QT450-10LT high-strength and high-toughness low-temperature nodular cast iron and preparation method thereof

Abstract

The invention provides QT450-10LT high-strength and high-toughness low-temperature nodular cast iron and a preparation method thereof, and belongs to the technical field of nodular cast iron. Comprising the following components in percentage by weight: 3.65%-3.85% of C, 1.8%-2.1% of Si, and the balance of Mnlt; the alloy comprises, by mass, 0.025% of iron, less than or equal to 0.01% of P, less than or equal to 0.01% of S, less than 0.8% of Ni, less than or equal to 0.045% of Mg (residue), less than 0.01% of other impurity elements, and the balance iron. According to the preparation method, a shell mold steel shot burying and multi-stage heat treatment process, namely high-temperature annealing treatment, three-phase region quenching treatment and stress relief annealing treatment is adopted, so that the prepared low-temperature nodular cast iron ensures that the low-temperature impact absorbing energy at-20 DEG C,-40 DEG C and-50 DEG C is greater than or equal to 12J on the basis of improving the tensile strength and the yield strength, and the application field of the low-temperature nodular cast iron is widened.

Description

Technical Field

[0001] The invention belongs to the technical field of ductile iron, and specifically relates to QT450-10LT high-strength, high-toughness, low-temperature ductile iron and a preparation method thereof. Background Art

[0002] Ductile iron is a high-strength cast iron material developed in the late 1940s. Its comprehensive performance is close to that of steel. Based on its excellent mechanical properties, it has been successfully used to cast some parts with complex stresses and high requirements for strength, toughness and wear resistance.

[0003] Ductile iron is a cast iron material containing spheroidal graphite obtained by spheroidizing and inoculating the original iron liquid. Since the stress concentration that may be caused by the graphite morphology is eliminated to the maximum extent, the mechanical properties of cast iron, especially the strength and plastic toughness, are effectively improved. So far, various grades of ductile iron material series have been formed from low to high strength to meet the different performance and special uses in the engineering field. For example, QT400-18LT is mainly used in the production of high-speed rail, wind power and automobile parts with its high low-temperature impact toughness. Its low-temperature impact absorption energy can reach more than 12J, which can meet the use requirements under high-cold climate conditions. However, with the promulgation of low-carbon, energy-saving and environmental protection laws and regulations in various countries around the world, lightweight and green manufacturing of mechanical equipment has become a general trend and has become an important feature of new quality productivity. Although in the ductile iron standard, as a common material grade, QT450-10 is widely used in the engineering field, due to its low low-temperature toughness, it is only suitable for the use of engineering components under ordinary working conditions and cannot meet the performance under low-temperature working conditions. However, the existing QT400-18LT material has low tensile strength and weak bearing capacity, which makes it difficult to meet the design and production needs of lightweight rail transit equipment such as high-speed rail. Therefore, it is urgent to develop a higher-grade high-strength, high-toughness low-temperature ductile iron material with a tensile strength of ≥450MPa and low-temperature impact absorption energy of ≥12J at -20℃, -40℃ and -50℃, so as to meet the requirements of lightweight manufacturing of mechanical equipment for the use of high-end ductile iron parts under low-temperature working conditions.

[0004] At present, there are many studies on ductile iron. For example, Chinese patent CN109930058A discloses a -40℃ low-temperature high-strength and high-toughness ductile iron and its preparation method and railway locomotive parts. The chemical composition and weight percentage of the ductile iron are: C 3.6%-3.9%, Si 1.9%-2.1%, Mn<0.2%, P<0.03%, S 0.003%-0.012%, Cu 0.35%-0.5%, Ni 1.1%-1.5%, Re≤0.03%, Mg 0.025%-0.05%, and the balance is iron and inevitable impurities. The composition of the ductile iron material of this invention achieves the organic fusion of high strength, high toughness and low-temperature impact toughness in ductile iron, which can meet higher use requirements and has technical foresight.

[0005] For another example, Chinese patent CN103194660A discloses a method for manufacturing low-temperature ferrite ductile iron material, the chemical composition of which is C: 3.5-3.9, Si: 1.9-2.3, Mn≤0.2, P≤0.03, S≤0.02, Mg: 0.04-0.06, Ni: 0.25-0.95; the performance of the material is: the impact energy is ≥12J at -40℃, -50℃, and -60℃, the room temperature tensile strength is ≥400MPa, the elongation is ≥18%, and other main mechanical performance indicators are qualified. It can be widely used in the manufacture of mechanical equipment products in cold areas and with low-temperature impact resistance and high toughness requirements.

[0006] However, there are not many studies on ductile iron with the grade QT450-10LT, and the mechanical properties of the currently reported QT450-10LT ductile iron, especially the low-temperature impact absorption energy, cannot meet the requirements well, which greatly limits the application field of QT450-10LT ductile iron. Therefore, it is necessary to develop a QT450-10LT high-strength, high-toughness low-temperature ductile iron and a preparation method thereof. Summary of the invention

[0007] Based on the deficiencies in the prior art, the present invention aims to provide a QT450-10LT high-strength, high-toughness, low-temperature ductile iron, which has excellent tensile strength, yield strength, elongation after fracture, Brinell hardness and impact energy at -20°C, -40°C and -50°C.

[0008] In order to achieve the above object, the present invention adopts the following technical solution: On the one hand, the present invention provides a high-strength and high-toughness QT450-10LT low-temperature ductile iron, comprising the following components in mass percentage: C: 3.65%-3.85%, Si: 1.8%-2.1%, Mn<0.025%, P≤0.01%, S≤0.01%, Ni<0.8%, Mg (residual)≤0.045%, the total content of other impurity elements is less than 0.01%, and the rest is iron.

[0009] As a preferred embodiment, the QT450-10LT high-strength, high-toughness low-temperature ductile iron comprises the following components in mass percentage: C: 3.75%, Si: 2.0%, Mn: 0.017%, P: 0.007%, S: 0.003%, Ni: 0.71%, Mg (residual): 0.034%, the total content of other impurity elements is less than 0.01%, and the rest is iron.

[0010] As another preferred embodiment, the QT450-10LT high-strength, high-toughness low-temperature ductile iron includes the following components in mass percentage: C: 3.81%, Si: 2.05%, Mn: 0.017%, P: 0.005%, S: 0.005%, Ni: 0.75%, Mg (residual): 0.037%, the total content of other impurity elements is less than 0.01%, and the rest is iron.

[0011] As another preferred embodiment, the QT450-10LT high-strength, high-toughness low-temperature ductile iron includes the following components in mass percentage: C: 3.85%, Si: 2.0%, Mn: 0.021%, P: 0.006%, S: 0.007%, Ni: 0.74%, Mg (residual): 0.038%, the total content of other impurity elements is less than 0.01%, and the rest is iron.

[0012] On the other hand, the present invention also provides a method for preparing the QT450-10LT high-strength, high-toughness, low-temperature ductile iron, comprising the following steps: Step 1: Smelting of raw iron liquid: High-purity pig iron and carbon scrap steel are used to melt the raw iron liquid in a medium-frequency induction furnace, and the temperature of the molten iron out of the furnace is 1500-1520℃; Step 2: Spheroidization and inoculation: The spheroidizing and inoculating treatment is carried out by using a cover ladle method; specifically, a low rare earth spheroidizing agent, a silicon-based inoculant and a covering agent are sequentially added to the bottom of the spheroidizing ladle, and then the raw iron liquid smelted in step 1 is quickly injected into the spheroidizing ladle for spheroidizing and inoculating treatment to obtain ductile iron liquid; Step 3: Casting mold preparation: The shell mold is back-filled with steel shot technology. The specific method is to close the mold in a special sand box and fill the outer periphery of the shell mold with steel shot to obtain a shell mold back-filled with steel shot with a higher cooling rate and greater rigidity. Step 4: Casting of molten iron: The ductile iron liquid prepared in step 2 is transferred into a casting ladle, and a secondary inoculation is performed in the casting ladle, and then the ductile iron liquid is poured into the coated sand shell mold cavity prepared in step 3, and the ductile iron with a cast ferrite matrix is ​​obtained after solidification, cooling and sand removal; Step 5: Microstructure regulation and treatment: The microstructure control treatment includes high temperature annealing treatment, three-phase region rapid cooling treatment and stress relief annealing treatment.

[0013] in, The high temperature annealing treatment is: subjecting the ductile iron obtained in step 4 to high temperature annealing treatment to eliminate grain boundary carbides or eutectic carbides and to make the composition uniform, with a heating temperature of 890-920° C., a holding time of 1-2 hours, and then cooling with the furnace.

[0014] The three-phase region rapid cooling treatment is to heat the ductile iron after high-temperature annealing to 720-800°C, keep it warm for 1-2 hours and then rapidly cool it. The cooling method includes mist cooling or salt bath cooling to obtain low-temperature ductile iron with a dual-phase matrix structure.

[0015] The stress relief annealing treatment is to heat the low-temperature ductile iron to 450-600°C, keep the temperature for 30-60 minutes, then take it out of the furnace and cool it to room temperature.

[0016] The low rare earth spheroidizer is a low rare earth magnesium ferrosilicon spheroidizer, and the rare earth content is 0.2%-0.5%.

[0017] The silicon-based inoculant is a barium-containing ferrosilicon-based inoculant, and the barium content is 1.8%-2.1%.

[0018] The amount of the low rare earth spheroidizer added is 1.0-1.2% of the total mass of the original molten iron; the amount of the silicon-based inoculant added is 0.3-0.5% of the total mass of the original molten iron.

[0019] The inoculant used in the secondary inoculation is a low rare earth magnesium ferrosilicon spheroidizer with a rare earth content of 0.2%-0.5%; the addition amount of the low rare earth magnesium ferrosilicon spheroidizer is 0.3-0.5% of the total mass of the ductile iron liquid.

[0020] The shell-type back-filled steel shot process includes the following steps: After the shell mold is bonded and assembled, it is transported to the steel shot burying box production line and placed in a special sand box. After the steel shot burying box line automatically fills the steel shot, it is transported to the pouring area and then molten iron is poured into the casting mold; the heating temperature of the core shooting machine is 200°C, the curing time is 4 minutes, and the sand shooting time is 8 seconds; the diameter of the steel shot is 3-8mm.

[0021] The beneficial effects compared with the prior art are: (1) The shell mold can obtain a good casting appearance, and the shell mold has high strength, which prevents the impact of high-temperature molten iron during pouring from causing the mold wall to move outward, which is conducive to the graphitization expansion of ductile iron for self-compensation.

[0022] (2) The present invention reasonably controls the weight percentage of various metal elements and the temperature parameters during the preparation process to make the prepared ductile iron have better tensile strength, yield strength and elongation at break, and can significantly improve the minimum impact absorption energy at -20°C, -40°C and -50°C, thereby broadening the application field of low-temperature ductile iron. DETAILED DESCRIPTION

[0023] The following non-limiting examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The following content is merely an exemplary description of the scope of the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, which should also fall within the scope of the present invention.

[0024] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those generally understood by those of ordinary skill in the art to which the present invention belongs.

[0025] The present invention is further described below by way of specific examples. Unless otherwise specified, the various chemical reagents used in the examples of the present invention are obtained through conventional commercial channels.

[0026] Example 1 A QT450-10LT high-strength, high-toughness, low-temperature ductile iron and its preparation method It includes the following components in weight percentage: C: 3.75%, Si: 2.0%, Mn: 0.017%, P: 0.007%, S: 0.003%, Ni: 0.71%, Mg (residual): 0.034%, and the rest are iron and unavoidable impurities.

[0027] The preparation method comprises the following steps: Step 1: Smelting of raw iron liquid: High-purity pig iron and carbon scrap steel are used to melt the raw iron liquid in a medium-frequency induction furnace, and the temperature of the molten iron out of the furnace is 1500-1520℃; Step 2: Spheroidization and inoculation: The spheroidizing and inoculating treatment is carried out by using a cover ladle method; specifically, a low rare earth spheroidizing agent, a silicon-based inoculant and a covering agent are sequentially added to the bottom of the spheroidizing ladle, and then the raw iron liquid smelted in step 1 is quickly injected into the spheroidizing ladle for spheroidizing and inoculating treatment to obtain ductile iron liquid; The low rare earth spheroidizer is a low rare earth magnesium ferrosilicon spheroidizer with a rare earth content of 0.2%-0.5%; the amount of the low rare earth spheroidizer added is 1.0% of the total mass of the original iron liquid The silicon-based inoculant is a barium-containing ferrosilicon-based inoculant with a barium content of 1.8%-2.1%; the amount of the silicon-based inoculant added is 0.3% of the total mass of the original molten iron.

[0028] Step 3: Casting mold preparation: The shell mold is formed by back-filling steel shot process; the specific method is to bond and assemble the shell mold and then transport it to the steel shot burying box production line, put it into a special sand box, and then transport it to the casting area after the steel shot burying box line automatically buries the steel shot; the heating temperature of the core shooting machine is 200℃, the curing time is 4min, and the sand shooting time is 8s; the diameter of the steel shot is 3-8mm; Step 4: Casting of molten iron: The ductile iron liquid prepared in step 2 is transferred into a casting ladle, and a secondary inoculation is performed in the casting ladle, and then the ductile iron liquid is poured into the coated sand shell mold cavity prepared in step 3, and the ductile iron with a cast ferrite matrix is ​​obtained after solidification, cooling and sand removal; The inoculant used in the secondary inoculation is a low rare earth magnesium ferrosilicon spheroidizer with a rare earth content of 0.2%-0.5%; the added amount of the secondary inoculant is 0.3 of the total mass of the ductile iron liquid.

[0029] Step 5: Microstructure regulation and treatment: The microstructure control treatment includes high temperature annealing treatment, three-phase region rapid cooling treatment and stress relief annealing treatment.

[0030] in, The high temperature annealing treatment is: subjecting the ductile iron obtained in step 4 to high temperature annealing treatment to eliminate grain boundary carbides or eutectic carbides and to make the composition uniform, with a heating temperature of 890-920° C., a holding time of 1-2 hours, and then cooling with the furnace.

[0031] The three-phase region rapid cooling treatment is to heat the ductile iron after high-temperature annealing to 720-800°C, keep it warm for 1-2 hours and then rapidly cool it. The cooling method includes mist cooling or salt bath cooling to obtain low-temperature ductile iron with a dual-phase matrix structure.

[0032] The stress relief annealing treatment is to heat the low-temperature ductile iron to 450-600°C, keep it warm for 30-60 minutes, then take it out of the furnace and cool it to room temperature. The sample is the low-temperature ductile iron.

[0033] Example 2 A QT450-10LT high-strength, high-toughness, low-temperature ductile iron and its preparation method It includes the following components in weight percentage: C: 3.81%, Si: 2.05%, Mn: 0.017%, P: 0.005%, S: 0.005%, Ni: 0.75%, Mg (residual): 0.037%, and the rest are iron and unavoidable impurities.

[0034] The preparation method comprises the following steps: Step 1: Smelting of raw iron liquid: High-purity pig iron and carbon scrap steel are used to melt the raw iron liquid in a medium-frequency induction furnace, and the temperature of the molten iron out of the furnace is 1500-1520℃; Step 2: Spheroidization and inoculation: The spheroidizing and inoculating treatment is carried out by using a cover ladle method; specifically, a low rare earth spheroidizing agent, a silicon-based inoculant and a covering agent are sequentially added to the bottom of the spheroidizing ladle, and then the raw iron liquid smelted in step 1 is quickly injected into the spheroidizing ladle for spheroidizing and inoculating treatment to obtain ductile iron liquid; The low rare earth spheroidizer is a low rare earth magnesium ferrosilicon spheroidizer with a rare earth content of 0.2%-0.5%; the addition amount of the low rare earth spheroidizer is 1.2% of the total mass of the original iron liquid.

[0035] The silicon-based inoculant is a barium-containing ferrosilicon-based inoculant with a barium content of 1.8%-2.1%; the amount of the silicon-based inoculant added is 0.5% of the total mass of the original molten iron.

[0036] Step 3: Casting mold preparation: The shell mold is formed by back-filling steel shot process; the specific method is to bond and assemble the shell mold and then transport it to the steel shot burying box production line, put it into a special sand box, and then transport it to the casting area after the steel shot burying box line automatically buries the steel shot; the heating temperature of the core shooting machine is 200℃, the curing time is 4min, and the sand shooting time is 8s; the diameter of the steel shot is 3-8mm; Step 4: Casting of molten iron: The ductile iron liquid prepared in step 2 is transferred into a casting ladle, and a secondary inoculation is performed in the casting ladle, and then the ductile iron liquid is poured into the coated sand shell mold cavity prepared in step 3, and the ductile iron with a cast ferrite matrix is ​​obtained after solidification, cooling and sand removal; The inoculant used in the secondary inoculation is a low rare earth magnesium ferrosilicon nodulizer with a rare earth content of 0.2%-0.5%; the amount of the secondary inoculant added is 0.5% of the total mass of the ductile iron liquid.

[0037] Step 5: Microstructure regulation and treatment: The microstructure control treatment includes high temperature annealing treatment, three-phase region rapid cooling treatment and stress relief annealing treatment.

[0038] in, The high temperature annealing treatment is: subjecting the ductile iron obtained in step 4 to high temperature annealing treatment to eliminate grain boundary carbides or eutectic carbides and to make the composition uniform, with a heating temperature of 890-920° C., a holding time of 1-2 hours, and then cooling with the furnace.

[0039] The three-phase region rapid cooling treatment is to heat the ductile iron after high-temperature annealing to 720-800°C, keep it warm for 1-2 hours and then rapidly cool it. The cooling method includes mist cooling or salt bath cooling to obtain low-temperature ductile iron with a dual-phase matrix structure.

[0040] The stress relief annealing treatment is to heat the low-temperature ductile iron to 450-600°C, keep it warm for 30-60 minutes, then take it out of the furnace and cool it to room temperature. The sample is the low-temperature ductile iron.

[0041] Example 3 A QT450-10LT high-strength, high-toughness low-temperature ductile iron and its preparation method It includes the following components in weight percentage: C: 3.85%, Si: 2.0%, Mn: 0.021%, P: 0.006%, S: 0.007%, Ni: 0.74%, Mg (residual): 0.038%, and the rest are iron and unavoidable impurities.

[0042] The preparation method comprises the following steps: Step 1: Smelting of raw iron liquid: High-purity pig iron and carbon scrap steel are used to melt the raw iron liquid in a medium-frequency induction furnace, and the temperature of the molten iron out of the furnace is 1500-1520℃; Step 2: Spheroidization and inoculation: The spheroidizing and inoculating treatment is carried out by using a cover ladle method; specifically, a low rare earth spheroidizing agent, a silicon-based inoculant and a covering agent are sequentially added to the bottom of the spheroidizing ladle, and then the raw iron liquid smelted in step 1 is quickly injected into the spheroidizing ladle for spheroidizing and inoculating treatment to obtain ductile iron liquid; The low rare earth spheroidizer is a low rare earth magnesium ferrosilicon spheroidizer with a rare earth content of 0.2%-0.5%; the addition amount of the low rare earth spheroidizer is 1.1% of the total mass of the original iron liquid.

[0043] The silicon-based inoculant is a barium-containing ferrosilicon-based inoculant with a barium content of 1.8%-2.1%; the amount of the silicon-based inoculant added is 0.4% of the total mass of the original molten iron.

[0044] Step 3: Casting mold preparation: The shell mold is formed by back-filling steel shot process; the specific method is to bond and assemble the shell mold and then transport it to the steel shot burying box production line, put it into a special sand box, and then transport it to the casting area after the steel shot burying box line automatically buries the steel shot; the heating temperature of the core shooting machine is 200℃, the curing time is 4min, and the sand shooting time is 8s; the diameter of the steel shot is 3-8mm; Step 4: Casting of molten iron: The ductile iron liquid prepared in step 2 is transferred into a casting ladle, and a secondary inoculation is performed in the casting ladle, and then the ductile iron liquid is poured into the coated sand shell mold cavity prepared in step 3, and the ductile iron with a cast ferrite matrix is ​​obtained after solidification, cooling and sand removal; The inoculant used in the secondary inoculation is a low rare earth magnesium ferrosilicon nodulizer with a rare earth content of 0.2%-0.5%; the amount of the secondary inoculant added is 0.4% of the total mass of the ductile iron liquid.

[0045] Step 5: Microstructure regulation and treatment: The microstructure control treatment includes high temperature annealing treatment, three-phase region rapid cooling treatment and stress relief annealing treatment.

[0046] in, The high temperature annealing treatment is: subjecting the ductile iron obtained in step 4 to high temperature annealing treatment to eliminate grain boundary carbides or eutectic carbides and to make the composition uniform, with a heating temperature of 890-920° C., a holding time of 1-2 hours, and then cooling with the furnace.

[0047] The three-phase region rapid cooling treatment is to heat the ductile iron after high-temperature annealing to 720-800°C, keep it warm for 1-2 hours and then rapidly cool it. The cooling method includes mist cooling or salt bath cooling to obtain low-temperature ductile iron with a dual-phase matrix structure.

[0048] The stress relief annealing treatment is to heat the low-temperature ductile iron to 450-600°C, keep it warm for 30-60 minutes, then take it out of the furnace and cool it to room temperature. The sample is the low-temperature ductile iron.

[0049] Comparative Example 1 The difference from Example 1 is that QT450-10LT high-strength, high-toughness low-temperature ductile iron includes the following components in weight percentage: C: 3.75%, Si: 1.72%, Mn: 0.017%, P: 0.007%, S: 0.003%, Ni: 0.71%, Mg (residual): 0.034%, and the rest are iron and unavoidable impurities. The preparation method is the same as that of Example 1.

[0050] Comparative Example 2 The difference from Example 1 is that QT450-10LT high-strength, high-toughness low-temperature ductile iron includes the following components in weight percentage: C: 3.75%, Si: 2.25%, Mn: 0.017%, P: 0.007%, S: 0.003%, Ni: 0.71%, Mg (residual): 0.034%, and the rest are iron and unavoidable impurities. The preparation method is the same as that of Example 1.

[0051] Comparative Example 3 The difference from Example 1 is that the rapid cooling treatment temperature of the three-phase region during the preparation process is 850° C., and the rest is the same as Example 1.

[0052] Comparative Example 4 The difference from Example 1 is that the stress relief annealing treatment temperature during the preparation process is 400° C., and the rest is the same as Example 1.

[0053] Performance data Experimental methods: (1) Tensile strength, yield strength and elongation after fracture: tested in accordance with GB / T 228.1-2010 "Test methods for tensile tests of metallic materials at room temperature"; (2) Brinell hardness: Tested in accordance with GB / T231.1-2002 “Metal Brinell Hardness Test Method”; (3) Minimum impact absorption energy: Tested in accordance with GB / T229-2007 “Metallic Materials Charpy Pendulum Impact Test Method”.

[0054] The test data is shown in Table 1 below.

[0055] Table 1

[0056] According to the test data in Table 1 above, it can be seen that the low-temperature ductile iron prepared in Examples 1-3 ensures that the low-temperature impact absorption energy at -20°C, -40°C, and -50°C is ≥12J on the basis of improving the tensile strength and yield strength, thereby broadening the application field of low-temperature ductile iron.

[0057] The weight percentage of silicon (Si) in Comparative Example 1 is 1.72%, which is not within the protection scope of the present invention (1.8-2.1%). The tensile strength of the obtained ductile iron cannot meet the standard requirement of 450 MPa in mechanical properties and is unqualified.

[0058] The weight percentage of silicon (Si) in Comparative Example 2 is 2.25%, which is not within the protection scope of the present invention (1.8-2.1%), and the tensile strength of the obtained ductile iron does not meet the standard requirement of 450 MPa in mechanical properties and is unqualified.

[0059] In comparative example 3, the three-phase zone rapid cooling treatment temperature of ductile iron during the preparation process is 850°C, which is not within the protection scope of the present invention (720-800°C) and does not meet the process requirements. The low-temperature impact absorption energy of the obtained ductile iron does not meet the standard requirement of ≥12J and is unqualified.

[0060] In comparative example 4, the stress relief annealing temperature of the ductile iron during the preparation process is 400°C, which is not within the protection scope of the present invention (450-600°C) and does not meet the process requirements. The tensile strength of the obtained ductile iron is greatly improved, but the low-temperature impact absorption energy does not reach the standard requirement of ≥12J and is unqualified.

[0061] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A QT450-10LT high-strength, high-toughness, low-temperature ductile iron, characterized by: It includes the following components in mass percentage: C: 3.65%-3.85%, Si: 1.8%-2.1%, Mn<0.025%, P≤0.01%, S≤0.01%, Ni<0.8%, Mg (residual)≤0.045%, the total content of other impurity elements is less than 0.01%, and the rest is iron; The method for preparing the QT450-10LT high-strength, high-toughness low-temperature ductile iron comprises the following steps: Step 1: Smelting of raw iron liquid: High-purity pig iron and carbon scrap steel are used to melt the raw iron liquid in a medium-frequency induction furnace, and the temperature of the molten iron out of the furnace is 1500-1520℃; Step 2: Spheroidization and inoculation: The spheroidizing and inoculating treatment is carried out by using a cover ladle method; specifically, a low rare earth spheroidizing agent, a silicon-based inoculant and a covering agent are sequentially added to the bottom of the spheroidizing ladle, and then the raw iron liquid smelted in step 1 is quickly injected into the spheroidizing ladle for spheroidizing and inoculating treatment to obtain ductile iron liquid; Step 3: Casting mold preparation: The shell mold is back-filled with steel shot technology. The specific method is to close the mold in a special sand box and fill the outer periphery of the shell mold with steel shot to obtain a shell mold back-filled with steel shot with a higher cooling rate and greater rigidity. Step 4: Casting of molten iron: The ductile iron liquid prepared in step 2 is transferred into a casting ladle, and a secondary inoculation is performed in the casting ladle, and then the ductile iron liquid is poured into the coated sand shell mold cavity prepared in step 3, and the ductile iron with a cast ferrite matrix is ​​obtained after solidification, cooling and sand removal; Step 5: Microstructure regulation and treatment: The microstructure control treatment includes high temperature annealing treatment, three-phase region rapid cooling treatment and stress relief annealing treatment; The three-phase region rapid cooling treatment is to heat the ductile iron after high-temperature annealing to 720-800°C, keep it warm for 1-2 hours, and then rapidly cool it. The cooling method includes mist cooling or salt bath cooling to obtain low-temperature ductile iron with a dual-phase matrix structure. The stress relief annealing treatment is to heat the low-temperature ductile iron to 450-600°C, keep the temperature for 30-60 minutes, then take it out of the furnace and cool it to room temperature.

2. The QT450-10LT high-strength, high-toughness, low-temperature ductile iron according to claim 1, characterized in that: The high temperature annealing treatment is: subjecting the ductile iron obtained in step 4 to high temperature annealing treatment to eliminate grain boundary carbides or eutectic carbides and to make the composition uniform, with a heating temperature of 890-920° C., a holding time of 1-2 hours, and then cooling with the furnace.

3. The QT450-10LT high-strength, high-toughness, low-temperature ductile iron according to claim 1, characterized in that: The low rare earth spheroidizer is a low rare earth magnesium ferrosilicon spheroidizer, and the rare earth content is 0.2%-0.5%.

4. The QT450-10LT high-strength, high-toughness, low-temperature ductile iron according to claim 1, characterized in that: The silicon-based inoculant is a barium-containing ferrosilicon-based inoculant, and the barium content is 1.8%-2.1%.

5. The QT450-10LT high-strength, high-toughness, low-temperature ductile iron according to claim 1, characterized in that: The amount of the low rare earth spheroidizer added is 1.0-1.2% of the total mass of the original molten iron; the amount of the silicon-based inoculant added is 0.3-0.5% of the total mass of the original molten iron.

6. The preparation method according to claim 1, characterized in that: The inoculant used in the secondary inoculation is a low rare earth magnesium ferrosilicon spheroidizer with a rare earth content of 0.2%-0.5%; the addition amount of the low rare earth magnesium ferrosilicon spheroidizer is 0.3-0.5% of the total mass of the ductile iron liquid.

7. The preparation method according to claim 1, characterized in that: The shell-type back-filled steel shot process includes the following steps: After the shell mold is bonded and assembled, it is transported to the steel shot burying box production line and placed in a special sand box. After the steel shot burying box line automatically fills the steel shot, it is transported to the pouring area and then molten iron is poured into the casting mold; the heating temperature of the core shooting machine is 200°C, the curing time is 4 minutes, and the sand shooting time is 8 seconds; the diameter of the steel shot is 3-8mm.

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