Production method of nodular cast iron

Abstract

The invention relates to a nodular cast iron production method which sequentially comprises the steps of smelting, hardening and tempering, in-ladle spheroidizing inoculation and stream inoculation, an inoculant adopted in the in-ladle spheroidizing inoculation process is selected from silicon-calcium-barium inoculants, and an inoculant adopted in the stream inoculation process is selected from silicon-calcium inoculants containing bismuth and rare earth elements. The inoculant adopted in the stream inoculation process is replaced with the silicon-calcium inoculant containing the bismuth element and the rare earth element from a silicon-calcium-barium inoculant, the content of ferrite in the cast iron can be increased through the bismuth element, the plasticity of the nodular cast iron is improved, formation of phosphorus eutectic is reduced through the bismuth element, the plasticity is improved, and the service life of the nodular cast iron is prolonged. The number of graphite nodules is increased by refining graphite through the bismuth element, the plasticity is improved, the structure uniformity of the cast iron can be improved through the bismuth element, and the strength is improved; the nickel element is added in the hardening and tempering process for solid solution strengthening, the matrix ferritic structure is strengthened, the yield strength is improved, and meanwhile the negative influence on the ductility of the material is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of casting, and in particular relates to a production method of ductile iron. Background Art

[0002] Green sand, also known as wet sand, refers to the sand mixture in casting production that is mixed with bentonite as a binder and then mixed with water and other additives. It can be used for molding and core making. The sand mold (core) does not need to be dried and can be directly poured. Green sand casting refers to the casting process using green sand as a mold. Green sand casting has the advantages of low cost, high flexibility (castings of various sizes can be cast, suitable for various casting needs), strong applicability (suitable for casting of various metal materials, such as steel, copper, aluminum, etc.), etc. It is widely used in automobiles (such as engines, chassis, brake systems, etc.), machinery manufacturing (such as gears, shafts, valves, etc.), aerospace (such as high-precision castings such as aircraft engines and spacecraft), construction, ships, railways, petrochemicals and other fields.

[0003] In the related technology, the green sand casting process is generally used to produce ductile iron QT400-600. However, ductile iron QT400-600 has relatively uniform composition and performance. The higher its strength, the worse its plasticity. For example, the tensile strength of ductile iron QT400-18 is much lower than that of ductile iron QT600-3, while the elongation of the former is much higher than that of the latter.

[0004] In recent years, with the development of the foundry industry and the intensification of market competition, the requirements for the comprehensive properties of ductile iron, such as strength, plasticity, low-temperature plasticity, and residual stress, have become increasingly higher. However, it is difficult to produce ductile iron with both high strength and high plasticity using the existing green sand casting process. Summary of the invention

[0005] In view of this, the present invention provides a method for producing ductile iron, so that the produced ductile iron has both high strength and high plasticity.

[0006] To achieve the above solution, the technical solution of the present invention is as follows:

[0007] A method for producing ductile iron comprises the steps of smelting, quenching and tempering, in-ladle spheroidizing inoculation and in-stream inoculation in sequence, wherein the inoculant used in the in-ladle spheroidizing inoculation process is selected from silicon-calcium-barium inoculant, and the inoculant used in the in-stream inoculation process is selected from silicon-calcium-inoculant containing bismuth and rare earth elements.

[0008] The present application replaces the inoculant used in the flow inoculation process with a silicon-calcium-barium inoculant with a silicon-calcium inoculant containing bismuth and rare earth elements, which can increase the ferrite content in the cast iron and improve the plasticity of the ductile iron through the bismuth element, and at the same time reduce the formation of phosphorus eutectic through the bismuth element to improve the plasticity of the ductile iron, and can refine the graphite through the bismuth element to increase the number of graphite nodules and improve the plasticity of the ductile iron. The bismuth element can also be used to improve the uniformity of the structure of the cast iron, thereby improving the strength of the ductile iron; nickel is added through the tempering process for solid solution strengthening, the matrix ferrite structure is strengthened, the yield strength is improved while the negative impact on the ductility of the material is reduced, thereby making the ductile iron have both high strength and high plasticity.

[0009] Optionally, in the silicon-calcium-barium inoculant, the mass percentage of barium element is 2.0wt%-3.0wt%, and the mass percentage of calcium element is 1.0wt%-2.0wt%.

[0010] Optionally, the mass percentage of aluminum element in the silicon-calcium-barium inoculant is less than 0.8wt%, preferably less than 0.5wt%.

[0011] Optionally, in the silicon-calcium inoculant, the mass percentage of calcium element is 1.00wt%-4.00wt%, the mass percentage of bismuth element is 0.50wt%-3.50wt%, and the mass percentage of rare earth element is 0.50wt%-3.50wt%.

[0012] Optionally, the mass percentage of aluminum element in the silicon-calcium-barium inoculant is less than 1.5wt%, preferably less than 1.0wt%.

[0013] Optionally, the mass ratio of the silicon-calcium-barium inoculant to molten iron is 0.50-0.60:100, preferably 0.55-0.60:100.

[0014] Optionally, the flow rate of the silicon-calcium inoculant is 7.0-8.0 g / s, preferably 7.2-8.0 g / s.

[0015] Optionally, the spheroidizing agent used in the in-package spheroidizing inoculation process is selected from lanthanide spheroidizing agents.

[0016] In the present application, by selecting a lanthanide spheroidizer with a smaller shrinkage tendency, the shrinkage tendency can be effectively reduced, and the adverse effects of shrinkage defects on mechanical properties and plasticity can be avoided, thereby ensuring the high strength and high plasticity of ductile iron.

[0017] Optionally, the lanthanide spheroidizer is selected from silicon-magnesium-calcium spheroidizer containing lanthanum.

[0018] Optionally, in the silicon-magnesium-calcium spheroidizer, the mass percentage of lanthanum element is 0.35wt%-0.65wt%.

[0019] Optionally, the rare earth element content in the silicon-magnesium-calcium spheroidizer is 0wt%, that is, no rare earth element is contained.

[0020] Optionally, in the silicon-magnesium-calcium spheroidizer, the mass percentage of magnesium element is 5.0wt%-7.0wt%, preferably 5.5wt%-7.0wt%.

[0021] Optionally, in the silicon-magnesium-calcium spheroidizer, the mass percentage of calcium element is 2.0wt%-3.5wt%, preferably 2.0wt%-3.0wt%.

[0022] Optionally, the mass percentage of aluminum element in the calcium-silicon-magnesium-calcium spheroidizer is less than 0.80wt%, and the mass percentage of rare earth element is 0wt%, that is, the calcium-silicon-magnesium-calcium spheroidizer does not contain rare earth element rhenium.

[0023] Optionally, the mass ratio of the lanthanide spheroidizer to molten iron is 1.10-1.20:100, preferably 1.15-1.20:100.

[0024] Optionally, the temperature of the spheroidization incubation in the bag is 1390-1500°C, preferably 1400-1500°C.

[0025] Optionally, the temperature of the incubation is 1380-1300°C, preferably 1350-1300°C.

[0026] Optionally, the smelting temperature is 1400-1500°C, preferably 1450-1500°C.

[0027] Optionally, the tempering includes: adding a copper source, a nickel source and a graphitized carburizer to the molten iron obtained by smelting, so that the mass percentage of the copper element is 0.60wt%-0.85wt%, the mass percentage of the nickel element is 0.55wt%-0.65wt% and the mass percentage of the carbon element is 3.72wt%-3.78wt%, heating to 1480-1510°C, then adjusting to 1510-1530°C, and standing.

[0028] Optionally, the fixed carbon content of the graphitized recarburizer is greater than or equal to 98.5wt%, preferably greater than or equal to 99.0wt%, and the mass percentage of sulfur element is less than 0.05wt%, preferably less than 0.03wt%.

[0029] In the present application, by adjusting the mass percentage of carbon element to 3.72wt%-3.78wt%, defects such as irregular graphite caused by too high carbon content and shrinkage and shrinkage holes caused by too low carbon content can be avoided, thereby ensuring the strength and plasticity of ductile iron.

[0030] In the present application, the iron-containing raw materials used for ductile iron include but are not limited to: pig iron, scrap steel, recycled materials, etc.

[0031] In the present application, the copper source includes but is not limited to: pure copper and other substances.

[0032] In the present application, the nickel source includes but is not limited to: pure nickel and other substances.

[0033] In this application, the standing time is 8-12 minutes.

[0034] In the present application, a copper source and a nickel source are added to the molten iron obtained by smelting, so that the mass percentage of the copper element is 0.60wt%-0.85wt%, and the mass percentage of the nickel element is 0.55wt%-0.65wt%. The property that the copper element can form a reinforcing phase with the carbon element in the cast iron can be utilized to improve the strength of the cast iron. At the same time, the content of pearlite in the cast iron can be increased by the copper element to improve the strength. By adding the nickel element for solid solution strengthening during the quenching and tempering process, the matrix ferrite structure is strengthened, the yield strength is improved, and the negative impact on the ductility of the material is reduced, thereby making the ductile iron have both high strength and high plasticity.

[0035] It should be noted that, in the present application, after the in-bag spheroidization inoculation and before the in-stream inoculation, the production method further comprises the following steps: detecting the mass percentage of chromium, silicon, manganese, sulfur, titanium, magnesium, tin, antimony, lead, bismuth, arsenic and aluminum in the product obtained by in-bag spheroidization inoculation, if the mass percentage of silicon is 2.50wt%-2.75wt%, the mass percentage of manganese is 0.34wt%-0.38wt%, the mass percentage of chromium is less than 0.05wt%, the mass percentage of sulfur is less than 0.1wt%, and the mass percentage of chromium is less than 0.05wt%. If the mass percentage of the element is 0.01wt%-0.018wt%, the mass percentage of the titanium element is less than or equal to 0.025wt%, the mass percentage of the magnesium element is 0.040wt%-0.060wt%, the mass percentage of the tin element is less than or equal to 0.035wt% and the sum of the mass percentages of tin, antimony, lead, bismuth, arsenic and aluminum is less than 0.08wt%, then flow inoculation is carried out; otherwise, re-smelting, tempering and in-ladle spheroidization inoculation are carried out until the contents of the corresponding elements in the product obtained by in-ladle spheroidization inoculation are within the corresponding ranges.

[0036] It should be noted that in the present application, the mass percentages of elements such as manganese, copper, nickel, chromium, sulfur, titanium, tin, antimony, lead, bismuth, arsenic and aluminum all refer to the mass percentages calculated based on the amount of spheroidized inoculant (the amount of raw materials such as silicon-calcium-barium inoculant, silicon-calcium inoculant, and spheroidizing agent is much less than the amount of molten iron, so the amount of raw materials such as silicon-calcium-barium inoculant, silicon-calcium inoculant, and spheroidizing agent can be ignored).

[0037] It should be noted that in the present application, when confirming the mass percentage of elements such as silicon and magnesium, the corresponding elements contained in the silicon-calcium-barium inoculant, silicon-calcium inoculant and spheroidizer need to be considered, and the mass percentage of elements such as silicon and magnesium refers to the mass percentage calculated based on the amount of spheroidized inoculant.

[0038] In the present application, by controlling the mass percentage of silicon element to 2.50wt%-2.75wt%, the strength of cast iron can be improved through the solid solution strengthening matrix effect of silicon element, and the adverse effect of excessive silicon content on the plasticity of cast iron can be avoided.

[0039] In the present application, by controlling the mass percentage of manganese element to 0.34wt%-0.38wt%, the austenite can be stabilized by manganese element, thereby improving the strength of the cast iron, and the grains of the cast iron can be refined by manganese element, thereby improving the plasticity of the cast iron.

[0040] In the present application, by controlling the mass percentage of chromium element to be less than 0.05wt%, the adverse effect of chromium element on the plasticity of cast iron can be avoided, thereby ensuring the plasticity of ductile iron.

[0041] In the present application, by controlling the mass percentage of sulfur element to 0.01wt%-0.018wt% and the mass percentage of titanium element to be less than or equal to 0.025wt%, the adverse effects of sulfur and titanium elements on the spheroidizing effect can be avoided, thereby ensuring the strength and plasticity of ductile iron.

[0042] In the present application, by controlling the mass percentage of magnesium element to 0.040wt%-0.055wt%, the integrity of graphite nodules can be improved, the spheroidization rate can be increased, the strength of ductile iron can be improved, and the plasticity of ductile iron can be improved through the combined action of magnesium element and silicon element in cast iron.

[0043] In the present application, by controlling the mass percentage of tin element to be less than or equal to 0.035wt% and the total mass percentage of tin element, antimony element, lead element, bismuth element, arsenic element and aluminum element to be less than 0.08wt%, the adverse effect of tin element on the plasticity of cast iron and the adverse effect of tin element, antimony element, lead element, bismuth element, arsenic element and aluminum element on the spheroidizing effect can be avoided, thereby ensuring the strength and plasticity of ductile iron. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A flow chart of the method for producing ductile iron of the present application;

[0045] Figure 2 Schematic diagram of ductile iron obtained in Examples 1-3. DETAILED DESCRIPTION

[0046] The present invention is further described below through specific examples, but it should be pointed out that the specific material ratios, process conditions and results described in the embodiments of the present invention are only used to illustrate the present invention and cannot be used to limit the scope of protection of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

[0047] like Figure 1 As shown, an embodiment of the present application provides a method for producing ductile iron, which sequentially includes the steps of smelting, quenching and tempering, in-ladle spheroidizing inoculation and in-stream inoculation;

[0048] The melting temperature is 1400-1500℃;

[0049] The tempering comprises: adding a copper source, a nickel source and a graphitized carburizer to the molten iron obtained by smelting, so that the mass percentage of the copper element is 0.60wt%-0.85wt%, the mass percentage of the nickel element is 0.55wt%-0.65wt% and the mass percentage of the carbon element is 3.72wt%-3.78wt%, the fixed carbon content of the graphitized carburizer is greater than or equal to 98.5wt%, and the mass percentage of the sulfur element is less than 0.05wt%, heating to 1480-1510°C, then adjusting to 1510-1530°C, and standing;

[0050] The temperature of the spheroidization inoculation in the ladle is 1390-1500° C. The inoculant used in the spheroidization inoculation process is selected from a silicon-calcium-barium inoculant, and the spheroidizer used is selected from a lanthanide spheroidizer. The mass ratio of the silicon-calcium-barium inoculant to the molten iron is 0.50-0.60:100; in the silicon-calcium-barium inoculant, the mass percentage of the barium element is 2.0wt%-3.0wt%, and the mass percentage of the calcium element is 1.0wt%-2.0wt%; the mass ratio of the lanthanide spheroidizer to the molten iron is 1.10-1.20:100, and the lanthanide spheroidizer is selected from a silicon-magnesium-calcium spheroidizer containing lanthanum. In the silicon-magnesium-calcium spheroidizer, the mass percentage of the lanthanum element is 0.35wt%-0.65wt% and the rare earth element content is 0wt%.

[0051] The temperature of the in-flow inoculation is 1380-1300° C. The inoculant used in the in-flow inoculation process is selected from a silicon-calcium inoculant containing bismuth and rare earth elements. The flow rate of the silicon-calcium inoculant is 7.0-8.0 g / s. In the silicon-calcium inoculant, the mass percentage of calcium element is 1.00wt%-4.00wt%, the mass percentage of bismuth element is 0.50wt%-3.50wt% and the mass percentage of rare earth element is 0.50wt%-3.50wt%.

[0052] The present invention is described in detail below by specific examples. It should also be understood that the following examples are only used to specifically illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values ​​​​exemplified below.

[0053] Example 1

[0054] A method for producing ductile iron (specifically an electric drive axle), comprising the following steps:

[0055] S1. Ingredients

[0056] Q12 pig iron, light material baled scrap steel and ductile iron recycled material are mixed in a mass ratio of 5:40:55 to obtain an iron-containing raw material, 1.5wt% of a high-temperature graphitized recarburizer (fixed carbon content is 98.63wt%, the mass percentage content of sulfur element is 0.023wt%, commercially available) is added to the iron-containing raw material, and the carbon content is detected by a carbon equivalent detector. After detection, the mass percentage content of the carbon element is 3.54wt%;

[0057] S2. Melting: The mixture is melted at 1490°C in a 10T medium frequency induction furnace to obtain 10.2t of molten iron;

[0058] S3. Tempering: Adding liquid pure nickel, liquid pure copper and high temperature graphitized carburizer (fixed carbon content of 98.63wt%, mass percentage of sulfur element of 0.023wt%, commercially available) to 10.2t molten iron, the mass percentage of copper element is 0.587wt% (in the range of 0.55wt%-0.65wt%), the mass percentage of nickel element is 0.559wt% (in the range of 0.55wt%-0.65wt%) and the mass percentage of carbon element is 3.73wt% (in the range of 3.72wt%-3.78wt%), heating to 1520°C in a 10T medium frequency induction furnace, power off and stand for 10min, at which time the molten iron temperature is reduced to 1500°C for spheroidization;

[0059] S4. In-package spheroidization inoculation: 18.60 kg of lanthanum-containing silicon-magnesium-calcium spheroidizer (mass percentage of silicon is 45.33 wt %, mass percentage of magnesium is 5.92 wt %, mass percentage of calcium is 3.03 wt %, mass percentage of lanthanum is 0.46 wt %, mass percentage of aluminum is 0.66 wt %, commercially available) is placed on one side of the spheroidizing package, and 9.50 kg of silicon-calcium-barium inoculant (mass percentage of silicon is 72.54 wt%, the mass percentage of calcium is 1.28wt%, the mass percentage of barium is 2.33wt%, the mass percentage of aluminum is 1.11wt%, commercially available), the quenched and tempered iron water is discharged in multiple bags, 1.6T of water is discharged in each bag into the water transfer bag, and then the water transfer bag is turned over to flush 1.6T of molten iron into the spheroidizing bag for spheroidizing inoculation treatment at 1450℃ for 60s, and the chromium, silicon, manganese, sulfur, titanium, magnesium, tin and antimony elements in the molten iron after inoculation treatment are detected by spectrometer detection method. The mass percentage of the elements lead, bismuth, arsenic and aluminum was tested to find that the mass percentage of the chromium element was 0.032wt% (less than 0.05wt%), the mass percentage of the silicon element was 2.71wt% (within the range of 2.50wt%-2.75wt%), the mass percentage of the manganese element was 0.355wt% (within the range of 0.34wt%-0.38wt%), the mass percentage of the sulfur element was 0.0117wt% (within the range of 0.01wt%-0.018wt%), and the mass percentage of the sulphur element was 0.016wt% (within the range of 0.02wt%-0.03wt%). wt% range), the mass percentage of titanium element is 0.0192wt% (less than or equal to 0.025wt%), the mass percentage of magnesium element is 0.0573wt% (in the range of 0.040wt%-0.060wt%), the mass percentage of tin element is 0.0076wt% (less than or equal to 0.035wt%), and the total mass percentage of tin element, antimony element, lead element, bismuth element, arsenic element and aluminum element is 0.045wt% (less than 0.08wt%);

[0060] S5. Flow inoculation: Preliminarily place a silicon-calcium inoculant containing bismuth and rare earth elements (the mass percentage of silicon is 64.15wt%, the mass percentage of calcium is 2.18wt%, the mass percentage of bismuth is 0.57wt%, the mass percentage of rare earth elements is 2.24wt%, the mass percentage of aluminum is 0.83wt%, commercially available) in a flow inoculation bucket, with a flow rate of 7.2g / s, pour the molten iron after the treatment in step S4, and carry out flow inoculation during the pouring process, at which time the material temperature is reduced from 1380°C to 1300°C, and cooled for 161min to obtain ductile iron (such as Figure 2 shown).

[0061] Example 2

[0062] A method for producing ductile iron, comprising the following steps:

[0063] S1. Ingredients

[0064] Q12 pig iron, light material baling scrap steel and ductile iron recycled material are mixed in a mass ratio of 5:40:55 to obtain an iron-containing raw material, 1.5wt% of a high-temperature graphitized carburizer (fixed carbon content is 98.63wt%, the mass percentage content of sulfur element is 0.023wt%, commercially available) is added to the iron-containing raw material, and the carbon content is detected by a carbon equivalent detector. After detection, the mass percentage content of the carbon element is 3.53wt%;

[0065] S2. Melting: The mixture is melted at 1490°C in a 10T medium frequency induction furnace to obtain 9.5t of molten iron;

[0066] S3. Tempering: Adding liquid pure nickel, liquid pure copper and high temperature graphitized carburizer (fixed carbon content of 98.63wt%, mass percentage of sulfur element of 0.023wt%, commercially available) to 9.5t molten iron, the mass percentage of copper element is 0.593wt% (in the range of 0.55wt%-0.65wt%), the mass percentage of nickel element is 0.606wt% (in the range of 0.55wt%-0.65wt%) and the mass percentage of carbon element is 3.74wt%, heated to 1520°C by 10T medium frequency induction furnace, turned off and stood for 10min, at which time the molten iron temperature was reduced to 1500°C for spheroidization;

[0067] S4. In-package spheroidization inoculation: 18.60 kg of lanthanum-containing silicon-magnesium-calcium spheroidizer (mass percentage of silicon is 45.33 wt %, mass percentage of magnesium is 5.92 wt %, mass percentage of calcium is 3.03 wt %, mass percentage of lanthanum is 0.46 wt %, mass percentage of aluminum is 0.66 wt %, commercially available) is placed on one side of the spheroidizing package, and 9.50 kg of silicon-calcium-barium inoculant (mass percentage of silicon is 72.54 wt%, the mass percentage of calcium element is 1.28wt%, the mass percentage of barium element is 2.33wt%, the mass percentage of aluminum element is 1.11wt%, commercially available), the iron water after tempering in the electric furnace is discharged in multiple bags, 1.6T of molten iron is discharged into the water transfer bag each time, and then the water transfer bag is turned over to flush 1.6T of molten iron into the spheroidizing bag for spheroidizing inoculation treatment at 1450℃ for 60s, and the chromium, silicon, manganese, sulfur, titanium, magnesium, tin and antimony elements in the molten iron after inoculation treatment are detected by spectrometer detection method. The mass percentage of chromium, lead, bismuth, arsenic and aluminum elements was tested to be 0.033wt% (less than 0.05wt%), 2.69wt% (within the range of 2.50wt%-2.75wt%), 0.352wt% (within the range of 0.34wt%-0.38wt%), 0.0122wt% (within the range of 0.01wt%-0.01wt%), and 0.10wt% (within the range of 0.10wt%-0.10wt%). 8wt%), the mass percentage of titanium element is 0.0199wt% (less than or equal to 0.025wt%), the mass percentage of magnesium element is 0.0432wt% (in the range of 0.040wt%-0.060wt%), the mass percentage of tin element is 0.0077wt% (less than or equal to 0.035wt%), and the total mass percentage of tin element, antimony element, lead element, bismuth element, arsenic element and aluminum element is 0.045wt% (less than 0.08wt%);

[0068] S5. Flow inoculation: Preliminarily place a silicon-calcium inoculant containing bismuth and rare earth elements (the mass percentage of silicon is 64.15wt%, the mass percentage of calcium is 2.18wt%, the mass percentage of bismuth is 0.57wt%, the mass percentage of rare earth elements is 2.24wt%, the mass percentage of aluminum is 0.83wt%, commercially available) in a flow inoculation bucket, with a flow rate of 7.2g / s, pour the molten iron after the treatment in step S4, and carry out flow inoculation during the pouring process, at which time the material temperature is reduced from 1380°C to 1300°C, and cooled for 152min to obtain ductile iron (such as Figure 2 shown).

[0069] Example 3

[0070] A method for producing ductile iron, comprising the following steps:

[0071] S1. Ingredients

[0072] Q12 pig iron, light material baling scrap steel and ductile iron recycled material are mixed in a mass ratio of 5:40:55 to obtain an iron-containing raw material, 1.5wt% of a high-temperature graphitized carburizer (fixed carbon content is 98.63wt%, the mass percentage content of sulfur element is 0.023wt%, commercially available) is added to the iron-containing raw material, and the carbon content is detected by a carbon equivalent detector. After detection, the mass percentage content of the carbon element is 3.53wt%;

[0073] S2. Melting: The mixture is melted at 1500°C in a 10T medium frequency induction furnace to obtain 11.0t of molten iron;

[0074] S3. Tempering: Adding liquid pure nickel, liquid pure copper and high temperature graphitized carburizer (fixed carbon content of 98.63wt%, mass percentage of sulfur element of 0.023wt%, commercially available) to 11.0t molten iron, the mass percentage of copper element is 0.572wt% (in the range of 0.55wt%-0.65wt%), the mass percentage of nickel element is 0.595wt% (in the range of 0.55wt%-0.65wt%) and the mass percentage of carbon element is 3.74wt%, heated to 1520°C by 10T medium frequency induction furnace, and the power is turned off and left to stand for 10min, at which time the molten iron temperature is reduced to 1500°C for spheroidization;

[0075] S4. In-package spheroidization inoculation: 18.60 kg of lanthanum-containing silicon-magnesium-calcium spheroidizer (mass percentage of silicon is 45.33 wt %, mass percentage of magnesium is 5.92 wt %, mass percentage of calcium is 3.03 wt %, mass percentage of lanthanum is 0.46 wt %, mass percentage of aluminum is 0.66 wt %, commercially available) is placed on one side of the spheroidizing package, and 9.50 kg of silicon-calcium-barium inoculant (mass percentage of silicon is 72.54 wt%, the mass percentage of calcium element is 1.28wt%, the mass percentage of barium element is 2.33wt%, the mass percentage of aluminum element is 1.11wt%, commercially available), the iron water after tempering in the electric furnace is discharged in multiple bags, 1.6T of molten iron is discharged into the water transfer bag each time, and then the water transfer bag is turned over to flush 1.6T of molten iron into the spheroidizing bag for spheroidizing inoculation treatment at 1450℃ for 60s, and the chromium, silicon, manganese, sulfur, titanium, magnesium, tin and antimony elements in the molten iron after inoculation treatment are detected by spectrometer detection method. The mass percentage of chromium, lead, bismuth, arsenic and aluminum elements was tested to find that the mass percentage of chromium was 0.033wt% (less than 0.05wt%), the mass percentage of silicon was 2.68wt% (within the range of 2.50wt%-2.75wt%), the mass percentage of manganese was 0.348wt% (within the range of 0.34wt%-0.38wt%), the mass percentage of sulfur was 0.010wt% (within the range of 0.01wt%-0.018wt%), and the mass percentage of chromium was 0.033wt% (less than 0.05wt%). wt% range), the mass percentage of titanium element is 0.0205wt% (less than or equal to 0.025wt%), the mass percentage of magnesium element is 0.0436wt% (in the range of 0.040wt%-0.060wt%), the mass percentage of tin element is 0.00875wt% (less than or equal to 0.035wt%), and the total mass percentage of tin element, antimony element, lead element, bismuth element, arsenic element and aluminum element is 0.046wt% (less than 0.08wt%);

[0076] S5. Flow inoculation: Preliminarily place a silicon-calcium inoculant containing bismuth and rare earth elements (the mass percentage of silicon is 64.15wt%, the mass percentage of calcium is 2.18wt%, the mass percentage of bismuth is 0.57wt%, the mass percentage of rare earth elements is 2.24wt%, the mass percentage of aluminum is 0.83wt%, commercially available) in a flow inoculation bucket, with a flow rate of 7.2g / s, pour the molten iron after the treatment in step S4, and carry out flow inoculation during the pouring process, at which time the material temperature is reduced from 1380°C to 1300°C, and cooled for 173min to obtain ductile iron (such as Figure 2 shown).

[0077] Comparative Example 1

[0078] The difference between this comparative example and Example 1 is that the silicon-calcium-barium inoculant, which is the same as that used in the ladle spheroidization inoculation, is used to replace the silicon-calcium inoculant containing bismuth and rare earth elements.

[0079] Comparative Example 2

[0080] The difference between this comparative example and Example 1 is that no liquid pure nickel is added to the molten iron, that is, the nickel content in the molten iron is not adjusted.

[0081] Comparative Example 3

[0082] The difference between this comparative example and Example 1 is that no liquid pure nickel is added during the tempering process, and a silicon-calcium-barium inoculant (that is, the same as the inoculant used for in-ladle spheroidization inoculation) is used instead of the silicon-calcium inoculant containing bismuth and rare earth elements.

[0083] Performance Testing

[0084] According to GB / T 228.1-2021 Tensile test of metallic materials Part 1: Room temperature test method, the tensile strength, yield strength and total elongation at break of the ductile iron obtained in Examples 1-3 and Comparative Examples 1-3 were tested. The sampling location was Figure 2 The results in the red frame area are shown in Table 1.

[0085] Table 1 Test results

[0086] Group Tensile strength, MPa Yield strength, MPa Total elongation at break, % Example 1 821 567 7.1 Example 2 812 592 8.5 Example 3 825 520 6.7 Comparative Example 1 812 475 4.7 Comparative Example 2 690 420 5.6 Comparative Example 3 780 468 5.5

[0087] As shown in Table 1, compared with Comparative Example 1 (using the same silicon-calcium-barium inoculant as the in-bag spheroidizing inoculation as the inoculant in the in-stream inoculation process), the yield strength and total elongation at break of Example 1 (using the silicon-calcium-barium inoculant containing bismuth and rare earth elements as the inoculant in the in-stream inoculation process) are significantly increased. The results show that the present application replaces the inoculant used in the in-stream inoculation process with the silicon-calcium-barium inoculant with the silicon-calcium inoculant containing bismuth and rare earth elements, which can increase the content of ferrite in cast iron through bismuth elements, improve the plasticity of ductile iron, and reduce the formation of phosphorus eutectic through bismuth elements, improve the plasticity of ductile iron, and can refine graphite through bismuth elements to increase the number of graphite nodules, improve the plasticity of ductile iron, and can also improve the uniformity of the structure of cast iron through bismuth elements, thereby improving the strength of ductile iron.

[0088] As shown in Table 1, compared with Comparative Example 2 (liquid pure nickel was not added to the molten iron, that is, the nickel content in the molten iron was not adjusted), the tensile strength, yield strength and total elongation at break of Example 1 (liquid pure copper and liquid pure nickel were added to the molten iron) were significantly increased. The results show that in this application, a nickel source is added to the molten iron obtained by smelting, so that the mass percentage of the nickel element is 0.55wt%-0.65wt%, and the matrix ferrite structure can be strengthened by adding nickel element solid solution strengthening, while the yield strength is improved and the negative impact on the ductility of the material is reduced, thereby making the ductile iron have both high strength and high plasticity.

[0089] As shown in Table 1, compared with Comparative Example 3 (liquid pure nickel was not added during the quenching and tempering process, and the same silicon-calcium-barium inoculant as the in-ladle spheroidizing inoculation was used as the inoculant in the in-stream inoculation process), Example 1 (liquid pure nickel was added during the quenching and tempering process, and the silicon-calcium inoculant containing bismuth and rare earth elements was used as the inoculant in the in-stream inoculation process) had significantly increased tensile strength, yield strength and total elongation at break. The results show that the method of the present application can produce ductile iron with both high strength and high plasticity.

[0090] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for producing ductile iron, comprising the steps of smelting, quenching and tempering, in-ladle spheroidizing inoculation and in-stream inoculation, characterized in that: The inoculant used in the in-package spheroidization inoculation process is selected from silicon-calcium-barium inoculant, and the inoculant used in the in-stream inoculation process is selected from silicon-calcium inoculant containing bismuth and rare earth elements.

2. The method for producing ductile iron according to claim 1, characterized in that: In the silicon-calcium-barium inoculant, the mass percentage of barium element is 2.0wt%-3.0wt%, and the mass percentage of calcium element is 1.0wt%-2.0wt%.

3. The method for producing ductile iron according to claim 1, characterized in that: In the silicon-calcium inoculant, the mass percentage of calcium element is 1.00wt%-4.00wt%, the mass percentage of bismuth element is 0.50wt%-3.50wt%, and the mass percentage of rare earth element is 0.50wt%-3.50wt%.

4. The method for producing ductile iron according to claim 1, characterized in that: The mass ratio of the silicon-calcium-barium inoculant to molten iron is 0.50-0.60:100; and / or, the flow rate of the silicon-calcium inoculant is 7.0-8.0 g / s; And / or, the spheroidizing agent used in the spheroidizing inoculation process is selected from lanthanide spheroidizing agents.

5. The method for producing ductile iron according to claim 4, characterized in that: The lanthanide spheroidizer is selected from silicon-magnesium-calcium spheroidizer containing lanthanum.

6. The method for producing ductile iron according to claim 5, characterized in that: In the silicon-magnesium-calcium spheroidizer, the mass percentage of lanthanum element is 0.35wt%-0.65wt%.

7. The method for producing ductile iron according to claim 4, characterized in that: The mass ratio of the lanthanide spheroidizer to molten iron is 1.10-1.20:

100.

8. The method for producing ductile iron according to claim 1, characterized in that: The temperature of the spheroidization incubation in the bag is 1390-1500°C; And / or, the temperature of the incubation is 1380-1300°C; And / or, the smelting temperature is 1400-1500°C.

9. The method for producing ductile iron according to claim 1, characterized in that: The tempering includes: adding a copper source, a nickel source and a graphitized carburizer to the molten iron obtained by smelting, so that the mass percentage of the copper element is 0.60wt%-0.85wt%, the mass percentage of the nickel element is 0.55wt%-0.65wt% and the mass percentage of the carbon element is 3.72wt%-3.78wt%, heating to 1480-1510°C, then adjusting to 1510-1530°C, and standing.

10. The method for producing ductile iron according to claim 9, characterized in that: The fixed carbon content of the graphitized recarburizer is greater than or equal to 98.5wt%, and the mass percentage of sulfur element is less than 0.05wt%.

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