CN108866427B - Method for manufacturing super-large section low-temperature high-toughness ferritic nodular iron casting - Google Patents

Method for manufacturing super-large section low-temperature high-toughness ferritic nodular iron casting Download PDF

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CN108866427B
CN108866427B CN201810795157.6A CN201810795157A CN108866427B CN 108866427 B CN108866427 B CN 108866427B CN 201810795157 A CN201810795157 A CN 201810795157A CN 108866427 B CN108866427 B CN 108866427B
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iron
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metal mold
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CN108866427A (en
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李克锐
卫东海
吴现龙
李新强
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Zhengzhou Research Institute of Mechanical Engineering Co Ltd
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Zhengzhou Research Institute of Mechanical Engineering Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C22C37/04—Cast-iron alloys containing spheroidal graphite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C9/00—Moulds or cores; Moulding processes
    • B22C9/06—Permanent moulds for shaped castings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C9/00—Moulds or cores; Moulding processes
    • B22C9/06—Permanent moulds for shaped castings
    • B22C9/065—Cooling or heating equipment for moulds
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/10—Making spheroidal graphite cast-iron
    • C21C1/105—Nodularising additive agents
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/08—Making cast-iron alloys
    • C22C33/10—Making cast-iron alloys including procedures for adding magnesium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C22C37/10—Cast-iron alloys containing aluminium or silicon

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)

Abstract

The invention discloses a method for manufacturing a super-large section low-temperature high-toughness ferritic nodular iron casting, the weight of the nodular iron casting exceeds 50 tons, the wall thickness reaches more than 400mm, and the nodular iron casting comprises the following components: c: 3.6-3.7%; siOriginal source：0.9~1.0%；SiFinal (a Chinese character of 'gan'): 1.9-2.0%; mn: less than or equal to 0.1 percent; p: less than or equal to 0.03 percent; s is less than or equal to 0.01 percent; mg: 0.03-0.08%; RE: 0.01-0.02%; ni: 0.6-0.8%; sb: 0.003 to 0.005%. The method adopts the technical measures of 'high-temperature pure base iron liquid + water-cooled metal mold + chilling block + nodulizer 5800+ composite reinforced inoculation + alloying + low-temperature boxing' and the like, so that the obtained super-large section low-temperature high-toughness ferritic nodular iron casting can reach the quality standard of the QT400-18 nodular iron and can meet the technical requirements of super-large section nodular iron castings of wind power, nuclear power and the like.

Description

Method for manufacturing super-large section low-temperature high-toughness ferritic nodular iron casting
Technical Field
The invention relates to a method for manufacturing a nodular cast iron part, in particular to a method for manufacturing an ultra-large section low-temperature high-toughness ferritic nodular cast iron part with the weight of more than 50 tons and the wall thickness of 400 mm.
Background
The annular super-large section low-temperature high-toughness ferritic nodular iron casting is increasingly widely applied to the fields of wind power, nuclear power and the like (such as hundred-ton grade nodular iron casting core waste material tanks, hubs for wind power, bases and the like), but higher requirements are also put forward on the quality of the nodular iron casting. In order to obtain the low-temperature impact property, the elongation and the fracture toughness which meet the requirements, the casting must be ensured to have a ferrite matrix, the spheroidization is good, and the distorted graphite such as a block shape cannot appear. Compared with normal-temperature ferritic nodular cast iron, the low-temperature ferritic nodular cast iron has more strict requirements on mechanical properties, component control, spheroidizing inoculation process, structure control and the like. Although China has achieved certain achievements in the development of low-temperature ferrite nodular cast iron, most domestic manufacturers still cannot master key technologies, and produced castings are small in tonnage, thin in wall thickness and simple in shape, cannot meet the increasingly developed market demands of nodular cast iron, and have a large gap compared with foreign countries: in the last 80 th century, Siempelkamp, Germany, produced a ductile iron pressure frame with a weight of 160t and a maximum wall thickness of 630mm and a spent fuel ductile iron container with a weight of 130 tons and a wall thickness of 500 mm; the company Thystem of France develops and produces the TN1300 type spent fuel nodular iron container with weight of 115t and wall thickness of 400mm, then Japan develops the nodular iron container with weight of 100t and wall thickness of 425mm for hundred tons in 1998, and China is still blank in the aspect of manufacturing nodular iron castings for hundred tons.
The main problems in the prior production of the ultra-large section low-temperature high-toughness nodular cast iron are as follows: the large-section ductile iron piece has large size, heavy weight, large wall thickness, large heat capacity during casting, slow solidification and easy spheroidization recession and inoculation recession, so that the structure of the casting is changed, particularly the final solidification region of the casting is more serious, and the large-section ductile iron piece mainly shows that the graphite sphere diameter is large, the number of graphite spheres is reduced, graphite floats, the graphite spheres are distorted, and various non-spherical graphite (mainly comprising pseudo-flakes, worms, bursts and broken blocks) is formed; meanwhile, due to redistribution of solute elements during solidification, a series of problems such as serious component segregation, intergranular carbides, white cast iron and the like can also occur, so that the mechanical property of the nodular cast iron is deteriorated, particularly, the elongation and the plasticity are obviously reduced, and the popularization and the use of the large-section nodular cast iron are restricted.
Disclosure of Invention
The invention aims to provide a method for manufacturing an ultra-large section low-temperature high-toughness ferritic nodular iron casting with the weight of more than 50 tons and the wall thickness of 400mm aiming at the defects in the prior art, so that the finished iron casting can obtain stable and excellent structure performance.
In order to achieve the purpose, the invention can adopt the following technical scheme:
the invention relates to a method for manufacturing a super-large section low-temperature high-toughness ferritic nodular iron casting, wherein the weight of the nodular iron casting is more than or equal to 50 tons, the wall thickness is more than or equal to 400mm, and the method comprises the following specific manufacturing steps:
step one, modeling: adopting a metal mold with a water cooling device and made of QT400-18 materials, and coating a zircon powder coating layer with the thickness of 1-1.5mm on the inner wall of the metal mold;
step two, baking: baking the cavity by using an air heater for more than or equal to 8 hours to enable the temperature of the cavity to reach 80-100 ℃;
step three, raw material preparation: the raw materials adopt chemical components as follows: c: 3.51 percent; si: 0.38 percent; mn: 0.012%; s: 0.008 percent; p: 0.007%; ti: 0.003%; cu: 0.0073 percent; cr: 0.0070 percent; v: 0.0048 percent of high-purity pig iron;
step four, smelting molten iron: adding high-purity pig iron into an intermediate frequency furnace for smelting; adding 75# ferrosilicon to adjust the silicon content of the iron liquid to 0.9-1.0%, wherein the overheating temperature of the iron liquid is 1510-1520 ℃, and then stirring and slagging off;
fifthly, spheroidizing: a balling method of a flushing method is adopted, a nodulizer is weighed according to 1.1-1.3% of the total weight of molten iron, and the nodulizer is uniformly scattered on one side of a dam at the bottom of a casting ladle;
sixthly, inoculation treatment: weighing two parts of high-calcium barium inoculant according to 0.3 percent and 0.4 percent of the total weight of the molten iron, weighing a sulfur-oxygen inoculant according to 0.15 percent of the total weight of the molten iron, uniformly scattering the 0.3 percent of high-calcium barium inoculant on a nodulizer after baking and preheating at 400 +/-10 ℃, using the 0.4 percent of high-calcium barium inoculant for iron tapping inoculation, and adding the 0.15 percent of sulfur-oxygen inoculant along with flow during pouring; 1% covering agent is added on the inoculant;
step seven, alloying treatment: adding alloy according to 0.603-1.3% of the total weight of the molten iron, wherein the alloy comprises the following alloy elements in percentage by weight: 0.6-1.3%, Sb: 0.003-0.005 percent of inoculant, which is uniformly scattered on the bottom of the casting ladle after being roasted and preheated at 400 +/-10 ℃;
eighth step, pouring: preheating a casting ladle to 700-800 ℃ (dark red), and casting when the temperature of molten iron is reduced to 1320 +/-10 ℃;
ninth, box beating and cleaning: and (3) when the temperature of the casting is cooled to below 300 ℃, boxing is carried out, and the component composition C is obtained: 3.4-3.7%; si: 1.7-2.0%; mn: less than or equal to 0.1 percent; p: less than or equal to 0.03 percent; s is less than or equal to 0.01 percent; mg: 0.03-0.08%; RE: 0.01-0.02%; ni: 0.6-1.3%; sb: 0.003-0.008% of finished products of the ductile iron castings.
Tests prove that the room-temperature tensile strength of the annular nodular iron casting is more than or equal to 250MPaThe yield strength is more than or equal to 200 MPa, and the elongation is more than or equal to 8 percent; the tensile strength is more than or equal to 240 MPa, the yield strength is more than or equal to 180 MPa, and the elongation is more than or equal to 8 percent at the high temperature of 100 ℃; impact at room temperature is more than or equal to 12J/cm2Low temperature impact at-40 ℃ is more than or equal to 4J/cm2(ii) a The metallographic structure reaches: the graphite shape V-VI is more than or equal to 80 percent, the IV is less than or equal to 20 percent, the II-III is less than or equal to 10 percent, the graphite size is more than or equal to 90 percent from 3 to 7, the ferrite is more than or equal to 80 percent, and the pearlite is less than or equal to 20 percent; fracture toughness at minus 40 ℃ is more than or equal to 50MPa m1/2。
In order to facilitate the processing, the metal mold used in the first step is formed by splicing six arc-shaped templates with the same structure.
The water cooling device adopted in the first step comprises a cooling pipe which is integrally cast in the metal mold and is provided with an inlet and an outlet, and the cooling pipe is arranged along the metal mold in an S-shaped curve; temperature measuring holes are uniformly arranged on the outer wall of the metal mold, the bottom of each temperature measuring hole is 30mm away from the inner wall of the metal mold, and a thermocouple is arranged in each temperature measuring hole; and positioning holes fixedly connected with an external sandbox are uniformly formed in the outer side wall of the metal mould.
Because the wall thickness of the ferritic nodular iron casting is larger, an enhanced cooling device can be arranged on the inner wall of the metal mold. The enhanced cooling device is fan-shaped cold iron blocks which are made of HT150 cast iron and are arranged at intervals along the inner wall of a metal mold, the gap between every two adjacent cold iron blocks is 20-30 mm, and chromite sand or zircon sand is filled in the gap; and a zircon powder coating layer with the thickness of 1-1.5mm is coated on the surface of the fan-shaped cold iron block.
After the raw materials are melted down in the fourth step, if recarburizing is needed, a recarburizing agent can be used; if carbon reduction is required, pure iron is used.
The nodulizer used in the fifth step is a nodulizer 5800 which comprises the following components: 44-48% of Si, 5.55-6.15% of Mg, 0.85-1.15% of RE, 0.8-1.2% of Ca, 0.10-0.12 Ce, 0.06-0.08 La and 0.20-0.24% of Y.
The particle size of the high-calcium barium inoculant used in the sixth step is 3-8 mm, and the high-calcium barium inoculant comprises the following components: si: 72-78%, Ca: 1.0-2.0%, Ba: 2.0-3.0% and Al < 1.5%; the particle size of the sulfur-oxygen inoculant is 0.2-0.7 mm, and the sulfur-oxygen inoculant comprises the following components: si: 70-76%, Ce: 1.5-2.0%, Ca: 0.75-1.25%, Al: 0.75-1.25%, S & O < 1%; the covering agent is iron sheet.
And before the eighth step of pouring, introducing cooling water (the water temperature at the normal temperature state is enough) into a cooling pipe in the metal mold, and stopping introducing water after 3 hours of pouring.
The method has the advantages that the method for manufacturing the high-temperature pure base iron liquid, the water-cooled metal mold, the chilling block, the nodulizer 5800, the composite reinforced inoculation, the alloying and the low-temperature boxing is adopted, so that the obtained ultra-large section low-temperature high-toughness ferritic nodular iron casting can reach the quality standard of the QT400-18 nodular iron and can meet the technical requirements of ultra-large section nodular iron castings of wind power, nuclear power and the like.
In the invention, high-purity pig iron is selected as a raw material, and a high-temperature pure iron liquid with proper and stable chemical components and low P, Mn and impurity elements is obtained, so that the component segregation is prevented; for the casting with larger wall thickness, a water cooling device is adopted to match with a chilling block to form a powerful cooling device, so that the cooling capacity of the metal mold can be effectively controlled and enhanced, the safety of the device is ensured, the solidification time of molten iron is shortened, the casting is solidified within 3 hours, and the problems that spheroidization inoculation is declined and special-shaped graphite is generated due to too slow solidification are avoided; the nodulizer 5800 and the stream inoculant are adopted, so that the nodulizing effect can be obviously improved, and the number of graphite spheres can be increased; the Sb and Sb elements are added to refine graphite, so that the roundness of graphite spheres is improved, the generation of broken graphite and graphite distortion at the core of a casting is prevented, and the strength and hardness of ductile iron are improved; by adding the alloy Ni, the tensile strength, the yield strength and the low-temperature impact toughness are improved under the condition of not losing the elongation, and the alloy Ni is beneficial to the fracture toughness, so that the strength, the elongation, the low-temperature impact toughness and the fracture toughness of the core of the ductile iron casting with the ultra-large section can meet the requirements; the thermocouple is arranged in the metal mold, so that the temperature change of the metal mold can be monitored in real time, and the safety of the metal mold is ensured.
Drawings
FIG. 1 is a schematic structural diagram of the metal mold of the present invention.
Figure 2 is a top view of the single piece arcuate template of figure 1.
Fig. 3 is a view from a-a of fig. 2.
Fig. 4 is a structure view of a single arc-shaped template with only a water cooling device.
FIG. 5 is a graphite photograph of a finished casting made by an embodiment of the present invention.
FIG. 6 is a photograph of a substrate of a finished casting made in accordance with an embodiment of the present invention.
FIG. 7 is a graph showing the temperature detection of the die used in the embodiment of the present invention.
Detailed Description
The present invention is described in more detail below by way of specific examples.
Manufacturing an ultra-large section low-temperature high-toughness ferritic nodular cast iron container which weighs 60 tons, has a diameter of 2575mm and a wall thickness of 560 mm:
the specific manufacturing steps are as follows:
step one, modeling: as shown in figures 1-3, a metal mold 1 with a water cooling device and made of QT400-18 is adopted, and for the convenience of processing, the metal mold 1 is formed by connecting six arc-shaped plates with the same structure by bolts; because the wall thickness of the manufactured container is larger, the invention adopts a water-cooling + chilling block powerful cooling device to cool the casting (if the wall thickness of the casting is thinner, a metal mold with a water-cooling device can also be only adopted, the structure diagram of a single arc-shaped template is shown in figure 4), the water-cooling device adopted by the invention comprises a cooling pipe 2 which is integrally cast in the metal mold 1 and is provided with an inlet and an outlet, the cooling pipe 2 is arranged along the metal mold 1 in an S-shaped curve (the water inlet and the water outlet on each arc-shaped template extend out of the metal mold through a connecting pipe and are communicated through an external water channel); temperature measuring holes 3 are uniformly arranged on the outer wall of the metal mold 1, the distance between the bottom of each temperature measuring hole 3 and the inner wall of the metal mold is 30mm, a thermocouple is arranged in each temperature measuring hole, the thermocouple can adopt a thermocouple (NiCr-NiAl) with the diameter phi of 0.5mmK, and the two poles of the thermocouple penetrate through double-hole ceramic beads, so that the temperature change of the cavity can be monitored in real time; the outer side wall of the metal mold 1 is uniformly provided with positioning holes fixedly connected with an external sandbox; fan-shaped cold iron blocks 4 made of HT150 cast iron are arranged along the inner wall of the metal mold 1 at intervals, the gap between every two adjacent cold iron blocks 4 is 20mm, and chromite sand 5 is filled in the gap; coating a zircon powder coating layer 6 with the thickness of 1.5mm on the surface of the fan-shaped chilling block, wherein the coating layer 6 can be brushed for five times to ensure that the thickness meets the requirement and the chilling block is firmly combined;
in the using process of the metal mold, cooling water or gas can be introduced into the cooling pipe 2 according to the casting solidification condition requirement, and the cooling capacity is controlled by adjusting parameters such as flow, pressure and the like, so that the casting is solidified within the required time, the quality of the casting is improved, and the metal mold has good use and popularization values.
Step two, baking: baking the cavity by using an air heater for 10 hours to enable the temperature of the cavity to reach 90 ℃;
step three, raw material preparation: the raw material adopts high-purity pig iron, and the chemical components of the raw material are as follows: c: 3.51 percent; si: 0.38 percent; mn: 0.012%; s: 0.008 percent; p: 0.007%; ti: 0.003%; cu: 0.0073 percent; cr: 0.0070 percent; v: 0.0048%;
step four, smelting molten iron: baking and preheating high-purity pig iron at 400 +/-10 ℃, and then adding the pig iron into an intermediate frequency furnace for smelting; after the raw materials are melted down, the carbon content is adjusted to 3.7 percent by adding a carburant, 75# ferrosilicon is added to adjust the silicon content of the original iron liquid to 0.9 percent, the overheating temperature of the iron liquid is 1515 ℃, and then stirring and slagging-off are carried out; during actual smelting, after raw materials are melted down, if carburetting is needed, a carburant can be used; if carbon reduction is needed, pure iron is used;
fifthly, spheroidizing: when the temperature of the molten iron is reduced to 1480 ℃, a spheroidizing method by a flushing method is adopted, and a spheroidizing agent 5800 accurately weighed according to 1.2 percent of the total weight of the molten iron is uniformly scattered on one side of a dam at the bottom of a ladle;
sixthly, inoculation treatment: weighing two parts of high-calcium barium inoculant according to 0.3 percent and 0.4 percent of the total weight of the molten iron, weighing a sulfur-oxygen inoculant according to 0.15 percent of the total weight of the molten iron, uniformly scattering the 0.3 percent of high-calcium barium inoculant on a nodulizer after baking and preheating at 400 +/-10 ℃, using the 0.4 percent of high-calcium barium inoculant for iron tapping inoculation, and adding the 0.15 percent of sulfur-oxygen inoculant along with flow during pouring; and 1% covering agent (iron sheet) is added on the inoculant;
step seven, alloying treatment: adding alloy according to 0.603-1.3% of the total weight of the molten iron, wherein the alloy comprises the following alloy elements in percentage by weight: 0.7%, Sb: 0.0035 percent, is evenly scattered on the inoculant at the bottom of the casting ladle after being roasted and preheated at the temperature of 400 +/-10 ℃;
eighth step, pouring: preheating a casting ladle to 700-800 ℃ (dark red), casting when the temperature of molten iron is reduced to 1320 +/-10 ℃, and introducing cooling water into a cooling pipe 2 before casting;
ninth, box beating and cleaning: and (3) when the temperature of the casting is cooled to below 300 ℃, boxing is carried out, and the component composition C is obtained: 3.7 percent; si: 1.92 percent; mn: 0.018%; p: 0.011 percent; s: 0.010%; mg: 0.069%; RE: 0.015 percent; ni: 0.69%; sb: 0.005% of nodular iron castings.
Tests show that the tensile strength at room temperature of the nodular iron casting is 375MPa, the yield strength is 237 MPa, and the elongation is 20.5%; the tensile strength at the high temperature of 100 ℃ is 364 MPa, the yield strength is 216 MPa, and the elongation is 16.7 percent; the impact at room temperature is 21.75J/cm2And the low-temperature impact at the temperature of minus 40 ℃ is 6.97J/cm2(ii) a The metallographic structure reaches: the graphite shapes V-VI are 88%, IV is 7%, II-III is 5%, the graphite size is more than or equal to 95% and ferrite is 100%; the fracture toughness at minus 40 ℃ is 6250 MPa m1/2。
FIG. 5 is a drawing of graphite as a casting in this example. FIG. 6 is a photograph of a base of a finished casting in this example. FIG. 7 is a graph showing a temperature detection curve of the die used in the examples.
As can be seen from FIGS. 5-7: the spheroidization rate of the finished casting reaches 88%, the spheroidization level is 2-3, the size of graphite nodules is 6-7, and round graphite nodules are uniformly distributed on a substrate which is a full ferrite; the mechanical property result is good, and the use requirement of the product can be met. The highest temperature of the water-cooling metal mold adopted by the invention in the using process is 280 ℃, which shows that the cooling effect is good, safe and reliable.

Claims (7)

1. A method for manufacturing ultra-large section low-temperature high-toughness ferritic nodular iron castings is characterized by comprising the following steps: the nodular iron casting is a torus with the weight of more than or equal to 50 tons and the wall thickness of more than or equal to 400 mm; the specific manufacturing steps are as follows:
step one, modeling: the method comprises the following steps of (1) adopting a metal mold which is made of QT400-18 and is provided with a water cooling device, wherein an enhanced cooling device is arranged on the inner wall of the metal mold, the enhanced cooling device is fan-shaped cold iron blocks which are made of HT150 cast iron and are arranged at intervals along the inner wall of the metal mold, the gap between every two adjacent cold iron blocks is 20-30 mm, and chromite sand or zircon sand is filled in the gap; coating a zircon powder coating layer with the thickness of 1-1.5mm on the surface of the fan-shaped chilling block;
step two, baking: baking the cavity by using an air heater for more than or equal to 8 hours to enable the temperature of the cavity to reach 80-100 ℃;
step three, raw material preparation: the raw materials adopt chemical components as follows: c: 3.51 percent; si: 0.38 percent; mn: 0.012%; s: 0.008 percent; p: 0.007%; ti: 0.003%; cu: 0.0073 percent; cr: 0.0070 percent; v: 0.0048 percent of high-purity pig iron;
step four, smelting molten iron: adding high-purity pig iron into an intermediate frequency furnace for smelting; adding 75# ferrosilicon to adjust the silicon content of the iron liquid to 0.9-1.0%, wherein the overheating temperature of the iron liquid is 1510-1520 ℃, and then stirring and slagging off;
fifthly, spheroidizing: a balling method of a flushing method is adopted, a nodulizer is weighed according to 1.1-1.3% of the total weight of molten iron, and the nodulizer is uniformly scattered on one side of a dam at the bottom of a casting ladle;
sixthly, inoculation treatment: weighing two parts of high-calcium barium inoculant according to 0.3 percent and 0.4 percent of the total weight of the molten iron, weighing a sulfur-oxygen inoculant according to 0.15 percent of the total weight of the molten iron, uniformly scattering the 0.3 percent of high-calcium barium inoculant on a nodulizer after baking and preheating at 400 +/-10 ℃, using the 0.4 percent of high-calcium barium inoculant for iron tapping inoculation, and adding the 0.15 percent of sulfur-oxygen inoculant along with flow during pouring; 1% covering agent is added on the inoculant;
step seven, alloying treatment: adding alloy according to 0.603-1.3% of the total weight of the molten iron, wherein the alloy comprises the following alloy elements in percentage by weight: 0.6-1.3%, Sb: 0.003-0.005 percent of inoculant, which is uniformly scattered on the bottom of the casting ladle after being roasted and preheated at 400 +/-10 ℃;
eighth step, pouring: preheating a casting ladle to 700-800 ℃, and casting when the temperature of molten iron is reduced to 1320 +/-10 ℃;
ninth, box beating and cleaning: and (3) when the temperature of the casting is cooled to 300 ℃, boxing is carried out, and the obtained component composition is C: 3.4-3.7%; si: 1.7-2.0%; mn: less than or equal to 0.1 percent; p: less than or equal to 0.03 percent; s is less than or equal to 0.01 percent; mg: 0.03-0.08%; RE: 0.01-0.02%; ni: 0.6-1.3%; sb: 0.003-0.008% of finished products of the ductile iron castings.
2. The method for manufacturing the ultra-large section low-temperature high-toughness ferritic nodular iron casting as claimed in claim 1, wherein: the metal mold used in the first step is formed by splicing six arc-shaped templates with the same structure.
3. The method for manufacturing the ultra-large section low-temperature high-toughness ferritic nodular iron casting as claimed in claim 1, wherein: the water cooling device adopted in the first step comprises a cooling pipe which is integrally cast in the metal mold and is provided with an inlet and an outlet, and the cooling pipe is arranged along the metal mold in an S-shaped curve; temperature measuring holes are uniformly arranged on the outer wall of the metal mold, the bottom of each temperature measuring hole is 30mm away from the inner wall of the metal mold, and a thermocouple is arranged in each temperature measuring hole; and positioning holes fixedly connected with an external sandbox are uniformly formed in the outer side wall of the metal mould.
4. The method for manufacturing the ultra-large section low-temperature high-toughness ferritic nodular iron casting as claimed in claim 1, wherein: and after the raw materials are melted down in the fourth step, a carburant is used for recarburizing, and pure iron is used for decarbonizing.
5. The method for manufacturing the ultra-large section low-temperature high-toughness ferritic nodular iron casting as claimed in claim 1, wherein: the nodulizer used in the fifth step is a nodulizer 5800 which comprises the following components: 44-48% of Si, 5.55-6.15% of Mg, 0.85-1.15% of RE, 0.8-1.2% of Ca, 0.10-0.12 Ce, 0.06-0.08 La and 0.20-0.24% of Y.
6. The method for manufacturing the ultra-large section low-temperature high-toughness ferritic nodular iron casting as claimed in claim 1, wherein: the particle size of the high-calcium barium inoculant used in the sixth step is 3-8 mm, and the high-calcium barium inoculant comprises the following components: si: 72-78%, Ca: 1.0-2.0%, Ba: 2.0-3.0% and Al < 1.5%; the particle size of the sulfur-oxygen inoculant is 0.2-0.7 mm, and the sulfur-oxygen inoculant comprises the following components: si: 70-76%, Ce: 1.5-2.0%, Ca: 0.75-1.25%, Al: 0.75-1.25%, S & O < 1%; the covering agent is iron sheet.
7. The method for manufacturing the ultra-large section low-temperature high-toughness ferritic nodular iron casting as claimed in claim 1, wherein: and before the eighth step of pouring, cooling water is introduced into the cooling pipe of the metal mold, and the water introduction is stopped after 3 hours.
CN201810795157.6A 2018-07-19 2018-07-19 Method for manufacturing super-large section low-temperature high-toughness ferritic nodular iron casting Active CN108866427B (en)

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