Smelting process of high-purity 304 stainless steel bar

Abstract

The invention discloses a smelting process of a high-purity 304 stainless steel bar. The smelting process comprises the steps of electric furnace melting, AOD furnace smelting, LF furnace smelting, ingot casting and drawing. In the smelting process, fluorite does not need to be additionally added, the inclusion grade can be reduced, the method has the advantages that the produced bar is high in purity and suitable for mass production, and the production cost is remarkably reduced compared with that of a traditional process.

Description

Technical Field

[0001] This invention relates to the field of metal smelting technology, and more specifically to a smelting process for high-purity 304 stainless steel bars. Background Technology

[0002] 304 stainless steel is a common type of stainless steel with a density of 7.93 g / cm³. It possesses excellent corrosion resistance, high and low temperature resistance, wear resistance, and a beautiful appearance, making it widely used in marine development, petrochemicals, automobiles, and construction, among other industries. It is an important steel material for national economic development.

[0003] 304 stainless steel is a general-purpose stainless steel. Inclusions in 304 stainless steel can damage the oxide film on the surface of the stainless steel, accelerate local corrosion, and thus reduce the corrosion resistance of the material. They can also disrupt the continuity of the material, leading to stress concentration, reducing the strength and toughness of the material, and have a significant impact on the performance of 304 stainless steel.

[0004] Currently, the smelting process for 304 stainless steel bars is: electric furnace + AOD furnace (decarburization period + primary reduction period + secondary reduction period) + LF furnace + ingot casting. The slag system used is MgO, Al2O3, SiO2, and CaO, which has poor fluidity and poor adsorption capacity for inclusions. The produced 304 stainless steel has an inclusion level of ≤2.0, which can only meet the needs of automotive and construction applications, and still cannot meet the needs of high-temperature and high-corrosion applications such as nuclear power, submarine, and aerospace.

[0005] Therefore, there is an urgent need for a smelting process for high-purity 304 stainless steel bars. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a smelting process for high-purity 304 stainless steel bars, so as to solve the problems in the background art.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows.

[0008] A smelting process for high-purity 304 stainless steel bars specifically includes the following steps: S1. Electric furnace melting: Add 304 Benxi steel return material, high carbon ferrochrome, and medium nickel ferrochrome to the electric furnace and heat to melt. After melting, measure the temperature and take a sample. Tap the steel to the AOD furnace. S2, AOD furnace smelting: S21, Decarburization: Blowing a mixed gas of O2-N2 with a volume ratio of 1:1 to 1:3 into the molten steel, and maintaining the molten steel at 1680-1740℃; S22, Primary Reduction: Calculate the FeSi addition amount based on oxygen consumption, reduce for at least 7 minutes until the Si content is reduced to 0.4-0.5%, the basicity of the reduction residue (R=CaO / SiO2) is ≥2.3, shake the furnace to measure temperature, take samples, and remove slag; S23. Secondary reduction: Add low-aluminum refining slag, quicklime, and aluminum granules, and make the slag system ratio as follows: MgO=5~7%; Al2O3=30~36%; SiO2=7~10%; CaO=50~60%. S24. AOD furnace tapping: Boron iron is added with the steel stream during tapping, and then the molten steel and slag are transferred together to the LF furnace. S3 and LF furnace smelting: S31. Connect the argon gas, stir and break the slag shell. After the ladle car is driven to the heating station, measure the temperature, take a sample, adjust the argon gas flow rate to 15-20 ln / min and turn on the power to heat up. S32. During the power supply and heating process, Al powder diffusion deoxidation is used to maintain a reducing atmosphere inside the package and control oxygen ≤25ppm. S33. After the slag has turned white and the temperature is ≥1560℃, take a sample and adjust the composition precisely according to the internal control composition based on the analysis results. The white slag should be maintained for ≥20 minutes. S34. Adjust the slag fluidity. After the slag melting point is in the low melting point range, start stirring with argon gas. After stirring for 8 minutes, when the diameter of the Ar gas ring is ≥300mm and does not protrude above the molten steel surface, start the soft blowing operation with argon gas for ≥20 minutes. Soft blow until the molten steel temperature is 1530~1540℃, then lift the ladle for casting. S4. Casting and drawing: S41. Pretreatment: The new steel ingot mold is annealed, and the cooled steel ingot mold and the base are baked so that the temperature of the base and the steel ingot mold reaches 30~100℃ and is uniform during casting. S42. Bricklaying of the chassis: Bricklaying of the chassis should be done while it is still hot to ensure that the steel flow system is fully dry. After the masonry is completed, it should be blown clean to remove debris from the steel flow system and ensure cleanliness. S43. Cleaning of steel ingot mold line: After cleaning, blow away the debris in the mold, and perform blowing and suction operation after the mold is set. Perform a second blowing and suction operation 30 minutes before refining and tapping the steel. S44. Preparation of protective slag: Add SD-HC protective slag before pouring molten steel. The protective slag is suspended and the dosage is 2.0 kg / t. S45. Casting: Add 2-2.5 kg / t of heating agent when the riser is 2 / 3 full, and add 1.5-2.5 kg / t of rice husk when the casting is finished; S46. Demolding: When the first batch of casting is almost finished, take a sample of the finished product. After the specified demolding time, the steel ingot is demolded and air-cooled. Then, the steel ingot is forged and drawn to obtain steel bars of the specified size.

[0009] To further optimize the technical solution, a carbon raiser is added to step S21 to ensure that C ≥ 2.3%.

[0010] To further optimize the technical solution, after step S43 is completed, the mold and the central column tube are covered with kraft paper or sheet metal to prevent debris from falling in.

[0011] To further optimize the technical solution, in step S44, prepare spare protective slag and add it promptly if leakage is found during the pouring process.

[0012] To further optimize the technical solution, the carbonized rice husks in step S45 should be spread evenly.

[0013] To further optimize the technical solution, step S45 of the pouring process requires the molten steel to rise smoothly without any cracking.

[0014] Due to the adoption of the above technical solutions, the technical progress achieved by this invention is as follows.

[0015] This invention provides a smelting process for high-purity 304 stainless steel bars. By adjusting the refining slag ratio used during the secondary reduction in an AOD furnace, the fluidity of the slag system is improved, and its ability to adsorb inclusions is enhanced, thereby increasing the purity of the molten steel and producing 304 bars with an inclusion level ≤1.5. This smelting process eliminates the need for additional fluorite, reduces the inclusion level, and offers advantages such as high-purity bars suitable for mass production, while significantly reducing production costs compared to traditional processes. Attached Figure Description

[0016] Figure 1 This is a view of the slag system according to an embodiment of the present invention; Figure 2 This is a slag system view for comparison with the present invention; Figure 3 This is a graph showing the effect of alkalinity on the activity of Al2O3 in this invention; Figure 4 This is a graph showing the effect of alkalinity on SiO2 activity according to the present invention. Figure 5 This is a diagram showing the effect of C / A ratio on the activity of Al2O3 according to the present invention; Figure 6 This is a diagram showing the effect of C / A ratio on SiO2 activity in this invention; Detailed Implementation

[0017] A smelting process for high-purity 304 stainless steel bars was developed. Experiments revealed that combining... Figure 3-6As shown, the activity of Al2O3 relatively decreases with increasing slag basicity and calcium-aluminum ratio, while the activity of CaO relatively increases with increasing slag basicity and calcium-aluminum ratio. However, when the calcium-aluminum ratio exceeds 2, the refining slag system deviates from the low melting point region. Therefore, only the case where the calcium-aluminum ratio is less than 2 is considered. It was found that when the calcium-aluminum ratio is between 1 and 2, the activity of Al2O3 is relatively minimum, and the activity of CaO is relatively maximum, which is beneficial for desulfurization and adsorption of aluminum inclusions. Based on the high desulfurization requirements, it is necessary to increase the basicity of the refining slag as much as possible, while keeping the activity of Al2O3 relatively low and the activity of CaO relatively high. Taking all factors into consideration, the basicity of the refining slag system should be controlled between 5 and 7.

[0018] A smelting process for high-purity 304 stainless steel bars specifically includes the following steps: S1. Electric Furnace Melting: 304 stainless steel recycled material, high-carbon ferrochrome, and medium-nickel ferrochrome are added to an electric furnace and heated to melt. After melting, temperature is measured and samples are taken. The steel is then tapped into an AOD furnace. The raw material ratio range is: 12000-12400 kg 304 stainless steel recycled material, 3000-4000 kg high-carbon ferrochrome, and 7000-8000 kg medium-nickel ferrochrome.

[0019] S2, AOD furnace smelting: S21. Decarburization: Blow a mixture of O2 and N2 gas with a volume ratio of 1:1 to 1:3 into the molten steel, maintaining the molten steel temperature at 1680-1740℃. If the heat source is sufficient, add a carburizing agent to make C ≥ 2.3%.

[0020] S22, Primary Reduction: Calculate the amount of FeSi added based on the oxygen consumption, reduce for at least 7 minutes until the Si content is reduced to 0.4-0.5%, the basicity of the reduction slag (R=CaO / SiO2) is ≥2.3, shake the furnace to measure the temperature, take samples, and remove slag.

[0021] S23, Secondary Reduction: Add low-aluminum refining slag, quicklime, and aluminum granules, and make the slag system ratio MgO=5~7%; Al2O3=30~36%; SiO2=7~10%; CaO=50~60%.

[0022] S24. AOD furnace tapping: Boron iron is added with the steel stream during tapping, and then the molten steel and slag are transferred together to the LF furnace.

[0023] S3 and LF furnace smelting: S31. Connect the argon gas, stir to break the slag shell, drive the ladle car to the heating station, measure the temperature, take a sample, adjust the argon gas flow rate to 15-20 ln / min and power on to raise the temperature.

[0024] S32. During the power supply and heating process, Al powder diffusion deoxidation is used to maintain a reducing atmosphere inside the package and control oxygen ≤25ppm.

[0025] S33. After the slag has turned completely white and the temperature is ≥1560℃, take a sample and adjust the composition precisely according to the internal control composition based on the analysis results. The white slag should be maintained for ≥20 minutes.

[0026] S34. Adjust the slag fluidity. After the slag melting point is in the low melting point range, start stirring with argon gas. After stirring for 8 minutes, when the diameter of the Ar gas ring is ≥300mm and does not protrude above the molten steel surface, start the soft blowing operation with argon gas for ≥20 minutes. Soft blow until the molten steel temperature reaches 1530~1540℃, then hoist the ladle for casting.

[0027] S4. Casting and drawing: S41. Pretreatment: The new steel ingot mold is annealed, and the cooled steel ingot mold and the base are baked so that the temperature of the base and the steel ingot mold reaches 30~100℃ and is uniform during casting.

[0028] S42. Bricklaying of the chassis: Bricklaying of the chassis should be done while it is still hot to ensure that the steel flow system is fully dry. After the masonry is completed, it should be blown clean to remove debris from the steel flow system and ensure cleanliness.

[0029] S43. Cleaning the ingot mold line: After cleaning, blow away any debris inside the mold. After setting the mold, perform a blowing and suction operation. After blowing, cover the mold and central column tube with kraft paper or sheet metal to prevent debris from falling in. Perform a second blowing and suction operation 30 minutes before refining and tapping the steel.

[0030] S44. Preparation of protective slag: Add SD-HC protective slag before pouring molten steel. The protective slag should be suspended, and the dosage is 2.0 kg / t. Prepare spare protective slag and add it promptly if any leakage is found during the pouring process.

[0031] S45. Casting: Add 2-2.5 kg / t of exothermic agent when the molten steel reaches 2 / 3 of the riser height. After casting, add 1.5-2.5 kg / t of rice husks. The carbonized rice husks should be evenly spread. The casting process should be smooth and free of scrambling during the molten steel rise.

[0032] S46. Demolding: When the first batch of casting is almost finished, take a sample of the finished product. After the specified demolding time, the steel ingot is demolded and air-cooled. Then, the steel ingot is forged and drawn to obtain steel bars of the specified size.

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Example

[0034] A smelting process for high-purity 304 stainless steel bars specifically includes the following steps: S1. Electric furnace melting: 12,000 kg of 304 Benxi steel return material, 4,000 kg of high-carbon ferrochrome, and 6,000 kg of medium-nickel ferrochrome are added to the electric furnace and heated to melt. After melting, the temperature is measured and samples are taken. The steel is then tapped to the AOD furnace.

[0035] S2, AOD furnace smelting: S21. Decarburization: Blow a 1:1 volume ratio O2-N2 mixture into the molten steel, maintaining the temperature at 1680-1740℃. If the heat source is sufficient, add a carburizing agent to make the carbon content 2.5%.

[0036] S22, Primary Reduction: Calculate the amount of FeSi added based on the oxygen consumption, reduce for at least 7 minutes until the Si content is reduced to 0.4% and the basicity of the reduction slag (R=CaO / SiO2) is 2.3. Shake the furnace to measure the temperature, take samples, and remove 95% of the slag.

[0037] S23, Secondary Reduction: Add low-alumina refining slag, quicklime, aluminum granules, and calcium silicate blocks to ensure that the slag system ratio is MgO=7%; Al2O3=36%; SiO2=7%; CaO=50%.

[0038] S24. AOD furnace tapping: Boron iron is added with the steel stream during tapping, and then the molten steel and slag are transferred together to the LF furnace.

[0039] S3 and LF furnace smelting: S31. Connect the argon gas, stir to break the slag shell, drive the ladle car to the heating station, measure the temperature, take a sample, adjust the argon gas flow rate to 18 ln / min and power on to raise the temperature.

[0040] S32. During the power supply and heating process, Al powder diffusion deoxidation is used to maintain a reducing atmosphere inside the package and control oxygen ≤25ppm.

[0041] S33. After the slag has fully turned white and reached a temperature of 1560℃, samples are taken. Based on the analysis results, the composition is precisely adjusted according to the internal control composition, and adjusted to: calcium-aluminum ratio of 1.66, basicity of 5.29, and slag system CaO, Al2O3, and SiO2 contents of 55.81%, 33.64%, and 10.55%, respectively. The white slag is maintained for 20 minutes.

[0042] S34. Adjust the slag fluidity. After the slag melting point is in the low melting point range, start stirring with argon gas. After stirring for 8 minutes, when the diameter of the Ar gas ring is ≥300mm and does not protrude above the molten steel surface, start soft blowing with argon gas for ≥20 minutes. Soft blow until the molten steel temperature reaches 1530℃, then hoist the ladle for casting.

[0043] S4. Casting and drawing: S41. Pretreatment: The new steel ingot mold is annealed, and the cooled steel ingot mold and the base are baked so that the temperature of the base and the steel ingot mold reaches 60℃ and is uniform during casting.

[0044] S42. Bricklaying of the chassis: Bricklaying of the chassis should be done while it is still hot to ensure that the steel flow system is fully dry. After the masonry is completed, it should be blown clean to remove debris from the steel flow system and ensure cleanliness.

[0045] S43. Cleaning the ingot mold line: After cleaning, blow away any debris inside the mold. After setting the mold, perform a blowing and suction operation. After blowing, cover the mold and central column tube with kraft paper or sheet metal to prevent debris from falling in. Perform a second blowing and suction operation 30 minutes before refining and tapping the steel.

[0046] S44. Preparation of protective slag: Add SD-HC protective slag before pouring molten steel. The protective slag should be suspended, and the dosage is 2.0 kg / t. Prepare spare protective slag and add it promptly if any leakage is found during the pouring process.

[0047] S45. Casting: Add 2.3 kg / t of exothermic agent when the molten steel reaches 2 / 3 of the riser height, and add 1.9 kg / t of rice husks at the end of the casting process. The carbonized rice husks should be evenly spread. The casting process should be smooth and free of sloshing during the molten steel rise.

[0048] S46. Demolding: When the first batch of casting is almost finished, take a sample of the finished product. After the specified demolding time, the steel ingot is demolded and air-cooled. Then, the steel ingot is forged and drawn to obtain steel bars of the specified size. Example

[0049] A smelting process for high-purity 304 stainless steel bars specifically includes the following steps: S1. Electric furnace melting: 12,400 kg of 304 Benxi steel return material, 3,000 kg of high-carbon ferrochrome, and 8,000 kg of medium-nickel ferrochrome are added to the electric furnace and heated to melt. After melting, the temperature is measured and samples are taken, and the steel is tapped to the AOD furnace.

[0050] S2, AOD furnace smelting: S21. Decarburization: Blow a mixture of O2 and N2 gas at a volume ratio of 1:2 into the molten steel, maintaining the molten steel temperature at 1680-1740℃. If the heat source is sufficient, add a carburizing agent to make the carbon content 2.3%.

[0051] S22, Primary Reduction: Calculate the amount of FeSi added based on the oxygen consumption, reduce for at least 7 minutes until the Si content is reduced to 0.5% and the basicity of the reduction slag (R=CaO / SiO2) is 3. Shake the furnace to measure the temperature, take samples, and remove slag at 92%.

[0052] S23, Secondary Reduction: Add low-alumina refining slag, quicklime, aluminum granules, and calcium silicate blocks to ensure that the slag system ratio is MgO=6%; Al2O3=30%; SiO2=8%; CaO=60%.

[0053] S24. AOD furnace tapping: Boron iron is added with the steel stream during tapping, and then the molten steel and slag are transferred together to the LF furnace.

[0054] S3 and LF furnace smelting: S31. Connect the argon gas, stir and break the slag shell. After the ladle car is driven to the heating station, measure the temperature, take a sample, adjust the argon gas flow rate to 15 ln / min and power on to raise the temperature.

[0055] S32. During the power supply and heating process, Al powder diffusion deoxidation is used to maintain a reducing atmosphere inside the package and control oxygen ≤25ppm.

[0056] S33. After the slag has fully turned white and reached a temperature of 1580℃, samples are taken. Based on the analysis results, the composition is precisely adjusted according to the internal control composition, and adjusted to: calcium-aluminum ratio of 1.66, basicity of 5.29, and slag system CaO, Al2O3, and SiO2 contents of 55.81%, 33.64%, and 10.55%, respectively. The white slag is maintained for 20 minutes.

[0057] S34. Adjust the slag fluidity. After the slag melting point is in the low melting point range, start stirring with argon gas. After stirring for 8 minutes, when the diameter of the Ar gas ring is ≥300mm and does not protrude above the molten steel surface, start soft blowing with argon gas for ≥20 minutes. Soft blow until the molten steel temperature reaches 1533℃, then hoist the ladle for casting.

[0058] S4. Casting and drawing: S41. Pretreatment: The new steel ingot mold is annealed, and the cooled steel ingot mold and the base are baked so that the temperature of the base and the steel ingot mold reaches 100℃ and is uniform during casting.

[0059] S42. Bricklaying of the chassis: Bricklaying of the chassis should be done while it is still hot to ensure that the steel flow system is fully dry. After the masonry is completed, it should be blown clean to remove debris from the steel flow system and ensure cleanliness.

[0060] S43. Cleaning the ingot mold line: After cleaning, blow away any debris inside the mold. After setting the mold, perform a blowing and suction operation. After blowing, cover the mold and central column tube with kraft paper or sheet metal to prevent debris from falling in. Perform a second blowing and suction operation 30 minutes before refining and tapping the steel.

[0061] S44. Preparation of protective slag: Add SD-HC protective slag before pouring molten steel. The protective slag should be suspended, and the dosage is 2.0 kg / t. Prepare spare protective slag and add it promptly if any leakage is found during the pouring process.

[0062] S45. Casting: Add 2.5 kg / t of exothermic agent when the molten steel reaches 2 / 3 of the riser height. Add 1.5 kg / t of rice husks at the end of the casting process. The carbonized rice husks should be evenly distributed. The casting process should be smooth and free of sloshing during the molten steel rise.

[0063] S46. Demolding: When the first batch of casting is almost finished, take a sample of the finished product. After the specified demolding time, the steel ingot is demolded and air-cooled. Then, the steel ingot is forged and drawn to obtain steel bars of the specified size. Example

[0064] A smelting process for high-purity 304 stainless steel bars specifically includes the following steps: S1. Electric furnace melting: 12,200 kg of 304 Benxi steel return material, 3,500 kg of high-carbon ferrochrome, and 7,000 kg of medium-nickel ferrochrome are added to the electric furnace and heated to melt. After melting, the temperature is measured and samples are taken, and the steel is tapped to the AOD furnace.

[0065] S2, AOD furnace smelting: S21. Decarburization: Blow a mixture of O2 and N2 gas at a volume ratio of 1:3 into the molten steel, maintaining the molten steel temperature at 1680-1740℃. If the heat source is sufficient, add a carburizing agent to make the carbon content 3.1%.

[0066] S22, Primary Reduction: Calculate the amount of FeSi added based on the oxygen consumption, reduce for at least 7 minutes until the Si content is reduced to 0.5% and the basicity of the reduction slag (R=CaO / SiO2) is 3.1. Shake the furnace to measure the temperature, take samples, and remove 90% of the slag.

[0067] S23, Secondary Reduction: Add low-alumina refining slag, quicklime, 0.6 kg / ton of aluminum granules, and calcium silicate blocks to ensure that the slag system ratio is MgO=5%; Al2O3=33%; SiO2=10%; CaO=55%.

[0068] S24. AOD furnace tapping: Boron iron is added with the steel stream during tapping, and then the molten steel and slag are transferred together to the LF furnace.

[0069] S3 and LF furnace smelting: S31. Connect the argon gas, stir to break the slag shell, drive the ladle car to the heating station, measure the temperature, take a sample, adjust the argon gas flow rate to 20 ln / min and power on to raise the temperature.

[0070] S32. During the power supply and heating process, Al powder diffusion deoxidation is used to maintain a reducing atmosphere inside the package and control oxygen ≤25ppm.

[0071] S33. After the slag has fully turned white and reached a temperature of 1560℃, samples are taken. Based on the analysis results, the composition is precisely adjusted according to the internal control composition, and adjusted to: calcium-aluminum ratio of 1.66, basicity of 5.29, and slag system CaO, Al2O3, and SiO2 contents of 55.81%, 33.64%, and 10.55%, respectively. The white slag is maintained for ≥20 minutes.

[0072] S34. Adjust the slag fluidity. After the slag melting point is in the low melting point range, start stirring with argon gas. After stirring for 8 minutes, when the diameter of the Ar gas ring is ≥300mm and does not protrude above the molten steel surface, start soft blowing with argon gas for ≥20 minutes. Soft blow until the molten steel temperature reaches 1540℃, then hoist the ladle for casting.

[0073] S4. Casting and drawing: S41. Pretreatment: The new steel ingot mold is annealed, and the cooled steel ingot mold and base are baked so that the temperature of the base and steel ingot mold reaches 30℃ and is uniform during casting.

[0074] S42. Bricklaying of the chassis: Bricklaying of the chassis should be done while it is still hot to ensure that the steel flow system is fully dry. After the masonry is completed, it should be blown clean to remove debris from the steel flow system and ensure cleanliness.

[0075] S43. Cleaning the ingot mold line: After cleaning, blow away any debris inside the mold. After setting the mold, perform a blowing and suction operation. After blowing, cover the mold and central column tube with kraft paper or sheet metal to prevent debris from falling in. Perform a second blowing and suction operation 30 minutes before refining and tapping the steel.

[0076] S44. Preparation of protective slag: Add SD-HC protective slag before pouring molten steel. The protective slag should be suspended, and the dosage is 2.0 kg / t. Prepare spare protective slag and add it promptly if any leakage is found during the pouring process.

[0077] S45. Casting: Add 2 kg / t of exothermic agent when the molten steel reaches 2 / 3 of the riser height, and add 2.5 kg / t of rice husks at the end of the casting process. The carbonized rice husks should be evenly spread. The casting process should be smooth and free of sloshing during the molten steel rise.

[0078] S46. Demolding: When the first batch of casting is almost finished, take a sample of the finished product. After the specified demolding time, the steel ingot is demolded and air-cooled. Then, the steel ingot is forged and drawn to obtain steel bars of the specified size.

[0079] Analysis of slag samples taken from each node showed that the calcium-aluminum ratio, alkalinity, and slag composition all met the requirements. Regarding the results of this slag system inspection, as follows... Figure 1 As shown, all slag samples are in the low melting point range (circles, squares, and triangles represent slag samples). Based on the microscopic detection method using the standard rating chart for the determination of non-metallic inclusions in steel provided in national standard GB / T10561-2023, the inclusion levels of the produced bars were determined and statistically analyzed. The determined indicators included coarse and fine inclusions of categories A, B, C, and D, as well as DS inclusions. The results are shown in Table 1 below: Table 1:

[0080] The slag system used in the production process is a common slag system: MgO=4~9%; Al2O3=5~8%; SiO2=22~35%; CaO=50~60%, and fluorite needs to be added to obtain 304 bar stock. The inclusion levels are shown in Table 2 below: Table 2:

[0081] Draw the Al-Si-Ca-Mg phase diagram of the refining slag system in the comparative example, as follows: Figure 2As shown, the inspection of inclusions in the produced 304 bar stock revealed the presence of coarse and fine inclusions of categories A, B, C, and D, as well as category DS inclusions. Moreover, the inspection results could not achieve a level of ≤1.5 for each category. Furthermore, the melting point of the refining slag from the five heats was outside the low melting point zone. In actual production, it is necessary to add approximately 300 kg of fluorite to improve the melting point and fluidity of the slag system.

[0082] In summary, the slag system of this invention has the advantages of improved slag fluidity, enhanced adsorption capacity for inclusions, and no need for additional fluorite. The produced 304 bars do not contain any Class C inclusions, and the inclusions of Class A, B, and D are significantly reduced compared to the examples. Class DS inclusions are extremely rare, and the level of all inclusions is ≤1.5, which significantly improves the purity of the 304 stainless steel bars and thus enhances their corrosion resistance, meeting the requirements of high-temperature and high-corrosion applications such as nuclear power, seabed, and aviation.

Claims

1. A smelting process for high-purity 304 stainless steel bars, characterized in that, Specifically, the following steps are included: S1. Electric furnace melting: Add 304 Benxi steel return material, high carbon ferrochrome, and medium nickel ferrochrome to the electric furnace and heat to melt. After melting, measure the temperature and take a sample. Tap the steel to the AOD furnace. S2, AOD furnace smelting: S21, Decarburization: Blowing a mixed gas of O2-N2 with a volume ratio of 1:1 to 1:3 into the molten steel, and maintaining the molten steel at 1680-1740℃; S22, Primary Reduction: Calculate the FeSi addition amount based on oxygen consumption, reduce for at least 7 minutes until the Si content is reduced to 0.4-0.5%, the basicity of the reduction residue (R=CaO / SiO2) is ≥2.3, shake the furnace to measure temperature, take samples, and remove slag; S23. Secondary reduction: Add low-aluminum refining slag, quicklime, and aluminum granules, and make the slag system ratio as follows: MgO=5~7%; Al2O3=30~36%; SiO2=7~10%; CaO=50~60%. S24. AOD furnace tapping: Boron iron is added with the steel stream during tapping, and then the molten steel and slag are transferred together to the LF furnace. S3 and LF furnace smelting: S31. Connect the argon gas, stir and break the slag shell. After the ladle car is driven to the heating station, measure the temperature, take a sample, adjust the argon gas flow rate to 15-20 ln / min and turn on the power to heat up. S32. During the power supply and heating process, Al powder diffusion deoxidation is used to maintain a reducing atmosphere inside the package and control oxygen ≤25ppm. S33. After the slag has turned white and the temperature is ≥1560℃, take a sample and adjust the composition precisely according to the internal control composition based on the analysis results. The white slag should be maintained for ≥20 minutes. S34. Adjust the slag fluidity. After the slag melting point is in the low melting point region, start stirring with argon gas. After stirring for 8 minutes, when the diameter of the Ar gas ring is ≥300mm and does not protrude above the molten steel surface, start the soft blowing argon operation. The soft blowing time is ≥20 minutes. The steel is blown to a temperature of 1530~1540℃, and then cast using a ladle. S4. Casting and drawing: S41. Pretreatment: The new steel ingot mold is annealed, and the cooled steel ingot mold and the base are baked so that the temperature of the base and the steel ingot mold reaches 30~100℃ and is uniform during casting. S42. Bricklaying of the chassis: Bricklaying of the chassis should be done while it is still hot to ensure that the steel flow system is fully dry. After the masonry is completed, it should be blown clean to remove debris from the steel flow system and ensure cleanliness. S43. Cleaning of steel ingot mold line: After cleaning, blow away the debris in the mold, and perform blowing and suction operation after the mold is set. Perform a second blowing and suction operation 30 minutes before refining and tapping the steel. S44. Preparation of protective slag: Add SD-HC protective slag before pouring molten steel. The protective slag is suspended and the dosage is 2.0 kg / t. S45. Casting: Add 2-2.5 kg / t of heating agent when the riser is 2 / 3 full, and add 1.5-2.5 kg / t of rice husk when the casting is finished; S46. Demolding: When the first batch of casting is almost finished, take a sample of the finished product. After the specified demolding time, the steel ingot is demolded and air-cooled. Then, the steel ingot is forged and drawn to obtain steel bars of the specified size.

2. The smelting process for high-purity 304 stainless steel bars according to claim 1, characterized in that: In step S21, a carbon raiser is added to ensure that C ≥ 2.3%.

3. The smelting process for high-purity 304 stainless steel bars according to claim 1, characterized in that: After step S43 is completed, the mold and central column tube are covered with kraft paper or sheet metal to prevent debris from falling in.

4. The smelting process for high-purity 304 stainless steel bars according to claim 1, characterized in that: In step S44, prepare spare protective slag and add it promptly if any leakage is found during the pouring process.

5. The smelting process for high-purity 304 stainless steel bars according to claim 1, characterized in that: In step S45, the carbonized rice husks should be spread evenly.

6. The smelting process for high-purity 304 stainless steel bars according to claim 1, characterized in that: The pouring process in step S45 requires that the molten steel rise smoothly and without any cracking.

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