Method for improving shrinkage porosity of reversing frame casting and reversing frame casting

Abstract

The invention belongs to the technical field of casting, and provides a method for improving shrinkage porosity of a reversing frame casting and the reversing frame casting, and the method comprises the following steps: obtaining a reversing frame by adopting the process steps of molten iron smelting, spheroidizing treatment, inoculation treatment and casting molding; wherein the carbon content in the casting is 3.8%, and the silicon content in the casting is 2.6%; the casting temperature is 1400 DEG C; a chilling block is arranged in the mold; the casting contains 0.0041%-0.0062% of bismuth, and the bismuth is added after spheroidizing and before inoculation. According to the method, by optimizing the technological conditions in the casting technology, the optimal technological conditions for casting are determined, the carbon content is 3.8%, the silicon content is 2.6%, the casting temperature is 1400 DEG C, and the chilling block is arranged, so that the shrinkage porosity and cavity defects of the casting are remarkably improved; and meanwhile, by further optimizing the components and the content relation of the casting, the strength performance of the casting is further improved on the premise that the shrinkage porosity and cavity defect improvement state is guaranteed, and the casting is made to be more suitable for the high-strength application scene requirement.

Description

Technical Field

[0001] The present invention belongs to the field of casting technology, and particularly relates to a method for improving shrinkage porosity of a rotary frame casting and a rotary frame casting. Background Art

[0002] Figure 1 Shown is a schematic structural diagram of a rotary frame. The perforated connecting ear at position A in this casting, as a connecting and key stress-bearing part, needs to meet corresponding strength requirements. For this rotary frame casting, the designed gating system is as Figure 2 shown. During casting, the perforated connecting ear at position A is placed downward. Among them, the orange is the sprue, the green is the connecting riser, the blue is the high-efficiency exothermic riser, the yellow is the casting, the gray is the runner, and the cyan is the chill.

[0003] However, considering the structure of this casting, through experimental simulation analysis and actual casting tests, it is found that due to the presence of multiple thick-thin wall connections, internal angles, and intersections in this casting, shrinkage porosity and shrinkage cavity defects are extremely likely to occur inside the casting. When the shrinkage porosity volume is at its highest, it even approaches 1 cm³, resulting in the failure to meet the strength requirements of the casting. Summary of the Invention

[0004] In order to solve the technical problem that the above-mentioned rotary frame casting is prone to internal shrinkage porosity and shrinkage cavity defects during casting, the present application proposes a method for improving shrinkage porosity of a rotary frame casting and a rotary frame casting. The specific technical solutions are as follows: In a first aspect, the present application provides a method for improving shrinkage porosity of a rotary frame casting. The method is as follows: A rotary frame is obtained by adopting the technological steps of melting molten iron, spheroidizing treatment, inoculation treatment, and casting molding; wherein the carbon content in the casting is 3.8%, the silicon content is 2.6%; the casting temperature is 1400 °C; and chills are arranged in the mold; the casting contains 0.0041 - 0.0062% bismuth, and the bismuth is added after spheroidizing and before inoculation.

[0005] Optionally, the casting contains 0.0062% bismuth.

[0006] Optionally, the casting contains antimony within 0.0015%.

[0007] Optionally, the casting contains 0.001% antimony.

[0008] Optionally, the casting contains 0.02% nickel.

[0009] In a second aspect, the present application provides a rotary frame casting, which is prepared by the above method.

[0010] The beneficial effects of the present invention are as follows: By optimizing the process conditions in the casting process, the optimal process conditions for casting are determined, including a carbon content of 3.8%, a silicon content of 2.6%, a casting temperature of 1400 °C, and the setting of chill blocks, thereby significantly improving the shrinkage porosity defects of the casting. At the same time, by further optimizing the components of the casting and their content relationships, on the premise of ensuring the improvement of shrinkage porosity defects, the strength performance of the casting is further improved, making it more suitable for the requirements of high-strength application scenarios. Brief Description of the Drawings

[0011] Figure 1 The structural schematic diagram of the slewing frame casting is shown; Figure 2 The schematic diagram of the gating system of the slewing frame casting is shown; Figure 3 The casting scheme combination of the slewing frame casting is shown; Figure 4 The optimal casting scheme of the slewing frame casting is shown. Detailed Description of the Embodiments

[0012] In the following description, certain specific details are set forth in order to provide a thorough understanding of the various embodiments. However, those skilled in the art will understand that the present invention may be practiced without these details. In other instances, well-known structures have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments. Unless the context otherwise requires, throughout the specification and the appended claims, the word "comprising" shall be interpreted in an open, inclusive sense, i.e., as "including but not limited to".

[0013] The following percentage fractions are all mass percentages.

[0014] Regarding the factors affecting the shrinkage porosity defects of the slewing frame casting during casting, there are carbon content, silicon content, casting temperature, and chill block thickness. In this application, different parameters are selected for these four factors, and 24 combination schemes are designed to cast and test the internal shrinkage volume. The specific settings are as follows: Chill block thickness: 10 mm, 20 mm, 25 mm, 30 mm, 40 mm, 50 mm; Carbon content: 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%; Silicon content: 2.5%, 2.6%, 2.7%, 2.8%; Casting temperature: 1360 °C, 1370 °C, 1380 °C, 1390 °C, 1400 °C.

[0015] The test results are shown in Figure 3 .

[0016] Combined with Figure 3As shown in the figure, it is found that when the carbon content in the casting is 3.8% and the silicon content is 2.6%, the temperature of the molten iron during casting is 1400 °C, and the thickness of the chill in the mold is set to 30 mm, the shrinkage porosity volume of the obtained casting is the smallest, which is 0.65 cm³. This combination scheme is as Figure 4 shown.

[0017] It should be noted that in the above different combination schemes, except for the adjustment of the carbon content and the silicon content, other elements (such as manganese, rare earth elements, magnesium, etc.) remain unchanged, and only the content of iron is adjusted to adapt to the change of the overall composition.

[0018] However, in fact, when the process conditions are set as the carbon content is 3.8%, the silicon content is 2.6%, the temperature of the molten iron during casting is 1400 °C, and the thickness of the chill in the mold is set to 30 mm, the carbon equivalent CE of the casting reaches 4.67. Although it can reduce the shrinkage porosity and shrinkage cavity defects during casting, the too high carbon equivalent CE will also lead to a decrease in strength and inability to withstand high loads. According to GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", after testing, the tensile strength of the slewing frame produced under this process condition is 506 MPa, the yield strength is 342 MPa, and the elongation is 14%.

[0019] Example 1 The slewing frame is obtained by adopting the technological steps of melting molten iron, spheroidizing treatment, inoculation treatment, and casting molding.

[0020] Among them, melting molten iron is to melt scrap steel, return materials, ferrosulfur alloy, and ferromanganese alloy into molten iron.

[0021] The melting of molten iron and spheroidizing treatment adopt conventional processes. The temperature of the molten iron is controlled between 1520 and 1550 °C and kept warm for more than 10 minutes; for spheroidizing treatment, the FeSiMg8Re3 alloy spheroidizing agent is put into the depression of the ladle and then flushed into the molten iron by the flushing method.

[0022] The inoculation treatment adopts in-stream inoculation. During casting, the inoculant is added through an in-stream inoculation machine, and the molten iron after inoculation enters the next step for casting molding. The inoculant contains metallic bismuth.

[0023] In the casting molding step, the temperature is controlled at about 1400 °C, the thickness of the chill in the mold is 30 mm, and it is cooled and formed naturally.

[0024] Before pouring the molten iron into the ladle, by analyzing the composition of the molten iron in front of the furnace, the mass percentage content of the chemical composition in front of the furnace is controlled as follows: C 3.8%, Si 2.6%, Mn 0.4%, S 0.0015%, P 0.03%, Bi 0.005%.

[0025] Example 2 The rotary frame is obtained by means of the technological steps of smelting molten iron, spheroidizing treatment, inoculation treatment, and casting and molding.

[0026] Among them, smelting molten iron is to smelt scrap steel, return materials, ferrosulfur alloy, and ferromanganese alloy into molten iron.

[0027] The melting of molten iron and the spheroidizing treatment adopt conventional processes. The temperature of the molten iron during melting is controlled between 1520 °C and 1550 °C, and it is kept warm for more than 10 minutes; for the spheroidizing treatment, the FeSiMg8Re3 alloy spheroidizing agent is put into the depression of the ladle by the impouring method and then the molten iron is impoured. The spheroidizing agent contains metallic bismuth.

[0028] The inoculation treatment adopts in-stream inoculation. During casting, the inoculant is added through an in-stream inoculation machine. After the inoculation is completed, the molten iron enters the next step for casting and molding.

[0029] In the step of casting and molding, the temperature is controlled at about 1400 °C, the thickness of the chill in the mold is 30 mm, and it is cooled and formed naturally.

[0030] Before pouring from the ladle, by analyzing the composition of the molten iron in front of the furnace, the mass percentage content of the chemical components in front of the furnace is controlled as follows: C 3.8%, Si 2.6%, Mn 0.4%, S 0.0017%, P 0.03%, Bi 0.005%.

[0031] Example 3 The rotary frame is obtained by means of the technological steps of smelting molten iron, spheroidizing treatment, inoculation treatment, and casting and molding.

[0032] Among them, smelting molten iron is to smelt scrap steel, return materials, ferrosilicon alloy, and ferromanganese alloy into molten iron.

[0033] The melting of molten iron and the spheroidizing treatment adopt conventional processes. The temperature of the molten iron during melting is controlled between 1520 °C and 1550 °C, and it is kept warm for more than 10 minutes; for the spheroidizing treatment, the FeSiMg8Re3 alloy spheroidizing agent is put into the depression of the ladle by the impouring method and then the molten iron is impoured.

[0034] After the spheroidizing treatment and before the inoculation treatment, metallic bismuth is added to the ladle alone and stirred and dispersed evenly.

[0035] The inoculation treatment adopts in-stream inoculation. During casting, the inoculant is added through a wire feeding machine. After the inoculation is completed, the molten iron enters the next step for casting and molding.

[0036] In the step of casting and molding, the temperature is controlled at about 1400 °C, the thickness of the chill in the mold is 30 mm, and it is cooled and formed naturally.

[0037] Before pouring the molten iron into the ladle, by analyzing the composition of the molten iron in front of the furnace, the mass percentage content of the chemical composition in front of the furnace is controlled as follows: C 3.8%, Si 2.6%, Mn 0.4%, S 0.002%, P 0.02%, Bi 0.005%.

[0038] For the slewing frame castings in Examples 1 to 3, the tensile strength, yield strength, and elongation of the slewing frame were detected using GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature"; the internal structure of the casting was reconstructed in three dimensions by combining GB / T 29034-2012 "Non-destructive testing - Guide for industrial computed tomography (CT)" to calculate the volume of shrinkage porosity; the number of graphite balls was observed by metallographic sectioning, and the results are shown in Table 1.

[0039] Table 1

[0040]

[0041] Combined with Table 1, it can be seen that adding bismuth during the casting process is not only beneficial to improving the strength of the casting, but also helps to reduce the tendency of shrinkage porosity in the casting; it was observed that the addition timing of bismuth in the casting process also has a relatively significant impact on the performance of the casting, and the effect is the best when bismuth is added after spheroidization and before inoculation.

[0042] Examples 4 to 11 As shown in Table 2 in detail, on the basis of Example 3, the process was not changed, only the content of bismuth was adjusted, and the slewing frame castings obtained in Examples 4 to 11 were tested.

[0043] Table 2

[0044]

[0045] Combined with Table 2, it can be seen that adding bismuth after spheroidization and before inoculation can not only reduce the tendency of shrinkage porosity in the casting and improve the strength of the casting at the same time, but the addition range condition of bismuth in this process is relatively narrow, and its effective range is 0.0041 - 0.0062%, and the preferred addition amount is 0.006 - 0.0062%. Under this condition, the tensile strength of the casting can be increased to 700 MPa, and it is ensured that the volume of shrinkage porosity does not exceed 0.65 cm³.

[0046] Example 12 The slewing frame was obtained by using the technological steps of melting molten iron, spheroidizing treatment, inoculation treatment, and casting molding.

[0047] Among them, melting molten iron is to melt scrap steel, return scrap, ferrosulfur alloy, and ferromanganese alloy into molten iron.

[0048] The molten iron and nodularizing treatment adopt conventional processes. The temperature of the molten iron is controlled between 1520 and 1550 °C and kept warm for more than 10 minutes. For nodularizing treatment, the FeSiMg8Re3 alloy nodulizer is placed in the pit of the ladle and then the molten iron is poured in by the in-pouring method.

[0049] After nodularizing treatment and before inoculation treatment, metallic bismuth is added to the ladle alone and stirred to disperse evenly.

[0050] Inoculation treatment adopts in-stream inoculation. When casting, the inoculant is added through an in-stream inoculation machine. After inoculation, the molten iron enters the next step for casting and forming.

[0051] In the casting and forming step, the temperature is controlled at about 1400 °C, the thickness of the chill in the mold is 30 mm, and it is cooled and formed naturally.

[0052] Before pouring from the ladle, by analyzing the composition of the molten iron in front of the furnace, the mass percentage content of the chemical composition in front of the furnace is controlled as follows: C 3.8%, Si 2.6%, Mn 0.4%, S 0.001%, P 0.02%, Bi 0.005%, Sb 0.001%, and antimony is added when melting the molten iron.

[0053] Example 13 The difference between this example and Example 12 is that: before pouring from the ladle, by analyzing the composition of the molten iron in front of the furnace, the mass percentage content of the chemical composition in front of the furnace is controlled as follows: C 3.8%, Si 2.6%, Mn 0.4%, S 0.001%, P 0.02%, Bi 0.005%, Sb 0.0015%, and antimony is added when melting the molten iron.

[0054] Example 14 The difference between this example and Example 12 is that: before pouring from the ladle, by analyzing the composition of the molten iron in front of the furnace, the mass percentage content of the chemical composition in front of the furnace is controlled as follows: C 3.8%, Si 2.6%, Mn 0.4%, S 0.001%, P 0.02%, Bi 0.005%, Sb 0.002%, and antimony is added when melting the molten iron.

[0055] Example 15 The difference between this example and Example 12 is that: before pouring from the ladle, by analyzing the composition of the molten iron in front of the furnace, the mass percentage content of the chemical composition in front of the furnace is controlled as follows: C 3.8%, Si 2.6%, Mn 0.4%, S 0.001%, P 0.02%, Bi 0.005%, Sb 0.001%, Ni 0.02%, and antimony and nickel are added when melting the molten iron.

[0056] Example 16 The difference between this embodiment and Embodiment 12 is that metallic bismuth is not separately added into the ladle after spheroidizing treatment and before inoculation treatment.

[0057] Before the molten iron in the ladle is cast, by analyzing the composition of the molten iron in front of the furnace, the mass percentage content of the chemical components in front of the furnace is controlled as follows: C 3.8%, Si 2.6%, Mn 0.4%, S 0.001%, P 0.02%, Sb 0.001%, and antimony is added when melting the molten iron.

[0058] For the slewing frame castings of Embodiments 12 to 15, GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature" is used to detect the tensile strength, yield strength, and elongation of the slewing frame; GB / T 29034-2012 "Non-destructive testing - Guide for industrial computed tomography (CT)" is used to combine three-dimensional reconstruction of the internal structure of the casting to calculate the volume of shrinkage porosity; metallographic sections are used to observe the number of graphite balls, and the results are shown in Table 3.

[0059] Table 3

[0060]

[0061] Combined with Table 3, it can be seen that when a relatively low content of antimony element is added to the slewing frame casting, the strength of the casting can be improved, and the control of shrinkage porosity and shrinkage cavity defects can be maintained. However, it should be noted that the antimony content cannot be higher than 0.0015%. Once the antimony is excessive, the graphite spheroidization will be affected, and further affect the strength performance of the casting; in addition, by comparing with Embodiment 16, it is found that adding a small amount of antimony alone has no obvious effect on the strength, indicating that antimony should coexist with bismuth in the casting to play a synergistic role; the casting in Embodiment 15 also contains nickel, and the strength of the casting is further improved. It can be seen that adding nickel to this slewing frame casting can also synergistically promote the improvement of the strength of the casting.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them.

Claims

1. A method for improving shrinkage of turret castings, characterized in that: The method is: The rotary frame is obtained by adopting the process steps of smelting molten iron, spheroidizing treatment, inoculation treatment and casting; the carbon content of the casting is 3.8%, the silicon content is 2.6%; the casting temperature is 1400°C; and a chill is set in the mold; The casting contains 0.0041-0.0062% bismuth, and the bismuth is added after spheroidization and before inoculation.

2. A method for improving shrinkage of turret castings according to claim 1, characterized in that: The casting contained 0.0062% bismuth.

3. The method for improving shrinkage of turret castings according to claim 1, characterized in that: The casting contains antimony within 0.0015%.

4. A method for improving shrinkage of turret castings according to claim 3, characterized in that: The casting contains 0.001% antimony.

5. The method for improving shrinkage of turret castings according to claim 3, characterized in that: The casting contained 0.02% nickel.

6. A slewing frame casting, characterized in that: The rotary frame casting is produced by the method described in any one of claims 1 to 5.

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