A spheroidal graphite cast iron material, a production method and a spheroidal graphite cast iron manufactured piece

Abstract

The application relates to the technical field of metal materials and manufacturing, in particular to a nodular cast iron material, a preparation method and a nodular cast iron manufacturing piece, wherein after spheroidizing treatment, the molten iron is rapidly cooled to a pseudo-eutectic zone to obtain a cast piece or profile with a complete eutectic structure; then the cast piece or profile is annealed to completely decompose eutectic carbides in the cast piece or profile into eutectic graphite balls and alloy elements dissolved in a metal matrix; finally, the cast piece or profile after the annealing treatment is secondarily annealed to form secondary graphite balls in the cast piece or profile, thereby obtaining the nodular cast iron material. Since a large number of secondary graphite balls are generated in the nodular cast iron material, the distance between two adjacent graphite balls is small, so that the nodular cast iron material has the advantages of small friction coefficient, high aluminum liquid corrosion resistance and good strength and toughness, and solves the problems of poor performance and short service life of cast iron profiles or cast pieces caused by small graphite density and large graphite distance in the prior art.

Description

Technical Field

[0001] This invention relates to the field of metal materials and manufacturing technology, specifically to a ductile iron material, its preparation method, and ductile iron manufactured parts. Background Technology

[0002] Increasing the number of graphite spheres and decreasing the spacing between them in ductile iron significantly improves its anti-friction, wear-resistance, resistance to aluminum melt corrosion, and toughness. This greatly enhances the performance and service life of ductile iron-manufactured components such as friction-resistant parts, aluminum alloy die-casting molds, and aluminum melt siphons, which has significant practical implications for promoting technological advancements in related industries. However, existing graphite spheres in ductile iron parts or profiles are obtained through solidification and are eutectic graphite spheres precipitated in a high-temperature liquid phase. Due to the rapid atomic diffusion in a high-temperature liquid phase, the resulting graphite spheres are generally large and widely spaced. For example, even in the highest-grade (Grade 8) standard of graphite sphere diameter specified in the national standard GB / T9441-2021, the graphite sphere diameter can still reach 15µm, and the spacing between two adjacent graphite spheres can be over 50µm. This does not meet the requirements for graphite sphere size and spacing in friction pair parts with high friction-reducing and wear-resistant properties, and in long-life aluminum alloy die-casting molds. Therefore, obtaining ductile iron parts with smaller diameter graphite spheres and smaller spacing between adjacent graphite spheres is of great significance for the manufacturing and application of high-performance ductile iron parts.

[0003] It is well known that for existing cast iron materials, solid-state phase transformation, i.e., heat treatment, cannot change the morphology, size, and distribution of graphite. When graphitization annealing is performed on cast iron, the resulting graphite morphology is nodular in white cast iron, while in other gray cast iron materials, the graphite formed by graphitization annealing generally adheres to the eutectic graphite obtained during solidification, without forming new graphite nuclei and grains. In other words, heat treatment of existing cast iron materials other than white cast iron only increases the size of the existing graphite, without changing the quantity of graphite.

[0004] Based on the above description, the graphite in existing cast iron materials is basically coarse eutectic graphite. Even with graphitization annealing, new graphite nuclei cannot be formed in the cast iron; it only increases the size of the existing eutectic graphite. This limits the acquisition of cast iron profiles or castings with high graphite density and small graphite spacing, high friction-reducing and wear-resistant properties, and excellent resistance to aluminum melt corrosion. Summary of the Invention

[0005] To address the problems of poor performance and short lifespan of cast iron profiles or castings caused by the low graphite density and large graphite spacing in existing cast iron materials, this invention provides a ductile iron material, a preparation method, and ductile iron manufactured parts.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] This invention provides a method for preparing ductile iron material, comprising the following steps:

[0008] S1: Rapidly cool the spheroidized molten iron to the pseudo-eutectic region to obtain castings or profiles with a fully eutectic structure;

[0009] S2: Annealing the casting or profile to completely decompose the eutectic carbides in the casting or profile into eutectic graphite spheres and alloying elements dissolved in the metal matrix;

[0010] S3: The annealed castings or profiles are subjected to secondary annealing to form secondary graphite spheres in the castings or profiles, thus obtaining ductile iron material.

[0011] Further, the casting or profile comprises, by mass percentage, the following components: 3.5%–3.8% C, 2.0%–2.7% Si, 0.5%–1.0% Cr, 1.0%–3.0% Mo or W, 0.5%–1.0% V, 2.0%–5.0% Ni, 0.40%–0.80% Mn, ≤0.1% P, and 0.03%–0.05% Mg. 残留 0.01% to 0.03% Ce and ≤0.02% S, with the balance being Fe and unavoidable impurities.

[0012] Preferably, the rapid cooling rate in S1 is ≥50℃ / s.

[0013] Furthermore, the annealing process in S2 is as follows: the casting or profile is heated to 950℃~1050℃ and held for 8~12 hours. Then, it is taken out of the furnace for quenching or air-cooled to room temperature to complete the annealing process.

[0014] Preferably, the heating rate for heating the casting or profile to 950℃~1050℃ is 300℃ / h~500℃ / h.

[0015] Furthermore, the secondary annealing method in S3 is as follows: the annealed castings or profiles are heated again to 680℃~730℃, held for 8~12 hours, and then air-cooled to room temperature to complete the secondary annealing.

[0016] Preferably, the heating rate for reheating the annealed casting or profile to 680℃~730℃ is 300℃ / h~500℃ / h.

[0017] Preferably, the ratio of the diameter of the secondary graphite spheres to the diameter of the eutectic graphite spheres is 1:(10-50), and the number of secondary graphite spheres is 10-50 times the number of eutectic graphite spheres.

[0018] A ductile iron material is prepared using the method described above.

[0019] A ductile iron component comprising the aforementioned ductile iron material.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention discloses a method for preparing ductile iron material. The method involves rapidly cooling spheroidized molten iron to the pseudo-eutectic region to obtain a casting or profile with a fully eutectic structure. At this time, the as-cast structure of the casting or profile consists of fine eutectic carbides formed during the rapid cooling of the metal matrix to the pseudo-eutectic region and coarse eutectic graphite spheres obtained by solidification of the molten iron. Then, the casting or profile is annealed to completely decompose the eutectic carbides in the casting or profile into eutectic graphite spheres and alloying elements dissolved in the metal matrix. Finally, the annealed casting or profile is annealed again to form secondary graphite spheres in the casting or profile. In summary, this invention completely graphitizes the as-cast eutectic carbides through two annealing processes, and precipitates them in the form of fine secondary graphite spheres. At the same time, carbon in the supersaturated metal solid solution in the as-cast state also precipitates in the form of fine secondary graphite spheres, so that the final ductile iron material structure includes a metal matrix, coarse eutectic graphite spheres obtained from the solidification of molten iron, and fine secondary graphite spheres formed by solid-state phase transformation. Because the ductile iron material prepared by this method produces a large number of secondary graphite spheres inside, the spacing between adjacent graphite spheres is small. Therefore, it has advantages such as low friction coefficient, high resistance to aluminum liquid corrosion, and good strength and toughness. It is an ideal material for manufacturing friction pair parts with excellent friction performance in mechanical transmission, an ideal material for aluminum alloy die casting molds, and a preferred material for long-life aluminum liquid siphon pipes. It has practical significance for promoting technological progress in the above fields, and at the same time has significant economic benefits for the industrial development of the above fields.

[0022] The castings or profiles comprise, by weight percentage: 3.5%–3.8% C, 2.0%–2.7% Si, 0.5%–1.0% Cr, 1.0%–3.0% Mo or W, 0.5%–1.0% V, 2.0%–5.0% Ni, 0.40%–0.80% Mn, ≤0.1% P, and 0.03%–0.05% Mg. 残留The composition consists of 0.01%–0.03% Ce and ≤0.02% S, with the balance being Fe and unavoidable impurities. By selecting and designing the content of Mo or W, elements that contribute to the formation of white iron in C but whose effect is not significant, the graphitization and size and quantity of carbide precipitates during solidification are controlled. Simultaneously, by utilizing the changes in the solidified carbides during the graphitization heat treatment, partial C dissolution is achieved. During cooling, the graphitization effect of Ni is utilized to precipitate the dissolved C as fine secondary graphite. Furthermore, by utilizing the solid solution of carbide-forming elements such as Cr and V after graphitization, the diffusion rate of dissolved C is controlled, reducing the growth rate of the secondary graphite spheres, thus refining the secondary graphite spheres and further increasing their quantity.

[0023] This invention provides a ductile iron material prepared using the above method. The microstructure of this ductile iron material contains a large number of eutectic graphite spheres and a large number of fine secondary graphite spheres. Due to the presence of secondary graphite spheres, the spacing between adjacent graphite spheres is greatly reduced, which meets the requirements of friction pair parts with low friction reduction and wear resistance, and aluminum alloy die-casting molds with long service life, regarding the size and spacing of graphite spheres.

[0024] The present invention also provides a ductile iron casting part comprising the above-mentioned graphite cast iron material, which has the advantages of low coefficient of friction, high resistance to aluminum melt corrosion and good strength and toughness. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a method for preparing ductile iron material according to the present invention.

[0026] Figure 2 This is a metallographic image of the ductile iron material prepared according to the present invention, after rapid cooling to the pseudo-eutectic region and solidification without corrosion.

[0027] Figure 3 This is a metallographic image of the ductile iron material prepared according to the present invention, after rapid cooling to the pseudo-eutectic region and solidification followed by etching.

[0028] Figure 4 The image shows the metallographic microstructure of the ductile iron material prepared according to this invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0030] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0031] See Figure 1 This invention provides a method for preparing ductile iron material, comprising the following steps:

[0032] S1: Rapidly cool the spheroidized molten iron to the pseudo-eutectic region to obtain a casting or profile with a fully eutectic structure. Specifically, this involves melting primary iron into molten iron at 1500℃~1550℃, and then subjecting the molten iron to inoculation and spheroidization treatment. Preferably, the inoculant is 75SiFe, and the amount of inoculant added is adjustable from 0.20% to 0.60% by mass percentage depending on the Si content of the primary iron; the spheroidizing agent is a silicon-iron rare earth magnesium alloy, and the amount added is adjusted from 1.0% to 1.50% by mass percentage depending on the S content of the original molten iron. After spheroidizing treatment, the molten iron is rapidly cooled to the pseudo-eutectic region at a rate of ≥50℃ / s to complete solidification, resulting in a casting or profile with a fully eutectic structure. The casting or profile comprises, by mass percentage: 3.5%–3.8% C, 2.0%–2.7% Si, 0.5%–1.0% Cr, 1.0%–3.0% Mo or W, 0.5%–1.0% V, 2.0%–5.0% Ni, 0.40%–0.80% Mn, ≤0.1% P, and 0.03%–0.05% Mg. 残留 0.01% to 0.03% Ce and ≤0.02% S, with the balance being Fe and unavoidable impurities.

[0033] S2: Annealing the casting or profile to completely decompose the eutectic carbides in the casting or profile into eutectic graphite spheres and alloying elements dissolved in the metal matrix, specifically:

[0034] The castings or profiles are heated to 950℃~1050℃ at a heating rate of 300℃ / h~500℃ / h and held at that temperature for 8~12h. Then, they are removed from the furnace and oil-quenched or air-cooled to room temperature to complete the annealing treatment. After annealing, the eutectic carbides in the castings or profiles are completely decomposed into graphite and alloying elements dissolved in the metal matrix; at the same time, the uneven distribution of composition caused by solidification in the castings or profiles is homogenized.

[0035] S3: The annealed castings or profiles are subjected to secondary annealing to form secondary graphite spheroids, resulting in ductile iron material. Specifically:

[0036] The annealed castings or profiles are then heated again to 680℃~730℃ at a rate of 300℃ / h~500℃ / h, held at that temperature for 8~12h, and then air-cooled to room temperature to complete the secondary annealing. At this time, a large number of tiny secondary graphite spheres are formed in the castings or profiles. The diameter ratio of the secondary graphite spheres to the diameter of the eutectic graphite spheres is 1:(10~50), and the number of secondary graphite spheres is 10~50 times the number of eutectic graphite spheres.

[0037] Example 1

[0038] Primary iron is melted into molten iron at 1500℃~1550℃, and the molten iron is then inoculated and spheroidized. The spheroidized molten iron is rapidly cooled to the pseudo-eutectic region at a rate of 50℃ / s to complete solidification, resulting in a casting or profile with a fully eutectic structure. The casting or profile comprises, by mass percentage, the following components: 3.5% C, 2.7% Si, 0.5% Cr, 1% Mo, 0.5% V, 2% Ni, 0.4% Mn, ≤0.1% P, and 0.03% Mg. 残留 0.01% Ce and ≤0.02% S, with the balance being Fe and unavoidable impurities.

[0039] The castings or profiles are heated to 950℃ at a heating rate of 300℃ / h and held for 12 hours. Then, they are removed from the furnace and oil-quenched or air-cooled to room temperature to complete the annealing treatment. The annealed castings or profiles are then heated again to 680℃ at a heating rate of 300℃ / h and held for 12 hours. They are then removed from the furnace and air-cooled to room temperature to complete the secondary annealing, resulting in ductile iron material.

[0040] Example 2

[0041] Primary iron is melted into molten iron at 1500℃~1550℃, and the molten iron is then inoculated and spheroidized. The spheroidized molten iron is rapidly cooled to the pseudo-eutectic region at a rate of 55℃ / s to complete solidification, resulting in a casting or profile with a fully eutectic structure. The casting or profile comprises, by mass percentage: 3.8% C, 2.0% Si, 1.0% Cr, 2.5% W, 1.0% V, 5.0% Ni, 0.80% Mn, ≤0.1% P, and 0.05% Mg. 残留 0.03% Ce and ≤0.02% S, with the balance being Fe and unavoidable impurities.

[0042] The castings or profiles are heated to 1050℃ at a heating rate of 450℃ / h and held for 8 hours. Then, they are removed from the furnace and oil-quenched or air-cooled to room temperature to complete the annealing treatment. The annealed castings or profiles are then heated again to 730℃ at a heating rate of 350℃ / h and held for 12 hours. They are then removed from the furnace and air-cooled to room temperature to complete the secondary annealing, resulting in ductile iron material.

[0043] Example 3

[0044] Primary iron is melted into molten iron at 1500℃~1550℃, and the molten iron is then inoculated and spheroidized. The spheroidized molten iron is rapidly cooled to the pseudo-eutectic region at a rate of 55℃ / s to complete solidification, resulting in a casting or profile with a fully eutectic structure. The casting or profile comprises, by mass percentage: 3.6% C, 2.4% Si, 0.8% Cr, 2.0% W, 0.8% V, 4.0% Ni, 0.60% Mn, ≤0.1% P, and 0.04% Mg. 残留 0.02% Ce and ≤0.02% S, with the balance being Fe and unavoidable impurities.

[0045] The castings or profiles are heated to 1000℃ at a heating rate of 500℃ / h and held for 10 hours. Then, they are removed from the furnace and oil-quenched or air-cooled to room temperature to complete the annealing treatment. The annealed castings or profiles are then heated again to 700℃ at a heating rate of 500℃ / h and held for 10 hours. Then, they are removed from the furnace and air-cooled to room temperature to complete the secondary annealing, obtaining ductile iron material.

[0046] Example 4

[0047] Primary iron is melted into molten iron at 1500℃~1550℃, and the molten iron is then inoculated and spheroidized. The spheroidized molten iron is rapidly cooled to the pseudo-eutectic region at a rate of 55℃ / s to complete solidification, resulting in a casting or profile with a fully eutectic structure. The casting or profile comprises, by mass percentage: 3.7% C, 2.2% Si, 0.65% Cr, 1.6% Mo, 0.6% V, 3.5% Ni, 0.50% Mn, ≤0.1% P, and 0.03% Mg. 残留 0.015% Ce and ≤0.02% S, with the balance being Fe and unavoidable impurities.

[0048] The castings or profiles are heated to 980℃ at a heating rate of 450℃ / h and held for 11 hours. Then, they are removed from the furnace and oil-quenched or air-cooled to room temperature to complete the annealing treatment. The annealed castings or profiles are then heated again to 690℃ at a heating rate of 500℃ / h and held for 10 hours. They are then removed from the furnace and air-cooled to room temperature to complete the secondary annealing, resulting in ductile iron material.

[0049] Example 5

[0050] Primary iron is melted into molten iron at 1500℃~1550℃, and the molten iron is then inoculated and spheroidized. The spheroidized molten iron is rapidly cooled to the pseudo-eutectic region at a rate of 60℃ / s to complete solidification, resulting in a casting or profile with a fully eutectic structure. The casting or profile comprises, by mass percentage: 3.65% C, 2.6% Si, 0.65% Cr, 2.5% W, 0.9% V, 2.8% Ni, 0.70% Mn, ≤0.1% P, and 0.035% Mg. 残留 0.025% Ce and ≤0.02% S, with the balance being Fe and unavoidable impurities.

[0051] The casting or profile is heated to 100℃ at a heating rate of 380℃ / h and held for 9 hours. Then, it is removed from the furnace and oil-quenched or air-cooled to room temperature to complete the annealing treatment. The annealed casting or profile is then heated again to 720℃ at a heating rate of 380℃ / h and held for 9 hours. Then, it is removed from the furnace and air-cooled to room temperature to complete the secondary annealing, obtaining ductile iron material.

[0052] See Figures 2 to 4 Metallographic microstructure testing was performed on the castings or profiles prepared during the ductile iron material preparation process in the above embodiments. It was observed that the size of the eutectic graphite spheres in the castings or profiles with a fully eutectic structure during rapid solidification was 20-30 μm, and the distance between two adjacent graphite spheres was more than 30 μm. The as-cast metallographic microstructure of the castings or profiles after corrosion showed that the solidified structure contained both coarse eutectic graphite spheres and coarse eutectic carbides. Finally, the microstructure of the castings or profiles after secondary annealing showed coarse eutectic graphite spheres and fine secondary graphite spheres. The diameter of the coarse eutectic graphite spheres was more than ten times that of the fine secondary graphite spheres, while their number was one-tenth or one-several tenths of that of the secondary graphite spheres. Due to the presence of secondary graphite spheres, the distance between two adjacent graphite spheres was greatly reduced from the initial distance between two adjacent eutectic graphite spheres, which is beneficial to improving the profile's resistance to aluminum melt corrosion and its mechanical properties.

[0053] This invention provides a ductile iron material prepared using the method described above. The microstructure of this ductile iron material contains a large number of eutectic graphite spheres and a large number of fine secondary graphite spheres. The presence of secondary graphite spheres significantly reduces the spacing between adjacent graphite spheres, thus meeting the requirements for graphite sphere size and spacing in friction pair parts with low friction-reducing and wear-resistant properties, and in long-life aluminum alloy die-casting molds.

[0054] The present invention also provides a ductile iron component, comprising the aforementioned ductile iron material. This component has advantages such as a low coefficient of friction, high resistance to molten aluminum corrosion, and good strength and toughness.

[0055] In summary, this invention provides a ductile iron material, a preparation method, and ductile iron castings. By rapidly cooling spheroidized molten iron to the pseudo-eutectic region, the as-cast microstructure of the casting or profile consists of a metal matrix, fine eutectic carbides formed during the rapid cooling process to the pseudo-eutectic region, and coarse eutectic graphite spheres obtained from the solidification of the molten iron. Then, through two annealing treatments, the as-cast eutectic carbides are completely graphitized and precipitated as fine secondary graphite spheres. Simultaneously, carbon in the supersaturated metal solid solution in the as-cast state also precipitates as fine secondary graphite spheres. This results in a final ductile iron material microstructure comprising a metal matrix, coarse eutectic graphite spheres obtained from the solidification of molten iron, and fine secondary graphite spheres formed by solid-state phase transformation. The small spacing between adjacent graphite spheres provides advantages such as a low coefficient of friction, high resistance to aluminum melt corrosion, and good strength and toughness. This solves the problem of low service life of existing friction pair parts due to their high coefficient of friction, and the severe corrosion of aluminum alloy die-casting molds and aluminum liquid siphons by the aluminum liquid.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A method for preparing ductile iron material, characterized in that, Includes the following steps: S1: Rapidly cool the spheroidized molten iron to the pseudo-eutectic region to obtain a casting or profile with a fully eutectic structure; wherein the rapid cooling rate is ≥50℃ / s, and the casting or profile comprises the following components by mass percentage: 3.5%~3.8% C, 2.0%~2.7% Si, 0.5%~1.0% Cr, 1.0%~3.0% Mo or W, 0.5%~1.0% V, 2.0%~5.0% Ni, 0.40%~0.80% Mn, ≤0.1% P, and 0.03%~0.05% Mg. 残留 0.01% to 0.03% Ce and ≤0.02% S, with the balance being Fe and unavoidable impurities; S2: Annealing the casting or profile to completely decompose the eutectic carbides in the casting or profile into eutectic graphite spheres and alloying elements dissolved in the metal matrix; the annealing method is as follows: Heat the castings or profiles to 950℃~1050℃, hold for 8~12 hours, then remove from the furnace and quench or air cool to room temperature to complete the annealing process. S3: The annealed castings or profiles are subjected to secondary annealing to form secondary graphite spheroids, resulting in ductile iron material; the secondary annealing method is as follows: After annealing, the castings or profiles are heated again to 680℃~730℃ and held for 8~12 hours. Then they are taken out of the furnace and air-cooled to room temperature to complete the secondary annealing.

2. The method for preparing ductile iron material according to claim 1, characterized in that, The heating rate for heating castings or profiles to 950℃~1050℃ is 300℃ / h~500℃ / h.

3. The method for preparing ductile iron material according to claim 1, characterized in that, The annealed castings or profiles are then heated again to 680℃~730℃ at a rate of 300℃ / h~500℃ / h.

4. The method for preparing ductile iron material according to claim 1, characterized in that, The ratio of the diameter of the secondary graphite spheres to the diameter of the eutectic graphite spheres is 1:(10-50), and the number of secondary graphite spheres is 10-50 times the number of eutectic graphite spheres.

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