Coating-free super weathering steel and manufacturing method therefor

Abstract

The present invention relates to the technical field of atmospheric corrosion-resistant steels, and disclosed are a coating-free super weathering steel and a manufacturing method therefor. The coating-free super weathering steel comprises the following chemical components in percentage by mass: C: 0.01-0.07%; Si: 0.20-0.80%; Mn: 0.3-0.9%; Cu: 0.15-0.25%; Cr: 1.25-1.8%; P: 0.06-0.10%; S≤0.02%; niobium (Nb): 0-0.10%; titanium (Ti): 0-0.10%; Nb+Ti: 0.05-0.12%; Cu / P: 2-4; Cr / Cu: 5-10; and the balance of Fe and inevitable impurities. The present invention improves the stability of rust layers in weathering steels by means of the synergistic effect of elements such as Cu, Cr and P, and achieves high strength and high toughness by means of Nb and Ti microalloying in conjunction with a controlled rolling and controlled cooling process, thereby achieving the effects of improving the economy and corrosion resistance of super weathering steels and realizing coating-free use.

Description

A paint-free super weathering steel and its manufacturing method Technical Field

[0001] This invention belongs to the field of atmospheric corrosion resistant steel technology, specifically relating to a paint-free super weather-resistant steel and its manufacturing method. Background Technology

[0002] Weathering steel is a type of steel made by adding small amounts of alloying elements such as copper, chromium, nickel, and molybdenum to ordinary carbon steel. While maintaining its mechanical properties, this steel has corrosion resistance 2 to 8 times that of ordinary carbon steel, and this increase in corrosion resistance becomes more pronounced over time. After several years of service in the atmosphere, a stable and dense rust layer forms on the surface of weathering steel, which slows down the corrosion of the substrate, allowing for paint-free use. Using weathering steel without painting significantly reduces painting costs, is environmentally friendly, shortens the construction cycle, and greatly reduces maintenance costs during the steel's service life, making it of great significance.

[0003] Studies have shown that the rust stabilization process of weathering steel is related to the steel's chemical composition, usage environment, and construction. In areas without severe air pollution or particularly humid conditions, weathering steel can gradually form a stable rust layer and can be directly exposed to the atmosphere. However, in heavily polluted areas, coastal regions, and other harsh corrosive environments, ordinary weathering steel struggles to form a stable rust layer, necessitating the use of super weathering steel to achieve paint-free application.

[0004] Most existing super weathering steels employ high-alloy systems, adding high levels of alloying elements such as Ni and Mo, which is detrimental to the economic efficiency of the steel plates. Furthermore, the highest-grade existing high-weathering steel is Q355GNH, with a strength level of only 355 MPa, which is insufficient to meet the development requirements of high strength, lightweight, and low carbon emissions. In addition, existing super weathering steels still suffer from poor rust layer stability and poor corrosion resistance in harsh corrosive environments during the initial stages of use, making it difficult to use without painting. Therefore, it is necessary to develop super weathering steels that balance economic efficiency and corrosion resistance to achieve paint-free use in harsh corrosive environments. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing a paint-free super weathering steel and its manufacturing method. The method improves the stability of the rust layer of weathering steel through the synergistic effect of elements such as Cu, Cr, and P, and obtains high strength and high toughness by combining niobium and titanium microalloying and controlled rolling and cooling processes. This achieves the effect of improving the economy and corrosion resistance of super weathering steel and enabling paint-free use.

[0006] To solve the technical problem proposed in this invention, this invention provides a paint-free super weathering steel. The chemical composition of the paint-free super weathering steel, by mass percentage, includes: C: 0.01-0.07%, Si: 0.20-0.80%, Mn: 0.3-0.9%, Cu: 0.15-0.25%, Cr: 1.25-1.8%, P: 0.06-0.10%, S≤0.02%, Nb: 0-0.10%, Ti: 0-0.10%, Nb+Ti: 0.05-0.12%, Cu / P: 2-4, Cr / Cu: 5-10, with the remainder being Fe and unavoidable impurities.

[0007] Preferably, the chemical composition of the uncoated super weathering steel, by mass percentage, includes: C: 0.01-0.07%, Si: 0.20-0.80%, Mn: 0.3-0.9%, Cu: 0.2-0.25%, Cr: 1.3-1.5%, P: 0.07-0.09%, S≤0.02%, Nb: 0-0.10%, Ti: 0-0.10%, Nb+Ti: 0.05-0.12%, Cu / P: 3-4, Cr / Cu: 6-7, with the remainder being Fe and unavoidable impurities.

[0008] Preferably, the mass percentage of Nb is 0-0.05% and the mass percentage of Ti is 0-0.08%.

[0009] In the above scheme, the metallographic structure of the uncoated super weathering steel is a polygonal ferrite structure with a grain size ≥11 and an inclusion level ≤0.5.

[0010] In the above scheme, the yield strength R of the uncoated super weathering steel t0.5 The tensile strength is 420–750 MPa, and the tensile strength R is... m The strength ranges from 520 to 860 MPa, with a yield strength ratio R. t0.5 / R m ≤0.9, elongation after fracture A 50mm ≥20%, impact energy at -20℃ KV2≥100J.

[0011] In the above scheme, the corrosion resistance of the uncoated super weathering steel is tested according to TB / T 2375-1993, and its corrosion rate is ≤1.6g / (m). 2 The relative corrosion rate of .h) is 40% lower than that of Q355 steel.

[0012] This invention also provides a method for manufacturing paint-free super weathering steel, comprising the following steps:

[0013] 1) Smelt in a converter according to the chemical composition of uncoated super weathering steel;

[0014] 2) Perform LF refining. After refining, the S content of the molten steel is ≤0.010%, and the P content is 0.06-0.1%.

[0015] 3) Perform RH vacuum treatment, with a vacuum degree ≤70Pa and a vacuum cycle time ≥10min;

[0016] 4) Continuous casting to form billets, heating the billets at a temperature of 1100~1250℃;

[0017] 5) Rolling is carried out, with the finishing rolling starting temperature at 850-950℃ and the finishing rolling ending temperature at 800-880℃;

[0018] 6) Perform laminar flow cooling at a rate of 15-30℃ / s, then curl the steel to obtain paint-free super weathering steel.

[0019] In the above scheme, the rolling process also includes roughing, with a roughing start temperature of 1000-1200℃, a roughing finish temperature of 880-970℃, and a total reduction rate of 65-85%.

[0020] In the above scheme, the cumulative reduction rate of the finishing rolling is ≥70%, and the thickness of the steel plate after finishing rolling is 1.5 to 5 mm.

[0021] In the above scheme, the curling temperature is 480-600℃.

[0022] Preferably, the vacuum degree of the RH vacuum treatment is ≤50Pa, the vacuum cycle time is 15-30min, and the vacuum end temperature is 1550-1650℃.

[0023] Preferably, the heating temperature of the casting is 1180–1210°C.

[0024] Preferably, the roughing start temperature is 1150–1180°C and the roughing finish temperature is 930–950°C.

[0025] Preferably, the finishing rolling start temperature is 890–930°C and the finishing rolling end temperature is 850–880°C.

[0026] Preferably, the cooling rate of the laminar flow cooling is 20-25°C / s.

[0027] The functions and mechanisms of each element in this invention are as follows:

[0028] Carbon (C): Carbon is a basic strengthening element in steel, but excessive carbon content is detrimental to the ductility and weldability of steel. Therefore, this invention uses a low-carbon composition, with the C content limited to 0.01–0.07%.

[0029] Silicon (Si): Silicon plays a role in deoxidation and solid solution strengthening, and the addition of silicon is beneficial to corrosion resistance. However, excessive silicon will deteriorate the mechanical properties of steel. Therefore, the Si content in this invention is limited to 0.20-0.8%.

[0030] Manganese (Mn): Manganese plays a role in solid solution strengthening, which can compensate for the strength reduction caused by low carbon content. However, during the metallurgical process, manganese easily causes microstructure segregation and the formation of MnS inclusions, which in turn deteriorates the mechanical properties and corrosion resistance of steel. Therefore, the Mn content in this invention is limited to 0.3%–0.9%.

[0031] Copper (Cu): Copper is a corrosion-resistant element that can significantly increase the self-corrosion potential of steel, forming a copper oxide film on the steel surface and improving the thermodynamic stability of the steel. In addition, copper can synergistically work with chromium and phosphorus to promote the refinement of the α-FeOOH crystals, a stable rust layer component, making the rust layer dense and stable, thereby improving the corrosion resistance of the steel. However, excessively high Cu content can adversely affect weldability; when the Cu content exceeds 0.25%, hot cracking and other problems are prone to occur during welding. This invention improves weldability and enhances the quality and reliability of welded joints by reducing the Cu content to 0.15%–0.25%. Moreover, reducing the Cu content can also significantly reduce production costs. Therefore, the Cu content of this invention is limited to 0.15%–0.25%, preferably 0.2%–0.25%.

[0032] Chromium (Cr): Chromium is an important corrosion-resistant element. It can form a dense chromium oxide protective film on the material surface, preventing the intrusion of corrosive media. When the Cr content increases to above 1.25%, chromium accumulates in large quantities in the rust layer, forming thermodynamically stable, amorphous α-Fe. 1-x Cr x OOH can significantly improve the corrosion resistance of materials, giving them a longer service life in harsh environments such as marine and industrial atmospheres. Cr can also strengthen through solid solution and precipitation, thereby improving the strength and hardness of the material. As the Cr content increases, the strength and hardness of the material gradually increase. However, excessive chromium will reduce the toughness and weldability of the steel. Therefore, the Cr content in this invention is limited to 1.25% to 1.8%, preferably 1.3% to 1.5%.

[0033] Phosphorus (P): Phosphorus is a harmful element in steel, deteriorating its toughness and weldability. However, phosphorus is an effective corrosion-resistant element; phosphoric acid can be converted into phosphates, blocking cracks and pores in the rust layer and significantly improving its protective properties. Phosphorus can also work synergistically with copper and chromium, mutually promoting its accumulation in the rust layer, forming a protective barrier against corrosive media on the steel surface, and improving the steel's resistance to atmospheric corrosion. Therefore, the P content in this invention is limited to 0.06–0.10%, preferably 0.07–0.09%.

[0034] To better leverage the synergistic effect of the three elements, the Cu / P content ratio is limited to 2–4, and the Cr / Cu content ratio is limited to 5–10. This is because Cu and P have a synergistic effect, mainly by forming a protective rust film and mutually promoting the increase of their content in the rust layer. Controlling their content ratio at 2–4 can better utilize their synergistic efficiency. Similarly, Cr and Cu mutually promote enrichment in the rust layer, and controlling their content ratio at 5–10 can effectively increase the enrichment of Cr in the rust layer.

[0035] Niobium (Nb) and Titanium (Ti): Both niobium and titanium are microalloying elements that can significantly refine grain size. Optimization of the grain structure can only be achieved by precisely controlling the addition amounts of Nb and Ti. A finer grain structure can improve the strength, toughness, and corrosion resistance of steel. Niobium and titanium not only play their respective roles in solid solution strengthening and precipitation strengthening in steel, but also exhibit a synergistic strengthening effect. Niobium's solid solution strengthening can improve the strength of steel, while titanium's precipitation strengthening can further improve the impact toughness of steel. The synergistic effect of both results in the steel of this invention having higher overall performance. Therefore, this invention limits the addition amounts of the two microalloys to Nb: 0–0.10%, Ti: 0–0.10%, and limits the total addition amount of Nb+Ti to the range of 0.05–0.12%. This fully utilizes the grain-refining and strength- and toughness-improving effects of niobium and titanium, while avoiding the adverse effects of excessive microalloying, such as reduced weld impact toughness, increased ductile-brittle transition temperature, and reduced low-temperature toughness.

[0036] Sulfur (S): Sulfur is a harmful element. It can combine with manganese to form manganese sulfide, a harmful inclusion that not only reduces the mechanical properties of steel but also its corrosion resistance. Therefore, this invention controls the S content to ≤0.020%.

[0037] The technical concept of the manufacturing method of this invention is as follows:

[0038] In this invention, after hot metal smelting in a converter, desulfurization is performed using an LF furnace and an RH vacuum furnace. Due to the use of a high-phosphorus (P) composition system, the desulfurization process in steelmaking can be reduced. Simultaneously, the LF furnace and RH vacuum furnace treatment ensures uniform distribution of niobium and titanium microalloying in the molten steel, inducing the formation of numerous fine, dispersed non-metallic inclusions, which become the nucleation site for ferrite. During rolling, the finishing rolling temperature is controlled within the range of 800–950°C to ensure uniform precipitation and distribution of niobium and titanium carbides and nitrides within and at grain boundaries. Furthermore, a cooling rate of 15–30°C / s is used after rolling to rapidly reduce the steel plate temperature to 480–600°C for curling, preventing coarsening of the ferrite structure. Therefore, this invention adopts a simplified high-P process, which reduces costs while improving corrosion resistance. By combining niobium and titanium microalloying with TMCP process, the microstructure is refined by controlling the finishing rolling and cooling rates. With the addition of niobium-titanium strengthening precipitates, steel with a fine polygonal ferrite structure is finally obtained, which compensates for the toughness loss caused by high P while ensuring strength.

[0039] To ensure effective microalloying of niobium and titanium and refinement of austenite grains, the finishing rolling temperature in this invention is controlled between 800 and 950°C (i.e., both the start and end temperatures of finishing rolling are within this range). 800–950°C falls within the austenite stability region, where deformation during finishing rolling can refine the austenite grains through dynamic recrystallization, laying the foundation for subsequent ferrite refinement after phase transformation. At this temperature, niobium and titanium carbonitrides undergo a precipitation-dissolution equilibrium: excessively high temperatures (>950°C) lead to excessive dissolution of precipitates, making it difficult to form sufficient dispersed precipitates during subsequent cooling, thus weakening the strengthening effect; excessively low temperatures (<800°C) result in premature and coarse precipitation of precipitates, and a sharp increase in rolling deformation resistance, increasing equipment load. Therefore, by controlling the finishing rolling temperature within this range, this invention simultaneously achieves austenite grain refinement and uniform precipitation of niobium-titanium compounds, ensuring final microstructure refinement and strength improvement.

[0040] Furthermore, this invention sets a core cooling parameter: laminar cooling rate (15–30 °C / s). This cooling rate is crucial for suppressing ferrite coarsening and strengthening precipitates, directly affecting the final microstructure. Specifically, this cooling rate (15–30 °C / s) shortens the residence time of the steel plate in the high-temperature region (>600 °C), preventing austenite grains from coarsening before phase transformation. Simultaneously, it promotes the rapid transformation of supercooled austenite into ferrite, resulting in finer ferrite grains. It also suppresses the coarsening of niobium and titanium carbonitrides, ensuring the precipitates remain fine and dispersed, thus enhancing precipitation strengthening. If the cooling rate is too slow (<15 °C / s), the ferrite will grow slowly at high temperatures, leading to microstructure coarsening and a significant decrease in toughness. If the cooling rate is too fast (>30 °C / s), it may cause supercooled austenite to transform into hard and brittle structures such as martensite, increasing brittleness. Therefore, the cooling rate of 15–30 °C / s used in this invention is the optimal range for balancing microstructure refinement, precipitation strengthening, and avoiding hard and brittle phases.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] First, most existing super weathering steels employ high-alloy systems, adding high levels of alloying elements such as Mn, Ni, and Mo. This is detrimental to the economic efficiency of the steel plates and results in lower strength, making it difficult to meet the development trend of high strength and low carbon. This invention does not add elements such as Ni and Mo. Instead, it improves rust layer stability and corrosion resistance through the synergistic effect of elements such as Cu, Cr, and P. Compared to existing technologies, the corrosion resistance is significantly enhanced, enabling paint-free use. Furthermore, the use of niobium and titanium microalloying, combined with TMCP controlled rolling and cooling processes, yields a fine-grained polygonal ferrite structure, giving it high strength and toughness.

[0043] Secondly, the paint-free super weathering steel described in this invention can not only meet the yield strength R t0.5 The tensile strength is 420–750 MPa, and the tensile strength R is... m The strength ranges from 520 to 860 MPa, with a yield strength ratio R. t0.5 / R m ≤0.9, elongation after fracture A 50mm ≥20%, impact energy at -20℃ KV2≥100J, and according to TB / T 2375-1993, its corrosion resistance is tested and its corrosion rate is ≤1.6g / (m²). 2 The corrosion rate of super weathering steel is less than 40% of that of Q355 steel, which significantly improves the corrosion resistance of super weathering steel and enables it to be used without painting.

[0044] Third, this invention employs a high phosphorus (P) content design, thereby reducing the cost of the P removal process. Furthermore, it adds small amounts of alloying elements such as Cu and Cr, while avoiding the use of precious metals like Ni, Mo, and Sn, further reducing alloy costs. Therefore, the paint-free super weathering steel described in this invention is more economically cost-effective. Attached Figure Description

[0045] Figure 1 is a metallographic photograph of the uncoated super weathering steel in Embodiment 1 of the present invention.

[0046] Figure 2 is a photograph of the inclusions in the uncoated super weathering steel in Embodiment 1 of the present invention. Detailed Implementation

[0047] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0048] Examples 1-10

[0049] The chemical composition of the uncoated super weathering steels in Examples 1-10 is shown in Table 1.

[0050] Table 1

[0051] Note: ① Comparative Example 1 is Q355GNH steel, whose chemical composition, in addition to that listed in the table, also includes: Ni 0.39%, Mo 0.12%, Zr 0.09%, V 0.05%; ② Comparative Example 2 is Q355GNH steel, whose chemical composition, in addition to that listed in the table, also includes: Ni 0.21%, Mo 0.27%, Zr 0.13%, V 0.07%.

[0052] The manufacturing method of the paint-free super weathering steel in Examples 1-10 includes the following steps:

[0053] 1) Smelt in a converter according to the chemical composition in Table 1;

[0054] 2) Perform LF refining. After refining, the S content of the molten steel is ≤0.010%, and the P content is 0.06-0.1%.

[0055] 3) Perform RH vacuum treatment, with a vacuum degree ≤70Pa, a vacuum cycle time of 10~30min, and a vacuum end temperature of 1550~1650℃;

[0056] 4) Continuous casting to form billets, heating the billets at a temperature of 1100~1250℃;

[0057] 5) Rolling is carried out. The roughing temperature starts at 1000-1200℃ and ends at 880-970℃, with a total reduction of 65-85%. The finishing temperature starts at 850-950℃ and ends at 800-880℃, with a cumulative reduction of ≥70%. The steel plate is rolled into a thickness of 1.5-5mm after 5-10 passes.

[0058] 6) Perform laminar flow cooling at a rate of 15-30℃ / s, cool to 480-600℃ and then curl to obtain paint-free super weathering steel.

[0059] The main process parameters involved in the manufacturing method are shown in Table 2.

[0060] Table 2

[0061] The mechanical properties, metallographic structure and inclusions of the uncoated super weathering steels in Examples 1 to 10 were tested, and the results are shown in Table 3.

[0062] Table 3

[0063] As can be seen from Table 3, the yield strength R of the paint-free super weathering steel of this invention is... t0.5 The tensile strength is 420–750 MPa, and the tensile strength R is... m The strength ranges from 520 to 860 MPa, with a yield strength ratio R. t0.5 / R m ≤0.9, elongation after fracture A 50mm ≥20%, impact energy at -20℃ KV2≥100J, which is a significant improvement over the comparative Q355GNH steel.

[0064] Figure 1 shows a metallographic photograph of the uncoated super weathering steel in Example 1. As can be seen from the figure, its metallographic structure is polygonal ferrite with a grain size of grade 11. Figure 2 shows a photograph of the inclusions in the uncoated super weathering steel in Example 1. As can be seen from the figure, the inclusions are type D inclusions with a grade of 0.5. Combining Figures 1-2 and Table 3, it can be seen that the uncoated super weathering steel of the present invention achieves a fine polygonal ferrite structure, and its grain size and inclusion grade are significantly improved compared to the Q355GNH steel in the comparative example.

[0065] To further verify the corrosion resistance of the uncoated super weathering steel, a 3-day immersion corrosion test was conducted in 0.01 mol / L sodium bisulfite solution according to the TB / T 1979-2023 standard "Special Metal Materials for Locomotives and Rolling Stock - Atmospheric Corrosion Resistant Steel". The results are shown in Table 4.

[0066] Table 4

[0067] As shown in Table 4, the corrosion rate of the uncoated super weathering steel of this invention is ≤1.6 g / (m²). 2 Compared to Q355 steel, the relative corrosion rate is 40% lower, and it is a significant improvement over Q355GNH steel, significantly improving corrosion resistance. It can be used without coating in C1 to C4 environments (as specified in ISO 9223:2012 standard), and with a certain thickness compensation (0.1 to 0.3 mm), it can meet the service life of structural components for more than 25 years.

[0068] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A paint-free super weathering steel, characterized in that, Its chemical composition, by mass percentage, includes: C: 0.01–0.07%, Si: 0.20–0.80%, Mn: 0.3–0.9%, Cu: 0.15–0.25%, Cr: 1.25–1.8%, P: 0.06–0.10%, S≤0.02%, Nb: 0–0.10%, Ti: 0–0.10%, Nb+Ti: 0.05–0.12%, Cu / P: 2–4, Cr / Cu: 5–10, with the remainder being Fe and unavoidable impurities.

2. The paint-free super weathering steel according to claim 1, characterized in that, Its chemical composition, by mass percentage, includes: C: 0.01–0.07%, Si: 0.20–0.80%, Mn: 0.3–0.9%, Cu: 0.2–0.25%, Cr: 1.3–1.5%, P: 0.07–0.09%, S≤0.02%, Nb: 0–0.10%, Ti: 0–0.10%, Nb+Ti: 0.05–0.12%, Cu / P: 3–4, Cr / Cu: 6–7, with the remainder being Fe and unavoidable impurities.

3. The paint-free super weathering steel according to claim 1, characterized in that, The metallographic structure of the uncoated super weathering steel is a polygonal ferrite structure with a grain size ≥11 and an inclusion level ≤0.

5.

4. The paint-free super weathering steel according to claim 1, characterized in that, The yield strength R of the uncoated super weathering steel t0.5 The tensile strength is 420–750 MPa, and the tensile strength R is... m The strength ranges from 520 to 860 MPa, with a yield strength ratio R. t0.5 / R m ≤0.9, elongation after fracture A 50mm ≥20%, impact energy at -20℃ KV2≥100J.

5. The paint-free super weathering steel according to claim 1, characterized in that, The uncoated super weathering steel was tested for corrosion resistance according to TB / T 2375-1993, and its corrosion rate was ≤1.6g / (m). 2 The relative corrosion rate of .h) is 40% lower than that of Q355 steel.

6. A method for manufacturing uncoated super weathering steel as described in any one of claims 1 to 5, characterized in that, Includes the following steps: 1) Smelt in a converter according to the chemical composition of uncoated super weathering steel; 2) Perform LF refining. After refining, the S content of the molten steel is ≤0.010%, and the P content is 0.06-0.1%. 3) Perform RH vacuum treatment, with a vacuum degree ≤70Pa and a vacuum cycle time ≥10min; 4) Continuous casting to form billets, heating the billets at a temperature of 1100~1250℃; 5) Rolling is carried out. The roughing rolling start temperature is 1000-1200℃, the roughing rolling end temperature is 880-970℃, the finishing rolling start temperature is 850-950℃, and the finishing rolling end temperature is 800-880℃. 6) Perform laminar flow cooling at a rate of 15-30℃ / s, then curl the steel to obtain paint-free super weathering steel.

7. The method for manufacturing uncoated super weathering steel according to claim 6, characterized in that, The vacuum degree of the RH vacuum treatment is ≤50Pa, the vacuum cycle time is 15-30min, and the vacuum end temperature is 1550-1650℃.

8. The method for manufacturing uncoated super weathering steel according to claim 6, characterized in that, The total reduction rate of the rough rolling is 65-85%, the cumulative reduction rate of the finishing rolling is ≥70%, and the thickness of the steel plate after finishing rolling is 1.5-5mm.

9. The method for manufacturing uncoated super weathering steel according to claim 6, characterized in that, The heating temperature of the casting is 1180-1210℃; the rough rolling start temperature is 1150-1180℃, and the rough rolling finish temperature is 930-950℃; the finish rolling start temperature is 890-930℃, and the finish rolling finish temperature is 850-880℃.

10. The method for manufacturing paint-free super weathering steel according to claim 6, characterized in that, The laminar flow cooling rate is 20–25 °C / s; the curling temperature is 480–600 °C.

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