Low-temperature nodular cast iron and preparation method and application thereof

Abstract

The invention belongs to the technical field of nodular cast iron manufacturing, and relates to low-temperature nodular cast iron and a preparation method and application thereof.The low-temperature nodular cast iron has the CEL of 4.25-4.3 and comprises, by mass, 3.4%-4.0% of C, 1.8%-2.3% of Si, smaller than or equal to 0.2% of Mn, smaller than or equal to 0.02% of S, smaller than or equal to 0.03% of P, 1.2%-1.6% of Ni and the balance Fe. The preparation method comprises the steps of raw material selection, burdening, smelting, spheroidizing inoculation, pouring and the like. Under the as-cast condition of the low-temperature nodular cast iron, at the normal temperature and the temperature as low as-40 DEG C, the tensile strength sigma b is larger than or equal to 450 MPa, the elongation is larger than or equal to 10%, and the average impact absorbing energy AKV of a sample with a V-shaped notch is larger than or equal to 10 J. According to the low-temperature nodular cast iron, the production cost of materials can be reduced, and the application range and application field of the low-temperature nodular cast iron can be widened; the application problem that the composite material needs to be applied in a low-temperature environment and needs parts with high strength and high plasticity and toughness is solved.

Description

Technical Field

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

[0002] Ductile iron is carbon in the form of spherical graphite. Its mechanical properties are far superior to those of gray iron and close to those of steel. It has excellent casting, cutting and wear resistance, and has a certain degree of elasticity. It is widely used in the manufacture of high-end castings such as crankshafts, gears, pistons, automobile wheel hub brackets, and various mechanical parts.

[0003] QT450-10 ductile iron is a ferritic ductile iron. Its main chemical components are as follows: C3.6~4.0, Si2.15~2.8, Mn≤0.46~0.66, S≤0.01~0.016, P≤0.035, Mg: 0.027~0.05, and the rest is iron. The material has high toughness and plasticity. At low temperatures, toughness turns to brittleness, but the low-temperature impact value is high, and it has a certain resistance to temperature changes and corrosion resistance. It has a wide range of uses. It is used in agricultural machinery for plows, plow posts, differential cases, etc.; in general machinery, it is used as valve bodies, high and low pressure cylinders, etc., and can also be used for steel caps of power transmission lines, etc.

[0004] Although the existing QT450-10 ductile iron has excellent mechanical properties, it still cannot meet the corresponding mechanical property requirements when used in the pads of railway track transportation in cold areas (under extreme conditions, the temperature reaches minus 40°C or even lower). Therefore, technical personnel in this field urgently need to develop a new low-temperature ductile iron and its preparation method and application. Summary of the invention

[0005] The purpose of the present invention is to provide a ductile iron with high strength and high plasticity at room temperature and as low as -40°C. Compared with the existing QT450-10 ductile iron, the ductile iron still has higher strength and high plasticity in a low temperature environment as low as -40°C.

[0006] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0007] A low-temperature ductile iron, wherein the CEL (carbon equivalent) of the low-temperature ductile iron is 4.25-4.3, and the mass percentage of the chemical components is:

[0008] C: 3.4%~4.0%, Si: 1.8%~2.3%, Mn≤0.2%, S≤0.02%, P≤0.03%, Ni: 1.2%~1.6%, and the balance is Fe.

[0009] Preferably, the mass percentage of the chemical components of the low-temperature ductile iron is:

[0010] C: 3.54%~4.0%, Si: 2.0%~2.19%, Mn: 0.084%~0.13%, S: 0.010%~0.015%, P: 0.018%~0.024%, Ni: 1.34%~1.6%, and the balance is Fe.

[0011] Preferably, at room temperature and as low as -40°C, the mechanical properties of the low-temperature ductile iron are: tensile strength σ b ≥450MPa, elongation ≥10%, average impact absorption energy AKV ≥10J for V-notch specimens.

[0012] The present invention also proposes a method for manufacturing the low-temperature ductile iron, comprising the following steps:

[0013] S1. Select raw materials: high-purity pig iron, high-purity scrap steel, petroleum coke recarburizer and electrolytic nickel plate;

[0014] S2, batching: the raw materials in step S1 are batched according to a certain ratio, and then smelted in a medium frequency furnace, the CEL and chemical composition of the molten iron are detected by a molten iron quality controller, and the CEL and chemical composition of the molten iron are adjusted to meet the CEL and chemical composition requirements of the low-temperature ductile iron by adjusting the batching ratio;

[0015] S3, smelting: according to the adjusted proportion of ingredients that meet the CEL and chemical composition requirements of low-temperature ductile iron, add raw materials for smelting, stop the furnace for inspection when the smelting temperature reaches 1450°C, and heat up after the composition is qualified. When the overheating temperature is 1500-1550°C, stop the furnace and let it stand for 3 minutes. After deslagging, pour the molten iron into the spheroidizing bag for spheroidizing inoculation treatment;

[0016] S4, pouring, after the spheroidization inoculation of step S3 is completed, the slag is removed, and then the molten iron is covered with insulation cotton and transferred to the pouring area for pouring operation, and low-temperature ductile iron is obtained after pouring.

[0017] Preferably, in step S3, the spheroidization inoculation treatment comprises the following steps:

[0018] According to the quality of the molten iron to be spheroidized and inoculated, a certain mass of spheroidizer, inoculant and iron filings are placed in the bottom of the spheroidizing ladle from bottom to top, and then the molten iron is flushed into the spheroidizing ladle by a one-time flushing method; wherein, the spheroidizer is 2-6 spheroidizer (where 2-6 is the brand of the spheroidizer, and 2 and 6 represent the percentage content of rare earth and magnesium respectively), the inoculant is silicon-barium-calcium inoculant, the spheroidizing temperature is 1480-1520°C, and the spheroidizing inoculation reaction time is not less than 60S.

[0019] Preferably, in step S3, the mass of molten iron poured into the spheroidizing bag is 200 kg (after the molten iron is injected, the liquid surface has a safety distance of 10-15 cm from the upper edge of the spheroidizing bag), the amount of spheroidizing agent added is 1.1% of the mass of the molten iron, the amount of inoculant added is 0.4% of the mass of the molten iron, and the amount of iron filings added is 1-2 kg.

[0020] Preferably, in step S3, the particle size of the 2-6 spheroidizing agent is 3-8 mm, and the particle size of the silicon-barium-calcium inoculant is 1-3 mm.

[0021] Preferably, during pouring in step S4, a flow inoculant is used for flow inoculation, the flow inoculant is a Bi-containing inoculant with a particle size of 40-140 mesh, the addition amount of the Bi-containing inoculant is 70 g / min, and the pouring temperature is 1340-1380°C.

[0022] The present invention also proposes the use of the low-temperature ductile iron in the pads of railway track transportation operating at temperatures between room temperature and -40°C.

[0023] The working principle of the present invention is that the chemical composition of ductile iron with high toughness and high strength at low temperature should adopt the principle of high carbon, low silicon, low manganese, low phosphorus, low sulfur and a certain content of nickel, wherein carbon is used to increase the graphitization degree of ductile iron and reduce the tendency of white cast iron. When the carbon content is high, it is beneficial to increase the spheroidization rate and graphite grade and improve the toughness of the material, but excessive carbon will cause graphite floating; silicon is an element that promotes graphitization and can improve the tensile strength, yield strength and hardness of ductile iron. For low-temperature and high-toughness ductile iron, increasing the silicon content will significantly reduce the impact toughness ak, and silicon can increase the brittle transition temperature of ductile iron; manganese is an element with a tendency to white cast, and manganese has a particularly adverse effect on impact toughness and elongation, so this application is to control the manganese content of ductile iron to the lowest level; sulfur is an anti-spheroidizing element; phosphorus is a phosphorus eutectic-forming element, which greatly affects the plasticity and toughness of ductile iron and increases the brittle transition temperature; nickel is a graphitizing element, and nickel-strengthening ferrite can improve the strength and impact toughness of ductile iron, and nickel reduces the brittle transition temperature, that is, nickel-containing ductile iron has higher impact toughness at low temperatures.

[0024] The beneficial effects of the present invention are:

[0025] The low-temperature ductile iron of the present invention has the following mechanical properties in the as-cast state at room temperature and as low as -40°C: tensile strength σ b ≥450MPa, elongation ≥10%, and the average impact absorption energy AKV of the V-notch specimen is ≥10J. The present invention can reduce the production cost of the material and expand its application range and application field, solving the application problem of parts that need to be used in low temperature environments and have high strength and high plasticity and toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a metallographic photograph of the material in Example 1.

[0027] Figure 2 This is a photo of the material matrix in Example 1. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to specific embodiments in conjunction with the accompanying drawings. The illustrative embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0029] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0030] There is no particular limitation on the purity of all raw materials in the present invention, and the present invention preferably adopts the conventional purity used in the art.

[0031] The devices used in the present invention are not particularly limited and can be any of the commonly used devices in the art.

[0032] Example 1

[0033] A low-temperature ductile iron has chemical components in percentage by weight: C: 3.84%, Si: 2.15%, Mn: 0.092%, S: 0.012%, P: 0.019%, Ni: 1.34%, and the balance is Fe.

[0034] Its metallographic and matrix photos (magnified 100 times) are as follows Figure 1 , Figure 2 As shown, it can be seen that the spheroidization rate of the material reaches 95%, the graphite grade reaches level 8, the ferrite accounts for 92%, and the pearlite accounts for 8%.

[0035] Example 2

[0036] A low-temperature ductile iron has the following chemical components in percentage by weight: C: 3.98%, Si: 2.19%, Mn: 0.105%, S: 0.010%, P: 0.024%, Ni: 1.38%, and the balance is Fe.

[0037] Example 3

[0038] A low-temperature ductile iron has the following chemical components in percentage by weight: C: 4.0%, Si: 2.07%, Mn: 0.108%, S: 0.012%, P: 0.021%, Ni: 1.507%, and the remainder is Fe.

[0039] Example 4

[0040] A low-temperature ductile iron has the following chemical components in percentage by weight: C: 4.0%, Si: 2.06%, Mn: 0.13%, S: 0.015%, P: 0.022%, Ni: 1.54%-1.55%, and the remainder is Fe.

[0041] Example 5

[0042] A low-temperature ductile iron has chemical components in percentage by weight: C: 3.54%, Si: 2.0%, Mn: 0.084%, S: 0.011%, P: 0.018%, Ni: 1.6%, and the balance is Fe.

[0043] The commissioned testing agency conducted mechanical property testing on the low-temperature ductile iron test blocks in the above Examples 1 to 5, and the test results are shown in the following table:

[0044] Mechanical properties test results of low temperature ductile iron test blocks in Examples 1 to 5

[0045]

[0046]

[0047] Note: The column of average impact absorption energy shows the test results of three impact tests.

[0048] The above test results show that the low-temperature ductile iron proposed in the present invention has the following mechanical properties at room temperature and as low as -40°C: tensile strength σ b ≥450MPa, elongation ≥10%, average impact absorption energy AKV ≥10J for V-notch specimens.

[0049] Example 6

[0050] This embodiment proposes a method for manufacturing low-temperature ductile iron based on the above embodiments 1 to 5, comprising the following steps:

[0051] S1. Select raw materials: high-purity pig iron, high-purity scrap steel, petroleum coke recarburizer and electrolytic nickel plate;

[0052] S2, batching: the raw materials in step S1 are batched according to a certain ratio, and then smelted in a medium frequency furnace, the CEL and chemical composition of the molten iron are detected by a molten iron quality controller, and the CEL and chemical composition of the molten iron are adjusted to meet the CEL and chemical composition requirements of the low-temperature ductile iron by adjusting the batching ratio;

[0053] S3, smelting: according to the adjusted proportion of ingredients that meet the CEL and chemical composition requirements of low-temperature ductile iron, add raw materials for smelting, stop the furnace for inspection when the smelting temperature reaches 1450°C, and heat up after the composition is qualified. When the overheating temperature is 1500-1550°C, stop the furnace and let it stand for 3 minutes. After deslagging, pour the molten iron into the spheroidizing bag for spheroidizing inoculation treatment;

[0054] S4, pouring, after the spheroidization inoculation of step S3 is completed, the slag is removed, and then the molten iron is covered with insulation cotton and transferred to the pouring area for pouring operation, and low-temperature ductile iron is obtained after pouring.

[0055] Specifically, in step S3, the spheroidization inoculation treatment includes the following steps:

[0056] According to the quality of the molten iron to be spheroidized and inoculated, a certain amount of spheroidizer, inoculant and iron filings are placed in the bottom of the spheroidizing ladle from bottom to top, and then the molten iron is flushed into the spheroidizing ladle by a one-time flushing method; wherein, the spheroidizer is 2-6 spheroidizer (where 2-6 is the brand of the spheroidizer, 2 and 6 represent the percentage content of rare earth and magnesium respectively), the inoculant is silicon-barium-calcium inoculant, the spheroidizing temperature is 1480-1520℃, and the spheroidizing and inoculating reaction time is not less than 60S. wherein, the particle size of the 2-6 spheroidizer is 3-8mm, and the particle size of the silicon-barium-calcium inoculant is 1-3mm.

[0057] Specifically, in step S3, the mass of molten iron poured into the spheroidizing bag is 200 kg (after the molten iron is injected, the liquid surface has a safety distance of 10-15 cm from the upper edge of the spheroidizing bag), the amount of spheroidizing agent added is 1.1% of the mass of the molten iron, the amount of inoculant added is 0.4% of the mass of the molten iron, and the amount of iron filings added is 1-2 kg.

[0058] Specifically, during pouring in step S4, a flow inoculant is used for flow inoculation, the flow inoculant is a Bi-containing inoculant with a particle size of 40-140 mesh, the addition amount of the Bi-containing inoculant is 70 g / min, and the pouring temperature is 1340-1380°C.

[0059] The working principle of the present invention is that the chemical composition of ductile iron with high toughness and high strength at low temperature should adopt the principle of high carbon, low silicon, low manganese, low phosphorus, low sulfur and a certain content of nickel, wherein carbon is used to increase the graphitization degree of ductile iron and reduce the tendency of white cast iron. When the carbon content is high, it is beneficial to increase the spheroidization rate and graphite grade and improve the toughness of the material, but excessive carbon will cause graphite floating; silicon is an element that promotes graphitization and can improve the tensile strength, yield strength and hardness of ductile iron. For low-temperature and high-toughness ductile iron, increasing the silicon content will significantly reduce the impact toughness ak, and silicon can increase the brittle transition temperature of ductile iron; manganese is an element with a tendency to white cast, which has a particularly adverse effect on impact toughness and elongation, so this application is to control the manganese content of ductile iron to the lowest level; sulfur is an anti-spheroidizing element; phosphorus is a phosphorus eutectic-forming element, which greatly affects the plasticity and toughness of ductile iron and increases the brittle transition temperature; nickel is a graphitizing element, and nickel-strengthening ferrite can improve the strength and impact toughness of ductile iron, and nickel can reduce the brittle transition temperature, that is, nickel-containing ductile iron has higher impact toughness at low temperatures.

[0060] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A low-temperature ductile iron, characterized in that: The CEL of the low-temperature ductile iron is 4.25-4.3, and the mass percentage of the chemical composition is: C: 3.4%~4.0%, Si: 1.8%~2.3%, Mn≤0.2%, S≤0.02%, P≤0.03%, Ni: 1.2%~1.6%, and the balance is Fe.

2. The low temperature ductile iron according to claim 1, characterized in that: The mass percentage of the chemical composition of the low temperature ductile iron is: C: 3.54%~4.0%, Si: 2.0%~2.19%, Mn: 0.084%~0.13%, S: 0.010%~0.015%, P: 0.018%~0.024%, Ni: 1.34%~1.6%, and the balance is Fe.

3. The low temperature ductile iron according to claim 1 or 2, characterized in that: At room temperature and as low as -40°C, the mechanical properties of the low-temperature ductile iron are: tensile strength σ b ≥450MPa, elongation ≥10%, average impact absorption energy AKV ≥10J for V-notch specimens.

4. A method for manufacturing low-temperature ductile iron according to claim 3, characterized in that: The following steps are involved: S1. Select raw materials: high-purity pig iron, high-purity scrap steel, petroleum coke recarburizer and electrolytic nickel plate; S2, batching: the raw materials in step S1 are batched according to a certain ratio, and then smelted in a medium frequency furnace, the CEL and chemical composition of the molten iron are detected by a molten iron quality controller, and the CEL and chemical composition of the molten iron are adjusted to meet the CEL and chemical composition requirements of the low-temperature ductile iron by adjusting the batching ratio; S3, smelting: according to the adjusted proportion of ingredients that meet the CEL and chemical composition requirements of low-temperature ductile iron, add raw materials for smelting, stop the furnace for inspection when the smelting temperature reaches 1450°C, and heat up after the composition is qualified. When the overheating temperature is 1500-1550°C, stop the furnace and let it stand for 3 minutes. After deslagging, pour the molten iron into the spheroidizing bag for spheroidizing inoculation treatment; S4, pouring, after the spheroidization inoculation of step S3 is completed, the slag is removed, and then the molten iron is covered with insulation cotton and transferred to the pouring area for pouring operation, and low-temperature ductile iron is obtained after pouring.

5. The method for producing low-temperature ductile iron according to claim 4, characterized in that: In step S3, the spheroidization inoculation treatment includes the following steps: According to the quality of the molten iron to be spheroidized and inoculated, a certain mass of spheroidizer, inoculant and iron filings are placed in the bottom of the spheroidizing ladle from bottom to top, and then the molten iron is flushed into the spheroidizing ladle by a one-time flushing method; wherein, the spheroidizer is 2-6 spheroidizer, the inoculant is silicon-barium-calcium inoculant, the spheroidizing temperature is 1480-1520℃, and the spheroidizing inoculation reaction time is not less than 60S.

6. The method for producing low-temperature ductile iron according to claim 5, characterized in that: In step S3, the mass of molten iron poured into the spheroidizing bag is 200 kg, the amount of spheroidizing agent added is 1.1% of the mass of molten iron, the amount of inoculant added is 0.4% of the mass of molten iron, and the amount of iron filings added is 1-2 kg.

7. The method for producing low-temperature ductile iron according to claim 5, characterized in that: In step S3, the particle size of the 2-6 spheroidizer is 3-8 mm, and the particle size of the silicon-barium-calcium inoculant is 1-3 mm.

8. The method for producing low-temperature ductile iron according to claim 4, characterized in that: During pouring in step S4, a flow inoculant is used for flow inoculation. The flow inoculant is a Bi-containing inoculant with a particle size of 40 to 140 meshes, the addition amount of the Bi-containing inoculant is 70 g / min, and the pouring temperature is 1340 to 1380°C.

9. Use of the low-temperature ductile iron according to claim 3 in a pad for railway track transportation operating at temperatures between room temperature and -40°C.

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