Spheroidizing inoculation method of nodular cast iron with high spheroidizing rate

Abstract

The invention discloses a spheroidizing and inoculating method for spheroidal graphite cast iron with high spheroidizing rate, which belongs to the technical field of spheroidal graphite cast iron, and comprises the following steps: preparing a composite inoculant, preparing a spheroidizing agent, fixing, spheroidizing and inoculating, and carrying out heat treatment, in the step of preparing the composite nucleating agent, silicon powder and carbon black are evenly mixed and then subjected to microwave sintering, and after microwave sintering is conducted for 30-35 min, grinding is conducted, and carbon is removed; the preparation of the spheroidizing agent comprises the following steps: crushing a rare earth magnesium silicon type spheroidizing agent to obtain a millimeter-level spheroidizing agent; then taking out one third of the millimeter-scale spheroidizing agent, continuously crushing and ball-milling, and mixing with the rest millimeter-scale spheroidizing agent to obtain a mixed rare earth magnesium silicon type spheroidizing agent; the method comprises the following steps: uniformly mixing a mixed rare earth magnesium silicon nodulizer with iron powder to obtain a mixture, and wrapping the mixture with a tinplate skin; according to the method, the spheroidizing rate, plasticity and toughness of the nodular cast iron can be improved, and the utilization rate of the spheroidizing agent used in nodular cast iron production is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of ductile iron, and particularly relates to a nodulizing and inoculating method for ductile iron with a high nodularity rate. Background Art

[0002] During casting, a certain amount of nodulizer and inoculant are added to the molten iron, and ductile iron with spherical graphite structure is obtained through nodulizing treatment and inoculating treatment. The emergence of ductile iron has broken the traditional perception that cast iron has low mechanical strength, poor plasticity and toughness. On the basis of retaining the original composition and excellent properties of ordinary cast iron, ductile iron has greatly improved its mechanical strength, toughness and plasticity. Compared with gray cast iron and malleable cast iron, it has better comprehensive properties. Compared with carbon steel, ductile iron can reduce costs while meeting performance requirements. Due to the above excellent properties, the application range of ductile iron is becoming wider and wider, and it has been widely used in technical fields such as automobiles, ships, wind power, pressure pipelines and industrial production.

[0003] For ductile iron, the nodularity rate of spherical graphite directly affects its overall performance. Because spherical graphite expands in volume during growth, it can effectively reduce shrinkage cavities and porosity problems during the solidification of ductile iron, thus ensuring its internal quality. When producing ductile iron, adding an appropriate amount of nodulizer and inoculant to the molten iron for nodulizing treatment and inoculating treatment can induce the formation of spherical graphite in the molten iron and promote its growth, thereby realizing the control of the nodularity rate of spherical graphite.

[0004] The microstructure of ductile iron is spherical graphite and its surrounding matrix structure. In addition to the nodularity rate of spherical graphite, other microstructures also have a great impact on the performance of ductile iron, such as the size of spherical graphite, the uniformity of the distribution of spherical graphite in the matrix structure, and the composition of the matrix structure. According to the composition of the matrix structure, ductile iron is mainly divided into ferritic ductile iron, pearlitic ductile iron, and ferritic-pearlitic mixed ductile iron. Ferrite can improve the plasticity and toughness of ductile iron, pearlite can improve the strength of ductile iron, and ferritic-pearlitic mixed ductile iron has the best comprehensive mechanical properties and the widest application range. By controlling the austenite phase transformation, the matrix structure of ductile iron can be changed. At present, the austenite phase transformation process is mainly affected by alloying and heat treatment, and nodulizing treatment and inoculating treatment will also have a certain impact on the austenite phase transformation process.

[0005] In summary, nodulizing treatment and inoculation treatment are the core operations in the production of ductile iron. Especially for ferritic-pearlitic ductile iron, nodulizing treatment and inoculation treatment can control the nodularity and size of spherical graphite in ductile iron, the uniformity of the distribution of spherical graphite in the matrix structure, and the ratio of ferrite and pearlite by influencing the microstructure of ductile iron. Furthermore, the properties of ferritic-pearlitic ductile iron can be controlled. The nodulizer in nodulizing treatment can promote the growth of graphite in the molten iron in a spherical manner, and the inoculant in inoculation treatment can establish more crystallization nuclei and also play roles such as dehydrogenation, deoxidation, desulfurization, and elimination of chill. The use of nodulizer and inoculant has a great impact on the treatment results of nodulizing treatment and inoculation treatment.

[0006] For nodulizers, the main components of the nodulizers commonly used in industry at present are magnesium, calcium, and rare earths. Among them, magnesium has the advantages of strong nodulizing ability and relatively low price. However, magnesium has a low boiling point, and during the nodulizing reaction, it will violently vaporize, reducing the safety of the production site and polluting the air quality. The boiling point of rare earths is significantly higher than that of magnesium, and the boiling situation in the molten iron is relatively stable, but the price is high, and when used alone as a nodulizer, the nodulizing ability is weak, and the roundness of graphite in the produced ductile iron is poor. The problems of calcium are similar to those of rare earths, that is, although the boiling situation in the molten iron is relatively stable, the nodulizing ability is weak. Therefore, in the production of ductile iron, composite nodulizers containing magnesium are often used. For inoculants, ferrosilicon inoculants are commonly used in industry at present. According to the requirements for the properties of ductile iron, calcium, aluminum, barium, titanium, copper, zirconium, tin, molybdenum, etc. are often added to the ferrosilicon inoculant.

[0007] In addition to the use of spheroidizing agents and inoculants, the methods of spheroidizing and inoculating treatment also have a great influence on the treatment results of spheroidizing and inoculating treatment. The methods of spheroidizing and inoculating treatment mainly include the flushing method, the covering method, the in-mold method, the transfer method, the wire feeding method, etc. Among them, the flushing method requires the use of a magnesium-containing composite spheroidizing agent. When producing ductile iron by the flushing method, the spheroidizing agent is first placed in the pit of the molten iron ladle, and the inoculant and the covering agent are covered on it, and then the molten iron is slowly poured in. During the pouring process, the molten iron is controlled to the other side of the pit, that is, the side without the spheroidizing agent. The flushing method has the advantages of simple and convenient operation and can achieve stable production, but in the process of pouring molten iron, there are the following problems: first, since the temperature of the molten iron is not less than 1400°C, the density and boiling point of the magnesium in the magnesium-containing composite spheroidizer are lower than those of the molten iron, and the magnesium will float up and be converted into a gaseous state, resulting in the problem of magnesium escape. Magnesium will also undergo oxidation and ablation, resulting in a low absorption rate of magnesium, and further, resulting in a large amount of magnesium-containing composite spheroidizer; second, the magnesium-containing composite spheroidizer used is generally in block form, and the gap between each composite spheroidizer is large, so the molten iron can easily drill in, resulting in a large amount of spheroidizer floating up quickly, and the internal spheroidizer has not been released yet, but has already floated to the surface of the molten iron, and a large amount of magnesium escapes, resulting in a further reduction in the absorption rate of magnesium.

[0008] In view of the above problems, after searching, the existing solutions are as follows: The first solution is to add a layer of iron filings after the spheroidizing agent, inoculant and covering agent are added in sequence to prevent the molten iron from quickly drilling into the spheroidizing agents and to control the speed of adding the molten iron. Specifically, when the molten iron is just started to be added, the speed of adding the molten iron is increased to quickly form a certain height of molten iron, extend the floating route of the magnesium-containing composite spheroidizing agent, reduce the oxidation and burning loss of magnesium, and further improve the absorption rate of magnesium.

[0009] The second solution is described in Development and Application of Powdered Nodulizer. Geng Gang. Dalian Jiaotong University Master of Engineering Thesis. 2009. This solution is to crush and grind the blocky magnesium-containing composite nodulizer into powdered magnesium-containing composite nodulizer, and then use tinplate to wrap the powdered magnesium-containing composite nodulizer to slow down the melting rate of the powdered magnesium-containing composite nodulizer. The gaps between the powdered magnesium-containing composite nodulizers are small, and the molten iron is not easy to penetrate, thus avoiding a large amount of composite nodulizers from floating up at the same time. In addition, the powdered magnesium-containing composite nodulizer has a large specific surface area and high activity, and will quickly react with the anti-spheroidizing factors in the molten iron, shortening the free growth time of the graphite balls. It will be quickly consumed during the floating process of the powdered magnesium-containing composite nodulizer, thus avoiding the problem of magnesium oxidation and burning caused by the powdered magnesium-containing composite nodulizer floating to the surface of the molten iron, and further improving the magnesium absorption rate.

[0010] The third solution can be found in Chinese Patent CN113337774B, a process for producing silicon-oxidized inoculated ductile iron. In this solution, a layer of spheroidizing agent and a layer of covering agent are sequentially added from bottom to top in the pit of the ladle. First, silicon iron blocks are added to the part of the ladle above the covering agent, and then molten iron is poured. As the molten iron is poured, silicon iron blocks are added again. The silicon iron blocks added for the first time and the second time will gradually float up during the reaction with the molten iron, then react with oxygen in the air to form silicate, and as the molten iron tumbles, the silicate is involved in the molten iron, increasing the speed of the spheroidization reaction. Further, the absorption rate of magnesium is increased.

[0011] However, through experiments and analysis, the above three methods have the following problems respectively: For the first solution, due to the relatively fast floating speed of the magnesium-containing composite spheroidizing agent, even though the floating route is extended, there is still a problem of a large amount of magnesium being oxidized and burned.

[0012] For the second solution, although the particle size of the powdered magnesium-containing composite spheroidizing agent is small, the molten iron cannot penetrate too deep into the spheroidizing agent, and the heated layer is thin, so the spheroidization reaction time can be extended. However, the process stability of the powdered magnesium-containing composite spheroidizing agent is poor. On the one hand, due to the too small gaps in the powdered magnesium-containing composite spheroidizing agent, the molten iron cannot penetrate, resulting in the inability to form a molten layer. Further, a large amount of the powdered magnesium-containing composite spheroidizing agent splashes violently under the impact of the molten iron. Therefore, only when the dosage of the powdered magnesium-containing composite spheroidizing agent is small can the absorption rate of magnesium be increased; on the other hand, when the dosage of the powdered magnesium-containing composite spheroidizing agent is large, due to the high activity of the powdered magnesium-containing composite spheroidizing agent, it easily combines with sulfur and oxygen in the molten iron to form sulfides or sulfur oxides, resulting in too fast growth rate of graphite crystals, over-spheroidization, and further a decrease in spheroidization rate. Therefore, it is difficult to produce ductile iron with a high spheroidization rate through the powdered magnesium-containing composite spheroidizing agent.

[0013] For the third solution, the main purpose is to promote the rapid oxidation of silicon in the silicon iron blocks to further promote the spheroidization reaction. However, silicon iron blocks are used as inoculants, and the dispersibility of the silicon iron blocks is poor, resulting in uneven dispersion in the molten iron, uneven distribution of spherical graphite and collective tissue in the produced ductile iron, and further a decrease in the plasticity and toughness of the ductile iron. Summary of the Invention

[0014] Aiming at the deficiencies of the existing technology, the present invention provides a spheroidization inoculation method for high-spheroidization-rate ductile iron, which can improve the spheroidization rate, plasticity and toughness of ductile iron, and improve the utilization rate of the spheroidizing agent used in the production of ductile iron.

[0015] To solve the above technical problems, the technical solutions adopted by the present invention are as follows: A nodulizing and inoculating method for high-spheroidization-rate ductile iron, comprising: preparing a composite inoculant, preparing a nodulizer, fixing, nodulizing and inoculating, and heat treatment; For the preparation of the composite inoculant, after mixing silicon powder and carbon black evenly, add them into a corundum crucible, transfer it into a microwave sintering furnace for microwave sintering. After microwave sintering for 30 - 35 minutes, take out the microwave sintering product from the corundum crucible, grind it, and remove carbon by aerobic burning to obtain the composite inoculant; In the preparation of the composite inoculant, the mass ratio of silicon powder to carbon black is 28:23 - 25; In the microwave sintering, the frequency of the microwave sintering furnace is 2.45 GHz, the temperature is 1000 - 1020 °C, and the vacuum degree is 0.08 - 0.085 MPa; For the grinding, the particle size after grinding is 5 - 6 μm; The D50 particle size of the silicon powder is 100 μm; The average particle size of the carbon black is 31 nm, and the specific surface area is 80 m 2 / g; For the preparation of the nodulizer, crush the rare earth magnesium silicon type nodulizer to obtain millimeter-sized nodulizer; then take out one-third of the millimeter-sized nodulizer, continue to crush, ball mill, and then mix it with the remaining millimeter-sized nodulizer to obtain a mixed rare earth magnesium silicon type nodulizer; mix the mixed rare earth magnesium silicon type nodulizer with iron powder evenly to obtain a mixture, and use tinplate to wrap the mixture to obtain the nodulizer; In the preparation of the nodulizer, the mass ratio of the mixed rare earth magnesium silicon type nodulizer to iron powder is 100:2.4 - 2.6; The particle size of the millimeter-sized nodulizer is 1 mm; For the continued crushing, the particle size after continued crushing is 100 - 150 μm; For the ball milling, the particle size after ball milling is 4 - 5 μm; When using tinplate to wrap the mixture, ensure that the tinplate just completely wraps all the mixture; In the rare earth magnesium silicon type nodulizer, the mass content of magnesium is 8%, the mass content of rare earth is 4.8%, the mass content of calcium is 2.5%, the mass content of silicon is 41.8%, the mass content of manganese is 1.8%, the mass content of aluminum is 0.2%, the mass content of titanium is 0.3%, and the rest is iron; The particle size of the iron powder is 100 - 150 μm; The thickness of the tinplate is 2 mm; For the fixing, add the nodulizer, covering agent, and inoculant into the pit of the molten iron ladle in sequence from bottom to top, and tamp them; In the fixing, the covering agent is rust-free iron filings with a particle size of 1 - 2 mm; The inoculant is FeSi75 with a particle size of 5 - 6 mm; The pit is cylindrical, and the ratio of the depth to the diameter of the pit is 1.8. The diameter of the pit accounts for one - third of the lower diameter of the ladle; After ramming, the remaining depth of the pit is 25 - 30 mm; For the spheroidizing inoculation, pour the molten iron into the other side of the pit in the ladle. First, quickly pour in 62 - 67% of the total mass of the molten iron, and the pouring time accounts for one - tenth of the total pouring time. Then add the composite inoculant and slowly pour in the remaining molten iron to obtain the casting; In the spheroidizing inoculation, the temperature of the molten iron is 1420 - 1460 °C. The mass content of carbon in the molten iron is 3.8%, the mass content of silicon is 2.5%, the mass content of copper is 0.48%, the mass content of molybdenum is 0.42%, the mass content of manganese is 0.26%, the mass content of tin is 0.07%, the mass content of magnesium is 0.04%, the mass content of phosphorus is 0.05%, the mass content of sulfur is 0.032%, and the rest is iron; The dosage of the mixed rare - earth magnesium - silicon type spheroidizing agent in the spheroidizing agent accounts for 1.4 - 1.5% of the total mass of the molten iron by mass fraction; The dosage of the inoculant accounts for 0.7 - 0.73% of the total mass of the molten iron by mass fraction; The dosage of the composite inoculant accounts for 0.2 - 0.22% of the total mass of the molten iron by mass fraction; For the heat treatment, heat the casting at a heating rate of 10 - 15 °C / min to 900 - 920 °C, hold it at 900 - 920 °C for 4.5 - 5 h, cool it at a cooling rate of 4 - 6 °C / min to 700 - 720 °C, hold it at 700 - 720 °C for 2 - 2.5 h, air - cool it to room temperature, then heat it at a heating rate of 10 - 15 °C / min to 900 - 920 °C, cool it at a cooling rate of 10 - 15 °C / min to 400 - 450 °C, hold it at 400 - 450 °C for 1 - 1.5 h, and air - cool it to room temperature to obtain ductile cast iron.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1)The nodulizing and inoculating method of high-spheroidization-rate ductile iron of the present invention. The preparation method of the composite inoculant used is to mix silicon powder and carbon black, then carry out microwave sintering, and by controlling the particle size of the silicon powder, the temperature and time of microwave sintering, ensure that only part of the silicon powder reacts with the carbon black to generate a mixture of silicon powder, carbon black, and nano-silicon carbide. Then grind it, and after removing carbon by aerobic burning, obtain the composite inoculant. The composite inoculant is a mixture of small-particle-size silicon powder and nano-silicon carbide. After adding the composite inoculant, the composite inoculant can be quickly dispersed as the molten iron is poured. The silicon in it generates silicate under the oxidation of air, promoting the nodulizing reaction. Nano-silicon carbide can play a role in grain refinement, improving the spheroidization rate and the uniformity of the distribution of spherical graphite and the collective structure; The preparation method of the nodulizer used is to crush the rare-earth magnesium silicon type nodulizer into millimeter-sized nodulizer, then take part of the millimeter-sized nodulizer and continue to grind and ball-mill it to micron-sized nodulizer. Then mix the millimeter-sized nodulizer, micron-sized nodulizer, and iron powder. By controlling the particle size distribution of the millimeter-sized nodulizer, micron-sized nodulizer, and iron powder, ensure that there are appropriate voids in the nodulizer 1 to promote the inflow of molten iron. The iron powder can further promote the inflow of molten iron, avoiding the problem that the molten iron cannot penetrate. At the same time, realize the step-by-step release of the nodulizer, that is, first the micron-sized nodulizer reacts quickly, quickly reacts with the anti-nodulizing factors in the molten iron, shortening the free growth time of graphite balls, and then the millimeter-sized nodulizer is released to continue nodulizing, thus avoiding the problem of too fast growth rate of graphite crystals caused by excessive activity of the nodulizer; (2)The nodulizing and inoculating method of high-spheroidization-rate ductile iron of the present invention can improve the spheroidization rate, plasticity and toughness of ductile iron, and improve the utilization rate of the nodulizer used in the production of ductile iron. In the nodulizing and inoculating method of the present invention, the absorption rate of magnesium is 54.2 - 55.5%, the spheroidization rate of the obtained ductile iron is 92.9 - 93.4%, the tensile strength is 926.7 - 945.2 MPa, the yield strength is 653.0 - 668.1 MPa, and the elongation is 9.0 - 9.2%. Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the nodulizing and inoculating method of ductile iron for Example 1 and Example 2; In the figure: 1 - nodulizer, 2 - covering agent, 3 - inoculant, 4 - molten iron ladle, 5 - composite inoculant; Figure 2 It is the metallographic structure diagram of the ductile iron obtained in Example 1. Detailed Embodiments

[0018] In order to have a clearer understanding of the technical features, objectives and effects of the present invention, the specific embodiments of the present invention are now described.

[0019] Example 1 A spheroidizing and inoculating method for high-spheroidization-rate ductile iron, specifically as follows: 1. Preparation of composite inoculant 5: Mix silicon powder and carbon black evenly according to a mass ratio of 28:23, add them into a corundum crucible, transfer them into a microwave sintering furnace for microwave sintering. Control the frequency of the microwave sintering furnace to 2.45 GHz, control the temperature in the microwave sintering furnace to 1000 °C, and control the vacuum degree to 0.08 MPa. After microwave sintering for 30 minutes, take out the microwave sintering product from the corundum crucible, grind it to a particle size of 5 μm, and obtain composite inoculant 5 after removing carbon by aerobic burning; The D50 particle size of the silicon powder is 100 μm; The average particle size of the carbon black is 31 nm, and the specific surface area is 80 m 2 / g; 2. Preparation of spheroidizing agent 1: Add a rare earth magnesium silicon type spheroidizing agent into a crusher and crush it to a particle size of 1 mm to obtain a millimeter-sized spheroidizing agent; then take out one-third of the millimeter-sized spheroidizing agent, continue to crush it to a particle size of 100 μm, transfer it into a ball mill, ball mill it to a particle size of 4 μm, and then mix it with the remaining millimeter-sized spheroidizing agent to obtain a mixed rare earth magnesium silicon type spheroidizing agent; mix the mixed rare earth magnesium silicon type spheroidizing agent and iron powder evenly according to a mass ratio of 100:2.4 to obtain a mixture, and use tinplate to wrap the mixture. When wrapping, ensure that the tinplate just completely wraps all the mixture to obtain spheroidizing agent 1; The mass content of magnesium in the rare earth magnesium silicon type spheroidizing agent is 8%, the mass content of rare earth is 4.8%, the mass content of calcium is 2.5%, the mass content of silicon is 41.8%, the mass content of manganese is 1.8%, the mass content of aluminum is 0.2%, the mass content of titanium is 0.3%, and the rest is iron; The particle size of the iron powder is 100 μm; The thickness of the tinplate is 2 mm; 3. Fixing: According to the schematic diagram of Figure 1 , add spheroidizing agent 1, covering agent 2, and inoculant 3 into the pit of the molten iron ladle 4 from bottom to top in sequence, and tamp it; The covering agent 2 is rust-free iron filings with a particle size of 1 mm; The inoculant 3 is FeSi75 with a particle size of 5 mm; The pit is cylindrical, the ratio of the pit depth to the diameter is 1.8, and the diameter of the pit accounts for one-third of the lower diameter of the molten iron ladle; After tamping, the remaining depth of the pit is 25 mm; 4. Spheroidizing and inoculating: According to Figure 1Schematic diagram. Pour molten iron into the other side of the pit in the molten iron ladle 4. First, quickly pour in 62% of the total mass of molten iron, and the pouring time accounts for one-tenth of the total pouring time. Then add the composite inoculant 5 and slowly pour in the remaining molten iron to obtain the casting; The temperature of the molten iron is 1420 °C. The mass content of carbon in the molten iron is 3.8%, the mass content of silicon is 2.5%, the mass content of copper is 0.48%, the mass content of molybdenum is 0.42%, the mass content of manganese is 0.26%, the mass content of tin is 0.07%, the mass content of magnesium is 0.04%, the mass content of phosphorus is 0.05%, the mass content of sulfur is 0.032%, and the rest is iron; The mass fraction of the amount of the mixed rare earth magnesium silicon type spheroidizing agent in the spheroidizing agent 1 accounts for 1.4 - 1.5% of the total mass of the molten iron; The mass fraction of the amount of the inoculant 2 accounts for 0.7% of the total mass of the molten iron; The mass fraction of the amount of the composite inoculant 5 accounts for 0.2% of the total mass of the molten iron; 5. Heat treatment: Heat the casting at a heating rate of 10 °C / min to 900 °C, hold it at 900 °C for 4.5 h, cool it at a cooling rate of 4 °C / min to 700 °C, hold it at 700 °C for 2 h, air-cool it to room temperature, then heat it at a heating rate of 10 °C / min to 900 °C, cool it at a cooling rate of 10 °C / min to 400 °C, hold it at 400 °C for 1 h, and air-cool it to room temperature to obtain ductile iron.

[0020] Perform metallographic structure diagram analysis on the ductile iron obtained in this example, and the obtained metallographic structure diagram is shown in Figure 2 . It can be seen from Figure 2 that the ductile iron obtained in this example is ferritic-pearlitic mixed ductile iron, and the spherical graphite is evenly distributed in the matrix structure.

[0021] Comparative Example 1 On the basis of the spheroidizing and inoculating method of high-spheroidization-rate ductile iron in Example 1, omit the first step of preparing the composite inoculant 5, and use a mixture of silicon carbide and silicon powder with equal mass to replace the composite inoculant 5 in the fourth step of spheroidizing and inoculating. The particle size of the mixture of silicon carbide and silicon powder is 5 μm, and the mass ratio of silicon carbide to silicon powder in the mixture of silicon carbide and silicon powder is 1:1.

[0022] The remaining operations are the same as those in Example 1.

[0023] Comparative Example 2 On the basis of the spheroidizing and inoculating method of high-spheroidization-rate ductile iron in Example 1, change the second step of preparing the spheroidizing agent 1 to: Add the rare earth magnesium silicon nodulizer to a crusher and crush it to a particle size of 1 mm to obtain a millimeter-sized nodulizer; then continue to crush the millimeter-sized nodulizer to a particle size of 100 μm, and then transfer it to a ball mill and ball mill it to a particle size of 4 μm to obtain a ball milled material. Wrap the ball milled material with tinplate. When wrapping, ensure that the tinplate just completely wraps all the ball milled material to obtain nodulizer 1; The mass content of magnesium in the rare earth magnesium silicon nodulizer is 8%, the mass content of rare earth is 4.8%, the mass content of calcium is 2.5%, the mass content of silicon is 41.8%, the mass content of manganese is 1.8%, the mass content of aluminum is 0.2%, the mass content of titanium is 0.3%, and the rest is iron; The thickness of the tinplate is 2 mm.

[0024] The remaining operations are the same as those in Example 1.

[0025] Example 2 A nodulizing and inoculating method for high nodularization rate ductile iron, specifically: 1. Prepare composite inoculant 5: Mix silicon powder and carbon black evenly according to a mass ratio of 28:25, add them to a corundum crucible, transfer them into a microwave sintering furnace for microwave sintering. Control the frequency of the microwave sintering furnace to 2.45 GHz, control the temperature in the microwave sintering furnace to 1020 °C, and control the vacuum degree to 0.085 MPa. After microwave sintering for 35 min, take out the microwave sintered product from the corundum crucible, grind it to a particle size of 6 μm, and remove carbon by aerobic burning to obtain composite inoculant 5; The D50 particle size of the silicon powder is 100 μm; The average particle size of the carbon black is 31 nm, and the specific surface area is 80 m 2 / g; 2. Prepare nodulizer 1: Add the rare earth magnesium silicon nodulizer to a crusher and crush it to a particle size of 1 mm to obtain a millimeter-sized nodulizer; then take out one-third of the millimeter-sized nodulizer, continue to crush it to a particle size of 150 μm, then transfer it to a ball mill and ball mill it to a particle size of 5 μm, and then mix it with the remaining millimeter-sized nodulizer to obtain a mixed rare earth magnesium silicon nodulizer; Mix the mixed rare earth magnesium silicon nodulizer and iron powder evenly according to a mass ratio of 100:2.6 to obtain a mixture. Wrap the mixture with tinplate. When wrapping, ensure that the tinplate just completely wraps all the mixture to obtain nodulizer 1; The mass content of magnesium in the rare earth magnesium silicon nodulizer is 8%, the mass content of rare earth is 4.8%, the mass content of calcium is 2.5%, the mass content of silicon is 41.8%, the mass content of manganese is 1.8%, the mass content of aluminum is 0.2%, the mass content of titanium is 0.3%, and the rest is iron; The particle size of the iron powder is 150 μm; The thickness of the tinplate is 2 mm; 3.Fix: According to Figure 1 Schematic diagram, in which a spheroidizing agent 1, a covering agent 2, and an inoculant 3 are added sequentially from bottom to top into the pit of the iron ladle 4 and compacted; The covering agent 2 is rust-free iron filings with a particle size of 2 mm; The inoculant 3 is FeSi75 with a particle size of 6 mm; The pit is cylindrical, the ratio of the pit depth to the diameter is 1.8, and the diameter of the pit accounts for one third of the lower diameter of the molten iron ladle; After tamping, the remaining depth of the pit is 30 mm; 4. Spheroidization inoculation: according to Figure 1 Schematic diagram, pouring molten iron into the other side of the pit in the iron ladle 4, first quickly pouring 62-67% of the total mass of molten iron, the pouring time accounts for one tenth of the total pouring time, and then adding the composite inoculant 5, slowly pouring the remaining molten iron to obtain a casting; The temperature of the molten iron is 1460° C., the mass content of carbon in the molten iron is 3.8%, the mass content of silicon is 2.5%, the mass content of copper is 0.48%, the mass content of molybdenum is 0.42%, the mass content of manganese is 0.26%, the mass content of tin is 0.07%, the mass content of magnesium is 0.04%, the mass content of phosphorus is 0.05%, the mass content of sulfur is 0.032%, and the rest is iron; The mass fraction of the mixed rare earth magnesium silicon type spheroidizer in spheroidizer 1 to the total mass of the molten iron is 1.5%; The mass fraction of inoculant 2 to the total mass of molten iron is 0.73%; The mass fraction of composite inoculant 5 in the total mass of molten iron is 0.22%; 5. Heat treatment: heat the casting to 920°C at a heating rate of 15°C / min, keep it at 920°C for 5 hours, cool it to 720°C at a cooling rate of 6°C / min, keep it at 720°C for 2.5 hours, air-cool it to room temperature, then heat it to 920°C at a heating rate of 15°C / min, cool it to 450°C at a cooling rate of 15°C / min, keep it at 450°C for 1.5 hours, air-cool it to room temperature, and obtain ductile iron.

[0026] Comparative Example 3 On the basis of the spheroidizing inoculation method for ductile iron with high spheroidization rate of Example 2, the step of preparing the composite inoculant 5 in step 1 is omitted, and in the spheroidizing inoculation step in step 4, an equal mass of a mixture of silicon carbide and silicon powder is used to replace the composite inoculant 5, the particle size of the mixture of silicon carbide and silicon powder is 6 μm, and the mass ratio of silicon carbide to silicon powder in the mixture of silicon carbide and silicon powder is 1:1.

[0027] The remaining operations are the same as those in Example 2.

[0028] Comparative Example 4 Based on the nodulizing and inoculating method of high-spheroidization-rate ductile iron in Example 2, the second step of preparing nodulizer 1 is changed to: Add the rare earth magnesium silicon type nodulizer into a crusher and crush it to a particle size of 1 mm to obtain millimeter-sized nodulizer; then continue to crush the millimeter-sized nodulizer to a particle size of 150 μm, and transfer it to a ball mill and ball mill it to a particle size of 5 μm to obtain ball-milled material. Wrap the ball-milled material with tinplate. When wrapping, ensure that the tinplate just completely wraps all the ball-milled material to obtain nodulizer 1; In the rare earth magnesium silicon type nodulizer, the mass content of magnesium is 8%, the mass content of rare earth is 4.8%, the mass content of calcium is 2.5%, the mass content of silicon is 41.8%, the mass content of manganese is 1.8%, the mass content of aluminum is 0.2%, the mass content of titanium is 0.3%, and the rest is iron; The thickness of the tinplate is 2 mm.

[0029] The remaining operations are the same as those in Example 2.

[0030] Test Example 1 Test the magnesium absorption rate in Examples 1-2 and Comparative Examples 1-4, and the spheroidization rate, tensile strength, yield strength, and elongation of the obtained ductile iron. The test results are as follows:

[0031] It can be seen from the above test results that the test results of Example 1 are better than those of Comparative Example 1 and Comparative Example 2, and the test results of Example 2 are better than those of Comparative Example 3 and Comparative Example 4. It shows that the composite inoculant 5 and nodulizer 1 used in Example 1 and Example 2 can both improve the magnesium absorption rate, and the spheroidization rate, tensile strength, yield strength, and elongation of ductile iron.

Claims

1. A spheroidizing and inoculating method for ductile iron with a high spheroidization rate, characterized in that, Including: Preparing a composite inoculant (5), preparing a spheroidizing agent (1), fixing, spheroidizing inoculation, and heat treatment; For the preparation of the composite inoculant (5), after uniformly mixing silicon powder and carbon black, microwave sintering is carried out. After microwave sintering for 30 - 35 min, grinding is performed, and carbon is removed to obtain the composite inoculant (5); For the preparation of the spheroidizing agent (1), the rare earth magnesium silicon type spheroidizing agent is crushed to obtain a millimeter-sized spheroidizing agent; then one-third is taken out from the millimeter-sized spheroidizing agent, further crushed and ball-milled, and then mixed with the remaining millimeter-sized spheroidizing agent to obtain a mixed rare earth magnesium silicon type spheroidizing agent; the mixed rare earth magnesium silicon type spheroidizing agent is uniformly mixed with iron powder to obtain a mixture, and the mixture is wrapped with tinplate to obtain the spheroidizing agent (1).

2. The nodulizing and inoculating method of ductile cast iron with high spheroidization rate according to claim 1, characterized in that, In the preparation of the composite inoculant (5), the mass ratio of silicon powder to carbon black is 28:23 - 25; The frequency of microwave sintering is 2.45 GHz, the temperature is 1000 - 1020 °C, and the vacuum degree is 0.08 - 0.085 MPa; For the grinding, the particle size after grinding is 5 - 6 μm; The D50 particle size of the silicon powder is 100 μm; The average particle size of the carbon black is 31 nm, and the specific surface area is 80 m 2 / g.

3. The spheroidizing inoculation method for ductile iron with a high spheroidization rate according to claim 1, characterized in that, In the preparation of the spheroidizing agent (1), the mass ratio of the mixed rare earth magnesium silicon type spheroidizing agent to iron powder is 100:2.4 - 2.6; The particle size of the millimeter-sized spheroidizing agent is 1 mm; For the further crushing, the particle size after further crushing is 100 - 150 μm; For the ball-milling, the particle size after ball-milling is 4 - 5 μm; When using tinplate to wrap the mixture, ensure that the tinplate just completely wraps all the mixture.

4. The spheroidizing inoculation method for ductile cast iron with a high spheroidization rate according to claim 1, characterized in that, In the preparation of the spheroidizing agent (1), in the rare earth magnesium silicon type spheroidizing agent, the mass content of magnesium is 8%, the mass content of rare earth is 4.8%, the mass content of calcium is 2.5%, the mass content of silicon is 41.8%, the mass content of manganese is 1.8%, the mass content of aluminum is 0.2%, the mass content of titanium is 0.3%, and the rest is iron; The particle size of the iron powder is 100 - 150 μm; The thickness of the tinplate is 2 mm.

5. The spheroidizing inoculation method of ductile cast iron with high spheroidization rate according to claim 1, characterized in that, For the fixing, the spheroidizing agent (1), the covering agent (2), and the inoculant (3) are successively added from bottom to top into the pit of the molten iron ladle and tamped.

6. The nodulizing and inoculating method of ductile iron with high spheroidization rate according to claim 5, characterized in that, In the fixing, the covering agent (2) is rust-free iron filings with a particle size of 1 - 2 mm; The inoculant (3) is FeSi75 with a particle size of 5 - 6 mm; The pit is cylindrical, the ratio of the depth to the diameter of the pit is 1.8, and the diameter of the pit accounts for one-third of the lower diameter of the molten iron ladle; After tamping, the remaining depth of the pit is 25 - 30 mm.

7. The spheroidizing inoculation method for ductile cast iron with a high spheroidization rate according to claim 1, characterized in that, For the spheroidizing inoculation, molten iron is poured into the other side of the pit in the molten iron ladle (4). First, pour in 62 - 67% of the total mass of molten iron, and the pouring time accounts for one-tenth of the total pouring time. Then add the composite inoculant (5), and pour in the remaining molten iron to obtain a casting.

8. The spheroidizing inoculation method for high-spheroidization-rate ductile cast iron according to claim 7, characterized in that, In the spheroidizing inoculation, the temperature of the molten iron is 1420 - 1460 °C, the mass content of carbon in the molten iron is 3.8%, the mass content of silicon is 2.5%, the mass content of copper is 0.48%, the mass content of molybdenum is 0.42%, the mass content of manganese is 0.26%, the mass content of tin is 0.07%, the mass content of magnesium is 0.04%, the mass content of phosphorus is 0.05%, the mass content of sulfur is 0.032%, and the rest is iron; In the spheroidizing agent (1), the mass fraction of the dosage of the mixed rare earth magnesium silicon type spheroidizing agent in the total mass of the molten iron is 1.4 - 1.5%; The dosage of the inoculant (2) accounts for 0.7 - 0.73% of the total mass of the molten iron by mass fraction; The dosage of the composite inoculant (5) accounts for 0.2 - 0.22% of the total mass of the molten iron by mass fraction.

9. The spheroidizing inoculation method for ductile iron with a high spheroidization rate according to claim 1, characterized in that, For the heat treatment, the casting is heated to 900 - 920 °C at a heating rate of 10 - 15 °C / min, held at 900 - 920 °C for 4.5 - 5 h, cooled to 700 - 720 °C at a cooling rate of 4 - 6 °C / min, held at 700 - 720 °C for 2 - 2.5 h, air-cooled to room temperature, then heated to 900 - 920 °C at a heating rate of 10 - 15 °C / min, cooled to 400 - 450 °C at a cooling rate of 10 - 15 °C / min, held at 400 - 450 °C for 1 - 1.5 h, and air-cooled to room temperature to obtain ductile cast iron.

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