A nodularizing wire for improving the vermicularization rate of castings and its preparation process

Abstract

This application relates to the technical field of the preparation of rare earth metal deep-processing products, and specifically discloses a nodularizing wire for improving the vermicularization rate of castings and its preparation process. The nodularizing wire includes an iron sheet shell and a powder inner core. The powder inner core is filled in the iron sheet shell. The components of the powder inner core include rare earth alloy powder and ferrosilicon powder. The weight of the rare earth alloy powder is 94-106% of the weight of the ferrosilicon powder. The rare earth alloy powder is obtained by melting and crushing alloy raw powder. The alloy raw powder includes the following components in parts by weight: 14-16 kg of magnesium powder, 68-72 kg of rare earth silicon, and 12-18 kg of calcium silicate powder. This application improves the performance of the nodularizing wire and increases the vermicularization rate of castings.

Description

Technical Field

[0001] This application relates to the technical field of the preparation of rare earth metal deep-processing products. More specifically, it relates to a nodularizing wire for improving the vermicularization rate of castings and its preparation process. Background Art

[0002] Vermicular graphite cast iron is a new type of engineering material. Traditional vermicular graphite cast iron uses rare earth metals as vermicularizing agents and is produced by the impouring method. In recent decades, with the improvement of technical levels, the wire feeding technology has begun to be applied to the production of vermicular graphite cast iron. A nodularizing wire is a cored wire obtained by covering a vermicularizing agent with iron sheet. During the production of vermicular graphite cast iron, the iron sheet can delay the direct contact between the vermicularizing agent and the molten iron, which helps to reduce pollution and improve the production environment.

[0003] In the related art, there is a nodularizing wire, which is obtained by the cored wire machine through the cored processing of the iron sheet and the powder inner core. Each batch of the powder inner core is composed of 100 kg of ferrosilicon powder and 50 kg of rare earth metal powder (lanthanum) mixed.

[0004] Regarding the above related art, the inventor believes that the iron content in the nodularizing wire in the related art is too high, which will have a negative impact on the vermicularization process of castings during the production process, resulting in the limitation of the vermicularization rate of castings. Summary of the Invention

[0005] In the related art, the high iron content in the nodularizing wire results in the limitation of the vermicularization rate of castings. To improve this defect, this application provides a nodularizing wire for improving the vermicularization rate of castings and its preparation process.

[0006] In the first aspect, this application provides a nodularizing wire for improving the vermicularization rate of castings, adopting the following technical solution:

[0007] A nodularizing wire for improving the vermicularization rate of castings, the nodularizing wire includes an iron sheet outer shell and a powder inner core, the powder inner core is filled in the iron sheet outer shell, the components of the powder inner core include rare earth alloy powder and ferrosilicon powder, the weight of the rare earth alloy powder is 94 - 106% of the weight of the ferrosilicon powder, the rare earth alloy powder is obtained by melting and crushing alloy raw powder, and the alloy raw powder includes the following components in parts by weight: 14 - 16 kg of magnesium powder, 68 - 72 kg of rare earth silicon, and 12 - 18 kg of calcium silicate powder.

[0008] By adopting the above technical solution, the present application uses rare earth silicon instead of rare earth metal powder, and adds magnesium powder and calcium silicate powder. After melting and crushing magnesium powder, calcium silicate powder and rare earth silicon, rare earth alloy powder is obtained. Then, the rare earth alloy powder is mixed with ferrosilicon powder to obtain the powder inner core. Compared with the powder inner core in the related art, the iron content of the powder inner core in the present application is reduced, so the product quality of the spheroidizing wire is improved, which helps to increase the vermicularization rate of the casting. In addition, since the rare earth alloy powder contains magnesium, and magnesium will vaporize in the molten iron, the magnesium vapor can promote the diffusion of rare earth in the molten iron, and can reduce the sulfur content in the molten iron, inhibiting the anti-spheroidizing effect of sulfur, which helps to increase the vermicularization rate of the casting.

[0009] Preferably, the weight of the rare earth alloy powder is 97-103% of the weight of the ferrosilicon powder.

[0010] By adopting the above technical solution, the dosage of the rare earth alloy powder is optimized, which helps to increase the vermicularization rate of the casting.

[0011] Preferably, the average particle size of the rare earth alloy powder is 0.5-2.5 mm.

[0012] By adopting the above technical solution, the average particle size of the rare earth alloy powder is optimized, improving the diffusion performance of the rare earth alloy powder in the molten iron, which helps to increase the vermicularization rate of the casting.

[0013] In a second aspect, the present application provides a preparation process for a spheroidizing wire for increasing the vermicularization rate of a casting, adopting the following technical solution.

[0014] A preparation process for a spheroidizing wire for increasing the vermicularization rate of a casting includes the following steps:

[0015] (1) Mix magnesium powder, rare earth silicon, and calcium silicate powder to obtain the original alloy powder. After melting the original alloy powder, it is then cooled in a mold to obtain an alloy block;

[0016] (2) After demolding the alloy block, it is then crushed to obtain rare earth alloy powder;

[0017] (3) Mix the rare earth alloy powder and ferrosilicon powder to obtain the powder inner core, and perform core wrapping processing on the powder inner core and the iron sheet outer shell to obtain a spheroidizing wire for increasing the vermicularization rate of the casting.

[0018] By adopting the above technical solution, the present application first obtains rare earth alloy powder through melting and crushing, then mixes the rare earth alloy powder with ferrosilicon powder to form the powder inner core, and finally performs core wrapping with an iron sheet outer shell to obtain a spheroidizing wire for increasing the vermicularization rate of the casting.

[0019] Preferably, the components of the powder inner core further include magnesium oxide powder and aluminum powder, and the magnesium oxide powder and aluminum powder are mixed with the rare earth alloy powder and ferrosilicon powder together in step (3) of preparing the spheroidizing wire.

[0020] By adopting the above technical solution, when the sulfur content in the molten iron is relatively high, the reaction between magnesium and sulfur causes a large consumption of magnesium. At this time, it is necessary to appropriately supplement magnesium metal to maintain a sufficient nodulizing rate of the casting. Compared with directly adding magnesium powder, magnesium oxide powder and aluminum powder can also produce magnesium metal through the thermite reaction to achieve the supplement of magnesium, and the cost of using magnesium oxide and aluminum powder to produce magnesium metal in molten iron is lower than directly putting magnesium metal, which helps to reduce the production cost. In addition, due to the increase in magnesium content, the desulfurization efficiency of the molten iron will also increase.

[0021] Preferably, the molar ratio of the magnesium oxide powder to the aluminum powder is 3:(2.04 - 2.08).

[0022] By adopting the above technical solution, the molar ratio range of the magnesium oxide powder to the aluminum powder is optimized. A slightly excessive amount of aluminum powder is beneficial to the complete reduction of magnesium oxide, realizing the full utilization of magnesium oxide. In addition, the excess aluminum powder can also participate in desulfurization in the molten iron, which helps to improve the desulfurization efficiency of the molten iron.

[0023] Preferably, the components of the inner core of the powder also include limestone powder, and the limestone powder is mixed with rare earth alloy powder and ferrosilicon powder together in step (3) of preparing the nodulizing wire.

[0024] By adopting the above technical solution, the carbon dioxide gas generated after the thermal decomposition of the limestone powder can promote the diffusion of rare earth in the molten iron, which helps to improve the nodulizing rate of the casting. In addition, the calcium oxide generated by the decomposition of calcium carbonate also has a certain desulfurization effect. When magnesium and calcium oxide coexist in the molten iron, it is more thermodynamically favorable for desulfurization of the molten iron than magnesium alone, which helps to improve the desulfurization efficiency of the molten iron.

[0025] Preferably, the dosage of the limestone powder is 8 - 12% of the weight of the rare earth alloy powder.

[0026] By adopting the above technical solution, the dosage of the limestone powder is optimized, which helps to achieve the balance between the production cost and the desulfurization effect.

[0027] Preferably, the components of the inner core of the powder also include nano-calcium carbonate, and the nano-calcium carbonate is mixed with rare earth alloy powder and ferrosilicon powder together in step (3) of preparing the nodulizing wire.

[0028] By adopting the above technical solution, although the calcium oxide produced by the decomposition of limestone powder can be desulfurized together with magnesium, when the silicon content in the molten iron is high, the dicalcium silicate produced by the reaction of calcium oxide and silicon will hinder the reaction of calcium oxide and sulfur, resulting in a decrease in desulfurization efficiency. In order to cope with this situation, the present application adds nano-calcium carbonate to the inner core of the powder. After the decomposition of nano-calcium carbonate, nano-scale calcium oxide particles are produced, which increases the specific surface area of ​​calcium oxide in the molten iron and reduces the influence of the generation of dicalcium silicate on the desulfurization effect of calcium oxide, which helps to improve the desulfurization efficiency in molten iron with a high silicon content.

[0029] Preferably, the dosage of the nano calcium carbonate is 14-16% of the weight of the limestone powder.

[0030] By adopting the above technical solution, the dosage of nano calcium carbonate is optimized, which helps to reduce the impact of silicon in molten iron on desulfurization efficiency.

[0031] In summary, this application has the following beneficial effects:

[0032] 1. The present application mixes rare earth silicon, magnesium powder and calcium silicon powder and melts them into an alloy, which is then crushed into rare earth alloy powder. The rare earth alloy powder is mixed with ferrosilicon powder to obtain a powder core with a relatively low iron content. By reducing the iron content of the powder core, the present application improves the performance of the spheroidized wire and increases the creep rate of the casting. In addition, by adding magnesium to the powder core, the magnesium vapor generated by magnesium in the molten iron promotes the diffusion of rare earth, which also helps to improve the creep rate of the casting.

[0033] 2. In the present application, the components of the preferred powder core also include magnesium oxide powder and aluminum powder. When the sulfur content of the molten iron is high, the magnesium oxide powder and aluminum powder can supplement the magnesium element through thermite reaction, thereby reducing the consumption of magnesium element by sulfur in the molten iron, and the cost is lower than directly adding magnesium element. DETAILED DESCRIPTION

[0034] The present application is further described in detail below in conjunction with embodiments, preparation examples and comparative examples. The raw materials involved in the present application can all be obtained commercially.

[0035] Example

[0036] Examples 1-5

[0037] The following description is given by taking Example 1 as an example.

[0038] Example 1 In this example, the spheroidized wire with improved creep rate of castings is prepared according to the following steps:

[0039] (1) Mix 14 kg of magnesium powder, 68 kg of rare earth silicon, and 12 kg of calcium silicon powder to obtain the original alloy powder. After melting the original alloy powder at 1300 °C, cool it in a mold to obtain an alloy block. In this step, the rare earth silicon is lanthanum silicide;

[0040] (2) Demold the alloy block and then crush it to obtain rare earth alloy powder with an average particle size of 2.8 mm;

[0041] (3) Mix the rare earth alloy powder and 100 kg of ferrosilicon powder to obtain the inner core of the powder. Perform cored wire processing on the inner core of the powder and the iron sheet shell to obtain a nodulizing wire that improves the vermicularization rate of the casting.

[0042] As shown in Table 1, the differences between Examples 1-5 mainly lie in the different raw material ratios of the original alloy powder.

[0043] Table 1 Raw material ratio of the original alloy powder

[0044] Sample Magnesium powder / kg Rare earth silicon / kg Calcium silicate powder / kg Example 1 14 68 12 Example 2 14.5 69 13.5 Example 3 15 70 15 Example 4 15.5 71 16.5 Example 5 16 72 18

[0045] Examples 6-9

[0046] As shown in Table 2, the difference between Examples 6-9 and Example 3 is that the average particle size of the rare earth alloy powder is different.

[0047] Table 2 Average particle size of the rare earth alloy powder

[0048] Sample Example 3 Example 6 Example 7 Example 8 Example 9 Average particle size / mm 2.8 2.5 1.5 0.5 0.2

[0049] Example 10

[0050] The difference between this example and Example 7 is that the components of the inner core of the powder also include magnesium oxide powder and aluminum powder. The magnesium oxide powder and aluminum powder are mixed with the rare earth alloy powder and ferrosilicon powder together in step (3) of preparing the nodulizing wire. The molar ratio of the magnesium oxide powder to the aluminum powder is 3:2.04, and the molar ratio of the magnesium oxide powder to the magnesium powder in step (1) is 1:10.

[0051] As shown in Table 3, the differences between Examples 10-14 lie in the different molar ratios of the magnesium oxide powder to the aluminum powder.

[0052] Table 3 Molar ratio of the magnesium oxide powder to the aluminum powder

[0053] Sample Example 10 Example 11 Example 12 Example 13 Example 14 Magnesium oxide: Aluminum powder 3：2.04 3：2.05 3：2.06 3：2.07 3：2.08

[0054] Example 15

[0055] The difference between this example and Example 12 is that the components of the inner core of the powder also include limestone powder with an average particle size of 10 μm. The limestone powder is mixed with the rare earth alloy powder and ferrosilicon powder together in step (3) of preparing the nodulizing wire. The dosage of the limestone powder is 8% of the weight of the rare earth alloy powder.

[0056] As shown in Table 4, the difference between Examples 15 - 19 lies in the different proportions of the amount of limestone powder to the weight of rare earth alloy powder.

[0057] Table 4 Proportion of the amount of limestone powder to the weight of rare earth alloy powder

[0058] Sample Example 15 Example 16 Example 17 Example 18 Example 19 Limestone dosage / % 8 9 10 11 12

[0059] Example 20

[0060] The difference between this example and Example 17 is that the components of the powder inner core further include nano - calcium carbonate. The nano - calcium carbonate is mixed with rare earth alloy powder and ferrosilicon powder together in step (3) of preparing the spheroidizing wire, and the amount of nano - calcium carbonate is 14% of the weight of the limestone powder.

[0061] As shown in Table 5, the difference between Examples 20 - 24 lies in the different proportions of the amount of nano - calcium carbonate to the weight of the limestone powder.

[0062] Table 5 Proportion of the amount of nano - calcium carbonate to the weight of the limestone powder

[0063] Sample Example 20 Example 21 Example 22 Example 23 Example 24 Nano calcium carbonate dosage / % 14 14.5 15 15.5 16

[0064] Comparative Example

[0065] Comparative Example 1

[0066] A spheroidizing wire is prepared according to the following steps:

[0067] Mix 50 kg of rare earth metal powder (lanthanum) and 100 kg of ferrosilicon powder to obtain a powder inner core, and perform core - covering processing on the powder inner core and the iron sheet shell to obtain a spheroidizing wire for improving the vermicularization rate of castings.

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 3 is that the components of the alloy raw powder do not include magnesium powder.

[0070] Comparative Example 3

[0071] The difference between this comparative example and Example 3 is that the components of the alloy raw powder do not include calcium silicate powder.

[0072] Comparative Example 4

[0073] The difference between this comparative example and Example 3 is that the powder inner core is composed of 100 kg of ferrosilicon powder and 80 kg of rare earth alloy powder.

[0074] Comparative Example 5

[0075] The difference between this comparative example and Example 3 is that the powder inner core is composed of 100 kg of ferrosilicon powder and 120 kg of rare earth alloy powder.

[0076] Performance testing method

[0077] Using hot metal with a sulfur content of 0.035 wt% and a silicon content of 1.4 wt%, vermicularizing treatment is carried out by the wire feeding method. The addition amount of the spheroidizing wire is 0.65 wt% (equivalent to hot metal). Pour round bar test blocks with a diameter of 18 mm and Y-shaped test blocks with a length of 180 mm, a thickness of 25 mm, and a height of 100 mm, and perform chemical composition analysis with a carbon-sulfur analyzer. The metallographic specimen is intercepted on the round bar test block with a diameter of 18 mm. After the specimen is polished, it is etched with a 4% nitric acid alcohol solution to inspect the matrix structure, observed under a 100-fold metallographic microscope, and the vermicularization rate is determined according to the metallographic standard atlas. The results are shown in Table 6.

[0078] Take 100 t of hot metal with a sulfur content of 0.035 wt%, and use the spheroidizing wires of each example and comparative example to carry out wire feeding treatment at the same rate until the sulfur content drops to 0.005 wt%. Record the time t consumed for the sulfur content to drop from 0.035 wt% to 0.005 wt%, and then calculate the ratio of the t value of each example and comparative example to the t value of Comparative Example 1, and record the result as the relative desulfurization time. The results are shown in Table 6.

[0079] Table 6

[0080]

[0081] Combined with Examples 1-5 and Comparative Example 1 and Table 6, it can be seen that the vermicularization rates measured in Examples 1-5 are all higher than that in Comparative Example 1, indicating that the spheroidizing wire of the present application improves the vermicularization effect of the casting by reducing the iron content of the powder inner core.

[0082] Combined with Example 3 and Comparative Examples 2-3 and Table 6, it can be seen that the vermicularization rates measured in Example 3 are all lower than those in Example 3, indicating that when the alloy raw powder does not contain magnesium powder or calcium silicate powder, the promoting effect of rare earth alloy powder on vermicularization is limited.

[0083] Combined with Example 3 and Comparative Examples 4-5 and Table 6, it can be seen that when the dosage of rare earth alloy powder is less than 94% of the weight of ferrosilicon powder, the vermicularization rate of the casting decreases; while when the dosage of rare earth alloy powder is higher than 106% of the weight of ferrosilicon powder, the improvement of the vermicularization rate of the casting is small.

[0084] It can be seen from Example 3 and Examples 6-9 and Table 6 that reducing the particle size of the rare earth alloy powder is beneficial to improving the creep rate of the casting and also helps to improve the desulfurization efficiency. When the particle size of the rare earth alloy powder is greater than 2.5 mm, the creep rate is relatively low, and when the particle size of the rare earth alloy powder is less than 0.5 mm, the creep rate does not increase significantly. Considering that the cost of refining the particle size will increase as the particle size decreases, the particle size of the rare earth alloy powder is preferably 0.5-2.5 mm.

[0085] Combining Example 7, Examples 10-14 and Table 6, it can be seen that the creep rates measured in Examples 10-14 are all higher than that in Example 7, and the relative desulfurization times are all shorter than that in Example 7, indicating that magnesium oxide and aluminum powder supplement magnesium element to molten iron through thermite reaction.

[0086] Combining Example 12, Examples 15-19 and Table 6, it can be seen that the carbon dioxide produced by the decomposition of calcium carbonate promotes the diffusion of rare earth in molten iron, thereby increasing the creep rate, while the calcium oxide produced by the decomposition of calcium carbonate slightly increases the desulfurization efficiency.

[0087] It can be seen from Example 17, Example 20-24 and Table 6 that the nano-scale calcium oxide produced by the decomposition of nano-calcium carbonate increases the average specific surface area of ​​calcium oxide in the molten iron, reducing the interference of the formation of dicalcium silicate on the desulfurization effect of calcium oxide. At the same time, the carbon dioxide produced by the decomposition of nano-calcium oxide also promotes the uniform dispersion of rare earth in the molten iron, thereby improving the creep rate of the casting.

[0088] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A spheroidizing wire for improving the vermicularization rate of castings, characterized in that, The spheroidizing wire includes an iron sheet shell and a powder inner core. The powder inner core is filled in the iron sheet shell. The components of the powder inner core include rare earth alloy powder and ferrosilicon powder. The weight of the rare earth alloy powder is 97-103% of the weight of the ferrosilicon powder. The rare earth alloy powder is obtained by melting and crushing alloy raw powder. The alloy raw powder includes the following components in parts by weight: 14-16 kg of magnesium powder, 68-72 kg of rare earth silicon, and 12-18 kg of calcium silicate powder. The average particle size of the rare earth alloy powder is 0.5-2.5 mm.

2. The preparation process of the spheroidizing wire for improving the vermicularization rate of castings according to claim 1, characterized in that, It includes the following steps: (1) Mix magnesium powder, rare earth silicon, and calcium silicate powder to obtain alloy raw powder. After melting the alloy raw powder, it is cooled in a mold to obtain an alloy block. (2) Demold the alloy block and then crush it to obtain rare earth alloy powder. (3) Mix the rare earth alloy powder and ferrosilicon powder to obtain a powder inner core. Perform core wrapping processing on the powder inner core and the iron sheet shell to obtain a spheroidizing wire for improving the vermicularization rate of castings.

3. The preparation process of the spheroidizing wire for improving the vermicularization rate of castings according to claim 2, characterized in that, The components of the powder inner core further include magnesium oxide powder and aluminum powder. The magnesium oxide powder and aluminum powder are mixed together with the rare earth alloy powder and ferrosilicon powder in step (3) of preparing the spheroidizing wire.

4. The preparation process of the spheroidizing wire for improving the vermicularization rate of castings according to claim 3, characterized in that, The molar ratio of the magnesium oxide powder to the aluminum powder is 3:(2.04-2.08).

5. The preparation process of the spheroidizing wire for improving the vermicularization rate of castings according to claim 3, characterized in that, The components of the powder inner core further include limestone powder. The limestone powder is mixed together with the rare earth alloy powder and ferrosilicon powder in step (3) of preparing the spheroidizing wire.

6. The preparation process of the spheroidizing wire for improving the vermicularization rate of castings according to claim 5, characterized in that, The dosage of the limestone powder is 8-12% of the weight of the rare earth alloy powder.

7. The preparation process of the spheroidizing wire for improving the vermicularization rate of castings according to claim 5, characterized in that, The components of the powder inner core further include nano calcium carbonate. The nano calcium carbonate is mixed together with the rare earth alloy powder and ferrosilicon powder in step (3) of preparing the spheroidizing wire.

8. The preparation process of the spheroidizing wire for improving the vermicularization rate of castings according to claim 7, characterized in that, The dosage of the nano calcium carbonate is 14-16% of the weight of the limestone powder.

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