Method for manufacturing high-purity rare earth weathering bridge steel

Abstract

The application discloses a kind of high-purity rare earth weathering bridge steel manufacturing method, comprising the following steps: S1, preparing raw materials;S2, impurity analysis and preparation;S3, vacuum induction furnace initial refining N;S4, vacuum induction furnace first material and refining;S5, vacuum induction furnace second material and charging adjustment;S6, vacuum induction furnace temperature adjustment and Ce;S7, cooling to form alloy ingot.The application uses vacuum electromagnetic induction melting process, improves alloy purity through high-purity raw materials and reasonable preparation process and process parameter control, and adds rare earth elements, and then significantly improves the strength, tensile and weathering performance of bridge steel.

Description

Technical Field

[0001] This invention relates to the field of bridge weathering steel technology, and in particular to a method for manufacturing high-purity rare earth weathering bridge steel. Background Technology

[0002] Steel corrosion is a very serious problem. To address this issue, weathering steel was developed. Weathering steel, also known as atmospheric corrosion resistant steel, refers to low-alloy high-strength steel with the addition of small amounts of corrosion-resistant elements such as copper and nickel. It possesses the strength, toughness, ductility, and fatigue resistance of high-quality steel, while also exhibiting excellent atmospheric corrosion resistance. Compared to ordinary carbon steel, weathering steel forms a denser and tougher rust layer when exposed to the atmosphere, hindering further corrosion. Atmospheric corrosion of bridge steel is one of the main factors affecting the service life of bridges, and weathering bridge steel can be used directly in atmospheric environments without painting, saving significant maintenance costs and extending service life. Therefore, developing high-performance weathering bridge steel is crucial.

[0003] In existing technologies, weathering bridge steel is typically smelted using electric furnaces or converters with ladle refining processes. However, since electric furnaces or converters are usually smelted in an atmospheric environment, the absorption of gases inevitably increases the content of oxygen, nitrogen, and other gases. It is generally believed that nitrogen in steel tends to segregate at grain boundaries to form carbonitrides, reducing the steel's toughness and plasticity; hydrogen also reduces the steel's toughness and plasticity, and is prone to precipitation during use, causing small cracks and hydrogen embrittlement; oxygen usually exists in the form of oxide inclusions, which can cause stress concentration, reducing the material's strength and processing performance, as well as its fatigue strength and corrosion resistance. In short, excessively high levels of oxygen, nitrogen, and hydrogen in steel will lead to a decrease in the strength and corrosion resistance of weathering bridge steel, affecting its normal use. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for manufacturing high-purity rare-earth weather-resistant bridge steel. The method employs a vacuum electromagnetic induction melting process, using high-purity raw materials and reasonable preparation processes and process parameter control to improve alloy purity. Furthermore, rare-earth elements are added, thereby significantly improving the strength, tensile strength, and weather resistance of the bridge steel.

[0005] The present invention adopts the following technical solution:

[0006] A method for manufacturing high-purity rare-earth weathering bridge steel includes the following steps:

[0007] S1. Prepare raw materials: C, Si, Mn, Nb, Al, Ti, Cr, Ni, Cu, Mo, Ce and Fe. All raw materials should be high-purity.

[0008] S2. Impurity Analysis and Preparation: Analyze the impurity content of each raw material and prepare the corresponding raw materials according to the composition ratio.

[0009] S3. Initial smelting and nitrogen removal in vacuum induction furnace: After the vacuum degree in the vacuum induction furnace is lower than 1Pa before smelting, add Fe to the bottom material bucket. Each time the material is added, wait until the previous bucket of material has basically melted before adding the next bucket of raw material. After the Fe is melted, reduce the power to ≤500KW and carry out initial smelting and nitrogen removal. During this period, the temperature should be measured to ensure that the temperature of the molten steel is 1530-1560℃.

[0010] S4. Vacuum Induction Furnace Primary Charging and Refining: After sampling and analysis, the N content in the molten steel is found to be below 40ppm. C, Ni, Mo, Cu, Nb, Mn, and Cr are added to the molten steel using a charging bucket, and the power is increased to ≤1000KW for charging. After the molten steel is cleared, the power is further increased to 700-1500KW for refining. The refining time is 30 minutes. During this time, the temperature of the molten steel should be measured to ensure that the temperature is 1550-1590℃. After refining, the power is reduced to ≤500KW again to extract N. During this time, the temperature of the molten steel should be measured to ensure that the temperature is 1530-1560℃.

[0011] S5. Secondary charging and charging adjustment of vacuum induction furnace: After sampling and analysis, the nitrogen content of the molten steel is found to be below 40ppm. The power is further reduced to ≤300KW. After the molten steel forms a crust, Ti and Si are added, and the power is increased to 300-700KW for charging. The purpose is to prevent excessive heat release during melting. After the molten steel is cleared, a sample is taken before the furnace is opened for composition analysis, and the charging is adjusted according to the target value.

[0012] S6. Temperature adjustment and Ce addition in vacuum induction furnace: After the composition of molten steel meets the internal control value, the temperature is measured and adjusted to 1560-1590℃. Ce is then added, and finally, vacuum casting with electricity is carried out as soon as possible.

[0013] S7. Cooling to form alloy ingot: Cool the ingot in a vacuum for more than 180 minutes, and then break the vacuum to obtain rare earth weathering bridge steel alloy ingot.

[0014] Furthermore, in step S1, C is a high-purity graphite block with a purity of 4N, Si is a crystalline silicon block with a purity of ≥98%, Mn is an electrolytic manganese sheet with a purity of 2N, Nb is a high-purity niobium block with a purity of 3N, Al is an electrolytic aluminum ingot with a purity of ≥99.7%, Ti is sponge titanium with a purity of 2N, Cr is a high-purity chromium block with a purity of 2N, Ni is a nickel bead or nickel plate with a purity of 3N, Cu is a TU1 oxygen-free copper block with a purity of 3N, Mo is a molybdenum block with a purity of 2N, Ce is high-purity metallic cerium, and Fe is an iron ingot with a purity of 2N.

[0015] Further, in step S2, the chemical composition of the raw materials by weight percentage is as follows: C: 0.05–0.08%, Si: 0.10–0.30%, Mn: 1.10–1.40%, Nb: 0.010–0.035%, Al: 0.020–0.050%, Ti: 0.010–0.020%, Cr: 0.40–0.50%, Ni: 0.30–0.50%, Cu: 0.30–0.40%, Mo: 0.05–0.15%, rare earth elements.

[0016] Ce: 0.0005-0.0015%, balance Fe and unavoidable impurities, wherein impurities are controlled as follows: P: ≤0.010%, S: ≤0.001%, and Pcm (%) ≤0.22, I (%) ≥6.2, ensuring low Pcm value and high I value.

[0017] Preferably, in step S1, the Fe needs to have its surface oxide layer removed using a roller derusting machine before use.

[0018] Preferably, in step S1, the Cr, Mo, Ni, Nb, and Cu are all baked in a drying oven at 40-80°C for more than 24 hours before use to remove moisture adhering to the surface of the raw materials.

[0019] Preferably, the newly made crucible lining is cleaned by smelting a furnace of pure iron, thereby improving the purity of the subsequent weathering bridge steel smelting.

[0020] Preferably, in step S1, the Fe can be replaced by H10L or high-quality bridge steel scrap or other high-purity raw material steel of known composition to improve the purity of the alloy.

[0021] Preferably, a small amount of raw materials such as Fe can be reserved during the feeding process to facilitate subsequent adjustments to the steel composition.

[0022] Preferably, the vacuum degree during the feeding and refining periods should be ≤5Pa. If the vacuum degree is >5Pa due to venting or other reasons, the power should be reduced to ≤300KW in time until the vacuum degree returns to normal. This is beneficial to reduce the gas content in the alloy.

[0023] Preferably, electromagnetic stirring can be performed every 10 minutes during the nitrogen extraction and refining periods, which helps to release gas from the molten steel and reduce component segregation.

[0024] Preferably, appropriately reducing the power during the charging period, i.e. maintaining it at 300-700KW, is beneficial for the raw materials to release gas while melting and to reduce molten steel splashing.

[0025] The present invention has the following beneficial effects:

[0026] 1) This invention provides a method for manufacturing high-purity rare earth weathering bridge steel. Rare earth weathering bridge steel ingots are produced by vacuum induction melting. The raw materials are heated by electromagnetic induction to prevent impurities from being mixed in. Furthermore, there is no need to cover the slag during the smelting process, thus avoiding the risk of slag inclusion.

[0027] 2) This invention provides a method for manufacturing high-purity rare earth weathering bridge steel. The entire smelting and casting process is kept in vacuum to prevent the alloy from absorbing gas in the atmosphere. It can also promote the release of gas and decomposition of inclusions in the raw materials, thereby improving the purity of the ingot.

[0028] 3) This invention provides a method for manufacturing high-purity rare earth weathering bridge steel, wherein the raw materials are all high-purity raw materials, and the steel undergoes pretreatment processes such as baking and rust removal before smelting to further improve its purity;

[0029] 4) This invention provides a method for manufacturing high-purity rare earth weathering bridge steel. Adding rare earth element Ce to molten steel can further degas the steel, improve the morphology of inclusions, reduce the size of inclusions, and improve the quality of molten steel. Fine rare earth inclusions can promote the formation of acicular ferrite, effectively improving the plasticity and corrosion resistance of the alloy.

[0030] 5) This invention provides a method for manufacturing high-purity rare-earth weathering bridge steel, applicable to the production of most bridge steels. Through a series of methods, the gas content in the steel is effectively reduced, thereby reducing the inclusion content, improving the alloy's hot working performance and corrosion resistance, which is beneficial for subsequent rolling, heat treatment, and other processes, achieving a good balance of weather resistance, processing performance, strength, and plasticity. Attached Figure Description

[0031] Figure 1 This is the metallographic structure of the high-purity rare earth weathering bridge steel of Embodiment 1 of the present invention. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0033] Example 1

[0034] This embodiment provides a method for manufacturing high-purity rare-earth weathering bridge steel, comprising the following steps:

[0035] S1. Prepare raw materials: C (high-purity graphite blocks, purity 4N); Si (crystalline silicon blocks, purity ≥98%); Mn (electrolytic manganese flakes, purity 2N); Nb (high-purity niobium blocks, purity 3N); Al (electrolytic aluminum ingots, purity ≥99.7%); Ti (sponge titanium, purity 2N); Cr (high-purity chromium blocks, purity 2N); Ni (nickel beads or nickel plates, purity 3N); Cu (TU1 oxygen-free copper blocks, purity 3N); Mo (molybdenum blocks, purity 2N); Ce (metallic cerium); Fe (iron ingots, purity 2N). Among them, Fe is derusted, and Cr, Mo, Ni, Nb, and Cu are baked in an 80℃ drying oven for 24 hours.

[0036] S2. Impurity Analysis and Preparation: Analyze the impurity content of each raw material and prepare the corresponding raw materials according to the composition ratio. The raw materials by weight percentage are: C: 0.078%, Si: 0.21%, Mn: 1.37%, Nb: 0.030%, Al: 0.035%, Ti: 0.015%, P: 0.010%, S: 0.001%, Cr: 0.45%, Ni: 0.40%, Cu: 0.35%, Mo: 0.10%, rare earth Ce: 0.0010%, with the balance being Fe and unavoidable impurities. The impurities are controlled as follows: P: ≤0.010%, S: ≤0.001%, and Pcm (%) = 0.20, I (%) = 6.22.

[0037] S3. Preliminary Nitrogen Removal in Vacuum Induction Furnace: Before smelting in the vacuum induction furnace, a batch of pure iron has been smelted to purify the crucible. After the vacuum degree reaches 0.5 Pa, Fe is added to the bottom material bucket. Each time, the previous bucket of material is added only after it has basically melted. After the Fe is completely melted, the power is reduced to 300 KW for "preliminary smelting" to remove nitrogen. During this process, the temperature is measured to ensure that the molten steel temperature is 1540℃.

[0038] S4. Vacuum Induction Furnace Primary Charging and Refining: After sampling and analysis confirming a nitrogen content of 30 ppm in the molten steel, C, Ni, Mo, Cu, Nb, Mn, and Cr are added to the molten steel using a charging bucket, and the power is increased to 1000 kW for charging. Once the molten steel is fully melted, the power is further increased to 1200 kW for refining for 30 minutes, during which the temperature of the molten steel should be monitored to ensure it reaches 1570℃. After refining, the power is reduced again to 300 kW to extract nitrogen, during which the temperature of the molten steel should be monitored to ensure it reaches 1540℃.

[0039] S5. Secondary charging and adjustment of the vacuum induction furnace: After sampling and analysis of the molten steel N content, which was found to be 35 ppm, the power was further reduced to 300 kW. After the molten steel formed a crust, Ti and Si were added, and the power was then increased to 500 kW for charging. After the molten steel was completely melted, a sample was taken before the furnace was cleaned for composition analysis, and the charging was adjusted according to the target values.

[0040] S6. Temperature adjustment and Ce addition in vacuum induction furnace: After the composition of molten steel meets the internal control value, the temperature is measured and adjusted to 1580℃. Ce is then added, and finally, vacuum casting with electricity is carried out as soon as possible.

[0041] S7. Cooling to form alloy ingot: Cool the ingot in a vacuum for 180 minutes, and then break the vacuum to obtain rare earth weathering bridge steel alloy ingot.

[0042] Example 2:

[0043] This embodiment provides a method for manufacturing high-purity rare-earth weathering bridge steel, comprising the following steps:

[0044] S1. Prepare raw materials: C (high-purity graphite blocks, purity 4N); Si (crystalline silicon blocks, purity ≥98%); Mn (electrolytic manganese flakes, purity 2N); Nb (high-purity niobium blocks, purity 3N); Al (electrolytic aluminum ingots, purity ≥99.7%); Ti (sponge titanium, purity 2N); Cr (high-purity chromium blocks, purity 2N); Ni (nickel beads or nickel plates, purity 3N); Cu (TU1 oxygen-free copper blocks, purity 3N); Mo (molybdenum blocks, purity 2N); Ce (metallic cerium); H10L (steel ingots); Fe (iron ingots, purity 2N). Among them, Fe and H10L are derusted, and Cr, Mo, Ni, Nb, and Cu are baked in an 80℃ drying oven for 24 hours.

[0045] S2. Impurity Analysis and Preparation: The impurity content of each raw material was analyzed, and the corresponding raw materials were prepared according to the composition ratio. The raw materials by weight percentage were: C: 0.078%, Si: 0.21%, Mn: 1.25%, Nb: 0.025%, Al: 0.040%, Ti: 0.015%, Cr: 0.50%, Ni: 0.45%, Cu: 0.36%, Mo: 0.12%, rare earth Ce: 0.0013%, with the balance being Fe and unavoidable impurities. The impurity control was P: ≤0.010%, S: ≤0.001%, and Pcm (%) = 0.199, I (%) = 6.33. Unlike Example 1, H10L has a higher Cr content. When the Cr content meets the requirements, no additional Cr needs to be added.

[0046] S3. Preliminary Nitrogen Removal in Vacuum Induction Furnace: After the vacuum degree in the vacuum induction furnace is set to 0.1 Pa before smelting, Fe and H10L are added to the feed bucket. Each time a feed bucket is added, the previous bucket of material must be basically melted before adding the next bucket of raw material. After the Fe is completely melted, the power is reduced to 400KW for "preliminary smelting" to remove nitrogen. During this process, electromagnetic stirring is performed every 10 minutes, and the temperature is measured to ensure that the molten steel temperature is 1530℃.

[0047] S4. Vacuum Induction Furnace Primary Charging and Refining: After sampling and analysis confirming a nitrogen content of 20 ppm in the molten steel, C, Ni, Mo, Cu, Nb, and Mn are added to the molten steel using a charging bucket, and the power is increased to 900 kW for charging. Once the molten steel is fully melted, the power is further increased to 1400 kW for refining for 30 minutes, during which electromagnetic stirring is performed every 10 minutes, and the temperature is monitored to ensure the molten steel temperature is 1570℃. After refining, the power is reduced again to 400 kW to extract nitrogen, during which electromagnetic stirring is performed every 10 minutes, and the temperature is monitored to ensure the molten steel temperature is 1530℃.

[0048] S5. Secondary charging and adjustment of the vacuum induction furnace: After sampling and analysis of the molten steel, the nitrogen content was found to be 20 ppm. The power was further reduced to 300 kW. After the molten steel formed a crust, Ti and Si were added, and the power was increased to 400 kW for charging. After the molten steel was completely melted, a sample was taken before the furnace was cleaned for composition analysis, and the charging was adjusted according to the target values.

[0049] S6. Temperature adjustment and Ce addition in vacuum induction furnace: After the composition of molten steel meets the internal control value, the temperature is measured and adjusted to 1580℃. Ce is then added, and finally, vacuum casting with electricity is carried out as soon as possible.

[0050] S7. Cooling to form alloy ingot: Cool the ingot in a vacuum for 240 minutes, and then break the vacuum to obtain rare earth weathering bridge steel alloy ingot.

[0051] Under the conditions of tempering temperature of 400℃ and tempering time of 45min, the tempering tensile properties of Example 1, Example 2 and Comparative Example 1 (using conventional Q420qNH weathering bridge steel products) were compared, as shown in Table 1:

[0052] Table 1 Comparison of the tempered tensile properties of Examples 1, 2 and Comparative Example 1

[0053] Example 1 596 711 0.84 30.5 Example 2 602 720 0.84 30.8 Comparative Example 1 486 624 0.78 28.5

[0054] Furthermore, the atmospheric corrosion resistance of Examples 1, 2, and Comparative Example 1 is compared, as shown in Table 2:

[0055] Table 2 Comparison of atmospheric corrosion resistance of Examples 1, 2 and Comparative Example 1

[0056] Example 1 34.5 Example 2 36.2 Comparative Example 1 43.3

[0057] The results in Tables 1 and 2 show that, compared with the weather-resistant bridge steel prepared in the comparative examples, the bridge steel prepared in Examples 1 and 2 of this invention has a higher yield strength R0. p0.2 and tensile strength R m The value is higher, and the yield strength ratio R is higher. e / R mIt has a larger elongation (A) and a slower corrosion rate, resulting in a significant improvement in overall performance. Meanwhile, from... Figure 1 It can also be seen that the metallographic structure of the bridge steel surface in Example 1 is more uniform and denser than that of ordinary bridge steel, with a better appearance, thus better meeting the requirements of bridge steel for operational strength and atmospheric corrosion resistance.

[0058] It should be noted that the above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Equivalent modifications made based on the above embodiments are all within the scope of protection of the present invention.

Claims

1. A method for manufacturing high-purity rare-earth weathering bridge steel, characterized in that, Includes the following steps: S1. Prepare raw materials: C, Si, Mn, Nb, Al, Ti, Cr, Ni, Cu, Mo, Ce and Fe. All raw materials should be high-purity. S2. Impurity Analysis and Preparation: Analyze the impurity content of each raw material and prepare the corresponding raw materials according to the composition ratio. In step S2, the chemical composition of the raw materials by weight percentage is as follows: C: 0.05-0.08%, Si: 0.10-0.30%, Mn: 1.10-1.40%, Nb: 0.010-0.035%, Al: 0.020-0.050%, Ti: 0.010-0.020%, Cr: 0.40-0.50%, Ni: 0.30-0.50%, Cu: 0.30-0.40%, Mo: 0.05-0.15%, rare earth Ce: 0.0005-0.0015%, with the balance being Fe and unavoidable impurities. The impurities are controlled as follows: P: ≤0.010%, S: ≤0.001%, and Pcm (%) ≤0.22, I (%) ≥6.

2. S3. Initial smelting and nitrogen removal in vacuum induction furnace: After the vacuum degree in the vacuum induction furnace is lower than 1Pa before smelting, add Fe to the bottom material bucket. Each time the material is added, wait for the previous bucket to melt before adding the next bucket of raw material. After the Fe is melted, reduce the power to ≤500KW and carry out initial smelting and nitrogen removal. During this period, the temperature should be measured to ensure that the temperature of the molten steel is 1530-1560℃. S4. Vacuum Induction Furnace Primary Charging and Refining: After sampling and analysis, the N content in the molten steel is found to be below 40ppm. C, Ni, Mo, Cu, Nb, Mn, and Cr are added to the molten steel using a charging bucket, and the power is increased to ≤1000KW for charging. After the molten steel is cleared, the power is further increased to 1200-1500KW for refining. The refining time is 30 minutes. During this time, the temperature of the molten steel should be measured to ensure that the temperature is 1550-1590℃. After refining, the power is reduced to ≤500KW again to extract N. During this time, the temperature of the molten steel should be measured to ensure that the temperature is 1530-1560℃. S5. Secondary charging and charging adjustment of vacuum induction furnace: After sampling and analysis, the N content of the molten steel is lower than 40ppm, and the power is further reduced to ≤300KW. After the molten steel forms a shell, Ti and Si are added, and the power is increased to 300-700KW for charging. After the molten steel is melted and cleared, a sample is taken before the furnace for composition analysis, and the charging is adjusted according to the target value. S6. Temperature adjustment and Ce addition in vacuum induction furnace: After the composition of molten steel meets the internal control value, the temperature is measured and adjusted to 1560-1590℃. Ce is then added, and finally, the steel is poured out under vacuum with electricity. S7. Cooling to form alloy ingot: Cool the ingot in a vacuum for more than 180 minutes, and then break the vacuum to obtain rare earth weathering bridge steel alloy ingot.

2. The method for manufacturing high-purity rare-earth weathering bridge steel according to claim 1, characterized in that: In step S1, C is a high-purity graphite block with a purity of 4N, Si is a crystalline silicon block with a purity of ≥98%, Mn is an electrolytic manganese sheet with a purity of 2N, Nb is a high-purity niobium block with a purity of 3N, Al is an electrolytic aluminum ingot with a purity of ≥99.7%, Ti is sponge titanium with a purity of 2N, Cr is a high-purity chromium block with a purity of 2N, Ni is a nickel bead or nickel plate with a purity of 3N, Cu is a TU1 oxygen-free copper block with a purity of 3N, Mo is a molybdenum block with a purity of 2N, Ce is high-purity metallic cerium, and Fe is an iron ingot with a purity of 2N.

3. The method for manufacturing high-purity rare-earth weathering bridge steel according to claim 1, characterized in that: In step S1, the Fe needs to have its surface oxide layer removed using a roller derusting machine before use.

4. The method for manufacturing high-purity rare-earth weathering bridge steel according to claim 1, characterized in that: In step S1, the Cr, Mo, Ni, Nb, and Cu are all baked in a drying oven at 40-80℃ for more than 24 hours before use to remove moisture adhering to the surface of the raw materials.

5. The method for manufacturing high-purity rare-earth weathering bridge steel according to claim 1, characterized in that: In step S1, the Fe is replaced with H10L or high-quality bridge steel scrap or other high-purity raw material steel.

6. The method for manufacturing high-purity rare-earth weathering bridge steel according to claim 1, characterized in that: In step S3, a small amount of Fe raw material is reserved during the feeding process to facilitate subsequent adjustments to the molten steel composition.

7. The method for manufacturing high-purity rare-earth weathering bridge steel according to claim 1, characterized in that: The vacuum level during the feeding and refining periods should be ≤5Pa. If the vacuum level is >5Pa, reduce the power to ≤300KW in time until the vacuum level returns to normal.

8. The method for manufacturing high-purity rare-earth weathering bridge steel according to claim 1, characterized in that: Electromagnetic stirring is performed every 10 minutes during the nitrogen extraction and refining processes to release gas from the molten steel and reduce component segregation.

9. The method for manufacturing high-purity rare-earth weathering bridge steel according to claim 1, characterized in that: Maintaining the power during the charging period at 300-700KW allows the raw materials to release gas while melting, and reduces molten steel splashing.

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