Low-carbon martensite spheroidal graphite cast iron material and its preparation method

Abstract

The disclosed spherulitic graphite cast iron material with low carbon martensite matrix is composed of the following raw material components in percentage by mass: C: 3.4-3.6%, Si: 2.3-2.6%, Mn: 0.1-0.3%, P: ≤0.1%, S: ≤0.015%, Mg: 0.03-0.05%, and the balance of Fe; the structure is composed of 10-15% by volume of spherulitic graphite + 85-90% by volume of low carbon martensite. The preparation method comprises the following steps: weighing pig iron, ferrosilicon, ferromanganese and carbon additive according to the component composition of the spherulitic graphite cast iron material, melting into molten iron in a medium-frequency induction furnace, pouring into a ladle into which spherulizing agent and inoculant have been added in advance, horizontal continuous casting to obtain a cast piece, selecting a part with high spherulitic graphite density of the cast piece, heat preservation in a vacuum tube furnace, cooling with the furnace, short-time heat preservation in a muffle furnace, taking out, quenching, and obtaining the spherulitic graphite cast iron material with low carbon martensite matrix.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, specifically relating to ductile iron materials with a low-carbon martensitic matrix. This invention also relates to a method for preparing ductile iron materials with a low-carbon martensitic matrix. Background Technology

[0002] During the die casting process of aluminum alloys, the mold not only has to withstand the strong friction caused by the rapid filling of the high-temperature aluminum alloy melt and the strong pressure applied to the mold by the high-pressure casting of the aluminum alloy melt, but also has to withstand the intermetallic compounds formed after the high-temperature aluminum alloy melt and the mold material interdiffusion, which cause strong corrosion on the mold surface. Therefore, the service life of aluminum alloy die casting molds is relatively short.

[0003] Existing aluminum alloy die casting mold materials generally use hot-work mold steels, such as 4Cr5MoV, 4Cr5W2VSi, and 4Cr5MoSiV. These materials can meet the mechanical performance requirements of aluminum alloy die casting molds under high-temperature service conditions. However, the Fe matrix and Al melt in the mold steel are prone to interdiffusion at high temperatures, forming intermetallic compounds. This results in poor resistance of existing steel molds to aluminum melt corrosion, easily causing surface cracking, pitting, and aluminum adhesion after corrosion. These problems seriously affect the surface quality of aluminum alloy die castings and reduce the service life of the molds.

[0004] Based on the physicochemical properties of aluminum melt not wetting graphite at temperatures not exceeding 800℃, the nearly 10 vol.% spherical graphite in ductile iron can not only reduce stress concentration at irregular spherical interfaces but also lower the coefficient of friction and reduce aluminum-iron adhesion strength, making it a promising material for aluminum alloy die-casting molds. However, the high carbon content in the martensite obtained after ordinary heat treatment of ductile iron results in poor plasticity and toughness, making it prone to cracking and fracture. Therefore, reducing the carbon content in its matrix can effectively improve the plasticity and toughness of the material. Summary of the Invention

[0005] The purpose of this invention is to provide a ductile iron material with a low-carbon martensitic matrix, which solves the problems of cracking and short service life caused by insufficient toughness of ductile iron aluminum alloy die casting mold materials. It provides a special material for aluminum alloy die casting molds that can resist aluminum melt erosion and whose mechanical properties can meet the service requirements.

[0006] Another object of the present invention is to provide a method for preparing ductile iron materials with a low-carbon martensitic matrix.

[0007] The technical solution adopted in this invention is a ductile iron material with a low-carbon martensitic matrix, which is composed of the following raw material components by mass percentage: C: 3.4%~3.6%, Si: 2.3%~2.6%, Mn: 0.1%~0.3%, P≤0.1%, S: ≤0.015%, Mg: 0.03%~0.05%, with the balance being Fe;

[0008] The microstructure of ductile iron material is: 10% to 15% by volume spherical graphite + 85% to 90% by volume low-carbon martensite.

[0009] Another technical solution adopted in this invention is a method for preparing ductile iron material with a low-carbon martensitic matrix, which is implemented according to the following steps:

[0010] Step 1: Weigh out the following components according to the composition of ductile iron: pig iron, ferrosilicon, ferromanganese, and carbon raiser. Place the weighed raw materials into a medium-frequency induction furnace and heat them to melt into molten iron.

[0011] Step 2: Pour the molten iron from Step 1 into a ladle that has been pre-filled with spheroidizing agent and inoculant;

[0012] Step 3: Pour the molten iron containing the spheroidizing agent and inoculant from Step 2 into the preheated horizontal continuous casting furnace and obtain the castings using the horizontal continuous casting method.

[0013] Step 4: Wire-cut samples from the edges and center of the casting and characterize their graphite density, selecting samples with a graphite density of not less than 300 particles / mm². 2 The next steps will be carried out on the affected area;

[0014] Step 5: Place the material selected in Step 4 into a vacuum tube furnace and heat it until it is fully austenitized, then cool it with the furnace.

[0015] Step 6: Place the cooled material from Step 5 into a muffle furnace for short-term heat preservation, then remove and quench to obtain ductile iron metal material with a low-carbon martensite matrix.

[0016] Another feature of the present invention is that,

[0017] In step 1, the total carbon equivalent in the raw materials is maintained at 4.3 wt.%, the heating rate of the medium-frequency induction furnace is 60℃ / min~80℃ / min, the melting time is 10min~30min, and the heating temperature is 1500℃~1600℃.

[0018] In step 2, the mass of the spheroidizing agent is 1.0% to 1.5% of the mass of the molten iron, and the mass of the inoculant is 1.1% to 1.6% of the mass of the molten iron.

[0019] In step 2, the inoculant is barium calcium inoculant, and the spheroidizing agent is ferrosilicon spheroidizing agent.

[0020] Step 4 involves wire cutting the edges and center of the casting obtained in Step 3, and using ImageJ software to analyze and characterize the graphite density of each cut area, selecting a graphite density of not less than 300 particles / mm². 2 The next steps will be carried out on the affected area.

[0021] In step 5, the vacuum degree of the vacuum tube furnace is -0.1MPa, the holding temperature is 900℃~950℃, the holding time is 2h~4h, and the furnace is cooled to 300℃~400℃.

[0022] In step 6, the short-time heat preservation is specifically to keep the material at a temperature of 900℃~950℃ for 2min~4min; the quenching medium is water, and the quenching temperature is 900℃~950℃; the interval between taking the material out of the muffle furnace and quenching it in water is no more than 5s.

[0023] The beneficial effects of this invention are:

[0024] The matrix of this invention is a low-carbon martensitic ductile iron material with a spherical graphite volume fraction of not less than 10%. It has certain self-lubricating properties and resistance to aluminum liquid corrosion, which can meet the wear resistance and corrosion resistance performance requirements of aluminum alloy die casting. It provides a special material for aluminum alloy die casting molds that can resist aluminum liquid erosion and whose mechanical properties can meet the service requirements.

[0025] The present invention relates to a method for preparing ductile iron material with a low-carbon martensitic matrix, wherein the graphite density of the casting used is not less than 300 particles / mm². 2 This provides more in-situ carbon points for carbon diffusion and re-dissolution during subsequent heat treatment. During heat treatment, the temperature is held at 900℃~950℃ for a short time for 2min~4min, which makes it difficult for carbon diffusion to be complete. As a result, the carbon content in the quenched martensite is low, which is low-carbon martensite. This makes the material strength meet the requirements while greatly improving the toughness. Attached Figure Description

[0026] Figure 1 This is a SEM image of the low-carbon martensitic ductile iron material prepared in Example 1 of the present invention. Detailed Implementation

[0027] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0028] The matrix of this invention is a low-carbon martensitic ductile iron material, which is composed of the following raw material components by mass percentage: C: 3.4% to 3.6%, Si: 2.3% to 2.6%, Mn: 0.1% to 0.3%, P ≤ 0.1%, S: ≤ 0.015%, Mg: 0.03% to 0.05%, with the balance being Fe.

[0029] The microstructure of ductile iron with a low-carbon martensitic matrix is ​​characterized by 10%–15% spheroidal graphite by volume and 85%–90% low-carbon martensite by volume. The spheroidal graphite by volume fraction of not less than 10% ensures the material's self-lubricating properties and resistance to aluminum melt adhesion, while the remaining microstructure is low-carbon martensite, which improves the material's ductility and toughness.

[0030] The method for preparing low-carbon martensitic ductile iron material according to the present invention is implemented according to the following steps:

[0031] Step 1: Weigh the raw materials according to the composition of ductile iron, including pig iron, ferrosilicon, ferromanganese, and carbon raiser. Heat the weighed raw materials in a medium-frequency induction furnace to high temperature and melt them into molten iron. The total carbon equivalent in the raw materials is maintained at 4.3 wt.%, the heating rate of the medium-frequency induction furnace is 60℃ / min~80℃ / min, the melting time is 10min~30min, and the high temperature for melting is 1500℃~1600℃.

[0032] Step 2: Pour the molten iron obtained in Step 1 into a ladle containing a spheroidizing agent and an inoculant. The inoculant is a barium-calcium inoculant, and the mass of the spheroidizing agent is 1.0% to 1.5% of the mass of the molten iron obtained in Step 1. The spheroidizing agent is a ferrosilicon spheroidizing agent, and the mass of the inoculant is 1.1% to 1.6% of the mass of the molten iron obtained in Step 1.

[0033] Step 3: Pour the molten iron containing the spheroidizing agent and inoculant from Step 2 into the preheated horizontal continuous casting furnace, and continuously cast the castings according to the horizontal continuous casting process specifications.

[0034] Step 4: Select a portion of the graphite with a higher density to prepare for subsequent heat treatment;

[0035] Specifically, the edges and center of the casting obtained in step 3 are wire-cut to obtain samples. The graphite density of each cut part is analyzed and characterized using ImageJ software, and samples with a graphite density of not less than 300 particles / mm² are selected. 2 The next steps will be carried out on the affected area.

[0036] Step 5: Place the material selected in Step 4 in a vacuum tube furnace at 900℃~950℃ and hold it for 2h~4h to fully austenitize it and obtain an austenitic structure. Then cool it with the furnace to 300℃~400℃. The purpose is to allow the carbon in the austenite to dissolve back into the graphite and obtain a fully ferrite matrix structure.

[0037] A vacuum furnace is selected to avoid decarburization of the material surface during the austenitization process.

[0038] Step 6: Place the all-ferritic material obtained in Step 5 into a muffle furnace at 900℃~950℃ and hold for 2min~4min for a short time. Then take it out and quench it in water at 900℃~950℃. The interval between taking the material out of the muffle furnace and quenching it in water should not exceed 5s. The short holding time is to minimize the amount of carbon dissolved in the austenite, ensuring that the martensite obtained in the ductile iron matrix during quenching is low-carbon martensite, so that the material strength meets the requirements while the toughness is greatly improved.

[0039] The present invention discloses a method for preparing low-carbon martensitic ductile iron material. By strictly controlling the proportions of each component in the raw materials and each step of the casting process, the quality and quantity of graphite spheres in the material are guaranteed, thereby obtaining a graphite density of not less than 300 spheres / mm². 2 The castings are designed to fully utilize the self-lubricating and anti-aluminum molten corrosion properties of ductile iron. The high-graphite-density castings are subjected to short-time quenching to obtain a low-carbon martensitic matrix structure, thereby improving the plasticity and toughness of the material while ensuring strength. Finally, ductile iron materials with spherical graphite and low-carbon martensite matrix structure are prepared.

[0040] Example 1

[0041] The matrix of this invention is a low-carbon martensitic ductile iron material, which is composed of the following raw material components by mass percentage: C: 3.4%, Si: 2.3%, Mn: 0.1%, P≤0.1%, S: ≤0.015%, Mg: 0.03%, with the balance being Fe;

[0042] The microstructure of ductile iron material is: 10% by volume spherical graphite + 90% by volume low-carbon martensite.

[0043] The method for preparing low-carbon martensitic ductile iron material according to the present invention is implemented according to the following steps:

[0044] Step 1: Weigh pig iron, ferrosilicon, ferromanganese, and carbon raiser according to the composition of ductile iron material. The total carbon equivalent in the raw materials should be maintained at 4.3 wt.%. Heat the weighed raw materials in a medium frequency induction furnace to 1550°C at a heating rate of 70°C / min and melt for 20 minutes to form molten iron.

[0045] Step 2: Pour the molten iron obtained in Step 1 into a ladle containing a spheroidizing agent and an inoculant. The inoculant is a barium-calcium inoculant, and the spheroidizing agent is a ferrosilicon spheroidizing agent. The mass of the spheroidizing agent is 1.0% of the mass of the molten iron obtained in Step 1, and the mass of the inoculant is 1.1% of the mass of the molten iron obtained in Step 1.

[0046] Step 3: Pour the molten iron containing the spheroidizing agent and inoculant from Step 2 into the preheated horizontal continuous casting furnace and obtain the castings using the horizontal continuous casting method.

[0047] Step 4: Wire-cut the edges and center of the casting obtained in Step 3. Use ImageJ software to analyze and characterize the graphite density of the sampled material, selecting a graphite density of not less than 300 particles / mm². 2 The next steps will be carried out on the affected area.

[0048] Step 5: Place the material selected in Step 4 in a vacuum tube furnace at 900℃ and keep it at that temperature for 4 hours to fully austenitize it, and then cool it down to 350℃ with the furnace.

[0049] Step 6: Place the cooled material from Step 5 into a muffle furnace at 900℃ and hold for 4 minutes. Then remove it and quench it in water. The interval between removing the material from the muffle furnace and quenching it in water is 3 seconds. The quenching temperature is 900℃. This yields ductile iron material with a low-carbon martensitic matrix.

[0050] like Figure 1 The image shows a SEM image of the microstructure of ductile iron with a low-carbon martensite matrix. The black spheres in the image are graphite with a volume fraction of 10%, which ensures the material's self-lubricating properties and resistance to aluminum melt adhesion. The remaining microstructure is low-carbon martensite, which improves the material's plasticity and toughness.

[0051] Example 2

[0052] The matrix of this invention is a low-carbon martensitic ductile iron material, which is composed of the following raw material components by mass percentage: C: 3.6%, Si: 2.6%, Mn: 0.3%, P≤0.1%, S: ≤0.015%, Mg: 0.05%, with the balance being Fe.

[0053] The microstructure of ductile iron material is: 12% by volume spherical graphite + 88% by volume low-carbon martensite.

[0054] The method for preparing low-carbon martensitic ductile iron material according to the present invention is implemented according to the following steps:

[0055] Step 1: Weigh pig iron, ferrosilicon, ferromanganese, and carbon raiser according to the composition of ductile iron material. The total carbon equivalent in the raw materials should be maintained at 4.3 wt.%. Heat the weighed raw materials in a medium frequency induction furnace to 1600℃ at a heating rate of 80℃ / min and melt for 10 minutes to form molten iron.

[0056] Step 2: Pour the molten iron obtained in Step 1 into a ladle containing a spheroidizing agent and an inoculant. The inoculant is a barium-calcium inoculant, and the spheroidizing agent is a ferrosilicon spheroidizing agent. The mass of the spheroidizing agent is 1.5% of the mass of the molten iron obtained in Step 1, and the mass of the inoculant is 1.6% of the mass of the molten iron obtained in Step 1.

[0057] Step 3: Pour the molten iron containing the spheroidizing agent and inoculant from Step 2 into the preheated horizontal continuous casting furnace and obtain the castings using the horizontal continuous casting method.

[0058] Step 4: Wire-cut the edges and center of the casting obtained in Step 3. Use ImageJ software to analyze and characterize the graphite density of the sampled material, selecting a graphite density of not less than 300 particles / mm². 2 The next steps will be carried out on the affected area.

[0059] Step 5: Place the material selected in Step 4 in a vacuum tube furnace at 925℃ and keep it at that temperature for 3 hours to fully austenitize it, and then cool it down to 400℃ with the furnace.

[0060] Step 6: Place the material from Step 5 in a muffle furnace at 950℃ and hold for 2 minutes. Then remove it and quench it in water. The interval between removing the material from the muffle furnace and quenching it in water is 4 seconds. The quenching temperature is 950℃. This yields a low-carbon martensitic ductile iron material with a matrix of 12% by volume of spherical graphite and 88% by volume of low-carbon martensitic ductile iron.

[0061] Example 3

[0062] The matrix of this invention is a low-carbon martensitic ductile iron material, composed of the following raw material components by mass percentage: C: 3.5%, Si: 2.4%, Mn: 0.1%, P≤0.1%, S: ≤0.015%, Mg: 0.03%, with the balance being Fe.

[0063] The microstructure of ductile iron material is: 15% by volume spheroidal graphite + 85% by volume low-carbon martensite.

[0064] The method for preparing low-carbon martensitic ductile iron material according to the present invention is implemented according to the following steps:

[0065] Step 1: Weigh pig iron, ferrosilicon, ferromanganese, and carbon raiser according to the composition of ductile iron material. The total carbon equivalent in the raw materials should be maintained at 4.3 wt.%. Heat the weighed raw materials in a medium frequency induction furnace to 1000℃ at a heating rate of 60℃ / min and melt for 30 minutes to form molten iron.

[0066] Step 2: Pour the molten iron obtained in Step 1 into a ladle containing a spheroidizing agent and an inoculant. The inoculant is a barium-calcium inoculant, and the spheroidizing agent is a ferrosilicon spheroidizing agent. The mass of the spheroidizing agent is 1.2% of the mass of the molten iron obtained in Step 1, and the mass of the inoculant is 1.4% of the mass of the molten iron obtained in Step 1.

[0067] Step 3: Pour the molten iron containing the spheroidizing agent and inoculant from Step 2 into the preheated horizontal continuous casting furnace and obtain the castings using the horizontal continuous casting method.

[0068] Step 4: Wire-cut the edges and center of the casting obtained in Step 3. Use ImageJ software to analyze and characterize the graphite density of the sampled material, selecting a graphite density of not less than 300 particles / mm². 2 The next steps will be carried out on the affected area.

[0069] Step 5: Place the material selected in Step 4 in a vacuum tube furnace at 950℃ and keep it at that temperature for 2 hours to fully austenitize it, and then cool it down to 300℃ with the furnace.

[0070] Step 6: Place the material from Step 5 in a muffle furnace at 925℃ and hold for 3 minutes. Then remove it and quench it in water. The interval between removing the material from the muffle furnace and quenching it in water is 5 seconds. The quenching temperature is 925℃. This yields a spherical graphite matrix with a volume fraction of 15% and a low-carbon martensitic ductile iron matrix with a volume fraction of 85%.

[0071] Example 4

[0072] The matrix of this invention is a low-carbon martensitic ductile iron material, which is composed of the following raw material components by mass percentage: C: 3.4%, Si: 2.5%, Mn: 0.2%, P≤0.1%, S: ≤0.015%, Mg: 0.04%, with the balance being Fe;

[0073] The microstructure of ductile iron material is: 14% by volume spheroidal graphite + 86% by volume low-carbon martensite.

[0074] The method for preparing low-carbon martensitic ductile iron material according to the present invention is implemented according to the following steps:

[0075] Step 1: Weigh pig iron, ferrosilicon, ferromanganese, and carbon raiser according to the composition of ductile iron material. The total carbon equivalent in the raw materials should be maintained at 4.3 wt.%. Heat the weighed raw materials in a medium frequency induction furnace to 1500℃ at a heating rate of 70℃ / min and melt for 20 minutes to form molten iron.

[0076] Step 2: Pour the molten iron obtained in Step 1 into a ladle containing a spheroidizing agent and an inoculant. The mass of the spheroidizing agent is 1.3% of the mass of the molten iron obtained in Step 1, and the mass of the inoculant is 1.2% of the mass of the molten iron obtained in Step 1.

[0077] Step 3: Pour the molten iron containing the spheroidizing agent and inoculant from Step 2 into the preheated horizontal continuous casting furnace and obtain the castings using the horizontal continuous casting method.

[0078] Step 4: Wire-cut the edges and center of the casting obtained in Step 3. Use ImageJ software to analyze and characterize the graphite density of the sampled material, selecting a graphite density of not less than 300 particles / mm². 2The next steps will be carried out on the affected area.

[0079] Step 5: Place the material selected in Step 4 in a vacuum tube furnace at 900℃ and keep it at that temperature for 3 hours to fully austenitize it. Then, cool it down to below 400℃ with the furnace.

[0080] Step 6: Place the material from Step 5 in a muffle furnace at 900℃ and hold for 4 minutes. Then remove it and quench it in water. The interval between removing the material from the muffle furnace and quenching it in water is 3 seconds. The quenching temperature is 900℃. This yields a low-carbon martensitic ductile iron material with a matrix of 14% by volume graphite and 86% by volume graphite.

[0081] Example 5

[0082] The matrix of this invention is a low-carbon martensitic ductile iron material, which is composed of the following raw material components by mass percentage: C: 3.5%, Si: 2.5%, Mn: 0.1%, P≤0.1%, S: ≤0.015%, Mg: 0.03%, with the balance being Fe;

[0083] The microstructure of ductile iron material is: 11% by volume of spherical graphite + 89% by volume of low-carbon martensite.

[0084] The method for preparing low-carbon martensitic ductile iron material according to the present invention is implemented according to the following steps:

[0085] Step 1: According to the composition of the cast iron material, weigh pig iron, ferrosilicon, ferromanganese and carbon raiser. The total carbon equivalent in the raw materials should be kept at 4.3 wt.%. Heat the weighed raw materials in a medium frequency induction furnace to 1550℃ at a heating rate of 70℃ / min and melt for 20 minutes to form molten iron.

[0086] Step 2: Pour the molten iron obtained in Step 1 into a ladle containing a spheroidizing agent and an inoculant. The mass of the spheroidizing agent is 1.4% of the mass of the molten iron obtained in Step 1, and the mass of the inoculant is 1.1% of the mass of the molten iron obtained in Step 1.

[0087] Step 3: Pour the molten iron containing the spheroidizing agent and inoculant from Step 2 into the preheated horizontal continuous casting furnace and obtain the castings using the horizontal continuous casting method.

[0088] Step 4: Wire-cut the edges and center of the casting obtained in Step 3. Use ImageJ software to analyze and characterize the graphite density of the sampled material, selecting a graphite density of not less than 300 particles / mm². 2 The next steps will be carried out on the affected area.

[0089] Step 5: Place the material selected in Step 4 in a vacuum tube furnace at 900℃ and keep it at that temperature for 2 hours to fully austenitize it. Then, cool it down to below 400℃ with the furnace.

[0090] Step 6: Place the material from Step 5 in a muffle furnace at 940℃ and hold for 3 minutes. Then remove it and quench it in water. The interval between removing the material from the muffle furnace and quenching it in water is 3 seconds. The quenching temperature is 940℃. This yields a low-carbon martensitic ductile iron material with a matrix of 11% by volume of spherical graphite and 89% by volume of low-carbon martensitic ductile iron.

Claims

1. A method for preparing ductile iron material with a low-carbon martensitic matrix, characterized in that, The specific steps are as follows: Step 1: Weigh out the following components according to the composition of ductile iron: pig iron, ferrosilicon, ferromanganese, and carbon raiser. Place the weighed raw materials into a medium-frequency induction furnace and heat them to melt into molten iron. Step 2: Pour the molten iron from Step 1 into a ladle that has been pre-filled with spheroidizing agent and inoculant; Step 3: Pour the molten iron containing the spheroidizing agent and inoculant added in Step 2 into the preheated horizontal continuous casting furnace and obtain the casting by horizontal continuous casting. Step 4: Wire-cut samples from the edges and center of the casting and characterize their graphite density, selecting samples with a graphite density of not less than 300 particles / mm². 2 The next steps will be carried out on the affected area; Step 5: Place the material selected in Step 4 into a vacuum tube furnace for heat preservation and austenitization, and then cool it with the furnace. Step 6: Place the cooled material from Step 5 into a muffle furnace for short-term heat preservation, remove and quench to obtain ductile iron metal material with a low-carbon martensite matrix. The ductile iron is composed of the following raw material components by mass percentage: C: 3.4%~3.6%, Si: 2.3%~2.6%, Mn: 0.1%~0.3%, P≤0.1%, S: ≤0.015%, Mg: 0.03%~0.05%, with the balance being Fe; The microstructure of the ductile iron material is: 10%~15% spherical graphite by volume + 85%~90% low-carbon martensite by volume. In step 6, the short-term heat preservation specifically refers to heat preservation at a temperature of 900℃~950℃ for 2min~4min; the quenching medium is water, and the quenching temperature is 900℃~950℃; the interval between the material being taken out of the muffle furnace and being placed in water for quenching is no more than 5s.

2. The method for preparing ductile iron material with a low-carbon martensitic matrix according to claim 1, characterized in that, In step 1, the total carbon equivalent in the raw materials is maintained at 4.3 wt.%, the heating rate of the medium-frequency induction furnace is 60℃ / min~80℃ / min, the melting time is 10min~30min, and the heating temperature is 1500℃~1600℃.

3. The method for preparing ductile iron material with a low-carbon martensitic matrix according to claim 1, characterized in that, In step 2, the mass of the spheroidizing agent is 1.0% to 1.5% of the mass of the molten iron, and the mass of the inoculant is 1.1% to 1.6% of the mass of the molten iron.

4. The method for preparing ductile iron material with a low-carbon martensitic matrix according to claim 1, characterized in that, In step 2, the inoculant is a barium-calcium inoculant, and the spheroidizing agent is a ferrosilicon spheroidizing agent.

5. The method for preparing ductile iron material with a low-carbon martensitic matrix according to claim 1, characterized in that, The specific operation of step 4 is as follows: wire cutting is performed on the edge and center of the casting obtained in step 3, and the graphite density of each cut part is analyzed and characterized using ImageJ software. A graphite density of not less than 300 particles / mm² is selected. 2 The next steps will be carried out on the affected area.

6. The method for preparing ductile iron material with a low-carbon martensitic matrix according to claim 1, characterized in that, In step 5, the vacuum degree of the vacuum tube furnace is -0.1MPa, the holding temperature is 900℃~950℃, the holding time is 2h~4h, and the furnace is cooled to 300℃~400℃.

Images