Preparation method of nodular cast iron for axle housing casting

Abstract

The invention discloses a preparation method of nodular cast iron for axle housing castings. The nodular cast iron comprises the following raw materials: 10-30% of pig iron, 30-60% of scrap steel and 15-40% of foundry returns. 1.5%-2.5% of a carburant and 1.5%-2.0% of 75 ferrosilicon; the preparation method comprises the following steps: preparing the following components in percentage by weight: 0.4%-0.8% of electrolytic copper, 0.1%-0.4% of a silicon carbide pretreating agent, 0.8%-0.95% of an Mg30-containing spheroidized core-spun yarn and 0.2%-0.6% of 0.05% to 0.15% of an Ikine 958 stream inoculant; and through the arrangement of the pretreatment step, the metallurgical reaction is more sufficient, the molten iron is pretreated, and preparation can be better made for subsequent spheroidizing treatment. According to the single-wire feeding spheroidizing method, the spheroidizing process and the inoculation process are separated, the waiting time between spheroidizing cored wire feeding and inoculation treatment is saved, the wire feeding time is shortened, and the production cost is reduced. And the spheroidizing ladle is additionally arranged between the smelting furnace and the pouring ladle, so that the reaction is more sufficient, and the production efficiency is improved. The nodular cast iron prepared by the method is good in comprehensive performance, the preparation cost is reduced, and an axle housing cast by the nodular cast iron is good in mechanical performance and long in service life.

Description

Technical Field

[0001] The invention relates to the technical field of preparation methods of ductile iron, and in particular to a preparation method of ductile iron for bridge housing castings. Background Art

[0002] In the prior art, the spheroidization method of ductile iron material mostly adopts the punching method, and the general production process of the punching method is:

[0003] ①Packaging (spheroidizer, inoculant, covering agent);

[0004] ②Temperature measurement and furnace exit;

[0005] ③Scraping;

[0006] ④Incubate and stir;

[0007] ⑤Package inverted;

[0008] ⑥ Transfer to the pouring station;

[0009] ⑦ Slag removal and temperature measurement;

[0010] ⑧Start pouring.

[0011] When the ductile iron produced by the above preparation method is used for bridge shell casting, the strength and toughness cannot meet the requirements of high strength and high toughness, resulting in poor mechanical properties of the casting and low qualified rate. In addition, the above preparation method has great environmental pollution and poor operability.

[0012] The comprehensive performance requirements of ductile iron for bridge housing parts in heavy-duty trucks are getting higher and higher. In order to meet the comprehensive performance requirements of ductile iron for bridge housing parts, it is necessary to develop a new preparation method of ductile iron for bridge housing castings. Summary of the invention

[0013] In order to overcome the deficiencies of the above-mentioned prior art, the technical problem to be solved by the present invention is to provide a method for preparing ductile iron for bridge housing castings. The prepared ductile iron has good comprehensive performance and can reduce the preparation cost. When used for casting bridge housing castings, the mechanical properties of the bridge housing are good, the service life is long, and the overall weight of the bridge housing can be reduced.

[0014] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0015] A method for preparing ductile iron for axle housing castings comprises the following steps:

[0016] a. Prepare raw materials: The raw materials include the first group of raw materials added to the smelting furnace, the second group of raw materials added to the spheroidizing bag, and the inoculant used in the pouring process.

[0017] The weight percentage of each component in the first group of raw materials is: 10% to 30% pig iron, 30% to 60% scrap steel, 15% to 40% recycled materials; 1.5% to 2.5% carburizer, 1.5% to 2.0% 75 ferrosilicon;

[0018] The weight percentage of each component in the second group of raw materials relative to the weight of the molten iron in the spheroidizing bag is: 0.4% to 0.8% electrolytic copper, 0.1% to 0.4% silicon carbide pretreatment agent, 0.8% to 0.95% spheroidizing core wire containing Mg30, and 0.2% to 0.6% Ba-containing inoculant;

[0019] The percentage of the inoculant relative to the weight of the molten iron is: 0.05% to 0.15% Aiken 958 flow inoculant;

[0020] b. Melting: adding the 10% to 30% pig iron, the 18% to 40% recycled materials, the 30% to 60% scrap steel and the 1.5% to 2.5% carburizer to the smelting furnace to melt the raw iron water, adding the 1.5% to 2.0% ferrosilicon to increase silicon at the end of smelting, heating to 1520° C. to 1550° C., standing at high temperature and keeping warm for 8 to 12 minutes, cutting off the power supply and adding materials to quickly cool down to the furnace discharge temperature (1490° C. to 1510° C.), at which temperature, the molten iron can be discharged and transferred;

[0021] c. Pretreatment: placing the 0.4% to 0.8% electrolytic copper and the 0.1% to 0.4% silicon carbide pretreatment agent at the bottom of the spheroidizing ladle, and discharging the molten iron in step b and transferring it to the spheroidizing ladle;

[0022] d. Spheroidizing treatment: before the spheroidizing bag filled with molten iron is transferred to the spheroidizing chamber, the temperature is measured, and the spheroidizing bag enters the spheroidizing chamber, and then single-wire feeding spheroidizing is performed, and the spheroidizing core wire containing 0.8% to 0.95% Mg30 is added;

[0023] e. Inoculation treatment: After spheroidization is completed, the spheroidizing ladle is transferred out of the spheroidizing chamber, and after slag removal, a Ba-containing inoculant with a weight percentage of 0.2% to 0.6% is poured into the spheroidizing ladle, and after stirring evenly, the molten iron is poured into the pouring ladle, and the pouring ladle is transferred to the pouring station;

[0024] f. Pouring: During pouring, 0.05% to 0.15% of Aiken 958 inoculant is evenly added along with the pouring molten iron flow for instantaneous inoculation. After pouring into the molding mold box, the mold box is opened after cooling for a period of time to prepare the ductile iron for the bridge housing casting.

[0025] Preferably, the mass percentage of each element component in the prepared ductile iron for the bridge housing casting is: C 3.3% ~ 3.9%, Si 2.3% ~ 2.9%, Mn 0.2 ~ 0.8%, S < 0.030%, P < 0.04%, Cu 0.4% ~ 0.8%, Cr < 0.08%, Mg 0.03% ~ 0.08%, Re ≤ 0.02%, and the balance is Fe.

[0026] Preferably: the mechanical properties of the ductile iron used for the bridge housing casting are: tensile strength greater than or equal to 700 MPa, elongation greater than or equal to 10%, spheroidization rate level greater than or equal to level 2, graphite size level 5 to 8, pearlite content 60% to 90%, carbide and phosphorus eutectic content less than 2%, and Brinell hardness 210HB to 290HB.

[0027] Preferably, the aspect ratio of the spheroidized package is 1.6.

[0028] Preferably: in the above step f, 0.05% to 0.15% of Aiken 958 inoculant is uniformly added with the pouring molten iron flow, and the cooling time is controlled to be greater than 130 minutes.

[0029] Preferably: ensure that the bridge housing casting is kept warm in the cavity of the molding mold box for 160 minutes.

[0030] After adopting the above technical solution, the beneficial effects of the present invention are:

[0031] The present invention provides a method for preparing ductile iron for bridge shell castings, which uses a single-wire feeding spheroidizing method to produce a high-strength and high-toughness ductile iron QT700-10 bridge shell. The setting of the pretreatment step makes the metallurgical reaction more complete, and the molten iron is pretreated, which can better prepare for the subsequent spheroidizing treatment. The single-wire feeding spheroidizing method separates the spheroidizing process and the inoculation process, saving the waiting time between the spheroidizing core wire feeding and the inoculation treatment, which is beneficial to shorten the wire feeding time and reduce the production cost. A spheroidizing bag is added between the smelting furnace and the casting bag to make the reaction more complete and the composition more uniform, and at the same time it is beneficial to improve production efficiency.

[0032] The ductile iron used for the bridge housing casting can meet the requirements of tensile strength greater than or equal to 700MPa, elongation greater than or equal to 10%, spheroidization rate greater than or equal to level 2, graphite size 5 to 8, pearlite content 60% to 90%, carbide and phosphorus eutectic content less than 2%, and Brinell hardness 210HB to 290HB. The bridge housing cast using the ductile iron has good mechanical properties, improves service life, reduces the overall weight of the bridge housing, shortens the spheroidization treatment time, reduces manufacturing costs, and promotes the development of lightweight heavy trucks. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is described in detail below in conjunction with specific embodiments to further understand the purpose, solution and effect of the present invention, but it is not intended to limit the scope of protection of the claims attached to the present invention.

[0034] Embodiment 1:

[0035] Embodiment 2 of the present invention discloses a method for preparing ductile iron for bridge housing castings, comprising the following steps:

[0036] a. Prepare raw materials: the raw materials include a first group of raw materials added to the smelting furnace, a second group of raw materials added to the spheroidizing bag, and an inoculant used in the pouring process, wherein the weight percentage of each component in the first group of raw materials is: 10% to 30% pig iron, 30% to 60% scrap steel, 15% to 40% recycled materials; 1.5% to 2.5% carburizer, 1.5% to 2.0% 75 ferrosilicon; the weight percentage of each component in the second group of raw materials relative to the weight of the molten iron in the spheroidizing bag is: 0.4% to 0.8% electrolytic copper, 0.1% to 0.4% silicon carbide pretreatment agent, 0.8% to 0.95% spheroidizing cored wire containing Mg30, and 0.2% to 0.6% Ba-containing inoculant;

[0037] The percentage of the inoculant relative to the weight of the molten iron is: 0.05% to 0.15% Aiken 958 flow inoculant;

[0038] b. Melting: 14.42% pig iron, 28.85% recycled materials, 52.89% scrap steel and 2.21% carburizer are added to the smelting furnace to melt the original molten iron. At the end of smelting, 1.63% ferrosilicon is added to increase silicon. The temperature is raised to 1550°C. After standing at high temperature and keeping warm for 8 minutes, the final adjusted original molten iron composition is C 3.75%, Si 2.10%, Mn 0.251%, P 0.020%, S0.018%, Cr 0.050%. The power is cut off and the material is added to quickly cool down to the furnace discharge temperature (1490°C to 1510°C). At this temperature, the molten iron can be discharged and transferred;

[0039] c. Pretreatment: 6.8 kg of electrolytic copper and 2 kg of silicon carbide pretreatment agent are placed in a wire feeding spheroidizing bag with a height-to-diameter ratio of 1.6. The spheroidizing bag can be taken out of the furnace only when the temperature drops to 1500±10°C. The weight of the molten iron is 1000±50 kg. The molten iron in step b is discharged and transferred to the spheroidizing bag.

[0040] d. Spheroidizing treatment: The temperature of the spheroidizing bag filled with molten iron is measured before it is transferred to the spheroidizing chamber. After testing, the temperature before entering the station is 1480℃. It enters the spheroidizing chamber and then performs single-wire feeding spheroidization, adding 0.8% to 0.95% Mg30-containing spheroidizing cored wire; according to the distribution ratio, quality and characteristics of each group of the above molten iron, the wire feeding speed is set to 28.8m / min and the wire feeding length is 21.6m.

[0041] e. Inoculation treatment: After spheroidization is completed, the spheroidizing ladle is transferred out of the spheroidizing chamber. After slag removal, a 0.2% by weight Ba-containing inoculant is poured into the spheroidizing ladle. After stirring evenly, the molten iron is poured into the pouring ladle, and the pouring ladle is transferred to the pouring station;

[0042] f. Pouring: During the entire pouring process, instantaneous inoculation is carried out. Along with the pouring of molten iron, 0.06% of Aiken 958 inoculant is evenly added for instantaneous inoculation. After pouring into the molding mold box, the casting needs to be kept warm in the mold cavity for 160 minutes. After the cooling time is greater than 130 minutes, the mold box is opened to prepare the ductile iron for the bridge housing casting.

[0043] After testing the chemical composition of the ductile iron used for the bridge housing casting, the mass percentage of each element is shown in Table 1, and the mechanical properties and metallographic structure test results of the bridge housing casting (the data are derived from the bulk sampling) are shown in Table 2.

[0044] Table 1 Chemical composition test results of ductile iron for bridge housing castings (%)

[0045] C Be Mn P S Mg Re Cr The 3.62 2.81 0.255 0.021 0.012 0.035 0.008 0.050 0.75

[0046] Table 2 Mechanical properties and metallographic structure test results

[0047]

[0048] In addition, the carbide and phosphorus eutectic contents are less than 2%.

[0049] The present invention uses a single-wire feeding spheroidizing method to produce a high-strength and high-toughness ductile iron QT700-10 bridge shell. During spheroidizing, the single-wire feeding length and feeding speed can be determined according to the molten iron composition, the temperature before the spheroidizing chamber, the amount of molten iron taken out, and the parameters of the spheroidizing cored wire.

[0050] Embodiment 2:

[0051] Embodiment 2 of the present invention discloses a method for preparing ductile iron for bridge housing castings, comprising the following steps:

[0052] a. Prepare raw materials: the raw materials include a first group of raw materials added to the smelting furnace, a second group of raw materials added to the spheroidizing bag, and an inoculant used in the pouring process, wherein the weight percentage of each component in the first group of raw materials is: 10% to 30% pig iron, 30% to 60% scrap steel, 15% to 40% recycled materials; 1.5% to 2.5% carburizer, 1.5% to 2.0% 75 ferrosilicon; the weight percentage of each component in the second group of raw materials relative to the weight of the molten iron in the spheroidizing bag is: 0.4% to 0.8% electrolytic copper, 0.1% to 0.4% silicon carbide pretreatment agent, 0.8% to 0.95% spheroidizing cored wire containing Mg30, and 0.2% to 0.6% Ba-containing inoculant;

[0053] The percentage of the inoculant relative to the weight of the molten iron is: 0.05% to 0.15% Aiken 958 flow inoculant;

[0054] b. Melting: 19.15% pig iron, 19.15% recycled materials, 57.44% scrap steel and 2.35% carburizer are added to the smelting furnace to melt the original molten iron. At the end of smelting, 1.91% ferrosilicon is added to increase silicon. The temperature is raised to 1540°C. After standing at high temperature and keeping warm for 10 minutes, the final adjusted original molten iron composition is C 3.78%, Si 2.05%, Mn 0.227%, P 0.023%, S 0.016%, Cr 0.046%. The power is cut off and the material is added to quickly cool down to the furnace discharge temperature (1490°C to 1510°C). At this temperature, the molten iron can be discharged and transferred;

[0055] c. Pretreatment: Place 7 kg of electrolytic copper and 2 kg of silicon carbide pretreatment agent in a wire feeding spheroidizing bag with a height-to-diameter ratio of 1.6. Wait until the temperature drops to 1500 ± 10 °C before taking it out of the furnace. The weight of the molten iron is 1000 ± 50 kg. Discharge the molten iron in step b and transfer it to the spheroidizing bag.

[0056] d. Spheroidizing treatment: The temperature of the spheroidizing bag filled with molten iron is measured before it is transferred to the spheroidizing chamber. After testing, the temperature before entering the station is 1470℃. It enters the spheroidizing chamber and then performs single-wire wire feeding spheroidization, adding 0.8% to 0.95% Mg30-containing spheroidizing cored wire; according to the distribution ratio, quality and characteristics of each group of molten iron, the wire feeding speed is set to 28.2m / min and the wire feeding length is 21.3m.

[0057] e. Inoculation treatment: After spheroidization is completed, the spheroidizing ladle is transferred out of the spheroidizing chamber. After slag removal, a 0.3% by weight Ba-containing inoculant is poured into the spheroidizing ladle. After stirring evenly, the molten iron is poured into the pouring ladle, and the pouring ladle is transferred to the pouring station;

[0058] f. Pouring: During the entire pouring process, instantaneous inoculation is carried out. Along with the pouring of molten iron, 0.1% of Aiken 958 inoculant is evenly added for instantaneous inoculation. After pouring into the molding mold box, the casting needs to be kept warm in the mold cavity for 160 minutes. After the cooling time is greater than 130 minutes, the mold box is opened to prepare the ductile iron for the bridge housing casting.

[0059] After testing the chemical composition of the ductile iron used for the bridge housing casting, the mass percentage of each element is shown in Table 3, and the mechanical properties and metallographic structure test results of the bridge housing casting (the data are derived from the bulk sampling) are shown in Table 4.

[0060] Table 3 Chemical composition test results of ductile iron for bridge housing castings (%)

[0061] C Be Mn P S Mg Re Cr The 3.67 2.74 0.231 0.023 0.010 0.037 0.008 0.047 0.71

[0062] Table 4 Mechanical properties and metallographic structure test results

[0063]

[0064] In addition, the carbide and phosphorus eutectic contents are less than 2%.

[0065] Embodiment three:

[0066] Embodiment 3 of the present invention discloses a method for preparing ductile iron for bridge housing castings, comprising the following steps:

[0067] a. Prepare raw materials: the raw materials include a first group of raw materials added to the smelting furnace, a second group of raw materials added to the spheroidizing bag, and an inoculant used in the pouring process, wherein the weight percentage of each component in the first group of raw materials is: 10% to 30% pig iron, 30% to 60% scrap steel, 15% to 40% recycled materials; 1.5% to 2.5% carburizer, 1.5% to 2.0% 75 ferrosilicon; the weight percentage of each component in the second group of raw materials relative to the weight of the molten iron in the spheroidizing bag is: 0.4% to 0.8% electrolytic copper, 0.1% to 0.4% silicon carbide pretreatment agent, 0.8% to 0.95% spheroidizing cored wire containing Mg30, and 0.2% to 0.6% Ba-containing inoculant;

[0068] The percentage of the inoculant relative to the weight of the molten iron is: 0.05% to 0.15% Aiken 958 flow inoculant;

[0069] b. Melting: 28.88% pig iron, 19.25% recycled materials, 48.13% scrap steel and 1.87% carburizer are added to the smelting furnace to melt the original molten iron. At the end of smelting, 1.87% ferrosilicon is added to increase silicon. The temperature is raised to 1537°C. After standing at high temperature and keeping warm for 10 minutes, the original molten iron composition after final adjustment is C 3.80%, Si 2.08%, Mn 0.213%, P 0.027%, S 0.013%, Cr 0.040%. The power is cut off and the material is added to quickly cool down to the furnace discharge temperature (1490°C to 1510°C). At this temperature, the molten iron can be discharged and transferred;

[0070] c. Pretreatment: 6.8 kg of electrolytic copper and 2 kg of silicon carbide pretreatment agent are placed in a wire feeding spheroidizing bag with a height-to-diameter ratio of 1.6. The spheroidizing bag can be taken out of the furnace only when the temperature drops to 1500±10°C. The weight of the molten iron is 1000±50 kg. The molten iron in step b is discharged and transferred to the spheroidizing bag.

[0071] d. Spheroidizing treatment: The temperature of the spheroidizing bag filled with molten iron is measured before it is transferred to the spheroidizing chamber. After testing, the temperature before entering the station is 1467℃. It enters the spheroidizing chamber and then performs single-wire feeding spheroidization, adding 0.8% to 0.95% Mg30-containing spheroidizing cored wire; according to the distribution ratio, quality and characteristics of each group of molten iron, the wire feeding speed is set to 27.8m / min and the wire feeding length is 21.0m.

[0072] e. Inoculation treatment: After spheroidization is completed, the spheroidizing ladle is transferred out of the spheroidizing chamber. After slag removal, a 0.2% by weight Ba-containing inoculant is poured into the spheroidizing ladle. After stirring evenly, the molten iron is poured into the pouring ladle, and the pouring ladle is transferred to the pouring station;

[0073] f. Pouring: During the entire pouring process, instantaneous inoculation is carried out. Along with the pouring of molten iron, 0.12% of Aiken 958 inoculant is evenly added for instantaneous inoculation. After pouring into the molding mold box, the casting needs to be kept warm in the mold cavity for 160 minutes. After the cooling time is greater than 130 minutes, the mold box is opened to prepare the ductile iron for the bridge housing casting.

[0074] After testing the chemical composition of the ductile iron used for the bridge housing casting, the mass percentage of each element is shown in Table 5, and the mechanical properties and metallographic structure test results of the bridge housing casting (the data are derived from the bulk sampling) are shown in Table 6.

[0075] Table 5 Chemical composition test results of ductile iron for bridge housing castings (%)

[0076] C Be Mn P S Mg Re Cr The 3.70 2.77 0.217 0.028 0.008 0.039 0.008 0.041 0.77

[0077] Table 6 Mechanical properties and metallographic structure test results

[0078]

[0079] In addition, the carbide and phosphorus eutectic contents are less than 2%.

[0080] The preparation method of ductile iron for bridge housing castings of the present invention adopts a wire feeding method instead of a punching method, so that the ductile iron bridge housing material can meet the requirements of tensile strength greater than or equal to 700MPa, elongation greater than or equal to 10%, spheroidization rate greater than or equal to level 2, graphite size 5 to 8, pearlite content 60% to 90%, carbide and phosphorus eutectic content less than 2%, and Brinell hardness 210HB to 290HB. The use of the ductile iron to cast the bridge housing increases the service life, reduces the overall weight of the bridge housing, shortens the spheroidization treatment time, reduces the manufacturing cost, and promotes the development of lightweight heavy trucks.

[0081] The technical solution of the present invention is described in detail above, but the present invention is not limited to the above embodiments. Those skilled in the art should understand that various changes made thereto in form and detail fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing ductile iron for bridge housing castings, characterized in that: The following steps are involved: a. Prepare raw materials: The raw materials include the first group of raw materials added to the smelting furnace, the second group of raw materials added to the spheroidizing bag, and the inoculant used in the pouring process. The weight percentage of each component in the first group of raw materials is: 10% to 30% pig iron, 30% to 60% scrap steel, 15% to 40% recycled materials; 1.5% to 2.5% carburizer, 1.5% to 2.0% 75 ferrosilicon; The weight percentage of each component in the second group of raw materials relative to the weight of the molten iron in the spheroidizing bag is: 0.4% to 0.8% electrolytic copper, 0.1% to 0.4% silicon carbide pretreatment agent, 0.8% to 0.95% spheroidizing core wire containing Mg30, and 0.2% to 0.6% Ba-containing inoculant; The percentage of the inoculant relative to the weight of the molten iron is: 0.05% to 0.15% Aiken 958 flow inoculant; b. Melting: adding the 10% to 30% pig iron, the 18% to 40% recycled materials, the 30% to 60% scrap steel and the 1.5% to 2.5% carburizer to the smelting furnace to melt the raw iron water, adding the 1.5% to 2.0% ferrosilicon to increase silicon at the end of smelting, heating to 1520° C. to 1550° C., standing at high temperature and keeping warm for 8 to 12 minutes, cutting off the power supply and adding materials to quickly cool down to the furnace discharge temperature (1490° C. to 1510° C.), at which temperature, the molten iron can be discharged and transferred; c. Pretreatment: placing the 0.4% to 0.8% electrolytic copper and the 0.1% to 0.4% silicon carbide pretreatment agent at the bottom of the spheroidizing ladle, and discharging the molten iron in step b and transferring it to the spheroidizing ladle; d. Spheroidizing treatment: before the spheroidizing bag filled with molten iron is transferred to the spheroidizing chamber, the temperature is measured, and the spheroidizing bag enters the spheroidizing chamber, and then single-wire feeding spheroidizing is performed, and the spheroidizing core wire containing 0.8% to 0.95% Mg30 is added; e. Inoculation treatment: After spheroidization is completed, the spheroidizing ladle is transferred out of the spheroidizing chamber, and after slag removal, a Ba-containing inoculant with a weight percentage of 0.2% to 0.6% is poured into the spheroidizing ladle, and after stirring evenly, the molten iron is poured into the pouring ladle, and the pouring ladle is transferred to the pouring station; f. Pouring: During pouring, 0.05% to 0.15% of Aiken 958 inoculant is evenly added along with the pouring molten iron flow for instantaneous inoculation. After pouring into the molding mold box, the mold box is opened after cooling for a period of time to prepare the ductile iron for the bridge housing casting.

2. The method for preparing ductile iron for axle housing castings according to claim 1, characterized in that: The mass percentage of each element component in the prepared ductile iron for the bridge housing casting is: C3.3%-3.9%, Si2.3%-2.9%, Mn0.2-0.8%, S<0.030%, P<0.04%, Cu0.4%-0.8%, Cr<0.08%, Mg 0.03%-0.08%, Re≤0.02%, and the balance is Fe.

3. The method for preparing ductile iron for axle housing castings according to claim 1, characterized in that: The mechanical properties of the ductile iron used for the bridge housing casting are as follows: tensile strength is greater than or equal to 700 MPa, elongation is greater than or equal to 10%, spheroidization rate level is greater than or equal to level 2, graphite size is 5 to 8, pearlite content is 60% to 90%, carbide and phosphorus eutectic content is less than 2%, and Brinell hardness is 210HB to 290HB.

4. The method for preparing ductile iron for bridge housing castings according to claim 1, characterized in that: The aspect ratio of the spheroidized package is 1.

6.

5. The method for preparing ductile iron for axle housing castings according to claim 1, characterized in that: In the above step f, 0.05% to 0.15% of Aiken 958 inoculant is uniformly added with the pouring molten iron flow, and the cooling time is controlled to be greater than 130 minutes.

6. The method for preparing ductile iron for axle housing castings according to claim 5, characterized in that: Ensure that the bridge housing casting is kept warm in the cavity of the forming mold box for 160 minutes.

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