Method for controlling hydrogen content in large steel casting production

Abstract

The invention relates to a method for controlling the hydrogen content in large steel casting production, and belongs to the technical field of casting. Comprising the steps of manufacturing a mold and preparing molding sand; performing shaping; making a core; spraying the sand core and the cavity of the steel casting with a coating, drying with flame, brushing the movable surface of the steel casting, and igniting; assembling the core; smelting is conducted; hot air is blown to a steel casting cavity through a pouring gate, and the hot air is removed 20-30 min before pouring; 15-20 min before pouring, argon is blown into a cavity through a pouring cup; after argon blowing is finished, the steel ladle is moved to be aligned with the pouring cup, an argon protection ring is placed above the pouring cup, a steel pipe is arranged on the protection ring, a paper cap clamp and an aluminum cap are placed above the protection ring, and argon filling, steel ladle falling and pouring are conducted 10-30 s before pouring; after pouring is completed, a covering agent is scattered into the open riser; removing a dead head and increment by adopting gas cutting or machining; and carrying out dehydrogenation heat treatment and performance heat treatment to obtain the steel casting. The steel casting produced through the method is low in hydrogen content.

Description

Technical Field

[0001] The invention relates to the technical field of casting, and in particular to a method for controlling hydrogen content in the production of large steel castings. Background Art

[0002] In the production of large thick-walled steel castings, during the processes of molding, core making, box assembly, smelting, ladle transfer and pouring, the molten steel has a high solubility for hydrogen and comes into contact with the sand mold and the atmosphere, causing hydrogen (H2O) in the sand mold and the atmosphere to enter the molten steel. As the wall thickness of the steel casting increases, this type of hydrogen will be stored in the steel casting for a long time and it is difficult to diffuse freely. The presence of hydrogen in the steel casting may cause casting defects such as white spots (cracking), cold cracks, hot cracks, and pores in the steel casting, which will seriously affect the plasticity of the main material of the steel casting.

[0003] At present, during the pouring process of large thick-walled steel castings, no special attention is paid to hydrogen elements or special process and technical measures are taken. The main reason is that the method of measuring the hydrogen content of large steel castings is to use cast test blocks with a wall thickness of 30mm-60mm for inspection. Due to the small size of the cast test blocks, most of the hydrogen elements overflow during the performance heat treatment process. Therefore, the use of cast test blocks for inspection cannot effectively verify the influence of the hydrogen content in the body of large thick-walled steel castings on the performance of the steel castings. However, in large steel castings with a wall thickness of more than 150mm cast under atmospheric conditions, even after performance heat treatment, there are still a large number of free hydrogen atoms in the body of the steel castings, which will cause crack defects in the steel castings or cause the plasticity index of the steel castings to be seriously reduced under large stress and high hydrogen content.

[0004] At present, the method of controlling the hydrogen content in the body of steel castings is basically to adopt a series of process technology measures or vacuum pouring during the molten steel smelting process, and no relevant process technology measures are taken during the casting modeling and pouring process to control the hydrogen content in the steel castings. Summary of the invention

[0005] In view of the above analysis, an embodiment of the present invention aims to provide a method for controlling the hydrogen content in the production of large steel castings, so as to solve the problem of high hydrogen content in large thick-walled steel castings produced by existing furan resin sand molding and gravity casting under atmospheric conditions, thereby improving the elongation of the steel castings.

[0006] The purpose of the present invention is mainly achieved through the following technical solutions:

[0007] The present invention provides a method for controlling hydrogen content in the production of large steel castings, comprising the following steps:

[0008] Step 1: Make the mold according to the drawing requirements, and prepare qualified molding sand according to the requirements of sand mold manufacturing and the types of steel castings;

[0009] Step 2: Modeling, using molding sand to form the cavity of the steel casting;

[0010] Step 3: core making to form the internal shape of the steel casting;

[0011] Step 4: Use alcohol-based zircon powder paint to spray the sand core and cavity of the steel casting, flame dry, and then use alcohol-based zircon powder paint to paint the live surface of the steel casting and ignite it;

[0012] Step 5: Assemble the core, put the sand core into the mold cavity, and close the upper and lower sand boxes;

[0013] Step 6: Melting: prepare the chemical composition according to the required metal composition, select a suitable melting furnace to melt the alloy material, and form qualified liquid metal;

[0014] Step 7: Determine the hot air blowing time and hot air temperature according to the gross weight of the steel casting, and then blow hot air into the cavity of the steel casting to be poured through the gate, and evacuate the hot air 20-30 minutes before pouring;

[0015] Step 8: 15-20 minutes before pouring, blow argon gas into the cavity of the steel casting to be poured through the pouring cup. During the blowing process, cover the top of the riser with a plastic film;

[0016] Step 9: After blowing argon, move the ladle to align with the pouring cup, place an argon protection ring above the pouring cup, set a steel pipe on the argon protection ring, place a paper cap clip and an aluminum cap above the argon protection ring, fill the argon protection ring with argon 10-30s before pouring, and then drop the ladle for pouring;

[0017] Step 10: After pouring is completed, sprinkle covering agent into the open riser;

[0018] Step 11: Use gas cutting or machining to remove the rough machining increments at the riser and other locations of the steel casting;

[0019] Step 12: Perform dehydrogenation heat treatment and performance heat treatment on the steel castings that have been gas-cut or machined to obtain steel castings with low hydrogen content.

[0020] Furthermore, in step 7, the gross weight of the steel casting is 0-5t, and the hot air blowing time is 3-4h; the gross weight of the steel casting is 5-30t, and the hot air blowing time is ≥12h; the gross weight of the steel casting is 30-50t, and the hot air blowing time is ≥24h; the gross weight of the steel casting is ≥50t, and the hot air blowing time is ≥48h.

[0021] Furthermore, in step 7, the gross weight of the steel casting is 0-5t, and the hot air temperature is 160-180°C; the gross weight of the steel casting is 5-30t, and the hot air temperature is 160-180°C; the gross weight of the steel casting is 30-50t, and the hot air temperature is 180-200°C; the gross weight of the steel casting is ≥50t, and the hot air temperature is 180-200°C.

[0022] Furthermore, in step 8, the ratio of the volume of the blown argon gas to the volume of the casting cavity is ≥4.

[0023] Furthermore, in step 9, the diameter of the argon protection ring is 500-800 mm.

[0024] Furthermore, in step 9, the argon filling rate is ≥5 L / s.

[0025] Furthermore, in step 10, the thickness of the covering agent is ≥ 100 mm.

[0026] Furthermore, in step 12, the dehydrogenation heat treatment is to heat the steel casting to a holding temperature at a heating rate of 30-50°C / h, and after holding, furnace cool it to below 200°C at a cooling rate of 10-50°C / h.

[0027] Furthermore, in step 12, the insulation temperature is 600-680°C.

[0028] Furthermore, in step 12, if the wall thickness of the steel casting is 150-300mm, the insulation time is ≥100h; if the wall thickness of the steel casting is 300-400mm, the insulation time is ≥150h; if the wall thickness of the steel casting is 400-500mm, the insulation time is ≥260h; if the wall thickness of the steel casting is >500mm, the insulation time is ≥600h. Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0029] 1. The method of the present invention controls hydrogen during the molding process and the pouring process and adds a dehydrogenation heat treatment process, so that the internal hydrogen content of the thick-walled steel casting obtained is reduced from ≥10ppm to ≤6ppm, thereby improving the elongation of the steel casting.

[0030] 2. The present invention reduces the moisture and organic matter in the sand core and cavity by spraying paint and flame baking the sand core and cavity during the molding process of large steel castings, and by painting the live surface of the steel castings and long-term ventilation baking in a hot air furnace, thereby reducing the content of hydrogen in the molding material.

[0031] 3. The present invention adopts the method of filling the mold cavity with inert atmosphere and protecting the casting with inert atmosphere during the casting process of large steel castings, thereby reducing the chance of hydrogen elements in the air entering the steel casting body during the casting process; and diffuses the hydrogen in the steel casting through a dehydrogenation heat treatment process, thereby reducing the hydrogen content in the steel casting.

[0032] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0034] Figure 1 This is a scanning electron microscope photo of the tensile fracture of a thick-walled steel casting according to Example 1 of the present invention;

[0035] Figure 2 This is a scanning electron microscope photograph of the tensile fracture of a thick-walled steel casting of comparative example 1 of the present invention. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0037] The present invention provides a method for controlling hydrogen content in the production of large steel castings, comprising the following steps:

[0038] Step 1: Make the mold according to the drawing requirements, and prepare qualified molding sand according to the requirements of sand mold manufacturing and the types of steel castings;

[0039] Step 2: Modeling, using molding sand to form the cavity of the steel casting;

[0040] Step 3: core making to form the internal shape of the steel casting;

[0041] Step 4: Use alcohol-based zircon powder paint to spray the sand core and cavity of the steel casting, flame dry, and then use alcohol-based zircon powder paint to paint the live surface of the steel casting and ignite it;

[0042] Step 5: Assemble the core, put the sand core into the mold cavity, and close the upper and lower sand boxes;

[0043] Step 6: Melting: prepare the chemical composition according to the required metal composition, select a suitable melting furnace to melt the alloy material, and form qualified liquid metal;

[0044] Step 7: Determine the hot air blowing time and hot air temperature according to the gross weight of the steel casting, and then blow hot air into the cavity of the steel casting to be poured through the gate, and evacuate the hot air 20-30 minutes before pouring;

[0045] Step 8: 15-20 minutes before pouring, blow argon gas into the cavity of the steel casting to be poured through the pouring cup. During the blowing process, cover the top of the riser with a plastic film;

[0046] Step 9: After blowing argon, move the ladle to align with the pouring cup, place an argon protection ring above the pouring cup, set a steel pipe on the argon protection ring, place a paper cap clip and an aluminum cap above the argon protection ring, fill the argon protection ring with argon 10-30s before pouring, and then drop the ladle for pouring;

[0047] Step 10: After pouring is completed, sprinkle covering agent into the open riser;

[0048] Step 11: Use gas cutting or machining to remove the rough machining increments at the riser and other locations of the steel casting;

[0049] Step 12: Perform dehydrogenation heat treatment and performance heat treatment on the steel castings that have been gas-cut or machined to obtain steel castings with low hydrogen content.

[0050] For steel castings with a wall thickness of ≤150mm, hydrogen can completely overflow during the performance heat treatment process without affecting the performance; however, for steel castings with a wall thickness of ≥150mm that are gravity-cast under atmospheric conditions, hydrogen cannot completely overflow during the heat treatment process. This is because the hydrogen overflow rate is seriously affected by the wall thickness, hydrogen content and temperature. The thicker the wall of the steel casting, the more difficult it is for hydrogen to overflow. Therefore, the location with a larger wall thickness has a higher hydrogen content. If a tensile test is performed at a location with a higher hydrogen content, it will be found that the elongation and cross-sectional shrinkage of the tensile specimen are significantly reduced, which cannot meet the technical requirements. However, according to the national standard, the inspection method for steel castings is to use a cast test block with a wall thickness of 30mm-60mm for inspection. The hydrogen of the cast test block with this wall thickness has completely overflowed during the performance heat treatment process. Therefore, the use of this thin-walled test block for inspection cannot effectively verify the impact of the hydrogen content in the steel casting body with a wall thickness of ≥150mm on the performance. Therefore, steel casting manufacturers basically do not pay attention to the problem of hydrogen content in large steel castings. Even if cracking of steel castings caused by hydrogen occurs, it will be difficult to determine due to problems with experience and technical capabilities. The method for controlling hydrogen content in the production of large steel castings provided by the present invention can effectively reduce the hydrogen content in large steel castings.

[0051] Specifically, in step 4, the sand mold and the cavity of the steel casting are sprayed with alcohol-based zircon powder coating, and flame drying is performed after spraying. The process of spraying and then flame drying is repeated 2-3 times; then the live surface of the steel casting is painted with alcohol-based zircon powder coating, and ignited after painting, which can improve the coating efficiency of large steel castings and improve the surface cleanliness of the steel castings.

[0052] Specifically, in step 7, the duration and temperature of hot air blowing are determined according to the gross weight of the steel casting, and then hot air is blown into the cavity of the steel casting to be poured through the gate using a hot air furnace to drive away the moisture in the runner; the hot air is evacuated 20-30 minutes before pouring. If the hot air is evacuated too early, the temperature of the cavity will decrease, and the cooling process will be a process of absorbing moisture. The gross weight of the steel casting is 0-5t, the duration of hot air blowing is 3-4h, and the hot air temperature is 160-180℃; the gross weight of the steel casting is 5-30t, the duration of hot air blowing is ≥12h, and the hot air temperature is 160-180℃; the gross weight of the steel casting is 30-50t, the duration of hot air blowing is ≥24h, and the hot air temperature is 180-200℃; the gross weight of the steel casting is ≥50t, the duration of hot air blowing is ≥48h, and the hot air temperature is 180-200℃; the duration of hot air blowing can be appropriately increased in humid weather during the rainy season.

[0053] Specifically, in step 8, 15-20 minutes before pouring, argon is blown into the cavity of the steel casting to be poured through the pouring cup. The argon is pure argon with a purity greater than 99.99%, so as to ensure that the cavity is in an inert gas atmosphere. Since the argon is discharged after mixing with the air in the cavity, the amount of argon blown in is at least 4 times the volume of the cavity, ensuring that the argon content in the cavity accounts for more than 80%; the oxygen content in the cavity is measured at the bottom of the cavity by an oxygen meter, and when the oxygen content in the cavity is ≤20%, the blowing of argon is stopped. During the process of blowing argon into the cavity, the top of the riser is sealed by covering with a plastic film to prevent the interaction between air and the introduced argon, while ensuring the cleanliness of the cavity.

[0054] Specifically, in step 9, the ladle is moved to align with the pouring cup, the ladle is lifted to a height of 700-1000 mm, a circular asbestos argon protection ring is placed under the ladle, the diameter of the protection ring is 500-800 mm, and the argon protection ring is provided with The steel pipe is used to pass argon, and the steel pipe is connected to the argon bottle through the argon belt. Two layers of paper cap clips and one layer of aluminum cap are placed above the argon protection ring to prevent the drainage agent from entering the cavity. The argon protection ring is filled with argon 10-30s before pouring. During pouring, the ladle falls and sticks to the argon protection ring. Argon filling is continued throughout the pouring process. The argon filling rate is ≥5L / s to ensure that the argon protection ring is in a continuous argon filling state.

[0055] Specifically, in step 10, after pouring is completed, a covering agent is sprinkled into the open riser. The thickness of the covering agent is greater than 100 mm to reduce the contact between air and the molten steel in the riser.

[0056] Specifically, in step 11, after pouring is completed, gas cutting or mechanical processing is used to remove the rough processing increments of the riser and other positions of the steel casting; this is because under normal circumstances, in order to ensure the sequential solidification of the steel casting and the product appearance dimensions, the steel casting blank will increase the size increments such as "increase in meat, subsidy, processing amount, and grinding amount" on the basis of the product drawings. This causes the wall thickness of the steel casting blank to be often much greater than the wall thickness of the actual product, and the overflow rate of hydrogen inside the steel casting is seriously affected by the wall thickness. Therefore, in order to ensure that hydrogen can be quickly removed from the steel casting later, the "riser, increase in meat, and subsidy" must be removed first, and the wall thickness increment must be reduced as much as possible by gas cutting or mechanical processing. According to the structural characteristics of the product, a margin of 5-30mm is retained at different positions.

[0057] Specifically, in step 12, hydrogen exists in the steel casting, which will produce diffusive shrinkage cavities during the casting process, causing serious reduction in mechanical properties. When the hydrogen content reaches a certain value, the "hydrogen embrittlement" phenomenon occurs. Therefore, the hydrogen content in the steel casting composition has an important influence on the performance of the steel casting. The present invention diffuses the hydrogen in the casting through dehydrogenation heat treatment, thereby reducing the hydrogen content in the steel casting. Specifically, the steel casting is heated to the holding temperature at a heating rate of 30-50°C / h, and after a certain period of holding, it is furnace cooled to below 200°C at a cooling rate of 10-50°C / h. The insulation time is related to the wall thickness of the steel casting. If the wall thickness of the steel casting is 150-300mm, the insulation time is ≥100h; if the wall thickness of the steel casting is 300-400mm, the insulation time is ≥150h; if the wall thickness of the steel casting is 400-500mm, the insulation time is ≥260h; if the wall thickness of the steel casting is >500mm, the insulation time is ≥600h; the choice of insulation temperature can be determined according to the different components of the steel casting, generally 600-680℃. After the dehydrogenation heat treatment is completed, according to the type of steel casting, select the appropriate process conditions, continue to perform performance heat treatment on the steel casting, and finally obtain a steel casting with low hydrogen content.

[0058] The control method of the present invention is used to control the hydrogen content of large steel castings during production. The hydrogen content of large steel castings after pouring and solidification is ≤6ppm, the hydrogen content of the steel castings finally prepared after performance heat treatment is ≤1ppm, and the cross-sectional elongation of the tensile specimen is ≥28%.

[0059] Example 1

[0060] The steel casting in this embodiment has a size of 650×450×450 mm, a gross weight of 1.1 tons, is made of carbon steel, and has a maximum wall thickness of 450 mm.

[0061] Step 1: Make wooden molds according to the drawing requirements, and prepare qualified surface sand and back sand according to the requirements of sand mold manufacturing and the types of steel castings;

[0062] Step 2: Modeling, using face sand to form the cavity of the steel casting;

[0063] Step 3: core making to form the internal shape of the steel casting;

[0064] Step 4: Use alcohol-based zircon powder coating to spray the sand mold and cavity of the steel casting, and then flame dry it. Repeat this process twice; then use alcohol-based zircon powder coating to paint the live surface of the steel casting, and then ignite it;

[0065] Step 5: Assemble the core, put the sand core into the cavity, and close the upper and lower sand boxes;

[0066] Step 6: Melting: prepare the chemical composition according to the required metal composition, select a suitable melting furnace to melt the alloy material, and form qualified liquid metal;

[0067] Step 7: Blow hot air into the cavity of the steel casting to be poured through the gate for 4 hours, with the hot air temperature of 160-180°C, and evacuate the hot air 20 minutes before pouring;

[0068] Step 8: 20 minutes before pouring, blow pure argon gas with Ar≥99.99% into the cavity of the steel casting to be poured through the pouring cup, and pass 0.6m 3 , after the argon gas with a pressure of 13MPa is blown in, the oxygen meter at the bottom of the cavity measures that the oxygen content in the cavity is ≤20%, and the blowing of argon gas is stopped; during the blowing of argon gas, a plastic film is used to cover the top of the riser;

[0069] Step 9: After blowing in argon, move the ladle to align with the pouring cup, lift the ladle to 700mm high, and place a circular asbestos argon protection ring under the ladle. The diameter of the argon protection ring is 800mm, and there is a The steel pipe is used to pass argon, and the steel pipe is connected to the argon bottle through an argon belt. The length of the argon belt is 10m. Two layers of paper cap clips and one layer of aluminum cap are placed above the argon protection ring. The argon protection ring is filled with argon 20s before pouring. During pouring, the ladle falls and sticks to the argon protection ring. Argon filling is continued throughout the pouring process. The argon filling rate is 6L / s to ensure that the argon protection ring is in a state of continuous argon filling until the pouring is completed.

[0070] Step 10: After pouring is completed, sprinkle a covering agent with a thickness of 110mm into the open riser;

[0071] Step 11: Use gas cutting to remove the riser and patch of the steel casting, and use cold working to make the single side allowance of the processed surface 10mm;

[0072] Step 12: For the steel castings that have been gas-cut or machined, perform dehydrogenation heat treatment: heat the steel castings to 650°C at a heating rate of 40°C / h, keep them warm for 360 hours, and then cool them to below 200°C at a cooling rate of 30°C / h; then perform performance heat treatment to obtain steel castings with low hydrogen content.

[0073] In this embodiment, after smelting and casting solidification, the center of the maximum wall thickness of the casting is sampled, and a cylindrical sample is used. When sampling, it is ensured to be oil-free and rust-free to prevent the escape of hydrogen, and the hydrogen content is tested in accordance with GB / T223.82-2018 "Determination of hydrogen content of steel by inert gas melting-thermal conductivity or infrared method"; and a tensile test is performed after performance heat treatment. The hydrogen content is 1.5ppm after smelting, 5.6ppm after casting solidification, 0.8ppm after performance heat treatment, and the cross-sectional elongation of the tensile sample is: 30%.

[0074] Example 2

[0075] The steel casting in this embodiment has a size of 650×450×450 mm, a gross weight of 1.1 tons, is made of carbon steel, and has a maximum wall thickness of 450 mm.

[0076] Step 1: Make wooden molds according to the drawing requirements, and prepare qualified surface sand and back sand according to the requirements of sand mold manufacturing and the types of steel castings;

[0077] Step 2: Modeling, using face sand to form the cavity of the steel casting;

[0078] Step 3: core making to form the internal shape of the steel casting;

[0079] Step 4: Use alcohol-based zircon powder coating to spray the sand mold and cavity of the steel casting, and then flame dry it. Repeat this process twice; then use alcohol-based zircon powder coating to paint the live surface of the steel casting, and then ignite it;

[0080] Step 5: Assemble the core, put the sand core into the cavity, and close the upper and lower sand boxes;

[0081] Step 6: Melting: prepare the chemical composition according to the required metal composition, select a suitable melting furnace to melt the alloy material, and form qualified liquid metal;

[0082] Step 7: Blow hot air into the cavity of the steel casting to be poured through the gate for 4 hours, with the hot air temperature of 160-180°C, and evacuate the hot air 20 minutes before pouring;

[0083] Step 8: 20 minutes before pouring, blow pure argon gas with Ar≥99.99% into the cavity of the steel casting to be poured through the pouring cup, and pass 0.56m 3 , after the argon gas with a pressure of 13MPa is blown in, the oxygen meter at the bottom of the cavity measures that the oxygen content in the cavity is ≤20%, and the blowing of argon gas is stopped; during the blowing of argon gas, a plastic film is used to cover the top of the riser;

[0084] Step 9: After blowing in argon, move the ladle to align with the pouring cup, lift the ladle to 700mm high, and place a circular asbestos argon protection ring under the ladle. The diameter of the argon protection ring is 600mm, and there is a The steel pipe is used to pass argon, and the steel pipe is connected to the argon bottle through an argon belt. The length of the argon belt is 10m. Two layers of paper cap clips and one layer of aluminum cap are placed above the argon protection ring. The argon protection ring is filled with argon 30s before pouring. During pouring, the ladle falls and sticks to the argon protection ring. Argon filling is continued throughout the pouring process. The argon filling rate is 5L / s to ensure that the argon protection ring is in a state of continuous argon filling until the pouring is completed.

[0085] Step 10: After pouring is completed, sprinkle a covering agent with a thickness of 100mm into the open riser;

[0086] Step 11: Use gas cutting to remove the riser and patch of the steel casting, and use cold working to make the single side allowance of the processed surface 10mm;

[0087] Step 12: For the steel castings that have been gas-cut or machined, perform dehydrogenation heat treatment: heat the steel castings to 680°C at a heating rate of 30°C / h, keep them warm for 300 hours, and then cool them to below 200°C at a cooling rate of 20°C / h; then perform performance heat treatment to obtain steel castings with low hydrogen content.

[0088] In this embodiment, after smelting and casting solidification, the center of the maximum wall thickness of the casting is sampled, and a cylindrical sample is used. When sampling, it is ensured to be oil-free and rust-free to prevent the escape of hydrogen, and the hydrogen content is tested in accordance with GB / T223.82-2018 "Determination of hydrogen content of steel by inert gas melting-thermal conductivity or infrared method"; and a tensile test is performed after performance heat treatment. The hydrogen content is 1.2ppm after smelting, 5.4ppm after casting solidification, 0.6ppm after performance heat treatment, and the cross-sectional elongation of the tensile sample is: 32%.

[0089] Example 3

[0090] The steel casting in this embodiment has dimensions of 3700×1175×1130 mm, a gross weight of 13 tons, is made of carbon steel, and has a maximum wall thickness of 310 mm.

[0091] Step 1: Make wooden molds according to the drawing requirements, and prepare qualified surface sand and back sand according to the requirements of sand mold manufacturing and the types of steel castings;

[0092] Step 2: Modeling, using face sand to form the cavity of the steel casting;

[0093] Step 3: core making to form the internal shape of the steel casting;

[0094] Step 4: Use alcohol-based zircon powder coating to spray the sand mold and cavity of the steel casting, and then flame dry it. Repeat this process twice; then use alcohol-based zircon powder coating to paint the live surface of the steel casting, and then ignite it;

[0095] Step 5: Assemble the core, put the sand core into the cavity, and close the upper and lower sand boxes;

[0096] Step 6: Melting: prepare the chemical composition according to the required metal composition, select a suitable melting furnace to melt the alloy material, and form qualified liquid metal;

[0097] Step 7: Blow hot air into the cavity of the steel casting to be poured through the gate for 15 hours, with the hot air temperature at 160-180°C, and evacuate the hot air 20 minutes before pouring;

[0098] Step 8: 20 minutes before pouring, blow pure argon gas with Ar≥99.99% into the cavity of the steel casting to be poured through the pouring cup, and pass 6.8m 3 , after the argon gas with a pressure of 13MPa is blown in, the oxygen meter at the bottom of the cavity measures that the oxygen content in the cavity is ≤20%, and the blowing of argon gas is stopped; during the blowing of argon gas, a plastic film is used to cover the top of the riser;

[0099] Step 9: After blowing in argon, move the ladle to align with the pouring cup, lift the ladle to a height of 700mm, and place a circular asbestos argon protection ring under the ladle. The diameter of the argon protection ring is 600mm, and there is a The steel pipe is used to pass argon, and the steel pipe is connected to the argon bottle through an argon belt. The length of the argon belt is 10m. Two layers of paper cap clips and one layer of aluminum cap are placed above the argon protection ring. The argon protection ring is filled with argon 20s before pouring. During pouring, the ladle falls and sticks to the argon protection ring. Argon filling is continued throughout the pouring process. The argon filling rate is 8L / s to ensure that the argon protection ring is in a state of continuous argon filling until the pouring is completed.

[0100] Step 10: After pouring is completed, sprinkle a covering agent with a thickness of 120 mm into the open riser;

[0101] Step 11: Use gas cutting to remove the riser and patch of the steel casting, and use cold working to make the single side allowance of the processed surface 10mm;

[0102] Step 12: For the steel castings that have been gas-cut or machined, perform dehydrogenation heat treatment: heat the steel castings to 650°C at a heating rate of 30°C / h, keep them warm for 180 hours, and then cool them to below 200°C at a cooling rate of 20°C / h; then perform performance heat treatment to obtain steel castings with low hydrogen content.

[0103] In this embodiment, after smelting and casting solidification, the center of the maximum wall thickness of the casting is sampled, and a cylindrical sample is used. When sampling, it is ensured to be oil-free and rust-free to prevent the escape of hydrogen, and the hydrogen content is tested in accordance with GB / T223.82-2018 "Determination of hydrogen content of steel by inert gas melting-thermal conductivity or infrared method"; and a tensile test is performed after performance heat treatment. The hydrogen content is 1.3ppm after smelting, 5.5ppm after casting solidification, 0.6ppm after performance heat treatment, and the cross-sectional elongation of the tensile sample is: 31%.

[0104] Example 4

[0105] The steel casting in this embodiment has a size of 1050×520×520 mm, a gross weight of 2.5 tons, is made of carbon steel, and has a maximum wall thickness of 520 mm.

[0106] Step 1: Make wooden molds according to the drawing requirements, and prepare qualified surface sand and back sand according to the requirements of sand mold manufacturing and the types of steel castings;

[0107] Step 2: Modeling, using face sand to form the cavity of the steel casting;

[0108] Step 3: core making to form the internal shape of the steel casting;

[0109] Step 4: Use alcohol-based zircon powder coating to spray the sand mold and cavity of the steel casting, and then flame dry it. Repeat this process twice; then use alcohol-based zircon powder coating to paint the live surface of the steel casting, and then ignite it;

[0110] Step 5: Assemble the core, put the sand core into the cavity, and close the upper and lower sand boxes;

[0111] Step 6: Melting: prepare the chemical composition according to the required metal composition, select a suitable melting furnace to melt the alloy material, and form qualified liquid metal;

[0112] Step 7: Blow hot air into the cavity of the steel casting to be poured through the gate for 4 hours, with the hot air temperature of 160-180°C, and evacuate the hot air 20 minutes before pouring;

[0113] Step 8: 20 minutes before pouring, blow pure argon gas with Ar≥99.99% into the cavity of the steel casting to be poured through the pouring cup, and pass 1.5m 3 , after the argon gas with a pressure of 13MPa is blown in, the oxygen meter at the bottom of the cavity measures that the oxygen content in the cavity is ≤20%, and the blowing of argon gas is stopped; during the blowing of argon gas, a plastic film is used to cover the top of the riser;

[0114] Step 9: After blowing in argon, move the ladle to align with the pouring cup, lift the ladle to a height of 700mm, and place a circular asbestos argon protection ring under the ladle. The diameter of the argon protection ring is 800mm, and there is a The steel pipe is used to pass argon, and the steel pipe is connected to the argon bottle through an argon belt. The length of the argon belt is 10m. Two layers of paper cap clips and one layer of aluminum cap are placed above the argon protection ring. The argon protection ring is filled with argon 20s before pouring. During pouring, the ladle falls and sticks to the argon protection ring. Argon filling is continued throughout the pouring process. The argon filling rate is 8L / s to ensure that the argon protection ring is in a state of continuous argon filling until the pouring is completed.

[0115] Step 10: After pouring is completed, sprinkle a covering agent with a thickness of 120 mm into the open riser;

[0116] Step 11: Use gas cutting to remove the riser and patch of the steel casting, and use cold working to make the single side allowance of the processed surface 10mm;

[0117] Step 12: For the steel castings that have been gas-cut or machined, perform dehydrogenation heat treatment: heat the steel castings to 660°C at a heating rate of 40°C / h, keep them warm for 650 hours, and then cool them to below 200°C at a cooling rate of 30°C / h; then perform performance heat treatment to obtain steel castings with low hydrogen content.

[0118] In this embodiment, after smelting and casting solidification, the center of the maximum wall thickness of the casting is sampled, and a cylindrical sample is used. When sampling, it is ensured to be oil-free and rust-free to prevent the escape of hydrogen, and the hydrogen content is tested in accordance with GB / T223.82-2018 "Determination of hydrogen content of steel by inert gas melting-thermal conductivity or infrared method"; and a tensile test is performed after performance heat treatment. The hydrogen content is 1.6ppm after smelting, 5.4ppm after casting solidification, 0.7ppm after performance heat treatment, and the cross-sectional elongation of the tensile sample is: 29%.

[0119] Comparative Example 1

[0120] The material, size, gross weight and maximum wall thickness of the steel casting of this comparative example are the same as those of Example 1. The size is 650×450×450 mm, the gross weight is 1.1 tons, the material is carbon steel, and the maximum wall thickness is 450 mm.

[0121] Step 1: Make wooden molds according to the drawing requirements, and prepare qualified surface sand and back sand according to the requirements of sand mold manufacturing and the types of steel castings;

[0122] Step 2: Modeling, using face sand to form the cavity of the steel casting;

[0123] Step 3: core making to form the internal shape of the steel casting;

[0124] Step 4: Assemble the core, put the sand core into the mold cavity, and close the upper and lower sand boxes;

[0125] Step 5: Melting: prepare the chemical composition according to the required metal composition, select a suitable melting furnace to melt the alloy material, and form qualified liquid metal;

[0126] Step 6: Pouring;

[0127] Step 7: After pouring is completed, sprinkle a covering agent with a thickness of 110mm into the open riser;

[0128] Step 8: Use gas cutting to remove the riser and patch of the steel casting, and make a 10mm allowance on one side of the processed surface through cold working;

[0129] Step 9: Perform performance heat treatment on the steel castings that have been gas cut or machined.

[0130] This comparative example does not take measures such as cavity baking, inert atmosphere protection, and dehydrogenation heat treatment during the molding and pouring process. After smelting and casting solidification, samples are taken at the center of the maximum wall thickness of the casting. Cylindrical samples are used. When sampling, it is ensured that there is no oil or rust to prevent the escape of hydrogen. The hydrogen content is tested in accordance with GB / T223.82-2018 "Determination of hydrogen content of steel by inert gas melting-thermal conductivity or infrared method"; and a tensile test is performed after performance heat treatment. The hydrogen content is 1.3ppm after smelting, 13.4ppm after casting solidification, 1.9ppm after performance heat treatment, and the cross-sectional elongation of the tensile sample is 14%.

[0131] Comparative Example 2

[0132] The material, size, gross weight and maximum wall thickness of the steel casting of this comparative example are the same as those of Example 1. The size is 650×450×450 mm, the gross weight is 1.1 tons, the material is carbon steel, and the maximum wall thickness is 450 mm.

[0133] Step 1: Make wooden molds according to the drawing requirements, and prepare qualified surface sand and back sand according to the requirements of sand mold manufacturing and the types of steel castings;

[0134] Step 2: Modeling, using face sand to form the cavity of the steel casting;

[0135] Step 3: core making to form the internal shape of the steel casting;

[0136] Step 4: Use alcohol-based zircon powder coating to spray the sand mold and cavity of the steel casting, and then flame dry it. Repeat this process twice; then use alcohol-based zircon powder coating to paint the live surface of the steel casting, and then ignite it;

[0137] Step 5: Assemble the core, put the sand core into the cavity, and close the upper and lower sand boxes;

[0138] Step 6: Melting: prepare the chemical composition according to the required metal composition, select a suitable melting furnace to melt the alloy material, and form qualified liquid metal;

[0139] Step 7: Blow hot air into the cavity of the steel casting to be poured through the gate for 4 hours, with the hot air temperature of 160-180°C, and evacuate the hot air 40 minutes before pouring;

[0140] Step 8: 20 minutes before pouring, blow pure argon gas with Ar≥99.99% into the cavity of the steel casting to be poured through the pouring cup, and pass 0.4m 3 , after the argon pressure reaches 13MPa, stop blowing argon; during the blowing of argon, use a plastic film to cover the top of the riser;

[0141] Step 9: After blowing in argon, move the ladle to align with the pouring cup, lift the ladle to 700mm high, and place a circular asbestos argon protection ring under the ladle. The diameter of the argon protection ring is 800mm, and there is a The steel pipe is used to pass argon, and the steel pipe is connected to the argon bottle through an argon belt. The length of the argon belt is 10m. Two layers of paper cap clips and one layer of aluminum cap are placed above the argon protection ring. The argon protection ring is filled with argon 20s before pouring. During pouring, the ladle falls and sticks to the argon protection ring. Argon filling is continued throughout the pouring process. The argon filling rate is 8L / s to ensure that the argon protection ring is in a state of continuous argon filling until the pouring is completed.

[0142] Step 10: After pouring is completed, sprinkle a covering agent with a thickness of 110mm into the open riser;

[0143] Step 11: Use gas cutting to remove the riser and patch of the steel casting, and use cold working to make the single side allowance of the processed surface 10mm;

[0144] Step 12: Directly perform performance heat treatment without dehydrogenation heat treatment.

[0145] In this comparative example, after smelting and pouring and solidification of steel castings, samples were taken at the center of the maximum wall thickness of the castings. Cylindrical samples were used. The samples were ensured to be oil-free and rust-free to prevent hydrogen from escaping. The hydrogen content was tested in accordance with GB / T223.82-2018 "Determination of hydrogen content of steel by inert gas fusion-thermal conductivity or infrared method"; and tensile tests were performed after performance heat treatment. The hydrogen content was 1.4ppm after smelting, 8.6ppm after pouring and solidification of steel castings, and 1.8ppm after performance heat treatment. The cross-sectional elongation of the tensile sample was: 17%.

[0146] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for controlling hydrogen content in the production of large steel castings, characterized in that: The following steps are involved: Step 1: Make the mold according to the drawing requirements, and prepare qualified molding sand according to the requirements of sand mold manufacturing and the types of steel castings; Step 2: Modeling, using molding sand to form the cavity of the steel casting; Step 3: core making to form the internal shape of the steel casting; Step 4: Use alcohol-based zircon powder paint to spray the sand core and cavity of the steel casting, flame dry, and then use alcohol-based zircon powder paint to paint the live surface of the steel casting and ignite it; Step 5: Assemble the core, put the sand core into the cavity, and close the upper and lower sand boxes; Step 6: Melting: prepare the chemical composition according to the required metal composition, select a suitable melting furnace to melt the alloy material, and form qualified liquid metal; Step 7: Determine the hot air blowing time and hot air temperature according to the gross weight of the steel casting, and then blow hot air into the cavity of the steel casting to be poured through the gate, and evacuate the hot air 20-30 minutes before pouring; Step 8: 15-20 minutes before pouring, blow argon gas into the cavity of the steel casting to be poured through the pouring cup. During the blowing process, cover the top of the riser with a plastic film; Step 9: After blowing argon, move the ladle to align with the pouring cup, place an argon protection ring above the pouring cup, set a steel pipe on the argon protection ring, place a paper cap clip and an aluminum cap above the argon protection ring, fill the argon protection ring with argon 10-30s before pouring, and then drop the ladle for pouring; Step 10: After pouring is completed, sprinkle covering agent into the open riser; Step 11: Use gas cutting or machining to remove the rough machining increments at the riser and other locations of the steel casting; Step 12: Perform dehydrogenation heat treatment and performance heat treatment on the steel castings that have been gas-cut or machined to obtain steel castings with low hydrogen content.

2. The control method according to claim 1, characterized in that: In step 7, the gross weight of the steel casting is 0-5t, and the hot air blowing time is 3-4h; the gross weight of the steel casting is 5-30t, and the hot air blowing time is ≥12h; the gross weight of the steel casting is 30-50t, and the hot air blowing time is ≥24h; the gross weight of the steel casting is ≥50t, and the hot air blowing time is ≥48h.

3. The control method according to claim 2, characterized in that: In step 7, the gross weight of the steel casting is 0-5t, and the hot air temperature is 160-180°C; the gross weight of the steel casting is 5-30t, and the hot air temperature is 160-180°C; the gross weight of the steel casting is 30-50t, and the hot air temperature is 180-200°C; the gross weight of the steel casting is ≥50t, and the hot air temperature is 180-200°C.

4. The control method according to claim 1, characterized in that: In step 8, the ratio of the volume of the blown argon gas to the volume of the casting cavity is ≥4.

5. The control method according to claim 1, characterized in that: In step 9, the diameter of the argon protection ring is 500-800 mm.

6. The control method according to claim 5, characterized in that: In step 9, the argon filling rate is ≥5 L / s.

7. The control method according to claim 1, characterized in that: In step 10, the thickness of the covering agent is ≥100 mm.

8. The control method according to claim 1, characterized in that: In step 12, the dehydrogenation heat treatment is to heat the steel casting to a holding temperature at a heating rate of 30-50°C / h, and then cool the casting to below 200°C at a cooling rate of 10-50°C / h.

9. The control method according to claim 8, characterized in that: In step 12, the insulation temperature is 600-680°C.

10. The control method according to claim 9, characterized in that: In step 12, the wall thickness of the steel casting is 150-300 mm, and the insulation time is ≥100 h; the wall thickness of the steel casting is 300-400 mm, and the insulation time is ≥150 h; the wall thickness of the steel casting is 400-500 mm, and the insulation time is ≥260 h; the wall thickness of the steel casting is >500 mm, and the insulation time is ≥600 h.

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