaller than 1 mm were screened out. The particle samples were then dried in an oven at 105°C for 2 hours to remove moisture.

[0127] Weighing: Using an analytical balance with an accuracy of 0.1 mg, accurately weigh approximately 10 g of the dried sample and record it as the initial mass (m0).

[0128] Chemical digestion: Place the weighed sample in a 500mL beaker and slowly add 200mL of aqua regia solution (hydrochloric acid to nitric acid volume ratio of 3:1). Place the beaker in an 80℃ constant temperature water bath and turn on the magnetic stirrer, continuing the reaction until no obvious bubbles are produced and the iron matrix is ​​completely dissolved. This process usually takes 6–8 hours.

[0129] Filtration and washing: Vacuum filtration was performed on the digested solution using quantitative slow-speed filter paper. The inner wall of the beaker and the filter residue were repeatedly rinsed with deionized water until no chloride ion precipitate was detected in the washing filtrate using silver nitrate solution. Subsequently, the filter residue was washed 2-3 times with anhydrous ethanol to facilitate rapid drying.

[0130] Drying and Weighing: Transfer the filter paper containing the filter residue into a pre-weighed weighing dish and dry it in an oven at 120°C for 4 hours until constant weight. After cooling to room temperature in a desiccator, accurately weigh the total mass and calculate the net mass (m1) of the acid-insoluble residue.

[0131] Calculation: The mass fraction (ω) of acid-insoluble residue is calculated using the formula ω = (m1 / m0) × 100%.

[0132] The experimental data are shown in Table 2:

[0133] Table 2. Mass fraction of acid-insoluble residue in samples from each group:

[0134] sample Initial mass (g) Residual mass (g) Residue mass fraction (%) Example 1 10.0152 0.1764 1.76 Comparative Example 1 10.0318 0.0068 0.07 Comparative Example 2 10.0225 0.0291 0.29 Comparative Example 3 10.0194 0.0563 0.56 Comparative Example 4 10.0287 0.1023 1.02

[0135] Summarize

[0136] First, after complete digestion with strong acid, the sample of Example 1 yielded a residue mass fraction as high as 1.76%, while the residue mass fraction of Comparative Example 1 (conventional gray cast iron), which served as the baseline, was only 0.07%. The significant difference in quantity between the two ruled out the possibility that the residue originated from inherent inclusions in the raw materials (such as SiO2), confirming that a large number of new, chemically stable phases were generated during the preparation process of Example 1.

[0137] Secondly, by comparing with Comparative Examples 2 and 3, the origin of this new phase can be clearly identified. While the residual mass fractions of Comparative Example 2 (containing only boron) and Comparative Example 3 (containing only titanium) (0.29% and 0.56%, respectively) were slightly higher than the baseline, they were significantly lower than those of Example 1. This indicates that the small amounts of borides or carbonitrides that may form by adding boron or titanium alone have limited acid resistance and yield, failing to achieve the technical effects of this invention. Only when both titanium and boron coexist can a large amount of acid-resistant reinforcing phase be generated through a synergistic reaction.

[0138] Finally, the comparison between Example 1 and Comparative Example 4 (where ferrotitanium and ferroboron were added simultaneously) highlights the necessity of the process of the present invention. Under the premise of identical chemical composition, Example 1, employing the sequential stepwise feeding process of the present invention, exhibited a significantly higher residual mass fraction (1.76%) than Comparative Example 4, which used a mixed feeding method (1.02%). This result indicates that the process route of adding titanium for pretreatment followed by adding boron for a transient reaction can more effectively promote the formation of TiB2 and improve the conversion rate of the target product.

[0139] Test Example 3: Room Temperature Mechanical Properties Test

[0140] Experimental description:

[0141] This test aims to systematically evaluate the comprehensive mechanical properties of the brake disc prepared by this invention at room temperature, mainly including three key indicators: hardness, tensile strength, and impact toughness.

[0142] Brinell hardness test;

[0143] An HBE-3000A electronic Brinell hardness tester was used, employing a 10mm diameter cemented carbide ball indenter. A test force of 29.4kN was applied, with a holding time of 15 seconds. The test sites were the friction surfaces of the casting samples from each group, after the surface machining layer was removed. To ensure data reliability, five non-interfering test points were selected on each sample, and their average value was calculated as the final Brinell hardness value (HBW).

[0144] Tensile strength test:

[0145] Test bars were radially cut from the flange area of ​​each group of castings (this area has a moderate cooling rate and can represent the properties of the casting itself), and machined into standard circular tensile specimens with a gauge length of 50 mm and a diameter of 10 mm. Using a WDW-100 microcomputer-controlled electronic universal testing machine, the specimens were stretched at a constant tensile rate of 2 mm / min at room temperature until fracture. The equipment software automatically recorded and calculated the tensile strength (Rt) of the material. m ).

[0146] Impact toughness test;

[0147] Samples were taken from the same location as the tensile specimens and machined into U-notch standard impact specimens measuring 10mm × 10mm × 55mm. The specimens were tested using a JB-300B pendulum impact testing machine, and the work consumed in the pendulum impacting the specimen and causing it to fracture was recorded, i.e., the impact absorption work (A). KU ).

[0148] The experimental data are shown in Table 3;

[0149] Table 3. Results of room temperature mechanical properties of samples in each group;

[0150] sample Brinell hardness (HBW) Tensile strength (MPa) Impact absorption energy (J) Example 1 246 343 9.3 Example 2 231 318 9.8 Example 3 262 367 8.1 Example 4 243 338 9.5 Comparative Example 1 207 262 11.2 Comparative Example 2 238 291 4.1 Comparative Example 3 216 283 10.5 Comparative Example 4 249 315 7.2 Comparative Example 5 239 308 7.8

[0151] Summarize

[0152] First, compared to the baseline Comparative Example 1, Examples 1-4 showed a significant improvement in both Brinell hardness and tensile strength. Taking Example 1 as an example, its hardness and tensile strength increased by 18.8% and 30.9%, respectively. This improvement is mainly attributed to the in-situ generated, dispersed TiB2 ceramic hard phase. These microparticles, acting as reinforcements, effectively hindered the movement of dislocations in the matrix and bore part of the load, thereby producing a significant dispersion strengthening effect.

[0153] Secondly, the data from Comparative Example 2 (boron only) is key to understanding the inventiveness of this invention. Although its hardness increased, its impact absorption energy dropped sharply to 4.1 J, exhibiting severe brittleness. This confirms that without titanium pretreatment, boron readily forms coarse network or needle-like borides, disrupting the matrix continuity and thus destructively affecting the material's toughness. This invention, through a titanium-first, boron-later process, successfully suppressed the formation of harmful phases, highlighting the necessity of the Ti-B synergistic effect. Meanwhile, the performance of Comparative Example 3 (titanium only) showed no substantial improvement compared to the baseline, further demonstrating that titanium alone cannot achieve the strengthening effect of this invention.

[0154] Furthermore, another advantage of the present invention can be observed by comparing it with Comparative Example 4 (chromium-added). Comparative Example 4 also achieved high hardness through conventional alloying methods, but its tensile strength was lower than that of Example 1, and its impact toughness loss was more severe. This indicates that the in-situ particle reinforcement path adopted in the present invention can better balance the toughness of the material while improving strength and hardness, achieving a better strength-toughness balance.

[0155] Finally, the comparison between Example 1 and Comparative Example 5 (without secondary inoculation) clarifies the importance of the composite inoculation process. Comparative Example 5, with the same core components as Example 1, showed a significant decrease in both tensile strength and impact toughness. This demonstrates that the unique secondary inoculation step (bismuth oxysilane + gadolinium silicon) of this invention plays a crucial role in optimizing graphite morphology, refining eutectic clusters, and eliminating casting defects, and is a necessary technical step to ensure the material achieves excellent overall performance.

[0156] Test Example 4: High Temperature Mechanical Property Test

[0157] Experimental description:

[0158] This test aims to evaluate the core mechanical properties of the brake disc prepared according to this invention under high-temperature conditions, which is crucial for simulating the material's performance during actual braking. The test includes two parts: high-temperature hardness and high-temperature wear.

[0159] The high-temperature hardness test was conducted using a high-temperature hardness tester under an inert gas protective environment to prevent oxidation of the samples at the test temperature. The test samples were Examples 1-4 and Comparative Examples 1, 4, and 5. A block-shaped sample measuring 20mm × 20mm × 10mm was placed in a heating furnace and heated to 600℃ at a rate of 10℃ / min, and held at this temperature for 20 minutes to ensure uniform temperature between the core and surface of the sample. Subsequently, a load was applied using a tungsten carbide ball indenter at 600℃, and the hot Brinell hardness value was measured.

[0160] The high-temperature wear performance test was conducted using an MMU-10G high-temperature friction and wear testing machine, employing a pin-disc grinding method. Pin-shaped specimens (Φ6mm × 12mm) were machined from the casting samples of Examples 1-4 and Comparative Examples 1, 4, and 5. The mating disc was made of high-chromium cast iron (HRC>60). Before testing, the initial mass of the pin-shaped specimens was weighed using an electronic balance with an accuracy of 0.1mg. The specimens were mounted on the testing machine, and the heating program was started to bring the contact area temperature of the friction pair to and stabilize at 600℃. The test parameters were set as follows: normal load 200N, rotational speed 400r / min, and wear time 60 minutes. After the test, the specimens were allowed to cool to room temperature, and the mass loss value was calculated again.

[0161] The experimental data are shown in Table 4:

[0162] Table 4. High-temperature mechanical property test results of samples in each group:

[0163] sample High temperature hardness (HBW, 600℃) Mass loss (mg) Example 1 185 31.6 Example 2 172 38.8 Example 3 198 24.3 Example 4 181 33.5 Comparative Example 1 115 89.4 Comparative Example 4 163 45.1 Comparative Example 5 175 39.2

[0164] Summarize;

[0165] First, the samples from Examples 1-4, at a high temperature of 600℃, maintained a higher level of hot hardness compared to the baseline Comparative Example 1, while the mass loss was reduced by more than 60%. The core reason for this result is that the TiB2 ceramic phase generated in situ in this invention possesses extremely high thermal stability and high-temperature hardness. When the matrix metal softens significantly due to high temperatures, these dispersed hard particles can effectively bear external loads, acting as a "skeleton" support, suppressing plastic deformation of the matrix, and resisting cutting and adhesion of the friction pair as a wear-resistant phase. This results in the material exhibiting excellent high-temperature strength and wear resistance as a whole.

[0166] Secondly, the comparison with Comparative Example 4 (with added chromium) further highlights the superiority of the present invention. Although the addition of chromium can also form carbides and improve the hot hardness of the material, the test results show that its actual effect (163 HBW, 45.1 mg) is still significantly inferior to that of Example 1 (185 HBW, 31.6 mg). This indicates that the TiB2 ceramic phase generated by the present invention has better strengthening and wear resistance at high temperatures than the carbide phase formed by traditional chromium alloying.

[0167] Finally, compared with Example 1, Comparative Example 5 (without secondary inoculation) showed a slight decrease in both high-temperature hardness and wear resistance. This indicates that a healthy matrix structure is crucial for the reinforcing phase to function effectively. The secondary inoculation step of this invention optimizes the matrix structure, enabling the matrix to more effectively encapsulate and fix TiB2 particles, thus slowing down the exfoliation of reinforcing particles during high-temperature friction and improving the overall high-temperature performance of the material.

Claims

1. A brake disc, characterized in that, It consists of the following chemical components by mass percentage; Iron 92.73-93.70%, Carbon 3.70-3.90%, Silicon 1.50-1.80%, Manganese 0.65-0.75%, Titanium 0.015-0.03%, Boron 0.07-0.14%, Copper 0.25-0.35%, Tin 0.03-0.05%, Phosphorus ≤0.05%, and Sulfur ≤0.08%; The titanium and boron are dispersed in the cast iron matrix of the brake disc in the form of in-situ generated titanium diboride reinforcing phase; The cast iron matrix of the brake disc has a pearlitic structure, and the graphite morphology is type A graphite. The preparation process includes the following steps; S1. Smelting and Composition Adjustment: Melt scrap steel and recycled materials to adjust the basic chemical composition; S2, In-situ composite reaction: At a preset temperature, titanium-iron alloy is first added to molten iron and stirred, followed by the addition of boron-iron alloy and stirring, so as to generate a reinforcing phase in situ in molten iron; S3. Composite Inoculation Treatment: The molten iron that has completed the in-situ composite reaction is subjected to primary inoculation, secondary inoculation and in-flow inoculation treatment in sequence; S4. Shaping and Casting: Casting is performed using the prepared sand mold; S5. Post-treatment: Cooling, cleaning, and low-temperature annealing of the castings; In step S2, the in-situ composite reaction is carried out at a temperature of 1535℃-1545℃; after adding the ferro-titanium alloy, the mixture is electromagnetically stirred for 3-4 minutes; then, the ferro-boron alloy is added, and the mixture is strongly electromagnetically stirred for 45-60 seconds. The specific steps of the combined incubation treatment in step S3 are as follows: First inoculation: A barium silicon inoculant, accounting for 0.3% of the total weight of the molten iron, is laid at the bottom of the ladle; Secondary inoculation: After pouring out the hot metal, add 0.15% to 0.2% of bismuth oxysilane inoculant and 0.15% to 0.2% of gadolinium silane inoculant, which account for 0.15% to 0.2% of the total weight of the molten iron, to the ladle; In-flow inoculation: During casting, add silicon-zirconium inoculant accounting for 0.1% of the total weight of molten iron.

2. A brake disc according to claim 1, characterized in that, The bismuth-silicon oxide inoculant used in the secondary inoculation has the following chemical composition by weight percentage: silicon 65.0%–72.0%, bismuth 1.0%–3.0%, calcium 0.5%–1.5%, with the balance being iron and trace oxides; the gadolinium silicon inoculant has the following chemical composition by weight percentage: silicon 55.0%–65.0%, gadolinium 4.0%–6.0%, calcium 0.5%–1.5%, with the balance being iron.

3. A brake disc according to claim 1, characterized in that, In step S1, the basic chemical composition of the molten iron is adjusted to: carbon 3.65%–3.75%, silicon 1.50%–1.80%, manganese 0.65%–0.75%, copper 0.25%–0.35%, tin 0.03%–0.05%, phosphorus ≤0.05%, sulfur ≤0.08%, with the balance being iron.

4. A brake disc according to claim 1, characterized in that, In step S4, the pouring is carried out at a pouring temperature of 1450°C.

5. A brake disc according to claim 1, characterized in that, The low-temperature annealing process in step S5 is as follows: the temperature is raised to 560℃-580℃ at a rate of 100℃ / h, held for 2.5 to 3 hours, and then cooled in the furnace at a rate of 40℃ / h to below 200℃ before being removed from the furnace.

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