CN116441496B - High-efficiency inoculant containing bismuth oxide for large-section ductile iron castings - Google Patents

High-efficiency inoculant containing bismuth oxide for large-section ductile iron castings Download PDF

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CN116441496B
CN116441496B CN202310307772.9A CN202310307772A CN116441496B CN 116441496 B CN116441496 B CN 116441496B CN 202310307772 A CN202310307772 A CN 202310307772A CN 116441496 B CN116441496 B CN 116441496B
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iron
silicon
inoculant
barium
molten iron
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CN116441496A (en
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赵平
倪钧
马寒坤
李振业
郭利霞
张亚南
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Inner Mongolia Shengquan Keliyuan New Material Technology Co ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D1/00—Treatment of fused masses in the ladle or the supply runners before casting
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/10—Making spheroidal graphite cast-iron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/02—Making non-ferrous alloys by melting
    • C22C1/03—Making non-ferrous alloys by melting using master alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C28/00—Alloys based on a metal not provided for in groups C22C5/00 - C22C27/00
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C22C33/06—Making ferrous alloys by melting using master alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/08—Making cast-iron alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)

Abstract

The invention discloses a high-efficiency inoculant for large-section ductile iron castings containing bismuth element oxide, which comprises, by mass, 30% -75% of Si,0% -10% of Sn,0.5% -10% of Bi,0.1% -5.0% of rare earth, 2.0% -8.0% of Ba,0% -5.0% of O,1% of impurities, and the balance of Fe, wherein rare earth metal is lanthanum, cerium or yttrium. Sequentially adding pig iron, ferrosilicon, a silicon-barium intermediate alloy and rare earth metal into an intermediate frequency furnace for smelting, carrying out slag skimming when the raw materials are completely melted into molten iron to form a homogeneous molten state, adding granular metal bismuth oxide and metal tin when the temperature of the molten iron reaches 1300-1350 ℃, and increasing the power of the intermediate frequency furnace to rapidly raise the temperature in the furnace to about 1400 ℃; and reducing the power of the intermediate frequency furnace, pouring molten iron into a spindle disk, naturally cooling to normal temperature, and then completely solidifying the molten iron, and manually drawing the inclined spindle disk into an iron tank, wherein the thickness of the spindle disk is 30-70 mm. The high-efficiency inoculant prepared by the method can be applied to spheroidal graphite cast iron, and has strong mechanical properties such as tensile strength, yield strength, elongation after fracture, reduction of area and the like.

Description

High-efficiency inoculant containing bismuth oxide for large-section ductile iron castings
Technical Field
The invention belongs to the technical field of production and preparation of large-section ductile iron castings, and in particular relates to an inoculant for large-section ductile iron castings containing bismuth oxide.
Background
The advent, application and development of spheroidal graphite cast iron can be said to be one of the most important technologies in the field of materials since the last century. Since the advent of the past, spheroidal graphite cast iron has been widely used in place of gray cast iron, wrought cast iron and cast steel in many ways, and is known as the "best" metal in both worlds, i.e., not only has the excellent corrosion resistance of conventional cast iron, but also has the strength properties of shoulder cast steel.
The existence forms of C element in cast iron are various, such as flake graphite in gray cast iron, vermicular graphite in vermicular cast iron, spheroidal graphite in spheroidal graphite cast iron and the like. Because of the lesser degree of fracture of the matrix structure compared to other cast irons, spheroidal graphite can provide cast irons with excellent matrix structure strength while retaining better toughness.
With the continuous transition of the times, the rapid development of science and technology, the spheroidal graphite cast iron output of China is rapidly increased year by year, wherein the spheroidal graphite cast iron with large cross section for wind power, such as a hub, a gear box body, a base and the like, which work in a low-temperature environment for a long time, has a non-negligible proportion in cast iron production. The wall thickness of the large-section ductile cast iron casting is generally more than 100mm, the ductile cast iron casting has good mechanical properties, and has obvious advantages in the aspects of production cost, casting process and the like compared with a large-size cast iron casting, and perfect equivalent substitution of the large-size cast iron casting can be realized.
The production process of the nodular cast iron for large-section wind power generally comprises the following steps of chemical component proportioning, production smelting process, pretreatment, spheroidization, inoculation, ladle casting, complete solidification and the like. The inoculation treatment is one of the important steps, and a small amount of alloy material is added into molten iron in the production process of the spheroidal graphite cast iron, so that the problem of the tendency of the white mouth of the spheroidal graphite cast iron can be effectively reduced, the mechanical properties of the casting are improved, in addition, the microstructure of the spheroidal graphite cast iron is improved, more graphite nodule nuclei are formed, the graphite morphology is effectively improved, the precipitation of the complete graphite nodule is improved and adjusted, and the uniformity of matrix structure and graphite distribution is effectively ensured. Development and perfection of inoculants is critical to achieving inoculant processing.
CN 102296226a discloses a secondary inoculant for large ductile iron castings and a manufacturing method thereof. The secondary inoculant comprises, by mass, 65% -75% of Si element and 5% -10% of Sb element. The production process is that after mechanical crushing of Si-Fe alloy and Sb metal, the mechanical property of spheroidal graphite cast iron is improved in a mode of uniformly stirring and mixing in proportion, but the utilization rate of the mechanical crushing in the scheme to raw materials is lower, in addition, the proportion control during mixing and stirring cannot be accurate, and element segregation is easy to occur.
Disclosure of Invention
According to the defects existing in the prior art, the invention aims to research and develop a high-efficiency inoculant containing bismuth element oxide, and particularly relates to a high-efficiency inoculant mainly applied to wind-power large-section ductile iron castings and a preparation method thereof, wherein the high-efficiency inoculant is low in raw material preparation cost and good in economic benefit, and wind-power large-section castings obtained by the inoculant not only have excellent inoculation effects of high spheroidization rate, more graphite nodules, uniform graphite nodules distribution and the like, but also have excellent mechanical properties such as tensile strength, yield strength, area shrinkage and the like.
In order to achieve the aim, the invention relates to a high-efficiency inoculant for large-section ductile iron castings containing bismuth element oxide, which comprises, by mass, 30% -75% of Si,0% -10% of Sn,0.5% -10% of Bi,0.1% -5.0% of rare earth, 2.0% -8.0% of Ba,0% -5.0% of O,1% of impurities (such as free oxides, carbides, sulfides and the like), and the balance of Fe, wherein the rare earth is La and Ce or Y.
In the efficient inoculant, one part of the silicon element exists in the form of intermetallic compound of silicon and barium, and the other part exists in the form of intermetallic compound of silicon and iron.
The bismuth element exists in the high-efficiency inoculant in the form of oxide.
The rare earth elements in the efficient inoculant exist in the form of simple substances (such as lanthanum, cerium and yttrium) or intermetallic compounds (such as lanthanum cerium metal)
The effect of the silicon element in the high-efficiency inoculant has the effect of promoting the graphitization of castings, effectively promotes the formation of ferrite matrixes, effectively reduces the formation of distorted tissues in ductile iron castings with large wall thickness and large section, and ensures that graphite nodules are fine in size and uniformly dispersed. However, excessive silicon element can cause oxide to form in molten iron, so that more slag inclusion is generated, and the mechanical properties of ductile iron are seriously affected.
The barium element belongs to spheroidizing elements and plays a great role in the inoculation effect of ductile iron. In the process of forming the ductile iron, the barium element has the function of a deoxidizer, and the oxygen element of other metal oxides is forcibly extracted to generate the barium oxide. In addition, the oxide has better stability and certain effect on purifying molten iron.
Bismuth is generally considered as an interfering element for spheroidization, distorting graphite nodules and destroying the overall morphology of graphite. However, the addition amount of the bismuth element is strictly controlled, the content of the bismuth element in the casting is effectively regulated, the distortion of graphite nodules can be effectively inhibited, ferrite is slightly increased, the spheroidization rate is greatly improved, the number of graphite nodules is increased, and the addition amount of the bismuth element needs to be controlled within a certain range.
The addition amount of the rare earth element is strictly controlled, a small amount of the rare earth element can enable graphite to be more round, the spheroidization rate is effectively improved, particularly in large-section spheroidal graphite cast iron, the addition of the rare earth element can better reduce the formation of distorted graphite, and in addition, the neutralization effect of the rare earth element on trace elements is more remarkable.
Tin is generally considered to be an element that inhibits the appearance of the crumb-like graphite, and a certain amount of tin can effectively strengthen the austenitic shell of the outer layer of graphite during the formation of graphite spheres, thereby reducing or even eliminating the possibility of distortion of the graphite.
The high-efficiency inoculant disclosed by the invention comprises 30% -75% of silicon element, such as 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 75%, including the values listed in the above parts but not limited to, preferably 35% -70%, and the mass units are calculated in percentage.
The tin element in the high-efficiency inoculant disclosed by the invention is 0% -10%, for example, can be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, and the above parts cover the numerical values listed therein but are preferably 2% -8%, and the mass units are calculated in percentage.
The bismuth element in the high-efficiency inoculant disclosed by the invention is 0.5% -10%, for example, can be 0.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, and the above parts comprise the numerical values listed therein but are preferably 2% -8%, and the mass units are calculated in percentage.
The rare earth element in the efficient inoculant disclosed by the invention is 0.1% -5.0%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% and 5%, wherein the above parts cover the values but are not limited to the values listed therein, and preferably 0.1% -4.5%, and the mass units are calculated in percentage.
The barium element in the high-efficiency inoculant disclosed by the invention is 3.0% -8.0%, for example, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5% or 8%, and the above parts cover the values listed therein but are preferably 3.5% -6.5%, and the mass units are calculated in percentage.
The invention relates to a preparation method of a high-efficiency inoculant for ductile iron castings, which is mainly applied to wind power large-section ductile iron castings, and comprises the following steps:
step one: preparation of high quality silicon barium intermediate alloy for production of efficient inoculant
(1) Proportioning and smelting high-quality raw ore, oxide skin and blue carbon according to a certain mass percentage, wherein the raw ore is silica and barium stone, the oxide skin is generally composed of iron oxides such as ferroferric oxide, ferrous oxide, ferric oxide and the like, the smelting time is 120-150min, the mass percentage of the raw materials is 40-70% of silica, 4-20% of barium stone, 5-15% of oxide skin and 20-40% of blue carbon;
(2) And opening a tap hole of the submerged arc furnace after molten iron smelting is completed, and enabling molten iron to flow into a ladle. And (3) conveying the casting ladle to an ingot bed, pouring molten iron into the ingot bed to obtain an ingot block with a certain thickness, standing for 15-30 min, taking the ingot block out of the ingot bed after the molten iron is completely solidified, cooling to room temperature, crushing, and screening out the ingot block with a proper size.
The silicon-barium intermediate alloy in the invention is divided into the following components according to the difference of the total mass of the alloy occupied by the barium content: low barium alloy with the content of barium element of 0.5-7.9%, medium barium alloy with the content of barium element of 8-19.9%, and high barium alloy with the content of barium element of 19.9-30% in percentage by mass.
The raw material oxide skin used in the preparation step (1) of the silicon-barium intermediate alloy can be replaced by steel scraps, gas cutting slag and the like, and the raw material oxide skin comprises but is not limited to the listed raw material substitutes.
The thickness of the ingot in the step (2) of producing the silicon-barium-based intermediate alloy of the present invention is 30mm to 70mm, and may be, for example, 30mm, 35mm, 40mm, 45mm, 50mm, 55mm, 60mm, 65mm and 70mm, and the above-mentioned values are covered by the above-mentioned portions, but not limited thereto.
The size of the crushed and sieved ingot in step (2) for the preparation of the silicon-barium-based intermediate alloy according to the invention is in the range of 1mm to 40mm, for example 1mm, 5mm, 10mm, 20mm, 30mm and 40mm, the above-mentioned values being covered by the above-mentioned parts but not limited thereto.
Step two: adding silicon-barium intermediate alloy to prepare high-efficiency inoculant containing bismuth oxide
(1) Sequentially adding pig iron, ferrosilicon, a silicon-barium intermediate alloy and rare earth metal into an intermediate frequency furnace for smelting, removing suspended visible impurities in the molten iron after the raw materials are completely melted into a homogeneous molten state, removing slag from the molten iron, adding granular metal bismuth oxide and metal tin when the temperature of the molten iron reaches 1300-1350 ℃, and increasing the power of the intermediate frequency furnace to rapidly raise the temperature in the furnace to about 1400 ℃, wherein the mass percentage of the raw materials is 20-40% of pig iron, 40-60% of ferrosilicon, 5-20% of silicon-barium intermediate alloy, 2-10% of rare earth metal, 3-10% of metal bismuth oxide and 2-8% of metal tin. Bismuth oxide and metallic tin with lower melting points are added after other raw materials are melted, so that burning loss caused by high temperature can be effectively avoided.
(2) And reducing the power of the intermediate frequency furnace, pouring molten iron into a spindle disk, naturally cooling to normal temperature, and then completely solidifying the molten iron, and manually drawing the inclined spindle disk into an iron tank, wherein the thickness of the spindle disk is 30-70 mm.
(3) Crushing and screening the inoculated ingots to obtain the high-efficiency inoculant for wind power castings of various types.
The pig iron in the step (1) for preparing the efficient inoculant is a high-quality raw material with low sulfur and carbon content of 1.0-2.0%. The ferrosilicon is common ferrosilicon with silicon content of 70-75 percent in mass percent. The oxide of the raw bismuth is bismuth trioxide particles with a particle size of 1um-50um, and the average particle size can be, for example, 1um, 10um, 20um, 30um, 40um, 50um, and the above-mentioned parts include the values listed therein but not limited thereto.
The raw material rare earth metal in the preparation step (1) of the efficient inoculant provided by the invention is lanthanum cerium metal, and can also be elemental lanthanum and elemental cerium with the content of more than 99%, high-grade lanthanum cerium alloy and elemental yttrium.
The temperature of the molten iron in the step (1) of preparing the high-efficiency inoculant of the present invention may be 1300-1350 ℃, such as 1300 ℃, 1310 ℃, 1320 ℃, 1330 ℃, 1340 ℃ and 1350 ℃, and the above-mentioned parts include the values listed therein but not limited thereto.
The particle size of the high-efficiency inoculant finally obtained after crushing and screening in the step (3) of preparing the high-efficiency inoculant in the invention is 0.1mm-20mm, for example, 0.1mm-0.3mm, 0.3mm-1mm, 1mm-3mm, 3mm-10mm, 10mm-20mm, preferably 0.3mm-1mm.
The numerical ranges exemplified in the inoculant preparation step of the present invention, including other specific values not exemplified, are within the scope of the present invention.
The high-efficiency inoculant prepared by the method can obtain strong mechanical properties such as tensile strength, yield strength, elongation after fracture, reduction of area and the like, graphite of the ductile iron matrix structure is distributed uniformly, the number of graphite balls in unit area is large, the size of the graphite balls is small, and meanwhile, the spheroidization rate is effectively improved. In addition, the high-efficiency inoculant not only can be applied to large-section wind power spherical graphite castings, but also can be applied to various spherical castings with thinner wall thickness.
Drawings
FIG. 1 is a diagram of the stair-step specimen wood pattern modeling.
FIG. 2 is a metallographic microscope image of a ductile iron casting of a high efficiency inoculant.
Detailed Description
The invention is further illustrated by the following examples and figures.
Example 1
The embodiment provides a preparation method of a high-efficiency inoculant for large-section ductile iron castings containing bismuth oxide, which comprises the following specific steps:
step one: production and preparation of silicon-barium intermediate alloy
(1) Raw ore (e.g., silica, barium stone), scale, and semi-coke of the weight shown in table 1 for each batch were charged into a submerged arc furnace for a smelting time of 135min.
(3) The ladle is baked, so that the temperature difference between molten iron and the ladle is prevented from being large during pouring.
(4) After the molten iron is smelted, a plurality of tapping holes of the submerged arc furnace are opened by adopting 25mm threaded steel, and the molten iron flows into a ladle. The ladle is transported to the ingot bed, and molten iron is poured into the ingot bed, and intermittent pouring is adopted in the process to avoid the molten iron from sticking to the ingot bed.
(5) Standing for 20min to obtain silicon-barium alloy ingot with thickness of 30-40 mm, taking out the ingot from the ingot bed after the molten iron is completely solidified, cooling to room temperature, crushing, and sieving to obtain silicon-barium alloy ingot with thickness of 5-10 mm. The silicon-barium alloy prepared by the method has high quality and low impurity content.
TABLE 1
Step two: preparation of efficient inoculant containing bismuth oxide
(1) The low-sulfur and low-phosphorus high-quality pig iron, ferrosilicon (silicon content is larger than or equal to 70%), no. 3 silicon barium alloy and rare earth metal with the weight shown in the table 2 are sequentially added into an intermediate frequency furnace for smelting, and when the raw materials are completely melted into a homogeneous molten state, visible impurities suspended in the molten iron are removed for slag skimming.
(3) The temperature of the molten iron reaches 1310 ℃, high-grade granular bismuth trioxide and metallic tin with the particle size of 20-30 um are added, the power of an intermediate frequency furnace is increased, and the temperature in the furnace is rapidly increased to 1400 ℃.
(4) And reducing the power of the intermediate frequency furnace, pouring molten iron into a spindle disk, naturally cooling to normal temperature, and then completely solidifying the molten iron, and manually drawing the inclined spindle disk into an iron groove, wherein the thickness of the spindle disk is 30-40 mm.
(5) Crushing and screening the inoculated ingots to obtain the efficient inoculant for the wind power castings, wherein the granularity is 0.3mm-1mm. The compositions of the inoculant tested are shown in Table 3.
TABLE 2
TABLE 3 Table 3
Application example of the invention
In order to verify the actual application condition of the high-efficiency inoculant (the high-efficiency inoculant containing bismuth element) to large-section ductile iron castings, the high-efficiency inoculant is specially adopted to carry out the actual application test of ductile iron castings, and the raw materials are 9:1, adopting furan resin self-hardening sand molding in percentage by mass, selecting ladle internal spheroidization, adopting FeSiMg6RE0.5 as a spheroidizing agent model, adding 1.2%, covering primary inoculant with granularity of 5-10 mm on the spheroidizing agent, adopting a thermocouple temperature measuring instrument to detect the temperature of molten iron in the ladle, adopting No. 2 inoculant as a stream inoculant, and adding 0.15%.
Comparative example of the invention
In order to prove that the inoculant can be applied to large-section ductile iron castings and thin-wall ductile iron castings, the test adopts a step-type sample wood die shape shown in fig. 1, wherein the wall thickness of the wood die is respectively 50mm, 100mm, 200mm and 300mm, the length of each step is respectively 150mm, the height of each step is respectively 200mm, and the inoculant is used for analyzing and comparing the inoculant effect of the invention under the condition of different wall thicknesses by respectively sampling the steps of the sample wood die.
The method is characterized in that other inoculants commonly used in markets at home and abroad are selected for comparison, the sulfur-oxygen inoculant widely applied to large-section ductile cast iron in the market is specially selected for comparison of inoculation effect, the application conditions of the sulfur-oxygen inoculant are consistent with the application steps of the method, the sulfur-oxygen inoculant is only adopted during stream inoculation, and other application test conditions are the same.
Under the condition of different wall thicknesses, the mechanical properties and the ductile iron structure of the ductile iron castings of the bismuth element oxide high-efficiency inoculant and the sulfur-oxygen inoculant are compared, the data reliability is ensured to avoid errors, 3 experimental samples are taken out from the same wall thickness, and all experimental results are averaged for three times.
Specific data are shown in tables 4 and 5 below, with the ductile iron numbered with inoculant type used on the left, inoculant sulfur oxide 1, inoculant No. 2 in example 1 and wall thickness (mm) on the right.
Table 4 inoculation effect comparison
Table 5 ductile iron structure comparison
From the data analysis in Table 4, the high-efficiency inoculant provided by the invention has good mechanical properties under various wall thickness conditions, is suitable for wind power large-size spheroidal graphite castings, and can be also applied to thin-wall castings with wall thickness smaller than 100 mm. In comparison with sulfur-oxygen inoculants, the inoculant disclosed by the invention can exceed the sulfur-oxygen inoculant under the condition of various wall thicknesses, and the inoculant has a good inoculation effect. The graphite nodules in the invention have more graphite nodules compared with sulfur-oxygen inoculant, and the size of the graphite nodules can reach 4 grades.
In addition, microstructure observation is carried out on the ductile iron casting with the high-efficiency inoculant by adopting a metallographic microscope, as shown in an example 2, graphite nodules formed by the ductile iron casting prepared by adopting the method are uniform in distribution and more in graphite nodule number under the condition of different wall thicknesses, and the ductile iron casting has higher spheroidization rate.
The ductile iron casting for large-section wind power has higher requirement on low-temperature impact toughness, and according to the comparison of the low-temperature impact energy at-20 ℃ and-40 ℃ in Table 6, the performance of the ductile iron casting is better, and at-20 ℃, the impact energy can reach 27J under the condition of large-section wall thickness.
Table 6 low temperature impact energy comparison
Ductile iron numbering -20 ℃ Low-temperature impact energy (J) -40 ℃ Low-temperature impact energy (J)
1-50 10 7
1-100 12 10
1-200 12 11
1-300 20 10
2-50 12 11
2-100 20 17
2-200 21 24
2-300 27 20

Claims (3)

1. The efficient inoculant for the large-section ductile iron castings is characterized by comprising, by mass, 30% -75% of Si,0% -10% of Sn, 0.5% -10% of Bi,0.1% -5.0% of rare earth, 2.0% -8.0% of Ba,0% -5.0% of O,1% of impurities and the balance of Fe, wherein the rare earth metal is lanthanum, cerium or yttrium;
The silicon element exists in a form that one part exists in the form of intermetallic compound of silicon and barium, and the other part exists in the form of intermetallic compound of silicon and iron;
the bismuth exists in the form of oxide;
the rare earth element exists in a simple substance form or in an intermetallic compound form;
the preparation method of the ductile iron casting high-efficiency inoculant comprises the following steps:
(1) Sequentially adding pig iron, ferrosilicon, a silicon-barium intermediate alloy and rare earth metal into an intermediate frequency furnace for smelting, removing suspended visible impurities in the molten iron when the raw materials are completely molten into a homogeneous molten state, removing slag from the molten iron, adding granular metal bismuth oxide and metal tin when the temperature of the molten iron reaches 1300-1350 ℃, and increasing the power of the intermediate frequency furnace to rapidly raise the temperature in the furnace to about 1400 ℃, wherein the raw materials comprise 20-40% of pig iron, 40-60% of ferrosilicon, 5-20% of silicon-barium intermediate alloy, 2-10% of rare earth metal, 3-10% of metal bismuth oxide and 2-8% of metal tin by mass;
(2) Reducing the power of an intermediate frequency furnace, pouring molten iron into a spindle disk, naturally cooling to normal temperature, completely solidifying the molten iron, manually drawing the inclined spindle disk into an iron tank, and ensuring the thickness of the spindle disk to be 30-70 mm;
The preparation method of the silicon-barium intermediate alloy comprises the following steps:
(101) Proportioning and smelting high-quality raw ore, oxide skin and blue carbon according to a certain mass percentage, wherein the smelting time is 120-150min, the raw ore is silica and barium stone, and the raw material comprises 40-70% of silica, 4-20% of barium stone, 5-15% of oxide skin and 20-40% of blue carbon;
(102) Opening a tap hole of the submerged arc furnace after molten iron smelting is completed, enabling molten iron to flow into a ladle, conveying the ladle to an ingot bed, pouring the molten iron into the ingot bed to obtain ingot blocks with certain thickness, standing for 15-30 min, taking out the ingot blocks from the ingot bed after the molten iron is completely solidified, cooling to room temperature, crushing, and screening out the ingot blocks with proper size, thus obtaining the silicon-barium intermediate alloy.
2. The efficient inoculant for large-section ductile iron castings containing bismuth element oxides according to claim 1, wherein the pig iron in the step (1) is a low-sulfur pig iron raw material with a carbon content of 1.0% -2.0%, the silicon iron is ordinary silicon iron with a silicon content of 70% -75%, the metallic bismuth oxide is bismuth trioxide particles with a granularity of 1um-50um, and the rare earth metal is elemental lanthanum, elemental cerium, elemental yttrium or lanthanum-cerium alloy with a content of more than 99%.
3. The use of the high-efficiency inoculant for large-section ductile iron castings containing bismuth element oxides according to any one of claims 1 to 2 in large-section ductile iron castings of wind power type.
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