Method for improving corrosion resistance of frozen earth steel bar

Abstract

The invention discloses a method for improving corrosion resistance of frozen earth steel bars, and relates to the technical field of steel metallurgy and surface protection. According to the method, by optimizing components of a low-carbon Cu-Ni-Cr-Sb-rare earth composite alloy system and combining an LF-VD refining purification and full-protection continuous casting process, the content of oxygen, sulfur and hydrogen in steel is remarkably reduced; in the controlled rolling and controlled cooling process, segmented accelerated cooling is adopted to refine grains and inhibit segregation; and then a Cu-Ni-Sb composite enrichment layer is formed through surface diffusion treatment at the temperature of 660-690 DEG C and tempering at the temperature of 450-480 DEG C, secondary passivation is conducted in a neutral phosphate-rare earth silicate system passivation solution, and a compact composite oxide film is obtained. According to the process, the impact energy of the reinforcing steel bar at the temperature of 40 DEG C can be improved by 30% or above, the salt spray corrosion rate is smaller than or equal to 0.012 g / m.h, the corrosion resistance in the frozen soil environment is remarkably improved, and the service life in the frozen soil environment is remarkably prolonged. The technological process is stable and suitable for industrial popularization.

Description

Technical Field

[0001] This invention relates to the field of steel metallurgy and surface protection technology, and in particular to a method for improving the corrosion resistance of steel bars in frozen soil. Background Technology

[0002] In cold and permafrost environments, reinforced concrete structures are subject to long-term chloride ion erosion, low-temperature embrittlement, and freeze-thaw cycles, which easily leads to steel corrosion and cracking, resulting in a shortened structural lifespan. Existing anti-corrosion technologies mainly include surface coating, galvanizing, and alloying protection, but these methods suffer from problems such as coating peeling, galvanic corrosion of the plating, and high alloy costs.

[0003] In recent years, research has shown that a dense, alloy-rich protective layer can be formed on the surface of reinforcing steel bars through rational alloy element design and microstructure control, significantly improving corrosion resistance. However, current corrosion-resistant reinforcing steel bars mostly use Cu-Cr-Ni or P-Mo composite systems, which still struggle to maintain high toughness and low corrosion rates below −40°C. Therefore, developing a method for preparing reinforcing steel bars that still exhibit excellent corrosion resistance, low-temperature toughness, and service stability in frozen soil environments has significant engineering application value. Summary of the Invention

[0004] The purpose of this invention is to provide a method for improving the corrosion resistance of steel bars in frozen soil. By optimizing the chemical composition of the steel bars, controlling the rolling and cooling process, and the surface densification treatment, a composite passivation layer rich in Ni, Cu, Sb, and Cr is formed on the surface of the steel bars, while maintaining excellent mechanical properties and low-temperature impact toughness, thereby significantly improving its corrosion resistance in freeze-thaw and chloride salt environments.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a method for improving the corrosion resistance of reinforcing steel bars in frozen soil, comprising:

[0007] (1) Ingredient design and raw material preparation:

[0008] The chemical system is mainly based on low-carbon Cu-Ni-Cr-Sb composite strengthening, supplemented by trace rare earth element purification. The chemical composition by mass fraction is controlled as follows: C 0.10~0.16%, Si 0.20~0.35%, Mn 1.0~1.3%, Cr 0.4~0.6%, Ni 0.4~0.7%, Cu 0.3~0.5%, Sb 0.05~0.10%, Nb 0.02~0.05%, V 0.03~0.06%, rare earth Ce 0.02~0.05%, P≤0.015%, S≤0.008%, with the balance being Fe and impurities. The raw materials are all made from high-purity molten iron and low-phosphorus, low-sulfur scrap steel, and the C content fluctuation at the furnace is controlled to be ≤0.02%.

[0009] (2) Smelting and refining purification:

[0010] The process involves converter smelting with a final carbon content of 0.08–0.10% and a tapping temperature of 1650–1670℃. After deep deoxidation with the addition of aluminum wire, the slag is transferred to LF refining, with the slag basicity controlled at 3.0–3.5, mainly consisting of the CaO-Al2O3-CaF2 system.

[0011] Ce-Si-Fe alloy was added at the end of the LF process to stabilize the rare earth Ce content at 0.02-0.05%, while deep desulfurization was carried out to achieve [S] ≤ 0.005%;

[0012] Subsequently, the molten steel is subjected to VD vacuum treatment for 15–20 min, with a vacuum degree ≤70 Pa, ensuring [H] ≤2 ppm and [O] ≤0.002%, to obtain high-purity molten steel.

[0013] (3) Continuous casting and billet heating:

[0014] The fully protected continuous casting process is adopted, with the superheat of the crystallizer controlled at 30±5℃, the secondary cooling water flow rate at 0.35~0.45L / kg, and the casting speed at 0.8~0.9m / min;

[0015] After cleaning the surface of the billet, heat it at 1180-1220℃ for 90-120 minutes to ensure a uniform microstructure without segregation.

[0016] (4) Controlled rolling and controlled cooling process

[0017] Rough rolling stage: temperature 950~980℃, reduction rate ≥60%;

[0018] Finishing rolling stage: The final rolling temperature is controlled at 830-860℃, and the cumulative deformation is ≥70%.

[0019] Immediately after rolling, a segmented accelerated cooling method is used to control the cooling rate:

[0020] Zone 1 830~860℃→650℃: Cooling rate 30±10℃ / s, preferably 30℃ / s;

[0021] Second zone 650→400℃: cooling rate 15±5℃ / s, preferably 15℃ / s;

[0022] Zone 3 400→200℃: Cooling rate 5±2℃ / s, preferably 5℃ / s;

[0023] After cooling is complete, air cooling should be performed to prevent excessive hardening of the tissue.

[0024] (5) Surface alloy diffusion and heat treatment

[0025] After rolling, the steel bars are fed into a continuous furnace for surface diffusion heat treatment.

[0026] The diffusion temperature is controlled at 660-690℃ and the holding time is 30-45min. An alloy enrichment layer with a thickness of 0.3-0.8μm is formed through the short-range migration of Cu, Ni and Sb elements on the surface, so that the surface structure is rich in Ni, Cu and Sb, and the density of the oxide film is improved.

[0027] Subsequently, a low-temperature tempering treatment was performed at 450–480℃ for 2 hours to release residual stress and promote the nucleation and growth of the composite passivation film.

[0028] (6) Surface passivation and densification treatment

[0029] Pickling in 10% HNO3 + 0.5% HF solution for 10-20 min removes the oxide scale. Then, it is treated in a phosphate-silicate passivation solution with a pH of 6.5-7.0 for 15-25 min, followed by secondary passivation in a rare earth activation solution containing 0.1% CeO2 for 8-15 min. Finally, a Cu2O-Cr2O3-Sb2O5-rare earth oxide composite film is formed, which significantly reduces the corrosion rate.

[0030] Furthermore, it also includes: (7) Testing and performance verification

[0031] Samples were taken for chemical composition, mechanical properties, low-temperature impact and salt spray corrosion tests; mechanical property tests were performed in accordance with GB / T228.1, low-temperature impact tests were performed in accordance with GB / T 229 at −40℃, and salt spray tests were performed for 1000h.

[0032] Furthermore, the chemical composition by mass fraction is controlled as follows: C 0.13%, Si 0.30%, Mn 1.20%, Cr 0.50%, Ni 0.55%, Cu 0.45%, Sb 0.07%, Nb 0.03%, V 0.05%, Ce 0.03%, P 0.010%, S 0.004%, with the balance being Fe and impurities.

[0033] Furthermore, the chemical composition by mass fraction is controlled as follows: C 0.11%, Si 0.28%, Mn 1.25%, Cr 0.45%, Ni 0.60%, Cu 0.50%, Sb 0.09%, Nb 0.04%, V 0.06%, La 0.02%, P 0.010%, S 0.005%, with the balance being Fe and impurities.

[0034] Furthermore, the chemical composition by mass fraction is controlled as follows: C 0.14%, Si 0.33%, Mn 1.18%, Cr 0.55%, Ni 0.65%, Cu 0.40%, Sb 0.08%, Nb 0.02%, V 0.04%, Ce 0.02%, P 0.012%, S 0.004%, with the balance being Fe and impurities.

[0035] Further, smelting and refining:

[0036] The converter final temperature is 1660℃. After tapping, 0.8 kg / t of aluminum is added for deoxidation. The basicity of the LF refining slag is 3.2. 0.8 kg / t of Ce-Si-Fe alloy is added. The VD vacuum treatment lasts for 18 min at a vacuum degree of 60 Pa.

[0037] Continuous casting and heating:

[0038] Continuous casting speed: 0.85 m / min; secondary cooling water flow rate: 0.40 L / kg; heating temperature: 1200℃; holding time: 110 min.

[0039] Controlled rolling and controlled cooling:

[0040] The roughing rolling final temperature is 970℃, the finishing rolling final temperature is 840℃, and the ACC cooling is divided into three stages: 30℃ / s→15℃ / s→6℃ / s.

[0041] Surface diffusion and tempering:

[0042] Diffusion heat treatment temperature 670℃×40min, tempering temperature 460℃×2h;

[0043] Surface passivation:

[0044] After pickling, the sample was treated in a phosphate passivation solution for 20 minutes, and then passed through a CeO2 rare earth solution for a second passivation for 10 minutes.

[0045] Furthermore, smelting conditions:

[0046] The final temperature was 1655℃, the basicity of the LF residue was 3.0, and the VD vacuum was maintained for 16 min.

[0047] Rolling process:

[0048] Heating temperature 1185℃, finishing rolling temperature 850℃, ACC cooling in three stages: 20℃ / s→15℃ / s→6℃ / s;

[0049] Diffusion and tempering:

[0050] Diffusion temperature 680℃×35min, tempering 470℃×2h.

[0051] Furthermore, the process conditions:

[0052] Heating temperature 1210℃, holding temperature 100min; finishing rolling temperature 855℃, ACC cooling in three stages: 25℃ / s→15℃ / s→6℃ / s; diffusion heat treatment temperature 685℃×45min, tempering temperature 475℃×2h.

[0053] Furthermore, the manufactured steel bars have a yield strength of 640–680 MPa, a tensile strength of 780–820 MPa, an impact absorption energy of ≥90 J at −40℃, and a salt spray corrosion rate of ≤0.012 g / m²·h.

[0054] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0055] (1) Significantly improve the corrosion resistance of steel bars: By introducing a Cu-Ni-Sb-Cr composite system into the steel and combining it with rare earth purification treatment, a dense and continuous Cu2O·Cr2O3·Sb2O5 composite passivation film is formed on the surface of the steel bars. The film thickness is about 0.5 to 1.0 μm, the resistivity is increased by 1.5 times, the salt spray corrosion rate is reduced by 40% to 60%, effectively blocking the penetration of chloride ions and moisture, and significantly extending the service life of steel bars in freeze-thaw environments. (2) Balance high strength and low temperature toughness: By optimizing the microstructure through controlled rolling and cooling and low temperature tempering processes, the matrix forms a refined tempered sorbite + lower bainite composite structure. The impact absorption energy at −40℃ is increased from 60J of traditional steel bars to more than 90J, and the yield strength is maintained in the range of 640 to 680MPa, achieving a balance between high strength and high toughness. (3) Rare earth purification effect enhances interfacial bonding: The introduction of rare earth elements (Ce, La) can adsorb inclusions and purify molten steel, and promote the formation of dispersed CeAlO3 and Ce2O3 particles as nucleation cores, improving the purity of grain boundaries and the adhesion of the film, making the corrosion products more stable and uniform. (4) Excellent resistance to chloride salt corrosion and crack resistance: After the steel bars of this invention were immersed in 3.5% NaCl solution for 2000 hours, the corrosion depth was reduced by about 50%, the rust layer was firmly bonded and there was no peeling; after 200 freeze-thaw cycles at −40℃, there was no obvious cracking on the surface, and the overall durability performance was far superior to the existing technology. Detailed Implementation

[0056] The present invention will be further described below with reference to the embodiments.

[0057] The method for improving the corrosion resistance of steel bars in frozen soil provided by this invention includes the following main steps:

[0058] (1) Ingredient design and raw material preparation:

[0059] Based on the service characteristics in permafrost environments, a chemical system primarily based on low-carbon, Cu-Ni-Cr-Sb composite strengthening was designed, supplemented by trace rare earth element purification. The chemical composition (mass fraction %) is controlled as follows: C 0.10–0.16%, Si 0.20–0.35%, Mn 1.0–1.3%, Cr 0.4–0.6%, Ni 0.4–0.7%, Cu 0.3–0.5%, Sb 0.05–0.10%, Nb 0.02–0.05%, V 0.03–0.06%, rare earth Ce 0.02–0.05%, P≤0.015%, S≤0.008%, with the balance being Fe. High-purity molten iron and low-phosphorus, low-sulfur scrap steel are used as raw materials, and the C content fluctuation upon entering the furnace is controlled to ≤0.02%.

[0060] (2) Smelting and refining purification:

[0061] The smelting process is carried out in a 120t converter with a final carbon content of 0.08-0.10% and a tapping temperature of 1650-1670℃. After deep deoxidation with aluminum wire, the slag is transferred to LF refining, with the slag basicity controlled at 3.0-3.5, mainly consisting of the CaO-Al2O3-CaF2 system.

[0062] Ce-Si-Fe alloy was added at the end of the LF process to stabilize the rare earth Ce content at 0.02-0.05%, while deep desulfurization ([S]≤0.005%) was carried out.

[0063] Subsequently, the molten steel is subjected to VD vacuum treatment for 15–20 minutes, with a vacuum degree ≤70Pa, ensuring [H] ≤2ppm and [O] ≤0.002%, to obtain high-purity molten steel.

[0064] (3) Continuous casting and billet heating:

[0065] The process employs a fully protected continuous casting method, with the crystallizer superheat controlled at 30±5℃, secondary cooling water flow rate at 0.35~0.45L / kg, and casting speed at 0.8~0.9m / min.

[0066] After cleaning the surface of the billet, heat it at 1180-1220℃ for 90-120 minutes to ensure uniform microstructure without segregation.

[0067] (4) Controlled rolling and controlled cooling process

[0068] Rough rolling stage: temperature 950~980℃, reduction rate ≥60%;

[0069] Finishing rolling stage: The final rolling temperature is controlled at 830-860℃, and the cumulative deformation is ≥70%.

[0070] Immediately after rolling, the cooling rate is controlled using segmented accelerated cooling (ACC) method:

[0071] Zone 1 830~860℃→650℃: Cooling rate 30±10℃ / s;

[0072] Second zone 650→400℃: Cooling rate 15±5℃ / s;

[0073] Zone 3 400→200℃: Cooling rate 5±2℃ / s;

[0074] After cooling is complete, air cooling should be performed to prevent excessive hardening of the tissue.

[0075] (5) Surface alloy diffusion and heat treatment

[0076] After rolling, the steel bars are fed into a continuous furnace for surface diffusion heat treatment.

[0077] The diffusion temperature is controlled at 660–690℃ and the holding time is 30–45 min. Through the short-range migration of Cu, Ni, and Sb elements in the surface layer, an alloy enriched layer (thickness 0.3–0.8 μm) is formed, making the surface structure rich in Ni, Cu, and Sb, and improving the density of the oxide film.

[0078] Subsequently, a low-temperature tempering treatment was performed at 450–480℃ for 2 hours to release residual stress and promote the nucleation and growth of the composite passivation film.

[0079] (6) Surface passivation and densification treatment

[0080] After acid washing to remove the oxide scale (acid washing in 10% HNO3 + 0.5% HF solution for 15 min), it is treated in a phosphate-silicate passivation solution with pH 6.5-7.0 for 20 min, and then subjected to a second passivation in a rare earth activation solution containing 0.1% CeO2 for 10 min, finally forming a Cu2O-Cr2O3-Sb2O5-rare earth oxide composite film.

[0081] The film layer is firmly bonded, the electrochemical impedance increases by 1.5 times, and the corrosion rate is significantly reduced.

[0082] (7) Testing and performance verification

[0083] Samples were taken for chemical composition, mechanical properties, low-temperature impact, and salt spray corrosion tests. Mechanical property tests were performed according to GB / T228.1, low-temperature impact tests were performed according to GB / T 229 at −40℃, and salt spray tests were conducted for 1000 hours.

[0084] This invention improves the inclusion morphology and interface bonding through the purification effect of rare earth elements, while Cu, Ni, and Sb form a stable composite oxide film, thereby increasing the resistivity of the passivation film.

[0085] Controlled rolling and cooling processes refine grains and reduce retained austenite, resulting in high toughness even at low temperatures. Diffusion and passivation treatments create a dense protective layer on the surface, preventing chloride ion penetration and stress corrosion.

[0086] Example 1:

[0087] Selected chemical components (mass fraction %):

[0088] C 0.13, Si 0.30, Mn 1.20, Cr 0.50, Ni 0.55, Cu 0.45, Sb 0.07, Nb 0.03, V 0.05, Ce 0.03, P 0.010, S 0.004, balance Fe and impurities.

[0089] Smelting and refining:

[0090] The converter final temperature is 1660℃. After tapping, 0.8 kg / t of aluminum is added for deoxidation. The basicity of the LF refining slag is 3.2. 0.8 kg / t of Ce-Si-Fe alloy is added. The VD vacuum treatment lasts for 18 min with a vacuum degree of 60 Pa.

[0091] Continuous casting and heating:

[0092] The continuous casting speed is 0.85 m / min, the secondary cooling water flow rate is 0.40 L / kg, the heating temperature is 1200℃, and the holding time is 110 min.

[0093] Controlled rolling and controlled cooling:

[0094] The final temperature of rough rolling is 970℃, and the final temperature of finish rolling is 840℃; ACC cooling is divided into three stages: 30℃ / s→15℃ / s→6℃ / s.

[0095] Surface diffusion and tempering:

[0096] The diffusion heat treatment temperature was 670℃ for 40 min, and the tempering temperature was 460℃ for 2 h.

[0097] Surface passivation:

[0098] After pickling, the sample was treated in a phosphate passivation solution for 20 minutes, and then passed through a CeO2 rare earth solution for a second passivation for 10 minutes.

[0099] result:

[0100] The impact absorption energy at -40℃ is 88J, the yield strength is 655MPa, and the salt spray corrosion rate is 0.012g / m²·h.

[0101] Example 2:

[0102] Selected chemical components (mass fraction %):

[0103] C 0.11, Si 0.28, Mn 1.25, Cr 0.45, Ni 0.60, Cu 0.50, Sb 0.09, Nb 0.04, V 0.06, La 0.02, P 0.010, S 0.005, balance Fe and impurities.

[0104] Smelting conditions:

[0105] The final temperature was 1655℃, the basicity of the LF residue was 3.0, and the vacuum temperature was 16 min.

[0106] Rolling process:

[0107] Heating temperature 1185℃, finishing rolling temperature 850℃; ACC cooling in three stages: 20℃ / s→15℃ / s→6℃ / s.

[0108] Diffusion and tempering:

[0109] Diffusion temperature 680℃×35min, tempering 470℃×2h.

[0110] result:

[0111] Impact energy at -40℃ is 92J, yield strength is 660MPa, corrosion rate is 0.011g / m²·h, and the surface film is dense and intact.

[0112] Example 3:

[0113] Selected chemical components (mass fraction %):

[0114] C 0.14, Si 0.33, Mn 1.18, Cr 0.55, Ni 0.65, Cu 0.40, Sb 0.08, Nb 0.02, V 0.04, Ce 0.02, P 0.012, S 0.004, balance Fe and impurities.

[0115] Process conditions:

[0116] Heating temperature 1210℃, holding temperature 100min; finishing rolling temperature 855℃; ACC cooling in three stages: 25℃ / s→15℃ / s→6℃ / s; diffusion heat treatment temperature 685℃×45min, tempering temperature 475℃×2h.

[0117] result:

[0118] Yield strength 668MPa, tensile strength 805MPa, impact energy at −40℃ 95J, salt spray corrosion rate 0.010g / m²·h, and the surface film is uniform and firmly bonded.

[0119] Comparative Example 1:

[0120] The composition is the same as in Example 1, but without the addition of Sb; the controlled rolling, cooling, and heat treatment are the same.

[0121] Results: Yield strength 645 MPa, impact energy 75 J, corrosion rate 0.017 g / m²·h. The surface film has many pores and is easily peeled off.

[0122] Comparative Example 2:

[0123] The components were modified by removing Ni and Cu elements; otherwise, they were the same as in Example 1.

[0124] Results: Impact energy at −40℃ was 68 J, and corrosion rate was 0.021 g / m²·h. The surface film was porous, and the resistivity of the passivation film decreased by 30%.

[0125] Comparative Example 3:

[0126] It adopts a conventional hot rolling + air cooling process, without diffusion and tempering treatment.

[0127] Results: Yield strength 630 MPa, impact energy 65 J, corrosion rate 0.026 g / m²·h. Grains are coarse, and the rust layer shows obvious delamination and peeling.

[0128] Table 1 Chemical composition of each example and comparative example

[0129] Sample number C Si Mn Cr Ni Cu Sb Nb V Rare Earth Ce Example 1 0.13 0.30 1.20 0.50 0.55 0.45 0.07 0.03 0.05 Ce0.03 Example 2 0.11 0.28 1.25 0.45 0.60 0.50 0.09 0.04 0.06 La0.02 Example 3 0.14 0.33 1.18 0.55 0.65 0.40 0.08 0.02 0.04 Ce0.02 Comparative Example 1 0.13 0.30 1.20 0.50 0.55 0.45 — 0.03 0.05 — Comparative Example 2 0.13 0.30 1.20 0.50 — — 0.07 0.03 0.05 — Comparative Example 3 0.13 0.30 1.20 0.50 0.55 0.45 0.07 0.03 0.05 —

[0130] Table 2 Process parameters for each embodiment and comparative example

[0131] Sample number Heating temperature (°C) Final rolling temperature (°C) Cooling rate (°C / s) Diffusion heat treatment (°C × min) Tempering temperature (°C × h) Example 1 1200 840 30℃ / s→15℃ / s→6℃ / s 670×40 460×2 Example 2 1185 850 20℃ / s→15℃ / s→6℃ / s 680×35 470×2 Example 3 1210 855 25℃ / s→15℃ / s→6℃ / s 685×45 475×2 Comparative Example 1 1200 840 30℃ / s→15℃ / s→6℃ / s 670×40 460×2 Comparative Example 2 1200 840 30℃ / s→15℃ / s→6℃ / s 670×40 460×2 Comparative Example 3 1200 840 air cooling none none

[0132] Table 3 Performance of each embodiment and comparative example

[0133] Sample number Yield strength (MPa) Tensile strength (MPa) Impact energy at -40℃ (J) Corrosion rate (g / m²·h) Rust layer characteristics Example 1 655 790 90 0.012 Dense and uniform Example 2 660 800 92 0.011 Dense and crack-free Example 3 668 805 95 0.010 Strong bond Comparative Example 1 645 770 75 0.017 Porous and prone to peeling Comparative Example 2 640 760 68 0.021 loose Comparative Example 3 630 755 65 0.026 Layered peeling

[0134] As can be seen from the above embodiments and comparative examples, the Cu-Ni-Sb-Cr-rare earth synergistic design and controlled rolling and cooling-diffusion-passivation composite process adopted in this invention can significantly improve the corrosion resistance and low-temperature toughness of frozen soil steel bars, reduce the corrosion rate by about 50%, and increase the impact energy at −40℃ by more than 25J. The process is stable, highly repeatable, and has significant engineering application and economic promotion value.

[0135] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for improving the corrosion resistance of reinforcing steel bars in frozen soil, characterized in that: include: (1) Ingredient design and raw material preparation: A chemical system primarily based on low carbon and Cu-Ni-Cr-Sb composite reinforcement, supplemented by trace rare earth element purification. The chemical composition by mass fraction is controlled as follows: C 0.10~0.16%, Si 0.20~0.35%, Mn 1.0~1.3%, Cr 0.4~0.6%, Ni 0.4~0.7%, Cu 0.3~0.5%, Sb 0.05~0.10%, Nb 0.02~0.05%, V 0.03~0.06%, rare earth Ce 0.02~0.05%, P≤0.015%, S≤0.008%, with the balance being Fe and impurities. The raw materials are all made from high-purity molten iron and low-phosphorus, low-sulfur scrap steel, and the C content fluctuation upon entering the furnace is controlled to be ≤0.02%. (2) Smelting and refining purification: The process involves converter smelting with a final carbon content of 0.08–0.10% and a tapping temperature of 1650–1670℃. After deep deoxidation with the addition of aluminum wire, the slag is transferred to LF refining, with the slag basicity controlled at 3.0–3.5, mainly consisting of the CaO-Al2O3-CaF2 system. Ce-Si-Fe alloy was added at the end of the LF process to stabilize the rare earth Ce content at 0.02-0.05%, while deep desulfurization was carried out to achieve [S] ≤ 0.005%; Subsequently, the molten steel is subjected to VD vacuum treatment for 15–20 min, with a vacuum degree ≤70 Pa, ensuring [H] ≤2 ppm and [O] ≤0.002%, to obtain high-purity molten steel. (3) Continuous casting and billet heating: The process employs a fully protected continuous casting method, with the superheat of the crystallizer controlled at 30±5℃, the secondary cooling water flow rate at 0.35~0.45L / kg, and the casting speed at 0.8~0.9m / min. After cleaning the surface of the billet, heat it at 1180-1220℃ for 90-120 minutes to ensure a uniform microstructure without segregation. (4) Controlled rolling and controlled cooling process Rough rolling stage: temperature 950~980℃, reduction rate ≥60%; Finishing rolling stage: The final rolling temperature is controlled at 830-860℃, and the cumulative deformation is ≥70%. Immediately after rolling, a segmented accelerated cooling method is used to control the cooling rate: Zone 1 830~860℃→650℃: Cooling rate 30±10℃ / s; Second zone 650→400℃: Cooling rate 15±5℃ / s; Zone 3 400→200℃: Cooling rate 5±2℃ / s; After cooling is complete, air cooling should be performed to prevent excessive hardening of the tissue. (5) Surface alloy diffusion and heat treatment After rolling, the steel bars are placed in a continuous furnace for surface diffusion heat treatment. The diffusion temperature is controlled at 660-690℃ and the holding time is 30-45min. An alloy enrichment layer with a thickness of 0.3-0.8μm is formed through the short-range migration of Cu, Ni and Sb elements on the surface, so that the surface structure is rich in Ni, Cu and Sb, and the density of the oxide film is improved. Subsequently, a low-temperature tempering treatment was performed at 450–480℃ for 2 hours to release residual stress and promote the nucleation and growth of the composite passivation film. (6) Surface passivation and densification treatment Pickling in 10% HNO3 + 0.5% HF solution for 10-20 min removes the oxide scale. Then, it is treated in a phosphate-silicate passivation solution with a pH of 6.5-7.0 for 15-25 min, followed by secondary passivation in a rare earth activation solution containing 0.1% CeO2 for 8-15 min. Finally, a Cu2O-Cr2O3-Sb2O5-rare earth oxide composite film is formed, which significantly reduces the corrosion rate.

2. The method for improving the corrosion resistance of steel reinforcement in frozen soil according to claim 1, characterized in that: Also includes: (7) Testing and performance verification Samples were taken for chemical composition, mechanical properties, low-temperature impact and salt spray corrosion tests; mechanical property tests were performed in accordance with GB / T 228.1, low-temperature impact tests were performed in accordance with GB / T 229 at −40℃, and salt spray tests were performed for 1000h.

3. The method for improving the corrosion resistance of steel reinforcement in frozen soil according to claim 1, characterized in that: The chemical composition by mass fraction is controlled as follows: C 0.13%, Si 0.30%, Mn 1.20%, Cr 0.50%, Ni 0.55%, Cu 0.45%, Sb 0.07%, Nb 0.03%, V 0.05%, Ce 0.03%, P 0.010%, S 0.004%, with the balance being Fe and impurities.

4. The method for improving the corrosion resistance of steel reinforcement in frozen soil according to claim 1, characterized in that: The chemical composition by mass fraction is controlled as follows: C 0.11%, Si 0.28%, Mn 1.25%, Cr 0.45%, Ni 0.60%, Cu 0.50%, Sb 0.09%, Nb 0.04%, V 0.06%, La 0.02%, P 0.010%, S 0.005%, with the balance being Fe and impurities.

5. The method for improving the corrosion resistance of steel reinforcement in frozen soil according to claim 1, characterized in that: The chemical composition by mass fraction is controlled as follows: C 0.14%, Si 0.33%, Mn 1.18%, Cr 0.55%, Ni 0.65%, Cu 0.40%, Sb 0.08%, Nb 0.02%, V 0.04%, Ce 0.02%, P 0.012%, S 0.004%, with the balance being Fe and impurities.

6. The method for improving the corrosion resistance of steel reinforcement in frozen soil according to claim 3, characterized in that: Smelting and refining: The converter final temperature is 1660℃. After tapping, 0.8 kg / t of aluminum is added for deoxidation. The basicity of the LF refining slag is 3.

2. 0.8 kg / t of Ce-Si-Fe alloy is added. The VD vacuum treatment lasts for 18 minutes with a vacuum degree of 60 Pa. Continuous casting and heating: Continuous casting speed: 0.85 m / min; secondary cooling water flow rate: 0.40 L / kg; heating temperature: 1200℃; holding time: 110 min. Controlled rolling and controlled cooling: The roughing rolling final temperature is 970℃, the finishing rolling final temperature is 840℃, and the ACC cooling is divided into three stages: 30℃ / s→15℃ / s→6℃ / s. Surface diffusion and tempering: Diffusion heat treatment temperature 670℃×40min, tempering temperature 460℃×2h; Surface passivation: After pickling, the sample was treated in a phosphate passivation solution for 20 minutes, and then passed through a CeO2 rare earth solution for a second passivation for 10 minutes.

7. The method for improving the corrosion resistance of steel reinforcement in frozen soil according to claim 4, characterized in that: Smelting conditions: The final temperature was 1655℃, the basicity of the LF residue was 3.0, and the VD vacuum was maintained for 16 min. Rolling process: Heating temperature 1185℃, finishing rolling temperature 850℃, ACC cooling in three stages: 20℃ / s→15℃ / s→6℃ / s; Diffusion and tempering: Diffusion temperature 680℃×35min, tempering 470℃×2h.

8. The method for improving the corrosion resistance of steel reinforcement in frozen soil according to claim 4, characterized in that: Heating temperature 1210℃, holding temperature 100min; finishing rolling temperature 855℃, ACC cooling in three stages: 25℃ / s→15℃ / s→6℃ / s; diffusion heat treatment temperature 685℃×45min, tempering temperature 475℃×2h.

9. The method for improving the corrosion resistance of steel reinforcement in frozen soil according to claim 1, characterized in that: The yield strength of the steel bars is 640-680 MPa, the tensile strength is 780-820 MPa, the impact absorption energy at −40℃ is ≥90 J, and the salt spray corrosion rate is ≤0.012 g / m²·h.