Atmospheric corrosion resistant HC260LA low-alloy high-strength steel and production method thereof

Abstract

The invention belongs to the technical field of manufacturing of low-alloy high-strength steel, and particularly relates to atmospheric corrosion resistant HC260LA low-alloy high-strength steel and a production method of the atmospheric corrosion resistant HC260LA low-alloy high-strength steel. 0.15% to 0.30% of Si; 0.40% to 0.60% of Mn; 0.06% to 0.10% of P; less than or equal to 0.015% of S; 0.02% to 0.08% of Al; 0.10% to 0.20% of Cu; 0 to 0.15% of Ti; 0 to 0.09 percent of Nb; 0.001% to 0.006% of N; and the balance of Fe and inevitable impurities. According to the method, the blocking effect of segregation of P-Cu elements on the grain boundary on a corrosion path is utilized, low-temperature rolling is combined, a three-dimensional corrosion-resistant system of fine grain strengthening, substructure strengthening and rust layer protection is constructed, and the weather resistance, the corrosion resistance and the mechanical property are jointly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of low-alloy high-strength steel manufacturing, and particularly relates to an atmospheric corrosion resistant HC260LA low-alloy high-strength steel and a production method thereof. BACKGROUND

[0002] HC260LA is a low-alloy high-strength steel for cold forming, and is widely used in the fields of automobile structural parts and outdoor machinery. The traditional HC260LA steel has limited atmospheric corrosion resistance, and is prone to rust in humid and acid rain environments. Therefore, an anti-corrosion layer needs to be additionally coated, which increases the cost and process complexity. In the prior art, weathering steels usually add alloy elements such as Cr and Ni to improve corrosion resistance, but this significantly increases the production cost and is contradictory to the cold forming performance of HC260LA.

[0003] The prior art patent application No. CN85108118 discloses a low-alloy atmospheric corrosion resistant steel adopting Cu-P-V-Re system, which needs to add V (0.02-0.12%) and Re (≤0.20%). The Re resource is abundant, but the adding cost is high and the process control is complex. The technology needs to rely on a specific smelting process (such as pouring by bottom pouring and neutral atmosphere control in soaking furnace), and the cold forming performance is not optimized. The patent application No. CN200810304295.6 discloses a high-strength atmospheric corrosion resistant steel and a production method thereof. The strength is high (yield ≥500 MPa), but the cold forming performance (such as elongation ≥20%) is not optimized, and the complex micro-alloying ratio (V-Ti-N-Nb) is relied on. The patent application No. CN200510111858.6 discloses a high-strength low-alloy atmospheric corrosion resistant steel and a production method thereof. The strength is high (yield ≥550 MPa), but the complex micro-alloying ratio (Nb ≤0.07%, Ti ≤0.025%, Mo ≤0.35%) and two-stage controlled rolling (cumulative reduction rate ≥80%) are relied on, the process is complex, and the cold forming performance is not optimized. The patent application No. CN201210317193.4 discloses a boron-containing micro-alloyed atmospheric corrosion resistant steel and a manufacturing method thereof. The special process (such as casting strip thickness 1-5 mm and dry ice cooling rate 200-300℃ / s) of double-roller thin strip continuous casting + dry ice strengthened cooling + online hot rolling is relied on, the equipment investment is large, and the process is complex. The yield strength ratio (≤0.8) is reduced by boron micro-alloying, but the high content of micro-alloying elements (such as Nb: 0.01-0.08%, V: 0.01-0.08%) is relied on, and the elongation is only ≥22%. The patent application No. CN201611138247.5 discloses a low-alloy weathering steel and a production method and application thereof. The expensive elements (such as Ni (0.15-0.50%) and Nb (0.04-0.07%)) are added, and the two-stage controlled rolling (coarse rolling final temperature 1000℃, and finishing rolling final temperature 800-850℃) and water spraying cooling process are relied on. The equipment investment is high. The elongation is ≥28.8%, but the cold bending performance is not optimized, and the corrosion resistance relies on the Cr / Ni cooperation (corrosion resistance index I ≈6.14).

[0004] Therefore, it is of important industrial value to develop a low-cost and high-performance atmospheric corrosion resistant HC260LA steel. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide an atmospheric corrosion resistant HC260LA low-alloy high-strength steel and a production method thereof. By means of P-Cu micro-alloying and low-temperature rolling, the corrosion resistance and cold forming property of the HC260LA steel are improved without greatly increasing the cost, and the problem that the corrosion resistance and mechanical properties of the traditional material are difficult to be considered simultaneously is solved.

[0006] To achieve the above object, the present application is realized by the following technical solutions: An atmospheric corrosion resistant HC260LA low alloy high strength steel, the chemical composition in the steel is as follows in terms of mass percentage: C: 0.04%~0.10%; Si: 0.15%~0.30%; Mn: 0.40%~0.60%; P: 0.06%~0.10%; S≤0.015%; Al: 0.02%~0.08%; Cu: 0.10%~0.20%; Ti: 0~0.15%; Nb: 0~0.09%; N: 0.001%~0.006%; the rest is Fe and inevitable impurities.

[0007] P-Cu synergistic effect: by controlling phosphorus (P: 0.06%~0.10%) and copper (Cu: 0.10%~0.20%), a dense rust layer is formed to inhibit corrosion propagation. The P-Cu micro-alloying system regulates the phase composition of the rust layer, combined with the low-temperature rolling induced grain boundary segregation effect, so that the adhesion of the rust layer is increased by more than 3 times (according to the salt spray test data of GB / T10125), forming a nanoscale composite protective layer.

[0008] Low C design: carbon content ≤0.10%, avoiding too much pearlite structure leading to corrosion resistance decline, while ensuring cold formability.

[0009] Micro-alloying: retaining Ti, Nb elements to refine grains and improve strength and formability.

[0010] When Ti and Nb are both added (such as Ti: 0.05%+Nb: 0.04%), N preferentially forms TiN (high temperature stability) with Ti, and the remaining N forms NbN with Nb, both of which synergistically inhibit austenite grain growth, and ferrite grains can be refined to 5~6μm; when only Ti is added (such as Ti 0.08%), N forms TiN with Ti, and Al forms AlN with the remaining N, double refining the grains; when neither Ti nor Nb is added, N forms AlN with Al, and by controlling the hot rolling final temperature (820~860℃) and the cold rolling reduction rate (70%~78%), the ferrite grain size can still be controlled in the range of 5~8μm, meeting the requirements of strength and formability. When Ti=0, Nb=0.03%~0.06%, Nb and N form NbN precipitates (size 8~12nm), which, together with AlN, double refine the grains, and P-Cu grain boundary segregation forms a dense rust layer, so that the balance between strength and corrosion resistance can be achieved without Ti.

[0011] A production method of an atmospheric corrosion resistant HC260LA low alloy high strength steel, comprising smelting, continuous casting, hot rolling, cold rolling, continuous annealing, and skin passing; wherein: 1) Hot rolling: The continuously cast billet is heated to 1180–1230℃ and held for ≥120 min to ensure full dissolution of alloying elements; the rough rolling temperature is ≥1150℃ and the number of rolling passes is ≥5 to break up the original microstructure of the billet; the finishing rolling temperature is 820–860℃ (low-temperature rolling refines ferrite grains); a front-section + rear-section segmented cooling method is adopted, and the coiling temperature is 580–620℃ to promote the uniform distribution of Cu and P elements. 2) Cold continuous rolling: After pickling, the total reduction rate of hot-rolled strip is controlled at 70%~78% to increase the dislocation density and form a subcrystalline structure, which provides driving force for subsequent annealing and recrystallization.

[0012] 3) Continuous annealing: The material is fed into a continuous annealing furnace, with a critical zone annealing temperature of 780~820℃ and a holding time of 120~180s. Combined with the control of the total reduction rate of cold rolling, the proportion of non-recrystallized ferrite is precisely controlled at 5%~10%, improving elongation and corrosion resistance; achieving the optimal match of yield strength ≥260MPa and elongation ≥28%. 4) Smoothing: Elongation is controlled at 1.0%~1.5% to eliminate yield plateau and improve surface quality.

[0013] The aforementioned smelting: Hot metal pretreatment: KR desulfurization process is adopted to control the sulfur content ≤0.003%; reducing the impact of sulfide inclusions on corrosion resistance. Converter smelting: Low oxygen blowing process is adopted to control the final oxygen content ≤0.003% to reduce oxide inclusions; LF refining: Calcium treatment is performed by adding silicon-calcium alloy, with an addition amount of 0.5-1.0 kg / ton of steel, improving the morphology of inclusions to spherical shape and enhancing the purity of molten steel.

[0014] The aforementioned continuous casting: The weak cooling process is adopted, with the cooling intensity of the crystallizer ≤800L / (m·min), and the equiaxed crystal ratio of the billet is controlled to ≥50%, reducing center segregation and laying a good microstructure foundation for subsequent rolling processes.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes a P-Cu micro-alloying synergistic low-temperature rolling process to regulate the phase composition of the rust layer, thereby improving its adhesion and density. This results in a highly adhesive, low-porosity α-FeOOH rust layer with a salt spray corrosion rate ≤0.01mm / a, significantly extending its salt spray corrosion life compared to the traditional HC260LA (referencing GB / T10125 standard, corrosion rate ≤0.01mm / a in a 5% NaCl solution spray test). This solves the rusting problem in outdoor environments and reduces coating costs and process complexity.

[0016] 2. This invention utilizes Ti-Nb microalloying combined with high-pressure cold rolling to refine ferrite grains to 5-8μm, while retaining 5-10% of unrecrystallized ferrite through critical zone annealing. This achieves a balanced performance of yield strength ≥260MPa, elongation ≥28%, and no cracks during cold bending (d=2a, 180°), resolving the process contradiction between high strength and high plasticity, and meeting the requirements of cold forming scenarios such as automotive structural parts.

[0017] 3. This invention is compatible with the low-cost production process of existing HC260LA production lines. By adjusting the rolling temperature (final rolling 820-860℃) and annealing parameters, no additional vacuum degassing or special cooling equipment is required. It also avoids reliance on precious metals such as Cr and Ni, achieving high efficiency and sustainability in industrial production. Compared to existing weathering steels that rely on precious metals like Cr and Ni, this invention eliminates the need for expensive alloying elements, reducing production costs by more than 15%. Furthermore, it clearly meets cold bending performance standards (d=2a, no cracks at 180°), making it more suitable for large-scale industrial production of automotive structural components and outdoor machinery.

[0018] 4. This invention utilizes the blocking effect of P-Cu element segregation at grain boundaries on corrosion paths, combined with the high-density dislocations and subgrain structure induced by low-temperature rolling, to construct a three-dimensional corrosion-resistant system of "fine grain strengthening + substructure strengthening + rust layer protection", thereby achieving a joint improvement in weather resistance, corrosion resistance and mechanical properties. Attached Figure Description

[0019] Figure 1 This is a 200x magnification metallographic image of the microstructure of Example 1. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0021] Example 1: HC260LA low-alloy high-strength steel, resistant to atmospheric corrosion, is made with P-Cu microalloying. The chemical composition of the steel, by mass percentage, is: C: 0.07%, Si: 0.25%, Mn: 0.55%, P: 0.08%, S: 0.012%, Als: 0.04%, Cu: 0.15%, Ti: 0.08%, Nb: 0.05%, N: 0.003%, with the remainder being Fe and unavoidable impurities.

[0022] The production method of atmospheric corrosion resistant HC260LA low alloy high strength steel includes: (steelmaking) hot metal pretreatment → converter smelting → ladle refining (LF) → continuous casting → (hot rolling) heating → rough rolling, finish rolling → controlled cooling → coiling → (cold continuous rolling) uncoiling, welding → pickling, cold continuous rolling → continuous annealing → leveling → surface and performance inspection → packaging → delivery. Specifically: The hot rolling finishing temperature is 840℃, and the coiling temperature is 600℃. The cold rolling reduction rate is 70%, the annealing temperature is 800℃, and the continuous annealing is carried out through the critical zone holding temperature to control the proportion of non-recrystallized ferrite at 8%, taking into account both strength and elongation.

[0023] The properties of HC260LA low-alloy high-strength steel are as follows: According to GB / T228.1-2021, the yield strength is 280MPa, the elongation is 28%, the porosity is 92%, the salt spray corrosion rate is 0.008mm / a, and the rust layer has a dark brown and dense structure.

[0024] Example 2: HC260LA low-alloy high-strength steel, resistant to atmospheric corrosion, has the following chemical composition by mass percentage: C: 0.09%, Si: 0.22%, Mn: 0.48%, P: 0.07%, S: 0.012%, Als: 0.035%, Cu: 0.12%, Ti: 0.10%, Nb: 0.06%, N: 0.003%, with the remainder being Fe and unavoidable impurities.

[0025] The preparation process of atmospheric corrosion resistant HC260LA low-alloy high-strength steel is the same as in Example 1, except that: The hot rolling finishing temperature is 820℃, and the coiling temperature is 580℃. The total reduction rate of cold continuous rolling is 71%, and the annealing temperature is 790℃. The annealing temperature is increased to 790℃ to promote ferrite recrystallization and ensure an elongation of 29%.

[0026] The properties of HC260LA low-alloy high-strength steel are as follows: According to GB / T228.1-2021, the yield strength is 290MPa, the elongation is 29%, the porosity is 91%, the salt spray corrosion rate is 0.009mm / a, and the grain size is 5.5μm.

[0027] Example 3: HC260LA low-alloy high-strength steel, resistant to atmospheric corrosion, has the following chemical composition by mass percentage: C: 0.06%, Si: 0.28%, Mn: 0.52%, P: 0.09%, S: 0.010%, Als: 0.045%, Cu: 0.18%, Ti: 0.07%, Nb: 0.04%, N: 0.002%, with the remainder being Fe and unavoidable impurities.

[0028] The preparation process of atmospheric corrosion resistant HC260LA low-alloy high-strength steel is the same as in Example 1, except that: The hot rolling finishing temperature is 850℃, and the coiling temperature is 610℃. The total reduction rate of cold continuous rolling is 70%, and the annealing temperature is 820℃ (the upper limit of the critical zone), which reduces pearlite precipitation and increases the elongation to 29%.

[0029] Properties of HC260LA low-alloy high-strength steel resistant to atmospheric corrosion: According to GB / T228.1-2021, the yield strength is 275 MPa, the elongation is 29%, and the porosity is ≥90%. The salt spray corrosion rate was 0.007 mm / a, and the elongation was 11.5% higher than that of control example 1. The rust layer had a significant self-healing ability, and a new protective film was formed at the scratch within 72 hours.

[0030] Example 4: Full-process optimization (P-Cu + low-temperature rolling + critical annealing): HC260LA low-alloy high-strength steel, resistant to atmospheric corrosion, has the following chemical composition by mass percentage: C: 0.07%, Si: 0.25%, Mn: 0.55%, P: 0.08%, S: 0.010%, Als: 0.04%, Cu: 0.15%, Ti: 0.08%, Nb: 0.05%, N: 0.003%, with the remainder being Fe and unavoidable impurities.

[0031] The preparation process of atmospheric corrosion resistant HC260LA low-alloy high-strength steel is the same as in Example 1, except that: The hot rolling finishing temperature is 830℃, and the coiling temperature is 590℃. The total reduction rate of cold continuous rolling is 70%, the annealing temperature is 800℃, and the degree of recrystallization is precisely controlled by critical zone annealing to achieve a balance between 28.5% elongation and 285MPa yield strength.

[0032] The properties of HC260LA low-alloy high-strength steel are as follows: According to GB / T228.1-2021, the yield strength is 285MPa, the elongation is 28.5%, the hole expansion rate is 93%, and there are no cracks when cold bending. The salt spray corrosion rate is 0.006 mm / a, and its comprehensive performance reaches the level of internationally advanced weathering steel.

[0033] Example 5: (Ti=0, Nb≠0 (single element missing)) 1. Atmospheric corrosion resistant HC260LA low alloy high strength steel. The chemical composition of the steel by mass percentage is: C: 0.07%, Si: 0.26%, Mn: 0.53%, P: 0.08%, S: 0.010%, Als: 0.045%, Cu: 0.16%, Ti: 0%, Nb: 0.04%, N: 0.003%, with the remainder being Fe and unavoidable impurities.

[0034] 2. Production method (in line with existing processes, no new equipment required) 1) Smelting + Continuous Casting: Same as Example 1 (S=0.002% after hot metal pretreatment, oxygen at the converter endpoint=0.002%, LF refining silicon-calcium alloy added 0.8kg / ton of steel, continuous casting equiaxed crystal ratio 55%). 2) Hot rolling: The billet is heated to 1220℃ (held for 130 min), rough rolled in 5 passes (initial rolling temperature 1160℃), and finished at a final rolling temperature of 845℃. After rolling, it is cooled to 600℃ at 12℃ / s and then coiled. 3) Cold continuous rolling: Total reduction rate 73%; 4) Continuous annealing: Annealing temperature 805℃ (intermediate value of the critical region), holding temperature 160s, annealing temperature 805℃, synergistic precipitation of NbN and AlN, refine grain to 6.8μm, and ensure strength and plasticity; 5) Smoothness: Elongation rate 1.2%.

[0035] 3. Performance Testing According to GB / T228.1-2021, the yield strength is 282 MPa, the tensile strength is 378 MPa, the elongation after fracture is 29%, and the porosity is 92%. Salt spray corrosion rate: 0.008 mm / a (≤0.01 mm / a, GB / T10125-2021); Microstructure: Ferrite + Pearlite (pearlite content 4% ≤ 5%), effective grain size 6.8 μm (5~8 μm), dislocation density 1.2 × 10⁻⁶ 10 / cm 2 (≥10) 10 / cm 2 ); Cold bending test (d=2a, 180°): No cracks.

[0036] Example 6: (Atmospheric Corrosion Resistant HC260LA Low Alloy High-Strength Steel with Ti=0 and Nb=0 and its Preparation Method) 1. Chemical composition (mass percentage) C: 0.08%, Si: 0.26%, Mn: 0.55%, P: 0.09%, S: 0.010%, Als: 0.06%, Cu: 0.17%, Ti: 0%, Nb: 0%, N: 0.004%, with the remainder being Fe and unavoidable impurities.

[0037] 2. Preparation method (full process parameters) 2.1 Smelting process Hot metal pretreatment: KR desulfurization process is adopted, with a desulfurizing agent (CaO-CaF2) addition of 5kg / t. After treatment, the sulfur content of the hot metal is ≤0.0025%, and the slag thickness is controlled at 25mm to reduce the impact of sulfide inclusions on subsequent corrosion resistance. Converter smelting: Employing a low-oxygen blowing process with an oxygen supply intensity of 1.0 m³ / s. 3 / (t·min), smelting temperature 1620℃, final oxygen content ≤0.0028%, final carbon content precisely controlled at 0.08%, to avoid excessive precipitation of pearlite due to excessive carbon content; LF refining: Add silicon-calcium alloy for calcium treatment, with an addition amount of 0.8 kg / ton of steel, an argon blowing flow rate of 250 L / min (standard state), and a refining time of 25 min to ensure uniform steel composition. At the same time, optimize the morphology of inclusions to spherical (size < 2 μm) to reduce pitting corrosion sensitivity.

[0038] 2.2 Continuous casting process The process employs a weak cooling method with a crystallizer cooling intensity of 780 L / (m·min), a continuous casting speed of 1.4 m / min, and a secondary cooling zone water content of 1.0 L / kg. By controlling the cooling parameters, the solidification process of the billet is regulated, ensuring that the equiaxed crystal ratio of the billet is ≥55% and the billet thickness is 220 mm. Non-destructive testing reveals no internal defects such as central segregation or cracks, thus providing high-quality billets for subsequent rolling.

[0039] 2.3 Hot rolling process Heating: The continuously cast billet is fed into a walking beam furnace and heated to 1220℃ for 130 minutes to ensure that alloying elements such as Als and Mn are fully dissolved and to avoid undissolved particles from affecting subsequent microstructure refinement. Rough rolling: The initial rolling temperature is 1160℃, and 5 rolling passes are used with a cumulative reduction of 60%. The original coarse grains of the billet are broken by a large reduction. The thickness of the billet after rough rolling is controlled to be 35mm. Finishing rolling: The entry temperature of finishing rolling is 980℃, and the final rolling temperature is 845℃ (in the low-temperature rolling range of 820~860℃). It adopts 7 passes of small reduction rolling, with a cumulative reduction rate of 75%. It precisely controls the plate shape and grain size, and the thickness of the finished hot-rolled strip is 3.0mm. Cooling and coiling are controlled by a front-section and rear-section segmented cooling mode. The front-section cooling rate is 12℃ / s and the rear-section cooling rate is 8℃ / s. The strip temperature is gradually reduced to 605℃ (which is within the coiling range of 580~620℃) before coiling. This promotes the uniform segregation of Cu and P elements at the grain boundaries, laying the foundation for the formation of the subsequent rust layer.

[0040] 2.4 Cold Continuous Rolling Process After the hot-rolled coil is uncoiled, it is welded and then pickled with hydrochloric acid to remove the surface iron oxide scale (pickling temperature 85℃, pickling time 5min). It is then fed into a cold continuous rolling mill, with the total reduction rate controlled at 74%. Through multiple rolling passes, the strip thickness is reduced from 3.0mm to 0.8mm. Ester-based rolling oil is used for lubrication during the rolling process, and the plate thickness accuracy is controlled within ±0.02mm. Simultaneously, the high reduction rate increases the internal dislocation density of the steel (reaching 1.1×10⁻⁶). 12 / cm 2 This forms a subcrystalline structure, providing a driving force for subsequent annealing and recrystallization.

[0041] 2.5 Continuous annealing process The cold-rolled strip steel is fed into a continuous annealing furnace and protected by a full hydrogen atmosphere (hydrogen content ≥ 99.99%). The specific annealing process is as follows: Heating section: rapidly heated to 810℃ at a rate of 100℃ / s and held for 160s to ensure complete recrystallization of the steel and eliminate cold rolling work hardening; Heat soaking section: Cool to 680℃ at a rate of 15℃ / s and hold for 200s to promote the combination of Als and N to form AlN precipitates (size 15-20nm) and achieve grain refinement. Rapid cooling section: Cools to 420℃ at a rate of 25℃ / s to suppress excessive carbide precipitation; After aging: Hold at 370℃ for 100 seconds to eliminate internal stress and stabilize the microstructure; Final cooling section: After cooling to 150°C at a rate of 8°C / s, the product is removed from the furnace to avoid residual stress caused by excessively rapid cooling.

[0042] 2.6 Leveling process A twin-roll leveler is used to level the annealed strip steel, with the leveling elongation controlled at 1.3%. The yield plateau is eliminated by slight rolling to avoid "slip lines" during subsequent cold forming. At the same time, the surface roughness of the strip steel is optimized (Ra≤0.8μm) to meet the surface quality requirements of steel for automotive structural parts and outdoor machinery.

[0043] 3. Performance test results Mechanical properties: Tested according to GB / T228.1-2021, yield strength 275MPa, tensile strength 380MPa, elongation after fracture 29%, and expansion rate 92%; after a 180° cold bending test with a mandrel diameter d=2a, there were no surface cracks, meeting the plasticity requirements of cold forming process; Corrosion resistance: According to GB / T10125-2021, a neutral salt spray test (5% NaCl solution, pH 6.5~7.2) was conducted, with a corrosion rate of 0.008 mm / a. The rust layer showed a dense, dark brown structure (the main phase was α-FeOOH), and no red rust was produced. Microstructure: Tested according to GB / T13298-2015, the microstructure at 1 / 2 the thickness of the steel plate is ferrite + pearlite, with a pearlite volume content of 4.5%, an effective grain size of 6.8 μm, and a dislocation density of 1.0 × 10⁻⁶. 10 / cm 2 The tissue has good homogeneity, with no obvious segregation or inclusions.

[0044] All examples consist of repeatable experimental data from at least three sets.

[0045] Comparative Example 1: Traditional HC260LA process Chemical composition (mass fraction %): C: 0.08, Si: 0.20, Mn: 0.50, P: 0.02, S: 0.01, Als: 0.03, Cu: 0.05, Ti: 0.08, Nb: 0.05.

[0046] Process parameters: The hot rolling finishing temperature is 890℃, and the coiling temperature is 640℃. The cold rolling reduction rate is 65%, and the annealing temperature is 810℃.

[0047] Performance results: Yield strength 270 MPa, elongation 26%; The salt spray corrosion rate is 0.025 mm / a, and the rust layer is loose and easily falls off.

[0048] The inspection results of the finished product in Example 1 are shown in Tables 1 and 2.

[0049] Table 1: Mechanical Properties Sample No. Yield strength MPa Tensile strength MPa Elongation A 80 ​ Cold bending performance (d = 2a, 180°) 1# 285 380 28.5 No cracks 2# 282 375 28 No cracks Table 2: Corrosion resistance test (GB / T10125 salt spray test) Sample No. Corrosion time (h) Corrosion rate (mm / a) Rust layer characteristics 1# 1000 0.006 Black-brown compact rust layer, no red rust 2# 1000 0.007 Black-brown compact rust layer, no red rust Metallographic structure: Samples were prepared according to GB / T13298-2015. They were water-cooled cut using a metallographic cutting machine, clamped, and ground with 180#, 320#, 600#, and 800# sandpaper. They were then coarsely polished with 3.5μm polishing compound, followed by fine polishing with 0.5μm compound, and etched with 4% nitric acid alcohol for 4 seconds. Figure 1 As shown, the ferrite grain size in the microstructure at 200x magnification, measured using the intercept method according to GB / T6394 standard, is 5.2±0.8μm. The grain boundary density is 2.3 times higher than that of traditional processes (grain size 12-15μm), effectively hindering the penetration path of corrosive media. This aligns with the patented process design of "low-temperature rolling (final rolling temperature 820-860℃) + Ti / Nb microalloying (Ti≤0.15%, Nb≤0.09%)". Refining the grains increases grain boundary resistance, hindering the penetration of corrosive media, while simultaneously improving strength (yield strength ≥260MPa), verifying the technical effectiveness of "microalloying to refine grains". Unlike traditional HC260LA steel, which is prone to intergranular corrosion due to excessive pearlite content (>15%), this invention controls the pearlite content to below 5% through a low C design (C≤0.10%), and combines calcium treatment to make the inclusion size <2μm, significantly reducing pitting corrosion sensitivity.

[0050] The metallographic structure directly verifies the rationality of the "microalloying design + low temperature rolling + high pressure cold continuous rolling" process. Its refined grains, dense rust layer and high purity characteristics explain the synergistic improvement of corrosion resistance and mechanical properties from a microscopic level.

[0051] Through microalloying design (P-Cu synergy) and full-process process control (low-temperature rolling, critical zone annealing, and high-pressure cold continuous rolling), this invention achieves a synergistic improvement in the atmospheric corrosion resistance and mechanical properties of HC260LA steel. Experimental data show that the corrosion rate of the optimized steel is significantly reduced, the elongation remains above 26%, and the process compatibility is good, requiring no large-scale equipment modification. This technology provides a new path for the application of low-alloy high-strength steel in outdoor lightweight structures, possessing significant industrial application value and economic benefits.

Claims

1. An atmospheric corrosion resistant HC260LA low alloy high strength steel, characterized in that, The chemical composition in the steel is as follows in percentage by mass: C: 0.04%~0.10%; Si: 0.15%~0.30%; Mn: 0.40%~0.60%; P: 0.06%~0.10%; S≤0.015%; Al: 0.02%~0.08%; Cu: 0.10%~0.20%; Ti: 0~0.15%; Nb: 0~0.09%; N: 0.001%~0.006%; and the rest is Fe and inevitable impurities.

2. The atmospheric corrosion resistant HC260LA low alloy high strength steel according to claim 1, characterized in that, The yield strength of the HC260LA low-alloy high-strength steel is 260~330MPa, the tensile strength is 340~420MPa, the elongation after fracture is ≥28%, the hole expansion ratio is ≥90%, the surface of the HC260LA low-alloy high-strength steel is free of cracks after a 180° cold bending test with a bending core diameter d=2a, and the corrosion rate of the steel plate is ≤0.01mm / a in a neutral salt spray test according to the GB / T10125-2021 standard.

3. The atmospheric corrosion resistant HC260LA low alloy high strength steel according to claim 1, characterized in that, The microstructure of the HC260LA low-alloy high-strength steel at a thickness of 1 / 2 of the steel plate is ferrite + pearlite, the volume content of the pearlite is ≤ 5%, the effective grain size is 5-8 μm, and the dislocation density is ≥ 10 10 / cm 2 .

4. The atmospheric corrosion resistant HC260LA low alloy high strength steel according to claim 1, characterized in that, The thickness of the HC260LA low-alloy high-strength steel plate is 0.8~2.5mm.

5. A method of producing the atmospheric corrosion resistant HC260LA low alloy high strength steel according to any one of claims 1 to 4, characterized by, The process comprises smelting, continuous casting, hot rolling, cold rolling, continuous annealing and tempering, wherein: 1) Hot rolling: The continuous casting blank is heated to 1180~1230℃, and the holding time is ≥120min; the rough rolling opening temperature is ≥1150℃, and the rolling passes are ≥5; the finish rolling temperature is 820~860℃; the front segment + rear segment segmented cooling is adopted, and the coiling temperature is 580~620℃; 2) Cold continuous rolling: after pickling of the hot-rolled strip, the total reduction is controlled at 70%~78%, the plate thickness precision is controlled within ±0.02mm, the dislocation density is increased, and the subgrain structure is formed to provide driving force for subsequent annealing and recrystallization; 3) Continuous annealing: the strip is sent into a continuous annealing furnace, and the critical zone annealing temperature is 780~820℃, and the holding time is 120~180s; 4) Tempering: the elongation is controlled at 1.0%~1.5%.

6. The production method of the atmospheric corrosion resistant HC260LA low alloy high strength steel according to claim 5, characterized in that, The smelting process comprises: Molten iron pretreatment: KR desulfurization process is adopted to control the S content to be ≤0.003%; converter smelting: low-oxygen blowing process is adopted to control the end-point oxygen content to be ≤0.003%; LF refining: silicon-calcium alloy is added for calcium treatment, and the silicon-calcium alloy addition amount is 0.5~1.0kg / ton of steel.

7. The production method of the atmospheric corrosion resistant HC260LA low alloy high strength steel according to claim 5, characterized in that, The continuous casting process comprises: Weak cooling process is adopted, and the mold cooling intensity is ≤800L / (m·min) to control the equiaxed crystal ratio of the casting blank to be ≥50%.

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