High-hardness nodular cast iron composition for engineering machinery and processing technology of high-hardness nodular cast iron composition

Abstract

The invention discloses a high-hardness nodular cast iron composition for engineering machinery and a processing technology thereof, and relates to the technical field of nodular cast iron. The preparation process comprises the following steps: smelting pig iron and waste steel, adding a nucleating agent, spraying nitrogen, stirring, removing impurities, adding silicon and the like to obtain alloyed iron liquid; carrying out spheroidizing treatment on the molten iron by using magnesium composite balls, carrying out metal-stream inoculation on titanium during casting, and instantly inoculating a phosphorus-containing inoculation block in a mold to obtain a casting blank; and after normalizing the casting blank, spraying a polyvinyl alcohol aqueous solution for cooling, and after self-tempering, preserving heat and cooling to obtain the product. The process solves the problems of difficult impurity removal, unstable nodulizing inoculation, complex heat treatment and the like in the prior art, and the prepared nodular cast iron is excellent in comprehensive mechanical property, balanced in hardness and toughness and suitable for key parts of engineering machinery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nodular cast iron, in particular to a high-hardness nodular cast iron composition for engineering machinery and a processing technology thereof. BACKGROUND

[0002] In the field of engineering machinery, key components such as excavator teeth, crusher jaw plates, and track plates are subjected to high-strength impact, severe friction, and alternating loads for a long time, which puts high requirements on the balance of hardness, wear resistance, and toughness of the material. Nodular cast iron has become an important material for manufacturing such components due to its good casting performance and high comprehensive mechanical properties. By controlling the graphite morphology to be spherical, nodular cast iron effectively improves the brittleness defects of traditional cast iron and has been widely used in the field of engineering machinery.

[0003] However, the existing nodular cast iron for engineering machinery still has obvious deficiencies in actual application.

[0004] Firstly, impurities are not completely removed during the melting stage, and traditional mechanical stirring cannot effectively promote the floating of impurities such as MnS and Al2O3, resulting in reduced toughness of the casting; secondly, high-magnesium composite spheres are often used for spheroidizing treatment, which can cause severe reaction and temperature fluctuations of the alloyed molten iron, and single inoculation method cannot stably control the graphite spherical morphology and distribution, affecting the hardness uniformity; thirdly, complex salt bath equipment is often required for heat treatment, which has high energy consumption and the cooling medium is easy to cause pollution, and the burning loss of micro-alloying elements such as boron and titanium is serious, resulting in low utilization rate.

[0005] Therefore, according to the limitations of the above-mentioned related technologies, it is urgent to develop a high-hardness nodular cast iron composition for engineering machinery and a processing technology thereof. SUMMARY

[0006] Therefore, according to the limitations of the above-mentioned related technologies, it is urgent to develop a high-hardness nodular cast iron composition for engineering machinery and a processing technology thereof.

[0007] The purpose of the present application can be achieved by the following technical solutions: On the one hand, the present application provides a processing technology of a high-hardness nodular cast iron composition for engineering machinery, characterized in that it comprises the following steps: Step S1: Mix pig iron and scrap steel and heat to melt, heat to a melting temperature, add nucleating agent, stir, add silicon, manganese, and red copper after skimming, and then cool after melting, to obtain an alloyed molten iron; Step S2: first, the magnesium composite ball is pre-installed in the spheroidizing package, and the alloyed iron liquid is treated by spheroidizing by using the pouring method; the alloyed iron liquid after spheroidizing is poured, and in the pouring process, titanium is added through the funnel for stream inoculation, and the pouring temperature is controlled according to the wall thickness of the casting; in addition, a phosphorus-containing inoculation block is placed in the pouring cup for in-mold transient inoculation, and after the pouring is completed and cooled, a cast formed blank is obtained; Step S3: the cast formed blank is heated at a constant heating rate to the normalizing temperature to perform normalizing treatment, and after insulation, polyvinyl alcohol aqueous solution is sprayed for cooling; then the furnace temperature is adjusted to the highest temperature reached on the surface of the blank during the self-tempering process, and the temperature is maintained for insulation, and cooled to room temperature to obtain a high-hardness ductile iron composition.

[0008] Further, in the step S1, the melting temperature is 1450-1500℃, the stirring speed is controlled at 60-90rpm, and the stirring time is 9-15min.

[0009] Further, in the step S1, after the slag is removed, silicon, manganese and red copper are added, and the temperature is lowered to 1420-1450℃.

[0010] Further, in the step S2, the pouring temperature is controlled at 1360-1380℃.

[0011] Further, in the step S3, the cast formed blank is heated at a constant heating rate of 100-150℃ / h to 820-900℃ for normalizing treatment, and after insulation for 2-3h, polyvinyl alcohol aqueous solution is sprayed for cooling to a surface temperature of 180-200℃; self-tempering utilizes the residual heat in the core to make the surface temperature rise to 300-390℃, the furnace temperature is controlled at 300-390℃ and insulation for 30-50min, and cooled to room temperature to obtain a high-hardness ductile iron composition.

[0012] Further, the mass ratio of pig iron to scrap steel is 10:0.5-2, the addition amount of silicon is 2.0%-2.5% of the mass of pig iron, the addition amount of manganese is 0.3%-0.6% of the mass of pig iron, and the addition amount of red copper is 0.1%-0.3% of the mass of pig iron.

[0013] Further, the carbon content of the pig iron is 4.0%-4.3%, and the carbon content of the scrap steel is 0.25%-0.6%.

[0014] Further, the nucleating agent is broken pig iron scrap, the size is 1-3mm, and the addition amount is 0.2%-0.4% of the mass of pig iron.

[0015] Further, the preparation method of the magnesium composite ball comprises the following steps: taking magnesium 5%-7%, molybdenum 0.5%-1.0%, vanadium 0.5%-1.0% and the rest iron according to the mass percentage; crushing the raw materials and uniformly mixing them, melting under the protection of argon, crushing after casting, and obtaining the magnesium composite ball.

[0016] Further, in the preparation method of the magnesium composite ball, the raw materials are crushed to a particle size of 3mm-8mm, uniformly mixed, melted at 1600℃-1700℃ under the protection of argon for 1.5h-2h, and crushed to a particle size of 10mm-20mm after casting, and the magnesium composite ball is obtained.

[0017] Further, the adding amount of the magnesium composite ball is 1.2%-1.6% of the mass of the alloyed iron liquid; and the pouring method comprises the following steps: placing the magnesium composite ball at the bottom of a spheroidizing ladle, separating by a dam, pouring the alloyed iron liquid at 1430℃-1460℃ into the spheroidizing ladle at a flow rate of 0.5m 3 / min-1.0m 3 / min, and making the alloyed iron liquid fully react with the magnesium composite ball.

[0018] Further, when the stream inoculation is performed, the adding amount of titanium is 0.03%-0.05% of the mass of the alloyed iron liquid.

[0019] Further, when the instant inoculation is performed, the adding amount of the phosphorus-containing inoculation block is 4%-8% of the mass of the alloyed iron liquid.

[0020] Further, the preparation method of the phosphorus-containing inoculation block comprises the following steps: taking silicon 55%-60%, chromium 8%-12%, nickel 5%-8%, phosphorus 3%-5% and the rest iron according to the mass percentage; crushing the raw materials and uniformly mixing them, melting under the protection of nitrogen, casting, and crushing after casting, and obtaining the phosphorus-containing inoculation block.

[0021] Further, in the preparation method of the phosphorus-containing inoculation block, the raw materials are crushed to a particle size of 5mm-10mm, mixed for 30min-40min, melted at 1500℃-1600℃ under the protection of nitrogen for 2h-3h, and crushed to a block shape of 20mm-30mm after casting, and the phosphorus-containing inoculation block is obtained.

[0022] Further, the pouring adopts a low-pressure pouring or gravity pouring mode; the mold is a sand mold or a metal mold, the sand mold is preheated to 200℃-300℃, and the metal mold is preheated to 150℃-200℃.

[0023] Further, the mass fraction of the polyvinyl alcohol aqueous solution is 8%-12%, and the spraying pressure is 0.2MPa-0.3MPa.

[0024] Further, the molecular weight of the polyvinyl alcohol is 25000-35000.

[0025] On the other hand, the present invention provides a processing technology for preparing a high-hardness ductile iron composition for use in engineering machinery.

[0026] The beneficial effects of this invention are: 1. This invention effectively overcomes the technical bottleneck of balancing hardness and toughness in traditional ductile iron. Through precisely designed melting, spheroidizing, and heat treatment processes, the material meets the requirements of engineering machinery for high hardness and high wear resistance while maintaining good toughness, avoiding the brittleness problem caused by the excessive pursuit of hardness in traditional materials. This balanced characteristic allows it to be stably applied to key components such as excavator bucket teeth and crusher jaw plates that are subjected to high-intensity impact and friction over long periods, significantly extending the service life of components and reducing equipment maintenance frequency and costs.

[0027] 2. The innovative spheroidization and inoculation process of this invention significantly improves the stability and uniformity of the material's microstructure. The use of pre-melted magnesium composite spheres combined with an injection method for spheroidization effectively mitigates the intensity of the reaction between traditional magnesium composite spheres and molten iron, avoids significant fluctuations in molten iron temperature, reduces the burn-off rate of alloying elements, and ensures consistent spheroidization results. Simultaneously, the dual inoculation system of "flow-based inoculation + instantaneous in-mold inoculation" plays a continuous role throughout the casting process. It refines graphite in the early stages of casting and stabilizes the morphology of graphite spheres during solidification, solving the problems of uneven graphite distribution and uncontrolled morphology in traditional single inoculation methods. This results in more uniform performance across different regions of the material, avoiding defects such as localized embrittlement or insufficient strength.

[0028] 3. This invention significantly improves the purity of castings by optimizing the impurity removal mechanism in the smelting process. By adding a specific nucleating agent and coordinating it with stirring during the smelting stage, the nucleating agent acts as an attachment nucleus for impurities, promoting the full flotation and removal of harmful inclusions such as MnS and Al2O3, thus reducing the damage to the material's toughness caused by impurities. Simultaneously, the nucleating agent provides ample nucleation sites for graphite spheres, promoting uniform graphite precipitation, refining the material microstructure, and further enhancing the stability of mechanical properties, making the castings less prone to failure due to localized stress concentration under complex working conditions.

[0029] 4. The process design of this invention combines environmental friendliness and economic efficiency, facilitating industrial-scale promotion. The heat treatment stage employs a combination of spray-dried polyvinyl alcohol aqueous solution cooling and self-tempering, replacing the traditional high-energy-consuming and high-polluting salt bath treatment. This not only simplifies equipment configuration and reduces energy consumption but also avoids the environmental pollution problems caused by salt bath media. Furthermore, the precise control of parameters at each stage of the process reduces raw material waste and alloy element loss, improves resource utilization, and lowers production costs. Simultaneously, the process steps are clear and controllable, requiring no complex special equipment, facilitating the modification of existing production lines and large-scale production, and possessing significant industrial application value. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a sphericity image of Example 1.

[0032] Figure 2 This is a sphericity image from Example 2. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1 A processing method for a high-hardness ductile iron composition used in engineering machinery includes the following steps: Preparation of magnesium composite spheres: Weigh 6% magnesium, 0.7% molybdenum, 0.7% vanadium, and the balance iron according to the mass percentage; crush each raw material to a particle size of 5mm and mix them evenly; melt at 1650℃ for 1.7h under argon protection; control the casting temperature at 1450℃; after casting, crush the mixture to a particle size of 15mm to obtain magnesium composite spheres.

[0035] Preparation of phosphorus-containing inoculum blocks: Weigh out 57% silicon, 10% chromium, 6% nickel, 4% phosphorus, and the balance iron by mass percentage; crush each raw material to a particle size of 7mm and mix for 35min; melt at 1550℃ for 2.5h under nitrogen protection; control the casting temperature at 1370℃; after casting, crush into 25mm blocks to obtain phosphorus-containing inoculum blocks.

[0036] Step S1: Weigh pig iron and scrap steel at a mass ratio of 10:0.53. The pig iron contains 4.2% carbon and the scrap steel contains 0.4% carbon. Mix them and heat them to smelt. When the temperature reaches 1480℃, add 0.3% of the mass of pig iron crushed pig iron chips with a size of 2mm as a nucleating agent. Control the stirring speed at 75rpm and stir for 10min to promote the floating of impurities. After removing the slag, add 2.2% of the mass of pig iron silicon, 0.5% of the mass of pig iron manganese, and 0.17% of the mass of pig iron copper. After melting and clearing, cool to 1445℃ to obtain alloyed iron liquid.

[0037] Step S2: Magnesium composite spheres, accounting for 1.4% of the mass of the alloyed molten iron, are pre-placed inside the spheroidizing ladle, separated by a dam. The alloyed molten iron at 1445℃ is then poured in at a rate of 0.75m... 3 The flow rate is 900 m / min, which is used to inject the spheroidizing solution into the spheroidizing ladle for spheroidization treatment. Gravity casting is adopted, and the sand mold is preheated to 250°C and the casting temperature is controlled at 1370°C. During the casting process, titanium accounting for 0.026% of the mass of the alloyed iron liquid is added through a funnel for in-flow inoculation. At the same time, phosphorus-containing inoculation blocks accounting for 6% of the mass of the alloyed iron liquid are placed in the pouring cup for instantaneous inoculation in the mold. After casting is completed and cooled, the cast blank is obtained.

[0038] Step S3: The cast blank is heated to 860℃ at a heating rate of 125℃ / h for normalizing treatment. After holding at this temperature for 2.5h, a 10% (w / w) polyvinyl alcohol aqueous solution (polyvinyl alcohol molecular weight 30000) is sprayed on it. The spraying pressure is controlled at 0.25MPa. The blank is then cooled to a surface temperature of 190℃. The residual heat in the core is used to raise the surface temperature back to 353℃. The furnace temperature is controlled at 353℃ and held for 40min. The blank is then cooled to room temperature to obtain a high-hardness ductile iron composition.

[0039] Example 2 A processing method for a high-hardness ductile iron composition used in engineering machinery includes the following steps: Preparation of magnesium composite spheres: Weigh 5% magnesium, 0.5% molybdenum, 0.5% vanadium, and the balance iron according to the mass percentage; crush each raw material to a particle size of 3mm and mix them evenly; melt them at 1600℃ for 1.5h under argon protection; control the casting temperature at 1420℃; after casting, crush them to a particle size of 10mm to obtain magnesium composite spheres.

[0040] Preparation of phosphorus-containing inoculum blocks: Weigh out 55% silicon, 8% chromium, 5% nickel, 3% phosphorus, and the balance iron by mass percentage; crush each raw material to a particle size of 5mm and mix for 30min; melt at 1500℃ for 2h under nitrogen protection; control the casting temperature at 1360℃; after casting, crush into 20mm blocks to obtain phosphorus-containing inoculum blocks.

[0041] Step S1: Weigh pig iron and scrap steel at a mass ratio of 10:0.5. The pig iron contains 4.0% carbon and the scrap steel contains 0.25% carbon. Mix them and heat them to smelt. When the temperature reaches 1450℃, add 0.2% of the mass of pig iron crushed pig iron chips with a size of 1mm as a nucleating agent. Control the stirring speed at 60rpm and stir for 9min to promote the floating of impurities. After removing the slag, add 2.0% of the mass of pig iron silicon, 0.3% of the mass of pig iron manganese, and 0.1% of the mass of pig iron copper. After melting and clearing, cool to 1420℃ to obtain alloyed iron liquid.

[0042] Step S2: Magnesium composite spheres, accounting for 1.2% of the mass of the alloyed molten iron, are pre-placed inside the spheroidizing ladle, separated by a dam. The alloyed molten iron at 1420℃ is then poured in a 0.5m... 3 The flow rate is 1 / min, which is used to inject the spheroidizing ladle for spheroidization treatment; a low-pressure casting method is adopted, the sand mold is preheated to 200℃, and the casting temperature is controlled at 1360℃; during the casting process, titanium accounting for 0.03% of the mass of alloyed iron liquid is added through a funnel for in-flow inoculation; at the same time, phosphorus-containing inoculation block accounting for 4% of the mass of pig iron is placed in the pouring cup for instantaneous in-mold inoculation. After casting is completed and cooled, the cast blank is obtained.

[0043] Step S3: The cast blank is heated to 820℃ at a heating rate of 100℃ / h for normalizing treatment. After holding at this temperature for 2 hours, it is sprayed with an 8% (w / w) polyvinyl alcohol aqueous solution (polyvinyl alcohol molecular weight 25000) at a controlled spraying pressure of 0.2MPa. The blank is then cooled to a surface temperature of 180℃. The surface temperature is then raised to 307℃ using the residual heat in the core. The furnace temperature is then controlled at 307℃ and held for 30 minutes. Finally, the blank is cooled to room temperature to obtain a high-hardness ductile iron composition.

[0044] Example 3 A processing method for a high-hardness ductile iron composition used in engineering machinery includes the following steps: Preparation of magnesium composite spheres: Weigh 7% magnesium, 1.0% molybdenum, 1.0% vanadium, and the balance iron according to the mass percentage; crush each raw material to a particle size of 8mm and mix them evenly; melt them at 1700℃ for 2h under argon protection; control the casting temperature at 1480℃; after casting, crush them to a particle size of 20mm to obtain magnesium composite spheres.

[0045] Preparation of phosphorus-containing inoculum blocks: Weigh out 60% silicon, 12% chromium, 8% nickel, 5% phosphorus, and the balance iron by mass percentage; crush each raw material to a particle size of 10mm and mix for 40min; melt at 1600℃ for 3h under nitrogen protection; control the casting temperature at 1480℃; after casting, crush into 30mm blocks to obtain phosphorus-containing inoculum blocks.

[0046] Step S1: Weigh pig iron and scrap steel at a mass ratio of 10:2. The pig iron contains 4.3% carbon and the scrap steel contains 0.6% carbon. Mix them and heat them to smelt. When the temperature reaches 1500℃, add 0.4% of the mass of pig iron crushed pig iron chips with a size of 3mm as a nucleating agent. Control the stirring speed at 90rpm and stir for 15min to promote the floating of impurities. After removing the slag, add 2.5% of the mass of pig iron silicon, 0.6% of the mass of pig iron manganese, and 0.3% of the mass of pig iron copper. After melting and clearing, cool to 1450℃ to obtain alloyed iron liquid.

[0047] Step S2: Magnesium composite spheres, comprising 1.6% of the mass of the alloyed molten iron, are pre-placed inside the spheroidizing ladle, separated by a dam. The alloyed molten iron at 1450℃ is then poured in at a rate of 1.0 m...3 The flow rate is 1 / min, which is used to inject the spheroidizing solution into the spheroidizing ladle for spheroidization treatment; gravity casting is adopted, the metal mold is preheated to 200℃, and the casting temperature is controlled at 1380℃; during the casting process, titanium accounting for 0.05% of the mass of the alloyed iron liquid is added through a funnel for in-flow inoculation; at the same time, phosphorus-containing inoculation blocks accounting for 8% of the mass of the alloyed iron liquid are placed in the pouring cup for instantaneous in-mold inoculation. After casting is completed and cooled, the cast blank is obtained.

[0048] Step S3: The cast blank is heated to 900℃ at a heating rate of 150℃ / h for normalizing treatment. After holding at this temperature for 3 hours, a 12% (w / w) polyvinyl alcohol aqueous solution (polyvinyl alcohol molecular weight 35000) is sprayed on it. The spraying pressure is controlled at 0.3MPa. The blank is then cooled to a surface temperature of 200℃. The residual heat in the core is used to raise the surface temperature back to 387℃. The furnace temperature is controlled at 387℃ and held for 50 minutes. The blank is then cooled to room temperature to obtain a high-hardness ductile iron composition.

[0049] Comparative Example 1 Compared with Example 1, the "magnesium composite spheres" in this comparative example are replaced with the same mass of "6% magnesium, 0.7% molybdenum, 0.7% vanadium, and the balance iron, which are weighed by mass percentage, crushed to 15mm particle size and mixed evenly to obtain a mixture". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, a high-hardness ductile iron composition is obtained.

[0050] Comparative Example 2 Compared with Example 1, this comparative example does not use the spheroidizing treatment of alloyed iron melt by the immersion method, but directly immerses magnesium composite balls into the alloyed iron melt. The remaining steps and parameters are the same, and will not be repeated in this comparative example. Finally, a high-hardness ductile iron composition is obtained.

[0051] Comparative Example 3 Compared with Example 1, the "phosphorus-containing inoculated block" in this comparative example is replaced with the same mass of "57% silicon, 10% chromium, 6% nickel, 4% phosphorus, and the balance being iron by mass percentage; after crushing each raw material to a particle size of 25mm, they are mixed evenly to obtain a phosphorus inoculated mixture". The remaining steps and parameters are the same, and will not be repeated in this comparative example. Finally, a high-hardness ductile iron composition is obtained.

[0052] Comparative Example 4 Compared with Example 1, this comparative example omits instantaneous inoculation and inoculates the phosphorus-containing inoculation block and titanium together with the flow. All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, a high-hardness ductile iron composition is obtained.

[0053] Comparative Example 5 Compared with Example 1, this comparative example did not include crushed pig iron filings, but all other steps and parameters were the same. The details of this comparative example will not be repeated here. The final result was a high-hardness ductile iron composition.

[0054] The high-hardness ductile iron compositions prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to performance testing. Detailed results are shown in Tables 1, 2 and 3.

[0055] Table 1: Spectrochemical Composition Table 2: Mechanical Properties Table 3: Metallographic and Other Tests Based on the analysis of test data, the high-hardness ductile iron compositions prepared in Examples 1-3 of this invention have the following advantages: Excellent comprehensive mechanical properties: The tensile strength of Examples 1-3 is 610MPa-685MPa, the yield strength is 452MPa-469MPa, the elongation after fracture is 7.50%-9.01%, and the hardness is 230HB-265HB. All indicators are better than the comparative examples, and a balance between high hardness and good toughness is achieved, which meets the requirements of engineering machinery parts for high strength, high wear resistance and impact resistance.

[0056] The metallographic structure is stable: the spheroidization rate reaches 82.35%-91.20%, the spheroidization grade is 3, and the average number of graphite particles per square meter is 650.2-756.8, indicating that the graphite morphology is spherical and uniformly distributed; the pearlite content is 59.80%-69.50%, and the ferrite content is moderate, which ensures the hardness and wear resistance of the material.

[0057] Precise composition control: In the spectrochemical composition, the content of harmful element S is low (0.008%-0.011%), and the alloying elements Cr, Ni, Ti, Mo, V and other elements are reasonably distributed with no obvious segregation, indicating that the smelting and inoculation processes have a significant effect on the control of composition.

[0058] A comparison of Comparative Example 1 and Example 1 shows that replacing the pre-melted magnesium composite spheres with an unmelted mixture of magnesium, molybdenum, vanadium, and iron in Comparative Example 1 resulted in a decrease in the spheroidization rate from 87.56% to 70.52%, the tensile strength from 653 MPa to 580 MPa, and the hardness from 248 HB to 220 HB. This indicates that pre-melted magnesium composite spheres can significantly improve the spheroidization effect and mechanical properties by stabilizing the spheroidization reaction and reducing the loss of alloying elements. In contrast, directly using the mixture would lead to a decrease in performance due to the intense reaction and uneven element distribution.

[0059] Comparing Comparative Example 2 and Example 1, it can be seen that in Comparative Example 2, by omitting the spheroidizing treatment using the injection method and directly adding the mixture to the molten iron, the spheroidization rate decreased to 72.00%, and the tensile strength decreased to 570 MPa. This indicates that the injection method, by separating and controlling the flow rate of the molten iron through dams, can slow down the intensity of the reaction between the magnesium composite spheres and the molten iron, avoid temperature fluctuations and element loss, and ensure the uniformity of spheroidization; while directly adding the mixture will destroy the spheroidization stability, leading to deterioration of the microstructure and properties.

[0060] A comparison of Comparative Example 3 and Example 1 shows that in Comparative Example 3, replacing the pre-formed phosphorus-containing inoculum block with an unformed mixture of silicon, chromium, nickel, phosphorus, and iron resulted in a decrease in spheroidization rate from 87.56% to 78.85% and tensile strength from 653 MPa to 595 MPa. This indicates that the phosphorus-containing inoculum block, through casting, can achieve precise release of instantaneous inoculation within the mold, stabilizing the graphite morphology; while the unformed mixture, due to uncontrolled release of inoculum elements, leads to uneven graphite distribution and decreased performance.

[0061] Comparing Comparative Example 4 and Example 1, it can be seen that: Comparative Example 4, by eliminating instantaneous inoculation within the mold and using only in-flow inoculation, saw the spheroidization rate decrease to 75.00%, and the elongation after fracture decrease from 8.85% to 6.50%. This indicates that the dual system of in-flow inoculation plus instantaneous inoculation within the mold can continuously refine graphite throughout the casting process. In-flow inoculation refines the graphite in the early stage and stabilizes it during the solidification stage of instantaneous inoculation. In contrast, single in-flow inoculation cannot cover the entire solidification process, leading to uncontrolled graphite morphology and decreased toughness.

[0062] Comparing Comparative Example 5 and Example 1, it can be seen that in Comparative Example 5, without the addition of crushed pig iron filings (nucleating agent), the spheroidization rate decreased to 68.32%, the tensile strength decreased to 562 MPa, and the ferrite content increased from 27.98% to 45.12%. This indicates that the nucleating agent can act as a nucleation site for impurities, promoting the flotation of inclusions such as MnS and Al2O3, while providing nucleation sites for graphite and reducing ferrite segregation. The absence of a nucleating agent leads to residual impurities and insufficient graphite nucleation, significantly reducing the overall performance of the material.

[0063] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A processing technology for a high-hardness ductile iron composition used in engineering machinery, characterized in that, Includes the following steps: Step S1: Mix pig iron and scrap steel and heat them to smelt. Heat to the smelting temperature, add nucleating agent, stir, remove slag, add silicon, manganese and copper, melt until clear, and then cool to obtain alloyed iron liquid. Step S2: First, magnesium composite spheres are pre-placed in the spheroidizing ladle, and the alloyed molten iron is spheroidized using the pouring method; the spheroidized alloyed molten iron is then poured, and during the pouring process, titanium is added through a funnel for in-flow inoculation, while the pouring temperature is controlled according to the casting wall thickness; in addition, a phosphorus-containing inoculation block is placed in the pouring cup for instantaneous in-mold inoculation, and after pouring and cooling, a cast blank is obtained; Step S3: The cast blank is heated to the normalizing temperature at a constant heating rate and then normalized. After holding at the temperature, it is cooled by spraying a polyvinyl alcohol aqueous solution. The furnace temperature was then adjusted to the highest temperature reached on the surface of the billet during the self-tempering process, and this temperature was maintained for heat preservation. The billet was then cooled to room temperature to obtain a high-hardness ductile iron composition.

2. The processing technology of the high-hardness ductile iron composition for engineering machinery according to claim 1, characterized in that, The mass ratio of pig iron to scrap steel is 10:0.5-2, the amount of silicon added is 2.0%-2.5% of the mass of pig iron, the amount of manganese added is 0.3%-0.6% of the mass of pig iron, and the amount of copper added is 0.1%-0.3% of the mass of pig iron.

3. The processing technology of the high-hardness ductile iron composition for engineering machinery according to claim 1, characterized in that, The nucleating agent is crushed pig iron filings with a size of 1mm-3mm, and the amount added is 0.2%-0.4% of the mass of pig iron.

4. The processing technology of the high-hardness ductile iron composition for engineering machinery according to claim 1, characterized in that, The preparation method of the magnesium composite ball is as follows: weigh 5%-7% magnesium, 0.5%-1.0% molybdenum, 0.5%-1.0% vanadium, and the balance iron according to the mass percentage; crush the raw materials, mix them evenly, melt them under argon protection, cast them into shape, and then crush them to obtain the magnesium composite ball.

5. The processing technology of the high-hardness ductile iron composition for engineering machinery according to claim 1, characterized in that, The amount of magnesium composite spheres added is 1.2%-1.6% of the mass of the alloyed molten iron; the pouring method is as follows: place the magnesium composite spheres at the bottom of the spheroidizing ladle, separate it with a dam, and pour the alloyed molten iron at 1430℃-1460℃ at a speed of 0.5m... 3 / min-1.0m 3 A flow rate of / min is injected into the spheroidizing ladle to allow the alloyed iron molten metal to fully react with the magnesium composite spheres.

6. The processing technology of the high-hardness ductile iron composition for engineering machinery according to claim 1, characterized in that, During the in-flow inoculation process, the amount of titanium added is 0.03%-0.05% of the mass of the alloyed molten iron.

7. The processing technology of the high-hardness ductile iron composition for engineering machinery according to claim 1, characterized in that, The preparation method of the phosphorus-containing inoculum block is as follows: Weigh 55%-60% silicon, 8%-12% chromium, 5%-8% nickel, 3%-5% phosphorus, and the balance iron according to the mass percentage; crush and mix the raw materials, melt them under nitrogen protection, cast them into shape, and then crush them to obtain the phosphorus-containing inoculum block.

8. The processing technology of the high-hardness ductile iron composition for engineering machinery according to claim 1, characterized in that, The casting process employs low-pressure casting or gravity casting; the mold is either a sand mold or a metal mold, with the sand mold preheated to 200℃-300℃ and the metal mold preheated to 150℃-200℃.

9. The processing technology of the high-hardness ductile iron composition for engineering machinery according to claim 1, characterized in that, The polyvinyl alcohol aqueous solution has a mass fraction of 8%-12% and a spraying pressure of 0.2MPa-0.3MPa.

10. A high-hardness ductile iron composition prepared by the processing technology of the high-hardness ductile iron composition for engineering machinery as described in any one of claims 1-9.

Images