Thermal fatigue resistant commercial vehicle brake disc and preparation method thereof

Abstract

The invention relates to a thermal fatigue resistant commercial vehicle brake disc and a preparation method thereof. A preparation method of the thermal-fatigue-resistant commercial vehicle brake disc comprises the steps that S1, raw materials are added into a smelting furnace to be smelted, and molten iron is obtained; s2, a ferrosilicon inoculant, a nitriding agent, ferromolybdenum and tin are added into a transfer ladle, and molten iron is injected into the transfer ladle for primary inoculation treatment; the use amount of the ferrosilicon inoculant is 0.30-0.45% of the mass of the molten iron, the use amount of the nitriding agent is 0.60% of the mass of the molten iron, the use amount of the ferromolybdenum is 0.60-0.65% of the mass of the molten iron, and the use amount of the tin is 0.06% of the mass of the molten iron; and S3, the molten iron obtained after primary inoculation treatment is transferred into a pouring ladle, then the molten iron is poured into a cavity of a brake disc pouring mold, a silicon-strontium-zirconium inoculant is added along with the flow during pouring for secondary inoculation treatment, and the brake disc is obtained after cooling.

Description

Technical Field

[0001] This invention relates to the field of cast iron alloy technology, and in particular to a heat-resistant fatigue-resistant commercial vehicle brake disc and its preparation method. Background Technology

[0002] Commercial vehicles (especially medium and heavy-duty trucks and large buses) are core equipment in logistics transportation and engineering operations, and their driving safety directly depends on the reliability of their braking systems. Disc brakes, with their advantages of high heat dissipation efficiency, rapid braking response, and strong braking stability, have gradually replaced traditional drum brakes and become the mainstream configuration for commercial vehicle braking systems. These brakes mainly consist of core components such as brake discs, brake calipers, friction pads, and caliper brackets. Their working principle involves the brake calipers driving the friction pads to generate friction against the rotating brake disc, converting the kinetic energy of the commercial vehicle into heat energy, thereby achieving deceleration or stopping.

[0003] In actual commercial vehicle operation scenarios, heavy-load, long-distance continuous driving, and frequent braking on mountain slopes are extremely common, causing disc brakes to continuously withstand high-intensity friction loads. Data shows that when commercial vehicles brake downhill under heavy load, the surface temperature of the brake disc can quickly rise to 300-600 ℃, and even exceed 800 ℃ under extreme conditions. At the same time, the braking and releasing cycle during the braking process causes key components such as the brake disc and friction pads to undergo repeated heating and cooling thermal cycles, forming periodic thermal stress. Under these conditions, the fatigue resistance of commercial vehicle disc brakes becomes a significant weakness: existing brake discs are mostly made of gray cast iron, alloy cast iron, or ordinary alloy steel. In high-temperature environments above 300 ℃, the tensile strength, yield strength, and impact toughness of these materials will decrease significantly, and the thermal conductivity will gradually decrease with increasing temperature. Under the coupled effect of periodic thermal stress and mechanical stress, microcracks are easily generated on the surface of the brake disc. After the cracks expand radially or circumferentially, they can cause the brake disc to crack, chip, or even break, which seriously shortens the service life of the brake disc and poses a safety hazard of sudden braking failure.

[0004] The aforementioned problem of poor fatigue resistance at high temperatures has become a key bottleneck restricting the reliability, safety, and service life of commercial vehicle braking systems. As commercial vehicles develop towards heavier loads, higher speeds, and longer ranges, the thermal load on braking systems is further increasing, highlighting the performance deficiencies of existing disc brakes. There is an urgent need to develop a commercial vehicle disc brake that can maintain excellent fatigue resistance under high-temperature conditions to meet the actual needs of safe commercial vehicle operation. Summary of the Invention

[0005] The purpose of this invention is to disclose a heat-resistant fatigue-resistant commercial vehicle brake disc and its manufacturing method, so as to solve one or more technical problems existing in the prior art and provide at least one beneficial option or create conditions.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention aims to provide a method for manufacturing a heat-fatigue resistant commercial vehicle brake disc. The manufacturing method includes the following steps: S1. Add the raw materials to a smelting furnace and smelt them to obtain molten iron; the molten iron includes the following components: C: 3.40~3.45%, Si: 1.50~1.60%, Mn: 0.30~0.35%, P<0.03%, S: 0.08~0.12%, Cr: 0.25~0.30% and Cu 0.40~0.45%, with the balance being Fe and unavoidable impurities; S2. Add ferrosilicon inoculant, nitriding agent, ferromolybdenum and tin to the transfer bag, and pour molten iron into the transfer bag for the first inoculation treatment; the amount of ferrosilicon inoculant is 0.30~0.45% of the mass of molten iron, the amount of nitriding agent is 0.60% of the mass of molten iron, the amount of ferromolybdenum is 0.60~0.65% of the mass of molten iron, and the amount of tin is 0.06% of the mass of molten iron; S3. The molten iron after the first inoculation treatment is transferred to the casting ladle and then poured into the cavity of the brake disc casting mold. During the pouring process, silicon strontium zirconium inoculant is added along with the flow for a second inoculation treatment. After cooling, the brake disc is obtained.

[0007] The chemical composition of the ferrosilicon inoculant includes: Si: 72-80%, Al: 1.5%, Ca: 1.0%, Mn: 0.5%, Cr: 0.5%, P: 0.04%, S: 0.02%, C: 0.2%. The chemical composition of the strontium-zirconium inoculant includes: Si: 73-78%, Ca≤0.1%, Sr: 0.6-1.0%, Zr: 1.0-1.5%, Al≤0.5%.

[0008] In some embodiments of the first aspect of the present invention, the raw materials for the molten iron in step S1 include, by mass percentage, 60.00-80.00% scrap steel, 17.00-37.00% recycled material, 1.40-2.00% silicon carbide, 1.70-2.50% carbon raiser, 0.24-0.50% copper, 0.10-0.25% ferromanganese, 0.17-0.45% ferrochrome, and 0.15-0.20% ferrisulfide.

[0009] The scrap steel, calculated as a percentage by mass, includes: C: 0.001~0.5%; Si≤0.40%; Mn≤1.70%; P≤0.035%; S≤0.035%; Cr≤0.25%; Ti≤0.22%; Al≤0.05%; The remainder consists of Fe and impurities.

[0010] The carbon raiser comprises, by mass percentage: C≥99.5%; S≤0.03%; N≤0.03%; H≤0.03%; Ash content ≤0.30%; Volatile matter ≤0.20%.

[0011] The recycled material is waste from the gray cast iron gating system. Its composition is approximately: C: 3.2~3.5%, Si: 1.8~2.2%, Mn: 0.4~0.8%, P < 0.03%, S: 0.08~0.12%, Cr: 0.2~0.4%, Cu: 0.2~0.7%, Sn: 0.02~0.08%, Mo: 0.05~0.4%.

[0012] In some embodiments of the first aspect of the present invention, the order of raw material smelting in step S1 of the molten iron is as follows: 1) Add some scrap steel; 2) Add the carbon raiser, silicon carbide, and ferrochrome together; 3) Add the remaining scrap steel; 4) Add recycled material; 5) Add ferrous sulfate, copper and ferromanganese together.

[0013] In some embodiments of the first aspect of the present invention, the smelting furnace is a medium-frequency electric furnace with a smelting power of 6000~8000 kW.

[0014] In some embodiments of the first aspect of the present invention, after the raw materials of molten iron are completely melted, the mixture is kept at 1450~1500 ℃ for 10~15 min until molten iron slag is precipitated, and the furnace temperature is 1480~1500 ℃.

[0015] In some embodiments of the first aspect of the present invention, the nitriding agent is iron manganese nitride, and its chemical composition includes: Mn≥70%, N:7~10%, C<1%, Si<3.5%, P<0.3%, S<0.02%.

[0016] In some embodiments of the first aspect of the present invention, the Mo content of the molten iron in step S2 is 0.33~0.38%, and the N content is 0.011~0.013%.

[0017] In some embodiments of the first aspect of the present invention, slag removal is performed before the molten iron is transferred to the ladle in step S3. Slag removal refers to the step of removing solid / semi-solid slag, unmelted inoculant particles, and reaction products floating on the surface of the molten iron by mechanical or manual means.

[0018] In some embodiments of the first aspect of the present invention, the pouring temperature in step S3 is 1380~1400 ℃.

[0019] In some embodiments of the first aspect of the present invention, the amount of silicon-strontium-zirconium inoculant used in step S3 for in-flow inoculation is 10±5 g / s.

[0020] A second aspect of this invention aims to provide a heat-fatigue-resistant commercial vehicle brake disc. The brake disc is manufactured using the method described in the first aspect of this invention, and has a tensile strength ≥250 MPa and a hardness of 185~240 HB.

[0021] The brake disc manufacturing process of this invention incorporates ferromolybdenum and a nitriding agent. Molybdenum dissolves in the iron matrix to form a substitutional solid solution, while nitrogen forms an interstitial solid solution. Both work together to hinder dislocation movement, achieving a synergistic effect of dual solid solution strengthening. Molybdenum refines the pearlite lamellars, while nitrogen promotes the formation of dense pearlite; together, they reduce fatigue crack initiation sources. Furthermore, nitrogen atoms are continuously adsorbed onto the graphite growth front during inoculation and dissolved within the graphite, hindering the growth of flake graphite, reducing its aspect ratio, increasing its curvature, blunting its ends, increasing branching, refining its structure, and reducing its cutting effect on the matrix, further lowering the likelihood of the brake disc cracking during use. Attached Figure Description

[0022] Figure 1 Metallographic image of the brake disc obtained in Example 1; Figure 2 Metallographic image of the brake disc prepared in Comparative Example 1; Figure 3 These are before-and-after comparison photos of the brake disc thermal fatigue test in Examples 1 to 4. Detailed Implementation

[0023] A method for manufacturing a heat fatigue resistant commercial vehicle brake disc includes the following steps: S1. Add the raw materials to the smelting furnace and smelt to obtain molten iron. The raw materials for the molten iron include 60.00~80.00% scrap steel, 17.00~37.00% recycled material, 1.40~2.00% silicon carbide, 1.70~2.50% recarburizer, 0.24~0.50% copper, 0.10~0.25% ferromanganese, 0.17~0.45% ferrochrome, and 0.15~0.20% ferrisulfide. Using a 12 t medium-frequency furnace, the smelting sequence of the raw materials is as follows: 1) Add 2 t of scrap steel; 2) Add the recarburizer, silicon carbide, and ferrochrome together; 3) Add the remaining (5.2 t) of scrap steel; 4) Add the recycled material; 5) Add the ferrisulfide, copper, and ferromolybdenum together. Melting at 6000~8000 kW for about 70~80 minutes, after the raw materials are completely melted into molten iron and the melting temperature reaches 1450~1500 ℃, let it stand for 10~15 minutes.

[0024] S2. Add ferrosilicon inoculant, nitriding agent, ferromolybdenum, and tin to the transfer bag, and pour the molten iron into the transfer bag for the first inoculation treatment; the amount of ferrosilicon inoculant is 0.30~0.45% of the molten iron mass, the amount of nitriding agent is 0.60% of the molten iron mass, the amount of ferromolybdenum is 0.60~0.65% of the molten iron mass, and the amount of tin is 0.06% of the molten iron mass. The partial chemical composition of the above 10 batches of inoculated molten iron is shown in Table 2.

[0025] S3. The molten iron after the first inoculation treatment is transferred to the casting ladle and then poured into the cavity of the brake disc casting mold. During the pouring process, silicon strontium zirconium inoculant is added along with the flow for a second inoculation treatment. After cooling, the brake disc is obtained.

[0026] Because the elemental composition of scrap steel and recycled materials differs, it is necessary to test the chemical composition of molten iron. Table 1 shows the composition data of molten iron produced from 10 batches of different scrap steel and recycled materials, which are respectively used as Examples 1 to 10.

[0027] Table 1 - Iron Composition Data

[0028] The mechanical properties of the 10 brake disc embodiments obtained above were tested according to GB / T228 Metallic Materials Tensile Testing and GB / T231 Metallic Materials Brinell Hardness Testing. Three parallel samples were set for each embodiment, and the test data are shown in Table 2.

[0029] Table 2 - Test data on the mechanical properties of the brake disc body

[0030] During the preparation process, a portion of the molten iron raw materials from two batches of Examples 9 and 10 was taken as a control group. No nitriding agent was added during the inoculation process, and the composition data of the produced molten iron are shown in Table 3.

[0031] Table 3 - Iron composition data of the control group

[0032] Similarly, the mechanical performance of the two comparative brake disc embodiments obtained above was tested, with three parallel samples set for each. The test data are shown in Table 4.

[0033] Table 4 - Test data on the mechanical properties of the brake disc body

[0034] Comparison of Tables 2 and 4 reveals that the tensile strength of the 10 brake discs ranges from 254.3 to 290.0 MPa, with an overall average of 271.2 MPa; the average hardness of individual discs ranges from 188.3 to 207.0 HB, with an overall average of 198.7 HB. In contrast, the average hardness of the two comparative samples is only 247.3 MPa and 250.3 MPa, respectively; their hardnesses are 182.7 HB and 184.0 HB, respectively. This demonstrates that the mechanical properties of the brake discs are significantly improved after the addition of nitriding agents.

[0035] Metallographic examination was performed on the brake discs of Example 1 and Comparative Example 1, respectively, and the results are as follows: Figure 1 and Figure 2 As shown, it can be observed that the graphite in Example 1 has a smaller aspect ratio, a more obvious degree of graphite curvature, blunt graphite ends, increased graphite branches, finer graphite, reduced graphite cutting effect on the matrix, and the brake disc is less prone to cracking during use.

[0036] Brake discs obtained from Examples 1 to 4 were extracted from the embodiments and subjected to bench tests according to the industry standard "QC / T239-2015 Technical Requirements and Bench Test Methods for Commercial Vehicle Service Brakes". The brake discs were required to withstand 350 braking cycles without failure. The test results are as follows: Figure 3 As shown in the figure, the upper part is a photo of the brake disc mounted on the test bench before the experiment, and the lower part is a photo after 350 braking tests. The brake discs of the four embodiments were still able to brake normally after the test. This shows that the heat-resistant fatigue-resistant commercial vehicle brake disc provided by the present invention can indeed maintain excellent fatigue resistance under high-temperature conditions, and can meet the actual needs of safe operation of commercial vehicles.

[0037] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a heat-fatigue resistant commercial vehicle brake disc, characterized in that, Including the following steps: S1. Add the raw materials to a smelting furnace and smelt them to obtain molten iron; the molten iron includes the following components: C: 3.40~3.45%, Si: 1.50~1.60%, Mn: 0.30~0.35%, P<0.03%, S: 0.08~0.12%, Cr: 0.25~0.30% and Cu 0.40~0.45%, with the balance being Fe and unavoidable impurities; S2. Add ferrosilicon inoculant, nitriding agent, ferromolybdenum, and tin to the transfer bag, and pour molten iron into the transfer bag for the first inoculation treatment; the amount of ferrosilicon inoculant is 0.30~0.45% of the molten iron mass, the amount of nitriding agent is 0.60% of the molten iron mass, the amount of ferromolybdenum is 0.60~0.65% of the molten iron mass, and the amount of tin is 0.06% of the molten iron mass; the chemical composition of the ferrosilicon inoculant includes: Si: 72~80%, Al: 1.5%, Ca: 1.0%, Mn: 0.5%, Cr: 0.5%, P: 0.04%, S: 0.02%, C: 0.2%; S3. The molten iron after the first inoculation treatment is transferred to a ladle and then poured into the cavity of the brake disc casting mold. During pouring, a silicon-strontium-zirconium inoculant is added along with the flow for a second inoculation treatment. After cooling, the brake disc is obtained. The chemical composition of the silicon-strontium-zirconium inoculant includes: Si: 73~78%, Ca≤0.1%, Sr: 0.6~1.0%, Zr: 1.0~1.5%, Al≤0.5%.

2. The preparation method according to claim 1, characterized in that, In step S1, the raw materials for the molten iron, by mass percentage, include 60.00-80.00% scrap steel, 17.00-37.00% recycled material, 1.40-2.00% silicon carbide, 1.70-2.50% carburizing agent, 0.24-0.50% copper, 0.10-0.25% ferromanganese, 0.17-0.45% ferrochrome, and 0.15-0.20% ferrisulfide; the scrap steel, by mass percentage, includes: C The carbon raiser comprises, by mass percentage: 0.001~0.5%, Si≤0.40%, Mn≤1.70%, P≤0.035%, S≤0.035%, Cr≤0.25%, Ti≤0.22%, and Al≤0.05%, with the remainder being Fe and impurities; the carbon raiser comprises, by mass percentage: C≥99.5%, S≤0.03%, N≤0.03%, H≤0.03%, ash ≤0.30%, and volatile matter ≤0.20%.

3. The preparation method according to claim 2, characterized in that, The order of raw material smelting in step S1 is as follows: 1) Add some scrap steel; 2) Add the carbon raiser, silicon carbide, and ferrochrome together; 3) Add the remaining scrap steel; 4) Add recycled material; 5) Add ferrous sulfate, copper and ferromanganese together.

4. The preparation method according to claim 2 or 3, characterized in that, The smelting furnace is a medium-frequency electric furnace with a smelting power of 6000~8000 kW. After the raw materials of the molten iron are completely melted, it is kept at 1450~1500 ℃ for 10~15 min, and the furnace exit temperature is 1480~1500 ℃.

5. The preparation method according to claim 1, characterized in that, The nitriding agent is manganese iron nitride, with the following chemical composition: Mn≥70%, N:7~10%, C<1%, Si<3.5%, P<0.3%, S<0.02%.

6. The preparation method according to claim 1, characterized in that, In step S2, the molten iron has a Mo content of 0.33~0.38% and a N content of 0.011~0.013%.

7. The preparation method according to claim 1, characterized in that, In step S3, slag removal is performed before the molten iron is transferred to the casting ladle.

8. The preparation method according to claim 1, characterized in that, The pouring temperature in step S3 is 1380~1400 ℃.

9. The preparation method according to claim 1, characterized in that, In step S3, the in-flow inoculation amount of silicon-strontium-zirconium inoculant is 10±5 g / s.

10. A heat-fatigue resistant commercial vehicle brake disc, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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