Grey cast iron material applied to brake drum and casting method

Abstract

This invention discloses a gray cast iron material and casting method for use in brake drums, relating to the technical field of gray cast iron materials. The gray cast iron material of this invention is composed of the following components by mass percentage: C 3.5%-3.7%, Si 1.8%-2.0%, Mn 0.8%-1.0%, S 0.06%-0.12%, P≤0.12%, Cu 0.18%-0.25%, Cr 0.25%-0.4%, composite modifier 0.05%-0.09%, with the balance being Fe; wherein the mass ratio of C to Si is 1:0.52-0.58; and the mass ratio of Cu to Cr is 1:1.3-2. The specific casting method and the introduction of the composite modifier, as well as the specific ratio of Cu to Cr, of this invention simultaneously improve the strength, thermal fatigue resistance, high-temperature stability, and impact resistance of the gray cast iron material.

Description

Technical Field

[0001] This invention relates to the field of gray cast iron materials technology, specifically to a gray cast iron material and casting method for use in brake drums. Background Technology

[0002] The brake drum is a core load-bearing component in the automotive braking system, responsible for converting the vehicle's kinetic energy into heat energy and achieving deceleration or stopping. Its performance and stability directly affect driving safety, especially in the commercial vehicle sector, where the reliability requirements for brake drums are even more stringent under harsh conditions such as heavy loads, long downhill slopes, and high-frequency braking. The choice of brake drum material directly determines its performance and safety level. The main material for brake drums is gray cast iron, with HT250 and GTHT200 being the most widely used. HT250, with its high tensile strength and hardness, can meet the load-bearing requirements of heavy-load conditions in commercial vehicles and is widely used in heavy-load scenarios such as cargo transportation. GTHT200, on the other hand, has superior resistance to thermal fatigue and can withstand the repeated temperature shocks caused by high-frequency braking, making it more suitable for scenarios with frequent braking, such as mountainous roads and urban delivery.

[0003] However, gray cast iron materials still have the following performance shortcomings in practical applications: First, it is difficult to balance strength and thermal fatigue resistance. Although HT250 meets the strength requirements, it is prone to thermal cracking under long-term high-temperature braking, while GTHT200 has excellent thermal fatigue resistance but cannot withstand the mechanical impact under heavy loads. Second, it lacks high-temperature stability. The temperature of the brake drum can rise to several hundred degrees Celsius during operation. Gray cast iron is prone to softening at this temperature, leading to increased brake clearance and reduced braking efficiency. Third, it has poor impact resistance. The brittle nature of gray cast iron makes it prone to stress concentration, which can induce cracking. Therefore, the compatibility of strength and thermal fatigue resistance, high-temperature stability, and impact resistance of existing gray cast iron materials used in brake drums still need to be improved. Summary of the Invention

[0004] The purpose of this invention is to provide a gray cast iron material for brake drums and a casting method thereon, thereby solving the following technical problems:

[0005] The existing gray cast iron materials used in brake drums still have problems with the compatibility of strength and thermal fatigue resistance, high temperature stability, and impact resistance.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A gray cast iron material for use in brake drums, the gray cast iron material being composed of the following components by mass percentage: C 3.5%-3.7%, Si 1.8%-2.0%, Mn 0.8%-1.0%, S 0.06%-0.12%, P≤0.12%, Cu 0.18%-0.25%, Cr 0.25%-0.4%, composite modifier 0.05%-0.09%, with the balance being Fe;

[0008] The mass ratio of C to Si is 1:0.52-0.58;

[0009] The mass ratio of Cu to Cr is 1:1.3-2;

[0010] The composite modifier is composed of Nd and Y in a mass ratio of 1:0.8-1.2.

[0011] Preferably, the preparation method of the composite deteriorator is as follows:

[0012] A1: Mix Nd and Y, then add anhydrous ethanol and mix at 30-40 r / min for 15-20 min to obtain a mixed raw material;

[0013] A2: The mixed raw materials are fed into a vacuum induction melting furnace for melting treatment, then poured into a copper mold at 200-300℃ and cooled at 80-100℃ / s, followed by crushing and sieving to obtain a 100-200 mesh composite modifier.

[0014] Preferably, the mass ratio of Nd, Y, and anhydrous ethanol in A1 is 1:0.8-1.2:0.2-0.4.

[0015] Preferably, the smelting process described in A2 is as follows: the temperature is raised to 1600-1650℃ at a heating rate of 5-8℃ / s under a furnace pressure of 3-5Pa, and held for 30-45 minutes, during which electromagnetic stirring is performed once every 10 minutes, and each stirring lasts for 3-5 minutes.

[0016] A casting method for gray cast iron material used in brake drums includes the following steps:

[0017] S1: After mixing old sand, new sand and molding sand powder into molding sand, the mixture is then subjected to molding treatment to obtain molding sand;

[0018] S2: Mix and melt pig iron, scrap steel, and recycled materials, then add a carbonizer to adjust the C content, then perform overheat treatment and add a slag remover to remove slag, then add bentonite, pig iron, ferrosilicon, ferromanganese, silicon carbide, copper, scrap steel, steel shot, and composite modifier, mix and melt, and then tap out of the furnace to obtain molten iron.

[0019] S3: After inoculation and casting of molten iron, the flowing iron is removed, and after cooling and sand removal, post-processing is carried out to obtain gray cast iron material for use in brake drums.

[0020] Preferably, the method for preparing molding sand in S1 is as follows: first, perform a wet mixing for 20-35 seconds, then perform a second wet mixing for 20-35 seconds, with a total cycle time of 130-140 seconds.

[0021] Preferably, the mass ratio of pig iron, scrap steel, and recycled material in S2 is 3:5:2;

[0022] The overheating temperature described in S2 is 1620-1700℃, and the overheating time is 30-50min;

[0023] The temperature of the molten iron described in S2 is 1560-1570℃.

[0024] Preferably, the inoculation and casting process described in S3 is as follows: molten iron is added to a transfer ladle and an inoculant of 0.2% of the total mass of molten iron is added for primary inoculation. Then, the molten iron is transferred to a casting ladle and an inoculant of 0.3% of the total mass of molten iron is added for secondary inoculation. Then, the ladle is slag-removed. Finally, the molten iron and an inoculant of 0.1% of the total mass of molten iron are poured together into the mold cavity for in-flow inoculation. The pouring time is 10-12 minutes and the pouring temperature is 1380-1410℃.

[0025] Preferably, the inoculant in S3 is a barium silicon inoculant, composed of the following components by mass percentage: Si 40%-45%, Ba 4%-6%, with the balance being Fe.

[0026] Preferably, the post-processing described in S3 is as follows: after separating the casting from the riser and gating system, the casting is picked up and placed by a robotic arm, then cooled by a chain conveyor for 2-6 hours, shot blasted for 4-7 minutes, then the casting is ground until there are no defects such as flash, missing material, or excess material, then the flash and riser residue are automatically ground, and finally the inner surface of the casting is sprayed.

[0027] The beneficial effects of this invention are:

[0028] This invention provides a gray cast iron material for use in brake drums and a casting method thereof. The invention improves the strength, thermal fatigue resistance, high temperature stability and impact resistance of gray cast iron material through the following methods.

[0029] (1) The specific Cr / Cu ratio of this invention can significantly increase the pearlite content and make the lamellar distribution more uniform, making it less likely to precipitate local hard and brittle phases under normal cooling conditions. Neither Cr nor Cu directly participates in graphite nucleation. Their synergistic effect can optimize the matrix structure balance. Combined with Nd-Y modifiers and inoculation processes, it can further improve the roundness of graphite and avoid graphite coarsening or deformity caused by the addition of a single element. Within the specific ratio and content range of this invention, Cr and Cu mainly exist in solid solution in ferrite and pearlite. Under normal cooling conditions, it is not easy for obvious Cr-C compounds or Cu-rich phases to precipitate. The matrix will not be split due to hard second-phase particles, effectively improving strength and hardness. At the same time, Cu alleviates the embrittlement effect of Cr and effectively improves impact toughness. Cr can inhibit the decomposition of pearlite at high temperature, while Cu maintains the high-temperature strength of ferrite through solid solution strengthening. The synergistic effect of the two can effectively avoid high-temperature softening and improve the retention rate of tensile strength at high temperature. Under the specific proportions of this invention, the pearlite is uniformly refined, which can effectively reduce thermal stress concentration, improve matrix toughness, reduce the microcrack propagation rate, and enhance oxide film stability, preventing crack initiation caused by oxidation at high temperatures, thereby improving resistance to thermal fatigue. At this proportion, the fluidity of the molten iron does not change significantly. Because the total Cr and Cu content is low and does not exceed the alloying upper limit of gray cast iron, it will not lead to increased molten iron viscosity or incomplete filling defects. The casting shrinkage rate is stable at 1.2%-1.5%, and the shrinkage stress is uniformly distributed. Combined with optimized molding sand processing, this can effectively reduce the crack defect rate. If the proportions deviate, uneven shrinkage stress will lead to an increased risk of localized cracking.

[0030] (2) In the composite modifier of this invention, Nd and Y are both surface-active elements that can be adsorbed at the graphite crystallization front, reducing the graphite nucleation work and inhibiting excessive graphite growth in a certain direction. The synergy of the two can transform graphite from coarse and long flakes to short, fine, and round flakes. Rare earth elements can refine austenite grains, thereby reducing the interlamellar spacing of pearlite in subsequent transformations. At the same time, Nd and Y have a strong affinity for S and O, and can preferentially form fine rare earth sulfides and oxides, avoiding the formation of coarse FeS and FeO inclusions, thus playing a role in purifying molten iron. The refinement of graphite flakes weakens the effect of cutting the matrix; the increase in pearlite content refines the flakes, improving the strength of the matrix itself; the reduction of harmful inclusions increases the resistance to crack propagation, effectively improving the hardness and tensile strength of gray cast iron. The improvement in graphite roundness weakens the stress concentration effect; the refinement of harmful inclusions lengthens the crack propagation path, thereby effectively improving the impact toughness. Refined and uniformly distributed graphite effectively improves thermal conductivity; enhanced pearlite stability makes the microstructure less prone to softening at high temperatures; refined inclusions reduce the likelihood of microcracks due to thermal expansion differences during thermal cycling, thus effectively increasing resistance to thermal fatigue. Rare earth sulfides and oxide inclusions can pin grain boundaries within a certain temperature range, hindering grain growth, maintaining microstructural stability, and effectively improving the material's high-temperature stability. Refined graphite slightly improves the fluidity of molten iron, reducing defects such as incomplete filling and cold shuts; reduced harmful inclusions lower the rate of casting cracks and porosity defects, improving production stability.

[0031] (3) The three-stage addition of the inoculation process in this invention ensures that there are sufficient nucleation cores throughout the entire process from tapping to casting, avoiding insufficient nucleation caused by temperature drop in the later stage, and preventing inoculation decline. The core function is to refine graphite and improve the uniformity and distribution of graphite nucleation. The continuous replenishment of graphite nucleation cores can further optimize the graphite morphology (more refined, higher roundness) and help increase the pearlite content and refine the interlamellar spacing. This improves the hardness, tensile strength, impact resistance, thermal fatigue resistance, pearlite stability at high temperatures, and the bonding force between graphite and the matrix of gray cast iron.

[0032] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The embodiments described below 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1: The gray cast iron material used in the brake drum is composed of the following components by mass percentage: C 3.64%, Si 2.0%, Mn 0.9%, S 0.09%, P 0.11%, Cu 0.25%, Cr 0.4%, composite modifier 0.07%, and the balance being Fe;

[0035] The mass ratio of C to Si is 1:0.55, and the mass ratio of Cu to Cr is 1:1.6.

[0036] A casting method for gray cast iron material used in brake drums is as follows:

[0037] S1: After mixing old sand, new sand, and molding sand powder, the mixture is subjected to a pressure of 110 N / cm. 2 The molding process yields molding sand;

[0038] S2: Mix and melt pig iron, scrap steel, and recycled materials, then add a carbonizer to adjust the C content, then perform overheat treatment and add a slag remover to remove slag, then add bentonite, pig iron, ferrosilicon, ferromanganese, silicon carbide, copper, scrap steel, steel shot, and composite modifier, mix and melt, and then tap out of the furnace to obtain molten iron at 1565℃.

[0039] S3: After inoculating and casting the molten iron, remove the flowing iron from the surface of the sand box, cool it for 2-5 hours, and then remove the sand (separating the sand box and the casting). After further processing, the gray cast iron material used in brake drums is obtained.

[0040] The molding sand is prepared by: using an online monitoring input mode, first performing a 30-second wet mixing, then performing a 30-second wet mixing, with a total cycle time of 135 seconds.

[0041] The molding sand has a compaction rate of 35%, a wet compressive strength of 0.16 MPa, a moisture content of 3.2%, a molding sand temperature of 27℃ during molding, an air permeability of 135, an effective clay content of 8.1%, an effective coal powder content of 4%, a mud content of 11.5%, an average fineness index of 60, a crushing index of 80%, a hot and wet tensile strength of 5 kPa, a gas generation rate of 17 mL / s, and a hardness of 93 HB.

[0042] The inoculation and casting process is as follows: molten iron is added to a transfer ladle and an inoculant of 0.2% of the total mass of molten iron is added for primary inoculation. Then, the molten iron is transferred to a casting ladle and an inoculant of 0.3% of the total mass of molten iron is added for secondary inoculation. The ladle is then slag-removed. Finally, the molten iron and an inoculant of 0.1% of the total mass of molten iron are poured together into the mold cavity for in-flow inoculation. The pouring time is 11 minutes and the pouring temperature is 1395℃. The inoculant is a barium silicon inoculant, whose main components are 43% Si, 5% Ba, and the balance Fe.

[0043] The post-processing is as follows: after separating the casting from the gating and riser, the casting is picked up and placed by a robotic arm, then cooled by a chain cooling for 4 hours, shot blasted for 6 minutes, and then the casting is ground until there are no defects such as flash, missing material, or excess material. Subsequently, the flash and riser residue are automatically ground, and finally the inner surface of the casting is sprayed.

[0044] The preparation method of the composite modifier is as follows:

[0045] A1: Take neodymium (Nd) blocks and yttrium (Y) blocks with a purity ≥99.9% and crush them into granules of 5-10mm. After removing the surface oxide scale, mix 1g of Nd and 1g of Y, add 0.3g of anhydrous ethanol and mix at 35r / min for 18min to obtain the mixed raw material.

[0046] A2: The mixed raw materials are fed into a vacuum induction melting furnace, and the furnace pressure is evacuated to 4Pa. Then, the temperature is increased to 1630℃ at a heating rate of 6℃ / s and held for 37 minutes. During this period, electromagnetic stirring is performed every 10 minutes (each stirring lasts for 4 minutes). The molten alloy is then injected into a copper mold preheated to 250℃ through a guide pipe and rapidly cooled by air cooling at 90℃ / s. Subsequently, it is crushed and sieved to obtain a 100-200 mesh composite modifier. The induction coil frequency of the medium vacuum induction melting furnace is 1250Hz.

[0047] Example 2: The gray cast iron material used in the brake drum is composed of the following components by mass percentage: C 3.7%, Si 1.92%, Mn 0.8%, S 0.06%, P 0.1%, Cu 0.19%, Cr 0.25%, composite modifier 0.05%, and the balance being Fe;

[0048] The mass ratio of C to Si is 1:0.52, and the mass ratio of Cu to Cr is 1:1.3.

[0049] A casting method for gray cast iron material used in brake drums is as follows:

[0050] S1: After mixing old sand, new sand, and molding sand powder, the mixture is subjected to a pressure of 60 N / cm. 2 The molding process yields molding sand;

[0051] S2: Mix and melt pig iron, scrap steel, and recycled materials, then add a carbonizer to adjust the C content, then perform overheat treatment and add a slag remover to remove slag, then add bentonite, pig iron, ferrosilicon, ferromanganese, silicon carbide, copper, scrap steel, steel shot, and composite modifier, mix and melt, and then tap out of the furnace to obtain molten iron at 1560℃.

[0052] S3: After inoculating and casting the molten iron, remove the flowing iron from the surface of the sand box, cool it for 2-5 hours, and then remove the sand (separating the sand box and the casting). After further processing, the gray cast iron material used in brake drums is obtained.

[0053] The molding sand is prepared by: using an online monitoring input mode, first performing a 20-second wet mixing, then performing a 20-second wet mixing, with a total cycle time of 130 seconds.

[0054] The molding sand has a compaction rate of 32%, a wet compressive strength of 0.14 MPa, a moisture content of 2.9%, a molding sand temperature of 15℃ during molding, an air permeability of 120, an effective clay content of 7.7%, an effective coal powder content of 3.2%, a mud content of 10.5%, an average fineness index of 55, a crushing index of 75%, a hot and wet tensile strength of 4.5 kPa, a gas generation rate of 13 mL / s, and a hardness of 90 HB.

[0055] The inoculation and casting process is as follows: molten iron is added to a transfer ladle and an inoculant of 0.2% of the total mass of molten iron is added for primary inoculation. Then, the molten iron is transferred to a casting ladle and an inoculant of 0.3% of the total mass of molten iron is added for secondary inoculation. The ladle is then slag-removed. Finally, the molten iron and an inoculant of 0.1% of the total mass of molten iron are poured together into the mold cavity for in-flow inoculation. The pouring time is 10 minutes and the pouring temperature is 138℃. The inoculant is a barium silicon inoculant, whose main components are 40% Si, 4% Ba, and the balance is Fe.

[0056] The post-processing is as follows: after separating the casting from the gating and riser, the casting is picked up and placed by a robotic arm, then cooled by a chain conveyor for 2 hours, shot blasted for 4 minutes, and then the casting is ground until there are no defects such as flash, missing material, or excess material. Subsequently, the flash and riser residue are automatically ground, and finally the inner surface of the casting is sprayed.

[0057] The preparation method of the composite modifier is as follows:

[0058] A1: Take neodymium (Nd) blocks and yttrium (Y) blocks with a purity ≥99.9% and crush them into granules of 5-10mm. After removing the surface oxide scale, mix 1g Nd with 0.8g Y, then add 0.2g anhydrous ethanol and mix at 30r / min for 15min to obtain the mixed raw material.

[0059] A2: The mixed raw materials are fed into a vacuum induction melting furnace, and the furnace pressure is evacuated to 3Pa. Then, the temperature is increased to 1600℃ at a rate of 5℃ / s and held for 30 minutes. During this period, electromagnetic stirring is performed every 10 minutes (each stirring lasts for 3 minutes). The molten alloy is then injected into a copper mold that has been preheated to 200℃ through a guide pipe. It is then rapidly cooled by air cooling at 80℃ / s, followed by crushing and sieving to obtain a 100-200 mesh composite modifier. The induction coil frequency of the medium vacuum induction melting furnace is 1000Hz.

[0060] Example 3: The gray cast iron material used in the brake drum is composed of the following components by mass percentage: C 3.5%, Si 2.0%, Mn 1.0%, S 0.12%, P 0.12%, Cu 0.18%, Cr 0.36%, composite modifier 0.09%, and the balance being Fe;

[0061] The mass ratio of C to Si is 1:0.58, and the mass ratio of Cu to Cr is 1:2.

[0062] A casting method for gray cast iron material used in brake drums is as follows:

[0063] S1: After mixing old sand, new sand and molding sand powder, molding sand is subjected to molding treatment with a pressure of 60-160 N / cm² to obtain molding sand;

[0064] S2: Mix and melt pig iron, scrap steel, and recycled materials, then add a carbonizer to adjust the C content, then perform overheat treatment and add a slag remover to remove slag, then add bentonite, pig iron, ferrosilicon, ferromanganese, silicon carbide, copper, scrap steel, steel shot, and composite modifier, mix and melt, and then tap out of the furnace to obtain molten iron at 1570℃.

[0065] S3: After inoculating and casting the molten iron, remove the flowing iron from the surface of the sand box, cool it for 2-5 hours, and then remove the sand (separating the sand box and the casting). After further processing, the gray cast iron material used in brake drums is obtained.

[0066] The molding sand is prepared by: using an online monitoring input mode, first performing a 35-second wet mixing, then performing a 20-35-second wet mixing, with a total cycle time of 140 seconds;

[0067] The molding sand has a compaction rate of 37%, a wet compressive strength of 0.18 MPa, a moisture content of 3.4%, a molding sand temperature of 40℃ during molding, an air permeability of 150, an effective clay content of 8.5%, an effective coal powder content of 4.8%, a mud content of 12.5%, an average fineness index of 65, a crushing index of 85%, a hot and wet tensile strength of 5 kPa, a gas generation rate of 21 mL / s, and a hardness of 95 HB.

[0068] The inoculation and casting process is as follows: molten iron is added to a transfer ladle and an inoculant of 0.2% of the total mass of molten iron is added for primary inoculation. Then, the molten iron is transferred to a casting ladle and an inoculant of 0.3% of the total mass of molten iron is added for secondary inoculation. The ladle is then slag-removed. Finally, the molten iron and an inoculant of 0.1% of the total mass of molten iron are poured together into the mold cavity for in-flow inoculation. The pouring time is 12 minutes and the pouring temperature is 1410℃. The inoculant is a barium silicon inoculant, whose main components are 45% Si, 6% Ba, and the balance is Fe.

[0069] The post-processing is as follows: after separating the casting from the gating and riser, the casting is picked up and placed by a robotic arm, then cooled by a chain cooling for 6 hours, shot blasted for 7 minutes, and then the casting is ground until there are no defects such as flash, missing material, or excess material. Subsequently, the flash and riser residue are automatically ground, and finally the inner surface of the casting is sprayed.

[0070] The preparation method of the composite modifier is as follows:

[0071] A1: Take neodymium (Nd) blocks and yttrium (Y) blocks with a purity ≥99.9% and crush them into granules of 5-10mm. After removing the surface oxide scale, mix 1g Nd with 1.2g Y, add 0.4g anhydrous ethanol and mix at 40r / min for 20min to obtain the mixed raw material.

[0072] A2: The mixed raw materials are fed into a vacuum induction melting furnace, and the furnace pressure is evacuated to 5Pa. Then, the temperature is increased to 1650℃ at a heating rate of 8℃ / s and held for 45min. During this period, electromagnetic stirring is performed every 10min (each stirring lasts for 5min). The molten alloy is then injected into a copper mold preheated to 300℃ through a guide pipe and rapidly cooled at 100℃ / s using air cooling. Subsequently, it is crushed and sieved to obtain a 100-200 mesh composite modifier. The induction coil frequency of the medium vacuum induction melting furnace is 1500Hz.

[0073] Comparative Example 1:

[0074] Compared with Example 1, this comparative example only replaces "the mass ratio of Cu to Cr is 1:1.6" with "the mass ratio of Cu to Cr is 1:1". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, gray cast iron material applied to brake drum is obtained.

[0075] Comparative Example 2:

[0076] Compared with Example 1, this comparative example only did not add the "composite modifier" in the preparation process of S2. All other steps and parameters were the same, and will not be repeated here. The final result was gray cast iron material for use in brake drums.

[0077] Comparative Example 3:

[0078] Compared with Example 1, this comparative example differs only in the inoculation and casting process of S3: "The molten iron was added to the transfer ladle and 0.2% inoculant was added for the first inoculation, then the molten iron was transferred to the ladle and 0.3% inoculant was added for the second inoculation, then the ladle was slag-removed, and finally the molten iron and 0.1% inoculant were poured into the mold cavity for in-flow inoculation, with a pouring time of 10 minutes and a pouring temperature of 1380°C;" is replaced with "The molten iron was added to the transfer ladle, then the molten iron was transferred to the ladle containing 0.6% inoculant for inoculation, then the ladle was slag-removed, and finally the molten iron was poured into the mold cavity, with a pouring time of 10 minutes and a pouring temperature of 1380°C;". The remaining steps and parameters are the same, and will not be repeated in this comparative example. The final result is gray cast iron material used in brake drums.

[0079] Performance testing:

[0080] Hardness determination:

[0081] Referring to GB / T 231.1-2018 standard, the Brinell hardness of the gray cast iron materials prepared in Examples 1-3 and Comparative Examples 1-3 of this invention was measured, and the test results are shown in Table 1.

[0082] Determination of tensile strength:

[0083] Referring to GB / T 228.1-2021 standard, the tensile strength (MPa) of the gray cast iron materials prepared in Examples 1-3 and Comparative Examples 1-3 of this invention was determined, and the test results are shown in Table 1.

[0084] Determination of resistance to thermal fatigue:

[0085] Referring to GB / T 37336-2019 (bench thermal fatigue test) standard, the number of braking cycles of the gray cast iron materials prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were determined, and the test results are shown in Table 1.

[0086] Stability determination:

[0087] Referring to GB / T 4338-2015 standard, the tensile strength retention rate (%) of the gray cast iron materials prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention at 300℃ was determined, and the test results are shown in Table 1.

[0088] Impact resistance testing:

[0089] Referring to GB / T 229-2007 standard, the impact strength (J / cm²) of the gray cast iron materials prepared in Examples 1-3 and Comparative Examples 1-3 of this invention was determined. 2The test results are shown in Table 1.

[0090] Table 1: Performance test results of Examples 1-3 and Comparative Examples 1-3

[0091] Data Analysis:

[0092] As can be seen from Table 1, the gray cast iron material for brake drums prepared in the embodiments of the present invention has excellent hardness, tensile strength, thermal fatigue resistance, high temperature stability, and impact resistance.

[0093] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A gray cast iron material for use in brake drums, characterized in that, The gray cast iron material is composed of the following components by mass percentage: C 3.5%-3.7%, Si 1.8%-2.0%, Mn 0.8%-1.0%, S 0.06%-0.12%, P≤0.12%, Cu 0.18%-0.25%, Cr 0.25%-0.4%, composite modifier 0.05%-0.09%, and the balance being Fe; The mass ratio of C to Si is 1:0.52-0.58; The mass ratio of Cu to Cr is 1:1.3-2; The composite modifier is composed of Nd and Y in a mass ratio of 1:0.8-1.

2.

2. The gray cast iron material for brake drums according to claim 1, characterized in that, The preparation method of the composite modifier is as follows: A1: Mix Nd and Y, then add anhydrous ethanol and mix at 30-40 r / min for 15-20 min to obtain a mixed raw material; A2: The mixed raw materials are fed into a vacuum induction melting furnace for melting treatment, then poured into a copper mold at 200-300℃ and cooled at 80-100℃ / s, followed by crushing and sieving to obtain a 100-200 mesh composite modifier.

3. The gray cast iron material for brake drums according to claim 2, characterized in that, The mass ratio of Nd, Y, and anhydrous ethanol in A1 is 1:0.8-1.2:0.2-0.

4.

4. The gray cast iron material for brake drums according to claim 2, characterized in that, The smelting process described in A2 is as follows: the temperature is raised to 1600-1650℃ at a heating rate of 5-8℃ / s under a furnace pressure of 3-5Pa, and held for 30-45 minutes. During this period, electromagnetic stirring is performed once every 10 minutes, and each stirring lasts for 3-5 minutes.

5. A casting method for gray cast iron material applied to brake drums according to any one of claims 1-4, characterized in that, Includes the following steps: S1: After mixing old sand, new sand and molding sand powder into molding sand, the mixture is then subjected to molding treatment to obtain molding sand; S2: Mix and melt pig iron, scrap steel, and recycled materials, then add a carbonizer to adjust the C content, then perform overheat treatment and add a slag remover to remove slag, then add bentonite, pig iron, ferrosilicon, ferromanganese, silicon carbide, copper, scrap steel, steel shot, and composite modifier, mix and melt, and then tap out of the furnace to obtain molten iron. S3: After inoculation and casting of molten iron, the flowing iron is removed, and after cooling and sand removal, post-processing is carried out to obtain gray cast iron material for use in brake drums.

6. The casting method for gray cast iron material applied to brake drums according to claim 5, characterized in that, The method for preparing molding sand described in S1 is as follows: first, perform a wet mixing for 20-35 seconds, then perform a second wet mixing for 20-35 seconds, with a total cycle time of 130-140 seconds.

7. The casting method for gray cast iron material applied to brake drums according to claim 5, characterized in that, The mass ratio of pig iron, scrap steel, and recycled material in S2 is 3:5:2; The overheating temperature described in S2 is 1620-1700℃, and the overheating time is 30-50min; The temperature of the molten iron described in S2 is 1560-1570℃.

8. The casting method for gray cast iron material applied to brake drums according to claim 5, characterized in that, The inoculation and casting process described in S3 is as follows: molten iron is added to a transfer ladle and an inoculant of 0.2% of the total mass of molten iron is added for primary inoculation. Then, the molten iron is transferred to a casting ladle and an inoculant of 0.3% of the total mass of molten iron is added for secondary inoculation. The ladle is then slag-removed. Finally, the molten iron and an inoculant of 0.1% of the total mass of molten iron are poured together into the mold cavity for in-flow inoculation. The pouring time is 10-12 minutes and the pouring temperature is 1380-1410℃.

9. The casting method for gray cast iron material applied to brake drums according to claim 5, characterized in that, The inoculant described in S3 is a barium silicon inoculant, composed of the following components by mass percentage: Si 40%-45%, Ba 4%-6%, with the balance being Fe.

10. The casting method for gray cast iron material applied to brake drums according to claim 5, characterized in that, The post-processing described in S3 is as follows: after separating the casting from the gating and riser, the casting is picked up and placed by a robotic arm, then cooled by a chain conveyor for 2-6 hours, shot blasted for 4-7 minutes, then the casting is ground until there are no defects such as flash, missing material, or excess material, then the flash and riser residue are automatically ground, and finally the inner surface of the casting is sprayed.

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