A method for producing high-silicon solid-solution-strengthened ferritic spheroidal graphite cast iron pipe fittings

Abstract

The application relates to the technical field of metal material smelting and casting, in particular to a production method of high-silicon solid-solution-strengthened ferritic spheroidal graphite cast iron pipe fittings. The production method of the high-silicon solid-solution-strengthened ferritic spheroidal graphite cast iron pipe fittings comprises the following steps: nano-enhanced body preparation, smelting and pretreatment, multi-element alloying, spheroidizing treatment, composite inoculation treatment, intelligent control pouring and multiple heat treatment. The prepared high-silicon solid-solution-strengthened ferritic spheroidal graphite cast iron pipe fittings has a tensile strength of greater than or equal to 640 MPa, a 500 DEG C high-temperature tensile strength of greater than or equal to 320 MPa, an elongation of greater than or equal to 19%, and an impact energy of greater than or equal to 16 J.

Description

Technical Field

[0001] This invention relates to the field of metal smelting and casting technology, and in particular to a method for producing high-silicon solid solution strengthened ferritic ductile iron pipe fittings. Background Technology

[0002] Ductile iron pipes are increasingly widely used due to their high strength, good seismic performance, corrosion resistance, and long service life, leading to a continuous increase in demand. According to existing pipe fitting standards, the material requirements for pipe fittings are a tensile strength ≥420MPa and an elongation ≥5%, and the wall thickness of existing pipe fittings is also calculated based on these indicators. This is an indicator that can be achieved using blast furnace iron through direct spheroidizing treatment. However, compared to current material levels and casting processes, this standard is significantly low. If the material properties are improved, while maintaining the same performance characteristics, the wall thickness of the pipe fittings can be reduced accordingly, thus reducing material consumption and lowering production costs.

[0003] Ductile iron, due to its near-steel strength, good ductility and toughness, and excellent casting properties, is widely used in pipeline systems for water supply, drainage, and gas transmission. Ferritic ductile iron pipe fittings, in particular, are the primary choice due to their superior ductility, toughness, and seismic resistance. However, with the development of modern industry, higher demands are placed on pipeline systems, especially in the high-temperature and high-pressure environments of thermal power and chemical industries. Traditional ferritic ductile iron pipe fittings have revealed the following inherent defects:

[0004] (1) Insufficient strength: The tensile strength of traditional ferritic ductile iron is usually in the range of 400-450 MPa, which is difficult to meet the design requirements of pipelines with higher pressure levels.

[0005] (2) Poor high temperature performance: In long-term working environment above 400℃, the pearlite in the ferrite matrix will decompose and graphitize, resulting in a significant decrease in strength and hardness; at the same time, the oxidation rate will accelerate sharply, seriously affecting the service life and safety of the pipe fittings.

[0006] CN101603143B discloses high-temperature resistant ductile iron pipe fittings and their production method. The cast iron has the following weight composition: C: 3.2-3.5%; Si: 3.5-4.0%; Mn: <0.5%; Mo: 1.5-2.0%; P: <1.0%; S: <0.02%. The preparation method includes the following steps: batching, smelting, and pre-furnace treatment. Compared with existing technologies, by increasing the silicon content and adding molybdenum to the ductile iron, the high-temperature resistance of the ductile iron is improved, thereby obtaining high-temperature resistant ductile iron pipe fittings. However, this method does not reduce the cost of the pipe fittings.

[0007] Therefore, the purpose of this invention is to develop high-silicon solid solution strengthened ferritic ductile iron pipe fittings to reduce production costs and improve key performance. Summary of the Invention

[0008] This invention provides a method for producing high-silicon solid solution strengthened ferritic ductile iron pipe fittings, comprising the following steps: preparation of nano-reinforcing bodies, smelting and pretreatment, multi-element alloying, spheroidization treatment, composite inoculation treatment, intelligent control casting, and multiple heat treatments. The chemical composition of the ferritic ductile iron pipe fittings, by mass percentage, is: C: 3.5-3.7%, Si: 4.0-4.9%, Mn: ≤0.2%, P: ≤0.03%, S: ≤0.008%, Mg: 0.04-0.06%, Cu: 0.4-0.6%, Mo: 0.3-0.5%, Ni: 0.3-0.5%, Re: 0.02-0.04%, Sb: 0.005-0.008%, Bi2O 3-Y₂O₃-La₂O₃: 0.1-0.3%, balance being Fe and unavoidable impurities. Carbon in the formula is a fundamental element of ductile iron, ensuring graphite spheroidization. A suitable high carbon content ensures sufficient graphitization, resulting in a moderate number of well-rounded graphite spheres. The presence of these graphite spheres effectively breaks up the matrix, interrupts stress concentration, and improves the material's toughness and shock resistance. Simultaneously, the high carbon content helps improve the fluidity of molten iron and reduce casting defects. Silicon is the core solid solution strengthening element of this invention. Silicon atoms are dissolved in the ferrite lattice, causing lattice distortion and significantly improving the strength and hardness of the matrix. This is the main source of the high strength of this invention. It also effectively inhibits pearlite formation, ensuring a ferrite matrix even at high cooling rates or with the addition of small amounts of pearlitizing elements (such as Cu). Furthermore, the high silicon content forms a dense, stable, and strongly adherent silica oxide film on the casting surface, greatly improving the material's oxidation and growth resistance at high temperatures. Magnesium is a spheroidizing element, and Mg has a strong affinity for S and O, enabling desulfurization and deoxidation, thus purifying molten iron. More importantly, residual Mg adsorbs at the graphite growth front, promoting the precipitation of graphite in a spherical morphology. Copper can assist in solid solution strengthening; even small amounts of copper atoms can dissolve in ferrite, providing additional strengthening effects and improving the corrosion resistance of pipe fittings in specific media. Molybdenum can also be used for solid solution strengthening. Mo is a strong carbide-forming element, but under conditions of high silicon and high carbon equivalent and sufficient inoculation, its carbide formation tendency is suppressed, and most Mo atoms dissolve in ferrite, producing a significant solid solution strengthening effect and significantly improving the strength and creep resistance of ferrite at high temperatures. Nickel can be used for solid solution strengthening and toughening. Ni is dissolved in ferrite and, while providing strengthening, is one of the very few elements that can simultaneously improve strength and toughness. It can effectively offset some of the embrittlement tendency caused by high silicon and help improve the uniformity of the microstructure of thick sections. The addition of Ni can adjust the plasticity and toughness of the material without sacrificing strength, forming a perfect complement and counterbalance with the embrittlement effect of Si.

[0009] Further, the preparation steps of the nano-reinforcement include: mixing bismuth-yttrium-lanthanum composite oxide, surfactant, and dispersant in a mass ratio of 100:1:0.5, and treating with high-energy ball milling for 4 hours to obtain nanoparticles with a particle size of 50-100 nm; then mixing the nanoparticles with copper powder in a mass ratio of 1:2 to prepare the nano-reinforcement. The molar ratio of Bi₂O₃, Y₂O₃, and La₂O₃ in the bismuth-yttrium-lanthanum composite oxide is 1:1:1. The surfactant is hydroxypropyl cellulose, and the dispersant is ammonium polyacrylate. By introducing nanoscale, thermodynamically stable oxide particles, the strength of the material at both room temperature and high temperature is significantly improved without significantly impairing toughness. The nano-reinforcement synergistically enhances high-temperature oxidation resistance with silicon, and magnesium and rare earth elements synergistically improve the morphology of graphite.

[0010] Furthermore, in the smelting and pretreatment steps: a 1T medium-frequency induction furnace is used to smelt pig iron, low-carbon scrap steel and recycled materials. After melting and cleaning, the temperature is raised to 1520-1550℃, carbon raiser and ferrosilicon are added, nano-reinforcement is added, and argon gas at a flow rate of 5L / min is introduced and stirred for 5-8 minutes to make the nanoparticles uniformly dispersed.

[0011] Further, in the multi-element alloying step: before tapping, high-carbon ferrochrome, electrolytic copper plate, ferromolybdenum, nickel plate, and antimony ingot are added sequentially to the bottom of the molten iron ladle, and stirred to fully dissolve the alloying elements. The high-carbon ferrochrome contains 55% Cr and 10% C, and the ferromolybdenum is FeMo60. Sb and Bi co-segregate at the eutectic solidification front, significantly reducing the interfacial energy of molten iron / graphite, increasing the number of effective nucleation cores, and increasing the number of graphite spheres. The addition of Cu inhibits the grain boundary embrittlement and creep tendency of Sb and Bi, and through its weak positive segregation tendency, makes the distribution of Sb and Bi more uniform, jointly promoting the formation of fine and round graphite. The three work together to form a composite micro-region (Fe, Cu, Sb, Bi) at the eutectic boundary, which can effectively pin the grain boundary, refine the eutectic cluster, and thus simultaneously improve strength and toughness.

[0012] Furthermore, the spheroidizing agent used in the spheroidizing process is Mg6RE2, a rare earth magnesium spheroidizing agent made of silicon iron, and the amount of spheroidizing agent added is 1.5-1.7% of the mass of molten iron. The spheroidizing process provides a nucleation substrate for nano-oxides and prevents their agglomeration.

[0013] Furthermore, the composite inoculation treatment includes two inoculation processes: the first inoculation uses barium-silicon ferroin inoculant FeSi75Ba, added at 0.7-0.9% of the molten iron mass; the second inoculation employs in-flow inoculation, using a mixture of strontium-silicon ferroin inoculant FeSi75Sr and nano-silicon-calcium inoculant, added at 0.2-0.3% of the molten iron mass, with a mass ratio of 1:1 between the strontium-silicon ferroin inoculant FeSi75Sr and the nano-silicon-calcium inoculant. Ca and Sr rapidly provide a large number of active nucleation sites in the early stages of inoculation, preventing white iron formation at thin-walled areas. Ba, with its large atomic radius and slow diffusion in molten iron, can continuously and stably protect the nucleation cores formed by Ca and Sr, significantly extending the effective inoculation time to over 15 minutes. This completely solves the problem of inoculation degradation caused by prolonged pouring time. The synergistic effect of these three factors ensures ample nucleation capacity throughout the entire process from pouring to solidification, thereby improving the uniformity of the microstructure at different wall thicknesses in the casting.

[0014] Furthermore, the intelligent control pouring process involves precisely controlling the pouring temperature at 1340-1360℃, employing an intelligent pouring system to adjust the pouring speed and cooling conditions in real time, and allowing the pipe fittings to cool slowly in the sand mold to below 600℃ before unpacking.

[0015] Furthermore, the multiple heat treatment includes: a first stage of heating to 940-960℃ at a rate of ≤80℃ / h and holding for 3-4 hours; this first stage fully dissolves carbides and segregated phases in the as-cast microstructure, preparing for subsequent precipitation and making the distribution of nano-oxides more uniform; a second stage of furnace cooling to 700-720℃ and holding for 5-7 hours; and a third stage of cooling to below 300℃ at a rate of 30-50℃ / h before unloading from the furnace, achieving precipitation strengthening and completing the final ferrite stabilization. The multiple heat treatment utilizes critical zone treatment to introduce a small amount of hard phase, which is then softened and granulated through subsequent processes. Ultimately, a multiphase strengthened structure composed of nano-oxides and fine sorbite islands is obtained on the ferrite matrix, achieving a perfect combination of strength and toughness.

[0016] The present invention also provides a high-silicon solid solution strengthened ferritic ductile iron pipe fitting produced by the above-described production method. The high-silicon solid solution strengthened ferritic ductile iron pipe fitting has a tensile strength ≥640MPa, a high-temperature tensile strength at 500℃ ≥320MPa, an elongation ≥19%, and an impact energy ≥16J.

[0017] The present invention has the following significant advantages:

[0018] 1. Breaking through performance barriers: Successfully solved the technical problem of the contradiction between strength and toughness, and strength and heat resistance in traditional ductile iron.

[0019] 2. Superior performance: Through a multi-component composite solid solution strengthening mechanism of "high silicon + Cu + Mo + Ni, etc.", high tensile strength and high elongation of ductile iron are achieved while maintaining the all-ferrite matrix.

[0020] 3. Excellent heat resistance: The high silicon content and dense oxide film give it good high-temperature oxidation resistance and higher strength.

[0021] 4. Reliable process: The production process is mature, the key points are clearly controlled, and it is easy to industrialize on existing production lines.

[0022] 5. Controllable cost: The main alloying element is silicon, supplemented with small amounts of copper, molybdenum and nickel, so the cost is controllable. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1

[0025] A method for producing high-silicon solid solution strengthened ferritic ductile iron pipe fittings includes the following steps:

[0026] Preparation of nano-reinforcement: Bismuth-yttrium-lanthanum composite oxide, hydroxypropyl cellulose and ammonium polyacrylate were mixed in a mass ratio of 100:1:0.5 and treated with high-energy ball milling for 4 hours to obtain nano-powder with a particle size of 50-100 nm. The nano-powder was then mixed with copper powder in a mass ratio of 1:2 to prepare nano-reinforcement. The molar ratio of Bi2O3, Y2O3 and La2O3 in the bismuth-yttrium-lanthanum composite oxide was 1:1:1.

[0027] Smelting and pretreatment: Pig iron, low carbon scrap steel and recycled materials are smelted in a 1T medium frequency induction furnace. After melting and cleaning, the temperature is raised to 1520-1550℃, carbon raiser and ferrosilicon are added, nano-reinforcement is added, and argon gas with a flow rate of 5L / min is introduced and stirred for 6 minutes to make the nanoparticles uniformly dispersed.

[0028] Multi-element alloying: Before tapping the iron, high-carbon ferrochrome, electrolytic copper plate, ferromolybdenum, nickel plate and antimony ingot are added to the bottom of the molten iron ladle in sequence, and stirred to fully dissolve the alloying elements. The high-carbon ferrochrome contains 55% Cr and 10% C, and the ferromolybdenum is FeMo60.

[0029] Spheroidizing treatment: The spheroidizing agent used in the spheroidizing treatment process is ferrosilicon rare earth magnesium spheroidizing agent Mg6RE2, and the amount of spheroidizing agent added is 1.6% of the mass of molten iron;

[0030] Composite inoculation treatment: The composite inoculation treatment includes two inoculation processes: the first inoculation uses barium ferrosilicon inoculant FeSi75Ba, with an addition amount of 0.8% of the molten iron mass; the second inoculation is a flow-inoculation process, using a mixture of strontium ferrosilicon inoculant FeSi75Sr and nano-silicon-calcium inoculant, with an addition amount of 0.2% of the molten iron mass, and the mass ratio of strontium ferrosilicon inoculant FeSi75Sr to nano-silicon-calcium inoculant is 1:1;

[0031] Intelligent control casting: The intelligent control casting steps are as follows: the casting temperature is precisely controlled at 1340-1360℃, an intelligent casting system is used to adjust the casting speed and cooling conditions in real time, and the pipe fittings are slowly cooled in the sand mold to 550℃ before being unpacked.

[0032] Multiple heat treatments: The multiple heat treatments include: the first stage of heating to 940-960℃ at a rate of 80℃ / h and holding for 3 hours; the second stage of cooling in the furnace to 700-720℃ and holding for 6 hours; and the third stage of cooling to 280℃ at a rate of 30-50℃ / h before unloading from the furnace.

[0033] The chemical composition of the ferritic ductile iron pipe fittings, by mass percentage, is as follows: C: 3.7%, Si: 4.2%, Mn: 0.05%, P: 0.02%, S: 0.004%, Mg: 0.04%, Cu: 0.5%, Mo: 0.35%, Ni: 0.34%, Re: 0.03%, Sb: 0.006%, Bi₂O 3- Y2O3-La2O3: 0.22%, balance being Fe and unavoidable impurities.

[0034] High-silicon solid solution strengthened ferritic ductile iron pipe fittings prepared by the above preparation method.

[0035] Example 2

[0036] A method for producing high-silicon solid solution strengthened ferritic ductile iron pipe fittings includes the following steps:

[0037] Preparation of nano-reinforcement: Bismuth-yttrium-lanthanum composite oxide, hydroxypropyl cellulose and ammonium polyacrylate were mixed in a mass ratio of 100:1:0.5 and treated with high-energy ball milling for 4 hours to obtain nano-powder with a particle size of 50-100 nm. The nano-powder was then mixed with copper powder in a mass ratio of 1:2 to prepare nano-reinforcement. The molar ratio of Bi2O3, Y2O3 and La2O3 in the bismuth-yttrium-lanthanum composite oxide was 1:1:1.

[0038] Smelting and pretreatment: Pig iron, low carbon scrap steel and recycled materials are smelted in a 1T medium frequency induction furnace. After melting and cleaning, the temperature is raised to 1520-1550℃, carbon raiser and ferrosilicon are added, nano-reinforcement is added, and argon gas with a flow rate of 5L / min is introduced and stirred for 6 minutes to make the nanoparticles uniformly dispersed.

[0039] Multi-element alloying: Before tapping the iron, high-carbon ferrochrome, electrolytic copper plate, ferromolybdenum, nickel plate and antimony ingot are added to the bottom of the molten iron ladle in sequence, and stirred to fully dissolve the alloying elements. The high-carbon ferrochrome contains 55% Cr and 10% C, and the ferromolybdenum is FeMo60.

[0040] Spheroidizing treatment: The spheroidizing agent used in the spheroidizing treatment process is ferrosilicon rare earth magnesium spheroidizing agent Mg6RE2, and the amount of spheroidizing agent added is 1.6% of the mass of molten iron;

[0041] Composite inoculation treatment: The composite inoculation treatment includes two inoculation processes: the first inoculation uses barium ferrosilicon inoculant FeSi75Ba, with an addition amount of 0.8% of the molten iron mass; the second inoculation is a flow-inoculation process, using a mixture of strontium ferrosilicon inoculant FeSi75Sr and nano-silicon-calcium inoculant, with an addition amount of 0.2% of the molten iron mass, and the mass ratio of strontium ferrosilicon inoculant FeSi75Sr to nano-silicon-calcium inoculant is 1:1;

[0042] Intelligent control casting: The intelligent control casting steps are as follows: the casting temperature is precisely controlled at 1340-1360℃, an intelligent casting system is used to adjust the casting speed and cooling conditions in real time, and the pipe fittings are slowly cooled in the sand mold to 550℃ before being unpacked.

[0043] Multiple heat treatments: The multiple heat treatments include: the first stage of heating to 940-960℃ at a rate of 80℃ / h and holding for 3 hours; the second stage of cooling in the furnace to 700-720℃ and holding for 6 hours; and the third stage of cooling to 280℃ at a rate of 30-50℃ / h before unloading from the furnace.

[0044] The chemical composition of the ferritic ductile iron pipe fittings, by mass percentage, is as follows: C: 3.7%, Si: 4.8%, Mn: 0.05%, P: 0.02%, S: 0.004%, Mg: 0.04%, Cu: 0.5%, Mo: 0.35%, Ni: 0.34%, Re: 0.03%, Sb: 0.006%, Bi₂O 3- Y2O3-La2O3: 0.22%, balance being Fe and unavoidable impurities.

[0045] High-silicon solid solution strengthened ferritic ductile iron pipe fittings prepared by the above preparation method.

[0046] Example 3

[0047] A method for producing high-silicon solid solution strengthened ferritic ductile iron pipe fittings includes the following steps:

[0048] Preparation of nano-reinforcement: Bismuth-yttrium-lanthanum composite oxide, hydroxypropyl cellulose and ammonium polyacrylate were mixed in a mass ratio of 100:1:0.5 and treated with high-energy ball milling for 4 hours to obtain nano-powder with a particle size of 50-100 nm. The nano-powder was then mixed with copper powder in a mass ratio of 1:2 to prepare nano-reinforcement. The molar ratio of Bi2O3, Y2O3 and La2O3 in the bismuth-yttrium-lanthanum composite oxide was 1:1:1.

[0049] Smelting and pretreatment: Pig iron, low carbon scrap steel and recycled materials are smelted in a 1T medium frequency induction furnace. After melting and cleaning, the temperature is raised to 1520-1550℃, carbon raiser and ferrosilicon are added, nano-reinforcement is added, and argon gas with a flow rate of 5L / min is introduced and stirred for 6 minutes to make the nanoparticles uniformly dispersed.

[0050] Multi-element alloying: Before tapping the iron, high-carbon ferrochrome, electrolytic copper plate, ferromolybdenum, nickel plate and antimony ingot are added to the bottom of the molten iron ladle in sequence, and stirred to fully dissolve the alloying elements. The high-carbon ferrochrome contains 55% Cr and 10% C, and the ferromolybdenum is FeMo60.

[0051] Spheroidizing treatment: The spheroidizing agent used in the spheroidizing treatment process is ferrosilicon rare earth magnesium spheroidizing agent Mg6RE2, and the amount of spheroidizing agent added is 1.6% of the mass of molten iron;

[0052] Composite inoculation treatment: The composite inoculation treatment includes two inoculation processes: the first inoculation uses barium ferrosilicon inoculant FeSi75Ba, with an addition amount of 0.8% of the molten iron mass; the second inoculation is a flow-inoculation process, using a mixture of strontium ferrosilicon inoculant FeSi75Sr and nano-silicon-calcium inoculant, with an addition amount of 0.2% of the molten iron mass, and the mass ratio of strontium ferrosilicon inoculant FeSi75Sr to nano-silicon-calcium inoculant is 1:1;

[0053] Intelligent control casting: The intelligent control casting steps are as follows: the casting temperature is precisely controlled at 1340-1360℃, an intelligent casting system is used to adjust the casting speed and cooling conditions in real time, and the pipe fittings are slowly cooled in the sand mold to 550℃ before being unpacked.

[0054] Multiple heat treatments: The multiple heat treatments include: the first stage of heating to 940-960℃ at a rate of 80℃ / h and holding for 3 hours; the second stage of cooling in the furnace to 700-720℃ and holding for 6 hours; and the third stage of cooling to 280℃ at a rate of 30-50℃ / h before unloading from the furnace.

[0055] The chemical composition of the ferritic ductile iron pipe fittings, by mass percentage, is as follows: C: 3.7%, Si: 4.2%, Mn: 0.06%, P: 0.02%, S: 0.006%, Mg: 0.05%, Cu: 0.5%, Mo: 0.35%, Ni: 0.35%, Re: 0.03%, Sb: 0.006%, Bi₂O 3- Y2O3-La2O3: 0.23%, balance being Fe and unavoidable impurities.

[0056] High-silicon solid solution strengthened ferritic ductile iron pipe fittings prepared by the above preparation method.

[0057] Comparative Example 1

[0058] The nano-reinforcement component in Example 1 was removed, and everything else was the same as in Example 1, so it will not be repeated here.

[0059] Comparative Example 2

[0060] The compound inoculation treatment in Example 1 was changed to adding all inoculation agents at once and inoculating at once. The rest is the same as in Example 1, and will not be repeated.

[0061] Comparative Example 3

[0062] The multiple heat treatments in Example 1 are removed, and everything else is the same as in Example 1, so they will not be repeated here.

[0063] The performance of the DN300 pipe fittings prepared in the above embodiments and comparative examples was tested. The performance at a thickness of 12mm was tested, and the results are shown in Table 1.

[0064] Table 1 Performance Test Results

[0065]

[0066] Table 1 shows that the products prepared in Examples 1-3 have a tensile strength ≥640MPa, a high-temperature tensile strength at 500℃ ≥320MPa, an elongation ≥19%, and an impact energy ≥16J. Excessive silicon content actually decreases product performance. Comparative Example 1 data indicates that the lack of nano-reinforcing components significantly reduces product performance. Comparative Example 2 data shows that the secondary composite inoculation technology is more effective. Comparative Example 3 data shows that multiple heat treatment steps can improve product performance.

Claims

1. A method for producing high-silicon solid solution strengthened ferritic ductile iron pipe fittings, characterized in that, Includes the following steps: The process involves nano-reinforcement preparation, smelting and pretreatment, multi-element alloying, spheroidization treatment, composite inoculation treatment, intelligent control casting, and multiple heat treatments. The chemical composition of the ferritic ductile iron pipe fittings, by mass percentage, is as follows: C: 3.5-3.7%, Si: 4.0-4.9%, Mn: ≤0.2%, P: ≤0.03%, S: ≤0.008%, Mg: 0.04-0.06%, Cu: 0.4-0.6%, Mo: 0.3-0.5%, Ni: 0.3-0.5%, RE: 0.02-0.04%, Sb: 0.005-0.008%, Bi2O 3- Y2O3-La2O3: 0.1-0.3%, balance being Fe and unavoidable impurities, the nano-reinforcement is added during the melting and pretreatment steps; The preparation steps of the nano-reinforcement include: mixing bismuth yttrium lanthanum composite oxide, surfactant and dispersant in a mass ratio of 100:1:0.5, and treating with high-energy ball milling for 4 hours to obtain nanoparticles with a particle size of 50-100 nm; then mixing the nanoparticles with copper powder in a mass ratio of 1:2 to prepare the nano-reinforcement. The molar ratio of Bi2O3, Y2O3 and La2O3 in the bismuth yttrium lanthanum composite oxide is 1:1:

1. The surfactant is hydroxypropyl cellulose and the dispersant is ammonium polyacrylate. The composite inoculation treatment includes two inoculation processes: the first inoculation uses barium ferrosilicon inoculant FeSi75Ba, with an addition amount of 0.7-0.9% of the molten iron mass; the second inoculation is a flow-inoculation process using a mixture of strontium ferrosilicon inoculant FeSi75Sr and nano-silicon-calcium inoculant, with an addition amount of 0.2-0.3% of the molten iron mass, and the mass ratio of strontium ferrosilicon inoculant FeSi75Sr to nano-silicon-calcium inoculant is 1:

1. The multiple heat treatment includes: a first stage of heating to 940-960℃ at a rate of ≤80℃ / h and holding for 3-4 hours; a second stage of cooling in the furnace to 700-720℃ and holding for 5-7 hours; and a third stage of cooling to below 300℃ at a rate of 30-50℃ / h before unloading from the furnace.

2. The production method according to claim 1, characterized in that, In the smelting and pretreatment steps: a 1T medium-frequency induction furnace is used to smelt pig iron, low-carbon scrap steel and recycled materials. After melting and cleaning, the temperature is raised to 1520-1550℃, carbon raiser and ferrosilicon are added, nano-reinforcement is added, and argon gas with a flow rate of 5L / min is introduced and stirred for 5-8 minutes to make the nanoparticles uniformly dispersed.

3. The production method according to claim 1, characterized in that, The multi-element alloying step is as follows: before tapping the iron, high-carbon ferrochrome, electrolytic copper plate, ferromolybdenum, nickel plate, and antimony ingot are added to the bottom of the molten iron ladle in sequence, and stirred to fully dissolve the alloying elements. The high-carbon ferrochrome contains 55% Cr and 10% C, and the ferromolybdenum is FeMo60.

4. The production method according to claim 1, characterized in that, The spheroidizing agent used in the spheroidizing process is ferrosilicon rare earth magnesium spheroidizing agent Mg6RE2, and the amount of spheroidizing agent added is 1.5-1.7% of the mass of molten iron.

5. The production method according to claim 1, characterized in that, The intelligent control pouring process involves precisely controlling the pouring temperature at 1340-1360℃, employing an intelligent pouring system to adjust the pouring speed and cooling conditions in real time, and allowing the pipes to be slowly cooled in the sand mold to below 600℃ before unpacking.

6. A high-silicon solid solution strengthened ferritic ductile iron pipe fitting produced by the production method according to any one of claims 1-5.

7. The high-silicon solid solution strengthened ferritic ductile iron pipe fitting according to claim 6, characterized in that, Tensile strength ≥640MPa, high temperature tensile strength at 500℃ ≥320MPa, elongation ≥19%, impact energy ≥16J.

Images