High-strength and high-toughness nodular iron casting with thick and large end face and casting method

Abstract

The invention discloses a high-strength and high-toughness nodular iron casting with a thick and large end face and a casting method, and belongs to the technical field of metal casting. The nodular iron casting comprises the following components in percentage by weight: 3.6-3.9% of C, 2.2-2.5% of Si, less than or equal to 0.15% of Mn, less than or equal to 0.035% of P, Slt and the balance of Fe. 0.012% of Mg, 0.030 to 0.060% of Mg, and 0.010 to 0.020% of Re; and the balance of Fe and inevitable impurities. The thickness of the nodular iron casting is larger than or equal to 300 mm, the tensile strength is larger than or equal to 390 MPa, the yield strength is larger than or equal to 260 MPa, the ductility is larger than or equal to 20%, and the impact energy is larger than or equal to 13 Meanwhile, the invention further provides a casting method of the nodular iron casting. The nodular iron casting completely meets the mechanical property requirements of fan bases and other large energy facility parts with the thickness exceeding 300 mm, and has high comprehensive performance.

Description

Technical Field

[0001] The invention belongs to the technical field of metal casting, and in particular relates to a ductile iron casting with a thick end surface, high strength and high toughness, and a casting method. Background Art

[0002] Ductile iron has been widely used in many fields such as automobile manufacturing, municipal facilities, large-scale engineering machinery, and key components of energy infrastructure due to its excellent mechanical properties close to those of steel and low processing costs. Although ductile iron has gradually developed into many grades with diverse performance since its rise in the 1950s, how to ensure high strength of ductile iron while having high elongation and better comprehensive mechanical properties has always been one of the difficulties in casting ductile iron.

[0003] With the continuous enlargement of equipment such as engineering machinery and energy facilities, the thickness of parts is also increasing. How to ensure that the product has comprehensive mechanical properties that meet the use requirements when the thickness continues to increase is one of the key research directions. At present, the wall thickness of many important parts of large facilities has exceeded the range of wall thickness specifications for ductile iron defined in the national standard (GB / T 1348-2019 Ductile Iron Parts) (i.e. 200mm). There is no clear standard for mechanical properties and metallographic structure of ultra-thick large-end ductile iron with a wall thickness of more than 200mm. In the casting process of ductile iron parts, due to the slow solidification speed at the thick and large end faces, solidification takes a long time, and structural defects such as graphite fragmentation, shrinkage, and shrinkage often occur, which in turn affects the final mechanical properties of ductile iron parts.

[0004] The prior art has reported on the performance improvement of thick and large end-face cast iron parts. For example, in order to improve the technical performance of ultra-thick and large end-face ferrite ductile iron parts with a wall thickness of more than 500mm used in ductile iron containers for nuclear spent fuel, the prior art CN111074145A discloses a low-temperature toughness ultra-thick and large end-face ferrite ductile iron part and a preparation method for the cast iron part. By adding general chill, adding Ni and Sb alloy elements, and strictly controlling the trace elements of the pig iron raw materials, it achieves high impact and high fracture toughness of Φ800mm×800mm size castings at -40℃. At the same time, the mechanical properties of tensile strength of 372MPa, yield strength of 246MPa and elongation of 21% are obtained at room temperature (20℃).

[0005] Prior art CN 116065085A discloses an ultra-thick ductile iron and its casting method, which controls the content of silicon, carbon and other elements in the cast iron and combines the sky furnace-electric furnace double smelting method to prepare a cast iron part with a maximum wall thickness of 1500mm. The main body sleeve prepared by the method has a tensile strength of 350MPa, a yield strength of 230MPa, an elongation of 10%, and a spheroidization rate of 90%.

[0006] The present invention is aimed at wind turbine bases with a wall thickness of more than 300 mm (operating environment temperature -30℃~40℃). The basic mechanical properties of this practical component are required to reach a tensile strength of at least 390MPa, a yield strength of at least 260MPa, an elongation of more than 20%, and an impact energy of more than 13J. Although the wall thickness and individual indicators of the cast iron parts prepared by the above-mentioned prior art have reached the technical requirements, they cannot meet the above-mentioned basic mechanical performance indicators at the same time, and there is still a gap between the comprehensive mechanical performance and the technical requirements. Summary of the invention

[0007] 1. Technical issues to be resolved The present invention aims to solve one of the following technical problems existing in the prior art or related technology: The existing thick and large end-face cast iron parts with a wall thickness exceeding 300 mm cannot simultaneously meet the application requirements in terms of tensile strength, flexural strength, elongation and impact energy.

[0008] (II) Technical solution In order to solve the above technical problems, the present invention provides a ductile iron casting with thick end surface, high strength and high toughness. The specific technical scheme adopted is as follows: A ductile iron casting with a thick end surface, high strength and high toughness, comprising the following components in weight percentage: C 3.6-3.9%, Si 2.2-2.5%, Mn≤0.15%, P≤0.035%, S<0.012%, Mg 0.030-0.060%, Re0.010-0.020%; the balance is Fe and unavoidable impurities; the ductile iron casting has a thickness of ≥300 mm, a tensile strength of ≥390 MPa, a yield strength of ≥260 MPa, an elongation of ≥20%, and an impact energy of ≥13 J.

[0009] Preferably, the cast iron part comprises the following components in weight percentage: C 3.75%, Si 2.26%, Mn≤0.15%, P≤0.035%, S<0.012%, Mg 0.044%, Re 0.010%; the balance is Fe and unavoidable impurities.

[0010] Preferably, the graphite grade of the ductile iron casting is 6-8, and the hardness is 130-180 HBW.

[0011] Another object of the present invention is to provide a casting method for the above-mentioned ductile iron casting, the steps of the method are as follows: (1) Molding and assembling: Use molding sand to make product sand molds and sand cores, and cover the thick end surface of the ductile iron casting to be cast with graphite chill before assembling, place pressure iron and bake the surrounding sand to form a sand mold to be poured; (2) Smelting: Add the charge into the unidirectional smelting furnace according to the batching and heat it to a molten state, detect the composition of the molten iron, and adjust the content of C, Si and S in the molten iron to obtain the original molten iron after the adjustment; (3) Spheroidizing and tapping: Sb, spheroidizing agent, silicon particles, inoculant and pretreatment agent are added to the molten iron in step (2) in order, and after the addition is completed, the temperature is raised to 1440-1450°C and then taken out of the furnace, and the molten iron is flushed into the spheroidizing pool for spheroidizing treatment; (4) Casting: The molten iron after the spheroidization treatment in step (3) is poured into the sand mold obtained in step (1). After the casting is completed and cooled, a ductile iron casting is obtained.

[0012] Preferably, the tensile strength of the sand mold and sand core in step (1) is 1.25±0.02 MPa, and the bending strength is 2.5±0.04 MPa.

[0013] Preferably, the ingredient list in step (2) comprises the following components in weight percentage: 45-70% pig iron, 10-20% scrap steel, 20-35% recycled materials, and 5-12% iron filings.

[0014] Preferably, the temperature of heating to the molten state in step (2) is 1420-1480° C.; the C content of the molten iron is 3.7±0.03%, the Si content is 1.10±0.02%, and S≤0.015%.

[0015] Preferably, the spheroidizing treatment time in step (3) is ≥150s; the amount of Sb added is 0.004-0.005% of the weight of the molten iron; the spheroidizing agent is Aiken spheroidizing agent, and the amount added is 0.95-1.05% of the weight of the molten iron; the silicon content in the silicon particles is 70-75%, and the amount added is 0.2-0.3% of the weight of the molten iron; the inoculant is Aiken 6217 inoculant, and the amount added is 0.25-0.30% of the weight of the molten iron; the pretreatment agent is Carr inoculant, with a particle size of 2-6mm, model TY-05, the Si content in the Carr inoculant is 60-67%, and the amount added is 0.3% of the weight of the molten iron.

[0016] Preferably, the pouring temperature of step (4) is 1360-1362° C.; the time from the start of spheroidization to the completion of pouring is ≤15 min; before pouring, Si in the molten iron accounts for 2.15±0.02% of the total weight of the molten iron, Mn accounts for ≤0.15% of the total weight of the molten iron, P accounts for ≤0.035% of the total weight of the molten iron, S accounts for <0.012% of the total weight of the molten iron, and Mg accounts for 0.035-0.045% of the total weight of the molten iron.

[0017] (III) Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: In view of the high comprehensive performance requirements of thick and large end-face cast iron parts with a wall thickness of more than 300mm, the composition of various trace elements in cast iron, the use of casting aids such as spheroidizers and inoculants, and the use of graphite chillers are rationally optimized to shorten the cooling time of castings, prevent shrinkage of castings, pearlite due to long cooling time, poor metallographic graphite, and other problems, and avoid the occurrence of structural defects such as graphite fragmentation, shrinkage, and shrinkage cavities caused by long cooling. At the same time, the performance gap between the attached casting and the main body kit is shortened. Finally, when the wall thickness exceeds 300mm, the tensile strength is greater than 390MPa, the yield strength is greater than 260MPa, the elongation is greater than 20%, and the impact energy is greater than 13J. The thick and large end-face ductile iron parts with excellent comprehensive performance are obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention. In the accompanying drawings: Figure 1 This is a metallographic image of the thick end surface of the graphite chilled iron body sample used in Example 1 before corrosion.

[0019] Figure 2 This is a metallographic image of the thick end surface of the main body sleeve sample using graphite chiller in Example 1 after corrosion.

[0020] Figure 3 This is the metallographic image of the thick end surface of the body sleeve sample without graphite chill in comparative example 1 before corrosion.

[0021] Figure 4 This is a metallographic image of the thick end surface of the body sleeve sample without graphite chill in comparative example 1 after corrosion.

[0022] Figure 5 This is the metallographic image of the thick end surface of the body sleeve sample using ordinary chilled iron in comparative example 2 before corrosion.

[0023] Figure 6 This is the metallographic image of the thick end surface of the main body sleeve sample after corrosion using ordinary cold iron in comparative example 2. DETAILED DESCRIPTION

[0024] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different embodiments as defined and covered by the claims.

[0025] Unless otherwise specified, the materials, reagents, instruments, and methods used in the following examples are conventional materials, reagents, instruments, and methods in the art, and can be obtained by ordinary technicians in the art through commercial channels, including but not limited to Elkem spheroidizers and inoculants.

[0026] The recycled materials used in the following examples refer to the waste parts, risers, pouring nozzles and other scrap metals generated in the production process of casting ductile iron parts using the method of the present invention, which are sent back to the furnace for re-smelting. The pig iron, scrap steel, recycled materials and iron filings used in the examples are all from the same batch. Among them, the pig iron is ordinary pig iron for wind power, which is measured to contain C 4.516%, Si0.6215%, Mn 0.0772%, P 0.0227%, S 0.0163%. The scrap steel is measured to contain C 0.041%, Si 0.0133%, Mn 0.197%, P 0.0043%, S 0.0023%. The recycled materials are measured to contain C 3.6879%, Si 2.26%, Mn 0.13%, P 0.021%, S 0.0078%. The iron filings were determined to contain C 3.6879%, Si 2.26%, Mn 0.13%, P 0.021%, and S0.0078%.

[0027] The modeling resin used in the following examples is silica furan resin, the dosage is 0.95%, and the dosage of curing agent G-1 is 50%. The coating for sand casting is purchased from Shandong Changyu Shengquan Coating Co., Ltd., product model: SQM-B26.

[0028] Example 1

[0029] This embodiment provides a casting method for a ductile iron casting of a 10MW wind turbine base with an average wall thickness of more than 300 mm. The outline size of the product is 4.8m×3.2m×1.5m and the weight is 23t. The specific casting process is as follows: (1) Molding and box assembly: Based on the designed fan base model, the sand mold and sand core of the ductile iron casting are manufactured using molding resin and curing agent. The tensile strength of the manufactured sand mold is 1.25±0.02MPa, and the bending strength is 2.50±0.04MPa. After the sand mold is solidified and demolded, the paint is brushed on the sand mold. After the paint is brushed, it is burned dry and baked with a hot air blower. After the core is assembled and the box is assembled, the pressure iron is placed and the surrounding sand is baked to form a sand mold to be poured. Before the box is assembled, large graphite chillers are placed in the upper box and the lower box on the thick end face of the casting, and the thick parts of the casting are respectively placed to ensure that the cooling time of the large end part of the casting does not have too much contrast and affect the performance of the casting. Among them, the specific size of the graphite chiller is 170mm×110mm×100mm.

[0030] (2) Melting: Add smelting charge into a medium frequency induction furnace according to the following batching list: 50% pig iron, 15% scrap steel, 25% recycled charge, and 10% iron filings; raise the temperature to 1420-1480°C to melt the charge to form molten iron; detect and control the contents of C, Si and S in the molten iron, where C: 3.74±0.03%; Si: 1.10±0.02%; S≤ 0.015%; (3) Nodularization and tapping: 0.004-0.005% of Sb by weight of the molten iron is added to the nodularization ladle in step (2) in order to improve the roundness of the graphite nodules, 0.95-1.05% of Aiken nodularizer (containing 45-47% Si and 5.5-6.5% Mg), 0.2-0.3% of 75 silicon particles (Si content is 75%), 0.25-0.30% of Aiken inoculant, Si content is 70-76%, and finally 0.3% of Carr inoculant, model TY-05, particle size 2-6mm, Si content 60-67% is added; after the above reagents are added to the ladle, the electric furnace is heated to 1440°C and the iron is tapped for spheroidization, and the spheroidization time is not less than 150s; (4) Pouring: Start pouring when the molten iron temperature is 1362℃, and complete the pouring within 15 minutes from the start of spheroidization. Before pouring, spread a layer of slag-blocking cotton on the surface of the molten iron to prevent slag from falling. During pouring, the molten iron contains Si: 2.15±0.02%, Mn≤ 0.15%, P≤ 0.035%, S<0.012%, and Mg: 0.035-0.045%. After pouring and cooling, ductile iron castings are obtained.

[0031] Example 2

[0032] This embodiment provides a method for casting a ductile iron casting of a 10MW wind turbine base with an average wall thickness exceeding 300 mm. The specifications and dimensions of the wind turbine base are the same as those in Embodiment 1. The specific casting process is as follows: (1) Molding and box assembly: Based on the designed fan hub base model, the sand mold and sand core of the ductile iron casting are manufactured using molding resin and curing agent. The tensile strength of the manufactured sand mold is 1.25±0.02MPa, and the bending strength is 2.50±0.04MPa. After the sand mold is solidified and demolded, the paint is brushed on the sand mold. After brushing the paint, it is burned dry and baked with a hot air blower. After the core is assembled and the box is assembled, the pressure iron is placed and the surrounding sand is baked to form a sand mold to be poured. Before the box is assembled, large graphite chills are placed in the cover box and the lower cover box on the large end face of the casting, and in the thick and large parts of the casting to ensure that the cooling time of the large end part of the casting does not have too much contrast and affect the performance of the casting. Among them, the specific size of the graphite chill is 170mm×110mm×100mm.

[0033] (2) Melting: Add smelting charge into a medium frequency induction furnace according to the following batching list: 45% pig iron, 20% scrap steel, 30% recycled charge, 5% iron filings; raise the temperature to 1420-1480°C to melt the charge to form molten iron; detect and control the contents of C, Si and S in the molten iron, where C: 3.74±0.03%; Si: 1.10±0.02%; S≤ 0.015%; (3) Spheroidizing and tapping: 0.004-0.005% Sb by weight of the molten iron, 0.95-1.05% Aiken spheroidizing agent (containing 45-47% Si and 5.5-6.5% Mg) are added to the spheroidizing ladle in step (2) in order, followed by 0.2-0.3% 75 silicon particles (containing 75% Si), 0.25-0.30% Aiken inoculant, containing 70-76% Si, and finally 0.3% Carr inoculant, model TY-05, particle size 2-6mm, Si content 60-67%. After the above reagents are added to the ladle, the electric furnace is heated to 1440°C and then the iron is tapped for spheroidizing, and the spheroidizing time is not less than 150s. (4) Pouring: Start pouring when the molten iron temperature is 1360℃, and complete the pouring within 15 minutes from the start of spheroidization. Before pouring, spread a layer of slag-blocking cotton on the surface of the molten iron to prevent slag from falling. During pouring, the molten iron contains Si: 2.15±0.02%, Mn≤ 0.15%, P≤ 0.035%, S<0.012%, and Mg: 0.035-0.045%. After pouring is completed and cooled, ductile iron castings are obtained.

[0034] Example 3

[0035] This embodiment provides a casting method for a ductile iron casting of a 10MW wind turbine base with an average wall thickness exceeding 300 mm. The specifications and dimensions of the wind turbine base are the same as those in Embodiment 1. The specific casting process is as follows: (1) Molding and box assembly: Based on the designed fan base model, the sand mold and sand core of the ductile iron casting are manufactured using molding resin and curing agent. The tensile strength of the manufactured sand mold is 1.25±0.02MPa, and the bending strength is 2.50±0.04MPa. After the sand mold is solidified and demolded, the paint is brushed on the sand mold. After the paint is brushed, it is burned dry and baked with a hot air blower. After the core is assembled and the box is assembled, the pressure iron is placed and the surrounding sand is baked to form a sand mold to be poured. Before the box is assembled, large graphite chillers are placed in the upper box and the lower box on the thick end of the casting to ensure that the cooling time of the large end of the casting does not have too much contrast and affect the performance of the casting. Among them, the specific size of the graphite chiller is 170mm×110mm×100mm.

[0036] (2) Melting: Add smelting charge into a medium frequency induction furnace according to the following batching list: 65% pig iron, 10% scrap steel, 20% recycled charge, 5% iron filings; raise the temperature to 1420-1480°C to melt the charge to form molten iron; detect and control the contents of C, Si and S in the molten iron, where C: 3.74±0.03%; Si: 1.10±0.02%; S≤ 0.015%; (3) Spheroidizing and tapping: add 0.004-0.005% Sb by weight of the molten iron, 0.95-1.05% Aiken spheroidizing agent (containing Si 45-47%, Mg 5.5-6.5%), 0.2-0.3% 75 silicon particles with Si content of 75%, 0.25-0.30% Aiken inoculant with Si content of 70-76%, and finally 0.3% Carr inoculant, model TY-05, particle size 2-6mm, Si content 60-67%; after the above reagents are added to the ladle, the electric furnace is heated to 1450℃ and then the iron is tapped for spheroidizing, and the spheroidizing time is not less than 150s; (4) Pouring: Start pouring when the molten iron temperature is 1360℃, and complete the pouring within 15 minutes from the start of spheroidization. Before pouring, spread a layer of slag-blocking cotton on the surface of the molten iron to prevent slag from falling. During pouring, the molten iron contains Si: 2.15±0.02%, Mn≤ 0.15%, P≤ 0.035%, S<0.012%, and Mg: 0.035-0.045%. After pouring is completed and cooled, ductile iron castings are obtained.

[0037] Comparative Example 1 This comparative example provides a method for casting a ductile iron casting of a 10MW wind turbine base with a wall thickness exceeding 300 mm. The specifications and dimensions of the wind turbine base are the same as those of Example 1. The specific casting process is as follows: (1) Molding and assembly: Based on the designed fan hub base model, use molding resin and curing agent to manufacture sand molds and sand cores for ductile iron castings. The tensile strength of the manufactured sand mold is 1.25±0.02MPa, and the bending strength is 2.50±0.04MPa. After the sand mold is solidified and demolded, paint is applied to the sand mold. After the core is assembled and dropped, the iron is placed and the surrounding sand is baked to form a sand mold to be cast.

[0038] (2) Melting: Add smelting charge into a medium frequency induction furnace according to the following batching list: 50% pig iron, 15% scrap steel, 25% recycled charge, 10% iron filings; raise the temperature to 1420-1480°C to melt the charge to form molten iron; detect and control the contents of C, Si and S in the molten iron, where C: 3.74±0.03%; Si: 1.10±0.02%; S≤ 0.015%; (3) Spheroidizing and tapping: 0.004-0.005% Sb by weight of the molten iron, 0.95-1.05% Aiken spheroidizing agent (containing Si 45-47%, Mg 5.5-6.5%), 0.2-0.3% 75 silicon particles (Si content 75%), 0.25-0.30% Aiken inoculant (Si content 70-76%), and finally 0.3% Carr inoculant, model TY-05, particle size 2-6mm, Si content 60-67% are added to the spheroidizing ladle in step (2) in order. After the above reagents are added to the ladle, the electric furnace is heated to 1480°C and the iron is tapped for spheroidization. The spheroidizing time is not less than 150s. (4) Pouring: Start pouring when the molten iron temperature is 1360℃, and complete the pouring within 15 minutes from the start of spheroidization. Before pouring, spread a layer of slag-blocking cotton on the surface of the molten iron to prevent slag from falling. During pouring, the molten iron contains Si: 2.15±0.02%, Mn≤ 0.15%, P≤ 0.035%, S<0.012%, and Mg: 0.035-0.045%. After pouring is completed and cooled, ductile iron castings are obtained.

[0039] Comparative Example 2 This comparative example provides a method for casting a ductile iron casting of a 10MW wind turbine base with a wall thickness exceeding 300 mm. The specifications and dimensions of the wind turbine base are the same as those of Example 1. The specific casting process is as follows: (1) Molding and assembly: Based on the designed fan hub base model, the sand mold and sand core of the ductile iron casting are manufactured using molding resin and curing agent. The tensile strength of the manufactured sand mold is 1.25±0.02MPa, and the bending strength is 2.50±0.04MPa. After the sand mold is solidified and demolded, the paint is brushed on the sand mold, and the chiller is brushed with paint. Before assembly, an ordinary chiller is placed on the upper and lower cover boxes on the large end of the casting to ensure that the cooling time of the large end of the casting does not have too much contrast and affect the performance of the casting. The size of the graphite chiller is 170mm×110mm×100mm. Dry it and bake it with a hot air blower. After the core is assembled and the core is assembled, the pressure iron is placed and the sand is baked to form a sand mold to be poured.

[0040] (2) Melting: Add smelting charge into a medium frequency induction furnace according to the following batching list: 50% pig iron, 15% scrap steel, 25% recycled charge, 10% iron filings; raise the temperature to 1420-1480°C to melt the charge to form molten iron; detect and control the contents of C, Si and S in the molten iron, where C: 3.74±0.03%; Si: 1.10±0.02%; S≤ 0.015%; (3) Spheroidizing and tapping: 0.004-0.005% Sb by weight of the molten iron, 0.95-1.05% Aiken spheroidizing agent (containing Si 45-47%, Mg 5.5-6.5%), 0.2-0.3% 75 silicon particles (Si content 75%), 0.25-0.30% Aiken inoculant (Si content 70-76%), and finally 0.3% Carr inoculant, model TY-05, particle size 2-6mm, Si content 60-67% are added to the spheroidizing ladle in step (2) in order. After the above reagents are added to the ladle, the electric furnace is heated to 1480°C and the iron is tapped for spheroidization. The spheroidizing time is not less than 150s. (4) Pouring: Start pouring when the molten iron temperature is 1360℃, and complete the pouring within 15 minutes from the start of spheroidization. Before pouring, spread a layer of slag-blocking cotton on the surface of the water to prevent slag from falling. During pouring, the molten iron contains Si: 2.15±0.02%, Mn≤ 0.15%, P≤ 0.035%, S<0.012%, and Mg: 0.035-0.045%. After pouring and cooling, ductile iron castings are obtained.

[0041] The chemical compositions of the cast test pieces of Examples 1-3 and Comparative Examples 1-2 were measured, and the results are shown in Table 1.

[0042] Table 1 Chemical composition determination results of the cast test blocks of Examples 1-3 and Comparative Example 1

[0043] According to the national standard GB / T 1348-2019, the tensile strength, yield strength, elongation, impact energy, graphite grade and hardness index of the cast test blocks and the body sleeve samples of Examples 1-3 and Comparative Example 1 were measured, and the results are shown in Table 2. The cast test blocks and the body sleeve samples were taken from the same part of the sample, and the wall thickness at the sampling point was 315 mm.

[0044] Table 2 Mechanical properties test results of the cast test blocks and body sleeve samples of Examples 1-3 and Comparative Examples 1-2

[0045] As can be seen from Table 2, the tensile strength and yield strength of the ductile iron parts prepared using graphite chilled iron are significantly higher than those without ordinary chilled iron (Comparative Example 1). In addition, the tensile strength, yield strength, elongation, impact energy and other mechanical performance indicators of the body sleeve samples prepared in Examples 1-3 all meet the performance requirements of the wind turbine base with an average wall thickness of more than 300 mm. In addition, the tensile strength and yield strength of the ductile iron parts using graphite chilled iron are higher than those of the ductile iron parts using ordinary chilled iron.

[0046] At the same time, metallographic images of the thick end surface (wall thickness exceeding 300 mm) of the body sleeve samples prepared in Example 1, Comparative Example 1 and Comparative Example 2 before and after corrosion were obtained using a metallographic microscope ( Figure 1-6 ).from Figure 1-6 It can be seen that only the metallographic image of the ductile iron body sleeve after corrosion using large graphite chilled iron has no pearlite ( Figure 2 ), no cold iron was used (Comparative Example 1, Figure 4 ) and the body set sample using ordinary cold iron (Comparative Example 2, Figure 6 ) shows about 10% pearlite in the metallographic images of the body sleeve samples of ductile iron castings after corrosion.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A ductile iron casting with a thick end surface, high strength and high toughness, characterized in that: The ductile iron casting comprises the following components in weight percentage: C 3.6-3.9%, Si 2.2-2.5%, Mn≤0.15%, P≤0.035%, S<0.012%, Mg 0.030-0.060%, Re0.010-0.020%; the balance is Fe and unavoidable impurities; the thickness of the ductile iron casting is ≥300 mm, the tensile strength is ≥390 MPa, the yield strength is ≥260 MPa, the elongation is ≥20%, and the impact energy is ≥13 J.

2. The thick end surface high strength and high toughness ductile iron casting according to claim 1 is characterized in that: The invention comprises the following components in weight percentage: C 3.75%, Si 2.26%, Mn≤0.15%, P≤0.035%, S<0.012%, Mg 0.044%, Re0.010%; the balance is Fe and unavoidable impurities.

3. The thick end surface high strength and high toughness ductile iron casting according to claim 1, characterized in that: The graphite grade of the ductile iron casting is 6-8 and the hardness is 130-180 HBW.

4. A method for casting a ductile iron casting according to any one of claims 1 to 3, characterized in that: Here are the steps: (1) Molding and assembling: Use molding sand to make product sand molds and sand cores, and cover the thick end surface of the ductile iron casting to be cast with graphite chill before assembling, place pressure iron and bake the surrounding sand to form a sand mold to be poured; (2) Smelting: Add the charge into the unidirectional smelting furnace according to the batching and heat it to a molten state, detect the composition of the molten iron, and adjust the content of C, Si and S in the molten iron to obtain the original molten iron after the adjustment; (3) Spheroidizing and tapping: Sb, spheroidizing agent, silicon particles, inoculant and pretreatment agent are added to the molten iron in step (2) in order, and after the addition is completed, the temperature is raised to 1440-1450°C and then taken out of the furnace, and the molten iron is flushed into the spheroidizing pool for spheroidizing treatment; (4) Casting: The molten iron after the spheroidization treatment in step (3) is poured into the sand mold obtained in step (1). After the casting is completed and cooled, a ductile iron casting is obtained.

5. The casting method according to claim 4, characterized in that: The tensile strength of the sand mold and sand core in step (1) is 1.25±0.02MPa, and the bending strength is 2.5±0.04MPa.

6. The casting method according to claim 4, characterized in that: The ingredient list of step (2) includes the following components in weight percentage: 45-70% pig iron, 10-20% scrap steel, 20-35% recycled materials, and 5-12% iron filings.

7. The casting method according to claim 4, characterized in that: The temperature of heating to the molten state in step (2) is 1420-1480°C; the C content of the molten iron is 3.7±0.03%, the Si content is 1.10±0.02%, and S≤0.015%.

8. The casting method according to claim 4, characterized in that: The spheroidizing time of step (3) is ≥150s; the amount of Sb added is 0.004-0.005% of the weight of the molten iron; the spheroidizing agent is Aiken spheroidizing agent, and the amount added is 0.95-1.05% of the weight of the molten iron; the silicon content in the silicon particles is 70-75%, and the amount added is 0.2-0.3% of the weight of the molten iron; the inoculant is Aiken 6217 inoculant, and the amount added is 0.25-0.30% of the weight of the molten iron; the pretreatment agent is Carr inoculant, with a particle size of 2-6mm, model TY-05, the Si content in the pretreatment agent is 60-67%, and the amount added is 0.3% of the weight of the molten iron.

9. The casting method according to claim 4, characterized in that: The pouring temperature of step (4) is 1360-1362°C; the time from the start of spheroidization to the completion of pouring is ≤15min; before pouring, Si in the molten iron accounts for 2.15±0.02% of the total weight of the molten iron, Mn accounts for ≤0.15% of the total weight of the molten iron, P accounts for ≤0.035% of the total weight of the molten iron, S accounts for <0.012% of the total weight of the molten iron, and Mg accounts for 0.035-0.045% of the total weight of the molten iron.

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