Low-temperature nodular cast iron production process

Abstract

The invention discloses a low-temperature nodular cast iron production process which specifically comprises the following steps: S1, raw material preparation, S2, smelting detection treatment, S3, spheroidizing inoculation treatment and S4, casting molding: the casting temperature is controlled to be 1340-1400 DEG C, the situation that the graphite spheroidizing rate is reduced due to high temperature is avoided, the raw materials are obliquely poured into a preheating mold, and surface burrs are cleaned after cooling; and S5, heat treatment. The invention relates to the technical field of metal material manufacturing. According to the low-temperature nodular cast iron production process, the prepared nodular cast iron has the tensile strength larger than or equal to 500 MPa, the impact absorbing energy larger than or equal to 15 J / cm < 2 > and the elongation larger than or equal to 18% in the environment of-60 DEG C, the tensile strength is obviously superior to the traditional QT400-18AL standard (the tensile strength is larger than or equal to 360 MPa, and the impact absorbing energy is larger than or equal to 12 J / cm < 2 >), graphite nodules are evenly distributed and regular in shape, the matrix ferrite proportion is larger than or equal to 85%, low-temperature brittle crack propagation is effectively inhibited, and the service life of the nodular cast iron and through an auxiliary pouring system and a segmented inoculation process, the pouring defect rate is reduced to 1% or below, and the production efficiency is improved by 20%.

Description

Technical Field

[0001] This invention relates to the field of metal material manufacturing technology, specifically a low-temperature ductile iron production process. Background Technology

[0002] Ductile iron is widely used in the automotive, energy, and rail transportation industries due to its excellent mechanical properties and machinability. However, in low-temperature environments (such as -60°C), traditional ductile iron is prone to significant reductions in tensile strength and impact toughness due to issues such as microstructure embrittlement and uneven distribution of graphite nodules, making it difficult to meet the reliability requirements of equipment in extremely cold regions. While existing technologies can improve low-temperature performance by adjusting chemical composition and heat treatment processes, problems such as insufficient graphite nodularity, uneven matrix structure, and high production costs still exist. Therefore, there is an urgent need to develop a low-temperature ductile iron production process that can stably operate at -60°C. Summary of the Invention

[0003] (1) Technical problems solved

[0004] To address the shortcomings of existing technologies, this invention provides a low-temperature ductile iron production process. By optimizing the chemical composition, spheroidization treatment, inoculation process, and heat treatment steps, the tensile strength, impact toughness, and elongation of the material at -60°C are significantly improved, meeting the application requirements in extreme low-temperature environments.

[0005] (II) Technical Solution

[0006] To achieve the above objectives, the present invention provides the following technical solution: a low-temperature ductile iron production process, specifically comprising the following steps:

[0007] S1. Raw material preparation: Mix ductile iron remelting material, pig iron and scrap steel in a mass ratio of 5:3:2, and add nickel-iron alloy, copper scrap and nano additives.

[0008] S2. Smelting and Testing: Medium-frequency induction furnace is used for smelting. The temperature of the molten iron is controlled at 1500–1550℃ to ensure uniform composition. Carbon raisers and alloying elements are added in stages. Pig iron and recycled materials are melted first, followed by scrap steel and alloy additives. During the smelting process, the composition of the molten iron is monitored in real time using a direct-reading spectrometer. The ratio is adjusted to the target range. After smelting, samples are taken for testing, and the carbon content is adjusted to 3.4% and the silicon content to 2.3%.

[0009] S3. Spheroidizing and inoculation treatment: Add low rare earth spheroidizing agent for spheroidizing treatment, and then use 75SiFe inoculating agent for two inoculations.

[0010] S4. Casting: The casting temperature is controlled at 1340-1400℃. The casting is tilted and poured into the preheated mold. After cooling, the surface burrs are cleaned.

[0011] S5. Heat treatment: After casting, heat the casting to 720–750℃, hold for 4–6 hours, cool with the furnace to 600℃, then air cool to room temperature, and then perform deep cryogenic treatment at -60℃ for 2–4 hours to obtain low-temperature ductile iron casting.

[0012] Preferably, the chemical composition of the low-temperature ductile iron in step S1 is as follows by mass percentage: C: 3.2%–3.6%, Si: 2.0%–2.5%, Mn: ≤0.3%, P: ≤0.03%, S: ≤0.015%, Mg: 0.03%–0.05%, Ni: 1.5%–2.5%, Cu: 0.1%–0.2%, nano-additives: 0.05%–0.1%, and the balance is iron (Fe).

[0013] Preferably, the spheroidizing treatment in step S3 uses FeSiMg8RE3 spheroidizing agent, and the amount added is 1.5%–2.0% of the mass of the molten iron.

[0014] Preferably, the two gestation processes in step S3 are as follows:

[0015] T1, Initial inoculation: Add 0.3%–0.5% inoculant before spheroidization treatment, with a particle size of 4–6 mm;

[0016] T2, Secondary Inoculation: Add 0.2%–0.4% inoculant 10–15 minutes before casting, with a particle size of 2–4 mm, and then refine the graphite spheres.

[0017] Preferably, in step S4, a pouring system with an auxiliary unloading rack is used for pouring, and the pouring angle is adjusted by pushing the cylinder to drive the telescopic sleeve rod, tilting it by 10°-15°.

[0018] Preferably, in step S4, the casting mold is preheated to 200-300°C to ensure that the molten iron solidifies quickly and forms a uniform structure.

[0019] Preferably, in step S5, after air cooling to room temperature, the matrix is ​​mainly ferrite with a yield strength ≥350MPa and an elongation ≥20%.

[0020] Preferably, the low-temperature ductile iron castings after the cryogenic treatment in step S5 are tested for mechanical properties according to ASTM E8 standard, and the results meet the application requirements in an environment of -60℃.

[0021] Preferably, the nano-additive in step S1 is either nano-silicon carbide or nano-alumina.

[0022] (III) Beneficial Effects

[0023] This invention provides a low-temperature ductile iron production process. Compared with existing technologies, it has the following advantages:

[0024] (1) The low-temperature ductile iron production process specifically includes the following steps: S1, Raw material preparation: Mix ductile iron remelting material, pig iron and scrap steel in a mass ratio of 5:3:2, and add nickel-iron alloy, copper scrap and nano additives; S2, Smelting and testing; S3, Spheroidizing and inoculation treatment: Add low rare earth spheroidizing agent for spheroidizing treatment, and after spheroidizing treatment, use 75SiFe inoculating agent for two inoculations; S4, Casting and molding: Control the casting temperature at 1340-1400℃ to avoid the graphite spheroidization rate from decreasing due to high temperature, pour it into the preheated mold at an angle, and clean the surface burrs after cooling; S5, Heat treatment: The prepared ductile iron has a tensile strength ≥500MPa and an impact absorption energy ≥15J / cm at -60℃. 2 Elongation ≥18%, significantly better than the traditional QT400-18AL standard (tensile strength ≥360MPa, impact energy ≥12J / cm). 2 The graphite spheres are evenly distributed and have regular shapes, and the ferrite content in the matrix is ​​≥85%, which effectively inhibits the propagation of low-temperature brittle cracks.

[0025] (2) The low-temperature ductile iron production process reduces the casting defect rate to below 1% and increases production efficiency by 20% through the auxiliary gating system and segmented inoculation process. Attached Figure Description

[0026] Figure 1 This is a flowchart of the production process of the present invention. Detailed Implementation

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] Please see Figure 1 The present invention provides four technical solutions: a low-temperature ductile iron production process, specifically including the following embodiments:

[0029] Example 1: A low-temperature ductile iron production process, specifically including the following steps:

[0030] S1. Raw material preparation: Mix ductile iron remelting material, pig iron and scrap steel in a mass ratio of 5:3:2, and add nickel-iron alloy, copper scrap and nano additives.

[0031] S2. Smelting and Testing: Medium-frequency induction furnace is used for smelting. The temperature of the molten iron is controlled at 1530℃ to ensure uniform composition. Carbon raisers and alloying elements are added in stages. Pig iron and recycled materials are melted first, followed by scrap steel and alloying additives. During the smelting process, the composition of the molten iron is monitored in real time using a direct-reading spectrometer. The ratio is adjusted to the target range. After smelting, samples are taken for testing, and the carbon content is adjusted to 3.4% and the silicon content to 2.3%.

[0032] S3. Spheroidizing and Inoculation Treatment: A low-rare-earth spheroidizing agent is added for spheroidizing treatment. After spheroidizing treatment, 75SiFe inoculant is used for two inoculations. FeSiMg8RE3 spheroidizing agent is used for spheroidizing treatment, and the amount added is 1.8% of the mass of molten iron. The specific process of the two inoculations is as follows:

[0033] T1, Initial inoculation: Add 0.4% inoculant before spheroidization treatment, particle size 5mm;

[0034] T2, Secondary Inoculation: Add 0.3% inoculant 13 minutes before casting, with a particle size of 3mm, and then refine the graphite spheres;

[0035] S4. Casting: The casting temperature is controlled at 1340℃ to avoid the graphite spheroidization rate from decreasing due to high temperature. The casting is tilted into the preheated mold. After cooling, the surface burrs are cleaned. The casting uses a casting system with an auxiliary feeding rack. The casting angle is adjusted by pushing the cylinder to drive the telescopic sleeve rod. The tilt is 13° to improve casting stability and reduce porosity defects. The casting mold is preheated to 250℃ to ensure that the molten iron solidifies quickly and forms a uniform structure.

[0036] S5. Heat treatment: The cast part is heated to 735℃ after pouring, held at that temperature for 5 hours, cooled to 600℃ in the furnace, held at that temperature for 2 hours, then lowered to 460℃ and furnace cooled to room temperature to further stabilize the microstructure and improve the low temperature toughness, thereby producing a low temperature ductile iron casting. After air cooling to room temperature, the matrix is ​​mainly ferrite, with a yield strength ≥350MPa and an elongation ≥20%. The mechanical properties of the low temperature ductile iron casting after cryogenic treatment are tested according to ASTM E8 standard, and the results meet the application requirements in an environment of -60℃.

[0037] In this embodiment of the invention, the chemical composition of the low-temperature ductile iron in step S1 is as follows by mass percentage: C: 3.4%, Si: 2.3%, Mn: 0.2%, P: 0.02%, S: 0.013%, Mg: 0.04%, Ni: 2%, Cu: 0.15%, nano-additives: 0.07%, and the balance is iron (Fe). By adding nickel and copper elements and combining them with nano-additives, the matrix structure is optimized to improve low-temperature toughness; the content of harmful elements such as sulfur and phosphorus is strictly controlled to reduce the formation of brittle phases.

[0038] In this embodiment of the invention, the nano-additive in step S1 is nano-silicon carbide.

[0039] Example 2: A low-temperature ductile iron production process, specifically including the following steps:

[0040] S1. Raw material preparation: Mix ductile iron remelting material, pig iron and scrap steel in a mass ratio of 5:3:2, and add nickel-iron alloy, copper scrap and nano additives.

[0041] S2. Smelting and Testing: Medium-frequency induction furnace is used for smelting. The temperature of the molten iron is controlled at 1500℃ to ensure uniform composition. Carbon raisers and alloying elements are added in stages. Pig iron and recycled materials are melted first, followed by scrap steel and alloy additives. During the smelting process, the composition of the molten iron is monitored in real time using a direct-reading spectrometer. The ratio is adjusted to the target range. After smelting, samples are taken for testing, and the carbon content is adjusted to 3.4% and the silicon content to 2.3%.

[0042] S3. Spheroidizing and Inoculation Treatment: A low-rare-earth spheroidizing agent is added for spheroidizing treatment. After spheroidizing treatment, 75SiFe inoculant is used for two inoculations. FeSiMg8RE3 spheroidizing agent is used for spheroidizing treatment, and the amount added is 1.5% of the mass of molten iron. The specific process of the two inoculations is as follows:

[0043] T1, Initial inoculation: Add 0.3% inoculant before spheroidization treatment, particle size 4mm;

[0044] T2, Secondary Inoculation: Add 0.2% inoculant 10 minutes before casting, with a particle size of 2mm, and then refine the graphite spheres;

[0045] S4. Casting: The casting temperature is controlled at 1340℃ to avoid the graphite spheroidization rate from decreasing due to high temperature. The casting is tilted into the preheated mold. After cooling, the surface burrs are cleaned. The casting uses a casting system with an auxiliary feeding rack. The casting angle is adjusted by pushing the cylinder to drive the telescopic sleeve rod. The tilt is 10° to improve casting stability and reduce porosity defects. The casting mold is preheated to 200℃ to ensure that the molten iron solidifies quickly and forms a uniform structure.

[0046] S5. Heat Treatment: The cast part is heated to 720℃ after pouring, held at that temperature for 4 hours, cooled to 600℃ in the furnace, and then air-cooled to room temperature. Then, the casting part is subjected to deep cryogenic treatment at -60℃ for 2 hours to further stabilize the microstructure and improve the low temperature toughness, thereby producing a low temperature ductile iron casting. After air cooling to room temperature, the matrix is ​​mainly ferrite, with a yield strength ≥350MPa and an elongation ≥20%. The mechanical properties of the low temperature ductile iron casting after deep cryogenic treatment are tested according to ASTM E8 standard, and the results meet the application requirements in the -60℃ environment.

[0047] In this embodiment of the invention, the chemical composition of the low-temperature ductile iron in step S1 is as follows by mass percentage: C: 3.2%, Si: 2.0%, Mn: 0.1%, P: 0.01%, S: 0.01%, Mg: 0.03%, Ni: 1.5%, Cu: 0.1%, nano-additives: 0.05%, and the balance is iron (Fe). By adding nickel and copper elements and combining them with nano-additives, the matrix structure is optimized to improve low-temperature toughness; the content of harmful elements such as sulfur and phosphorus is strictly controlled to reduce the formation of brittle phases.

[0048] In this embodiment of the invention, the nano-additive in step S1 is nano-alumina.

[0049] Example 3: A low-temperature ductile iron production process, specifically including the following steps:

[0050] S1. Raw material preparation: Mix ductile iron remelting material, pig iron and scrap steel in a mass ratio of 5:3:2, and add nickel-iron alloy, copper scrap and nano additives.

[0051] S2. Smelting and Testing: Medium-frequency induction furnace is used for smelting. The temperature of the molten iron is controlled at 1550℃ to ensure uniform composition. Carbon raisers and alloying elements are added in stages. Pig iron and recycled materials are melted first, followed by scrap steel and alloy additives. During the smelting process, the composition of the molten iron is monitored in real time using a direct-reading spectrometer. The ratio is adjusted to the target range. After smelting, samples are taken for testing, and the carbon content is adjusted to 3.4% and the silicon content to 2.3%.

[0052] S3. Spheroidizing and Inoculation Treatment: A low-rare-earth spheroidizing agent is added for spheroidizing treatment. After spheroidizing treatment, 75SiFe inoculant is used for two inoculations. FeSiMg8RE3 spheroidizing agent is used for spheroidizing treatment, and the amount added is 2.0% of the mass of molten iron. The specific process of the two inoculations is as follows:

[0053] T1, Initial inoculation: Add 0.5% inoculant before spheroidization treatment, particle size 6mm;

[0054] T2, Secondary Inoculation: Add 0.4% inoculant 15 minutes before casting, with a particle size of 4mm, and then refine the graphite spheres;

[0055] S4. Casting: The casting temperature is controlled at 1400℃ to avoid the graphite spheroidization rate from decreasing due to high temperature. The casting is tilted into the preheated mold. After cooling, the surface burrs are cleaned. The casting uses a casting system with an auxiliary feeding rack. The casting angle is adjusted by pushing the cylinder to drive the telescopic sleeve rod. The tilt is 15° to improve casting stability and reduce porosity defects. The casting mold is preheated to 300℃ to ensure that the molten iron solidifies quickly and forms a uniform structure.

[0056] S5. Heat Treatment: The cast part is heated to 750℃ after pouring, held at that temperature for 6 hours, cooled to 600℃ in the furnace, and then air-cooled to room temperature. Then, the casting part is subjected to deep cryogenic treatment at -60℃ and held at that temperature for 4 hours to further stabilize the microstructure and improve the low temperature toughness, thereby producing a low temperature ductile iron casting. After air cooling to room temperature, the matrix is ​​mainly ferrite, with a yield strength ≥350MPa and an elongation ≥20%. The mechanical properties of the low temperature ductile iron casting after deep cryogenic treatment are tested according to ASTM E8 standard, and the results meet the application requirements in the -60℃ environment.

[0057] In this embodiment of the invention, the chemical composition of the low-temperature ductile iron in step S1 is as follows by mass percentage: C: 3.6%, Si: 2.5%, Mn: 0.3%, P: 0.03%, S: 0.015%, Mg: 0.05%, Ni: 2.5%, Cu: 0.2%, nano-additives: 0.1%, and the balance is iron (Fe). By adding nickel and copper elements, combined with nano-additives, the matrix structure is optimized to improve low-temperature toughness; the content of harmful elements such as sulfur and phosphorus is strictly controlled to reduce the formation of brittle phases.

[0058] In this embodiment of the invention, the nano-additive in step S1 is nano-silicon carbide.

[0059] Example 4: Raw material preparation: Mix ductile iron remelting material, pig iron and scrap steel in a mass ratio of 5:3:2, and add nickel-iron alloy (Ni 1.8%), copper scrap (Cu 0.15%) and nano silicon carbide (0.08%).

[0060] Smelting and testing: The medium-frequency furnace is heated to 1520℃, and samples are taken for testing after smelting. The carbon content is adjusted to 3.4% and the silicon content to 2.3%.

[0061] Spheroidization and inoculation: FeSiMg8RE3 spheroidizing agent (2.0%) was added, followed by 75SiFe inoculating agent (0.4% + 0.3%) in two separate additions.

[0062] Casting and molding: Casting temperature 1320℃, pour at an angle into a preheated mold, and clean the surface burrs after cooling.

[0063] Heat treatment: Anneal to 730℃ and hold for 5 hours, then cool to 600℃ and air cool; followed by cryogenic treatment at -60℃ for 3 hours.

[0064] Performance testing: Mechanical properties were tested according to ASTM E8 standard, and the results meet the application requirements at -60℃.

[0065] In summary, the ductile iron prepared by this invention exhibits a tensile strength ≥500MPa and an impact absorption energy ≥15J / cm² at -60℃. 2Elongation ≥18%, significantly better than the traditional QT400-18AL standard (tensile strength ≥360MPa, impact energy ≥12J / cm). 2 The graphite spheres are evenly distributed and regularly shaped, with a ferrite content of ≥85% in the matrix, which effectively inhibits the propagation of low-temperature brittle cracks. Through the auxiliary casting system and segmented inoculation process, the casting defect rate is reduced to below 1%, and the production efficiency is increased by 20%.

[0066] Furthermore, any content not described in detail in this specification is existing technology known to those skilled in the art.

[0067] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0068] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A low-temperature ductile iron production process, characterized in that: Specifically, the following steps are included: S1. Raw material preparation: Mix ductile iron remelting material, pig iron and scrap steel in a mass ratio of 5:3:2, and add nickel-iron alloy, copper scrap and nano additives. S2. Smelting and Testing: Medium-frequency induction furnace is used for smelting. The temperature of the molten iron is controlled at 1500–1550℃ to ensure uniform composition. Carbon raisers and alloying elements are added in stages. Pig iron and recycled materials are melted first, followed by scrap steel and alloy additives. During the smelting process, the composition of the molten iron is monitored in real time using a direct-reading spectrometer. The ratio is adjusted to the target range. After smelting, samples are taken for testing, and the carbon content is adjusted to 3.4% and the silicon content to 2.3%. S3. Spheroidizing and inoculation treatment: Add low rare earth spheroidizing agent for spheroidizing treatment, and then use 75SiFe inoculating agent for two inoculations. S4. Casting: The casting temperature is controlled at 1340-1400℃. The casting is tilted and poured into the preheated mold. After cooling, the surface burrs are cleaned. S5. Heat treatment: After casting, heat the casting to 720–750℃, hold for 4–6 hours, cool with the furnace to 600℃, then air cool to room temperature, and then perform deep cryogenic treatment at -60℃ for 2–4 hours to obtain low-temperature ductile iron casting.

2. The low-temperature ductile iron production process according to claim 1, characterized in that: In step S1, the chemical composition of the low-temperature ductile iron is as follows by mass percentage: C: 3.2%–3.6%, Si: 2.0%–2.5%, Mn: ≤0.3%, P: ≤0.03%, S: ≤0.015%, Mg: 0.03%–0.05%, Ni: 1.5%–2.5%, Cu: 0.1%–0.2%, nano-additives: 0.05%–0.1%, and the balance is iron (Fe).

3. The low-temperature ductile iron production process according to claim 1, characterized in that: In step S3, the spheroidizing treatment uses FeSiMg8RE3 spheroidizing agent, and the amount added is 1.5%–2.0% of the mass of the molten iron.

4. The low-temperature ductile iron production process according to claim 1, characterized in that: The two gestation processes in step S3 are as follows: T1, Initial inoculation: Add 0.3%–0.5% inoculant before spheroidization treatment, with a particle size of 4–6 mm; T2, Secondary Inoculation: Add 0.2%–0.4% inoculant 10–15 minutes before casting, with a particle size of 2–4 mm, and then refine the graphite spheres.

5. The low-temperature ductile iron production process according to claim 1, characterized in that: In step S4, a pouring system with an auxiliary unloading rack is used for pouring. The pouring angle is adjusted by pushing the cylinder to drive the telescopic sleeve rod, tilting it by 10°-15°.

6. The low-temperature ductile iron production process according to claim 1, characterized in that: In step S4, the casting mold is preheated to 200-300°C to ensure that the molten iron solidifies quickly and forms a uniform structure.

7. The low-temperature ductile iron production process according to claim 1, characterized in that: In step S5, after air cooling to room temperature, the matrix is ​​mainly ferrite with a yield strength ≥350MPa and an elongation ≥20%.

8. The low-temperature ductile iron production process according to claim 1, characterized in that: The cryogenic castings after the deep cryogenic treatment in step S5 were tested for mechanical properties according to ASTM E8 standard, and the results met the application requirements in an environment of -60℃.

9. The low-temperature ductile iron production process according to claim 1, characterized in that: The nano-additive in step S1 is either nano-silicon carbide or nano-alumina.

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