Nodular cast iron and preparation method and application thereof

Abstract

The invention discloses nodular cast iron and a preparation method and application thereof, and belongs to the technical field of cast iron. The nodular cast iron comprises C, Si, Mn, Mg, Re, Mo, W, Al, Sn, Ti and the like. When the nodular cast iron is prepared, Mo, W and Ti are added in the form of powder, and composition segregation caused by dissolution lag is avoided. When the cast ingot is subjected to heat treatment, a double-stage austenitizing treatment process is adopted, (Mo, W) C composite carbide can be fully dissolved through first-stage treatment, and casting stress is eliminated; and the second-stage treatment can inhibit the generation of pearlite and promote the precipitation of nanoscale (Mo, W) C. The spheroidal graphite cast iron successfully solves the problems of insufficient high-temperature strength, poor structure stability, weak environmental resistance and the like of a traditional material through multi-stage synergism and antagonism effects among elements, so that the spheroidal graphite cast iron can also have excellent comprehensive performance in a high-temperature environment.

Description

Technical Field

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

[0002] Ductile iron is widely used in internal combustion engines, hydraulic components, heavy machinery and other fields due to its excellent mechanical properties and castability. Traditional ductile iron (such as QT400-18, QT600-3) is mainly composed of Fe-C-Si-Mn-Mg, and its room temperature tensile strength is generally lower than 700MPa. It is prone to creep deformation and structural degradation when in service at temperatures above 400℃, which seriously restricts its application in high temperature conditions (such as gas turbine casings, high temperature valves, etc.).

[0003] In the prior art, the solution of improving high temperature performance by adding alloying elements has significant defects. For example, the prior art discloses a Mo-containing ductile iron (Mo 0.2-0.4%), which can improve the short-term high temperature strength, but excessive Mo will cause carbide coarsening, and the creep rate at 600°C is still as high as 5×10 -8 / s, and the graphite balls are distorted after long-term heat exposure (the spheroidization rate drops to below 75%); the prior art also discloses a ductile cast iron, which uses Sb (0.02-0.05%) to inhibit pearlite transformation, but aggravates the grain boundary segregation of low-melting-point elements such as Sn and Sb, causing the 600°C tensile strength decay rate to exceed 40%; there are also reports in the prior art that the oxidation resistance of ductile iron is improved by adding Al (0.5-1.0%), but the interaction between Al and Si is not coordinated, resulting in the increase of the eutectic size to more than 200μm, significantly reducing fatigue life. In addition, the rare earth treatment of conventional ductile iron mostly uses Ce-based alloys (such as Fe-Si-Mg-Ce), which are prone to form coarse Ce when the Re content exceeds 0.1%. 2 O 3 Inclusions (size > 10 μm) cause microscopic defects and accelerate high temperature crack propagation. Although the addition of trace Sn (< 0.03%) can improve the ferrite morphology, the non-equilibrium segregation of Sn at the grain boundary makes the material sensitive to stress corrosion under thermal cycling conditions.

[0004] The above technical bottlenecks indicate that there is an urgent need to develop a new type of ductile iron material that, while ensuring process feasibility, can achieve a comprehensive improvement in high-temperature strength, creep resistance and oxidation resistance through multi-component synergistic alloying and precise control of the microstructure, so as to meet the stringent demands of advanced energy equipment for high-temperature resistant structural materials. Summary of the invention

[0005] In view of the above-mentioned prior art, the present invention provides a ductile iron and a preparation method and application thereof, so as to solve the technical problems of the prior ductile iron such as poor high temperature strength and poor creep resistance.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is to provide a ductile iron, which includes the following components in mass percentage:

[0007] C 3.4~3.6%, Si 2.8~3.2%, Mn 0.6~0.8%, Mg 0.04~0.07%, Re 0.03~0.05%, Mo 0.3~0.5%, W 0.2~0.4%, Al 0.8~1.2%, Sn 0.05~0.08%, Ti 0.15~0.25%, S≤0.012%, P≤0.025%, and the balance is iron.

[0008] Based on the above technical solution, the present invention can also be improved as follows.

[0009] Further, the ductile iron includes the following components in percentage by mass:

[0010] C 3.5%, Si 3.0%, Mn 0.7%, Mg 0.05%, Re 0.04%, Mo 0.4%, W 0.3%, Al 1.0%, Sn 0.06%, Ti 0.2%, S ≤ 0.012%, P ≤ 0.025%, and the balance is iron.

[0011] Furthermore, Re includes Y and La, the mass percentage of Y in the ductile iron is 0.02-0.04%, and the mass percentage of La in the ductile iron is 0.01-0.02%.

[0012] The present invention also discloses a method for preparing the ductile iron, comprising the following steps:

[0013] (1) crushing Q12 pig iron into iron blocks with a particle size of 30 to 50 mm; cutting low-sulfur and phosphorus scrap steel into sheets of 50×50 mm; subjecting the recycled materials to magnetic separation and impurity removal treatment; preparing alloy powders of 80 to 120 μm from Mo-Fe master alloy, W-Fe master alloy and Fe-Ti master alloy; crushing Al blocks into particles of 3 to 5 mm; preparing cored wires from Sn particles and Fe-Mn alloy;

[0014] (2) Q12 pig iron, low sulfur and phosphorus scrap steel and recycled materials are sequentially loaded into a medium frequency induction furnace from bottom to top, and the temperature is raised to 1540-1560° C. using a step power, and then Mo-Fe master alloy powder, W-Fe master alloy powder, Fe-Ti master alloy powder and Al particles are added, and electromagnetic stirring is performed; after all are melted, the content of each element in the molten iron is detected, and the content of each element is adjusted to the formula requirement;

[0015] (3) placing the rare earth magnesium alloy into the preheated spheroidizing bag, then filling it with molten iron, and simultaneously filling it with liquid modifier and silicon carbide particles, and simultaneously injecting the cored wire prepared in step (1) by wire feeding method; the liquid modifier is Fe-Ti alloy powder;

[0016] (3) pouring to obtain a casting;

[0017] (4) heating the casting to 900-950°C, keeping it at that temperature for 2-4 hours, then cooling it to 850-880°C, keeping it at that temperature for 1-3 hours; then cooling it to 300°C at a cooling rate of 30-50°C / min, and then air cooling it to room temperature;

[0018] (5) The ingot treated in step (4) is heated to 450° C., kept at this temperature for 4 h, and then air-cooled to room temperature.

[0019] Furthermore, in step (2), the mass ratio of Q12 pig iron, low sulfur and phosphorus scrap steel and recycled materials is 55:30:15.

[0020] Furthermore, in step (2), the step power heating method is to first heat at a power of 800 kW for 20 minutes, then adjust the power to 1500 kW, heat for 20 minutes, and then adjust the power to 2000 kW, and heat to the final temperature.

[0021] Furthermore, the preheating temperature of the spheroidizing bag in step (3) is 800°C.

[0022] Furthermore, the rare earth magnesium alloy is Y-Mg alloy and La-Mg alloy.

[0023] Furthermore, in step (3), the charging rates of the liquid modifier and silicon carbide particles are both 0.1-0.3 kg / min; and the particle size of the silicon carbide particles is 50-100 nm.

[0024] The invention also discloses the application of the ductile iron in preparing high temperature resistant structural parts.

[0025] The beneficial effects of the present invention are:

[0026] 1. The constituent elements of the ductile iron in the present invention include C, Si, Mn, Mg, Re, Mo, W, Al, Sn, Ti, etc. Among them, Ti preferentially forms a TiC primary phase, which can serve as a substrate for heterogeneous nucleation of (Mo, W) C, promoting the formation of nanocarbides in the ductile iron. The presence of nanocarbides can pin dislocations, thereby improving the high-temperature strength of the ductile iron; Mo and W form a composite solid solution in austenite, which can effectively reduce the diffusion coefficient of carbon and synergistically promote the uniform precipitation of (Mo, W) C carbides, thereby forming uniformly distributed fine grains in the ductile iron, thereby reducing the high-temperature creep rate of the ductile iron. Al and Si form Al during high-temperature oxidation. 2 O 3 -SiO 2 Interpenetrating network structure, fills the microcracks of a single oxide film, and Re segregates at the oxide film / matrix interface, inhibits oxygen from diffusing inward along the grain boundary, and improves the oxidation resistance of ductile iron. Sn and Re co-segregate at the austenite grain boundary to form Sn-Re atomic clusters, occupying segregation sites of harmful elements such as P and S, thereby reducing impurity concentration; and Mg and Re form Mg-Re-O composite inclusions, which can effectively adsorb free S impurities, effectively reduce the generation of MgS brittle phase, and thus improve the strength of ductile iron. In addition, the present application can expand the eutectic reaction interval by increasing the content of C and Si, and can effectively promote the formation of a small and uniform ferrite matrix, and Al is dissolved in the ferrite, which can compensate for the strength loss caused by high Si, not only ensuring the strength of cast iron, but also improving the ductility of cast iron.

[0027] 2. When preparing spheroidal cast iron, the present invention first prepares Mo-Fe master alloy, W-Fe master alloy and Fe-Ti master alloy into alloy powder, which can shorten the smelting time and avoid component segregation caused by dissolution lag. Sn particles and Fe-Mn alloy are made into cored wires, and the Fe-Mn / Sn cored wires are injected with the flow, which can effectively avoid the volatilization of Sn and the oxidation of Mn, and ensure the effective synergy of Sn / Mn elements; liquid modifiers and silicon carbide particles are also injected with the flow, and Ti in the liquid modifier forms a TiC primary phase, which increases the number of graphite balls in the cast iron, and silicon carbide particles, as a silicon-based nucleation substrate, can increase the number and regularity of graphite balls. The present invention adopts a two-stage austenitizing treatment process when heat treating the ingot, wherein the first stage treatment (900-950°C / 2-4h) can fully dissolve the (Mo, W)C composite carbide and eliminate the casting stress; the second stage treatment (850-880°C / 1-3h) can inhibit the formation of pearlite and promote the precipitation of nano-scale (Mo, W)C; after the two-stage treatment, uniformly dispersed graphite balls are formed inside the ductile iron, and the performance of the ductile iron is guaranteed.

[0028] 3. The ductile iron in the present invention successfully solves the problems of insufficient high-temperature strength, poor organizational stability, and weak environmental resistance of traditional materials through multi-level synergistic and antagonistic effects between elements, so that it can also have excellent comprehensive performance in high-temperature environments. DETAILED DESCRIPTION

[0029] The specific implementation modes of the present invention are described in detail below with reference to the embodiments.

[0030] Example 1

[0031] A ductile iron comprising the following components in percentage by mass:

[0032] C 3.5%, Si 3.0%, Mn 0.7%, Mg 0.05%, Y 0.02%, La 0.02%, Mo 0.4%, W0.3%, Al 1.0%, Sn 0.06%, Ti 0.2%, S≤0.012%, P≤0.025%, and the balance is iron.

[0033] The ductile iron in the present embodiment is prepared by the following steps:

[0034] (1) crushing Q12 pig iron into iron blocks with a particle size of about 40 mm; cutting low-sulfur and phosphorus scrap steel into sheets of 50×50 mm; subjecting the recycled materials to magnetic separation and impurity removal treatment; making Mo-Fe master alloy, W-Fe master alloy and Fe-Ti master alloy into alloy powders of about 100 μm; crushing Al blocks into particles of about 4 mm; making Sn particles and Fe-Mn alloy into cored wires;

[0035] (2) Q12 pig iron, low sulfur and phosphorus scrap steel and recycled materials are sequentially loaded into a medium frequency induction furnace from bottom to top, with the mass ratio of the three being 55:30:15; firstly, heating is performed at a power of 800 kW for 20 min, then adjusting the power to 1500 kW for 20 min, and then adjusting the power to 2000 kW for heating to 1550° C.; then, Mo-Fe master alloy powder, W-Fe master alloy powder, Fe-Ti master alloy powder and Al particles are added, and electromagnetic stirring is performed; after all are melted, the content of each element in the molten iron is detected, and the content of each element is adjusted to the formula requirement;

[0036] (3) placing the formulated amount of Y-Mg alloy and La-Mg alloy into a spheroidizing bag preheated to 800° C., then charging molten iron, and simultaneously charging Fe-Ti alloy powder and silicon carbide particles with a particle size of about 80 nm, both at a charging rate of 0.2 kg / min; and simultaneously injecting the cored wire prepared in step (1) by a wire feeding method;

[0037] (3) pouring to obtain a casting;

[0038] (4) The casting was heated to 920°C, kept at this temperature for 3 h, then cooled to 860°C, kept at this temperature for 2 h; then cooled to 300°C at a cooling rate of 40°C / min, and then air-cooled to room temperature;

[0039] (5) The ingot treated in step (4) is heated to 450° C., kept at this temperature for 4 h, and then air-cooled to room temperature.

[0040] Example 2

[0041] A ductile iron comprising the following components in percentage by mass:

[0042] C 3.4%, Si 3.2%, Mn 0.6%, Mg 0.07%, Y 0.02%, La 0.01%, Mo 0.5%, W0.2%, Al 1.2%, Sn 0.05%, Ti 0.25%, S≤0.012%, P≤0.025%, and the balance is iron.

[0043] The ductile iron in the present embodiment is prepared by the following steps:

[0044] (1) crushing Q12 pig iron into iron blocks with a particle size of about 30 mm; cutting low-sulfur and phosphorus scrap steel into sheets of 50×50 mm; subjecting the recycled materials to magnetic separation and impurity removal treatment; making Mo-Fe master alloy, W-Fe master alloy and Fe-Ti master alloy into alloy powders of about 80 μm; crushing Al blocks into particles of about 3 mm; making Sn particles and Fe-Mn alloy into cored wires;

[0045] (2) Q12 pig iron, low sulfur and phosphorus scrap steel and recycled materials are sequentially loaded into a medium frequency induction furnace from bottom to top, with the mass ratio of the three being 55:30:15; firstly, heating is performed at a power of 800 kW for 20 min, then adjusting the power to 1500 kW for 20 min, and then adjusting the power to 2000 kW for heating to 1540° C.; then, Mo-Fe master alloy powder, W-Fe master alloy powder, Fe-Ti master alloy powder and Al particles are added, and electromagnetic stirring is performed; after all are melted, the content of each element in the molten iron is detected, and the content of each element is adjusted to the formula requirement;

[0046] (3) placing the formulated amount of Y-Mg alloy and La-Mg alloy into a spheroidizing bag preheated to 800° C., then charging molten iron, and simultaneously charging Fe-Ti alloy powder and silicon carbide particles with a particle size of about 50 nm, both at a charging rate of 0.1 kg / min; and simultaneously injecting the cored wire prepared in step (1) by a wire feeding method;

[0047] (3) pouring to obtain a casting;

[0048] (4) The casting was heated to 900°C, kept at this temperature for 4 h, then cooled to 850°C, kept at this temperature for 3 h; then cooled to 300°C at a cooling rate of 30°C / min, and then air-cooled to room temperature;

[0049] (5) The ingot treated in step (4) is heated to 450° C., kept at this temperature for 4 h, and then air-cooled to room temperature.

[0050] Example 3

[0051] A ductile iron comprising the following components in percentage by mass:

[0052] C 3.6%, Si 2.8%, Mn 0.8%, Mg 0.04%, Y 0.04%, La 0.01%, Mo 0.3%, W0.4%, Al 0.8%, Sn 0.08%, Ti 0.15%, S≤0.012%, P≤0.025%, and the balance is iron.

[0053] The ductile iron in the present embodiment is prepared by the following steps:

[0054] (1) crushing Q12 pig iron into iron blocks with a particle size of about 50 mm; cutting low-sulfur and phosphorus scrap steel into sheets of 50×50 mm; subjecting the recycled materials to magnetic separation and impurity removal treatment; making Mo-Fe master alloy, W-Fe master alloy and Fe-Ti master alloy into alloy powders of about 120 μm; crushing Al blocks into particles of about 5 mm; making Sn particles and Fe-Mn alloy into cored wires;

[0055] (2) Q12 pig iron, low sulfur and phosphorus scrap steel and recycled materials are sequentially loaded into a medium frequency induction furnace from bottom to top, with the mass ratio of the three being 55:30:15; firstly, heating is performed at a power of 800 kW for 20 min, then adjusting the power to 1500 kW for 20 min, and then adjusting the power to 2000 kW for heating to 1560° C.; then, Mo-Fe master alloy powder, W-Fe master alloy powder, Fe-Ti master alloy powder and Al particles are added, and electromagnetic stirring is performed; after all are melted, the content of each element in the molten iron is detected, and the content of each element is adjusted to the formula requirement;

[0056] (3) placing the formulated amount of Y-Mg alloy and La-Mg alloy into a spheroidizing bag preheated to 800° C., then charging molten iron, and simultaneously charging Fe-Ti alloy powder and silicon carbide particles with a particle size of about 100 nm, both at a charging rate of 0.3 kg / min; and simultaneously injecting the cored wire prepared in step (1) by a wire feeding method;

[0057] (3) pouring to obtain a casting;

[0058] (4) Heat the casting to 950°C, keep it at that temperature for 2 hours, then cool it to 880°C, keep it at that temperature for 1 hour; then cool it to 300°C at a cooling rate of 50°C / min, and then air cool it to room temperature;

[0059] (5) The ingot treated in step (4) is heated to 450° C., kept at this temperature for 4 h, and then air-cooled to room temperature.

[0060] Comparative Example 1

[0061] A ductile iron comprising the following components in percentage by mass:

[0062] C 3.5%, Si 3.0%, Mn 0.7%, Mg 0.05%, Y 0.02%, La 0.02%, Mo 0.4%, W0.3%, Sn 0.06%, S≤0.012%, P≤0.025%, and the balance is iron.

[0063] The ductile iron in this comparative example is prepared by the following steps:

[0064] (1) crushing Q12 pig iron into iron blocks with a particle size of about 40 mm; cutting low-sulfur and phosphorus scrap steel into sheets of 50×50 mm; subjecting the recycled materials to magnetic separation and impurity removal treatment; making Mo-Fe master alloy and W-Fe master alloy into alloy powders of about 100 μm; and making Sn particles and Fe-Mn alloy into cored wires;

[0065] (2) Q12 pig iron, low sulfur and phosphorus scrap steel and recycled materials are sequentially loaded into a medium frequency induction furnace from bottom to top, with the mass ratio of the three being 55:30:15; firstly, heating is performed at a power of 800 kW for 20 min, then adjusting the power to 1500 kW for 20 min, and then adjusting the power to 2000 kW for heating to 1550° C.; then, Mo-Fe master alloy powder and W-Fe master alloy powder are added, and electromagnetic stirring is performed; after all are melted, the content of each element in the molten iron is detected, and the content of each element is adjusted to the formula requirement;

[0066] (3) placing the formulated amount of Y-Mg alloy and La-Mg alloy into a spheroidizing bag preheated to 800° C., then charging molten iron, and charging silicon carbide particles with a particle size of about 80 nm at a rate of 0.2 kg / min; and simultaneously injecting the cored wire prepared in step (1) by a wire feeding method;

[0067] (3) pouring to obtain a casting;

[0068] (4) The casting was heated to 920°C, kept at this temperature for 3 h, then cooled to 860°C, kept at this temperature for 2 h; then cooled to 300°C at a cooling rate of 40°C / min, and then air-cooled to room temperature;

[0069] (5) The ingot treated in step (4) is heated to 450° C., kept at this temperature for 4 h, and then air-cooled to room temperature.

[0070] Comparative Example 2

[0071] A ductile iron comprising the following components in percentage by mass:

[0072] C 3.5%, Si 3.0%, Mn 0.7%, Mg 0.05%, Y 0.02%, La 0.02%, Al 1.0%, Sn0.06%, Ti 0.2%, S≤0.012%, P≤0.025%, and the balance is iron.

[0073] The ductile iron in this comparative example is prepared by the following steps:

[0074] (1) crushing Q12 pig iron into iron blocks with a particle size of about 40 mm; cutting low-sulfur and phosphorus scrap steel into sheets of 50×50 mm; subjecting the recycled materials to magnetic separation and impurity removal treatment; making Fe-Ti master alloy into alloy powder of about 100 μm; crushing Al blocks into particles of about 4 mm; and making Sn particles and Fe-Mn alloy into cored wires;

[0075] (2) Q12 pig iron, low sulfur and phosphorus scrap steel and recycled materials are sequentially loaded into a medium frequency induction furnace from bottom to top, with the mass ratio of the three being 55:30:15; firstly, the furnace is heated at a power of 800 kW for 20 min, then the power is adjusted to 1500 kW, and the furnace is heated for 20 min, and then the power is adjusted to 2000 kW, and the furnace is heated to 1550° C.; then, Fe-Ti master alloy powder and Al particles are added, and electromagnetic stirring is performed; after all the materials are melted, the content of each element in the molten iron is detected, and the content of each element is adjusted to the formula requirements;

[0076] (3) placing the formulated amount of Y-Mg alloy and La-Mg alloy into a spheroidizing bag preheated to 800° C., then charging molten iron, and simultaneously charging Fe-Ti alloy powder and silicon carbide particles with a particle size of about 80 nm, both at a charging rate of 0.2 kg / min; and simultaneously injecting the cored wire prepared in step (1) by a wire feeding method;

[0077] (3) pouring to obtain a casting;

[0078] (4) The casting was heated to 920°C, kept at this temperature for 3 h, then cooled to 860°C, kept at this temperature for 2 h; then cooled to 300°C at a cooling rate of 40°C / min, and then air-cooled to room temperature;

[0079] (5) The ingot treated in step (4) is heated to 450° C., kept at this temperature for 4 h, and then air-cooled to room temperature.

[0080] Experimental example

[0081] The high temperature strength of the ductile iron prepared in the above-mentioned embodiments and comparative examples was tested by the method described in ASTM E21, and the morphology of the ductile iron prepared in the above-mentioned embodiments and comparative examples was studied by the method described in ASTM A247. The results are shown in Table 1.

[0082] Table 1 Performance test results of ductile iron

[0083] High temperature strength (600°C, MPa) VI-type spheroidization rate (%) Example 1 478 98.3 Example 2 471 97.7 Example 3 474 97.9 Comparative Example 1 407 93.2 Comparative Example 2 402 88.7

[0084] Although the specific implementation of the present invention is described in detail in conjunction with the embodiments, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A ductile iron, characterized in that: The ductile iron comprises the following components in percentage by mass: C 3.4~3.6%, Si 2.8~3.2%, Mn 0.6~0.8%, Mg 0.04~0.07%, Re 0.03~0.05%, Mo 0.3~0.5%, W 0.2~0.4%, Al 0.8~1.2%, Sn 0.05~0.08%, Ti 0.15~0.25%, S≤0.012%, P≤0.025%, and the balance is iron.

2. The ductile iron according to claim 1, characterized in that: The ductile iron comprises the following components in percentage by mass: C 3.5%, Si 3.0%, Mn 0.7%, Mg 0.05%, Re 0.04%, Mo 0.4%, W 0.3%, Al 1.0%, Sn 0.06%, Ti 0.2%, S ≤ 0.012%, P ≤ 0.025%, and the balance is iron.

3. The ductile iron according to claim 1 or 2, characterized in that: The Re includes Y and La, the mass percentage of Y in the ductile iron is 0.02-0.04%, and the mass percentage of La in the ductile iron is 0.01-0.02%.

4. The method for preparing ductile iron according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) crushing Q12 pig iron into iron blocks with a particle size of 30 to 50 mm; cutting low-sulfur and phosphorus scrap steel into sheets of 50×50 mm; subjecting the recycled materials to magnetic separation and impurity removal treatment; preparing alloy powders of 80 to 120 μm from Mo-Fe master alloy, W-Fe master alloy and Fe-Ti master alloy; crushing Al blocks into particles of 3 to 5 mm; preparing cored wires from Sn particles and Fe-Mn alloy; (2) Q12 pig iron, low sulfur and phosphorus scrap steel and recycled materials are sequentially loaded into a medium frequency induction furnace from bottom to top, and the temperature is raised to 1540-1560° C. using a step power, and then Mo-Fe master alloy powder, W-Fe master alloy powder, Fe-Ti master alloy powder and Al particles are added, and electromagnetic stirring is performed; after all are melted, the content of each element in the molten iron is detected, and the content of each element is adjusted to the formula requirement; (3) placing the rare earth magnesium alloy into the preheated spheroidizing bag, then filling it with molten iron, and then filling it with liquid modifier and silicon carbide particles, and at the same time injecting the cored wire prepared in step (1) by wire feeding method; the liquid modifier is Fe-Ti alloy powder; (3) pouring to obtain a casting; (4) heating the casting to 900-950°C, keeping it at that temperature for 2-4 hours, then cooling it to 850-880°C, keeping it at that temperature for 1-3 hours; then cooling it to 300°C at a cooling rate of 30-50°C / min, and then air cooling it to room temperature; (5) The ingot treated in step (4) is heated to 450° C., kept at this temperature for 4 h, and then air-cooled to room temperature.

5. The preparation method according to claim 4, characterized in that: In step (2), the mass ratio of Q12 pig iron, low sulfur and phosphorus scrap steel and recycled materials is 55:30:

15.

6. The preparation method according to claim 4, characterized in that: In step (2), the step power heating method is to first heat at a power of 800 kW for 20 minutes, then adjust the power to 1500 kW, heat for 20 minutes, and then adjust the power to 2000 kW, and heat to the final temperature.

7. The preparation method according to claim 4, characterized in that: The preheating temperature of the spheroidizing bag in step (3) is 800°C.

8. The preparation method according to claim 4, characterized in that: The rare earth magnesium alloy is Y-Mg alloy and La-Mg alloy.

9. The preparation method according to claim 4, characterized in that: In step (3), the filling rates of the liquid modifier and silicon carbide particles are both 0.1-0.3 kg / min; the particle size of the silicon carbide particles is 50-100 nm.

10. Use of the ductile iron according to any one of claims 1 to 3 in the preparation of high temperature resistant structural parts.