LU502567B1

LU502567B1 - Crystal-seed nodularizer, and preparation method and use thereof

Info

Publication number: LU502567B1
Application number: LU502567A
Authority: LU
Inventors: Yufang Wang; Jianchen Cong
Original assignee: Univ Shandong Technology; Henglilai New Mat Limited
Priority date: 2022-07-26
Filing date: 2022-07-26
Publication date: 2023-01-26

Abstract

The present invention discloses a crystal-seed nodularizer, and a preparation method and use thereof. The crystal-seed nodularizer according to the present invention comprises 5-15% by weight (wt%) of magnesium, 20-45 wt% of silicon, 2-8 wt% of rare earth, and 0.4-2.8 wt% of tellurium, with the balance being iron and inevitable impurities or trace elements. The method for preparing the crystal-seed nodularizer comprises mixing and melting ferrosilicon, rare earth ferrosilicon, and steel scrap; then adding a tellurium mass, stirring until uniform and deslagging; then adding a magnesium ingot, fully melting with stirring, cooling and casting; and crushing to obtain the nodularizer as a seed crystal. Use of the crystal-seed nodularizer in the preparation of nodular cast iron is provided to increase the number of graphite balls in nodular cast iron, and improve the nodularization effect.

Description

Crystal-seed nodularizer, and preparation method and use thereof 502567

FIELD OF THE INVENTION

The present invention relates to the technical field of nodularizers, and in particular, to a crystal-seed nodularizer, and a preparation method and use thereof.

DESCRIPTION OF THE RELATED ART

In 2020, the output of nodular cast iron in China is more than 15 million tons. The nodularizer, essential for the production of nodular cast iron, is particularly important in the production of nodular cast iron. The theory of nodularization has revealed that nodularizing elements in the nodularizer play a key role, since the nodularizing elements have high affinity to sulfur, oxygen, and other elements in molten iron, and increase the surface tension of molten iron. As a result, the morphology of graphite changes from flakes to balls. The key elements in the current nodularizer are as follows: 1. Nodularizing elements

Many types of nodularizers are available in China and other countries, and the nodularizing elements in the nodularizers mainly include magnesium and rare earth.

Mg: magnesium has an atomic number and density that are smaller than those of molten iron, and has a melting point of 650°C, and a boiling point of 1108°C. At the processing temperature of molten iron, the vapor pressure produced by magnesium is very high (over 1 MPa). The heat of fusion of magnesium is 21J/g, and the latent heat of vaporization is 406J/g. Therefore, when magnesium is added to molten iron, it is vaporized, and cause the molten iron to surge.

Magnesium has strong affinity to sulfur, and oxygen. The resulting MgO and MgS have high melting points, and also have a density far lower than iron, so they can be easily separated from iron. Therefore, in the molten iron treated with magnesium, the sulfur and oxygen content are quite low. When their residual content in molten iron exceeds 0.035%, graphite can be nodularized.

Re: Among the rare earth elements, cerium in light rare earth elements and yttrium in heavy rare earth elements have significant effect in the nodularization of graphite. 502567

Cerium and yttrium based rare earth elements have stronger desulfurization and deoxidation ability than magnesium, and the produced rare earth sulfide, rare earth oxide, and other compounds have high melting point, and excellent stability. The rare earth elements can also form stable compounds with nodularization interfering elements in molten iron. Therefore, a nodularizer containing rare earth has stronger anti- interference ability than a magnesium-containing nodularizer.

The residual amount of rare earth elements has a significant effect on the nodularization of graphite. In eutectic molten iron treated with rare earth, graphite can be nodularized very stably when the residual content of rare earth is 0.04%. When used to treat hypoeutectic molten iron, the amount of rare earth added needs to be increased.

However, the roundness of graphite in nodular iron treated with rare earth is worse than the roundness of graphite in nodular iron treated with magnesium, and chunky graphite occurs. In addition, the nodular iron treated with rare earth tends to be white, so the amount of rare earth added needs to be controlled.

To allow the reaction with the nodularizer to progress stably, calcium and magnesium are usually blended with rare earth, to achieve stable nodularization, and reduce the tendency of serious white iron caused by rare earth. 2. Anti-nodularization elements (nodularization-interfering elements)

This class of elements mainly refers to elements that destroy and hinder the nodularization of graphite, and according to the mechanism of action, they can be roughly divided into three types.

The first type is the consumption-type anti-nodularization elements, such as sulfur, oxygen, selenium, tellurium, and others. They react with magnesium and rare earth elements to produce various compounds, and hinder the formation of graphite balls by consuming nodularizing elements.

The second type is nodularization-interfering elements of grain boundary segregation, including tin, antimony, arsenic, copper, boron, titanium, and aluminum etc. These elements are enriched to the grain boundaries, causing carbon to form degenerated dendritic graphite when crystallized in the later eutectic stage. 502967

The third type is some intermediate nodularization-interfering elements, such as aluminum, and bismuth. When the content is low, they mainly contribute to graphite degeneration through segregation; and when the content is low, they consume nodularizing elements.

At present, it is strictly forbidden to add the three types of anti-nodularization elements in the nodularizer production process in China and other countries. 3. Type of nodularizers

According to the principle of configuration of nodularizing and anti-nodularizing elements, a variety of nodularizers are developed in China and other countries, which generally include the following.

Pure magnesium: This is a nodularizer commonly used in other countries, but less used in China.

Copper-magnesium, and nickel-magnesium: They are not only high in cost, but also limited by the structure required by nodular iron.

Silicon-magnesium-iron alloys: The magnesium content is at least 3.5-4.5%, and at most 10-15%. The commonly used alloy comprises magnesium of 5-10%, and silicon of 42-47%, with the balance being iron. With decreasing magnesium content, the nodularization reaction becomes increasingly stable, and the recovery rate of magnesium becomes much higher (the alloy containing 4% of magnesium is 10% higher in the recovery rate than the alloy containing 9% of magnesium). However, the low-magnesium nodularizer increases the silicon content in molten iron. This type of nodularizer is mainly used in the treatment of molten iron with low content of sulfur and anti-nodularizing elements.

Rare earth-magnesium alloys: They include rare earth-silicon-magnesium, rare earth- calcium-magnesium, rare earth-copper-magnesium, and other alloys. Regardless of the components in the sub-types, they are rare earth-magnesium alloy nodularizers.

Particularly, rare earth-magnesium-calcium alloy is the main nodularizer widely used in China

The above nodularizers are notably characterized in that the nodularizing elements 502567 (magnesium and rare earth) in the nodularizer have high affinity to sulfur, oxygen, and other elements in molten iron, and increase the surface tension of molten iron, to finally nodularize the graphite. Since the anti-nodularization elements either consume the nodularizing element, or reduce the surface tension of molten iron, anti-nodularization elements are strictly prohibited in nodularizer. Therefore, there is an urgent need to develop a new nodularizer to satisfy the existing production.

SUMMARY OF THE INVENTION

To solve the above technical problems, the present invention provides a crystal-seed nodularizer, and a preparation method and use thereof. The crystal-seed nodularizer of the present invention comprises a crystal seed compound for nucleation of graphite, specifically, an alloy of a crystal seed promoting the nucleation of graphite with nodular iron prepared into a nodularizer for use in the casting of nodular cast iron.

A first object of the present invention is to provide a crystal-seed nodularizer, which comprises: 5-15% by weight (wt%) of magnesium, 20-45% of silicon, 2-8% of rare earth, and 0.4-2.8% of tellurium, with the balance being iron and inevitable impurities or trace elements.

In an embodiment of the present invention, the crystal-seed nodularizer comprises 8%- 15% of magnesium, 35-45% of silicon, 2-8% of rare earth, and 0.5-2.5% of tellurium, with the balance being iron and inevitable impurities or trace elements.

In an embodiment of the present invention, the rare earth is selected from a conventional commercial rare earth, for example, rare earth 18, rare earth 20, and others.

In an embodiment of the present invention, the iron content is not less than 30%, or not higher than 60%.

In an embodiment of the present invention, the content of the inevitable impurities or trace elements is not higher than 5%.

In an embodiment of the present invention, the manganese content in the trace elements is less than 0.2%, the aluminum content is less than 0.6%, and the phosphorus content is less than 1%. 502967

In an embodiment of the present invention, the weight ratio of rare earth to tellurium is 3:1-5:1.

A second object of the present invention is to provide a method for preparing the crystal- 5 seed nodularizer, which comprises the following steps: mixing and melting ferrosilicon, rare earth ferrosilicon, and steel scrap; then adding a tellurium mass, stirring until uniform and deslagging; then adding a magnesium ingot, fully melting with stirring, cooling and casting; and crushing to obtain the nodularizer as a seed crystal.

Fusion casting is a main method for producing this composition. In the method, a rare earth ferrosilicon alloy or a rare earth extract, a tellurium mass, metal magnesium, ferrosilicon and steel scrap are used as raw materials. The total manganese content in these raw materials is less than 0.2%, to prevent the consumption of tellurium during melting. If the manganese content is higher, the amount of tellurium needs to be increased accordingly. Ferrosilicon, rare earth ferrosilicon, and steel scrap are sequentially added to an intermediate frequency furnace, and melted, and then the tellurium mass is added. At this time, in addition to stirring by the self-induction of the intermediate frequency furnace, manual stirring is also required where appropriate, to homogenize the alloy composition during the smelting process. Deslagging is performed. Then the magnesium ingot is pressed into the molten metal in the furnace by pressing method, and fully melted with stirring. The melt is poured into an iron mold after removal from the furnace, cooled and crushed to obtain the composition.

A third object of the present invention is to provide use of the crystal-seed nodularizer in the preparation of nodular cast iron.

In an embodiment of the present invention, the nodular cast iron is prepared through a method comprising: (1) mixing pig iron, steel scrap, and recycled scrap, and melting by heating, wherein ferrosilicon, and a recarburizer is added during the melting process, heating the obtained molten iron to 1500°C-1520°C, and holding for 3-4 min;

(2) cooling the obtained molten iron obtained in Step (1) to 1500°C-1460°C, and 502967 nodularizing the molten iron with the crystal-seed nodularizer; (3) casting the molten iron after nodularization in Step (2), to obtain the nodular cast iron.

In an embodiment of the present invention, in Step (1), the sulfur content in the molten iron obtained after pig iron, steel scrap, and recycled scrap are melted is <0.009 wt%.

In an embodiment of the present invention, in Step (1), the recarburizer meets the YB-

T4403 standard.

In an embodiment of the present invention, in Step (2), the amount of the crystal-seed nodularizer is 0.09%-0.14%.

In the study of the graphite ball structure, it is found that graphite is not formed of pure carbon, and there are inclusions at or near the center of the graphite ball. These inclusions can act as a nucleus of graphite nucleation to adsorb carbon. It is found in experiments that rare earth in nodularizing elements and tellurium in anti-nodularizing elements are combined in the form of an alloy to provide an unexpected nucleus of graphite nucleation (ReTe/ResTes), that is, the crystal seed in the crystal-seed nodularizer of the present invention.

First, the present invention mainly concerns specific combinations of Re and tellurium at various ratios, and these combinations will cause a large number of dispersed non- metallic inclusion (ReTe/RezTez) particles in the molten iron after nodularization. In this case, tellurium not only loses its anti-nodularization effect, and acts a nucleus of graphite nucleation in the casting formed after casting, thus greatly increasing the number of graphite balls. In addition, in the preparation process of the nodularizer, this specific combination, that is, crystal seed, is prepared into a nodularizer, to facilitate the nodularization of molten iron, and exerting an effect of crystal seed to increase the number of graphite balls, and improve the nodularization effect of a casting. Use of such a combined alloy of the present invention can easily improve the quality of castings, particularly increase the number of graphite balls; and suppress nodularization fade much regularly. The test result of the combination of magnesium, silicon, rare earth,

tellurium and iron in the critical range defined in the present invention proves that use 502567 of the composition in alloy production and mass production of nodular iron brings about a certain regularity.

Compared with the prior art, the technical solution of the present invention has the following advantages:

The alloy of the crystal-seed nodularizer according to the present invention can increase the number of graphite balls in nodular cast iron, and, improve the nodularization effect.

Tellurium in the alloy binds to the metal, and exists in the form of a compound, instead of a simple substance. Therefore, tellurium will not interfere with the nodularization.

On the contrary, these compounds, particularly, compounds of tellurium with rare earth, have a density close to that of molten iron and thus are uniformly distributed in molten iron; and mainly serve as a nucleus of graphite nucleation. The telluride and other inclusions having a low density, for example, magnesia, ferric sulfide, and others will float up with the slag and are removed during nodularization.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be further described below in connection with specific examples, so that those skilled in the art can better understand and implement the present invention; however, the present invention is not limited thereto.

Afirst object of the present invention is to provide a crystal-seed nodularizer, which comprises: 5-15% by weight (wt%) of magnesium, 20-45% of silicon, 2-8% of rare earth, and 0.4-2.8% of tellurium, with the balance being iron and inevitable impurities or trace elements. Further, the crystal-seed nodularizer comprises 8%-15% of magnesium, 35-45% of silicon, 2-8% of rare earth, and 0.5-2.5% of tellurium, with the balance being iron and inevitable impurities or trace elements.

A second object of the present invention is to provide a method for preparing the crystal-seed nodularizer, which comprises the following steps: mixing and melting ferrosilicon, rare earth ferrosilicon, and steel scrap; then adding a tellurium mass, stirring until uniform and deslagging; then adding a magnesium ingot, fully melting with stirring, cooling and casting; and crushing to obtain the nodularizer as a seed crystal. HUS02567

The pig iron, magnesium ingot, carbon steel scrap, recycled ferrosilicon, recarburizer, rare earth, tellurium, small pot scrap, and other raw materials are all commercially available products.

Example 1

In this example, nodular cast iron is produced according to an existing conventional technology.

That is, pig iron, steel scrap and recycled scrap are used as raw materials, and a low sulfur content of <0.012% is controlled in base molten iron. Then, the molten iron is nodularized and cast into a shaft-type nodular iron casting having a diameter of 50 mm, and a weight of 13 Kg.

The shaft-type nodular iron casting is prepared through a method as follows. (1) 50% of pig iron, 30% of carbon steel scrap and 20% of recycled scrap are used as raw materials. A material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed, added to an electric furnace, and melted. (2) Ferrosilicon and a recarburizer are added during the melting process of molten iron. After melting, a sample is taken and analyzed, and the components in molten iron are adjusted to have a carbon content of 3.9%-4.0%, a silicon content of 1.7%-1.8%, and a manganese content of 0.3%-0.4%. (3) The molten iron is heated to 1510 °C, held for 3-4 min, and then cooled to 1450 °C at which the molten iron is nodularized in a nodularizing ladle by tundish-cover process. (Nodularization process: The weighed nodularizer is added to an alloy pit in the nodularizing ladle, 5-10 kg of small pot scrap is added to fully cover the nodularizer, and then, the molten iron is poured into the nodularizing ladle). (4) The molten iron after nodularization is cast in a ready-to-use mould, to obtain the nodular cast iron.

The nodularizer is a crystal-seed nodularizer comprising 7.8% of magnesium, 45% of silicon, 2.8% of rare earth, and 0.59% of tellurium, with the balance being iron and inevitable trace clements.

The method for preparing the crystal-seed nodularizer comprises mixing and melting 17506567 ferrosilicon, rare earth ferrosilicon, and steel scrap; then adding a tellurium mass, stirring until uniform and deslagging; then adding a magnesium ingot, fully melting with stirring, cooling and casting; and crushing to obtain the nodularizer as a seed crystal.

Comparative Example 1

In this comparative example, nodular cast iron is produced according to an existing conventional technology. That is, pig iron, steel scrap, and recycled scrap are used as raw materials, and a low sulfur content of <0.012% is controlled in base molten iron. Then, the molten iron is nodularized and cast into a shaft-type nodular iron casting having a diameter of 50 mm, and a weight of 13 Kg. The shaft-type nodular iron casting is prepared through a method as follows. (1) 50% of pig iron, 30% of carbon steel scrap and 20% of recycled scrap are used as raw materials. A material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed, added to an electric furnace, and melted. (2) Ferrosilicon and a recarburizer are added during the melting process of molten iron. After melting, a sample is taken and analyzed, and the components in molten iron are adjusted to have a carbon content of 3.9%-4.0%, a silicon content of 1.7%-1.8%, and a manganese content of 0.3%-0.4%. (3) The molten iron is heated to 1510 °C, held for 3-4 min, and then cooled to 1450 °C at which the molten iron is nodularized in a nodularizing ladle by tundish-cover process. (Nodularization process: The weighed nodularizer is added to an alloy pit in the nodularizing ladle, 5-10 kg of small pot scrap is added to fully cover the nodularizer, and then, the molten iron is poured into the nodularizing ladle). (4) The molten iron after nodularization is cast in a ready-to-use mould, to obtain the nodular cast iron.

In this comparative example, a conventional nodularizer is used, which comprises 7.86% of magnesium, 45.1% of silicon, and 2.8% of rare earth, with the balance being iron and inevitable trace elements.

All other production processes and raw materials are the same as those in Example 1. 17506567

Example 2

That is, pig iron, steel scrap, and recycled scrap are used as raw materials, and a low sulfur content of <0.015% is controlled in base molten iron. Then, the molten iron is nodularized and cast into a shaft-type nodular iron casting having a diameter of 102 mm, and a weight of 86 Kg.

The shaft-type nodular iron casting 1s prepared through a method as follows. (1) 50% of pig iron, 30% of carbon steel scrap and 20% of recycled scrap are used as raw materials. À material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed, added to an electric fumace, and melted. (2) Ferrosilicon and a recarburizer are added during the melting process of molten iron. After melting, a sample is taken and analyzed, and the components in molten iron are adjusted to have a carbon content of 3.9%-4%, a silicon content of 1.5%-1.6%, and a manganese content of 0.4-0.5%. (3) The molten iron is heated to 1510 °C, held for 3-4 min, and then cooled to 1450 °C at which the molten iron is nodularized in a nodularizing ladle by tundish-cover process. (Nodularization process: The weighed nodularizer is added to an alloy pit in the nodularizing ladle, 5-10 kg of small pot scrap is added to fully cover the nodularizer, and then, the molten iron is poured into the nodularizing ladle). (4) The molten iron after nodularization is cast into a ready-to-use mould, to obtain the shaft- type nodular iron casting.

The nodularizer is a crystal-seed nodularizer comprising 10.2% of magnesium, 43.6% of silicon, 3.7% of rare earth, and 1.45% of tellurium, with the balance being iron and inevitable trace elements.

Comparative Example 2

In the comparative example, nodular cast iron is produced according to an existing conventional technology. That is, pig iron, steel scrap, and recycled scrap are used as raw materials, and a low sulfur content of <0.015% is controlled in base molten iron. Then, the molten iron is 10502567 nodularized and cast into a shaft-type nodular iron casting having a diameter of 102 mm, and a weight of 86 Kg. The shaft-type nodular iron casting 1s prepared through a method as follows. (1) 50% of pig iron, 30% of carbon steel scrap and 20% of recycled scrap are used as raw materials. À material list is formulated, and entered into an automatic material weighing system: and the materials are automatically weighed, added to an electric furnace, and melted. (2) Ferrosilicon and a recarburizer are added during the melting process of molten iron. After melting, a sample is taken and analyzed, and the components in molten iron are adjusted to have a carbon content of 3.9%-4%, a silicon content of 1.5%-1.6%, and a manganese content of 0.4-0.5%. (3) The molten iron is heated to 1510 °C, held for 3-4 min, and then cooled to 1450 °C at which the molten iron is nodularized in a nodularizing ladle by tundish-cover process. (Nodularization process: The weighed nodularizer is added to an alloy pit in the nodularizing ladle, 5-10 kg of small pot scrap is added to fully cover the nodularizer, and then, the molten iron is poured into the nodularizing ladle). (4) The molten iron after nodularization is cast into a ready-to-use mould, to obtain the shaft- type nodular iron casting.

In this comparative example, a conventional nodularizer is used, which comprises 10.6% of magnesium, 45.3% of silicon, and 3.75% of rare earth, with the balance being iron and inevitable trace elements.

All other production processes and raw materials are the same as those in Example 2.

Example 3

That is, pig iron, steel scrap and recycled scrap are used as raw materials, and a low sulfur content of <0.009% is controlled in base molten iron. Then, the molten iron is nodularized and cast into a shaft-type nodular iron casting having a diameter of 258 mm, and a weight of 463

Kg. The shaft-type nodular iron casting is prepared through a method as follows. (1) 50% of pig iron, 30% of carbon steel scrap and 20% of recycled scrap are used as raw materials. À material list is formulated, and entered into an automatic material weighing system; 17506567 and the materials are automatically weighed, added to an electric fumace, and melted. (2) Ferrosilicon and a recarburizer are added during the melting process of molten iron. After melting, a sample is taken and analyzed, and the components in molten iron are adjusted to have a carbon content of 3.8%-3.9%, a silicon content of 1.3%-1.4%, and a manganese content of 0.5%-0.6%. (3) The molten iron is heated to 1510 °C, held for 3-4 min, and then cooled to 1450 °C at which the molten iron is poured into the nodularizing ladle and nodularized. (Nodularization process:

The weighed nodularizer is added to an alloy pit in the nodularizing ladle, 5-10 kg of small pot scrap is added to fully cover the nodularizer, and then, the molten iron is poured into the nodularizing ladle). (4) The molten iron after nodularization is cast into a ready-to-use mould.

The nodularizer is a crystal-seed nodularizer comprising 12.6% of magnesium, 41.3% of silicon, 5.65% of commercially available rare earth, and 2.15% of tellurium, with the balance being iron and inevitable trace elements.

Comparative Example 3

In the comparative example, nodular cast iron is produced according to an existing conventional technology. That is, pig iron, steel scrap and recycled scrap are used as raw materials, and a low sulfur content of <0.009% is controlled in base molten iron. Then, the molten iron is nodularized and cast into a shaft-type nodular iron casting having a diameter of 258 mm, and a weight of 463 Kg. The shaft-type nodular iron casting is prepared through a method as follows. (1) 50% of pig iron, 30% of carbon steel scrap and 20% of recycled scrap are used as raw materials. A material list is formulated, and entered into an automatic material weighing system; and the materials are automatically weighed, added to an electric furnace, and melted. (2) Ferrosilicon and a recarburizer are added during the melting process of molten iron. After melting, a sample is taken and analyzed, and the components in molten iron are adjusted to have a carbon content of 3.8%-3.9%, a silicon content of 1.3%-1.4%, and a manganese content of 0.5%-0.6%.

(3) The molten iron is heated to 1510 °C, held for 3-4 min, and then cooled to 1450 °C at which 17506567 the molten iron is poured into the nodularizing ladle and nodularized. (Nodularization process:

In this comparative example, a conventional nodularizer is used, which comprises 12.6% of magnesium, 41.3% of silicon, and 5.65% of rare earth, with the balance being iron and inevitable trace elements.

All other production processes and raw materials are the same as those in Example 3.

Test examples

The nodularization effects of graphite in each part of related nodular iron castings obtained in the Examples 1-3 and Comparative Examples 1-3 are tested. The test results are shown in Table 1

The test samples are taken from a central portion of a representative thick part in a shaft-type nodular iron casting (graphite in the central portion is prone to growth and degeneration due to differential cooling, that is, the diameter of the ball is large and the nodularization rate is poor).

Test method: According to GB/T9441 "Metallographic Test for Spheroidal Graphite Cast Iron" in connection with image analysis, the nodularization rate, the ball diameter and the number density of graphite in the sample are determined.

Table 1. Comparison of nodularization rate and number density of graphite of examples and comparative examples me [Er ma [ern [een

Test item el e Example 1 | e2 e Example 2 | ¢ 3 e Example 3 pes qq oe qe fe 95.5 82.3 90.2 73.2 85.9 68.1 n rate (%) esi CC OO CO OO EO 7 4 5 3-4 (grade)

Number LU502567 density of 266 205 193 146 158 105 graphite

As can be seen from Table 1, Using the crystal-seed nodularizer of the present invention, the effect of nodularization is obviously better than that of the currently commonly used nodularizer.

For a casting of 259 mm or less, the nodularization rate is increased by 16% or more, the diameter is increased by 1 grade or more, and the number density of graphite is increased by 29% ormore. Especially for a thick and large casting of 259 mm, the number density of graphite is increased by 50% or more.

Apparently, the above-described embodiments are merely examples provided for clarity of description, and are not intended to limit the implementations of the present invention. Other variations or changes can be made by those skilled in the art based on the above description.

The embodiments are not exhaustive herein. Obvious variations or changes derived therefrom also fall within the protection scope of the present invention.

Claims

WHAT IS CLAIMED IS: HUS02567

1. A crystal-seed nodularizer, comprising: 5-15% by weight (wt%) of magnesium, 20-45 wt% of silicon, 2-8 wt% of rare earth, and 0.4-2.8 wt% of tellurium, with the balance being iron and inevitable impurities or trace elements.

2. The crystal-seed nodularizer according to claim 1, comprising: 8-15% of magnesium, 35- 45% of silicon, 2-8% of rare earth, and 0.5-2.5% of tellurium, with the balance being iron and inevitable impurities or trace elements.

3. The crystal-seed nodularizer according to claim 1, wherein the iron content is not less than 30%, or not higher than 60%.

4. The crystal-seed nodularizer according to claim 1, wherein the content of the inevitable impurities or trace elements is not higher than 5%.

5. The crystal-seed nodularizer according to claim 1, wherein the manganese content in the trace elements is less than 0.2%, the aluminum content is less than 0.6%, and the phosphorus content is less than 1%.

6. The crystal-seed nodularizer according to claim 1, wherein the weight ratio of rare earth to tellurium is 3:1-5:1.

7. A method for preparing a crystal-seed nodularizer according to any one of claims 1 to 6, comprising the following steps: mixing and melting ferrosilicon, rare earth ferrosilicon, and steel scrap; then adding a tellurium mass, stirring until uniform and deslagging; then adding a magnesium ingot, fully melting with stirring, cooling and casting; and crushing to obtain the nodularizer as a seed crystal.

8. Use of the crystal-seed nodularizer according to any one of claims 1 to 6 in the preparation of nodular cast iron.

9. The use according to claim 8, wherein the nodular cast iron is prepared through a method comprising: (1) mixing pig iron, steel scrap, and recycled scrap, and melting by heating, wherein ferrosilicon, and a recarburizer is added during the melting process; heating the obtained molten iron to 1500 ‘C-1520°C, and holding for 3-4 min; (2) cooling the obtained molten iron obtained in Step (1) to 1500°C -1460°C, and nodularizing the molten iron with the crystal-seed nodularizer; 17506567 (3) casting the molten iron after nodularization in Step (2), to obtain the nodular cast iron.

10. The use according to claim 9, wherein in Step (1), the sulfur content in the molten iron obtained after pig iron, steel scrap, and recycled scrap are melted is <0.009 wt%.

11. The use according to claim 9, wherein in Step (1), the recarburizer meets the YB-T4403 standard.

12. The use according to claim 9, wherein in Step (2), the amount of the crystal-seed nodularizer is 0.09%-0.14%.