A rare earth alloyed inoculant

Abstract

The application relates to the technical field of casting materials, and particularly discloses a rare earth alloyed inoculant. The rare earth alloyed inoculant adds rare earth elements to a traditional silicon-based inoculant, the rare earth elements can react with S, O and N in iron liquid to generate rare earth sulfide, oxide and nitride particles, and the particles can be used as nucleation substrates of graphite. Since the melting points of the particles are higher than the temperature of the iron liquid, the nucleation quantity of the rare earth inoculant is not only large but also has a long anti-degradation time, so that the inoculation effect can be ensured, the graphite is finer, and the strength of a casting is improved.

Description

Technical Field

[0001] This application relates to the field of casting materials technology, and more specifically, to a rare earth alloying inoculant. Background Technology

[0002] Cast iron refers to a general term for cast iron-carbon alloys with a carbon content of 2.06% or higher. It is typically produced by smelting pig iron, scrap steel, and ferroalloys in varying proportions. It can be generally classified into gray cast iron, ductile cast iron, vermicular graphite cast iron, malleable cast iron, alloy cast iron, white cast iron, and inoculated cast iron. Inoculated cast iron refers to gray cast iron that has undergone inoculation treatment. Inoculation treatment involves adding a small amount of inoculant to the molten iron before pouring, forming numerous highly dispersed refractory particles. These particles become the nuclei for graphite crystallization, promoting graphite nucleation and resulting in a fine pearlite matrix and finely and uniformly distributed flake graphite. After inoculation treatment, the matrix structure, graphite flake shape, and eutectic clusters of the cast iron are refined, thus inoculated cast iron has superior strength and toughness compared to ordinary gray cast iron. Because inoculated cast iron possesses high strength and toughness, and its microstructure and properties are relatively uniform across castings of different wall thicknesses, it is often used to manufacture large castings with high mechanical performance requirements and significant variations in cross-sectional dimensions.

[0003] Ferrosilicon alloys used as inoculants are typically ferroalloys containing 75% silicon. Using this inoculant yields a gray cast iron structure and refines graphite flakes, reducing the destructive effect of graphite on the matrix. Its significant advantages include low wall thickness sensitivity and uniform microstructure throughout the casting. Barium silicon inoculant is a long-acting inoculant with a strong ability to promote graphitization, improving the morphology and distribution of graphite in thin-walled castings, and also slowing down inoculation fading. Generally, barium silicon inoculant has a stronger ability to increase the number of eutectic clusters and improve cross-sectional uniformity than ferrosilicon.

[0004] Regarding the aforementioned technologies, the inventors believe that traditional silicon-based inoculants are unable to fully overcome the harmful effects of sulfur, resulting in poor melting effects in molten iron and limited inoculation effects, thus failing to adequately improve the overall performance of castings. Summary of the Invention

[0005] In related technologies, traditional silicon-based inoculants struggle to overcome the harmful effects of sulfur, resulting in poor melting in molten iron and limited inoculation effects, thus failing to adequately improve the overall performance of castings. To address this deficiency, this application provides a rare-earth alloying inoculant.

[0006] This application provides a rare earth alloying inoculant, employing the following technical solution:

[0007] A rare earth alloying inoculant, wherein the inoculant comprises the following components by weight percentage: silicon 65.0-70.0%, calcium 1.5-2.5%, manganese 4.0-6.0%, chromium 6.0-8.0%, rare earth elements 0.8-1.2%, and the balance being iron and unavoidable trace elements; the unavoidable trace elements include aluminum, wherein the weight percentage of aluminum in the inoculant is <1.0%.

[0008] By adopting the above technical solution, this application adds rare earth elements, chromium and manganese to the inoculant, where manganese and chromium are alloying elements, and rare earth elements work synergistically with calcium, silicon and iron to play an inoculation role. The addition of rare earth elements can produce the following effects: (1) Rare earth elements can react with sulfur, oxygen and nitrogen in molten iron to generate rare earth sulfides, rare earth oxides and rare earth nitride particles, which can serve as nucleation substrates for graphite. Since the melting point of these particles is higher than the temperature of molten iron, the number of nuclei inoculated by rare earth elements is not only large, but also has a long anti-fading time, thus ensuring the inoculation effect and making the graphite finer. Fine graphite can optimize the internal structure of cast iron, make the carbide distribution more uniform, thereby improving the mechanical properties of cast iron, increasing the tensile strength, yield strength and hardness of cast iron, and inhibiting the surface oxidation of cast iron, reducing the generation of fatigue cracks. (2) Rare earth elements can also enhance the corrosion resistance of cast iron by forming a dense oxide film on the surface of cast iron, preventing the intrusion of corrosive media, thereby extending the service life of cast iron. (3) Rare earth elements can improve the machinability of cast iron, resulting in better surface quality, reduced cutting forces, fewer chips and defects, and improved machining efficiency and quality. Through these effects, the application of rare earth elements in inoculated cast iron can significantly improve the performance and machining quality of cast iron, meeting different application requirements.

[0009] Chromium is a strong carbide stabilizing element. The addition of chromium can produce the following effects: (1) It can form a dense oxide layer on the surface of cast iron, significantly improving the corrosion resistance of cast iron. (2) Chromium can form chromium carbide compounds with high hardness, thereby improving the hardness and strength of cast iron. (3) The addition of chromium can make the grains of cast iron finer, which not only helps to improve the mechanical properties of cast iron, but also improves its casting performance. Fine grains can reduce surface defects of castings and improve the surface quality of castings. (4) Chromium can increase the solidification temperature of iron-carbon-silicon ternary alloys, reduce the depth of molten iron, prevent surface defects of castings, and thus improve the surface quality of castings. In addition, chromium can stabilize cementite and reduce the formation of non-fine graphite, thereby improving the wear resistance of cast iron.

[0010] Manganese is an alloying element that can counteract the harmful effects of sulfur and improve the melting characteristics of inoculants in molten iron. The addition of manganese can produce the following effects: (1) It refines the grains of the casting, thereby increasing the hardness and wear resistance of the casting, significantly improving the hardness and strength of the casting, enabling it to withstand greater mechanical stress and wear, and extending the service life of the casting. (2) It improves the toughness of cast iron, giving it better impact and shock resistance, which is especially important for castings that need to withstand dynamic loads. (3) Manganese can combine with carbon in cast iron to form cementite, which makes the microstructure of the casting more dense and uniform. An appropriate amount of manganese can adjust the ratio of ferrite and pearlite in the casting, thereby changing the performance of the casting.

[0011] The inoculant of this application not only overcomes the harmful effects of sulfur, but also has a low melting point, dissolving in molten iron at 1180-1200℃, thus making it easier to exert its inoculation effect during the casting process. With the synergistic effect of rare earth elements, chromium, manganese, and other elements, the rare earth alloying inoculant of this application combines alloying and inoculation functions, exhibiting good anti-fading ability. This is beneficial for obtaining high-strength, high-hardness, and high cross-sectional uniformity cast iron parts, effectively improving the overall performance of the castings and overcoming the shortcomings of traditional inoculants.

[0012] Preferably, the inoculant comprises the following components by weight percentage: silicon 65.0-67.0%, calcium 1.5-2.0%, manganese 4.0-5.0%, chromium 6.0-7.0%, rare earth elements 0.8-1.0%, and the balance being iron and unavoidable trace elements.

[0013] Preferably, the inoculant comprises the following components by weight percentage: silicon 66.0-68.0%, calcium 1.7-2.2%, manganese 4.5-5.5%, chromium 6.5-7.5%, rare earth elements 0.9-1.1%, and the balance being iron and unavoidable trace elements.

[0014] Preferably, the inoculant comprises the following components by weight percentage: silicon 67.0-70.0%, calcium 1.8-2.5%, manganese 5.0-6.0%, chromium 7.0-8.0%, rare earth elements 1.0-1.2%, and the balance being iron and unavoidable trace elements.

[0015] Preferably, the inoculant is made from the following raw materials: ferrosilicon, ferromanganese, ferrochrome, rare earth ferrosilicon, and silicon-calcium alloy.

[0016] By adopting the above technical solution, this application uses ferromanganese to provide manganese, ferrochrome to provide chromium, and rare earth ferrosilicon to provide rare earth elements. Rare earth ferrosilicon is a rare earth alloy with a relatively large supply and low price. Its melting point is 1082-1089℃, and its average specific gravity is 4.7 g / cm³. Rare earth elements themselves have the effect of promoting white cast iron formation; however, when the amount of rare earth added is less than the "critical addition amount," rare earth compounds are formed due to the deoxidation and desulfurization effects of rare earths. The formation of rare earth compounds not only causes rare earths to lose their original effect of promoting white cast iron formation, but also reduces the strong inhibitory effect of impurities such as oxygen and sulfur on graphitization. Simultaneously, rare earth compounds are refractory small particles in molten iron; these particles can act as nuclei for graphitization, resulting in a reduction in the white cast iron content. Therefore, rare earth ferrosilicon alloy is actually a composite inoculant. It not only possesses the inoculation effects of ferrosilicon and calcium silicon, but also purifies molten iron, improves casting performance, refines the graphite and matrix structure, makes the distribution more uniform, reduces the tendency to undercool, and improves the mechanical properties and wear resistance of cast iron. Generally speaking, if it is a ferrosilicon inoculant, its addition amount must be properly controlled. Too much addition will not only fail to achieve good results but will also reduce the strength of the cast iron. Compared with ferrosilicon, the negative impact of rare earth ferrosilicon addition on the inoculation effect is less significant, thus helping to maintain good strength properties in cast iron.

[0017] Preferably, the ferrosilicon comprises FeSi90Al1.5 and FeSi75Al0.5-A.

[0018] By adopting the above technical solution, since rare earth ferrosilicon is added in this application, the amount of ferrosilicon can be controlled, which can effectively avoid the situation where the casting strength is poor when the ferrosilicon content is too high.

[0019] Preferably, the ferromanganese is Mn88C0.2.

[0020] By adopting the above technical solution, ferromanganese can be used as an inoculant and spheroidizing agent for ductile iron, preventing carbide formation and promoting graphite precipitation, thereby shortening the spheroidizing time, improving the quality and performance of cast iron. In addition, the addition of ferromanganese can reduce clogging of the smelting furnace nozzles, effectively extending the service life of the smelting furnace.

[0021] Preferably, the ferrochrome is FeCr65C0.06.

[0022] By adopting the above technical solution, the tendency of ferrochrome to turn white can be effectively neutralized by rare earth elements, which helps to improve the overall performance of the castings.

[0023] Preferably, the inoculant is made from the following raw materials in parts by weight: 260-272 parts of FeSi90Al1.5 ferrosilicon, 498-520 parts of FeSi75Al0.5-A ferrosilicon, 41-62 parts of Mn88C0.2 ferromanganese, 90-119 parts of FeCr65C0.06 ferrochromium, 36-53 parts of rare earth ferrosilicon, and 19-46 parts of silicon-calcium alloy.

[0024] By adopting the above technical solution, this application has optimized the raw material composition of the inoculant, which helps to improve the overall performance of the casting.

[0025] In summary, this application has the following beneficial effects:

[0026] 1. The rare earth alloying inoculant of this application adds rare earth elements to traditional silicon-based inoculants. These rare earth elements can react with S, O, and N in molten iron to generate rare earth sulfides, oxides, and nitride particles, which can serve as a nucleation substrate for graphite. Because the melting point of these particles is higher than the temperature of the molten iron, the number of nuclei formed by rare earth inoculation is not only greater but also has a longer resistance to fading, thus ensuring the inoculation effect, resulting in finer graphite and improved casting strength.

[0027] 2. The inoculant of this application not only overcomes the harmful effects of sulfur, but also has a lower melting point, making it easier to exert its inoculation effect during the casting process. Under the synergistic effect of rare earth elements, chromium, manganese, and other elements, the rare earth alloying inoculant of this application has both alloying and inoculation functions, exhibits good anti-fading ability, and is conducive to obtaining cast iron parts with high hardness and high cross-sectional uniformity. It can fully improve the comprehensive performance of castings, thereby overcoming the defects of traditional inoculants.

[0028] 3. The rare earth alloying inoculant of this application can promote graphitization, making the graphite morphology in cast iron finer and more uniformly distributed, thereby improving the mechanical properties of cast iron.

[0029] 4. The rare earth alloying inoculant of this application can eliminate or reduce the tendency of defects in cast iron and avoid problems such as cold shuts and slag inclusions.

[0030] 5. The rare earth alloying inoculant of this application can refine grains and improve matrix structure, significantly improve the mechanical properties of gray cast iron, reduce the wall thickness sensitivity of castings, and reduce the differences in microstructure and hardness between thin and thick walls.

[0031] 6. When manufacturing cylinder blocks and cylinder heads for automobile or tractor engines, the rare earth alloying inoculant of this application can reduce processing defects such as inclusions or micro-shrinkage. Detailed Implementation

[0032] The present application will be further described in detail below with reference to the embodiments and comparative examples. All raw materials involved in the present application can be obtained commercially.

[0033] Example

[0034] Examples 1-6

[0035] The following description uses Example 1 as an example.

[0036] Example 1

[0037] In this embodiment, the raw materials used to prepare the rare earth alloying inoculant are as follows:

[0038] GB / T2272-2009 Ferrosilicon, Grade: FeSi90Al1.5, Chemical Composition (%): Si, 87.0-95.0; Al < 1.5; Ca < 1.5; Mn < 0.4; Cr < 0.2; P < 0.040; S < 0.020; C < 0.20; Balance Fe.

[0039] 《GB / T2272-2009 Ferrosilicon》, grade FeSi75Al0.5-A, chemical composition (%): Si, 74.0-80.0; Al<0.5; Ca<1.0; Mn<0.4; Cr<0.3; P<0.035; S<0.020; C<0.10; balance Fe.

[0040] GB / T 3795-2014 Ferromanganese Low carbon ferromanganese, grade: Mn88C0.2, chemical composition (%): Mn, 85.0-92.0; C≤0.2; Si≤1.0-2.0; P≤0.10-0.20; S≤0.02; balance Fe.

[0041] The chemical composition (%) of ferrochrome grade FeCr65C0.06 in GB / T 5683-2008 is as follows: Cr, 60.0~70.0; C<0.06; Si<1.0; P<0.03; S<0.025; balance Fe.

[0042] 《GB / T4137-2004 Rare Earth Ferrosilicon Alloys》Grade: 195023. Chemical composition (%): RE, 21.0-24.0; Si < 44.0; Mn < 2.5; Ca < 5.0; Ti < 2.0; Balance Fe.

[0043] The chemical composition (%) of grade Ca28Si60 in YB / T 5051-2007 silicon-calcium alloy is as follows: Ca < 28.0; Si, 50.0-65.0; C < 1.0; Al < 2.4; P < 0.04; S < 0.06.

[0044] This embodiment provides a rare earth alloying inoculant, which comprises the following components by weight percentage: 65.0% silicon, 1.5% calcium, 4.0% manganese, 6.0% chromium, 0.8% rare earth elements, with the balance being iron and unavoidable trace elements, the unavoidable trace element being aluminum, which accounts for 0.6% by weight.

[0045] This embodiment provides a method for preparing a rare earth alloying inoculant, including the following steps:

[0046] (1) Weigh 260kg of ferrosilicon FeSi90Al1.5, 498kg of ferrosilicon FeSi75Al0.5-A, 19kg of silicon-calcium alloy, 41kg of manganese-iron, 90kg of ferrochrome, and 36kg of rare earth ferrosilicon alloy, dry them and crush them into particles with an average particle size of 1mm.

[0047] (2) Put the particles obtained in step (1) into a mixer and stir at a speed of 10 r / min for 10 min to obtain a rare earth alloying inoculant.

[0048] As shown in Table 1, the main difference between Examples 1-6 lies in the elemental composition and raw material ratio of the rare earth alloying inoculant.

[0049] Table 1. Elemental composition and raw material ratio of rare earth alloying inoculants

[0050]

[0051]

[0052] Comparative Example

[0053] Comparative Example 1

[0054] This comparative example uses commercially available ferrosilicon alloy particles (average particle size 1 mm) as the inoculant. The ferrosilicon alloy grade is FeSi75Al0.5-A, which conforms to the requirements of GB / T2272-2009 Ferrosilicon. According to the regulations, its chemical composition (%) is as follows: Si, 74.0-80.0; Al < 0.5; Ca < 1.0; Mn < 0.4; Cr < 0.3; P < 0.035; S < 0.020; C < 0.10; balance Fe.

[0055] Comparative Example 2

[0056] This comparative example uses commercially available barium silicon inoculant (average particle size 1 mm). The elemental composition of the barium silicon inoculant is as follows: silicon 75%, barium 4.0%, calcium 1.8%, aluminum 1.4%, with the balance made up to 100% by iron.

[0057] Performance testing methods

[0058] HT200 gray cast iron, conforming to GB / T 9439-2023 standard for gray cast iron parts, was used as the test material. Its chemical composition was: carbon 3.2%, silicon 2.0%, manganese 0.8%, phosphorus 0.04%, sulfur 0.08%, with the balance being iron. The HT200 gray cast iron was melted in an electric furnace to 1540℃. After holding the molten iron at 1540℃ for 5 minutes, an inoculant equivalent to 0.35% of the total weight of the molten iron was added to the bottom of the ladle. The molten iron was then cooled to 1510℃ and poured into the ladle. After the reaction was complete, the slag was removed, and the ladle was then transported to the casting machine for casting.

[0059] Tensile tests were conducted using specimens prepared from casting test bars with cooling conditions similar to those of the castings. Type B specimens were used in the tensile tests, and the results of the tensile strength tests are shown in Table 2.

[0060] Table 2 Tensile Strength

[0061]

[0062]

[0063] As can be seen from Examples 1-6 and Comparative Examples 1-2, and Table 2, the tensile strength measured in Examples 1-6 is higher than that in Comparative Examples 1 and 2. This is because the inoculant of this application provides heterogeneous nucleation sites for the molten iron, achieving the purpose of refining grains, improving microstructure, and enhancing material properties. Furthermore, the inoculant of this application possesses superior characteristics compared to traditional inoculants, such as rapid dissolution, high absorption efficiency, and numerous nucleation sites, resulting in refined microstructure of gray cast iron and improved tensile strength, hardness, and other properties. After inoculation, the mechanical properties of HT200 gray cast iron have reached the level of HT250 gray cast iron.

[0064] The differences between the probiotic in this application and traditional probiotics are mainly in the following aspects:

[0065] Firstly, this application adds rare earth elements to traditional silicon-based inoculants and introduces alloying elements. Through the synergistic effect of rare earth elements, chromium, manganese, and other elements, the rare earth alloying inoculant of this application possesses both alloying and inoculation functions, exhibiting good anti-fading ability. This is beneficial for obtaining cast iron parts with high hardness and high cross-sectional uniformity, and can significantly improve the overall performance of castings even with relatively low addition amounts. For traditional inoculants, sulfur in cast iron is detrimental to strength improvement, while manganese can counteract the harmful effects of sulfur, thereby improving the melting characteristics of the inoculant in molten iron. The inoculant of this application not only overcomes the harmful effects of sulfur but also has a low melting point, dissolving in molten iron at 1180-1200℃. Therefore, it more easily exerts its inoculation effect during the casting process, overcoming the shortcomings of traditional inoculants.

[0066] Secondly, rare earth elements can react with sulfur, oxygen, and nitrogen in molten iron to form rare earth sulfides, rare earth oxides, and rare earth nitride particles. These particles can serve as a nucleation substrate for graphite. Because the melting point of these particles is higher than the temperature of molten iron, the number of nuclei formed by rare earth elements is not only large, but also has a long resistance to fading, thus ensuring effective inoculation and resulting in finer graphite. Fine graphite optimizes the internal structure of cast iron, making the carbide distribution more uniform, thereby improving the mechanical properties of cast iron, increasing its tensile strength, yield strength, and hardness, while also inhibiting surface oxidation and reducing fatigue crack formation. Meanwhile, manganese improves the toughness of cast iron, giving it better impact and shock resistance, which is particularly important for castings that need to withstand dynamic loads.

[0067] Thirdly, rare earth elements can improve the machinability of cast iron, resulting in better surface quality, reduced cutting forces, fewer chips and defects, and improved machining efficiency and quality. Chromium, as a strong carbide stabilizing element, can make the grains of cast iron finer, which not only helps improve the mechanical properties of cast iron but also its casting performance. Fine grains can reduce surface defects in castings. Chromium can increase the solidification temperature of iron-carbon-silicon ternary alloys, reduce the depth of molten iron, and prevent surface defects in castings. Through synergistic effects with rare earth elements, it improves the surface quality of castings. Manganese can combine with carbon in cast iron to form cementite, which makes the microstructure of castings denser and more uniform. Appropriate amounts of manganese can adjust the ratio of ferrite and pearlite in castings, thereby changing the properties of the castings.

[0068] Fourthly, rare earth elements can prevent the intrusion of corrosive media by forming a dense oxide film on the surface of cast iron, significantly improving the corrosion resistance of cast iron. Chromium can also form a dense oxide film on the surface of cast iron. At the same time, chromium can stabilize cementite and reduce the formation of non-refined graphite, and can form high-hardness chromium carbide compounds, thereby improving the hardness and strength of cast iron and enhancing its wear resistance. Manganese, by refining the grains of castings, can improve the hardness and wear resistance of castings, significantly increasing their hardness and strength, enabling them to withstand greater mechanical stress and wear. The synergistic effect of these three elements effectively extends the service life of cast iron.

[0069] The above embodiments are merely explanations of this application and are not intended to limit it. After reading this specification, those skilled in the art can make modifications to the embodiments of this application without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of this application.

Claims

1. A rare earth alloying inoculant, characterized in that, The inoculant comprises the following components by weight percentage: silicon 65.0-70.0%, calcium 1.5-2.5%, manganese 4.0-6.0%, chromium 6.0-8.0%, rare earth elements 0.8-1.2%, with the balance being iron and unavoidable trace elements; the unavoidable trace elements include aluminum, and the weight percentage of aluminum in the inoculant is <1.0%; The inoculant is made from the following raw materials: ferrosilicon, ferromanganese, ferrochrome, rare earth ferrosilicon, and silicon-calcium alloy; The ferrosilicon comprises FeSi90Al1.5 and FeSi75Al0.5-A; The inoculant is made from the following raw materials in parts by weight: 260-272 parts of FeSi90Al1.5 ferrosilicon, 498-520 parts of FeSi75Al0.5-A ferrosilicon, 41-62 parts of Mn88C0.2 ferromanganese, 90-119 parts of FeCr65C0.06 ferrochromium, 36-53 parts of rare earth ferrosilicon, and 19-46 parts of silicon-calcium alloy.

2. The rare earth alloying inoculant according to claim 1, characterized in that, The inoculant comprises the following components by weight percentage: silicon 65.0-67.0%, calcium 1.5-2.0%, manganese 4.0-5.0%, chromium 6.0-7.0%, rare earth elements 0.8-1.0%, with the balance being iron and unavoidable trace elements.

3. The rare earth alloying inoculant according to claim 1, characterized in that, The inoculant comprises the following components by weight percentage: silicon 66.0-68.0%, calcium 1.7-2.2%, manganese 4.5-5.5%, chromium 6.5-7.5%, rare earth elements 0.9-1.1%, with the balance being iron and unavoidable trace elements.

4. The rare earth alloying inoculant according to claim 1, characterized in that, The inoculant comprises the following components by weight percentage: silicon 67.0-70.0%, calcium 1.8-2.5%, manganese 5.0-6.0%, chromium 7.0-8.0%, rare earth elements 1.0-1.2%, with the balance being iron and unavoidable trace elements.

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