A ductile iron and its preparation method and application

Abstract

The invention discloses a ductile iron and a preparation method and application thereof, belonging to the technical field of alloys; the ductile iron is composed of the following elements in mass fraction: C, 2.0% to 3.0%; Ni, 1.8% to 2.0%; Cu, 1.1% to 1.2%; Mn, 0.4% to 0.5%; Sn, 0.45% to 0.50%; Ti, 0.20% to 0.25%; N, 0.1% to 0.2%; Si, 0.12% to 0.15%; Mg, 0.1% to 0.12%; RE, 0.01% to 0.04% and the balance is Fe. The ductile iron of the invention controls the content of each preparation element, thereby achieving control of the hardness of the ductile iron; the invention also generates titanium nitride and titanium nitride in the process of spheroidizing titanium dioxide, and the above two phases are reinforcing phases in the ductile iron, thereby improving the hardness of the ductile iron.

Description

Technical Field

[0001] The invention belongs to the technical field of alloys, and in particular relates to ductile iron and a preparation method and application thereof. Background Art

[0002] Ductile iron is a high-strength cast iron material whose comprehensive properties are close to those of steel, precisely based on its excellent performance.

[0003] The related technology provides a ductile iron grinding ball, the chemical composition of which includes, by mass percentage, C: 3.6% to 3.7%, Si: 2.5% to 2.8%, Mn: 1.6% to 1.8%, Sn: 0.07% to 0.1%, Mg: 0.03% to 0.05%, Re: 0.02% to 0.03%, S: ≤0.06%, P: ≤0.1% and the rest is Fe; the hardness of the grinding ball is 63.4HRC, which is relatively low.

[0004] Therefore, the present invention provides a ductile iron to solve at least one aspect of the problems and defects mentioned in the above background technology. Summary of the invention

[0005] An object of the present invention is to provide a ductile iron to solve at least one aspect of the problems and defects mentioned in the above background technology.

[0006] The invention also provides a method for preparing the ductile iron.

[0007] The invention also provides application of the ductile iron.

[0008] Specifically, the first aspect of the present invention provides a ductile iron, which is composed of the following elements by mass fraction:

[0009] C, 2.0% ~ 3.0%; Ni, 1.8% ~ 2.0%; Cu, 1.1% ~ 1.2%; Mn, 0.4% ~ 0.5%; Sn, 0.45% ~ 0.50%; Ti, 0.20% ~ 0.25%; N, 0.1% ~ 0.2%; Si, 0.12% ~ 0.15%; Mg, 0.1% ~ 0.12%; RE, 0.01% ~ 0.04% and the balance is Fe.

[0010] According to a technical solution of the ductile iron technical solution of the present invention, at least the following beneficial effects are achieved:

[0011] C is the main element for forming eutectic carbides, which play an important role in wear resistance. The carbon content determines the amount of carbides. However, if the carbon content is too high, the toughness will decrease. Comprehensive consideration is taken to determine the carbon content within the above range.

[0012] Ti is an element that forms titanium carbide and titanium nitride. It can form appropriate amounts of carbides / nitrides with carbon / nitrogen to increase the hardness of the grinding ball.

[0013] Cu can promote graphitization during eutectic transformation, reduce the critical temperature of austenite transformation, promote the formation of pearlite, and is beneficial to reducing or eliminating the formation of free cementite, thereby improving the toughness of ductile iron.

[0014] The role of Mn is to deoxidize, strengthen the matrix and form carbides. Too high a manganese content increases the stability of austenite, reduces the Ms point, and is not conducive to the transformation of cast austenite; a small amount of manganese has a refining effect on troostite.

[0015] During the isothermal quenching transformation process, silicon can inhibit the formation of carbides. The carbon discharged while forming acicular ferrite can be enriched in the retained austenite, which is beneficial to the formation of carbide-free acicular ferrite and the stability of residual austenite, and has a refining effect on the acicular ferrite. However, when the silicon content is too high, it mainly exists in the matrix in the form of solid solution, causing lattice distortion and reducing the plastic toughness of the material.

[0016] Sn has a strong effect of promoting pearlite transformation and improving the toughness and strength of grinding ball materials by refining pearlite. However, as the tin content increases, the shape of graphite becomes flaky, which is not conducive to improving the hardness of the grinding ball.

[0017] Rare earth elements (RE) have strong desulfurization and deoxidation effects in raw molten iron, which is beneficial to purifying molten iron and spheroidizing it, reducing casting defects and stabilizing production.

[0018] Magnesium mainly plays a role in spheroidizing graphite and removing part of the sulfur in the molten iron.

[0019] An appropriate amount of magnesium and rare earth elements can not only ensure good graphite spheroidization, but also improve the strength and elongation of ductile iron. However, too high a content will deteriorate the graphite morphology and reduce the spheroidization rate. Therefore, in order to ensure the spheroidization effect, the content of magnesium and rare earth elements needs to be controlled.

[0020] According to some embodiments of the present invention, the mass fraction of C in the ductile iron is 2.5% to 2.8%.

[0021] According to some embodiments of the present invention, the mass fraction of N in the ductile iron is 0.12% to 0.15%.

[0022] According to some embodiments of the present invention, the RE element is lanthanum.

[0023] The second aspect of the present invention provides a method for preparing the ductile iron, comprising the following preparation steps:

[0024] S1. Smelting pig iron, copper, iron-nickel alloy, ferromanganese alloy and ferrotin alloy to obtain a melt;

[0025] S2, mixing the melt, silicon nitride, titanium dioxide and a spheroidizing agent, performing a spheroidizing reaction, and then incubating and pouring;

[0026] The pouring temperature is 1300°C to 1500°C.

[0027] According to one technical solution of the preparation method technical solution of the present invention, at least beneficial effects are achieved:

[0028] The present invention adds titanium dioxide and silicon nitride during the spheroidizing process, utilizes the good wettability of titanium dioxide and silicon nitride, improves the plasticity of the alloy structure by preventing the aggregation of repelled electrons, and makes the prepared ductile iron material have excellent hardenability, high hardness after quenching, small deformation and uniform structure.

[0029] At the same time, titanium dioxide will also generate titanium nitride and titanium nitride in this process. The above two phases are reinforcing phases in ductile iron, thereby increasing the hardness of ductile iron.

[0030] According to some embodiments of the present invention, the smelting temperature is 1450°C to 1500°C.

[0031] According to some embodiments of the present invention, the spheroidizing agent is FeSiMg6RE2.

[0032] The present invention ensures a certain amount of residual magnesium in the molten iron by selecting FeSiMg6RE2 as the spheroidizing agent, and also ensures the appropriate ratio requirement of the magnesium content and the rare earth element content in the ductile iron during the spheroidizing treatment, effectively preventing the graphite shape distortion caused by the excessive rare earth element content in the molten iron, reducing the white cast iron tendency, and obtaining a better spheroidizing effect.

[0033] According to some embodiments of the present invention, an inoculant is added during the inoculation process, and the inoculant is ferrosilicon alloy.

[0034] According to some embodiments of the present invention, the mass fraction of silicon in the ferrosilicon alloy is 70% to 80%.

[0035] In the present invention, ductile iron is made of ferrosilicon alloy during the inoculation process. Ferrosilicon alloy has a strong chemical affinity with oxygen and is a very good diffusion deoxidizer, which can significantly improve the strength and hardness of ductile iron.

[0036] According to some embodiments of the present invention, D50 of the titanium dioxide is 0.2 μm to 0.3 μm.

[0037] The invention controls the particle size of the reinforcing phase by controlling the particle size of titanium dioxide, thereby controlling the hardness of the ductile iron.

[0038] According to some embodiments of the present invention, a casting is obtained after pouring; and the casting is further subjected to heat treatment.

[0039] According to some embodiments of the present invention, the heat treatment comprises the following steps:

[0040] The casting is sequentially heated for the first time, kept warm for the first time, cooled for the first time, cooled for the second time, heated for the second time, kept warm for the third time, cooled for the fourth time, heated for the third time, kept warm for the third time and cooled for the fifth time.

[0041] According to some embodiments of the present invention, the final temperature of the first heating is 800°C to 850°C.

[0042] According to some embodiments of the present invention, the first insulation time is 5 h to 6 h.

[0043] According to some embodiments of the present invention, the first cooling rate is 10° C. / min to 12° C. / min.

[0044] According to some embodiments of the present invention, the final temperature of the first cooling is 550°C to 600°C.

[0045] According to some embodiments of the present invention, the final temperature of the second cooling is 20°C to 30°C.

[0046] According to some embodiments of the present invention, the second cooling is performed by air cooling.

[0047] According to some embodiments of the present invention, the final temperature of the second heating is 630°C to 680°C.

[0048] According to some embodiments of the present invention, the second insulation time is 3h to 5h.

[0049] According to some embodiments of the present invention, the third cooling rate is 6°C / min to 8°C / min.

[0050] According to some embodiments of the present invention, the final temperature of the third cooling is 550°C to 600°C.

[0051] According to some embodiments of the present invention, the final temperature of the fourth cooling is 20°C to 30°C.

[0052] According to some embodiments of the present invention, the fourth cooling method is air cooling.

[0053] According to some embodiments of the present invention, the final temperature of the third heating is 400°C to 450°C.

[0054] According to some embodiments of the present invention, the third insulation time is 1 h to 2 h.

[0055] According to some embodiments of the present invention, the fifth cooling is performed by air cooling.

[0056] In the preparation process of ductile iron, the melting temperature and pouring temperature must be strictly controlled. By keeping warm and cooling at a specific temperature, the growth of microstructures that can improve the surface hardness is promoted. By controlling the heat treatment procedure, the best surface state can be obtained, thereby improving the performance of ductile iron.

[0057] A third aspect of the present invention provides the use of the ductile iron in the preparation of manhole covers. DETAILED DESCRIPTION

[0058] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0059] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0060] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0061] In the embodiment of the present invention, the RE element is lanthanum.

[0062] Example 1

[0063] This embodiment is a ductile iron composed of the following elements:

[0064] C, 3.0%; Ni, 1.9%; Cu, 1.2%; Mn, 0.5%; Sn, 0.45%; Ti, 0.25%; N, 0.1%; Si, 0.15%; Mg, 0.12%; RE, 0.04% and the balance is Fe.

[0065] The preparation method of ductile iron in this embodiment consists of the following preparation steps:

[0066] S1. Prepare materials:

[0067] Prepare materials according to the element requirements of ductile iron:

[0068] The raw materials for preparation are as follows:

[0069] Pig iron, copper, iron-nickel alloy, manganese-iron alloy, tin-iron alloy, titanium dioxide (D50 is 0.2 μm), silicon nitride, spheroidizing agent (FeSiMg6RE2), inoculant (ferrosilicon alloy, the mass fraction of silicon is 75%).

[0070] S2. Melting:

[0071] Pig iron, copper, iron-nickel alloy, manganese-iron alloy and tin-iron alloy are mixed and smelted, the temperature is raised to 1500° C., smelted until clear, and allowed to stand for 10 minutes to obtain a melt.

[0072] S3, Spheroidization:

[0073] Silicon nitride, titanium dioxide and a spheroidizing agent are added to the melt for spheroidization (cap spheroidization method) at a temperature of 1420°C.

[0074] S4, breeding:

[0075] Adding the inoculant to the melt after the spheroidization treatment in step S3, and performing a pouring treatment after the treatment is completed;

[0076] The temperature of the pouring treatment is 1380°C, and the casting is cast;

[0077] S5, heating the casting to 850°C, keeping it warm for 5h, cooling it to 550°C at a rate of 12°C / min, and then air-cooling it to 25°C; obtaining the first treated casting;

[0078] The first treated casting was heated to 650°C, kept at this temperature for 3 hours, cooled to 550°C at a rate of 6°C / min, and then air-cooled to 25°C to obtain the second treated casting;

[0079] The second treated casting is then heated to 450°C, kept warm for 2 hours, and then air-cooled to 25°C to obtain ductile iron.

[0080] Example 2

[0081] This embodiment is a method for preparing ductile iron, which is different from Embodiment 1 in that the D50 of titanium dioxide is 0.3 μm.

[0082] Example 3

[0083] This embodiment is a ductile iron composed of the following elements:

[0084] C, 2.0%; Ni, 2.0%; Cu, 1.1%; Mn, 0.4%; Sn, 0.5%; Ti, 0.22%; N, 0.10%; Si, 0.12%; Mg, 0.12%; RE, 0.04% and the balance is Fe.

[0085] The preparation method of ductile iron in this embodiment is carried out with reference to Example 1.

[0086] Example 4

[0087] This embodiment is a method for preparing ductile iron, which differs from Embodiment 1 in that:

[0088] S5, heating the casting to 850°C, keeping it warm for 5h, cooling it to 550°C at a rate of 12°C / min, and then air-cooling it to 25°C; obtaining the first treated casting;

[0089] The first treated casting was heated to 650°C, kept warm for 3 hours, cooled to 550°C at a rate of 6°C / min, and then air-cooled to 25°C to obtain ductile iron.

[0090] Example 5

[0091] This embodiment is a method for preparing ductile iron, which differs from Embodiment 1 in that:

[0092] S5, heating the casting to 850°C, keeping it warm for 5h, cooling it to 550°C at a rate of 12°C / min, and then air-cooling it to 25°C; obtaining the first treated casting;

[0093] The first treated casting is then heated to 450°C, kept warm for 2 hours, and then air-cooled to 25°C to obtain ductile iron.

[0094] Example 6

[0095] This embodiment is a method for preparing ductile iron, which differs from Embodiment 1 in that:

[0096] S5, heating the casting to 650°C, keeping it warm for 3h, cooling it to 550°C at a rate of 6°C / min, and then air cooling it to 25°C; obtaining the first treated casting;

[0097] The first treated casting is then heated to 450°C, kept warm for 2 hours, and then air-cooled to 25°C to obtain ductile iron.

[0098] Example 7

[0099] This embodiment is a method for preparing ductile iron, which differs from Embodiment 1 in that:

[0100] S5. Heat the casting to 850°C, keep it warm for 5 hours, cool it to 550°C at a rate of 12°C / min, and then air-cool it to 25°C to obtain ductile iron.

[0101] Example 8

[0102] This embodiment is a method for preparing ductile iron, which differs from Embodiment 1 in that:

[0103] S5. Heat the casting to 650°C, keep it warm for 3 hours, cool it to 550°C at a rate of 6°C / min, and then air-cool it to 25°C to obtain ductile iron.

[0104] Example 9

[0105] This embodiment is a method for preparing ductile iron, which differs from Embodiment 1 in that:

[0106] S5. Heat the casting to 450°C, keep it warm for 2 hours, and then air-cool it to 25°C to obtain ductile iron.

[0107] Comparative Example 1

[0108] This comparative example is a ductile iron composed of the following elements:

[0109] C, 1.5%; Ni, 1.8%; Cu, 1.15%; Mn, 0.43%; Sn, 0.45%; Ti, 0.18%; N, 0.08%; Si, 0.15%; Mg, 0.12%; RE, 0.04% and the balance is Fe.

[0110] The preparation method of ductile iron in this comparative example is carried out with reference to Example 1.

[0111] Comparative Example 2

[0112] This comparative example is a ductile iron composed of the following elements:

[0113] C, 3.0%; Ni, 1.9%; Cu, 1.2%; Mn, 0.5%; Sn, 0.45%; Ti, 0.25%; N, 0.1%; Si, 0.15%; Mg, 0.16%; RE, 0.05% and the balance is Fe.

[0114] The preparation method of ductile iron in this comparative example is carried out with reference to Example 1.

[0115] Comparative Example 3

[0116] This comparative example is a ductile iron composed of the following elements:

[0117] C, 3.5%; Ni, 1.9%; Cu, 1.2%; Mn, 0.8%; Sn, 0.45%; Ti, 0.25%; N, 0.1%; Si, 0.17%; Mg, 0.11%; RE, 0.03% and the balance is Fe.

[0118] The preparation method of ductile iron in this comparative example is carried out with reference to Example 1.

[0119] The performance test results of the ductile iron prepared in Examples 1 to 9 of the present invention and Comparative Examples 1 to 3 are shown in Table 1.

[0120] Table 1 Performance test results of ductile iron obtained in Examples 1 to 9 of the present invention and Comparative Examples 1 to 3

[0121] - Hardness(HRC) Example 1 69.3 Example 2 68.9 Example 3 68.5 Example 4 65.3 Example 5 64.7 Example 6 66.4 Example 7 63.8 Example 8 62.1 Example 9 61.8 Comparative Example 1 59.2 Comparative Example 2 58.1 Comparative Example 3 60.9

[0122] In summary, the ductile iron of the present invention controls the content of each preparation element, thereby achieving control of the hardness of the ductile iron; the present invention also adds titanium dioxide and silicon nitride during the spheroidizing process, utilizes titanium dioxide and silicon nitride to show good wettability, and improves the plasticity of the alloy structure by preventing the aggregation of repelling electrons, so that the prepared ductile iron material has excellent hardenability, high hardness after quenching, small deformation, and uniform structure. In addition, titanium dioxide will also generate titanium nitride and titanium nitride in the process, and the above two phases are reinforcing phases in the ductile iron, thereby improving the hardness of the ductile iron.

[0123] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A ductile iron, characterized in that: It is composed of the following elements in mass fractions: C, 2.0%~3.0%; Ni, 1.8%~2.0%; Cu, 1.1%~1.2%; Mn, 0.4%~0.5%; Sn, 0.45%~0.50%; Ti, 0.20%~0.25%; N, 0.1%~0.2%; Si, 0.12%~0.15%; Mg, 0.1%~0.12%; RE, 0.01%~0.04% and the balance is Fe; The preparation method of the spheroidal milled cast iron comprises the following preparation steps: S1. Smelting pig iron, copper, iron-nickel alloy, ferromanganese alloy and ferrotin alloy to obtain a melt; S2, mixing the melt, silicon nitride, titanium dioxide and a spheroidizing agent, performing a spheroidizing reaction, and then incubating and pouring; The pouring temperature is 1300°C to 1500°C; After the pouring, a casting is obtained; and the casting is subjected to heat treatment; The heat treatment comprises the following steps: The casting is sequentially heated for the first time, kept warm for the first time, cooled for the first time, cooled for the second time, heated for the second time, kept warm for the third time, cooled for the fourth time, heated for the third time, kept warm for the third time, and cooled for the fifth time; The final temperature of the first heating is 800°C to 850°C; The first insulation time is 5h~6h; The first cooling rate is 10°C / min~12°C / min; The final temperature of the first cooling is 550°C to 600°C; The final temperature of the second cooling is 20°C to 30°C; The second cooling method is air cooling; The final temperature of the second heating is 630°C to 680°C; The second insulation time is 3h~5h; The third cooling rate is 6°C / min~8°C / min; The final temperature of the third cooling is 550°C to 600°C; The final temperature of the fourth cooling is 20°C to 30°C; The fourth cooling method is air cooling; The final temperature of the third heating is 400°C to 450°C; The third insulation time is 1h~2h; The fifth cooling method is air cooling.

2. The ductile iron according to claim 1, characterized in that: The mass fraction of C is 2.5% to 2.8%.

3. The ductile iron according to claim 1, characterized in that: The mass fraction of N is 0.12% to 0.15%.

4. The ductile iron according to claim 1, characterized in that: The smelting temperature is 1450°C to 1500°C.

5. The ductile iron according to claim 1, characterized in that: The spheroidizing agent is FeSiMg6RE2.

6. The ductile iron according to claim 1, characterized in that: In the inoculation process, an inoculant is added, and the inoculant is ferrosilicon alloy.

7. The ductile iron according to claim 6, characterized in that: The mass fraction of silicon in the ferrosilicon alloy is 70% to 80%.

8. The ductile iron according to claim 1, characterized in that: The D50 of the titanium dioxide is 0.2 μm to 0.3 μm.

9. Use of the ductile iron according to any one of claims 1 to 8 in the preparation of manhole covers.