An anti-fatigue high-strength cast iron material suitable for complex curved surface structures, a preparation method and applications

Abstract

The application belongs to the technical field of cast iron, and particularly relates to a fatigue-resistant high-strength cast iron material suitable for complex curved surface structures, a preparation method and application. The material comprises C, Si, Mn, Cr, S, P, Ni, Mo, SiC, Ge, Ti, rare earth elements, Co, Cu, Zr, V and Fe in residual amount by weight fraction. The preparation method comprises the steps of graphite precursor liquid smelting, ultrasonic treatment, hot metal inoculation, medium-frequency smelting, alloy homogenization, ladle treatment and controlled temperature pouring. Through the synergistic effect of multi-element strengthening alloy design and process control, the low-cycle and high-cycle fatigue strength, tensile strength and wear resistance of the material are significantly improved, and the material is suitable for high-performance castings manufacturing under complex curved surface and alternating load working conditions.

Description

Technical Field

[0001] This invention belongs to the technical field of cast iron, specifically relating to a fatigue-resistant high-strength cast iron material suitable for complex curved surface structures, its preparation method, and its application. Background Technology

[0002] Cast iron is widely used in machinery manufacturing, automobiles, and engineering structures due to its excellent casting properties, low cost, and adaptability to various working conditions. In modern equipment manufacturing, many key components have complex curved surface structures, such as engine blocks, crankcases, turbine housings, and some support structures. These structures often bear alternating loads and thermal stresses, making them prone to fatigue cracks and fractures. Therefore, higher requirements are placed on the fatigue strength and service life of cast iron materials.

[0003] Traditional gray cast iron and ductile cast iron can provide good mechanical and machinability under certain conditions, but they are prone to casting defects such as shrinkage porosity, cracks, and graphite segregation in complex curved thin-walled structures, and their fatigue strength is limited, making it difficult to meet the long service life requirements under high-frequency alternating load environments.

[0004] For complex components with large curvature variations, problems such as uneven thermal stress distribution and stress concentration in the microstructure exist. Complex curved surface structures often experience uneven cooling and localized stress concentration during casting, easily leading to microscopic defects such as poor graphite spheroidization, eutectic segregation, or embrittlement of the carburized layer, thereby further reducing their fatigue life. Therefore, there is an urgent need to develop a new type of high-strength cast iron material that combines excellent casting performance, microstructural stability, and fatigue resistance, particularly suitable for the manufacturing needs of complex curved surface structures. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a fatigue-resistant, high-strength cast iron material suitable for complex curved surface structures. As a technical solution, by weight fraction, it comprises the following raw materials: C: 3.5%–3.9%, Si: 2.0%–2.6%, Mn: 0.6%–0.9%, Cr: 0.22%–0.28%, S: 0.02%–0.05%, P: 0.05%–0.1%, Ni: 0.2%–0.25%, Mo: 0.3%–0.5%, SiC: 0.15%–0.25%, Ge: 0.02%–0.05%, Ti: 0.1%–0.2%, rare earth elements: 0.06%–0.1%, Co: 0.2%–0.35%, Cu: 0.2%–0.25%, Zr: 0.15%–0.2%, V: 0.1%–0.2%, Fe: balance.

[0006] In one optimized technical solution, the raw materials, by weight fraction, include the following: C: 3.6%–3.8%, Si: 2.2%–2.4%, Mn: 0.7%–0.8%, Cr: 0.24%–0.26%, S: 0.03%–0.045%, P: 0.06%–0.08%, Ni: 0.21%–0.24%, Mo: 0.35%–0.45%, SiC: 0.18%–0.22%, Ge: 0.03%–0.045%, Ti: 0.12%–0.18%, rare earth elements: 0.07%–0.09%, Co: 0.25%–0.32%, Cu: 0.21%–0.24%, Zr: 0.16%–0.18%, V: 0.12%–0.18%, Fe: balance.

[0007] In one optimized technical solution, the raw materials, by weight fraction, include the following: C: 3.7%, Si: 2.3%, Mn: 0.75%, Cr: 0.25%, S: 0.035%, P: 0.07%, Ni: 0.22%, Mo: 0.4%, SiC: 0.2%, Ge: 0.04%, Ti: 0.15%, rare earth elements: 0.08%, Co: 0.28%, Cu: 0.22%, Zr: 0.17%, V: 0.15%, Fe: balance.

[0008] In one optimized technical solution, the rare earth elements include neodymium and gadolinium.

[0009] In one optimized technical solution, the mass ratio of neodymium to gadolinium is (1~1.5):1.

[0010] In one optimized technical solution, the mass ratio of neodymium to gadolinium is (1.1~1.3):1.

[0011] In one optimized technical solution, the mass ratio of neodymium to gadolinium is 1.2:1.

[0012] This invention also provides a method for preparing fatigue-resistant high-strength cast iron materials suitable for complex curved surface structures, comprising the following steps:

[0013] S1. Weigh and prepare the raw materials according to the above proportions;

[0014] S2. To prepare the inoculation molten iron, C, Si, Mn, Cr, S, P and SiC are added to Fe in sequence, and the mixture is heated and stirred until it reaches a molten state to obtain the inoculation molten iron.

[0015] S3. Heat the molten iron before inoculation to 1600-1650℃ and treat it with circulating ultrasound for 80-100 minutes to obtain graphitized molten iron.

[0016] S4. Subsequent alloying treatment is carried out by adding Ge, Ti, rare earth elements, Co, Cu, Zr and V to the dry molten iron ladle in sequence, spraying superheating agent, and then injecting graphitized molten iron into the ladle for inoculation treatment to obtain a high-strength cast iron matrix.

[0017] S5. High-strength cast iron matrix is ​​smelted in a medium-frequency furnace, Ni and Mo are gradually added, the smelting and stirring are carried out and homogenization treatment is performed to obtain smelted cast iron.

[0018] S6. Pour the molten cast iron into the mold and cool it to room temperature with the furnace to obtain fatigue-resistant high-strength cast iron.

[0019] In one optimized technical solution, step S5 further includes a ladle-pouring step, which involves pouring the high-strength cast iron matrix into another spare ladle to cool to room temperature before it is completely melted.

[0020] In one optimized technical solution, the mass of the unmelted portion in the high-strength cast iron matrix accounts for 5% to 10% of the total mass.

[0021] In one optimized technical solution, the voltage of the intermediate frequency furnace is 150-200 volts and the current is 15-25 amps.

[0022] In one optimized technical solution, after adding Mo, homogenization is performed, and the mixture is kept at 1500℃ for 10-15 minutes.

[0023] The present invention also provides the application of the aforementioned fatigue-resistant high-strength cast iron material in parts having at least one curved surface structure.

[0024] The present invention also provides the application of the aforementioned fatigue-resistant high-strength cast iron material in complex curved surface structure parts.

[0025] Beneficial effects:

[0026] 1. Synergistic Design of Multiple Strengthening Elements: By introducing elements such as Mo, Ni, Cr, Co, Cu, V, Zr, and Ti, fine and dispersed strengthening phases are formed in the matrix, while simultaneously increasing the pearlite content, thereby enhancing the matrix strength and hardening ability. Among them, Mo and V can inhibit cementite coarsening, Cr and Zr improve thermal stability, and Ni and Co improve the continuity of crack propagation paths, effectively improving fatigue life.

[0027] 2. The effects of rare earth element modification on graphite spheroidization control: A rare earth system composed of neodymium and gadolinium improves the graphite nucleation environment, inhibits the formation of flake graphite, promotes the refinement and distribution of spheroidal graphite, reduces stress concentration sources, and raises the crack initiation threshold. Rare earth elements can also purify inclusions, improve grain boundary strength, and enhance high-cycle fatigue performance.

[0028] 3. SiC and Ge synergistic inoculation promotes graphite nucleation and microstructure uniformity: SiC, as a carbon-silicon compensation source, provides nucleation sites for graphite, while Ge, as a trace modifier, can change the surface energy state of molten iron. The two work together to improve the nucleation mechanism, increase the graphite spheroidization rate, and enhance the structural density and thermal cycling stability.

[0029] 4. Ultrasonic Treatment and Reverse Wrapping for Microstructure Refinement: By applying cyclic ultrasonic excitation of 20-25 kHz during the high-temperature melting stage, the original coarse grain nuclei are effectively broken up, the distribution of alloying elements is refined, and the number and uniformity of graphite nuclei are enhanced. The reverse wrapping process allows the unmelted portion to cool rapidly, promoting non-equilibrium solidification, which helps to obtain a fine equiaxed grain structure and improves the complexity of fatigue crack propagation paths.

[0030] 5. Medium-frequency melting and Mo homogenization and heat preservation treatment enhance matrix integrity: Medium-frequency melting after inoculation treatment can further improve the uniformity of the structure and the element dissolution efficiency; heat preservation treatment after the addition of Mo helps to strengthen the directional precipitation and dispersion distribution of the phase, and improve the long-term service stability of the material. Attached Figure Description

[0031] Figure 1 This is a photograph of the fracture of a sample from Embodiment 1 of the present invention (fracture centered).

[0032] Figure 2 This is a photograph of the fractured sample from Embodiment 1 of the present invention (fracture at the upper arc).

[0033] Figure 3 This is a photograph of the fractured sample from Embodiment 1 of the present invention (fracture at the lower arc).

[0034] Figure 4 A microscopic photograph of the centrally fractured specimen of Embodiment 1 of the present invention;

[0035] Figure 5 This is a schematic diagram of the comparative experiment (fatigue strength) of the present invention;

[0036] Figure 6 This is a schematic diagram of the comparative experiment (tensile strength) of the present invention;

[0037] Figure 7 This is a schematic diagram of the comparative experiment (average wear loss) of the present invention. Detailed Implementation

[0038] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0039] Example 1

[0040] This embodiment provides a fatigue-resistant high-strength cast iron material suitable for complex curved surface structures, which comprises the following raw materials by weight fraction: C: 3.7%, Si: 2.3%, Mn: 0.75%, Cr: 0.25%, S: 0.035%, P: 0.07%, Ni: 0.22%, Mo: 0.4%, SiC: 0.2%, Ge: 0.04%, Ti: 0.15%, rare earth elements: 0.08%, Co: 0.28%, Cu: 0.22%, Zr: 0.17%, V: 0.15%, Fe: balance; wherein the rare earth elements are composed of neodymium and gadolinium, and the mass ratio of neodymium to gadolinium is 1.2:1.

[0041] The specific preparation method is as follows:

[0042] S1. Weigh the raw materials of each component according to the above proportions, use industrial pure iron as the base iron, and place it in an induction melting furnace to preheat to 150°C for later use.

[0043] S2. Add C, Si, Mn, Cr, S, P and SiC, rapidly heat to above the melting point, control the furnace temperature at 1550℃, and stir continuously for 15 minutes to form a homogeneous molten iron before inoculation.

[0044] S3. The precursor liquid is further heated to 1640℃ and subjected to cyclic ultrasonic treatment with a frequency of 20 kHz and a power of 12 kW for 90 minutes to obtain graphitized molten iron with uniform structure and enhanced graphite nucleation ability.

[0045] S4. Ge, Ti, rare earth elements (neodymium and gadolinium), Co, Cu, Zr, and V are pre-placed in a ladle of molten iron that has been dried at 500°C for 2 hours, and a 2 mm thick superheating agent layer is sprayed onto the surface; then the graphitized molten iron is slowly poured into the ladle to carry out an inoculation reaction and form a high-strength cast iron matrix.

[0046] S5. Transfer the inoculated molten iron to a medium-frequency melting furnace, control the voltage at 180 volts and the current at 20 amps, and continue melting and heating to 1560°C. During this process, Ni and Mo are added in sequence and stirred continuously for 10 minutes to allow them to fully dissolve and diffuse. After adding Mo, continue the heat treatment at 1500°C for 12 minutes to stabilize the distribution of the strengthening phase and improve the continuity of the matrix.

[0047] In this step, a ladle-turning operation is performed, that is, when about 8% of the solid metal in the cast iron matrix has not been completely melted, it is poured into another spare ladle preheated to 300°C and allowed to cool naturally to room temperature, in order to enhance the refinement effect of the non-equilibrium solidification structure.

[0048] S6. Finally, pour the molten iron into a metal mold preheated to 350°C. Control the cooling time to 6 hours. After demolding, obtain an integrally formed fatigue-resistant high-strength cast iron sample.

[0049] Example 2

[0050] This embodiment provides a fatigue-resistant high-strength cast iron material suitable for complex curved surface structures, which comprises the following raw materials by weight fraction: C: 3.5%, Si: 2.0%, Mn: 0.6%, Cr: 0.22%, S: 0.02%, P: 0.05%, Ni: 0.2%, Mo: 0.3%, SiC: 0.15%, Ge: 0.02%, Ti: 0.1%, rare earth elements: 0.06%, Co: 0.2%, Cu: 0.2%, Zr: 0.15%, V: 0.1%, Fe: balance; the rare earth elements are composed of neodymium and gadolinium, and the mass ratio of neodymium to gadolinium is 1:1.

[0051] The preparation method is the same as in Example 1.

[0052] Example 3

[0053] This embodiment provides a fatigue-resistant high-strength cast iron material suitable for complex curved surface structures, which comprises the following raw materials by weight fraction: C: 3.9%, Si: 2.6%, Mn: 0.9%, Cr: 0.28%, S: 0.05%, P: 0.1%, Ni: 0.25%, Mo: 0.5%, SiC: 0.25%, Ge: 0.05%, Ti: 0.2%, rare earth elements: 0.1%, Co: 0.35%, Cu: 0.25%, Zr: 0.2%, V: 0.2%, Fe: balance; the rare earth elements include neodymium and gadolinium, and the mass ratio of neodymium to gadolinium is 1.5:1.

[0054] The preparation method is the same as in Example 1.

[0055] Comparative Example 1

[0056] To verify the technical effect of the component ratio of the present invention, a fatigue-resistant high-strength cast iron was implemented in this comparative example, comprising the following raw materials by weight fraction: C: 4.1%, Si: 1.8%, Mn: 1.0%, Cr: 0.30%, S: 0.06%, P: 0.12%, Ni: 0.18%, Mo: 0.25%, SiC: 0.28%, Ge: 0.01%, Ti: 0.09%, rare earth elements: 0.11%, Co: 0.38%, Cu: 0.26%, Zr: 0.22%, V: 0.22%, Fe: balance; wherein the rare earth elements are composed of neodymium and gadolinium, and the mass ratio of neodymium to gadolinium is 1.6:1.

[0057] The same preparation process as that used in this invention is employed:

[0058] S1. Weigh the above raw materials, use industrial pure iron as the base iron, and preheat them for later use;

[0059] S2. Add C, Si, Mn, Cr, S, P and SiC in sequence, heat to 1550℃, stir for 15 minutes to obtain molten iron before inoculation;

[0060] S3. Continue heating to 1650℃ and treat with ultrasonic waves at a frequency of 25 kHz and a power of 15 kW for 100 minutes to obtain graphitized molten iron.

[0061] S4. Place Ge, Ti, rare earth elements (neodymium and gadolinium), Co, Cu, Zr, and V in a drying bag, spray with superheating agent, and then pour in molten iron to complete the inoculation.

[0062] S5. Transfer to medium-frequency furnace, control voltage 200V and current 25A, heat to 1570℃, add Ni and Mo, stir and homogenize for 12 minutes, perform the unmelted portion operation, the unmelted portion accounts for 10%;

[0063] S6. Pour the mixture into the mold, cool it to room temperature in the furnace, and demold to obtain sample C1.

[0064] After adding Mo, maintain the temperature at 1500℃ for 15 minutes.

[0065] Comparative Example 2

[0066] This comparative example describes a fatigue-resistant, high-strength cast iron comprising the following raw materials by weight fraction: C: 3.7%, Si: 2.3%, Mn: 0.75%, Cr: 0.25%, S: 0.035%, P: 0.07%, Ni: 0.22%, Mo: 0.4%, Fe: balance. Ti, Ge, rare earth elements, Co, Zr, V, SiC, and Cu were not added in this comparative example.

[0067] The preparation process is the same as that of this invention, specifically including:

[0068] S1. Weigh the above raw materials, use industrial pure iron as the base iron, and heat it to 150°C in an induction furnace for later use.

[0069] S2. Add C, Si, Mn, Cr, S and P in sequence, heat to 1550℃ and stir for 15 minutes to form molten iron before inoculation;

[0070] S3. Heat to 1620℃ and apply ultrasonic treatment at a frequency of 20 kHz and a power of 10 kW for 80 minutes to obtain graphitized molten iron.

[0071] S4. Since SiC and rare earth modifiers were not used, the graphitization treatment was performed directly before pouring into the mold without subsequent inoculation.

[0072] S5. The molten iron was transferred into the medium-frequency melting furnace with a voltage of 180 volts and a current of 20 amps. The melting temperature was controlled at 1560℃. Ni and Mo were added, and the mixture was stirred and homogenized for 10 minutes. No ladle transfer was performed.

[0073] S6. Pour the molten iron into a sand mold. The mold is preheated to 250°C and allowed to cool naturally in the furnace for 6 hours. The C2 sample is then demolded. No heat preservation treatment was performed after adding Mo. The temperature was directly lowered after pouring.

[0074] Comparative Example 3

[0075] This comparative example describes a fatigue-resistant high-strength cast iron, which comprises the following raw materials by weight fraction: C: 3.7%, Si: 2.3%, Mn: 0.75%, Cr: 0.25%, S: 0.035%, P: 0.07%, Ni: 0.22%, Mo: 0.4%, SiC: 0.2%, Ge: 0.04%, Ti: 0.15%, rare earth elements: 0.08%, Co: 0.28%, Cu: 0.22%, Zr: 0.17%, V: 0.15%, Fe: balance; wherein the rare earth elements consist of neodymium and gadolinium in a mass ratio of 1.2:1.

[0076] Although all elements and proportions in this formula are within the technical scope of this invention, several key steps have been omitted from the process flow. The specific process is as follows:

[0077] S1. Weigh the above-mentioned raw materials, use industrial pure iron as the base iron, and preheat to 150°C for later use.

[0078] S2. Add C, Si, Mn, Cr, S, P, SiC, etc. into an induction furnace, heat to 1550℃, stir and melt for 15 minutes to obtain molten iron before inoculation;

[0079] S3. Without ultrasonic treatment, the precursor solution was heated to 1600℃ and directly entered the incubation stage.

[0080] S4. Place Ge, Ti, rare earth elements (neodymium and gadolinium), Co, Cu, Zr, and V into a molten iron ladle at room temperature (without drying or superheating agent), and directly pour in the molten iron to carry out a simple inoculation reaction;

[0081] S5. The molten iron was not subjected to secondary medium-frequency melting, nor was the ladle-turning operation performed. Ni and Mo were added directly and stirred rapidly for 5 minutes. After the temperature was raised to 1560℃, it was ready for pouring.

[0082] S6. After melting, the sample was directly poured into the mold. The mold was preheated to 200°C. No Mo heat preservation treatment was performed. The sample was demolded after cooling to room temperature with the furnace to obtain C3 sample.

[0083] Comparative Example 4

[0084] This comparative example is based on the conventional ductile iron formulation and traditional preparation process used in the prior art. By weight fraction, it includes the following raw materials: C: 3.6%, Si: 2.0%, Mn: 0.4%, S: 0.02%, P: 0.08%, Mg: 0.04%, Fe: balance. No alloying strengthening components such as Mo, Ni, Cr, Co, Cu, V, Zr, Ti, Ge, SiC, or rare earth elements were added.

[0085] The manufacturing process adopts the traditional ductile iron casting process, as follows:

[0086] S1. Use industrial pure iron as the base iron, preheat to 150℃ for later use;

[0087] S2. Add basic components such as C, Si, Mn, S, and P to an induction furnace, heat to 1500℃ and stir for 10 minutes to obtain basic molten iron.

[0088] S3. Magnesium alloy spheroidizing agent was added at 1600℃, and after rapid stirring, the slag was removed. No inoculation treatment was performed, and the graphite spheres were formed solely by the spheroidizing reaction.

[0089] S4. Ultrasonic treatment was not performed, a circulating smelting process was not set up, and the molten iron was not transferred to an induction furnace for refining.

[0090] S5. Molten iron was poured directly into a regular sand mold without preheating, and no inverting or local heat preservation was performed. After naturally cooling to room temperature, the iron was demolded to obtain the C4 sample.

[0091] Comparative experiment

[0092] To further verify the comprehensive performance advantages of the fatigue-resistant high-strength cast iron material described in this invention under complex curved surface structures and alternating load conditions, a systematic comparative test was conducted.

[0093] The experiment selected three different formulation examples of the present invention (Examples 1, 2, and 3) and four comparative examples (Comparative Examples 1, 2, 3, and 4) for comparison. These examples covered typical cases such as excessive component limits, lack of key elements, missing process flow, and existing conventional materials, and have good technical comparability and coverage.

[0094] The experimental projects include:

[0095] 1. Low-cycle fatigue strength under high load:

[0096] Experimental equipment: Servo hydraulic fatigue testing machine (frequency: 1 Hz);

[0097] Experimental standard: "Method for controlling axial force in fatigue testing of metallic materials" (GB / T 3075-2021);

[0098] Loading method: axially symmetrical tension-compression cycle, with the loading stress set at 80% of the material's yield strength;

[0099] Termination conditions: Material fracture or completion of 10,000 cycles;

[0100] Measurement index: Number of cycles before fracture occurs; converted to equivalent low-cycle fatigue strength (MPa).

[0101] 2. High-cycle fatigue strength under low load:

[0102] Experimental equipment: High-frequency electromagnetic fatigue testing machine (frequency: 100 Hz);

[0103] Experimental standard: "Metallic materials axial constant amplitude low cycle fatigue test method" (GB / T 15248-2008);

[0104] Loading method: axially symmetrical tension-compression cycle, with stress amplitude gradually increasing;

[0105] Termination condition: The system is considered safe if it survives 10 million cycles without breaking.

[0106] Measurement parameters: 3 pieces per group, and the lowest fracture stress is taken as the high cycle fatigue strength (MPa).

[0107] The fatigue test specimens were prepared from cast iron using standard machining processes, and their structural parameters are as follows:

[0108] Overall length: 80 mm; gauge length diameter: Φ5 mm; clamping section diameter: Φ10 mm; parallel gauge length: 30 mm; transition radius at both ends: R30 mm; clamping section length at both ends: 30 mm each; machining accuracy: IT7 grade, surface roughness Ra ≤ 0.8 μm. The entire specimen was machined on a CNC lathe, and the specimen surface underwent descaling, fine grinding, and cleaning.

[0109] 3. Strength Test (Ultimate Tensile Strength):

[0110] Experimental equipment: Electronic universal testing machine;

[0111] Standard: Performed in accordance with GB / T 228.1-2021 Metallic materials - Tensile testing - Part 1: Test at room temperature;

[0112] Sample size: Standard round bar specimen with a diameter of 10 mm and an effective length of 50 mm;

[0113] Measurement index: Maximum tensile stress (MPa).

[0114] 4. Wear resistance test:

[0115] Experimental equipment: Dry friction reciprocating wear tester;

[0116] Test parameters: load 60 N, stroke 5 mm, frequency 5 Hz, test time 60 min;

[0117] Measurement method: Weigh the sample before and after weighing, and calculate the weight loss due to wear (mg).

[0118] Sample shape: cylindrical flat-end pressing plate Φ12 mm × 10 mm.

[0119] The experimental results are shown in Table 1:

[0120] Table 1 Comparative Experimental Results

[0121]

[0122] Data Analysis

[0123] To comprehensively evaluate the performance advantages of the fatigue-resistant high-strength cast iron material described in this invention, four indicators—microstructure, low-cycle fatigue, high-cycle fatigue, tensile strength, and wear resistance—were tested on samples from Examples 1, 2, and 3 and Comparative Examples 1, 2, 3, and 4, respectively. The results were compared and analyzed, and are as follows:

[0124] 1. Microscopic morphology analysis:

[0125] Figure 1 , Figure 2 , Figure 3 The image shows a fracture photograph of a specimen from a low-cycle fatigue test in Embodiment 1 of the present invention. A micrograph of the specimen fractured in the center was taken at its port (e.g., Figure 1 (as shown in the sample), obtained Figure 4 In Embodiment 1 of the present invention, ductile iron particles with uniform distribution and diameter are formed in both the edge and center regions of the cross-section, and no obvious defect areas or obvious abrupt fracture areas are observed.

[0126] 2. Low-cycle fatigue strength analysis under high load:

[0127] like Figure 5As shown, the low-cycle fatigue strengths of Examples 1, 2, and 3 are 390 MPa, 360 MPa, and 375 MPa, respectively, all significantly higher than those of Comparative Examples 1, 2, 3, and 4. Although Comparative Examples 1, 2, and 3 use some alloying elements, due to imbalanced proportions or process deficiencies, their fatigue strengths are only 280 MPa, 250 MPa, and 270 MPa, respectively. Comparative Example 4, made of ordinary gray cast iron, has the lowest low-cycle fatigue strength at only 160 MPa, making it prone to crack initiation and propagation under repeated loading, and thus unable to meet the requirements of complex working conditions.

[0128] 3. High-cycle fatigue strength analysis under low load:

[0129] like Figure 5 As shown, in terms of high-cycle fatigue strength, the sample in Example 1 reached 260 MPa, while Examples 2 and 3 reached 240 MPa and 255 MPa, respectively, demonstrating good fatigue crack resistance and crack propagation inhibition capabilities. In contrast, Comparative Examples 1, 2, and 3 reached 180 MPa, 160 MPa, and 170 MPa, respectively, exhibiting problems such as early crack initiation and rapid crack propagation. In particular, Comparative Example 4 only reached 100 MPa, verifying the limitations of traditional ductile iron or gray cast iron materials in high-cycle environments.

[0130] 4. Tensile strength analysis:

[0131] like Figure 6 As shown, the tensile strengths of samples in Examples 1, 2, and 3 are 615 MPa, 580 MPa, and 600 MPa, respectively, which are significantly higher than those of conventional cast iron materials. The tensile strengths of Comparative Examples 1, 2, and 3 are between 440 and 480 MPa, slightly lower than those of mid-range ductile iron. The tensile strength of sample in Comparative Example 4 is only 300 MPa, verifying that the present invention, through multi-element alloying and process optimization, achieves a significant improvement in overall strength while ensuring ductility.

[0132] 5. Abrasion resistance analysis:

[0133] like Figure 7 As shown, in the reciprocating friction test, the average wear loss of samples 1 and 3 was 18.4 mg and 15.2 mg, respectively, demonstrating excellent wear resistance. Sample 3 was slightly better than Sample 1 due to its slightly higher alloy content and denser microstructure. The wear loss of sample 2 was 23.7 mg, slightly higher than Sample 1, but still better than all comparative samples. Comparative samples 1, 2, 3, and 4 showed significantly accelerated wear, with wear losses of 39.5 mg, 56.8 mg, 72.3 mg, and 65.4 mg, respectively. These samples exhibited problems such as non-dense microstructure, uneven distribution of hard phase, or graphite flakes, leading to rapid acceleration of friction loss and making them unsuitable for long-term moving parts.

[0134] Conclusion Summary:

[0135] The comparative results show that the fatigue-resistant high-strength cast iron of the present invention (Examples 1, 2, and 3) exhibits significant advantages in terms of fatigue strength, tensile strength, and wear resistance. In particular, the sample of Example 1 is the most outstanding in terms of performance balance and is suitable for long-term stable use under complex curved surface castings, alternating loads, or wear conditions.

[0136] The test results of samples 1, 2, 3, and 4 fully demonstrate that if the formula design exceeds the limits, key alloying elements are missing, or important steps (such as ultrasonic treatment, inverted packaging, and heat preservation) are omitted in the preparation process, even if some performance indicators are slightly improved, it is difficult to achieve a systematic enhancement of performance, and the microstructure is unstable, posing a significant risk to service life.

[0137] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A fatigue-resistant high-strength cast iron material suitable for complex curved surface structures, characterized in that, By weight fraction, it includes the following raw materials: C: 3.5%–3.9%, Si: 2.0%–2.6%, Mn: 0.6%–0.9%, Cr: 0.22%–0.28%, S: 0.02%–0.05%, P: 0.05%–0.1%, Ni: 0.2%–0.25%, Mo: 0.3%–0.5%, SiC: 0.15%–0.25%, Ge: 0.02%–0.05%, Ti: 0.1%–0.2%, Nd and Gd: 0.06%–0.1%, with a mass ratio of Nd to Gd of (1–1.5):1; Co: 0.2%–0.35%, Cu: 0.2%–0.25%, Zr: 0.15%–0.2%, V: 0.1%–0.2%, Fe: balance; The method for preparing the fatigue-resistant high-strength cast iron material includes the following steps: S1. Weigh and prepare the raw materials according to the specified proportions; S2. To prepare the inoculation molten iron, C, Si, Mn, Cr, S, P and SiC are added to Fe in sequence, and the mixture is heated and stirred until it reaches a molten state to obtain the inoculation molten iron. S3. Heat the molten iron before inoculation to 1600-1650℃ and treat it with circulating ultrasound for 80-100 minutes to obtain graphitized molten iron. S4. Subsequent alloying treatment is carried out. Ge, Ti, Nd, Gd, Co, Cu, Zr and V are added sequentially to the dry molten iron ladle. After spraying with superheating agent, graphitized molten iron is injected into the ladle for inoculation treatment to obtain a high-strength cast iron matrix. S5. High-strength cast iron matrix is ​​smelted in medium frequency furnace, Ni and Mo are gradually added, the smelting is stirred and homogenized, and after adding Mo, it is homogenized and held at 1500℃ for 10 to 15 minutes to obtain smelted cast iron. S6. Pour the molten cast iron into the mold and cool it to room temperature with the furnace to obtain fatigue-resistant high-strength cast iron.

2. The fatigue-resistant high-strength cast iron material suitable for complex curved surface structures according to claim 1, characterized in that: By weight fraction, it includes the following raw materials: C: 3.6%–3.8%, Si: 2.2%–2.4%, Mn: 0.7%–0.8%, Cr: 0.24%–0.26%, S: 0.03%–0.045%, P: 0.06%–0.08%, Ni: 0.21%–0.24%, Mo: 0.35%–0.45%, SiC: 0.18%–0.22%, Ge: 0.03%–0.045%, Ti: 0.12%–0.18%, Nd and Gd: 0.07%–0.09%, Co: 0.25%–0.32%, Cu: 0.21%–0.24%, Zr: 0.16%–0.18%, V: 0.12%–0.18%, Fe: balance.

3. A fatigue-resistant high-strength cast iron material suitable for complex curved surface structures according to claim 1 or 2, characterized in that: Step S5 also includes a ladle-pouring step, in which the high-strength cast iron matrix is ​​poured into another spare ladle to cool to room temperature before it is completely melted.

4. A fatigue-resistant high-strength cast iron material suitable for complex curved surface structures according to claim 1 or 2, characterized in that: The unmelted portion of the high-strength cast iron matrix accounts for 5% to 10% of the total mass.

5. A fatigue-resistant high-strength cast iron material suitable for complex curved surface structures according to claim 1 or 2, characterized in that: The voltage of the medium-frequency furnace is 150-200 volts, and the current is 15-25 amps.

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