Thin-wall as-cast high-elongation nodular iron casting, preparation method and cast iron oil pan

Abstract

The invention discloses a thin-wall as-cast high-elongation nodular iron casting, a preparation method and a cast iron oil pan, and belongs to the field of iron casting manufacturing. According to the thin-wall as-cast high-elongation nodular iron casting provided by the invention, the conditions of graphite floating and graphite blooming during manufacturing are prevented by improving the nodular iron material components, improving the material performance and optimizing the graphite distribution state, and the manufactured nodular iron casting has high elongation. According to the preparation method of the thin-wall as-cast high-elongation nodular iron casting, the graphite form and distribution can be effectively controlled, the nodular iron casting with the characteristics of large size, high fall and large-range limit thin wall is prevented from forming cementite during manufacturing, cold shut at the thin wall is effectively controlled, the local hardness difference is controlled within 20 HB, and the product quality is guaranteed. The cast iron oil pan provided by the invention is prepared on the basis of the preparation method, and has good comprehensive mechanical properties in the aspects of tensile strength, yield strength, ductility, local hardness difference and the like.

Description

Technical Field

[0001] The present invention belongs to the field of manufacturing cast iron parts, and particularly relates to thin-wall as-cast ductile iron parts with high elongation rate, a preparation method thereof, and a cast iron oil pan. Background Art

[0002] As one of the important parts of an engine, the cast iron oil pan plays an important role in storing engine oil and lubricating the moving parts in the cylinder, and is commonly used in fields such as automobiles, construction machinery, and agricultural machinery. The cast iron oil pan of a large tractor is a casting with a large-range thin-wall structure, having a large outer contour size and a minimum wall thickness of only 4 mm. When the tractor is working under external loads, the front end of the cast iron oil pan connected to the front axle of the tractor will bear the load and vibration on the front axle wheel, resulting in the cast iron oil pan needing to bear a large tensile stress and bending moment. Therefore, high requirements are imposed on the strength and stiffness of the oil pan.

[0003] Currently, when selecting materials for traditional cast iron oil pans of large tractors, gray cast iron materials with a grade of HT250 are mostly used. However, as a traditional material, gray cast iron is difficult to meet the performance requirements of such thin-wall cast iron parts, and manufacturing defects are likely to occur in actual production, resulting in poor product quality. In fact, when casting cast iron oil pans using such materials, the cooling rate of the molten iron is often too fast due to the too-thin wall thickness of the casting, causing the carbon element to be unable to complete sufficient graphitization and forming cementite, i.e., white cast iron structure, significantly reducing the plasticity and impact resistance of the material; it will also cause a large hardness difference in different areas of the manufactured cast iron oil pan, affecting the machining consistency. Under some extreme working conditions, oil leakage or fracture of the cast iron oil pan of large tractors often occurs, causing the entire tractor to stop working and seriously affecting the construction progress.

[0004] Ductile iron is a high-strength cast iron material. Due to its excellent comprehensive performance, it is often used to replace cast steel and forged steel to manufacture various parts with large loads, complex stress, and wear resistance. However, the solidification shrinkage rate of ductile iron materials is much higher than that of gray cast iron materials, and the process control is relatively difficult. During the manufacturing process of thin-wall cast iron parts such as cast iron oil pan bodies, it will still cause a large hardness difference in different parts of the cast iron parts, and it is also difficult to control the formation of cementite, unable to guarantee the product quality, making the current ductile iron materials still difficult to be used to manufacture such cast iron parts with large size, high drop, and large-range extreme thin-wall characteristics, resulting in the obstruction of the expansion of the application range of ductile iron materials. Summary of the Invention

[0005] To solve the above technical problems, the object of the present invention is to provide a thin-walled as-cast ductile iron casting, a preparation method thereof, and a cast iron oil pan. Aiming at the defects of the above-mentioned prior art, the present invention optimizes the preparation method of the thin-walled as-cast ductile iron casting and improves the composition of the ductile iron, so that the thin-walled as-cast ductile iron casting and the cast iron oil pan products obtained by the preparation method of the present invention have more excellent tensile properties and yield properties, and have higher elongation and smaller local hardness differences, ensuring the comprehensive mechanical properties of the products.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] In the first aspect, the present invention provides a thin-walled as-cast ductile iron casting with high elongation. By weight percentage, the ductile iron is composed of the following components: C: 3.8% - 3.950%; Si: 2.65% - 2.85%; Mn: 0.100% - 0.40%; S: 0.020% - 0.042%; P: 0.01% - 0.035%; Sb: 0.020% - 0.060%; Mg: 0.028% - 0.042%; and trace elements with a content of less than 0.020%, the trace elements being one or a combination of more of Cr, Mo, V, Ti, Ni, Al, As, Bi, Ca, Nb, Cd, Co, La, N, Pb, Se, Sn, Te, W, Zn or Zr, and the rest being iron.

[0008] In the second aspect, the present invention provides a preparation method for the thin-walled as-cast ductile iron casting with high elongation in the first aspect, including the following steps:

[0009] S1: Form a batching form according to the materials required for the aforementioned ductile iron casting, and proportion and weigh the materials according to the batching form; the materials in the batching form at least include scrap steel, return scrap, silicon carbide, carburizer, and ferrosilicon alloy;

[0010] S2: Put the materials prepared in step S1 into an induction furnace, and raise the temperature of the induction furnace to 1425°C - 1495°C, and then conduct a primary melting; when the raw materials in the induction furnace are melted and molten into molten iron, control the temperature of the induction furnace between 1505°C - 1525°C, and keep it warm and static for 5 - 8 minutes;

[0011] S3: Use spectroscopy to analyze the composition of the molten iron; judge whether the carbon and silicon contents in the molten iron in the furnace reach the preset standards; if the carbon and silicon contents in the molten iron do not reach the preset standards, enter step S4, otherwise enter step S5;

[0012] S4: Add scrap steel, carburizer or ferrosilicon alloy to the molten iron, heat up the induction furnace to 1525°C - 1545°C, and conduct re-melting; after the newly added raw materials in the induction furnace are completely melted, control the temperature of the induction furnace between 1565°C - 1575°C, keep it warm and static for 1 - 2 minutes, and return to step S3;

[0013] S5: According to the weight percentage, lay in turn on one side inside the nodulizing ladle a rare earth magnesium silicon nodulizer with a dosage of 0.8% - 1.0% of the molten iron, a pretreatment agent with a dosage of 0.1% - 0.15% of the molten iron, and a primary inoculant with a dosage of 0.95% - 1.05% of the molten iron, and then cover the primary inoculant with a covering agent;

[0014] S6: Pour the molten iron whose carbon and silicon contents reach the preset standard after melting into the other side inside the nodulizing ladle without nodulizer and primary inoculant for nodulizing and inoculating; after the nodulizing reaction ends, immediately conduct slag skimming;

[0015] S7: Pour the molten iron in the pouring ladle into the resin-coated sand mold; and uniformly add strontium-silicon in-stream inoculant with the molten iron for secondary inoculation during pouring; among them, according to the weight percentage, the dosage of the strontium-silicon in-stream inoculant is 0.05% - 0.08% of the molten iron.

[0016] Further, in the said step S3, according to the weight percentage, the preset standard for the carbon and silicon contents in the molten iron is C: 3.8% - 3.950%; Si: 1.95% - 2.05%.

[0017] Further, in the said step S5, according to the weight percentage, the dosage of the rare earth magnesium silicon nodulizer is 0.8% - 1.0% of the molten iron; among them, the rare earth magnesium silicon nodulizer is composed of the following components: Mg: 5.0% - 5.5%, Re: 1.5% - 2%, Al < 1%, Si < 48%, Ca < 1%, and the balance is iron.

[0018] Further, in the said step S5, the primary inoculant added in the nodulizing ladle is a silicon-barium-calcium composite inoculant; according to the weight percentage, the dosage of the silicon-barium-calcium composite inoculant is 0.95% - 1.05% of the molten iron; among them, the silicon-barium-calcium composite inoculant is composed of the following components: Si: 70% - 72%, Ca: 1% - 2%, Ba: 1% - 2%, AI < 1.5%, and the balance is iron.

[0019] Further, in the said step S6, according to the weight percentage, the dosage of the pretreatment agent added in the nodulizing ladle is 0.1% - 0.15% of the molten iron; among them, the pretreatment agent used is a low-sulfur and low-nitrogen carburizer, and the particle size of the low-sulfur and low-nitrogen carburizer is between 0.2 mm - 0.8 mm.

[0020] Further, in the step S7, the addition amount of the strontium-silicon in-stream inoculant is 0.05% to 0.08% of the molten iron by weight percentage; and, in the components of the strontium-silicon in-stream inoculant, the proportion of strontium is Sr: 1% to 2%.

[0021] Further, in the step S6, the temperature when pouring the molten iron into the nodulizing ladle is controlled between 1555 °C and 1575 °C.

[0022] Further, in the step S7, the temperature during pouring is controlled between 1475 °C and 1520 °C.

[0023] Thirdly, the present invention also provides a cast iron oil pan, which is prepared by using the preparation method of the thin-wall as-cast high-elongation ductile iron casting described in any one of the above.

[0024] In addition, referring to the test method of "Ductile Iron - GB / T 1348-2017", the cast iron oil pan prepared by the preparation method described in the second aspect is detected, and the results are shown in the following table:

[0025]

[0026] The beneficial effects of the present invention are as follows:

[0027] 1. By optimizing the components of the thin-wall as-cast high-elongation ductile iron casting, the present invention ensures the carbon equivalent, prevents cold laps and insufficient pouring during the subsequent mold filling process; by controlling the Mn component content, it ensures that the produced ductile iron casting has a high elongation; and by controlling the Mg content, it ensures that the formed state of graphite is round.

[0028] 2. By optimizing and improving the preparation method of the thin-wall as-cast high-elongation ductile iron casting, the present invention effectively controls the graphite morphology and distribution, prevents the formation of cementite in the manufacture of such ductile iron castings with large size, high drop, and large-range extreme thin-wall characteristics, effectively controls the cold laps at the thin-walled parts of the ductile iron castings, and ensures that the local hardness difference is within 20 HB, thus guaranteeing the quality of the produced products.

[0029] 3. The present invention also provides a cast iron oil pan, which is made based on the preparation method of the thin-wall as-cast high-elongation ductile iron casting. The matrix structure of this cast iron oil pan product is uniform, the graphite spheroidization is good, there is no fragmented defective graphite, there is no carbide in the tissue, the actual tensile strength is greater than 510 N / mm 2 , and the yield strength is greater than 410 N / mm 2 , it has a high elongation of about 13%, and the local hardness difference is within 20 HB, and the comprehensive mechanical properties are good. Description of the Drawings

[0030] Figure 1Schematic structure of the connection between the cast iron oil pan and the gating system of the present invention Figure 1 ;

[0031] Figure 2 Schematic structure of the connection between the cast iron oil pan and the gating system of the present invention Figure 2 ;

[0032] Figure 3 Schematic structure of the connection between the cast iron oil pan and the gating system of the present invention Figure 3 ;

[0033] Figure 4 Schematic diagram of the graphite morphology of Test Example 1 of the present invention magnified 200 times;

[0034] Figure 5 Schematic diagram of the graphite morphology of Test Example 2 of the present invention magnified 200 times;

[0035] Figure 6 Metallographic structure diagram of the test example of the present invention magnified 100 times;

[0036] In the drawings: 1, pouring cup; 21, upper sprue; 22, upper cross sprue; 23, lower sprue; 24, lower cross sprue; 25, upper ingate; 26, lower ingate; 3, cast iron oil pan; 4, overflow riser. Detailed implementation manners

[0037] The present invention will be further described in detail below in conjunction with the drawings and specific implementation manners, but the present invention is not limited to the following embodiments.

[0038] Embodiment 1:

[0039] The following is the first embodiment of the present invention. This embodiment provides a thin-walled as-cast ductile iron casting. By mass percentage, the ductile iron is composed of the following components: C: 3.8% - 3.950%; Si: 2.65% - 2.85%; Mn: 0.100% - 0.40%; S: 0.020% - 0.042%; P: 0.01% - 0.035%; Sb: 0.020% - 0.060%; Mg: 0.028% - 0.042%; and trace elements with a content of less than 0.020%, the trace elements being one or a combination of more of Cr, Mo, V, Ti, Ni, Al, As, Bi, Ca, Nb, Cd, Co, La, N, Pb, Se, Sn, Te, W, Zn or Zr, and the rest being iron.

[0040] In this embodiment, by optimizing the components of ductile iron, a relatively high C and Si content in the components is ensured to guarantee the carbon equivalent, which helps improve the fluidity of the molten iron and prevent cold shuts and misruns during the mold filling process of the casting. Furthermore, it can prevent graphite floating and graphite blooming from occurring at thick and large positions during the manufacturing process of ductile iron castings made of this ductile iron material. In the components of ductile iron, if the Mn content is too high, it will lead to an excessive proportion of pearlite in the matrix, reducing the plastic deformation ability of the material and being unfavorable for controlling high elongation in the as-cast state. Therefore, the Mn content in the present invention is controlled below 0.40%, meeting the requirement of the pearlite content in the matrix, and thus ensuring that the produced ductile iron castings have high elongation. Mg is the key to forming round graphite. An excessive Mg content will increase the shrinkage tendency of ductile iron castings, while an insufficient Mg content will easily result in abnormal graphite in the metallographic structure of ductile iron castings. Therefore, the Mg content in the present invention is controlled between 0.028% and 0.042% to ensure the roundness of the graphite formation state.

[0041] Embodiment 2:

[0042] See Appendix Figures 1 to 6 The following is the second embodiment of the present invention. This embodiment provides a method for preparing a thin-walled as-cast ductile iron casting with high elongation. Among them, this preparation method is implemented based on the thin-walled as-cast ductile iron casting provided in Embodiment 1, and its steps specifically include:

[0043] S1: Form a batching form according to the materials required for the ductile iron casting described in Claim 1, and proportion and weigh the materials according to the batching form; the materials in the batching form at least include scrap steel, return scrap, silicon carbide, carburizer, and ferrosilicon alloy;

[0044] S2: Put the materials prepared in step S1 into an induction furnace, and raise the temperature of the induction furnace to 1425°C - 1495°C, and then conduct the first melting; when the raw materials in the induction furnace are melted into molten iron, control the temperature of the induction furnace between 1505°C and 1525°C, and keep it warm and static for 5 - 8 minutes;

[0045] S3: Use spectroscopy to analyze the composition of the molten iron; judge whether the carbon and silicon contents in the molten iron in the furnace reach the preset standards; if the carbon and silicon contents in the molten iron do not reach the preset standards, enter step S4, otherwise enter step S5;

[0046] S4: Add scrap steel or carburizer or ferrosilicon alloy to the molten iron, and raise the temperature of the induction furnace to 1525°C - 1545°C for re-melting; when the newly added raw materials in the induction furnace are completely melted, control the temperature of the induction furnace between 1565°C and 1575°C, and keep it warm and static for 1 - 2 minutes, then return to step S3;

[0047] S5: Lay the rare earth magnesium silicon spheroidizing agent accounting for 0.8% - 1.0% of the molten iron, the pretreatment agent accounting for 0.1% - 0.15% of the molten iron, and the primary inoculant accounting for 0.95% - 1.05% of the molten iron on one side inside the spheroidizing ladle in sequence according to the weight percentage, and then cover the primary inoculant with a covering agent.

[0048] S6: Pour the molten iron with the carbon and silicon contents reaching the preset standard after melting into the other side inside the spheroidizing ladle without the spheroidizing agent and the primary inoculant for spheroidizing inoculation; immediately perform slag skimming after the spheroidizing reaction ends.

[0049] S7: Pour the molten iron in the pouring ladle into the resin-coated sand mold; and uniformly add strontium silicon in-stream inoculant for secondary inoculation along with the molten iron during pouring; wherein, according to the weight percentage, the dosage of the strontium silicon in-stream inoculant is 0.05% - 0.08% of the molten iron.

[0050] Among them, step S1 is the furnace charge proportioning step, and in the batching form, the proportion of the return charge is 20%. And steps S2 - S5 are the melting pretreatment steps, melting, component analysis and melting adjustment are carried out according to the batching provided by step S1 to obtain the molten iron meeting the preset standards of carbon and silicon contents. Step S6 is the spheroidizing inoculation step, adding a spheroidizing agent, an inoculant and a pretreatment agent into the spheroidizing ladle, and adopting the impouring method for spheroidizing inoculation to change the graphite form into spherical graphite, increase graphite nucleation, improve the inoculation effect, stabilize the graphite form, and at the same time reduce the chill tendency of cast iron parts such as thin-wall ductile iron castings with characteristics of large size, high drop and large-range extreme thin walls through the strontium silicon inoculant to prevent the occurrence of cementite and cold lap defects. Step S7 is the pouring and in-stream inoculation step, and finally obtain thin-wall as-cast high-elongation ductile iron castings by carrying out secondary inoculation while pouring the molten iron. According to the above manufacturing method, the forming quality of the thin-wall ductile iron oil pan casting can be improved.

[0051] Example Three:

[0052] See Appendix Figures 1 to 6 The following is the third embodiment of the present invention. On the basis of the second embodiment, the preparation method of the thin-wall as-cast high-elongation ductile iron casting further includes:

[0053] In the step S3, according to the weight percentage, the preset standards of the carbon and silicon contents in the molten iron are C: 3.8% - 3.950%; Si: 1.95% - 2.05%.

[0054] In the step S5, according to the weight percentage, the dosage of the rare earth magnesium silicon spheroidizing agent is 0.8% - 1.0% of the molten iron; wherein, the rare earth magnesium silicon spheroidizing agent is composed of the following components: Mg: 5.0% - 5.5%, Re: 1.5% - 2%, Al < 1%, Si < 48%, Ca < 1%, and the balance is iron.

[0055] In the step S5, the primary inoculant added in the spheroidizing ladle is a calcium-silicon-barium composite inoculant; by weight percentage, the dosage of the calcium-silicon-barium composite inoculant is 0.95% - 1.05% of the molten iron; wherein, the calcium-silicon-barium composite inoculant is composed of the following components: Si: 70% - 72%, Ca: 1% - 2%, Ba: 1% - 2%, AI: <1.5%, and the balance is iron.

[0056] In the step S6, by weight percentage, the dosage of the pretreatment agent added in the spheroidizing ladle is 0.1% - 0.15% of the molten iron; wherein, the pretreatment agent used is a low-sulfur and low-nitrogen recarburizer, and the particle size of the low-sulfur and low-nitrogen recarburizer is between 0.2 mm and 0.8 mm.

[0057] In the step S7, by weight percentage, the addition amount of the strontium-silicon in-stream inoculant is 0.05% - 0.08% of the molten iron; and, in the components of the strontium-silicon in-stream inoculant, the proportion of strontium is Sr: 1% - 2%.

[0058] In the step S6, the temperature when pouring the molten iron into the spheroidizing ladle is controlled between 1555 °C and 1575 °C.

[0059] In the step S7, the temperature during pouring is controlled between 1475 °C and 1520 °C.

[0060] In this embodiment, first, by precisely controlling the carbon and silicon contents of the molten iron, it is ensured that the molten iron has a good basis for spheroidization reaction, avoiding abnormal graphite morphology or matrix tissue defects caused by composition deviation. Secondly, by controlling the dosages and compositions of the rare earth magnesium silicon spheroidizing agent, calcium-silicon-barium composite inoculant, pretreatment agent, and strontium-silicon in-stream inoculant, the spheroidization reaction effect is guaranteed, the product matrix is made uniform, and the product has higher tensile strength and elongation. In addition, the spheroidization effect is also ensured by controlling the temperature of the molten iron injected during the spheroidization process, and the fluidity of the molten iron and the final forming quality are ensured by controlling the temperature during pouring.

[0061] Example 4:

[0062] See the appendix Figures 1 to 6 The following is the fourth embodiment of the present invention. This embodiment provides a cast iron oil pan, wherein, this cast iron oil pan is implemented based on the preparation method of thin-wall as-cast high-elongation ductile iron castings provided in Example 3.

[0063] In this embodiment, this cast iron oil pan is a thin-wall ductile iron oil pan with a large-range thin-wall structure. Figure 1Shows the outer shape of the cast iron oil pan obtained according to the preparation method and the gating system used for casting the cast iron oil pan. Specifically, the outer contour dimensions of the cast iron oil pan made are 608mm * 332mm * 235mm, and except for the mounting surface, other positions are large-scale thin-walled structures, and the wall thickness of the casting at the thin-walled part is 4mm. The cast iron oil pan has obvious thin-walled characteristics, a large specific surface area, and a large height drop. In the preparation method of thin-walled as-cast ductile iron castings provided in Example 3, the mold used to manufacture the cast iron oil pan is specifically a "one mold with multiple parts" structure, that is, multiple cast iron oil pans can be cast simultaneously using one mold. Specifically, as Figure 1 shown, three cast iron oil pans can be cast simultaneously using one oil pan mold.

[0064] In this embodiment, the cast iron oil pan can be applied to the engines of automobiles, construction machinery, and agricultural machinery, such as being used as a thin-walled ductile iron oil pan for tractors.

[0065] In this embodiment, based on the above preparation method, referring to the test method in "GB / T 1348-2017 Ductile Iron", the graphite morphology diagram and metallographic structure diagram of the cast iron oil pan product are detected, specifically as Figures 4 to 6 shown.

[0066] In this embodiment, referring to the test method in "GB / T 1348-2017 Ductile Iron", the mechanical properties of the cast iron oil pan made according to the preparation method of thin-walled as-cast ductile iron castings provided in Example 3 are tested, and the results are as follows:

[0067]

[0068]

[0069] In this embodiment, Specimens 1 and 2 in the test example are two cast iron parts cast simultaneously in the same mold. It can be seen from the results in the above table that the performance gap between the two is small, and they have good production consistency.

[0070] In this embodiment, the process conditions of the comparative example are as follows:

[0071] Comparative Example 1: For the thin-walled ductile iron oil pan with a large specific surface area, the difference in its preparation steps from the test example is that in step S6, no pretreatment agent is added;

[0072] Comparative Example 2: A thin-walled ductile iron oil pan with a large specific surface area. The difference in its preparation steps from those of the test example lies in that in step S6, the tapping temperature of the molten iron is 1550 °C, and no pretreatment agent is added. A high-magnesium spheroidizing agent is used, and the composition of the high-magnesium spheroidizing agent is as follows: Mg: 5.5%-6.5%, Re: 1.5%-2%, Al: <1%, Si: <48%, Ca <1%, and the balance is iron; the addition amount of the spheroidizing agent is 1.15% of the weight of the molten iron. Then, after covering the spheroidizing agent with an inoculant in the ladle, the in-pouring method is implemented for treatment.

[0073] As can be seen from the data in the table, for Test Examples 1 and 2 prepared by the method for preparing thin-walled as-cast ductile iron castings with high elongation provided in Example 3, their mechanical property data are superior to those of other schemes. The matrix structure is uniform, the graphite spheroidization is good, there is no fragmented defective graphite, there is no carbide in the tissue, and the comprehensive mechanical properties are good, and the material requirements of QT400-15 can be achieved under as-cast conditions.

[0074] In Comparative Example 1, no pretreatment agent was added in the pretreatment stage, and the number of inoculation nuclei was small, which made the graphite in the obtained thin-walled as-cast ductile iron castings with a large specific surface area larger. Due to the large supercooling degree of the molten iron after spheroidization, carbides were precipitated in the casting matrix structure. In Comparative Example 2, by changing the tapping temperature of the molten iron, not adding a pretreatment agent, and using a high-magnesium spheroidizing agent, the temperature drop of the molten iron during the spheroidization process was large, the casting was under-cast, the graphite in the oil pan was larger, the inoculation was poor, carbides were precipitated in the casting matrix structure, and the comprehensive mechanical properties were affected. In addition, when the gating system in Comparative Example 1 or Comparative Example 2 only adopts the conventional bottom-water inlet scheme, the thin-walled ductile iron oil pan will ultimately not be able to be formed due to incomplete pouring.

[0075] Example 5:

[0076] See the appendix Figures 1 to 6 The following is the fifth embodiment of the present invention. This embodiment provides a gating system, wherein the gating system is implemented based on the method for preparing thin-walled as-cast ductile iron castings with high elongation provided in Example 3 and the cast iron oil pan provided in Example 4.

[0077] In this embodiment, the gating system is applied to step S7 of the preparation method described in Embodiment III. The gating system includes a sprue cup 1 and at least one gating channel communicating with the sprue cup 1. The gating channel includes a top sprue 21, a top runner 22, a bottom sprue 23, a bottom runner 24, a top ingate 25, and a bottom ingate 26 that are connected in sequence. The gating channel is connected to the outside of the mold for forming the cast iron oil pan 3 and communicates with the bottom cavity of the mold through the bottom ingate 26. By optimizing the design of the gating channel in this embodiment, the top ingate 25 and the bottom ingate 26 are separately provided, and the bottom ingate 26 is connected to the relatively thick and large cavity part in the mold to divert the injected molten iron, ensuring the forming quality of the cast iron oil pan and improving casting defects such as sand washing and slag inclusion caused by the conventional green sand casting process.

[0078] Specifically, the number of gating channels can be set to one or more according to actual pouring requirements. As Figure 1 shown, three molds for casting the iron oil pan castings 3 share a gating system, and the gating channels are three. In addition, a plurality of overflow risers 4 are connected to the edge of the top of the mold, which can discharge the low-temperature molten iron, gas, and impurities at the initial stage of pouring, avoiding affecting the forming effect of the cast iron oil pan 3.

[0079] Embodiment VI:

[0080] See Appendix Figures 1 to 6 The following is the sixth embodiment of the present invention. This embodiment provides a forming method for a cast iron oil pan. Among them, the cast iron oil pan is implemented based on the preparation method of thin-wall as-cast high-elongation ductile iron castings provided in Embodiment III and the gating system provided in the fifth embodiment.

[0081] In this embodiment, the forming method can be applied to step S7 of the preparation method described in Embodiment III to obtain the cast iron oil pan described in Embodiment IV. The cast iron oil pan is formed by sand casting, and the manufacturing temperature of the mold used for sand casting is controlled between 185°C and 215°C to ensure the strength and air permeability of the sand mold. In addition, air vents are provided on the cast iron oil pan 3. During the pouring process of the cast iron oil pan, by igniting the air vents to introduce air, the volatile gases in the mold are accelerated to be discharged, improving the forming quality.

[0082] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A thin-walled as-cast ductile iron casting with high elongation rate, characterized in that: By weight percentage, the ductile iron consists of the following components: C: 3.8% to 3.950%; Si: 2.65% to 2.85%; Mn: 0.100% to 0.40%; S: 0.020% to 0.042%; P: 0.01% to 0.035%; Sb: 0.020% to 0.060%; Mg: 0.028% to 0.042%; and trace elements with a content less than 0.020%, the trace elements being one or more combinations of Cr, Mo, V, Ti, Ni, Al, As, Bi, Ca, Nb, Cd, Co, La, N, Pb, Se, Sn, Te, W, Zn or Zr, and the rest being iron.

2. Preparation method of thin-wall as-cast ductile iron casting with high elongation rate, characterized in that, It includes the following steps: S1: Form a batching form according to the materials required for the ductile iron casting described in Claim 1, and proportion and weigh the materials according to the batching form; the materials in the batching form at least include scrap steel, return scrap, silicon carbide, carburizer and ferrosilicon alloy; S2: Put the materials prepared in step S1 into an induction furnace, and raise the temperature of the induction furnace to 1425°C to 1495°C, and then carry out a primary melting; when the raw materials in the induction furnace are melted and molten into molten iron, control the temperature of the induction furnace between 1505°C and 1525°C, and keep it warm and static for 5 to 8 minutes; S3: Use spectroscopy to analyze the composition of the molten iron; judge whether the carbon and silicon contents in the molten iron in the furnace reach the preset standards; if the carbon and silicon contents in the molten iron do not reach the preset standards, enter step S4, otherwise enter step S5; S4: Add scrap steel or carburizer or ferrosilicon alloy to the molten iron, and raise the temperature of the induction furnace to 1525°C to 1545°C for secondary melting; when the newly added raw materials in the induction furnace are completely melted, control the temperature of the induction furnace between 1565°C and 1575°C, and keep it warm and static for 1 to 2 minutes, and return to step S3; S5: According to the weight percentage, lay in turn on one side inside the nodulizing ladle a rare earth magnesium silicon nodulizer with a dosage accounting for 0.8% to 1.0% of the molten iron, a pretreatment agent with a dosage accounting for 0.1% to 0.15% of the molten iron, and a primary inoculant with a dosage accounting for 0.95% to 1.05% of the molten iron, and then cover the primary inoculant with a covering agent; S6: Pour the molten iron with the carbon and silicon contents reaching the preset standards after melting into the other side inside the nodulizing ladle without nodulizer and primary inoculant for nodulizing and inoculating; immediately carry out slag skimming after the nodulizing reaction ends; S7: Pour the molten iron in the pouring ladle into the coated sand mold; and uniformly add strontium silicon in-mold inoculant with the molten iron during pouring for secondary inoculation; among them, according to the weight percentage, the dosage of the strontium silicon in-mold inoculant is 0.05% to 0.08% of the molten iron.

3. The preparation method of the thin-wall as-cast ductile iron casting with high elongation rate according to claim 2, characterized in that, In the said step S3, according to the weight percentage, the preset standards for the carbon and silicon contents in the molten iron are C: 3.8% to 3.950%; Si: 1.95% to 2.05%.

4. The preparation method of the thin-wall as-cast ductile iron casting with high elongation rate according to claim 2, characterized in that, In the step S5, by weight percentage, the dosage of the rare earth magnesium silicon nodulizer is 0.8% - 1.0% of the molten iron; wherein, the rare earth magnesium silicon nodulizer is composed of the following components: Mg: 5.0% - 5.5%, Re: 1.5% - 2%, Al: <1%, Si: <48%, Ca <1%, and the balance is iron.

5. The preparation method of the thin-walled as-cast ductile iron casting with high elongation rate according to claim 2, characterized in that, In the step S5, the primary inoculant added in the nodulizing ladle is a silicon barium calcium composite inoculant; by weight percentage, the dosage of the silicon barium calcium composite inoculant is 0.95% - 1.05% of the molten iron; wherein, the silicon barium calcium composite inoculant is composed of the following components: Si: 70% - 72%, Ca: 1% - 2%, Ba: 1% - 2%, AI: <1.5%, and the balance is iron.

6. The preparation method of the thin-walled as-cast ductile iron casting with high elongation rate according to claim 2, characterized in that, In the step S6, by weight percentage, the dosage of the pretreatment agent added in the nodulizing ladle is 0.1% - 0.15% of the molten iron; wherein, the pretreatment agent used is a low sulfur and low nitrogen recarburizer, and the particle size of the low sulfur and low nitrogen recarburizer is between 0.2 mm and 0.8 mm.

7. The preparation method of the thin-wall as-cast ductile iron casting with high elongation rate according to claim 2, characterized in that, In the step S7, by weight percentage, the addition amount of the strontium silicon in-stream inoculant is 0.05% - 0.08% of the molten iron; and, in the components of the strontium silicon in-stream inoculant, the proportion of strontium is Sr: 1% - 2%.

8. The preparation method of the thin-wall as-cast ductile iron casting with high elongation rate according to claim 2, characterized in that, In the step S6, the temperature when pouring the molten iron into the nodulizing ladle is controlled between 1555 °C and 1575 °C.

9. The preparation method of the thin-walled as-cast ductile iron casting with high elongation rate according to claim 2, characterized in that, In the step S7, the temperature during pouring is controlled between 1475 °C and 1520 °C.

10. A cast iron oil pan, characterized in that: Prepared by the method according to any one of claims 2 to 9.

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