Method for controlling hydrogen content in production of large steel castings

Abstract

This invention relates to a method for controlling hydrogen content in the production of large cast steel parts, belonging to the field of casting technology. The method includes: mold making and molding sand preparation; molding; core making; spraying a coating onto the sand core and mold cavity of the cast steel part, flame drying, brushing the live surface of the cast steel part, and igniting; core assembly; melting; blowing hot air into the mold cavity of the cast steel part through the gating gate, removing the hot air 20-30 minutes before pouring; blowing argon gas into the mold cavity through the pouring cup 15-20 minutes before pouring; after argon blowing, moving the ladle to align with the pouring cup, placing an argon gas protective ring above the pouring cup, with a steel pipe on the protective ring, and placing a paper cap clamp and an aluminum cap above the protective ring; filling with argon gas 10-30 seconds before pouring, lowering the ladle, and pouring; after pouring, sprinkling a covering agent into the exposed riser; removing the riser and excess material by gas cutting or machining; performing dehydrogenation heat treatment and performance heat treatment to obtain the cast steel part. The cast steel parts produced by this method have low hydrogen content.

Description

Technical Field

[0001] This invention relates to the field of casting technology, and in particular to a method for controlling the hydrogen content in the production of large cast steel parts. Background Technology

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

[0003] Currently, hydrogen content in large, thick-walled cast steel parts is generally not given special attention or special processing techniques are employed during the casting process. This is primarily because the method for measuring hydrogen content in large cast steel parts involves using attached casting blocks with a wall thickness of 30mm-60mm. However, due to the small size of these blocks, most of the hydrogen escapes during the performance heat treatment process. Therefore, this method cannot effectively verify the impact of hydrogen content within the cast steel part itself on its performance. However, in large cast steel parts with a wall thickness exceeding 150mm, cast under atmospheric conditions, even after performance heat treatment, a large number of free hydrogen atoms still remain within the casting body. Under high stress and with high hydrogen content, this can lead to cracking defects or a significant reduction in the casting's plasticity.

[0004] Currently, the methods for controlling the hydrogen content in cast steel parts are mainly to adopt a series of technological measures during the steel smelting process or to use vacuum casting. However, no relevant technological measures are taken during the casting molding and casting process to control the hydrogen content in the cast steel parts. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a method for controlling hydrogen content in the production of large cast steel parts, in order to solve the problem of high hydrogen content in large, thick-walled cast steel parts produced by existing furan resin sand molding and gravity casting under atmospheric conditions, thereby improving the elongation of the cast steel parts.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] This invention provides a method for controlling hydrogen content in the production of large cast steel parts, 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 different types of cast steel parts;

[0009] Step 2: Shaping, using molding sand to form the cavity of the cast steel part;

[0010] Step 3: Core making, forming the internal shape of the cast steel part;

[0011] Step 4: Spray the cast steel sand core and cast steel cavity with alcohol-based zircon powder coating, and then flame dry it. Then, apply alcohol-based zircon powder coating to the live surface of the cast steel part and ignite it.

[0012] Step 5: Core assembly. Place the sand core into the cavity and close the upper and lower sand boxes.

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

[0014] Step 7: Determine the duration and temperature of hot air blowing based on the gross weight of the cast steel part. Then blow hot air into the cavity of the cast steel part to be poured through the gate. Remove the hot air 20-30 minutes before pouring.

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

[0016] Step 9: After the argon gas blowing is finished, move the ladle to align with the pouring cup, place the argon gas protection ring above the pouring cup, set the steel pipe on the argon gas protection ring, and place the paper cap clamp and aluminum cap above the argon gas protection ring. Fill the argon gas protection ring with argon gas 10-30 seconds before pouring, drop the ladle, and pour.

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

[0018] Step 11: Remove the roughing increments from the riser and other locations of the cast steel parts by gas cutting or machining;

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

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

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

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

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

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

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

[0026] Furthermore, in step 12, the dehydrogenation heat treatment involves heating the cast steel part to the holding temperature at a heating rate of 30-50℃ / h, and then furnace cooling it to below 200℃ at a cooling rate of 10-50℃ / h.

[0027] Furthermore, in step 12, the heat preservation temperature is 600-680℃.

[0028] Further, in step 12, the wall thickness of the cast steel part is 150-300mm, and the heat preservation time is ≥100h; the wall thickness of the cast steel part is 300-400mm, and the heat preservation time is ≥150h; the wall thickness of the cast steel part is 400-500mm, and the heat preservation time is ≥260h; the wall thickness of the cast steel part is >500mm, and the heat preservation 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 and casting process and adds a dehydrogenation heat treatment process, which reduces the internal hydrogen content of the thick-walled cast steel parts from ≥10ppm to ≤6ppm, thereby improving the elongation of the cast steel parts.

[0030] 2. This invention reduces the moisture and organic matter in the sand core and cavity by spraying paint and baking the sand core and cavity with flame during the molding process of large cast steel parts. This is achieved by brushing the surface of the cast steel parts and baking them with a hot air furnace for a long time, thereby reducing the hydrogen content in the molding materials.

[0031] 3. This invention reduces the chance of hydrogen from the air entering the cast steel part during the casting process by using an inert atmosphere to fill the cavity and an inert atmosphere for protection during casting. The hydrogen content in the cast steel part is reduced by using a dehydrogenation heat treatment process to diffuse hydrogen from the cast steel part.

[0032] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0033] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0034] Figure 1 This is a scanning electron microscope image of the tensile fracture surface of a thick-walled cast steel part according to Embodiment 1 of the present invention;

[0035] Figure 2 This is a scanning electron microscope image of the tensile fracture surface of a thick-walled cast steel part, which is a comparative example of the present invention. Detailed Implementation

[0036] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form 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 intended to limit the scope of the present invention.

[0037] This invention provides a method for controlling hydrogen content in the production of large cast steel parts, 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 different types of cast steel parts;

[0039] Step 2: Shaping, using molding sand to form the cavity of the cast steel part;

[0040] Step 3: Core making, forming the internal shape of the cast steel part;

[0041] Step 4: Spray the cast steel sand core and cast steel cavity with alcohol-based zircon powder coating, and then flame dry it. Then, apply alcohol-based zircon powder coating to the live surface of the cast steel part and ignite it.

[0042] Step 5: Core assembly. Place the sand core into the cavity and close the upper and lower sand boxes.

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

[0044] Step 7: Determine the duration and temperature of hot air blowing based on the gross weight of the cast steel part. Then blow hot air into the cavity of the cast steel part to be poured through the gate. Remove the hot air 20-30 minutes before pouring.

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

[0046] Step 9: After the argon gas blowing is finished, move the ladle to align with the pouring cup, place the argon gas protection ring above the pouring cup, set the steel pipe on the argon gas protection ring, and place the paper cap clamp and aluminum cap above the argon gas protection ring. Fill the argon gas protection ring with argon gas 10-30 seconds before pouring, drop the ladle, and pour.

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

[0048] Step 11: Remove the roughing increments from the riser and other locations of the cast steel parts by gas cutting or machining;

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

[0050] For cast steel parts with a wall thickness ≤150mm, hydrogen can completely escape during the performance heat treatment process without affecting performance. However, for cast steel parts with a wall thickness ≥150mm cast under atmospheric gravity casting, hydrogen cannot completely escape during the heat treatment process. This is because the hydrogen escape rate is greatly affected by the wall thickness, hydrogen content, and temperature. The thicker the wall of the cast steel part, the more difficult it is for hydrogen to escape. Therefore, the hydrogen content is higher in areas with larger wall thickness. If tensile testing is performed in areas with higher hydrogen content, it will be found that the elongation and reduction of area of ​​the tensile specimen are significantly reduced, failing to meet the technical requirements. However, according to national standards, the inspection method for cast steel parts uses attached casting blocks with a wall thickness of 30mm-60mm. During the performance heat treatment process, hydrogen has completely escaped from these thin-walled blocks. Therefore, using these thin-walled blocks cannot effectively verify the impact of hydrogen content in the cast steel part body with a wall thickness ≥150mm on its performance. Consequently, cast steel part manufacturers generally do not pay attention to the hydrogen content in large cast steel parts. Even if hydrogen-induced cracking occurs, it is difficult to determine the cause due to a lack of experience and technical expertise. The hydrogen content control method for large cast steel parts production provided by this invention can effectively reduce the hydrogen content in large cast steel parts.

[0051] Specifically, in step 4, alcohol-based zircon powder coating is used to spray the sand mold and cavity of the cast steel part, and then flame-drying is performed after spraying. The process of spraying and then flame-drying is repeated 2-3 times. Then, alcohol-based zircon powder coating is applied to the live surface of the cast steel part and ignited after application. This can improve the coating efficiency of large cast steel parts and improve the surface cleanliness of the cast steel parts.

[0052] Specifically, in step 7, the duration and temperature of hot air blowing are determined based on the gross weight of the cast steel part. Then, hot air is blown into the cavity of the cast steel part to be poured through the gating gate using a hot air furnace to drive away the moisture in the runner. The hot air is removed 20-30 minutes before pouring. Removing the hot air too early will lower the temperature of the cavity, and the cooling process will actually absorb moisture. For cast steel parts with a gross weight of 0-5t, the hot air blowing time is 3-4 hours, and the hot air temperature is 160-180℃; for cast steel parts with a gross weight of 5-30t, the hot air blowing time is ≥12 hours, and the hot air temperature is 160-180℃; for cast steel parts with a gross weight of 30-50t, the hot air blowing time is ≥24 hours, and the hot air temperature is 180-200℃; for cast steel parts with a gross weight of ≥50t, the hot air blowing time is ≥48 hours, and the hot air temperature is 180-200℃. The hot air blowing time can be appropriately increased during rainy and humid weather.

[0053] Specifically, in step 8, 15-20 minutes before pouring, argon gas with a purity greater than 99.99% is blown into the cavity of the cast steel part through the pouring cup. This ensures the cavity is in an inert gas atmosphere. Since the argon gas mixes with the air in the cavity before being expelled, the amount of argon gas blown in is at least four times the cavity volume, ensuring that the argon content in the cavity reaches more than 80%. The oxygen content in the cavity is measured at the bottom of the cavity using an oxygen analyzer. When the oxygen content in the cavity is ≤20%, the blowing of argon gas is stopped. During the blowing of argon gas into the cavity, the area above the riser is sealed with a plastic film to prevent air from interacting with the introduced argon gas and to ensure the cavity is clean.

[0054] Specifically, in step 9, the ladle is moved and aligned with the pouring cup, and the ladle is lifted 700-1000mm high. A circular asbestos argon gas protection ring with a diameter of 500-800mm is placed under the ladle. The argon gas protection ring is equipped with... The steel pipe is used to pass argon gas, and it is connected to the argon cylinder via an argon gas hose. Two layers of paper caps and one layer of aluminum caps are placed above the argon protection ring to prevent the diverting agent from entering the mold cavity. Argon filling of the argon protection ring begins 10-30 seconds before pouring. During pouring, the ladle falls and presses against the argon protection ring. Argon filling is continuous throughout the pouring process, with a filling rate ≥5L / s, ensuring that the argon protection ring is continuously filled with argon gas.

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

[0056] Specifically, in step 11, after casting, the riser and other rough machining increments in the cast steel part are removed by gas cutting or machining. This is because, under normal circumstances, in order to ensure the sequential solidification of the cast steel part and the product's external dimensions, the cast steel blank will have dimensional increments such as "extra material, additional materials, machining allowance, and grinding allowance" added based on the product drawings. This results in the wall thickness of the cast steel blank often being much larger than the wall thickness of the actual product. The rate of hydrogen overflow inside the cast steel part is severely affected by the wall thickness. Therefore, in order to ensure that the cast steel part can quickly remove hydrogen in the future, the "riser, extra material, and additional materials" must be removed first. Gas cutting or machining should be used to minimize the wall thickness increment as much as possible. Depending on the product's structural characteristics, a margin of 5-30mm should be retained in different locations.

[0057] Specifically, in step 12, hydrogen present in the cast steel part can cause diffusing shrinkage cavities during the casting process, resulting in a severe reduction in mechanical properties. When the hydrogen content reaches a certain value, "hydrogen embrittlement" occurs. Therefore, the hydrogen content in the cast steel part has a significant impact on its performance. This invention reduces the hydrogen content in the cast steel part by diffusing hydrogen through dehydrogenation heat treatment. Specifically, the cast steel part is heated to the holding temperature at a heating rate of 30-50℃ / h, held for a certain period of time, and then furnace cooled to below 200℃ at a cooling rate of 10-50℃ / h. The holding time is related to the wall thickness of the cast steel part. For cast steel parts with a wall thickness of 150-300mm, the holding time should be ≥100h; for 300-400mm, ≥150h; for 400-500mm, ≥260h; and for >500mm, ≥600h. The holding temperature can be selected based on the composition of the cast steel part, generally 600-680℃. After the dehydrogenation heat treatment, appropriate process conditions are selected according to the type of cast steel part, and the part is further subjected to performance heat treatment to finally obtain a cast steel part with low hydrogen content.

[0058] The hydrogen content of large cast steel parts is controlled by the control method of the present invention. After casting and solidification, the hydrogen content of the large cast steel parts is ≤6ppm. After performance heat treatment, the hydrogen content of the final cast steel parts is ≤1ppm, and the tensile test specimen cross-sectional elongation is ≥28%.

[0059] Example 1

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

[0061] Step 1: Make a wooden mold according to the drawing requirements, and prepare qualified face sand and back sand according to the requirements of sand mold manufacturing and the different types of cast steel parts;

[0062] Step 2: Shaping, using face sand to form the cavity of the cast steel part;

[0063] Step 3: Core making, forming the internal shape of the cast steel part;

[0064] Step 4: Spray the sand mold and cavity of the cast steel part with alcohol-based zircon powder coating, and then flame dry it after spraying. Repeat this process twice. Then, apply alcohol-based zircon powder coating to the live surface of the cast steel part and ignite it after application.

[0065] Step 5: Core assembly. Place the sand core into the cavity and close the upper and lower sand boxes.

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

[0067] Step 7: Blow hot air into the cavity of the cast steel part to be poured through the gate for 4 hours. The hot air temperature is 160-180℃. Remove the hot air 20 minutes before pouring.

[0068] Step 8: 20 minutes before pouring, blow pure argon gas (Ar ≥ 99.99%) into the cavity of the cast steel part through the pouring cup, and introduce 0.6m... 3 After argon gas at a pressure of 13 MPa is introduced, the oxygen content in the cavity is measured by an oxygen analyzer at the bottom of the cavity and is ≤20%, at which point the argon gas blowing is stopped; during the argon gas blowing process, a plastic film is used to cover the top of the riser;

[0069] Step 9: After argon gas injection is complete, move the ladle to align with the pouring cup, lift the ladle 700mm high, and place a circular asbestos argon gas protection ring under the ladle. The argon gas protection ring has a diameter of 800mm and is equipped with... The steel pipe is used to pass argon gas. The steel pipe is connected to the argon gas cylinder through an argon gas belt, which is 10m long. Two layers of paper caps and one layer of aluminum caps are placed above the argon gas protection ring. Argon gas is filled into the argon gas protection ring 20 seconds before pouring. During pouring, the steel ladle falls and is placed close to the argon gas protection ring. Argon gas is continuously filled throughout the pouring process at a filling rate of 6L / s to ensure that the argon gas protection ring is in a state of continuous argon gas filling until the pouring is completed.

[0070] Step 10: After pouring is complete, sprinkle a 110mm thick covering agent into the open riser;

[0071] Step 11: Remove the riser and patch of the cast steel part by gas cutting, and leave a 10mm allowance on each side of the machined surface by cold working;

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

[0073] In this embodiment, after smelting and solidification of the cast steel part, a cylindrical sample was taken from the center of the location with the greatest wall thickness. The sample was taken to ensure it was free of oil and rust to prevent hydrogen escape. The hydrogen content was tested according to GB / T223.82-2018 "Determination of Hydrogen Content in Iron and Steel - Inert Gas Fusion-Thermal Conductivity or Infrared Method". Tensile strength testing was performed after performance heat treatment. The hydrogen content was 1.5 ppm after smelting, 5.6 ppm after solidification of the cast steel part, and 0.8 ppm after performance heat treatment. The elongation of the tensile test specimen was 30%.

[0074] Example 2

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

[0076] Step 1: Make a wooden mold according to the drawing requirements, and prepare qualified face sand and back sand according to the requirements of sand mold manufacturing and the different types of cast steel parts;

[0077] Step 2: Shaping, using face sand to form the cavity of the cast steel part;

[0078] Step 3: Core making, forming the internal shape of the cast steel part;

[0079] Step 4: Spray the sand mold and cavity of the cast steel part with alcohol-based zircon powder coating, and then flame dry it after spraying. Repeat this process twice. Then, apply alcohol-based zircon powder coating to the live surface of the cast steel part and ignite it after application.

[0080] Step 5: Core assembly. Place the sand core into the cavity and close the upper and lower sand boxes.

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

[0082] Step 7: Blow hot air into the cavity of the cast steel part to be poured through the gate for 4 hours. The hot air temperature is 160-180℃. Remove the hot air 20 minutes before pouring.

[0083] Step 8: 20 minutes before pouring, blow pure argon gas (Ar ≥ 99.99%) into the cavity of the cast steel part to be poured through the pouring cup, and introduce 0.56m... 3 After argon gas at a pressure of 13 MPa is introduced, the oxygen content in the cavity is measured by an oxygen analyzer at the bottom of the cavity and is ≤20%, at which point the argon gas blowing is stopped; during the argon gas blowing process, a plastic film is used to cover the top of the riser;

[0084] Step 9: After argon gas injection is complete, move the ladle to align with the pouring cup, lift the ladle 700mm high, and place a circular asbestos argon gas protection ring under the ladle. The argon gas protection ring has a diameter of 600mm and is equipped with... The steel pipe is used to pass argon gas. The steel pipe is connected to the argon gas cylinder through an argon gas belt, which is 10m long. Two layers of paper caps and one layer of aluminum caps are placed above the argon gas protection ring. Argon gas is filled into the argon gas protection ring 30 seconds before pouring. During pouring, the steel ladle falls and is placed close to the argon gas protection ring. Argon gas is continuously filled throughout the pouring process at a filling rate of 5L / s to ensure that the argon gas protection ring is in a state of continuous argon gas filling until the pouring is completed.

[0085] Step 10: After pouring, sprinkle a 100mm thick covering agent into the open riser;

[0086] Step 11: Remove the riser and patch of the cast steel part by gas cutting, and leave a 10mm allowance on each side of the machined surface by cold working;

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

[0088] In this embodiment, after smelting and solidification of the cast steel part, a cylindrical sample was taken from the center of the location with the greatest wall thickness. The sample was taken to ensure it was free of oil and rust to prevent hydrogen escape. The hydrogen content was tested according to GB / T223.82-2018 "Determination of Hydrogen Content in Iron and Steel - Inert Gas Fusion-Thermal Conductivity or Infrared Method". Tensile strength testing was performed after performance heat treatment. The hydrogen content was 1.2 ppm after smelting, 5.4 ppm after solidification of the cast steel part, and 0.6 ppm after performance heat treatment. The elongation of the tensile test specimen was 32%.

[0089] Example 3

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

[0091] Step 1: Make a wooden mold according to the drawing requirements, and prepare qualified face sand and back sand according to the requirements of sand mold manufacturing and the different types of cast steel parts;

[0092] Step 2: Shaping, using face sand to form the cavity of the cast steel part;

[0093] Step 3: Core making, forming the internal shape of the cast steel part;

[0094] Step 4: Spray the sand mold and cavity of the cast steel part with alcohol-based zircon powder coating, and then flame dry it after spraying. Repeat this process twice. Then, apply alcohol-based zircon powder coating to the live surface of the cast steel part and ignite it after application.

[0095] Step 5: Core assembly. Place the sand core into the cavity and close the upper and lower sand boxes.

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

[0097] Step 7: Blow hot air into the cavity of the cast steel part to be poured through the gate for 15 hours. The hot air temperature is 160-180℃. Remove the hot air 20 minutes before pouring.

[0098] Step 8: 20 minutes before pouring, blow pure argon gas (Ar ≥ 99.99%) into the cavity of the cast steel part to be poured through the pouring cup, and introduce 6.8m... 3 After argon gas at a pressure of 13 MPa is introduced, the oxygen content in the cavity is measured by an oxygen analyzer at the bottom of the cavity and is ≤20%, at which point the argon gas blowing is stopped; during the argon gas blowing process, a plastic film is used to cover the top of the riser;

[0099] Step 9: After argon gas injection is complete, move the ladle to align with the pouring cup, lift the ladle to a height of 700mm, and place a circular asbestos argon gas protection ring under the ladle. The argon gas protection ring has a diameter of 600mm and is equipped with... The steel pipe is used to pass argon gas. The steel pipe is connected to the argon gas cylinder through an argon gas belt, which is 10m long. Two layers of paper caps and one layer of aluminum caps are placed above the argon gas protection ring. Argon gas is filled into the argon gas protection ring 20 seconds before pouring. During pouring, the steel ladle falls and is placed close to the argon gas protection ring. Argon gas is continuously filled throughout the pouring process at a filling rate of 8L / s to ensure that the argon gas protection ring is in a state of continuous argon gas filling until the pouring is completed.

[0100] Step 10: After pouring is complete, sprinkle a 120mm thick covering agent into the open riser;

[0101] Step 11: Remove the riser and patch of the cast steel part by gas cutting, and leave a 10mm allowance on each side of the machined surface by cold working;

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

[0103] In this embodiment, after smelting and solidification of the cast steel part, a cylindrical sample was taken from the center of the location with the greatest wall thickness. The sample was taken to ensure it was free of oil and rust to prevent hydrogen escape. The hydrogen content was tested according to GB / T223.82-2018 "Determination of Hydrogen Content in Iron and Steel - Inert Gas Fusion-Thermal Conductivity or Infrared Method". Tensile strength testing was performed after performance heat treatment. The hydrogen content was 1.3 ppm after smelting, 5.5 ppm after solidification of the cast steel part, and 0.6 ppm after performance heat treatment. The elongation of the tensile test specimen was 31%.

[0104] Example 4

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

[0106] Step 1: Make a wooden mold according to the drawing requirements, and prepare qualified face sand and back sand according to the requirements of sand mold manufacturing and the different types of cast steel parts;

[0107] Step 2: Shaping, using face sand to form the cavity of the cast steel part;

[0108] Step 3: Core making, forming the internal shape of the cast steel part;

[0109] Step 4: Spray the sand mold and cavity of the cast steel part with alcohol-based zircon powder coating, and then flame dry it after spraying. Repeat this process twice. Then, apply alcohol-based zircon powder coating to the live surface of the cast steel part and ignite it after application.

[0110] Step 5: Core assembly. Place the sand core into the cavity and close the upper and lower sand boxes.

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

[0112] Step 7: Blow hot air into the cavity of the cast steel part to be poured through the gate for 4 hours. The hot air temperature is 160-180℃. Remove the hot air 20 minutes before pouring.

[0113] Step 8: 20 minutes before pouring, blow pure argon gas (Ar ≥ 99.99%) into the cavity of the cast steel part through the pouring cup, and introduce 1.5m of gas. 3 After argon gas at a pressure of 13 MPa is introduced, the oxygen content in the cavity is measured by an oxygen analyzer at the bottom of the cavity and is ≤20%, at which point the argon gas blowing is stopped; during the argon gas blowing process, a plastic film is used to cover the top of the riser;

[0114] Step 9: After argon gas injection is complete, move the ladle to align with the pouring cup, lift the ladle to a height of 700mm, and place a circular asbestos argon gas protection ring under the ladle. The argon gas protection ring has a diameter of 800mm and is equipped with... The steel pipe is used to pass argon gas. The steel pipe is connected to the argon gas cylinder through an argon gas belt, which is 10m long. Two layers of paper caps and one layer of aluminum caps are placed above the argon gas protection ring. Argon gas is filled into the argon gas protection ring 20 seconds before pouring. During pouring, the steel ladle falls and is placed close to the argon gas protection ring. Argon gas is continuously filled throughout the pouring process at a filling rate of 8L / s to ensure that the argon gas protection ring is in a state of continuous argon gas filling until the pouring is completed.

[0115] Step 10: After pouring is complete, sprinkle a 120mm thick covering agent into the open riser;

[0116] Step 11: Remove the riser and patch of the cast steel part by gas cutting, and leave a 10mm allowance on each side of the machined surface by cold working;

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

[0118] In this embodiment, after smelting and solidification of the cast steel part, a cylindrical sample was taken from the center of the location with the greatest wall thickness. The sample was taken to ensure it was free of oil and rust to prevent hydrogen escape. The hydrogen content was tested according to GB / T223.82-2018 "Determination of Hydrogen Content in Iron and Steel - Inert Gas Fusion-Thermal Conductivity or Infrared Method". Tensile strength testing was performed after performance heat treatment. The hydrogen content was 1.6 ppm after smelting, 5.4 ppm after solidification of the cast steel part, and 0.7 ppm after performance heat treatment. The elongation of the tensile test specimen was 29%.

[0119] Comparative Example 1

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

[0121] Step 1: Make a wooden mold according to the drawing requirements, and prepare qualified face sand and back sand according to the requirements of sand mold manufacturing and the different types of cast steel parts;

[0122] Step 2: Shaping, using face sand to form the cavity of the cast steel part;

[0123] Step 3: Core making, forming the internal shape of the cast steel part;

[0124] Step 4: Core assembly. Place the sand core into the cavity and close the upper and lower sand boxes.

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

[0126] Step 6: Pouring;

[0127] Step 7: After pouring is complete, sprinkle a 110mm thick covering agent into the open riser;

[0128] Step 8: Remove the riser and patch of the cast steel part by gas cutting, and leave a 10mm allowance on each side of the machined surface by cold working;

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

[0130] This comparative example does not employ cavity baking, inert atmosphere protection, or dehydrogenation heat treatment during molding and casting. After smelting and solidification of the cast steel parts, samples are taken from the center of the thickest part of the casting using cylindrical specimens. Sampling is ensured to be oil-free and rust-free to prevent hydrogen escape. Hydrogen content is tested according to GB / T223.82-2018 "Determination of Hydrogen Content in Iron and Steel - Inert Gas Melting-Thermal Conductivity or Infrared Method". Tensile strength is tested after performance heat treatment. The hydrogen content after smelting is 1.3 ppm, after solidification of the cast steel parts is 13.4 ppm, and after performance heat treatment is 1.9 ppm. The elongation of the tensile specimen is 14%.

[0131] Comparative Example 2

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

[0133] Step 1: Make a wooden mold according to the drawing requirements, and prepare qualified face sand and back sand according to the requirements of sand mold manufacturing and the different types of cast steel parts;

[0134] Step 2: Shaping, using face sand to form the cavity of the cast steel part;

[0135] Step 3: Core making, forming the internal shape of the cast steel part;

[0136] Step 4: Spray the sand mold and cavity of the cast steel part with alcohol-based zircon powder coating, and then flame dry it after spraying. Repeat this process twice. Then, apply alcohol-based zircon powder coating to the live surface of the cast steel part and ignite it after application.

[0137] Step 5: Core assembly. Place the sand core into the cavity and close the upper and lower sand boxes.

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

[0139] Step 7: Blow hot air into the cavity of the cast steel part to be poured through the gate for 4 hours. The hot air temperature is 160-180℃. Remove the hot air 40 minutes before pouring.

[0140] Step 8: 20 minutes before pouring, blow pure argon gas (Ar ≥ 99.99%) into the cavity of the cast steel part to be poured through the pouring cup, and introduce 0.4m... 3 After introducing argon gas at a pressure of 13 MPa, stop blowing in argon gas; during the argon gas blowing process, cover the top of the riser with a plastic film;

[0141] Step 9: After argon gas injection is complete, move the ladle to align with the pouring cup, lift the ladle 700mm high, and place a circular asbestos argon gas protection ring under the ladle. The argon gas protection ring has a diameter of 800mm and is equipped with... The steel pipe is used to pass argon gas. The steel pipe is connected to the argon gas cylinder through an argon gas belt, which is 10m long. Two layers of paper caps and one layer of aluminum caps are placed above the argon gas protection ring. Argon gas is filled into the argon gas protection ring 20 seconds before pouring. During pouring, the steel ladle falls and is placed close to the argon gas protection ring. Argon gas is continuously filled throughout the pouring process at a filling rate of 8L / s to ensure that the argon gas protection ring is in a state of continuous argon gas filling until the pouring is completed.

[0142] Step 10: After pouring is complete, sprinkle a 110mm thick covering agent into the open riser;

[0143] Step 11: Remove the riser and patch of the cast steel part by gas cutting, and leave a 10mm allowance on each side of the machined surface by cold working;

[0144] Step 12: Perform performance heat treatment directly without dehydrogenation heat treatment.

[0145] In this comparative example, after smelting and solidification of the cast steel parts, samples were taken from the center of the location with the greatest wall thickness. Cylindrical specimens were used, and sampling was ensured to be free of oil and rust to prevent hydrogen escape. Hydrogen content was tested according to GB / T223.82-2018 "Determination of Hydrogen Content in Iron and Steel - Inert Gas Fusion-Thermal Conductivity or Infrared Method". Tensile strength testing was performed after performance heat treatment. The hydrogen content was 1.4 ppm after smelting, 8.6 ppm after solidification of the cast steel parts, and 1.8 ppm after performance heat treatment. The elongation of the tensile specimen was 17%.

[0146] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling hydrogen content in the production of large cast steel parts, characterized in that, Includes the following steps: 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 different types of cast steel parts; Step 2: Shaping, using molding sand to form the cavity of the cast steel part; Step 3: Core making, forming the internal shape of the cast steel part; Step 4: Spray the cast steel sand core and cast steel cavity with alcohol-based zircon powder coating, and then flame dry it. Then, apply alcohol-based zircon powder coating to the live surface of the cast steel part and ignite it. Step 5: Core assembly. Place the sand core into the cavity and close the upper and lower sand boxes. Step 6: Smelting. Prepare the chemical composition according to the required metal composition, select a suitable melting furnace to melt the alloy material, and form a qualified liquid metal liquid. Step 7: Determine the duration and temperature of hot air blowing based on the gross weight of the cast steel part. Then blow hot air into the cavity of the cast steel part to be poured through the gate. Remove the hot air 20-30 minutes before pouring. Step 8: 15-20 minutes before pouring, blow argon gas into the cavity of the cast steel part to be poured through the pouring cup. During the blowing of argon gas, cover the riser with plastic film. Step 9: After the argon gas blowing is finished, move the ladle to align with the pouring cup, place the argon gas protection ring above the pouring cup, set the steel pipe on the argon gas protection ring, and place the paper cap clamp and aluminum cap above the argon gas protection ring. Fill the argon gas protection ring with argon gas 10-30 seconds before pouring, drop the ladle, and pour. Step 10: After pouring is complete, sprinkle covering agent into the open riser; Step 11: Remove the roughing increments from the riser and other locations of the cast steel parts by gas cutting or machining; Step 12: Perform dehydrogenation heat treatment and performance heat treatment on the cast steel parts that have been gas cut or machined to obtain cast steel parts with low hydrogen content; In step 12, the dehydrogenation heat treatment involves heating the cast steel part to the holding temperature at a heating rate of 30-50℃ / h, and then furnace cooling it to below 200℃ at a cooling rate of 10-50℃ / h. In step 12, the heat preservation temperature is 600-680℃; In step 12, the wall thickness of the cast steel part is 150-300mm, and the heat preservation time is ≥100h; the wall thickness of the cast steel part is 300-400mm, and the heat preservation time is ≥150h; the wall thickness of the cast steel part is 400-500mm, and the heat preservation time is ≥260h; the wall thickness of the cast steel part is >500mm, and the heat preservation time is ≥600h.

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

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

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

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

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

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

8. The control method according to claim 1, characterized in that, In step 12, the dehydrogenation heat treatment involves heating the cast steel part to the holding temperature at a heating rate of 30-40℃ / h, and then furnace cooling it to below 200℃ at a cooling rate of 20-30℃ / h.

9. The control method according to claim 8, characterized in that, In step 12, the heat preservation temperature is 650-680℃.

10. The control method according to claim 9, characterized in that, In step 12, the wall thickness of the cast steel part is 150-300mm, and the heat preservation time is ≥100h; the wall thickness of the cast steel part is 300-400mm, and the heat preservation time is ≥180h; the wall thickness of the cast steel part is 400-500mm, and the heat preservation time is ≥300h; the wall thickness of the cast steel part is >500mm, and the heat preservation time is ≥650h.

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