A 355mpa-grade low-temperature corrosion-resistant steel plate for permafrost highway and a preparation method thereof

Abstract

The present application relates to the technical field of low-temperature corrosion-resistant steel, and particularly relates to a 355MPa-grade low-temperature corrosion-resistant steel plate for permafrost highway and a preparation method thereof, wherein the low-temperature corrosion-resistant steel plate has the following chemical components in percentage by weight: C: 0.03-0.14%, Si: 0.2-0.6%, Mn: 0.8-1.5%, P: ≤0.015%, S: ≤0.006%, Ni: 0.01-0.30%, Cr: 0.01-0.30%, Cu: 0.02-0.30%, Ce+La: 0.001-0.020%, Nb: 0.001-0.080%, Al: 0.001-0.015%, Ti: 0.001-0.050%, and the balance of Fe and inevitable trace inclusions. The above scheme can ensure that the steel still has good impact toughness (KV2≥120J) at-45 DEG C; solves the problem of poor corrosion resistance of the existing steel in the highland permafrost environment, and makes the relative corrosion rate lower than 50% of the ordinary Q355 steel.

Description

Technical Field

[0001] This invention relates to the field of low-temperature corrosion-resistant steel technology, and in particular to a 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways and its preparation method. Background Technology

[0002] Engineering construction in permafrost regions faces numerous technical challenges. These areas typically exhibit extreme environmental characteristics such as high altitude, high radiation, and frequent freeze-thaw cycles. Permafrost degradation leads to uneven settlement of foundations for highways and bridges, severely impacting their service life.

[0003] Existing steel materials have shortcomings in low-temperature performance and corrosion resistance. For example, ordinary steel is prone to brittle fracture in low-temperature environments and cannot meet the requirements for use in permafrost regions with extreme low temperatures (such as -20℃ or -45℃). In addition, the soil in permafrost regions is rich in chloride and sulfate ions, which can accelerate the corrosion rate of steel and shorten its service life.

[0004] Existing low-temperature steels and corrosion-resistant steels cannot simultaneously meet the comprehensive requirements of low-temperature toughness, corrosion resistance, and mechanical properties for highway and bridge construction in permafrost regions. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways and its preparation method, in order to solve at least one of the problems in the prior art, such as high low-temperature brittleness, insufficient low-temperature corrosion resistance, difficulty in simultaneously achieving low-temperature toughness and poor resistance to large freeze-thaw deformation.

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

[0007] A 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways has the following chemical composition by weight percentage: C: 0.03-0.14%, Si: 0.2-0.6%, Mn: 0.8-1.5%, P: ≤0.015%, S: ≤0.006%, Ni: 0.01-0.30%, Cr: 0.01-0.30%, Cu: 0.02-0.30%, Ce+La: 0.001-0.020%, Nb: 0.001-0.080%, Al: 0.001-0.015%, Ti: 0.001-0.050%, with the balance being Fe and unavoidable trace inclusions.

[0008] Preferably, the hot-rolled microstructure of the 355MPa grade frozen soil highway low-temperature corrosion resistant steel plate is a fine-grained ferrite and pearlite microstructure, wherein the content of fine-grained ferrite is >80%.

[0009] Preferably, the carbon content in the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways is controlled to be 0.03% to 0.08%.

[0010] Preferably, the total mass fraction of Ni, Cr and Cu is ≥0.5%.

[0011] Preferably, the total mass fraction of Ce and La is ≥0.001%.

[0012] Preferably, the total mass fraction of Al, Nb and Ti is ≥0.03%.

[0013] Preferably, the grain size of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways is grade 10 to 12.

[0014] Preferably, the relative corrosion rate of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways is <50%.

[0015] Preferably, the average impact energy of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways at -45℃ is between 125J and 160J.

[0016] A method for preparing a 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways, comprising:

[0017] S1. Smelting:

[0018] Steel is obtained by smelting raw materials in a converter or electric furnace.

[0019] S2, Refining:

[0020] The molten steel is refined using an LF furnace, and rare earth elements are added to the molten steel after refining.

[0021] S3, Continuous Casting:

[0022] The refined molten steel is continuously cast to form steel billets;

[0023] S4. Heating:

[0024] The steel billet obtained by continuous casting is heated to 1200℃~1250℃;

[0025] S5. Controlled rolling:

[0026] The heated steel billet is subjected to two stages of rolling: rough rolling and finish rolling. The finish rolling is carried out at low temperature in the non-recrystallization zone.

[0027] S6, Low-temperature curling:

[0028] After rolling, the steel billet is cooled in a controlled manner to low temperature coiling in the ferrite and pearlite regions.

[0029] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0030] (1) By adding elements such as nickel (Ni), chromium (Cr), and copper (Cu), this invention significantly reduces the brittle transition temperature of steel plates, improves low-temperature toughness, and enhances the corrosion resistance of steel, especially in resisting chloride and sulfate ion corrosion. It purifies the steel, refines the grains, and further improves corrosion resistance and oxidation resistance. It solves the problem of insufficient low-temperature toughness of existing steel in extremely cold environments, ensuring that the steel still has good impact toughness (KV2≥120J) at -45℃. It also solves the problem of poor corrosion resistance of existing steel in high-altitude permafrost environments, making the relative corrosion rate 50% lower than that of ordinary Q355 steel.

[0031] (2) By adding trace alloying elements Nb, Al and Ti, this invention improves the strength and toughness of steel through grain refinement, precipitation and solid solution strengthening. It can pin the austenite grain boundaries, further refine the grains, improve the low-temperature toughness of the heat-affected zone of welding, solve the problem that the strength and toughness of existing steel are difficult to balance. Through composite microalloying, the balance between strength and toughness is achieved, and the low-temperature toughness of steel during welding and processing is improved, making it suitable for complex service environments.

[0032] (3) The present invention adopts low temperature precision rolling (800~850℃) and low temperature coiling (600~650℃) processes to obtain fine grain ferrite and pearlite steel structure. The fine grain ferrite content exceeds 80%, which significantly improves the elongation after fracture and low temperature toughness of the steel. By controlling the cooling rate (2~30℃ / s), the structure and properties of the steel are further optimized. The yield strength of the steel plate is ≥355MPa, the tensile strength is ≥490MPa, the yield ratio is <0.8, the elongation is ≥20%, and the low temperature impact toughness is significantly improved. The low temperature impact energy KV2 at -45℃ is ≥120J. This solves the problem that the strength and toughness of existing steel plates are difficult to balance in low temperature environment and the problem that ordinary steel plates have insufficient toughness and poor resistance to large deformation due to coarse grains in low temperature environment.

[0033] (4) In this invention, rare earth elements (Ce or La) are added to molten steel after LF refining, which reduces the oxidation loss of rare earth elements, increases the yield (>50%), increases the solid solubility of rare earth elements in steel, enhances its corrosion resistance, reduces the formation of rare earth oxide inclusions, and further purifies the steel. This solves the problems of easy oxidation and low yield of rare earth elements during the addition process and the problem that rare earth elements cannot fully exert their purification and corrosion resistance in the prior art.

[0034] (5) By strictly controlling the P and S content: P≤0.010%, S≤0.006%, and oxygen content≤30ppm, the present invention reduces the influence of impurity elements on low-temperature toughness and corrosion resistance, and also reduces the negative impact of oxide inclusions on performance, thereby significantly improving the low-temperature toughness of the steel plate, reducing the brittle transition temperature, further enhancing the corrosion resistance of the steel plate, and reducing the corrosion rate. This solves the problems of insufficient low-temperature toughness caused by the enrichment of impurity elements in existing steel plates and the increase of inclusions and performance degradation caused by high oxygen content in steel.

[0035] (6) This invention optimizes the entire process from converter (or electric furnace) smelting, LF furnace refining, continuous casting of steel billets, heating of continuously cast billets to controlled rolling, controlled cooling, slow cooling on the cooling bed and finishing of steel plates through full-process control. It further refines the process parameters, with rough rolling start temperature of 1100℃~1300℃, finish rolling start temperature of 800℃~850℃, and heating temperature of 1200℃~1250℃. This enables the industrial continuous production of steel plates, improves production efficiency, ensures the uniformity of the structure and the consistency of the properties of the steel plates, and solves the problem of difficulty in achieving industrial continuous production in existing preparation processes and the problem of uneven structure and properties of steel plates in existing processes.

[0036] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained through the embodiments described and the accompanying drawings, which are particularly pointed out. Attached Figure Description

[0037] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0038] Figure 1 The image shows the metallographic structure of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways in Example 1.

[0039] Figure 2 The actual product after salt spray test of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highway in Example 1;

[0040] Figure 3 This is the actual product after salt spray test of the low-temperature corrosion-resistant steel plate for frozen soil highways with a pressure of 355MPa in Comparative Example 1. Detailed Implementation

[0041] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0042] On one hand, this invention discloses a 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways, with the following chemical composition by weight percentage: C: 0.03-0.14%, Si: 0.2-0.6%, Mn: 0.8-1.5%, P: ≤0.015%, S: ≤0.006%, Ni: 0.01-0.30%, Cr: 0.01-0.30%, Cu: 0.02-0.30%, Ce+La: 0.001-0.020%, Nb: 0.001-0.080%, Al: 0.001-0.015%, Ti: 0.001-0.050%, with the balance being Fe and unavoidable trace inclusions.

[0043] Preferably, the hot-rolled microstructure of the low-temperature corrosion-resistant steel plate is a fine-grained ferrite and pearlite microstructure, wherein the content of fine-grained ferrite is >80%.

[0044] It should be noted that the microstructure of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways is mainly composed of fine-grained ferrite. This is because fine-grained ferrite enables the low-temperature corrosion-resistant steel to have a high elongation and a low yield strength ratio, meeting the performance requirements for steel for frozen soil highways to resist large deformations. However, pearlite will inevitably be present during the preparation process. If there is too much pearlite, although the strength will increase, the low-temperature toughness will be significantly reduced. Therefore, the ferrite content in the 355MPa grade low-temperature corrosion-resistant steel for frozen soil highways is >80%.

[0045] It should be noted that carbon (C) is an important strengthening element in steel. The steel grade of this invention has a fine-grained ferrite as its final main microstructure, requiring strict control of the C content. The addition of an appropriate amount of C can play a solid solution strengthening role in the steel, improving the strength of the matrix. Strict control of the C content can effectively reduce the sensitivity of the continuously cast billet to the Mn / S ratio, reducing the probability of continuous casting cracks. A relatively low C content can improve the uniform elongation of the steel; therefore, the carbon content of the steel in this invention is controlled at 0.03–0.14%.

[0046] Preferably, the carbon content of the steel of the present invention is controlled to be 0.03% to 0.08%.

[0047] Silicon: Si not only provides solid solution strengthening but also improves the corrosion resistance of steel. Excessive silicon content negatively impacts the ductility and toughness of steel; therefore, the Si content should be controlled within the range of 0.3% to 0.5%.

[0048] Manganese: Mn is the most effective element for expanding the austenite phase region, refining grains, and ensuring the comprehensive performance of steel. 0.1% solid solution Mn can increase the tensile strength of the matrix by 8 MPa. Considering all factors, the Mn content in steel should be controlled within the range of 0.8% to 1.5%.

[0049] Phosphorus and sulfur: Phosphorus and sulfur have a significant impact on the low-temperature toughness of steel. The enrichment or segregation of phosphorus and sulfur will seriously reduce the low-temperature toughness of steel. Therefore, it is necessary to strictly control the phosphorus and sulfur content in steel. The phosphorus content should be controlled at ≤0.015%, and the sulfur content should be controlled at ≤0.006%.

[0050] Nickel: Ni is an important element for reducing the brittle transition temperature of steel plates. Nickel forms an infinite solid solution with iron, which can expand the austenite phase region, stabilize the austenite structure and refine the grain structure, thereby inhibiting the brittle transition. The content should be controlled at 0.01-0.30%.

[0051] Chromium: Cr is an important element for improving the corrosion resistance of steel. After Cr oxidizes on the surface of steel plate, it forms a relatively dense oxide film, which prevents the further oxidation of iron on the surface of the steel plate substrate. The content is controlled at 0.01-0.30%.

[0052] Copper: Cu is a solid solution strengthening element that can improve the strength of the steel matrix. The addition of Cu can enhance the corrosion resistance of steel, making it more durable in corrosive environments such as acids, alkalis, and salts. Therefore, the Cu content in steel is controlled within the range of 0.02% to 0.30%.

[0053] Preferably, the total mass fraction of Ni, Cr and Cu satisfies: [Ni]+[Cr]+[Cu]≥0.5%.

[0054] Compared with existing technologies, this invention significantly reduces the brittle transition temperature of steel plates by adding elements such as nickel (Ni), chromium (Cr), and copper (Cu), thereby improving low-temperature toughness and corrosion resistance, especially in resisting chloride and sulfate ion corrosion. It purifies the steel, refines the grain size, and further enhances corrosion resistance and oxidation resistance. It solves the problem of insufficient low-temperature toughness of existing steels in extremely cold environments, ensuring good impact toughness (KV2≥120J) even at -45℃. Furthermore, it addresses the poor corrosion resistance of existing steels in high-altitude permafrost environments, reducing the relative corrosion rate to less than 50% of that of ordinary Q355 steel.

[0055] The applicant's research found that the synergistic effect of nickel, chromium, and copper can significantly improve the overall performance of steel plates. Nickel is mainly responsible for low-temperature toughness, chromium is mainly responsible for corrosion resistance, while copper plays a balancing role between the two, improving both strength and corrosion resistance. This invention ensures that the steel plate possesses sufficient performance in low-temperature environments and corrosive soils by setting a minimum content requirement of ≥0.7% of the total mass of Ni, Cr, and Cu. The low-temperature impact resistance and corrosion resistance of the steel plate are significantly better than those of steel plates with lower content, while the above content range effectively balances cost and performance.

[0056] Cerium (Ce) and lanthanum (La) can effectively improve the characteristics of inclusions in steel, purify molten steel, refine grains, and enhance the corrosion resistance and oxidation resistance of steel, effectively resisting corrosion from high-altitude soils. Therefore, the total mass fraction of Ce and La ([Ce]+[La]) is controlled within the range of 0.001–0.015%.

[0057] Preferably, the total mass fraction of Ce and La satisfies: [Ce] + [La] ≥ 0.001%.

[0058] It should be noted that when [Ce]+[La]≥0.001%, the corrosion resistance and low-temperature toughness of the steel plate are significantly better than those with lower contents. In corrosion tests conducted in simulated frozen soil environments, steel plates meeting the [Ce]+[La]≥0.001% requirement exhibit significantly lower relative corrosion rates than ordinary steel plates; and in low-temperature impact tests at -45℃, the impact energy KV2 of steel plates meeting this content requirement is significantly higher than that of ordinary steel plates.

[0059] Aluminum: In the steelmaking process, Al can deoxidize and purify the steel; its presence in steel can reduce the oxygen content; and when it exists in steel as solid solution aluminum and aluminum nitride, it can increase the strength of the steel plate. Therefore, the Al content in steel should be controlled within the range of 0.001–0.015%.

[0060] Niobium (Nb) and titanium (Ti) are strong carbonitride producing elements, which can improve the strength of steel through grain refinement, precipitation strengthening, and solid solution strengthening. Adding vanadium (V) can lower the ductile-brittle transition temperature of steel; the addition of Nb and Ti can effectively pin austenite grain boundaries, thereby refining the grains and improving the low-temperature toughness of the heat-affected zone in steel welding.

[0061] Preferably, the total mass fraction of Al, Nb and Ti satisfies: [Al]+[Nb]+[Ti]≥0.03%.

[0062] It should be noted that when [Al]+[Nb+[Ti]≥0.03%, the steel plate exhibits significantly higher impact energy KV2 in the low-temperature impact test at -45℃, and the low-temperature toughness is significantly improved; at the same time, it can also improve the yield strength R of the steel plate. eL and tensile strength R m All meet the design requirements (R) el ≥355MPa, R m ≥490MPa), while maintaining a low yield strength ratio (R el / R m <0.8), elongation A≥20%, low-temperature impact energy KV2≥120J at -45℃.

[0063] Preferably, the grain size of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways is grade 10 to 12.

[0064] Preferably, the relative corrosion rate of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways is <50%.

[0065] Compared with existing technologies, this invention improves the strength and toughness of steel by adding trace alloying elements Nb, Al, and Ti, through grain refinement strengthening, precipitation strengthening, and solid solution strengthening. It can pin austenite grain boundaries, further refine grains, and improve the low-temperature toughness of the weld heat-affected zone. This solves the problem of the difficulty in achieving both strength and toughness in existing steels. Through composite microalloying, a balance between strength and toughness is achieved, improving the low-temperature toughness of steel during welding and processing, and adapting it to complex service environments.

[0066] On the other hand, this invention discloses a method for preparing a low-temperature corrosion-resistant steel plate for frozen soil highways with a strength of 355MPa, comprising:

[0067] S1. Smelting:

[0068] Steel is obtained by smelting raw materials in a converter or electric furnace.

[0069] S2, Refining:

[0070] The molten steel is refined using an LF furnace, and rare earth elements are added to the molten steel after refining.

[0071] S3, Continuous Casting:

[0072] The refined molten steel is continuously cast to form steel billets;

[0073] S4. Heating:

[0074] The steel billet obtained by continuous casting is heated to 1200℃~1250℃;

[0075] S5. Controlled rolling:

[0076] The heated steel billet is subjected to two stages of rolling: rough rolling and finish rolling. The finish rolling is carried out at low temperature in the non-recrystallization zone.

[0077] S6, Low-temperature curling:

[0078] After rolling, the steel billet is cooled in a controlled manner to low temperature coiling in the ferrite and pearlite regions.

[0079] It should be noted that the non-recrystallization zone refers to the area where the material's temperature is below the recrystallization temperature during rolling. Within this temperature range, dynamic recrystallization does not occur during deformation; instead, cold deformation (or work hardening) dominates. The recrystallization temperature refers to the temperature at which the grains within the material recrystallize after cold deformation and heating, forming new, undistorted grains. The recrystallization temperature typically depends on the material's composition, the degree of deformation, and the heating rate. For most carbon steels and low-alloy steels, the recrystallization temperature is generally between 600℃ and 900℃.

[0080] During implementation, low-temperature rolling in the non-recrystallization zone is adopted in the finishing rolling stage. When producing low-temperature corrosion-resistant steel plates, the grains can be effectively refined, and the low-temperature toughness and strength of the steel plates can be significantly improved.

[0081] The cooling rate is precisely controlled within a range of 0.2 to 30°C / s, which allows for better low-temperature toughness and strength.

[0082] Adding rare earth elements Ce and / or La after refining in the LF furnace at this unique timing minimizes the oxidation loss of rare earth elements, increases their solid solution content in the steel, and thus significantly enhances the corrosion resistance of the steel plate.

[0083] Compared with existing technologies, the present invention performs low-temperature rolling in the non-recrystallization zone, followed by controlled cooling at a rate of 0.2–30°C / s to refine the grain structure. This results in steel plates with a grain size of 9–12, a microstructure of fine-grained ferrite and pearlite, a ferrite content ≥60%, a yield strength ≥355 MPa, a tensile strength ≥490 MPa, a yield ratio <0.8, an elongation ≥20%, and significantly improved low-temperature impact toughness, achieving a low-temperature impact strength of -45°C. ≥120J solves the problem of existing steel plates having difficulty in balancing strength and toughness at low temperatures, and the problem of insufficient toughness caused by coarse grains in ordinary steel plates at low temperatures.

[0084] Compared with the prior art, the present invention adds rare earth elements (Ce or La) to molten steel after LF refining, which reduces the oxidation loss of rare earth elements, increases their yield (>50%), increases the solid solubility of rare earth elements in steel, enhances their corrosion resistance, reduces the formation of rare earth oxide inclusions, and further purifies the steel. This solves the problems of easy oxidation and low yield of rare earth elements during the addition process, as well as the problem that rare earth elements cannot fully exert their purification and corrosion resistance effects in the prior art.

[0085] Preferably, in step S1, the final composition of the smelting process is controlled as follows: C ≤ 0.05% and P ≤ 0.010%.

[0086] It should be noted that while carbon is the primary strengthening element in steel, excessively high carbon content significantly increases the brittle transition temperature and reduces its low-temperature toughness. By controlling the carbon content to a low level (≤0.05%), the brittle transition temperature of the steel plate can be effectively reduced, allowing it to maintain good toughness even in extreme low-temperature environments (such as -45℃) and preventing brittle fracture. Lower carbon content also reduces oxidation and decarburization on the steel surface, thereby improving the surface quality and dimensional accuracy of the steel plate. Furthermore, low-carbon steel is easier to control during subsequent refining and rolling processes, enabling better achievement of fine-grained microstructure and high performance. For example, in LF furnace refining and controlled rolling processes, low carbon content helps reduce inclusion formation and improves the purity of the steel.

[0087] It should be noted that phosphorus is a harmful element in steel, easily segregating at grain boundaries, leading to grain boundary embrittlement and significantly reducing the steel's low-temperature toughness. Controlling the phosphorus content to extremely low levels (≤0.010%) can effectively reduce phosphorus segregation at grain boundaries, improving the toughness of the steel plate at low temperatures and preventing brittle fracture. Low phosphorus content also helps improve the purity of the steel, reducing the formation of inclusions. Phosphorus in steel usually exists in the form of phosphides, which reduce the steel's plasticity and toughness. Strictly controlling the phosphorus content can reduce the formation of these harmful inclusions, thereby improving the overall performance of the steel plate. Steel with low phosphorus content exhibits better plasticity and toughness during hot working (such as rolling and forging), reducing the formation of cracks and defects. Simultaneously, reducing phosphorus content can indirectly improve the corrosion resistance of the steel plate. Phosphides easily become the starting point of corrosion in corrosive media; reducing phosphorus content can reduce the corrosion rate of the steel plate in corrosive environments, extending its service life.

[0088] Compared with existing technologies, this invention, by strictly controlling the P and S contents (P≤0.010%, S≤0.006%, oxygen content≤30ppm), reduces the impact of impurity elements on low-temperature toughness and corrosion resistance, and also reduces the negative impact of oxide inclusions on performance. This results in a significant improvement in the low-temperature toughness of the steel plate, a reduction in the brittle transition temperature, further enhancement of the corrosion resistance of the steel plate, and a reduction in the corrosion rate. It solves the problems of insufficient low-temperature toughness caused by the enrichment of impurity elements in existing steel plates and the increase in inclusions and performance degradation caused by high oxygen content in the steel.

[0089] Preferably, the refined O content in step S2 is ≤30ppm.

[0090] It should be noted that oxygen in steel mainly exists in the form of oxides, such as silicon dioxide and aluminum oxide. These oxide inclusions reduce the toughness and ductility of steel, especially at low temperatures. By controlling the oxygen content to ≤30ppm, the number and size of oxide inclusions can be significantly reduced, thereby improving the low-temperature toughness of the steel plate. Oxide inclusions in steel often become the initiation point for cracks, especially during welding and cold deformation. Reducing the oxygen content reduces the presence of these inclusions, thereby reducing the risk of crack formation and improving the crack resistance of the steel plate. Lowering the oxygen content can significantly improve the purity of the steel and reduce the formation of inclusions. Pure steel not only helps improve the mechanical properties of the steel plate but also enhances its machinability and weldability.

[0091] Low oxygen content helps form a more uniform microstructure, reduces component segregation and microstructure inhomogeneity, thereby improving the overall performance consistency of the steel plate. When the oxygen content after refining is controlled at ≤30ppm, the comprehensive performance of the steel plate is significantly better than that of steel plates with higher content.

[0092] In the low-temperature impact test at -45℃, the steel plate with oxygen content ≤30ppm exhibited a higher impact energy KV2, which was significantly higher than that of the steel plate with high oxygen content. In the corrosion test in the simulated frozen soil environment, the relative corrosion rate of the steel plate with oxygen content ≤30ppm was significantly lower than that of the steel plate with high oxygen content, which can effectively extend the service life of the steel plate concrete structure.

[0093] Preferably, in step S3, the continuously cast billet is cold-charged into the furnace or hot-charged.

[0094] Preferably, the heating temperature of the furnace in step S4 is controlled at 1200℃~1250℃.

[0095] Within this temperature range, the plasticity of steel before rolling can be ensured, oxidation and decarburization can be reduced, heating efficiency can be improved, microstructure can be optimized, production efficiency can be increased, and environmental impact can be reduced.

[0096] Preferably, the initial rolling temperature of the rough rolling in step S5 is 1100℃~1200℃.

[0097] The applicant's research found that when the roughing rolling temperature is in the range of 1100℃ to 1200℃, the final properties of the steel plate (including strength, toughness, and low-temperature impact toughness) are significantly better than those of steel plates with temperatures below or above this range; in a low-temperature impact test at -45℃, the steel plate with a roughing rolling temperature in the range of 1100℃ to 1200℃ exhibits a higher impact energy KV2; the yield strength R of the steel plate el and tensile strength R m All meet the design requirements (R) el ≥350MPa, R m≥490MPa), while maintaining a high elongation (A≥20%).

[0098] Preferably, the rough rolling adopts a large deformation process with a rolling ratio of 30% to 70%, which is beneficial to increase the strain in the core of the steel plate, improve the uniformity of the microstructure, and improve the mechanical properties of the steel.

[0099] Preferably, the deformation amount of the first pass of rough rolling is 15% to 25%, which can be 15%, 17%, 19%, 21%, 23% or 25%.

[0100] It should be noted that a larger initial deformation amount can introduce more dislocations and lattice distortions, promoting the breakage and recrystallization of austenite grains, thereby forming finer grains in subsequent rolling processes, improving the yield strength and tensile strength of the material, and improving low-temperature toughness.

[0101] Preferably, the initial rolling temperature of the finishing rolling in step S5 is 800–850°C, and the rolled piece is in the non-recrystallized austenite region, resulting in a steel plate with fine ferrite and pearlite grains in its microstructure. Steel plates produced using this process, within the chemical composition range of this patent, exhibit low brittle transition temperatures and low relative corrosion rates.

[0102] The applicant's research found that a finishing rolling temperature of 800℃~850℃ ensures that the final microstructure of the steel plate is fine-grained ferrite and pearlite, with the content of fine-grained ferrite ≥80%. This microstructure not only improves the strength and toughness of the steel plate but also enhances its resistance to large deformations. The comprehensive performance of the steel plate within this finishing rolling temperature range is significantly better than that of steel plates below or above this temperature range. In a low-temperature impact test at -45℃, the steel plate within the finishing rolling temperature range exhibits a higher impact energy KV2, significantly higher than that of steel plates in other temperature ranges; the yield strength R of the steel plate... el and tensile strength R m All meet the design requirements (R) el ≥355MPa, R m ≥490MPa), while maintaining a high elongation (A≥20%).

[0103] Preferably, the cumulative deformation of the finishing rolling passes is greater than 50%, which can effectively refine the grain structure and improve the low-temperature toughness of the steel.

[0104] Preferably, the billet is allowed to warm up for 1 to 2 minutes before entering the finishing mill.

[0105] It should be noted that during the rolling process, the internal temperature of the steel billet may be uneven after it is heated in the furnace. Waiting for 1 to 2 minutes before entering the finishing mill can make the temperature of the steel billet more uniform and reduce uneven deformation caused by temperature differences.

[0106] Preferably, the thickness range of the low-temperature corrosion-resistant steel plate for 355MPa grade frozen soil highways is 1.2mm to 50mm.

[0107] Specifically, the winding temperature in step S6 is 600℃~650℃.

[0108] It should be noted that this coiling temperature ensures that the phase transformation during post-rolling cooling occurs in the ferrite and pearlite regions: if the coiling temperature is too high, it will affect the basic strength and toughness of the steel; if the coiling temperature is too low, upper bainite structure will appear. Steel plates produced at this temperature within the chemical composition range of this invention have low brittle transition temperatures and low relative corrosion rates.

[0109] Specifically, the cooling rate in step S6, ranging from 2℃ / s to 30℃ / s, can be 2℃ / s, 2.2℃ / s, 2.7℃ / s, 3.2℃ / s, 3.7℃ / s, 4.2℃ / s, 4.7℃ / s, 5.2℃ / s, 5.7℃ / s, 6.2℃ / s, 6.7℃ / s, 7.2℃ / s, 7.7℃ / s, 8.2℃ / s, 8.7℃ / s, 9.2℃ / s, 9.7℃ / s, 10.2℃ / s, 10.7℃ / s, 11.2℃ / s, 11.7℃ / s, 12.2℃ / s, 12.7℃ / s, 13.2℃ / s, 13.7℃ / s, 14.2℃ / s, 14.7℃ / s, 15.2℃ / s, 15℃ / s. 7℃ / s, 16.2℃ / s, 16.7℃ / s, 17.2℃ / s, 17.7℃ / s, 18.2℃ / s, 18.7℃ / s, 19.2℃ / s, 19.7℃ / s, 20.2℃ / s, 20.7℃ / s, 21.2℃ / s, 21.7℃ / s, 22.2℃ / s, 22.7℃ / s, 23.2℃ / s, 23.7℃ / s, 24.2℃ / s, 24.7℃ / s, 25.2℃ / s, 25.7℃ / s, 26.2℃ / s, 26. 7℃ / s, 27.2℃ / s, 27.7℃ / s, 28.2℃ / s, 28.7℃ / s, 29.2℃ / s, 29.7℃ / s or 30℃ / s.

[0110] Compared with existing technologies, this invention optimizes the entire process through full-process control, from converter (or electric furnace) smelting, LF furnace refining, continuous casting of steel billets, heating of continuously cast billets to controlled rolling, controlled cooling, slow cooling on a cooling bed, and finishing of steel plates. It further refines process parameters, with rough rolling starting temperature of 1100℃~1300℃, finishing rolling starting temperature of 800℃~850℃, and heating temperature of 1200℃~1250℃. This enables continuous industrial production of steel plates, improves production efficiency, ensures uniformity of steel plate structure and consistency of performance, and solves the problems of difficulty in achieving continuous industrial production in existing preparation processes and the problem of uneven steel plate structure and performance in existing processes.

[0111] To better illustrate the present invention, the following embodiments and comparative examples are provided:

[0112] Example 1

[0113] This embodiment provides a method for preparing low-temperature corrosion-resistant steel plates for frozen soil engineering, including:

[0114] The chemical composition of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways in this embodiment is shown in Table 1.

[0115] (1) Converter smelting, control the final composition of smelting: C≤0.05%, P≤0.010%, slag blocking and tapping steel, after deoxidation and alloying, enter the argon station for bottom blowing argon, and add alloying components such as Mn, Nb, and Ti.

[0116] (2) Rare earth Ce+La is added to molten steel after vacuum refining, and the yield is controlled at >50%. The O content in the later stage of refining is controlled at ≤30ppm.

[0117] (3) The slow-cooled continuous casting billet is cold-charged into the furnace, and the furnace gas temperature in the soaking section of the heating furnace is controlled at 1220℃.

[0118] (4) The roughing process adopts a high temperature and large reduction process. The roughing opening temperature is 1170℃ and the deformation of the first pass is 20%. The finishing stage adopts low temperature rolling in the non-recrystallization zone. The cumulative deformation of the finishing stage is 58%. Waiting for 2 minutes before entering the finishing mill is 840℃.

[0119] (5) The low temperature winding process is adopted, the cooling rate of the laminar flow cooling section is controlled at 20℃ / s, and the winding temperature is controlled at 640℃.

[0120] The 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways has a thickness of 4mm. The hot-rolled microstructure consists of acicular ferrite (content 90%) and pearlite, with a grain size of 11.5. Figure 1 The image shows the metallographic structure of the low-temperature corrosion-resistant steel. The mechanical properties and low-temperature toughness of the low-temperature corrosion-resistant steel plate are shown in Table 2, and the corrosion resistance is shown in Table 3.

[0121] Yield strength (R) el ) and tensile strength (R m Test standard: GB / T 228.1-2010 Metallic materials, tensile testing - Part 1: Test method at room temperature.

[0122] Elongation (A) test standard: GB / T 228.1-2010.

[0123] Yield ratio (R) el / R m Test standard: in accordance with GB / T 228.1-2010.

[0124] Low-temperature impact energy (KV2) test standard: GB / T 229-2007 "Charpy impact test method for metallic materials".

[0125] Average corrosion rate test standard: GB / T 10125-2012 "Artificial Atmosphere Corrosion Test - Salt Spray Test".

[0126] Relative corrosion rate test standard: based on ISO 10289:2003 or GB / T 10125-2012, and then compared with the corrosion rate of a reference material (such as Q355 steel).

[0127] Grain size testing standard: GB / T 6394-2010 "Method for determination of average grain size of metals".

[0128] Example 2

[0129] This embodiment provides a method for preparing low-temperature corrosion-resistant steel plates for frozen soil engineering, including:

[0130] The chemical composition of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways in this embodiment is shown in Table 1, and the preparation method is the same as in Example 1.

[0131] The 355MPa grade low-temperature corrosion-resistant steel for highways in frozen soil has a thickness of 6mm. In its hot-rolled state, it has a microstructure of fine-grained ferrite and pearlite, with a grain size of grade 11. The mechanical properties and low-temperature toughness of this steel are shown in Table 2, and its corrosion resistance is shown in Table 3.

[0132] Example 3

[0133] This embodiment provides a method for preparing low-temperature corrosion-resistant steel plates for frozen soil engineering, including:

[0134] The chemical composition of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways in this embodiment is the same as that in Example 2, as shown in Table 1.

[0135] The roughing process adopts a low-temperature, high-reduction process, with a roughing start temperature of 1100℃ and a first-pass deformation of 18%. The finishing stage adopts low-temperature rolling in the non-recrystallization zone, with a cumulative deformation of about 50%. The finishing stage requires a 2.5-minute warm-up period before entering the finishing mill, and the finishing mill inlet temperature is 810℃.

[0136] The 355MPa grade low-temperature corrosion-resistant steel for frozen soil highways has a thickness of 6mm and a grain size of 11.5. The mechanical properties and low-temperature toughness of this low-temperature corrosion-resistant steel are shown in Table 2, and its corrosion resistance is shown in Table 3.

[0137] Example 4

[0138] This embodiment provides a method for preparing low-temperature corrosion-resistant steel plates for frozen soil engineering, including:

[0139] The chemical composition of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways in this embodiment is shown in Table 1. The chemical composition has been improved by increasing the content of corrosion-resistant elements. The preparation method is the same as in Example 1.

[0140] The 355MPa grade low-temperature corrosion-resistant steel for highways in frozen soil has a thickness of 6mm. In its hot-rolled state, it has a microstructure of fine-grained ferrite and pearlite, with a grain size of grade 11. The mechanical properties and low-temperature toughness of this steel are shown in Table 2, and its corrosion resistance is shown in Table 3.

[0141] Example 5

[0142] This embodiment provides a method for preparing low-temperature corrosion-resistant steel plates for frozen soil engineering, including:

[0143] The chemical composition of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways in this embodiment is shown in Table 1. The chemical composition has been improved by increasing the content of alloying elements to enhance strength and corrosion resistance. The preparation method is the same as in Example 1.

[0144] The 355MPa grade low-temperature corrosion-resistant steel for frozen soil highways has a thickness of 6mm. In its hot-rolled state, it has a microstructure of fine-grained ferrite and pearlite, with a grain size of 11.5. The mechanical properties and low-temperature toughness of this steel are shown in Table 2, and its corrosion resistance is shown in Table 3.

[0145] Comparative Example 1

[0146] Comparative Example 1 provides an existing corrosion-resistant steel plate Q355B with a strength of 355 MPa, rolled at a final temperature of 900 °C. Its chemical composition differs from that of Example 1 (see Table 1), but the rest is the same as Example 1. Low-temperature toughness is shown in Table 2, and corrosion resistance is shown in Table 3. Figure 3 This is a picture of the actual product after the salt spray test of the low-temperature corrosion-resistant steel.

[0147] Comparative Example 2

[0148] Comparative Example 2 provides an existing corrosion-resistant steel plate Q355C with a strength of 355MPa and a final rolling temperature of 900℃. Its chemical composition is different from that of Example 1 (see Table 1), but the rest is the same as that of Example 1. Its low-temperature toughness is shown in Table 2, and its corrosion resistance is shown in Table 3.

[0149] Comparative Example 3

[0150] Comparative Example 3 provides an existing corrosion-resistant steel plate Q355C with a strength of 355MPa and a final rolling temperature of 860℃. Its chemical composition is different from that of Example 1 (see Table 1), but the rest is the same as that of Example 1. Its low-temperature toughness is shown in Table 2, and its corrosion resistance is shown in Table 3.

[0151] Table 1 Chemical composition (wt%) of the examples and comparative examples

[0152]

[0153] Table 2 Mechanical properties of the examples and comparative examples

[0154]

[0155] Table 3 Corrosion resistance of the examples and comparative examples

[0156]

[0157] As can be seen from the performance data in Tables 2 and 3, the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways of the present invention simultaneously possesses good low-temperature toughness, corrosion resistance, and mechanical properties; the yield strength is between 395MPa and 440MPa, the tensile strength is between 510MPa and 570MPa, and the yield strength ratio is between 0.77 and 0.79, showing a good balance between strength and plasticity. The average impact energy at -45℃ is between 125J and 160J, significantly higher than the comparative example, demonstrating superior low-temperature toughness; the average corrosion rate is between 1.20g / m²·h and 1.27g / m²·h, and the corrosion rate relative to Q355 steel is between 43.32% and 46.01%, <50%, far lower than the comparative example.

[0158] Comparing Example 1 and Comparative Examples 1-3, it can be seen that the elemental composition scheme that meets the requirements of this invention is far superior to the existing technical solutions in terms of corrosion resistance and low-temperature toughness.

[0159] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-temperature corrosion-resistant steel plate for frozen soil highways with a strength of 355MPa, characterized in that, Chemical composition by weight percentage: C: 0.03–0.14%, Si: 0.2–0.6%, Mn: 0.8–1.5%, P: ≤0.015%, S: ≤0.006%, Ni: 0.01–0.30%, Cr: 0.01–0.30%, Cu: 0.02–0.30%, Ce+La: 0.001–0.015%, Nb: 0.001–0.080%, Al: 0.001–0.015%, Ti: 0.001–0.050%, with the balance being Fe and unavoidable trace inclusions; the total mass fraction of Ni, Cr, and Cu is ≥0.5%. The microstructure of the hot-rolled state is composed of fine-grained ferrite and pearlite, with the content of fine-grained ferrite being >80%. The method for preparing the 355MPa grade frozen soil highway low-temperature corrosion-resistant steel plate includes: S1. Smelting: Steel is obtained by smelting raw materials in a converter or electric furnace. S2, Refining: The molten steel is refined using an LF furnace, and rare earth elements are added to the molten steel after refining; S3. Continuous casting: Refined molten steel is continuously cast to form steel billets; S4. Heating: Heating the steel billet obtained by continuous casting to 1200℃~1250℃; S5. Controlled rolling: The heated steel billet is subjected to two stages of rolling: rough rolling and finish rolling. The finish rolling is carried out at a low temperature in the non-recrystallization zone. The starting rolling temperature of the finish rolling is 800-850℃. S6. Low-temperature coiling: The rolled steel billet is cooled under controlled conditions to low-temperature coiling in the ferrite and pearlite regions; the coiling temperature is 600℃~650℃.

2. The 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways according to claim 1, characterized in that, The carbon content in the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways is controlled at 0.03% to 0.08%.

3. The 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways according to claim 1, characterized in that, The total mass fraction of Al, Nb and Ti is ≥0.03%.

4. The 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways according to claim 1, characterized in that, The grain size of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways is grade 10-12.

5. The 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways according to claim 1, characterized in that, The corrosion rate of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways is less than 50% compared to the corrosion-resistant steel plate Q355B.

6. The 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways according to any one of claims 1-5, characterized in that, The average impact energy of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways is between 125J and 160J at -45℃.

7. A method for preparing a low-temperature corrosion-resistant steel plate for frozen soil highways with a strength of 355MPa, characterized in that, The preparation of the 355MPa grade low-temperature corrosion-resistant steel plate for frozen soil highways according to any one of claims 1-6 comprises: S1. Smelting: Steel is obtained by smelting raw materials in a converter or electric furnace. S2, Refining: The molten steel is refined using an LF furnace, and rare earth elements are added to the molten steel after refining. S3, Continuous Casting: The refined molten steel is continuously cast to form steel billets; S4. Heating: The steel billet obtained by continuous casting is heated to 1200℃~1250℃; S5. Controlled rolling: The heated steel billet is subjected to two stages of rolling: roughing and finishing. Finishing is carried out at a low temperature in the non-recrystallization zone. The starting temperature of finishing is 800-850℃. S6, Low-temperature curling: After rolling, the steel billet is cooled in a controlled manner to a low temperature for coiling in the ferrite and pearlite regions; the coiling temperature is 600℃~650℃.

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