High-spheroidization-rate spheroidal graphite cast iron for silicon carbide auxiliary spheroidization inoculation and preparation method thereof

Abstract

The invention discloses high-spheroidization-rate spheroidal graphite cast iron for silicon carbide auxiliary spheroidization inoculation and a preparation method thereof, and belongs to the technical field of metal material casting. The preparation method of the high-spheroidization-rate nodular cast iron for silicon carbide auxiliary spheroidization inoculation comprises the six steps of preparation of an auxiliary spheroidizing agent, preparation of an auxiliary nucleating agent, burdening, smelting, spheroidization inoculation and pouring. The tensile strength of the obtained nodular cast iron casting finished product is 463-498 MPa, the yield strength is 310-320 MPa, the elongation is 7.2-9.8%, the brinell hardness is 180-220, the minimum impact energy is 49-55 J, the graphite spheroidization level is 1-2 levels, the spheroidization rate is 95-97%, and the size level of graphite nodules is 6-7 levels.

Description

Technical Field

[0001] The invention relates to high-spheroidization-rate ductile iron assisted by silicon carbide for spheroidization inoculation and a preparation method thereof, belonging to the technical field of metal material casting. Background Art

[0002] Ductile iron is a cast iron alloy with silver-gray cross section. Through spheroidizing inoculation treatment, graphite is spherical or flocculent, with certain strength and toughness. Ductile iron has excellent mechanical, chemical and physical properties, and is widely used in hydraulic and automotive parts. In recent years, due to environmental factors, most ductile iron manufacturers have switched to the wire feeding spheroidizing method to produce ductile iron. Its technical advantages are: high magnesium absorption rate, less secondary oxidation slag, less flash and smoke during spheroidizing treatment, and improved working conditions; online control can be achieved, and the length of the core wire is determined according to the sulfur content in the original iron liquid; but it also has certain disadvantages: the number of graphite nuclei in the production of ductile iron by the wire feeding method is small, and the castings produced have a greater tendency to shrink and white. Therefore, when using the wire feeding method to produce ductile iron castings with a spheroidizing rate greater than 90%, there are still prominent problems such as difficulty in obtaining a higher spheroidizing rate and low graphite spheroidizing level.

[0003] Chinese patent CN108624802A discloses a spheroidizing inoculation method for ductile iron, comprising the following steps: placing a spheroidizing agent on one side of the bottom of a spheroidizing bag, covering the spheroidizing agent with a layer of silicon carbide powder, covering the silicon carbide powder with a first inoculant, uniformly covering the first inoculant with iron filings, uniformly covering the casting perlite on the iron filings and tamping; injecting molten iron into the spheroidizing bag along the other side of the spheroidizing bag by a flushing method, the temperature of the molten iron is 1400-1430°C, and performing spheroidizing treatment and in-bag inoculation treatment; when the amount of molten iron flushed into the spheroidizing bag accounts for 2 / 3 of the total mass of the molten iron, adding a second inoculant for in-mold inoculation treatment, and continuing to flush the remaining molten iron; adding a third inoculant with the flow while pouring for in-flow inoculation. The patent does not disclose the specific value of the spheroidization rate of ductile iron prepared by the spheroidization inoculation method described in the patent, but the patent does not use the more advanced wire feeding spheroidization method, and the uniformity of the spheroidization effect is difficult to guarantee.

[0004] Chinese patent CN105316564A discloses a high-nickel austenitic ductile iron production process using wire feeding spheroidizing treatment, which includes batching, smelting and composition adjustment, spheroidizing treatment, pouring, unpacking and post-processing and heat treatment steps; characterized in that the spheroidizing treatment is wire feeding spheroidizing treatment; it can avoid the metallographic problems of castings, make the castings stable in quality, low in production cost and low in defect rate; at the same time, it can improve labor intensity and working conditions, and improve work efficiency; the dust generated in the spheroidizing process is easy to control and more environmentally friendly. Although the wire feeding spheroidizing treatment process adopted by the patent has the above-mentioned advantages, the spheroidizing rate of the ductile iron obtained still appears as a low value of 80%. It can be seen that the wire feeding spheroidizing treatment process of the patent is not particularly stable, and it is still difficult to ensure a particularly high spheroidizing rate.

[0005] From the above, we can see that the current wire feeding spheroidizing treatment process for ductile iron still has problems such as low spheroidizing rate, unstable spheroidizing index, and relatively low graphite spheroidizing level, which makes it difficult to obtain high-performance ductile iron. Therefore, finding a better spheroidizing agent and exploring a more efficient wire feeding spheroidizing treatment process are the only way to prepare ductile iron with high spheroidizing rate and high graphite spheroidizing level. Summary of the invention

[0006] In view of the shortcomings of the above-mentioned prior art, the present invention provides a ductile iron with high spheroidization rate and a preparation method thereof assisted by silicon carbide spheroidization inoculation, so as to achieve the following invention objectives: ductile iron with high spheroidization rate and high graphite spheroidization level is prepared by utilizing high melting point materials mainly composed of silicon carbide, in combination with rare earth magnesium spheroidizer and silicon barium inoculant, and by optimizing the wire feeding spheroidization treatment process and inoculation process.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: A silicon carbide-assisted spheroidizing inoculated high-spheroidizing ductile iron and a preparation method thereof, wherein the silicon carbide-assisted spheroidizing inoculated high-spheroidizing ductile iron preparation method comprises six steps of preparing an auxiliary spheroidizing agent, preparing an auxiliary inoculant, batching, smelting, spheroidizing inoculation, and pouring; The following are further improvements to the above technical solution: Step 1: Preparation of auxiliary spheroidizing agent Add zirconium oxychloride aqueous solution, zirconium disilicide powder, micron-sized silicon carbide, magnesium diboride powder, stabilizer Y2O3 and polyethylene glycol into a high-speed dispersion kettle, control the dispersion rate at 8000-10000 rpm, and after high-speed dispersion for 4-9 hours, reduce the dispersion rate to 800-1400 rpm, then drop ammonia water with a mass concentration of 10-20wt% at a rate of 0.1-1.3g / min until the pH value of the solution reaches 9-10 to obtain a sol, then stop stirring, let stand and age for 36-60 hours to obtain a gel, and then wash the gel with deionized water for 3-5 times, the mass of deionized water used for each washing is the mass of the gel The gel is placed in a dry and dust-free environment at room temperature for 80 to 100 hours, and then dried at 80 to 100°C for 13 to 20 hours. After cooling to room temperature in a dry environment, the dried gel is ground into a powder of 400 to 1000 meshes. The powder is then placed in a calcining furnace, and heated and maintained at a constant temperature of 500 to 770°C at a heating rate of 3 to 9°C / min in a reducing atmosphere of hydrogen. After isothermal reduction calcination for 1.5 to 3 hours, the powder is cooled to room temperature under the protection of a reducing atmosphere of hydrogen to obtain an auxiliary spheroidizing agent. The zirconium oxychloride aqueous solution, wherein the mass fraction of zirconium oxychloride is 15-35wt%; The particle size of the zirconium disilicide powder is 0.5-4 μm; The particle size of the micron-sized silicon carbide is 1 to 500 μm; The particle size of the magnesium boride powder is 0.5-5 μm; The stabilizer Y2O3 is nano-scale Y2O3 powder with a particle size of 10-100nm; The number average molecular weight of the polyethylene glycol is 400-800 g / mol; The mass ratio of the zirconium oxychloride aqueous solution, zirconium disilicide powder, micron-sized silicon carbide, magnesium diboride powder, stabilizer Y2O3, and polyethylene glycol is 100-180:5-25:60-100:6-20:0.1-1:0.3-1.3.

[0008] Step 2: Preparation of auxiliary inoculant Add polyvinyl pyrrolidone and divalent iron salt aqueous solution into a dispersion reactor, first maintain a slow dispersion rate, and after the polyvinyl pyrrolidone is completely dissolved, increase the dispersion rate to 8000-12000 rpm, then add nano silicon carbide and nano zirconium carbide, and after strong dispersion for 8-15 hours, reduce the dispersion rate to 2000-4500 rpm, and then add zinc powder into the reactor at a rate of 1-8 g / min. After the addition of zinc powder, continue the dispersion reaction for 1-2 hours, stop the dispersion, stand and age for 20-30 hours, filter, wash the filtered solid with deionized water for 3-5 times, dry it at 60-90°C for 3-6 hours, and then put it into a calcining furnace protected by hydrogen atmosphere, and heat it up and keep it at a constant temperature to 550-800°C at a heating rate of 2-7°C / min, and reduce and calcine it at a constant temperature for 1-2 hours, and then cool it to room temperature under the protection of hydrogen reducing atmosphere to obtain an auxiliary inoculant; The grade of the polyvinyl pyrrolidone is K30, and the molecular weight is 40000-60000 g / mol; The divalent iron salt aqueous solution is one of a ferrous sulfate aqueous solution and a ferrous chloride aqueous solution, wherein the mass concentration of divalent iron ions is 10-25wt%; The particle size of the nano silicon carbide is 10-100 nm; The particle size of the nano zirconium carbide is 10-100 nm; The particle size of the zinc powder is 0.3-2 μm; The mass ratio of the polyvinyl pyrrolidone, the divalent iron salt aqueous solution, the nano-silicon carbide, the nano-zirconium carbide and the zinc powder is 0.2-1:100-250:10-50:4-20:8-40.

[0009] Step 3: Ingredients The main raw materials are cast iron, carbon scrap steel and recycled materials, graphite is used as a recarburizer to adjust the carbon content, the spheroidizing agent is a spheroidizing core wire composed of a rare earth magnesium spheroidizing agent and an auxiliary spheroidizing agent, the inoculant and the stream inoculant are both a mixture of a silicon-barium inoculant and an auxiliary inoculant, and the mass ratio of all the above raw materials is determined according to the requirements of the ductile iron grade QT450 for the main components, that is, the content of the main elements in the ductile iron casting obtained after the pouring step is completed should meet the requirements of QT450 for the main elements; The main component requirements of QT450 are C3.70-4.00wt%, Si2.15-2.93wt%, Mn0.46-0.66wt%, Mg0.027-0.050wt%, P<0.027wt%, S<0.016wt%, RE0.026-0.043wt%, and the remaining less than 100wt% is Fe and other trace elements; The composition of the cast iron is required to be C4.0~5.0wt%, Si1.3~2.0%, P≤0.04wt%, S≤0.025wt%, Mn≤0.3wt%, Sn≤0.0006wt%, Sb≤0.005wt%, Ti≤0.06wt%, Al≤0.004wt%, As≤0.0012wt%, Bi≤0.0003wt%, Pb≤0.0005wt%, and the remaining part less than 100wt% is Fe; The composition requirements of the carbon scrap steel are C0.06-0.22wt%, Mn≤0.35wt%, Si≤0.30wt%, S≤0.015wt%, P≤0.030wt%, Cr≤0.050wt%, Mo≤0.050wt%, Cu≤0.050wt%, Ti≤0.050wt%, Pb≤0.001wt%, Sb≤0.010wt%, As≤0.020wt%, Al≤0.20wt%, V≤0.01wt%, and the remaining less than 100wt% is Fe; The components of the recycled materials are C3.70-4.00wt%, Si2.15-2.93wt%, Mn0.46-0.66wt%, Mg0.027-0.050wt%, P<0.027wt%, S<0.016wt%, RE0.026-0.043wt%, and the remaining less than 100wt% is Fe and other trace elements; The rare earth magnesium spheroidizer comprises Si35-50wt%, Mg25-35wt%, RE2-10wt%, Ba1-2wt%, Ca0-1wt%, Bi0-0.6wt%, and the rest less than 100wt% is Fe; The particle size of the rare earth magnesium spheroidizer is 3-50 μm; In the spheroidized cored wire, the mass ratio of the rare earth magnesium spheroidizer to the auxiliary spheroidizer is 13:6-15; In the inoculant in the package, the mass ratio of silicon-barium inoculant to auxiliary inoculant is 15:8-20; In the inoculant, the mass ratio of silicon-barium inoculant to auxiliary inoculant is 30:13-37; The silicon-barium inoculant comprises Si70-75wt%, Ba4-6wt%, Ca0.8-1.5wt%, Al≤1.5wt%, and the remaining portion less than 100wt% is Fe; The particle size of the silicon-barium inoculant is 1-3 mm.

[0010] Step 4: Melting According to the mass ratio determined in the batching step, cast pig iron, carbon scrap steel, recycled materials and graphite recarburizer are added into the induction furnace in sequence, and the temperature is raised to 1490-1510°C. After melting into liquid, a slag remover is sprinkled, the slag is removed, samples are taken for testing and the composition of the original molten iron is adjusted, and the temperature is then raised to 1520-1560°C, the slag floating on the liquid surface is removed, and the molten iron is obtained, and then spheroidization inoculation is carried out.

[0011] Step 5: Spheroidization The spheroidizing inoculation treatment is carried out by the in-launder flushing method. Before the smelting iron liquid is flushed in, the inoculant in the ladle is first placed in the bottom pit of the dam-type ladle according to the mass ratio determined in the batching step, and then the smelting iron liquid is flushed into the dam-type ladle, the ladle cover is covered, and then the dam-type ladle is transferred to the wire feeding spheroidizing station, and automatic wire feeding spheroidization is started. The amount of spheroidizing core wire added is 10-11 meters / ton of molten iron, and the wire feeding speed is 17-23 meters / minute. During the spheroidizing inoculation treatment, the temperature of the molten iron in the dam-type ladle is maintained at 1460-1500°C. After the spheroidizing inoculation is completed, the spheroidizing inoculated iron liquid is quickly transferred to the pouring section for preparation of pouring. The time from spheroidizing inoculation treatment to the pouring section is controlled at 3-4 minutes.

[0012] Step 6: Pouring The spheroidized inoculated iron liquid transferred to the pouring section is injected into the molding sand from the pouring port reserved for the casting sand made by the casting mold and the molding machine. During the pouring process, the flowing inoculant is uniformly added into the spheroidized inoculated iron liquid along with the pouring liquid flow according to the mass ratio determined in the batching step. During the whole pouring process, the temperature of the spheroidized inoculated iron liquid at the pouring port is maintained above 1320-1400° C. The pouring time is controlled within 5-8 minutes. After the pouring is completed, it is naturally cooled by a cooling belt and runs to a sand-falling drum. The sand and the ductile iron casting are separated by the sand-falling drum to obtain the ductile iron casting.

[0013] Compared with the prior art, the present invention achieves the following beneficial effects: 1. The auxiliary spheroidizing agent mainly composed of micron-sized silicon carbide, zirconium disilicide powder and magnesium diboride powder is added in the present invention. Micron-sized silicon carbide is different from ferrosilicon. Micron-sized silicon carbide has a high melting point. It does not melt in molten iron but slowly dissolves. In the dissolution process, it continuously provides silicon atoms and carbon atoms to the surrounding area, playing the dual role of increasing carbon and silicon. At the same time, micron-sized silicon carbide forms many fine particles around it during the dissolution of molten iron. These particles dissolve again to form many carbon atom clusters after dissolution. These carbon atom clusters serve as the basis for subsequent graphite nucleation, increase the number of crystal nucleus points in the molten iron to promote graphite nucleation. At the same time, micron-sized silicon carbide has the advantages of significantly reducing the tendency of chilling, eliminating anti-chickening, improving cast iron microstructure, playing the role of grain boundary refinement, improving the toughness and strength of ductile iron, preventing the "slag inclusion" phenomenon of castings, and reducing the porosity of castings. The role of zirconium disilicide in the auxiliary spheroidizing agent is mainly to provide zirconium atoms. Zirconium can improve the strength and wear resistance of ductile iron by refining grains and optimizing microstructure, as well as improving hardenability and temper brittleness, thereby improving the overall performance of ductile iron. Magnesium diboride powder has a relatively low melting point, and it begins to strongly promote the relative flow of molten iron at a relatively low temperature. In the process of spheroidizing high-temperature molten iron, it can play a role in forced thermal agitation and promote the strengthening of convection of molten iron. The boron element dissociated by heat can form boron-carbon compounds with graphite to improve the wear resistance and hardness of ductile iron. The magnesium element dissociated by heat is mainly used to supplement the insufficient magnesium content in the rare earth magnesium spheroidizing agent, further increase the concentration of magnesium element, and maintain a high spheroidization rate. In addition, in the present invention, the surface of the powdered material of the auxiliary spheroidizing agent is coated with zirconium by the sol-gel method, which can enhance the wettability of the auxiliary spheroidizing agent by the molten iron, so that the auxiliary spheroidizing agent can be more quickly melted into the entire high-temperature molten iron, promote the rapid progress of the spheroidizing reaction, and also promote the completeness of the spheroidizing reaction, so that the spheroidizing rate is better improved; 2. The in-package inoculant and the flow inoculant added in the present invention are composed of a silicon-barium inoculant and an auxiliary inoculant. The silicon-barium inoculant has a strong anti-decay ability, and its anti-decay time is twice that of the ferrosilicon inoculant. Its added amount is half that of the ferrosilicon. It can make graphite small, round and spherical, prevent the accompanying spheroidal graphite decay, and reduce the wall thickness sensitivity. The auxiliary inoculant used in conjunction with the silicon-barium inoculant is composed of nano-silicon carbide and nano-zirconium carbide. Both of these substances are nano-scale foreign heterogeneous nuclei, which can increase the graphitized core exponentially, promote the super-refining of graphite balls, and thus obtain a ductile iron microstructure with small graphite ball size, high roundness, and more uniform shape. This uniform and unified microstructure ultimately gives the ductile iron higher toughness, strength, and plasticity. In addition, the present invention uses zinc powder to replace the reaction of divalent iron ions, and the surface of nano-silicon carbide and nano-zirconium carbide is coated with single iron elements, which greatly improves the surface wetting effect of high-temperature iron liquid on nano-silicon carbide and nano-zirconium carbide, so that nano-scale silicon carbide and zirconium carbide are quickly dissolved and quickly dispersed in the iron liquid, so that the area of ​​the inoculation reaction increases exponentially, thereby promoting the uniformity and thoroughness of the inoculation reaction, and ensuring that a microscopic graphite ball core metallographic structure with a high spheroidization rate and good graphite sphericity can be bred in the final ductile iron; 3. The ductile iron casting product obtained by the present invention has a tensile strength of 463-498 MPa, a yield strength of 310-320 MPa, an elongation of 7.2-9.8%, a Brinell hardness of 180-220, a minimum impact energy of 49-55 J, a graphite spheroidization level of 1-2, a spheroidization rate of 95-97%, and a graphite ball size level of 6-7. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a metallographic microscope photograph of the cross section of the finished ductile iron casting obtained in Example 1, magnified 200 times; Figure 2 This is a metallographic microscope photograph of the cross section of the finished ductile iron casting obtained in Comparative Example 1, magnified 200 times; Figure 3 This is a metallographic microscope photograph of the cross section of the finished ductile iron casting obtained in Comparative Example 2, magnified 200 times; Figure 4 This is a metallographic microscope photograph of the cross section of the finished ductile iron casting obtained in Comparative Example 3, magnified 200 times; Figure 5 This is a metallographic microscope photograph of the cross section of the finished ductile iron casting obtained in Comparative Example 4, magnified 200 times. DETAILED DESCRIPTION

[0015] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0016] Example 1: A method for preparing high spheroidization rate ductile iron by silicon carbide assisted spheroidization inoculation Step 1: Preparation of auxiliary spheroidizing agent Zirconium dichloride aqueous solution, zirconium disilicide powder, micron-sized silicon carbide, magnesium diboride powder, stabilizer Y2O3 and polyethylene glycol were added to a high-speed dispersion kettle, and the dispersion rate was controlled at 9000 rpm. After 7 hours of high-speed dispersion, the dispersion rate was reduced to 1000 rpm, and then ammonia water with a mass concentration of 17wt% was added dropwise at a rate of 0.8g / min until the pH value of the solution reached 9.6 to obtain a sol, and then the stirring was stopped and the solution was allowed to stand for 44 hours to obtain a gel, and then the gel was washed 4 times with deionized water, and the mass of the deionized water used for each washing was the mass of the gel. The gel was placed in a dry and dust-free environment at room temperature for 96 hours, and then dried at 95°C for 13-20 hours. After cooling to room temperature in a dry environment, the dried gel was ground into 800-mesh powder. The powder was then placed in a calcining furnace, heated and kept at a constant temperature of 650°C at a heating rate of 5°C / min in a hydrogen reducing atmosphere, and then cooled to room temperature under the protection of a hydrogen reducing atmosphere to obtain an auxiliary spheroidizing agent. The zirconium oxychloride aqueous solution, wherein the mass fraction of zirconium oxychloride is 20wt%; The particle size of the zirconium disilicide powder is 1 μm; The particle size of the micron-sized silicon carbide is 300 μm; The particle size of the magnesium boride powder is 3 μm; The stabilizer Y2O3 is nano-scale Y2O3 powder with a particle size of 80nm; The number average molecular weight of the polyethylene glycol is 700 g / mol; The mass ratio of the zirconium oxychloride aqueous solution, zirconium disilicide powder, micron-sized silicon carbide, magnesium diboride powder, stabilizer Y2O3, and polyethylene glycol is 150:15:90:15:0.8:1.

[0017] Step 2: Preparation of auxiliary inoculant Add polyvinyl pyrrolidone and divalent iron salt aqueous solution into a dispersion reactor, first maintain a slow dispersion rate, and after the polyvinyl pyrrolidone is completely dissolved, increase the dispersion rate to 9000 rpm, then add nano silicon carbide and nano zirconium carbide, and disperse vigorously for 11 hours, then reduce the dispersion rate to 4000 rpm, and then add zinc powder into the reactor at a rate of 4 g / min. After the addition of zinc powder, continue the dispersion reaction for 1.6 hours, stop the dispersion, stand and age for 24 hours, filter, wash the filtered solid with deionized water for 4 times, first dry it at 69°C for 5 hours, and then put it into a calcining furnace protected by hydrogen atmosphere, and heat it up and keep it at a constant temperature to 700°C at a heating rate of 5°C / min. After isothermal reduction calcination for 1.6 hours, cool it to room temperature under the protection of hydrogen reducing atmosphere to obtain an auxiliary inoculant; The grade of the polyvinyl pyrrolidone is K30, and the molecular weight is 50000 g / mol; The divalent iron salt aqueous solution is one of a ferrous sulfate aqueous solution and a ferrous chloride aqueous solution, wherein the mass concentration of divalent iron ions is 13wt%; The particle size of the nano silicon carbide is 30nm; The particle size of the nano zirconium carbide is 20 nm; The particle size of the zinc powder is 1 μm; The mass ratio of the polyvinyl pyrrolidone, the divalent iron salt aqueous solution, nano-silicon carbide, nano-zirconium carbide and zinc powder is 0.7:180:40:13:30.

[0018] Step 3: Ingredients The main raw materials are cast iron, carbon scrap steel and recycled materials, graphite is used as a recarburizer to adjust the carbon content, the spheroidizing agent is a spheroidizing core wire composed of a rare earth magnesium spheroidizing agent and an auxiliary spheroidizing agent, the inoculant and the stream inoculant are both a mixture of a silicon-barium inoculant and an auxiliary inoculant, and the mass ratio of all the above raw materials is determined according to the requirements of the ductile iron grade QT450 for the main components, that is, the content of the main elements in the ductile iron casting obtained after the pouring step is completed should meet the requirements of QT450 for the main elements; The main component requirements of QT450 are C3.80wt%, Si2.20wt%, Mn0.55wt%, Mg0.029wt%, P0.022wt%, S0.014wt%, RE0.036wt%, and the remaining less than 100wt% is Fe and other trace elements; The composition of the cast iron is required to be C4.6wt%, Si1.8%, P0.03wt%, S0.022wt%, Mn0.1wt%, Sn0.0004wt%, Sb0.002wt%, Ti0.03wt%, Al0.002wt%, As0.001wt%, Bi0.0001wt%, Pb0.0002wt%, and the remaining less than 100wt% is Fe; The composition of the carbon scrap steel is required to be C0.09wt%, Mn0.31wt%, Si0.24wt%, S0.015wt%, P0.020wt%, Cr0.020wt%, Mo0.030wt%, Cu0.020wt%, Ti0.030wt%, Pb0.0008wt%, Sb0.006wt%, As0.013wt%, Al0.10wt%, V0.006wt%, and the remaining part less than 100wt% is Fe; The components of the recycled materials are C3.80wt%, Si2.20wt%, Mn0.55wt%, Mg0.029wt%, P0.022wt%, S0.014wt%, RE0.036wt%, and the remaining less than 100wt% is Fe and other trace elements; The rare earth magnesium spheroidizer comprises Si 45wt%, Mg 28wt%, RE 7wt%, Ba 1.6wt%, Ca 0.7wt%, Bi 0.4wt%, and the remaining less than 100wt% is Fe; The particle size of the rare earth magnesium spheroidizer is 20 μm; In the spheroidized cored wire, the mass ratio of the rare earth magnesium spheroidizer to the auxiliary spheroidizer is 13:11; In the inoculant in the package, the mass ratio of silicon-barium inoculant to auxiliary inoculant is 15:13; In the inoculant, the mass ratio of silicon-barium inoculant to auxiliary inoculant is 30:25; The silicon-barium inoculant comprises Si73wt%, Ba5wt%, Ca1.3wt%, Al1.1wt%, and the remaining portion less than 100wt% is Fe; The particle size of the silicon-barium inoculant is 2 mm.

[0019] Step 4: Melting According to the mass ratio determined in the batching step, cast pig iron, carbon scrap steel, recycled materials and graphite recarburizer are added into the induction furnace in sequence, the temperature is raised to 1505°C, and after melting into liquid, a slag remover is sprinkled, the slag is removed, samples are taken for testing and the composition of the original molten iron is adjusted, the temperature is then raised to 1545°C, the slag floating on the liquid surface is removed, the molten iron is obtained, and then spheroidization inoculation is carried out.

[0020] Step 5: Spheroidization The spheroidizing inoculation treatment is carried out by the in-launder flushing method. Before the smelting molten iron is flushed in, the inoculant in the ladle is first placed in the bottom pit of the dam-type ladle according to the mass ratio determined in the batching step, and then the pretreated molten iron is flushed into the dam-type ladle, the ladle cover is covered, and then the dam-type ladle is transferred to the wire feeding spheroidizing station, and automatic wire feeding spheroidization is started. The amount of spheroidizing core wire added is 10.6 meters / ton of molten iron, and the wire feeding speed is 19 meters / minute. During the spheroidizing inoculation treatment, the temperature of the molten iron in the dam-type ladle is maintained at 1490°C. After the spheroidizing inoculation is completed, the spheroidizing inoculated molten iron is quickly transferred to the pouring section for preparation of pouring. The time from spheroidizing inoculation treatment to the pouring section is controlled at 3.6 minutes.

[0021] Step 6: Pouring The spheroidized inoculated iron liquid transferred to the pouring section is injected into the molding sand from the pouring port reserved for the casting sand made by the casting mold and the molding machine. During the pouring process, the flowing inoculant is uniformly added into the spheroidized inoculated iron liquid along with the pouring liquid flow according to the mass ratio determined in the batching step. During the whole pouring process, the temperature of the spheroidized inoculated iron liquid at the pouring port is kept above 1350° C. The pouring time is controlled within 6 minutes. After the pouring is completed, it is naturally cooled by a cooling belt and runs to a sand-falling drum. The sand and the ductile iron casting are separated by the sand-falling drum to obtain the ductile iron casting.

[0022] Example 2: A method for preparing high spheroidization rate ductile iron by silicon carbide assisted spheroidization inoculation Step 1: Preparation of auxiliary spheroidizing agent Zirconium dichloride aqueous solution, zirconium disilicide powder, micron-sized silicon carbide, magnesium diboride powder, stabilizer Y2O3 and polyethylene glycol were added to a high-speed dispersion kettle, and the dispersion rate was controlled at 8000 rpm. After 4 hours of high-speed dispersion, the dispersion rate was reduced to 800 rpm, and then ammonia water with a mass concentration of 10wt% was added dropwise at a rate of 0.1g / min until the pH value of the solution reached 9 to obtain a sol, and then the stirring was stopped and the solution was allowed to stand for 36 hours to obtain a gel, and then the gel was washed 3 times with deionized water, and the mass of the deionized water used for each washing was the mass of the gel. The gel was placed in a dry and dust-free environment at room temperature for 80 hours, and then dried at 80°C for 13 hours. After cooling to room temperature in a dry environment, the dried gel was ground into a 400-mesh powder. The powder was then placed in a calcining furnace, heated and kept at a constant temperature of 500°C at a heating rate of 3°C / min in a hydrogen reducing atmosphere, and calcined at a constant temperature for 1.5 hours. Then, the powder was cooled to room temperature under the protection of a hydrogen reducing atmosphere to obtain an auxiliary spheroidizing agent. The zirconium oxychloride aqueous solution, wherein the mass fraction of zirconium oxychloride is 15wt%; The particle size of the zirconium disilicide powder is 0.5 μm; The particle size of the micron-sized silicon carbide is 1 μm; The particle size of the magnesium boride powder is 0.5 μm; The stabilizer Y2O3 is nano-scale Y2O3 powder with a particle size of 10nm; The number average molecular weight of the polyethylene glycol is 400 g / mol; The mass ratio of the zirconium oxychloride aqueous solution, zirconium disilicide powder, micron-sized silicon carbide, magnesium diboride powder, stabilizer Y2O3, and polyethylene glycol is 100:5:60:6:0.1:0.3.

[0023] Step 2: Preparation of auxiliary inoculant Add polyvinyl pyrrolidone and divalent iron salt aqueous solution into a dispersion reactor, first maintain a slow dispersion rate, and after the polyvinyl pyrrolidone is completely dissolved, increase the dispersion rate to 8000 rpm, then add nano silicon carbide and nano zirconium carbide, and after strong dispersion for 8 hours, reduce the dispersion rate to 2000 rpm, and then add zinc powder into the reactor at a rate of 1 gram per minute. After the addition of zinc powder, continue the dispersion reaction for 1 hour, stop the dispersion, stand and age for 20 hours, filter, wash the filtered solid with deionized water for 3 times, first dry it at 60°C for 3 hours, and then put it into a calcining furnace protected by a hydrogen atmosphere, and heat it up and keep it at a constant temperature to 550°C at a heating rate of 2°C / min. After isothermal reduction calcination for 1 hour, cool it to room temperature under the protection of a hydrogen reducing atmosphere to obtain an auxiliary inoculant; The grade of the polyvinyl pyrrolidone is K30, and the molecular weight is 40000 g / mol; The divalent iron salt aqueous solution is one of a ferrous sulfate aqueous solution and a ferrous chloride aqueous solution, wherein the mass concentration of divalent iron ions is 10wt%; The particle size of the nano silicon carbide is 10 nm; The particle size of the nano zirconium carbide is 10 nm; The particle size of the zinc powder is 0.3 μm; The mass ratio of the polyvinyl pyrrolidone, the divalent iron salt aqueous solution, nano-silicon carbide, nano-zirconium carbide and zinc powder is 0.2:100:10:4:8.

[0024] Step 3: Ingredients The main raw materials are cast iron, carbon scrap steel and recycled materials, graphite is used as a recarburizer to adjust the carbon content, the spheroidizing agent is a spheroidizing core wire composed of a rare earth magnesium spheroidizing agent and an auxiliary spheroidizing agent, the inoculant and the stream inoculant are both a mixture of a silicon-barium inoculant and an auxiliary inoculant, and the mass ratio of all the above raw materials is determined according to the requirements of the ductile iron grade QT450 for the main components, that is, the content of the main elements in the ductile iron casting obtained after the pouring step is completed should meet the requirements of QT450 for the main elements; The main component requirements of QT450 are C3.70wt%, Si2.15wt%, Mn0.46wt%, Mg0.027wt%, P0.027wt%, S0.016wt%, RE0.026wt%, and the remaining less than 100wt% is Fe and other trace elements; The composition of the cast iron is required to be C4.0wt%, Si1.3%, P0.04wt%, S0.025wt%, Mn0.3wt%, Sn0.0006wt%, Sb0.005wt%, Ti0.06wt%, A0.004wt%, As0.0012wt%, Bi0.0003wt%, Pb0.0005wt%, and the remaining part less than 100wt% is Fe; The composition of the carbon scrap steel is required to be C0.06wt%, Mn0.35wt%, Si0.30wt%, S0.015wt%, P0.030wt%, Cr0.050wt%, Mo0.050wt%, Cu0.050wt%, Ti0.050wt%, Pb0.001wt%, Sb0.010wt%, As0.020wt%, Al0.20wt%, V0.01wt%, and the remaining part less than 100wt% is Fe; The components of the recycled materials are C3.70wt%, Si2.15wt%, Mn0.46wt%, Mg0.027wt%, P0.027wt%, S0.016wt%, RE0.026wt%, and the remaining less than 100wt% is Fe and other trace elements; The rare earth magnesium spheroidizer comprises Si35wt%, Mg25wt%, RE2wt%, Ba1wt%, Ca0wt%, Bi0wt%, and the remaining less than 100wt% is Fe; The particle size of the rare earth magnesium spheroidizer is 3 μm; In the spheroidized cored wire, the mass ratio of the rare earth magnesium spheroidizer to the auxiliary spheroidizer is 13:6; In the inoculant in the package, the mass ratio of silicon-barium inoculant to auxiliary inoculant is 15:8; In the said inoculant, the mass ratio of silicon-barium inoculant to auxiliary inoculant is 30:13; The silicon-barium inoculant comprises Si70wt%, Ba4wt%, Ca0.8wt%, Al1.5wt%, and the remaining portion less than 100wt% is Fe; The particle size of the silicon-barium inoculant is 1 mm.

[0025] Step 4: Melting According to the mass ratio determined in the batching step, cast pig iron, carbon scrap steel, recycled materials and graphite recarburizer are added into the induction furnace in sequence, the temperature is raised to 1490°C, and after melting into liquid, a slag remover is sprinkled, the slag is removed, samples are taken for testing and the composition of the original molten iron is adjusted, the temperature is then raised to 1520°C, the slag floating on the liquid surface is removed, the molten iron is obtained, and then spheroidization inoculation is carried out.

[0026] Step 5: Spheroidization The spheroidizing inoculation treatment is carried out by the in-launder flushing method. Before the smelting iron liquid is flushed in, the inoculant in the ladle is first placed in the bottom pit of the dam-type ladle according to the mass ratio determined in the batching step, and then the smelting iron liquid is flushed into the dam-type ladle, the ladle cover is covered, and then the dam-type ladle is transferred to the wire feeding spheroidizing station, and automatic wire feeding spheroidization is started. The amount of spheroidizing core wire added is 10 meters / ton of molten iron, and the wire feeding speed is 17 meters / minute. During the spheroidizing inoculation treatment, the temperature of the molten iron in the dam-type ladle is maintained at 1460°C. After the spheroidizing inoculation is completed, the spheroidizing inoculated iron liquid is quickly transferred to the casting section for preparation of casting. The time from spheroidizing inoculation treatment to the casting section is controlled within 3 minutes.

[0027] Step 6: Pouring The spheroidized inoculated iron liquid transferred to the pouring section is injected into the molding sand from the pouring port reserved for the casting sand made by the casting mold and the molding machine. During the pouring process, the flowing inoculant is uniformly added into the spheroidized inoculated iron liquid along with the pouring liquid flow according to the mass ratio determined in the batching step. During the whole pouring process, the temperature of the spheroidized inoculated iron liquid at the pouring port is kept above 1320° C. The pouring time is controlled within 5 minutes. After the pouring is completed, it is naturally cooled by a cooling belt and runs to a sand-falling drum. The sand and the ductile iron casting are separated by the sand-falling drum to obtain the ductile iron casting.

[0028] Example 3: A method for preparing high spheroidization rate ductile iron by silicon carbide assisted spheroidization inoculation Step 1: Preparation of auxiliary spheroidizing agent Zirconium dichloride aqueous solution, zirconium disilicide powder, micron-sized silicon carbide, magnesium diboride powder, stabilizer Y2O3 and polyethylene glycol were added to a high-speed dispersion kettle, and the dispersion rate was controlled at 10000 rpm. After high-speed dispersion for 9 hours, the dispersion rate was reduced to 1400 rpm, and then ammonia water with a mass concentration of 20wt% was added dropwise at a rate of 1.3g / min until the pH value of the solution reached 10 to obtain a sol, and then the stirring was stopped and the solution was allowed to stand for 60 hours to obtain a gel, and then the gel was washed 5 times with deionized water, and the mass of the deionized water used for each washing was the mass of the gel. The gel was placed in a dry and dust-free environment at room temperature for 100 hours, and then dried at 100°C for 20 hours. After cooling to room temperature in a dry environment, the dried gel was ground into a 1000-mesh powder. The powder was then placed in a calcining furnace, heated and kept at a constant temperature of 770°C at a heating rate of 9°C / min in a hydrogen reducing atmosphere, and calcined at a constant temperature for 3 hours. Then, the powder was cooled to room temperature under the protection of a hydrogen reducing atmosphere to obtain an auxiliary spheroidizing agent. The zirconium oxychloride aqueous solution, wherein the mass fraction of zirconium oxychloride is 35wt%; The particle size of the zirconium disilicide powder is 4 μm; The particle size of the micron-sized silicon carbide is 500 μm; The particle size of the magnesium boride powder is 5 μm; The stabilizer Y2O3 is nano-scale Y2O3 powder with a particle size of 100nm; The number average molecular weight of the polyethylene glycol is 800 g / mol; The mass ratio of the zirconium oxychloride aqueous solution, zirconium disilicide powder, micron-sized silicon carbide, magnesium diboride powder, stabilizer Y2O3, and polyethylene glycol is 180:25:100:20:1:1.3.

[0029] Step 2: Preparation of auxiliary inoculant Add polyvinyl pyrrolidone and divalent iron salt aqueous solution into a dispersion reactor, first maintain a slow dispersion rate, and after the polyvinyl pyrrolidone is completely dissolved, increase the dispersion rate to 12000 rpm, then add nano silicon carbide and nano zirconium carbide, and disperse vigorously for 15 hours, then reduce the dispersion rate to 4500 rpm, and then add zinc powder into the reactor at a rate of 8 g / min. After the addition of zinc powder, continue the dispersion reaction for 2 hours, stop the dispersion, stand and age for 30 hours, filter, wash the filtered solid with deionized water for 5 times, first dry at 90°C for 6 hours, and then put it into a calcining furnace protected by hydrogen atmosphere, and heat it up and keep the temperature constant to 800°C at a heating rate of 7°C / min, and reduce and calcine at constant temperature for 2 hours, and then cool it to room temperature under the protection of hydrogen reducing atmosphere to obtain an auxiliary inoculant; The grade of the polyvinyl pyrrolidone is K30, and the molecular weight is 60000 g / mol; The divalent iron salt aqueous solution is one of a ferrous sulfate aqueous solution and a ferrous chloride aqueous solution, wherein the mass concentration of divalent iron ions is 25wt%; The particle size of the nano silicon carbide is 100 nm; The particle size of the nano zirconium carbide is 100 nm; The particle size of the zinc powder is 2 μm; The mass ratio of the polyvinyl pyrrolidone, the divalent iron salt aqueous solution, nano-silicon carbide, nano-zirconium carbide and zinc powder is 1:250:50:20:40.

[0030] Step 3: Ingredients The main raw materials are cast iron, carbon scrap steel and recycled materials, graphite is used as a recarburizer to adjust the carbon content, the spheroidizing agent is a spheroidizing core wire composed of a rare earth magnesium spheroidizing agent and an auxiliary spheroidizing agent, the inoculant and the stream inoculant are both a mixture of a silicon-barium inoculant and an auxiliary inoculant, and the mass ratio of all the above raw materials is determined according to the requirements of the ductile iron grade QT450 for the main components, that is, the content of the main elements in the ductile iron casting obtained after the pouring step is completed should meet the requirements of QT450 for the main elements; The main components of QT450 are C4.00wt%, Si2.93wt%, Mn0.66wt%, Mg0.050wt%, P0.027wt%, S0.016wt%, RE0.043wt%, and the remaining less than 100wt% is Fe and other trace elements; The composition of the cast iron is required to be C5.0wt%, Si2.0%, P0.04wt%, S0.025wt%, Mn0.3wt%, Sn0.0006wt%, Sb0.005wt%, Ti0.06wt%, Al0.004wt%, As0.0012wt%, Bi0.0003wt%, Pb0.0005wt%, and the remaining part less than 100wt% is Fe; The composition of the carbon scrap steel is required to be C0.22wt%, Mn0.35wt%, Si0.30wt%, S0.015wt%, P0.030wt%, Cr0.050wt%, Mo0.050wt%, Cu0.050wt%, Ti0.050wt%, Pb0.001wt%, Sb0.010wt%, As0.020wt%, Al0.20wt%, V0.01wt%, and the remaining part less than 100wt% is Fe; The components of the recycled materials are C4.00wt%, Si2.93wt%, Mn0.66wt%, Mg0.050wt%, P0.027wt%, S0.016wt%, RE0.043wt%, and the remaining less than 100wt% is Fe and other trace elements; The rare earth magnesium spheroidizer comprises Si 50wt%, Mg 35wt%, RE 10wt%, Ba 2wt%, Ca 1wt%, Bi 0.6wt%, and the remaining part less than 100wt% is Fe; The particle size of the rare earth magnesium spheroidizer is 50 μm; In the spheroidized cored wire, the mass ratio of the rare earth magnesium spheroidizer to the auxiliary spheroidizer is 13:15; In the inoculant in the package, the mass ratio of silicon-barium inoculant to auxiliary inoculant is 15:20; In the said inoculant, the mass ratio of silicon-barium inoculant to auxiliary inoculant is 30:37; The silicon-barium inoculant comprises Si75wt%, Ba6wt%, Ca1.5wt%, Al1.5wt%, and the remaining portion less than 100wt% is Fe; The particle size of the silicon-barium inoculant is 3 mm.

[0031] Step 4: Melting According to the mass ratio determined in the batching step, cast pig iron, carbon scrap steel, recycled materials and graphite recarburizer are added into the induction furnace in sequence, the temperature is raised to 1510°C, and after melting into liquid, a slag remover is sprinkled, the slag is removed, samples are taken for testing and the composition of the original molten iron is adjusted, the temperature is then raised to 1560°C, the slag floating on the liquid surface is removed, the molten iron is obtained, and then spheroidization inoculation is carried out.

[0032] Step 5: Spheroidization The spheroidizing inoculation treatment is carried out by the in-launder flushing method. Before the smelting iron liquid is flushed in, the inoculant in the ladle is first placed in the bottom pit of the dam-type ladle according to the mass ratio determined in the batching step, and then the smelting iron liquid is flushed into the dam-type ladle, the ladle cover is covered, and then the dam-type ladle is transferred to the wire feeding spheroidizing station, and automatic wire feeding spheroidization is started. The amount of spheroidizing core wire added is 11 meters / ton of molten iron, and the wire feeding speed is 23 meters / minute. During the spheroidizing inoculation treatment, the temperature of the molten iron in the dam-type ladle is maintained at 1500℃. After the spheroidizing inoculation is completed, the spheroidizing inoculated iron liquid is quickly transferred to the pouring section for preparation of pouring. The time from spheroidizing inoculation treatment to the pouring section is controlled within 4 minutes.

[0033] Step 6: Pouring The spheroidized inoculated iron liquid transferred to the pouring section is injected into the molding sand from the pouring port reserved for the casting sand made by the casting mold and the molding machine. During the pouring process, the flowing inoculant is uniformly added into the spheroidized inoculated iron liquid along with the pouring liquid flow according to the mass ratio determined in the batching step. During the whole pouring process, the temperature of the spheroidized inoculated iron liquid at the pouring port is kept above 1400° C. The pouring time is controlled within 8 minutes. After the pouring is completed, it is naturally cooled by a cooling belt and runs to a sand-falling drum. The sand and the ductile iron casting are separated by the sand-falling drum to obtain the ductile iron casting.

[0034] Comparative Example 1: Based on Example 1, step 1, preparation of the auxiliary spheroidizing agent, is not performed. In step 3, in the ingredients, 11 parts of the auxiliary spheroidizing agent in the spheroidized cored wire are replaced with 11 parts of rare earth magnesium spheroidizing agent in equal amounts. The specific operation is as follows: Step 1, preparation of an auxiliary spheroidizing agent is not performed; The operation of step 2 is the same as that of embodiment 1; Step 3: Ingredients The 11 parts of auxiliary spheroidizing agent in the spheroidized cored wire are replaced with 11 parts of rare earth magnesium spheroidizing agent in equal amounts, and the other operations are the same as in Example 1; The operations of steps 4, 5 and 6 are the same as those of Example 1.

[0035] Comparative Example 2: Based on Example 1, step 1, preparation of the auxiliary spheroidizing agent, is not performed. In step 3, in the ingredients, 11 parts of the auxiliary spheroidizing agent in the spheroidized cored wire are replaced by 11 parts of a mixture of zirconium disilicide powder, micron-sized silicon carbide, and magnesium diboride powder. The mixing mass ratio of the three powders is the same as the mass ratio of the three powders in the auxiliary spheroidizing agent preparation step in Example 1. The specific operation is as follows: Step 1, preparation of an auxiliary spheroidizing agent is not performed; The operation of step 2 is the same as that of embodiment 1; Step 3: Ingredients The 11 parts of auxiliary spheroidizing agent in the spheroidized cored wire are replaced by 11 parts of a mixture of zirconium disilicide powder, micron-sized silicon carbide, and magnesium diboride powder; In the mixture of zirconium disilicide powder, micron-sized silicon carbide and magnesium diboride powder, the mass ratio of zirconium disilicide powder, micron-sized silicon carbide and magnesium diboride powder is 15:90:15; The particle size of the zirconium disilicide powder is 1 μm; The particle size of the micron-sized silicon carbide is 300 μm; The particle size of the magnesium boride powder is 3 μm; Other operations are the same as in Example 1; The operations of steps 4, 5 and 6 are the same as those of Example 1.

[0036] Comparative Example 3: Based on Example 1, step 2, preparation of the auxiliary inoculant, is not performed. In step 3, in the batching, 13 parts of the auxiliary inoculant in the inoculant in the bag are replaced by 13 parts of silicon-barium inoculant, and 25 parts of the auxiliary inoculant in the flow-through inoculant are replaced by 25 parts of silicon-barium inoculant. The specific operation is as follows: The operation of step 1 is the same as that of embodiment 1; Step 2, preparation of auxiliary inoculant, is not performed; Step 3: Ingredients 13 parts of auxiliary inoculants in the inoculant in the bag are replaced by 13 parts of silicon-barium inoculants, and 25 parts of auxiliary inoculants in the flowing inoculant are replaced by 25 parts of silicon-barium inoculants. Other operations are the same as in Example 1; The operations of steps 4, 5 and 6 are the same as those of Example 1.

[0037] Comparative Example 4: On the basis of Example 1, step 2, preparation of the auxiliary inoculant is not performed. In step 3, in the batching, 13 parts of the auxiliary inoculant in the bag are replaced by 13 parts of a mixture of nano-silicon carbide and nano-zirconium carbide, and 25 parts of the auxiliary inoculant in the flow inoculant are replaced by 25 parts of a mixture of nano-silicon carbide and nano-zirconium carbide. In the mixture of nano-silicon carbide and nano-zirconium carbide, the mass ratio of nano-silicon carbide and nano-zirconium carbide is the same as the mass ratio of the two in the auxiliary inoculant preparation step in Example 1. The specific operation is as follows: The operation of step 1 is the same as that of embodiment 1; Step 2, preparation of auxiliary inoculant, is not performed; Step 3: Ingredients 13 parts of auxiliary inoculants in the inoculant in the bag are replaced by 13 parts of a mixture of nano-silicon carbide and nano-zirconium carbide, and 25 parts of auxiliary inoculants in the stream inoculant are replaced by 25 parts of a mixture of nano-silicon carbide and nano-zirconium carbide; In the mixture of nano-silicon carbide and nano-zirconium carbide, the mass ratio of nano-silicon carbide to nano-zirconium carbide is 40:13; The particle size of the nano silicon carbide is 30nm; The particle size of the nano zirconium carbide is 20 nm; Other operations are the same as in Example 1; The operations of steps 4, 5 and 6 are the same as those of Example 1.

[0038] Performance Test: With reference to GB / T 1348-2009 Ductile iron castings and GB / T 9441-2009 Metallographic inspection of ductile iron, the finished ductile iron castings obtained in Examples 1, 2, 3 and Comparative Examples 1, 2, 3 were tested for relevant performance indicators. The larger the graphite spheroidization level, the lower the spheroidization rate and the worse the performance, while the graphite ball size level is just the opposite, the larger the level, the better the performance. The test data are shown in Table 1: Table 1

[0039] It can be seen from the data in Table 1 that the mechanical properties of Examples 1-3 are relatively good, the graphite spheroidization level is 1~2, the graphite ball size level also reaches 6~7, and the spheroidization rate is 95~97%. It can be seen that the present invention uses high melting point materials mainly composed of silicon carbide, combined with rare earth magnesium spheroidizers and silicon barium inoculants, and at the same time optimizes the wire feeding spheroidization treatment process and inoculation process to prepare ductile iron with high spheroidization rate and high graphite spheroidization level; in Comparative Example 1, no auxiliary spheroidizer is added, and the spheroidized cored wire only contains rare earth magnesium spheroidizer. Compared with Example 1, the mechanical properties of Comparative Example 1 are greatly reduced, and the graphite spheroidization level is 95~97%. The graphite spheroidization level is reduced to level 4, the graphite ball size level is also reduced to level 4, and the spheroidization rate is reduced to 76%. It can be seen that the auxiliary spheroidizing agent plays an extremely critical role in improving the spheroidization rate, improving the graphite spheroidization level and ultimately improving the macroscopic mechanical properties of ductile iron; in Comparative Example 2, the three components of the auxiliary spheroidizing agent, zirconium disilicide powder, micron-sized silicon carbide, and magnesium diboride powder, are not coated with zirconium on the surface. The mechanical properties, spheroidization rate and graphite spheroidization level of Comparative Example 2 are also significantly lower than those of Example 1, but the above indicators of Comparative Example 2 are significantly better than those of Comparative Example 1, which shows that the powder of the auxiliary spheroidizing agent is not coated with zirconium on the surface. Zirconium coating can also improve the spheroidization rate of ductile iron, graphite spheroidization level and mechanical properties, but the auxiliary spheroidizer powder coated with zirconium has a better improvement effect. This may be because after zirconium coating, the auxiliary spheroidizer has better compatibility with molten iron, is easier to be infiltrated by molten iron, and then is easier to enter the lattice of ductile iron, and finally more efficiently improves the various properties of ductile iron; in Comparative Example 3, the inoculant in the bag and the inoculant with the flow are both single silicon-barium inoculant, and the performance of Comparative Example 3 is significantly lower than that of Example 1. It can be seen that the auxiliary inoculant prepared by the present invention can be matched with The invention discloses a composite silicon-barium inoculant, and can obtain a better inoculation effect than a single silicon-barium inoculant; in comparative example 4, the nano-silicon carbide and nano-zirconium carbide contained in the inoculant in the bag and the auxiliary inoculant added with the flow inoculant are not surface coated, and the various properties of comparative example 4 are also significantly lower than those of embodiment 1, but better than those of comparative example 3, which indicates that the surface-coated nano-silicon carbide and nano-zirconium carbide are easier to disperse in the molten iron and are easier to be infiltrated by the molten iron, thereby being able to more effectively improve the inoculation effect of ductile iron, and finally being able to obtain ductile iron with high spheroidization rate and high graphite spheroidization level.

[0040] Attached Figure 1 , 2 , 3, 4, 5 are metallographic microscope photos of the finished cross-section of the ductile iron castings obtained in Example 1 and Comparative Examples 1, 2, 3, 4, magnified 200 times, respectively. Figure 1 The graphite sphericity is very good, and it is also obvious that the spheroidization rate is very high. This also shows from the microstructure that the spheroidization rate of Example 1 can reach 95%, and the graphite spheroidization grade reaches Grade 1; Figure 2 The spheroidization rate of the graphite ball is the worst, and the sphericity of the graphite ball is also relatively poor, which is consistent with the spheroidization rate of comparative example 1 being only 76%, and the graphite spheroidization grade being reduced to grade 4. Figure 3 , 4 The spheroidization rates of Comparative Examples 2, 3, and 4 gradually improve, but the degree of graphite spheroidization does not improve significantly with the improvement of the spheroidization rate. This is consistent with the test data of the graphite spheroidization grade and spheroidization rate of Comparative Examples 2, 3, and 4 in Table 1, indicating that Comparative Examples 2, 3, and 4 are somewhat improved compared with Comparative Example 1, but are much worse than Example 1.

[0041] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing ductile iron with high spheroidization rate by silicon carbide assisted spheroidization inoculation, characterized in that: The method for preparing high-spheroidization-rate ductile iron by silicon carbide-assisted spheroidization inoculation comprises six steps of preparing an auxiliary spheroidizing agent, preparing an auxiliary inoculant, batching, smelting, spheroidization inoculation, and pouring; The auxiliary spheroidizing agent is prepared by adding zirconium oxychloride aqueous solution, zirconium disilicide powder, micron-sized silicon carbide, magnesium diboride powder, stabilizer Y2O3 and polyethylene glycol into a high-speed dispersion kettle, controlling the dispersion rate at 8000-10000 rpm, and dispersing at high speed for 4-9 hours, reducing the dispersion rate to 800-1400 rpm, then dripping ammonia water with a mass concentration of 10-20wt% at a speed of 0.1-1.3 g / min until the pH value of the solution reaches 9-10 to obtain a sol, then stopping stirring, standing and aging for 36-60 hours to obtain a gel, and then washing the gel with deionized water for 3-5 times, with the deionized water used for each washing being 10% to 20% by weight. The mass of the gel is twice that of the gel, and then washed with anhydrous ethanol for 2 to 4 times, the mass of the anhydrous ethanol used for each washing being equal to the mass of the gel, and then the gel is placed in a dry and dust-free room temperature environment for 80 to 100 hours, and then dried at 80 to 100°C for 13 to 20 hours, and after cooling to room temperature in a dry environment, the dried gel is ground into a powder of 400 to 1000 meshes, and then the powder is placed in a calcining furnace, and in a hydrogen reducing atmosphere, the temperature is increased and kept constant at 500 to 770°C at a heating rate of 3 to 9°C / min, and after constant temperature reduction calcination for 1.5 to 3 hours, it is cooled to room temperature under the protection of a hydrogen reducing atmosphere to obtain an auxiliary spheroidizing agent; The zirconium oxychloride aqueous solution, wherein the mass fraction of zirconium oxychloride is 15-35wt%; The particle size of the zirconium disilicide powder is 0.5-4 μm; The particle size of the micron-sized silicon carbide is 1 to 500 μm; The particle size of the magnesium boride powder is 0.5-5 μm; The stabilizer Y2O3 is nano-scale Y2O3 powder with a particle size of 10-100nm; The number average molecular weight of the polyethylene glycol is 400-800 g / mol; The preparation of the auxiliary inoculant comprises the following steps: adding polyvinyl pyrrolidone and a divalent iron salt aqueous solution into a dispersion reactor, first maintaining a slow dispersion rate, and then increasing the dispersion rate to 8000-12000 rpm after the polyvinyl pyrrolidone is completely dissolved, then adding nano silicon carbide and nano zirconium carbide, and after strong dispersion for 8-15 hours, reducing the dispersion rate to 2000-4500 rpm, and then adding zinc powder into the reactor at a rate of 1-8 g / min. After the addition of zinc powder, continuing the dispersion reaction for 1-2 hours, stopping the dispersion, standing and aging for 20-30 hours, filtering, washing the filtered solid with deionized water for 3-5 times, first drying at 60-90° C. for 3-6 hours, and then placing it in a calcining furnace protected by a hydrogen atmosphere, heating and maintaining the temperature to 550-800° C. at a heating rate of 2-7° C. / min, and performing constant temperature reduction calcination for 1-2 hours, and then cooling to room temperature under the protection of a hydrogen reducing atmosphere to obtain an auxiliary inoculant; The grade of the polyvinyl pyrrolidone is K30, and the molecular weight is 40000-60000 g / mol; The divalent iron salt aqueous solution is one of a ferrous sulfate aqueous solution and a ferrous chloride aqueous solution, wherein the mass concentration of divalent iron ions is 10-25wt%; The particle size of the nano silicon carbide is 10-100 nm; The particle size of the nano zirconium carbide is 10-100 nm; The particle size of the zinc powder is 0.3-2 μm; The ingredients are mainly cast iron, carbon scrap steel and recycled materials, graphite is used as a recarburizer to adjust the carbon content, the spheroidizing agent is a spheroidizing core wire composed of a rare earth magnesium spheroidizing agent and an auxiliary spheroidizing agent, the inoculant and the stream inoculant are both a mixture of a silicon-barium inoculant and an auxiliary inoculant, and the mass ratio of all the above raw materials is determined according to the requirements of the ductile iron grade QT450 for the main components, that is, the content of the main elements in the ductile iron casting obtained after the pouring step is completed should meet the requirements of QT450 for the main elements; The rare earth magnesium spheroidizer comprises Si35-50wt%, Mg25-35wt%, RE2-10wt%, Ba1-2wt%, Ca0-1wt%, Bi0-0.6wt%, and the rest less than 100wt% is Fe; The particle size of the rare earth magnesium spheroidizer is 3-50 μm; In the spheroidized cored wire, the mass ratio of the rare earth magnesium spheroidizer to the auxiliary spheroidizer is 13:6-15; In the inoculant in the package, the mass ratio of silicon-barium inoculant to auxiliary inoculant is 15:8-20; In the inoculant, the mass ratio of silicon-barium inoculant to auxiliary inoculant is 30:13-37; The silicon-barium inoculant comprises Si70-75wt%, Ba4-6wt%, Ca0.8-1.5wt%, Al≤1.5wt%, and the remaining portion less than 100wt% is Fe; The particle size of the silicon-barium inoculant is 1-3 mm.

2. The method for preparing ductile iron with high spheroidization rate by silicon carbide-assisted spheroidization inoculation according to claim 1, characterized in that: The mass ratio of the zirconium oxychloride aqueous solution, zirconium disilicide powder, micron-sized silicon carbide, magnesium diboride powder, stabilizer Y2O3, and polyethylene glycol is 100-180:5-25:60-100:6-20:0.1-1:0.3-1.

3.

3. The method for preparing ductile iron with high spheroidization rate by silicon carbide assisted spheroidization inoculation according to claim 1, characterized in that: The mass ratio of the polyvinyl pyrrolidone, the divalent iron salt aqueous solution, the nano-silicon carbide, the nano-zirconium carbide and the zinc powder is 0.2-1:100-250:10-50:4-20:8-40.

4. The method for preparing ductile iron with high spheroidization rate by silicon carbide assisted spheroidization inoculation according to claim 1, characterized in that: The main component requirements of QT450 are C3.70-4.00wt%, Si2.15-2.93wt%, Mn0.46-0.66wt%, Mg0.027-0.050wt%, P<0.027wt%, S<0.016wt%, RE0.026-0.043wt%, and the remaining less than 100wt% is Fe and other trace elements; The composition of the cast iron is required to be C4.0~5.0wt%, Si1.3~2.0%, P≤0.04wt%, S≤0.025wt%, Mn≤0.3wt%, Sn≤0.0006wt%, Sb≤0.005wt%, Ti≤0.06wt%, Al≤0.004wt%, As≤0.0012wt%, Bi≤0.0003wt%, Pb≤0.0005wt%, and the remaining part less than 100wt% is Fe; The composition requirements of the carbon scrap steel are C0.06-0.22wt%, Mn≤0.35wt%, Si≤0.30wt%, S≤0.015wt%, P≤0.030wt%, Cr≤0.050wt%, Mo≤0.050wt%, Cu≤0.050wt%, Ti≤0.050wt%, Pb≤0.001wt%, Sb≤0.010wt%, As≤0.020wt%, Al≤0.20wt%, V≤0.01wt%, and the remaining less than 100wt% is Fe; The components of the recycled materials are C3.70-4.00wt%, Si2.15-2.93wt%, Mn0.46-0.66wt%, Mg0.027-0.050wt%, P<0.027wt%, S<0.016wt%, RE0.026-0.043wt%, and the remaining part less than 100wt% is Fe and other trace elements.

5. The method for preparing ductile iron with high spheroidization rate by silicon carbide assisted spheroidization inoculation according to claim 1, characterized in that: In the smelting, cast iron, carbon scrap steel, recycled materials and graphite recarburizer are added into an induction furnace in order according to the mass ratio determined in the batching step, the temperature is raised to 1490-1510° C., and after melting into liquid, a slag remover is sprinkled, slag is removed, sampling is performed for testing and the composition of the original molten iron is adjusted, the temperature is then raised to 1520-1560° C., the slag floating on the liquid surface is removed, molten iron is obtained, and then spheroidization inoculation is performed.

6. The method for preparing ductile iron with high spheroidization rate by silicon carbide assisted spheroidization inoculation according to claim 1, characterized in that: The spheroidizing inoculation adopts the in-launder flushing method to carry out the spheroidizing inoculation treatment. Before the smelting iron liquid is flushed in, the inoculant in the launder is first placed in the bottom pit of the dam-type ladle according to the mass ratio determined in the batching step, and then the smelting iron liquid is flushed into the dam-type ladle, and the ladle cover is covered. Then the dam-type ladle is transferred to the wire feeding spheroidizing station, and automatic wire feeding spheroidization is started. The amount of spheroidizing core wire added is 10-11 meters / ton of molten iron, and the wire feeding speed is 17-23 meters / minute. During the spheroidizing inoculation treatment, the temperature of the molten iron in the dam-type ladle is maintained at 1460-1500°C. After the spheroidizing inoculation is completed, the spheroidizing inoculated iron liquid is quickly transferred to the casting section to prepare for casting. The time from the spheroidizing inoculation treatment to the casting section is controlled to be 3-4 minutes.

7. The method for preparing ductile iron with high spheroidization rate by silicon carbide assisted spheroidization inoculation according to claim 1, characterized in that: The pouring comprises the following steps: injecting the spheroidized inoculated iron liquid transferred to the pouring section into the molding sand from a pouring port reserved for the casting sand made by the casting mold and the molding machine; during the pouring process, the flowing inoculant is uniformly added into the spheroidized inoculated iron liquid along with the pouring liquid flow according to the mass ratio determined in the batching step; during the whole pouring process, the temperature of the spheroidized inoculated iron liquid at the pouring port is maintained above 1320-1400° C., the pouring time is controlled within 5-8 minutes, and after the pouring is completed, the spheroidized inoculated iron liquid is naturally cooled by a cooling belt and runs to a sand-falling drum, and the molding sand is separated from the ductile iron casting by the sand-falling drum to obtain the ductile iron casting.

8. The high spheroidization rate ductile iron obtained by silicon carbide assisted spheroidization inoculation according to any one of claims 1 to 7, characterized in that: The high-spheroidization-rate ductile iron inoculated by silicon carbide-assisted spheroidization has a tensile strength of 463-498 MPa, a yield strength of 310-320 MPa, an elongation of 7.2-9.8%, a Brinell hardness of 180-220, a minimum impact energy of 49-55 J, a graphite spheroidization level of 1-2, a spheroidization rate of 95-97%, and a graphite ball size level of 6-7.

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