Surface-treatment-free corrosion-resistant building structural steel and preparation method thereof

Abstract

The invention discloses surface-treatment-free corrosion-resistant building structural steel and a preparation method thereof, and relates to the technical field of building steel structure manufacturing. The corrosion-resistant building structural steel comprises the following chemical components in percentage by mass: 0.20 to 0.60 percent of Cr, 0.20 to 0.60 percent of Cu, 0.01 to 0.05 percent of Ti and 0.01 to 0.05 percent of Nb. The preparation method comprises the following steps of converter smelting, LF refining, continuous casting, heating, rolling, cooling and coiling. The heating process comprises a preheating section, a heating section and a soaking section; the preheating section is performed in a weak reducing atmosphere, and the weak reducing atmosphere comprises, by volume, 5-8% of H2O, 2-3% of CO and the balance N2. According to the surface-treatment-free corrosion-resistant building structural steel and the preparation method thereof, a compact oxide layer can be naturally formed without surface treatment, through innovative alloy component design and process optimization, the corrosion resistance and service performance are improved, the production cost and environmental pollution are reduced, and a green and efficient corrosion-resistant solution is provided for the field of building structural steel.

Description

Technical Field

[0001] The invention relates to the technical field of building steel structure manufacturing, in particular to a surface treatment-free corrosion-resistant building structural steel and a preparation method thereof. Background Art

[0002] In modern construction, steel structures, with their advantages of high strength, light weight, and short construction periods, are widely used in high-rise buildings, long-span bridges, and offshore platforms. However, traditional structural steels (such as Q355B and Q460C) face multiple technical bottlenecks in production and service, particularly in corrosion resistance, which severely restricts the green development and longevity of steel structures. During the production process, traditional structural steel forms an oxide scale composed of FeO (approximately 60-70%), Fe2O3 (approximately 20-30%), and a small amount of Fe3O4. This oxide scale has inherent structural defects: the FeO layer is a porous, flaky structure with a porosity of 15-20%. Its bonding strength with the substrate is only 5-8 MPa, making it susceptible to moisture absorption and rust in humid environments. This can lead to coating peeling and blistering during subsequent painting. According to statistics, conventional building structural steel will develop visible red rust after being stored in a humid environment for 1 to 3 months. The average annual corrosion rate in the atmospheric environment is 0.1 to 0.2 mm. In coastal salt spray areas or industrial acid rain areas, the annual corrosion rate can reach 0.3 to 0.5 mm, posing a serious threat to building safety.

[0003] To remove this loose layer of iron oxide, traditional processes typically require surface treatments such as shot blasting and sandblasting. However, these surface treatments not only increase production costs but also pollute the environment. While other surface treatment technologies, such as thermal spraying and chemical coatings, can improve corrosion resistance, they suffer from high costs, complex processes, and poor adhesion to the substrate, making them difficult to apply on a large scale.

[0004] Furthermore, existing technologies often enhance corrosion resistance by adding elements such as Cu, Cr, and Ni. However, the surface oxide layer of such structural steel is still primarily composed of FeO (typically >60%), which is easily further oxidized in air to form loose Fe2O3, failing to fundamentally address the rust caused by the oxide layer. Furthermore, existing research has largely focused on the impact of a single component or process on the oxide layer, failing to integrate alloy composition design with oxidation process optimization. This inability to achieve coordinated regulation of the oxide layer's composition and structure has resulted in limited improvements in the surface corrosion resistance of structural steel.

[0005] Therefore, there is an urgent need to provide a corrosion-resistant building structural steel with good corrosion resistance, low production cost and environmental protection to promote the greening and long-life development of steel structures. Summary of the Invention

[0006] In order to overcome the shortcomings of the above-mentioned technology, the purpose of the present invention is to provide a surface treatment-free corrosion-resistant building structural steel and a preparation method thereof, so as to solve the problems of poor corrosion resistance and high surface treatment cost of existing building structural steel.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows: A surface treatment-free corrosion-resistant building structural steel has the following characteristics: the steel comprises the following chemical components in percentage by mass: Cr: 0.20-0.60%, Cu: 0.20-0.60%, Ti: 0.01-0.05%, and Nb: 0.01-0.05%.

[0008] As a preferred solution, the building structural steel also includes the following chemical components in percentage by mass: C≤0.20%, Si: 0.05~0.60%, Mn: 0.80~1.5%, P≤0.015%, S≤0.015%, and the balance is Fe and unavoidable impurities.

[0009] Furthermore, the building structural steel includes the following chemical components in mass percentage: C: 0.05~0.18%, Si: 0.20~0.50%, Mn: 1.00~1.20%, P≤0.015%, S≤0.01%, Cr: 0.30~0.50%, Cu: 0.30~0.50%, Ti: 0.02~0.04%, Nb: 0.02~0.04%, and the balance is Fe and unavoidable impurities.

[0010] Furthermore, the mass proportion of Fe3O4 in the surface oxide layer of the building structural steel is ≥60%, the thickness of the surface oxide layer is 8~15μm, and the bonding strength between the surface oxide layer and the matrix is ​​≥15MPa; the yield strength of the building structural steel is ≥600MPa, and the elongation after fracture is ≥20%.

[0011] The present invention also provides a preparation method for the above-mentioned corrosion-resistant building structural steel that does not require surface treatment, which is special in that it includes the following steps: converter smelting, LF refining, continuous casting, heating, rolling, cooling, and coiling; the heating process includes a preheating section, a heating section, and a soaking section; the preheating section is carried out in a weak reducing atmosphere, and the weak reducing atmosphere includes 5-8% by volume of H2O, 2-3% by volume of CO, and the rest is N2.

[0012] As a preferred solution, the temperature of the preheating section is 850~950℃, and the heating time is 30~40min; the temperature of the soaking section is 1150~1200℃, and the heating time is 80~90min, and the O2 concentration in the controlled environment is 1~1.5%.

[0013] As a preferred solution, the rolling process includes: Use 18~20MPa high pressure dephosphorization water to remove phosphorus before rough rolling; Finish rolling is performed after secondary dephosphorization; in the secondary dephosphorization, the dephosphorization water contains CuSO4, and the concentration of CuSO4 in the dephosphorization water is 0.1~0.35w / v%.

[0014] Furthermore, during the rough rolling process, the starting rolling temperature is 1100-1190° C., and the reduction ratio of each pass is ≥15%; during the finishing rolling process, the final rolling temperature is 850-900° C., and the reduction ratio of the last two passes is ≤10%.

[0015] As a preferred solution, the cooling process adopts segmented laminar cooling, with the front section cooled to 740~760℃ and the middle section cooled to 600℃; the cooling rate of the front section is 40~50℃ / s, and the cooling rate of the middle section is 20~30℃ / s.

[0016] Furthermore, the middle section cooling is carried out in hot and humid air with a humidity of 80-90%.

[0017] As a preferred solution, in the coiling process, the coiling temperature is 550-600°C.

[0018] The functions of each element and process in the present invention are as follows: The carbon content of the present invention is selected to be ≤ 0.20%. Carbon is an effective element for increasing steel strength, but higher carbon contents reduce the steel's low-temperature toughness and increase its susceptibility to weld cold cracking. However, too low a carbon content, such as less than 0.03%, can result in insufficient steel plate strength, a low hard phase content, and difficulty controlling the yield strength ratio. The preferred carbon content is 0.05-0.18%.

[0019] The Si content of the present invention is between 0.05% and 0.60%. During heating, Si forms internal oxidation products between the scale and the steel substrate, increasing scale adhesion. This results in subsequent incomplete scale removal and poor compactness. Controlling the Si content can reduce the damage to the scale's compactness caused by internal oxidation. Furthermore, the addition of Si can improve the corrosion resistance of steel materials. Therefore, considering comprehensive performance considerations such as scale control and corrosion resistance, the Si content in the present invention is preferably between 0.20% and 0.50%.

[0020] The Mn content of the present invention is between 0.80% and 1.50%. Mn is an important strengthening and toughening element and an austenite stabilizing element. It can expand the austenite region in the iron-carbon phase diagram and promote medium-temperature microstructural transformation. Higher Mn contents can easily cause severe center segregation in the steel, deteriorating its low-temperature toughness and causing cracks in the heat-affected zone (HAZ) of the steel plate during welding. This is unnecessary for achieving the mechanical properties of the present steel. However, too low a Mn content can easily reduce the steel's strength. The preferred Mn content is between 1.00% and 1.20%.

[0021] In the present invention, P is ≤0.015%. A higher P content will significantly improve the weather resistance of the steel, but will also reduce the weldability of the steel, increase the cold brittleness tendency of the steel, and cause relatively serious center segregation.

[0022] The S content of the present invention is ≤0.015%. A higher content of S will reduce the corrosion resistance, low-temperature toughness and Z-direction performance of the steel.

[0023] The Cu content of the present invention is 0.20-0.60%. Cu is an important element for improving weather resistance. Cu improves the quality of the rust layer by concentrating in defects such as cracks and holes in the rust layer. However, when Cu is added in an amount greater than 0.50%, Cu segregates at grain boundaries during high-temperature rolling, causing grain boundary oxidation and cracking, which seriously affects surface quality and reduces the toughness of the heat-affected zone of the steel plate. The optimal Cu content is preferably 0.30-0.50%.

[0024] The Cr content in the present invention is 0.20-0.60%. Appropriate Cr content can increase the strength of steel and significantly improve its weather resistance. However, excessive Cr content, such as exceeding 0.80%, can increase welding difficulty. Adding Cr alone or at a content of less than 0.30% does not form a passivation film and cannot reduce the corrosion-induced sensitivity of the steel substrate. Cu and Cr work synergistically to form a (Fe, Cu)3O4 solid solution in the oxide layer, reducing lattice distortion and improving density. Compared with traditional Ni, an element that enhances corrosion resistance, Cr is less expensive. The Cr content is preferably 0.30-0.50%.

[0025] The content of Ti and Nb in the present invention is 0.01-0.05%. Ti and Nb can refine the grains, reduce oxidation defects at the grain boundaries, and enhance the adhesion of the iron oxide scale. The Ti and Nb content of the present invention is preferably 0.02-0.04%.

[0026] The present invention strictly controls the rolling temperature, reduces the thickness of the iron oxide scale, and controls the reduction rate of the last two passes of finishing rolling to retain the integrity of the surface oxide layer; CuSO4 solution is added to the descaling solution of the secondary dephosphorization, and its redox catalytic effect and micro-electrochemical effect are used to increase the nucleation rate of the oxide layer, refine the FeO grains, and promote their interaction with Fe 3+ Rapid reaction generates Fe3O4, reducing the FeO content in the oxide scale. The specific reaction is as follows: Cu 2+ +Fe→Cu+Fe 2+ ; 6Fe 2+ +4H2O+2O2→2Fe3O4+8H + .

[0027] In addition, when cooling to the coiling temperature after hot rolling, the initial cooling rate is controlled at 40~50℃ / s to inhibit the growth of FeO, and a humid and hot environment is introduced in the middle section of laminar cooling for the first time to promote the in-situ conversion of FeO to Fe3O4, avoiding the problem of incomplete FeO decomposition in traditional processes; if high-temperature coiling is used, the volume of the iron oxide scale will expand and crack, and the diffusion rate of oxygen will also increase at high temperatures, and the bonding force between the iron oxide scale and the matrix will also decrease, which will easily cause the iron oxide scale to decompose again and cause internal oxidation. By controlling the coiling temperature within 550~600℃, the oxide layer can be ensured to be densely crystallized.

[0028] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a surface-treatment-free corrosion-resistant building structural steel and a preparation method thereof, which can naturally form a dense oxide layer without surface treatment. Through innovative alloy composition design and process optimization, the corrosion resistance and service performance are improved, the production cost and environmental pollution are reduced, and a green and efficient corrosion-resistant solution is provided for the field of building structural steel.

[0029] The present invention provides a new corrosion-resistant building structural steel that does not require surface treatment. The mass proportion of Fe3O4 in the surface oxide layer is ≥60%, the thickness is 8~15μm, and the bonding strength with the matrix is ​​≥15MPa; the yield strength of the building structural steel is ≥600MPa, and the elongation after fracture is ≥20%. Its corrosion resistance is improved by more than 37% compared with traditional building structural steel, and it has both high strength and corrosion resistance.

[0030] The present invention uses Cu-Cr-Ti-Nb multi-element alloying and the "weak reduction heating-copper-containing descaling-wet heat conversion" process to form a dense oxide layer mainly composed of Fe3O4 (Fe3O4≥60%) on the surface of building structural steel. No surface treatment is required, which reduces costs. The dense oxide film acts as a physical barrier to block corrosive media, and the micro-alloying effect increases the electrode potential, thereby extending the service life of building structural steel in harsh environments such as industrial atmosphere and coastal atmosphere, thereby achieving cost reduction, efficiency improvement and greening throughout the "manufacturing-service" life cycle. DETAILED DESCRIPTION

[0031] In order to better explain the present invention, the main contents of the present invention are further illustrated below in conjunction with specific examples, but the contents of the present invention are not limited to the following examples.

[0032] The present invention provides a surface treatment-free corrosion-resistant building structural steel, which comprises the following chemical components in percentage by mass: C≤0.20%, Si: 0.05-0.60%, Mn: 0.80-1.5%, P≤0.015%, S≤0.015%, Cr: 0.20-0.60%, Cu: 0.20-0.60%, Ti: 0.01-0.05%, Nb: 0.01-0.05%, and the balance is Fe and unavoidable impurities.

[0033] The method for preparing the corrosion-resistant building structural steel without surface treatment comprises the following steps: 1) Converter smelting.

[0034] 2) LF refining.

[0035] 3) Continuous casting to obtain ingots.

[0036] 4) Slab heating, including preheating, heating, and soaking sections. The preheating stage is conducted in a weakly reducing atmosphere at 850-950°C for 30-40 minutes. The weakly reducing atmosphere consists of 5-8% by volume H2O, 2-3% by volume CO, and the remainder N2. The heating stage is heated to the soaking temperature using conventional methods. The soaking stage is maintained at 1150-1200°C for 80-90 minutes, with an ambient O2 concentration of 1-1.5%.

[0037] 5) Rolling: Dephosphorization is performed using 18-20 MPa high-pressure dephosphorization water before rough rolling, the starting rolling temperature is 1100-1150° C., and the pass reduction ratio is ≥15%; after secondary dephosphorization, finish rolling is performed, the final rolling temperature is 850-900° C., and the last two passes reduction ratios are ≤10%. The dephosphorization water used in the secondary dephosphorization contains CuSO4, and the concentration of CuSO4 in the dephosphorization water is 0.1-0.35 w / v%.

[0038] 6) Cooling: adopt segmented laminar cooling, with the front section cooled to 740~760℃ and the middle section cooled to 600℃; the cooling rate of the front section is 40~50℃ / s, and the cooling rate of the middle section is 20~30℃ / s; the middle section cooling is carried out in hot and humid air with a humidity of 80~90%.

[0039] 7) Coiling: the coiling temperature is 550~600℃.

[0040] The method of the present invention and its advantages are further illustrated below by specific examples 1 to 5 and comparative examples 1 to 4.

[0041] Examples 1 to 5 The chemical composition and content of the building structural steel in Examples 1 to 5 are shown in Table 1. The preparation method adopts the preparation method of the present invention, except that the process parameters are different. The specific process parameters are shown in Tables 2 to 4.

[0042] Comparative Example 1 A traditional building structural steel, the chemical composition and content of which are shown in Table 1. The preparation method is produced according to the following process parameters: During the heating process: conventional heating at 1200℃, without preheating and soaking control; During the rolling process: the rough rolling temperature was 980°C, the finishing temperature was 820°C, the final finishing reduction was 14%, and the conventional dephosphorization water was 20 MPa. The finishing temperature did not meet the requirements of the present invention, and the final two finishing reductions were not controlled to be ≤10%, and the dephosphorization water did not contain CuSO4. The cooling rate was 20°C; segmented laminar cooling was not used, and the air humidity during the intermediate cooling was not controlled; Coiling temperature 600℃.

[0043] Comparative Example 2 The ingredients of this comparative example are the same as those of Example 1, and the difference between the preparation method and the preparation method in Example 1 is that the preheating stage in Comparative Example 2 does not adopt the weak reducing atmosphere of the present invention, but adopts the ordinary reducing atmosphere N2:H2=7:3.

[0044] Comparative Example 3 The components of this comparative example are the same as those of Example 1, but the difference between the preparation method and the preparation method in Example 1 is that the dephosphorization water for secondary dephosphorization in Comparative Example 3 does not contain CuSO4, and conventional dephosphorization water is used.

[0045] Comparative Example 4 The ingredients of this comparative example are the same as those of Example 1, but the difference between the preparation method and the preparation method in Example 1 is that the middle section cooling in Comparative Example 4 adopts a conventional method, and the air humidity is not controlled within the range of 80-90%.

[0046] The steel products obtained by the methods of Examples 1-5 and Comparative Examples 1-4 were tested for mechanical properties, oxide layer properties, and corrosion resistance. Mechanical properties were tested in accordance with national standards GB / T 228.1-2010 and GB / T 229-2007, corrosion resistance was tested in accordance with TB / T 1979-2023, Fe₃O₄ content was determined by cross-sectional observation, and bonding strength with the substrate was determined by pull-off testing. The test results are shown in Table 5. In Table 5, the relative corrosion rates of the steel products in Examples 1-5 and Comparative Examples 2-4 are the corrosion rates of the steel products in Examples 1-5 and Comparative Examples 2-4 relative to the steel product in Comparative Example 1.

[0047] Table 1: Chemical composition and content of the embodiments of the present invention and comparative examples, the balance being Fe and unavoidable impurities, mass percentage, %

[0048] Table 2: Heating process parameters

[0049] Table 3: Rolling process parameters

[0050] Table 4: Cooling process parameters

[0051] Table 5: Performance test results of Examples and Comparative Examples

[0052] As can be seen from Table 5, the yield strength, tensile strength, elongation after fracture, Fe3O4 content in the oxide scale, and bonding strength with the matrix of the conventional building structural steel produced in Comparative Example 1 using existing conventional components and preparation processes are significantly lower than those in the embodiment, and the oxide scale thickness and relative corrosion rate are significantly higher.

[0053] In the building structural steel and its preparation process in Comparative Examples 2 to 4, the composition and content control of the present invention are adopted, but the relevant parameter control in the preparation process of the present invention is not adopted at the same time. Compared with the examples of the present invention, the yield strength, tensile strength, elongation after fracture, Fe3O4 content in the oxide scale, and bonding strength with the substrate are significantly lower than those of the examples, and the oxide scale thickness and relative corrosion rate are increased.

[0054] The structural steel produced using the method of the present invention in Examples 1-5 requires no surface treatment. The surface oxide layer comprises ≥62% Fe₃O₄, has a thickness of 10-15 μm, and exhibits a bonding strength of ≥15 MPa with the substrate. The steel also exhibits a yield strength of ≥600 MPa and an elongation after fracture of ≥20%. Compared to conventional structural steel, this exhibits corrosion resistance improved by up to 52%, achieving a combination of high strength and corrosion resistance.

[0055] In summary, the present invention provides a surface-treatment-free corrosion-resistant building structural steel and a preparation method thereof, which can naturally form a dense oxide layer without surface treatment. Through innovative alloy composition design and process optimization, it improves corrosion resistance and service performance, reduces production costs and environmental pollution, and provides a green and efficient corrosion-resistant solution for the field of building structural steel.

[0056] The present invention provides a new corrosion-resistant building structural steel that does not require surface treatment. The Fe3O4 content of the surface oxide layer is ≥62%, the thickness is 10~15μm, and the bonding strength with the substrate is ≥15MPa; the yield strength of the building structural steel is ≥600MPa, and the elongation after fracture is ≥20%. Its corrosion resistance is improved by more than 37% compared with traditional building structural steel, and it has both high strength and corrosion resistance.

[0057] The present invention uses Cu-Cr-Ti-Nb multi-element alloying and the "weak reduction heating-copper-containing descaling-wet heat conversion" process to form a dense oxide layer mainly composed of Fe3O4 (Fe3O4≥60%) on the surface of building structural steel. No surface treatment is required, which reduces costs. The dense oxide film acts as a physical barrier to block corrosive media, and the micro-alloying effect increases the electrode potential, thereby extending the service life of building structural steel in harsh environments such as industrial atmosphere and coastal atmosphere, thereby achieving cost reduction, efficiency improvement and greening throughout the "manufacturing-service" life cycle.

Claims

1. A corrosion-resistant building structural steel that does not require surface treatment, characterized in that: It includes the following chemical components in percentage by mass: Cr: 0.20~0.60%, Cu: 0.20~0.60%, Ti: 0.01~0.05%, Nb: 0.01~0.05%.

2. The corrosion-resistant building structural steel according to claim 1, characterized in that: The building structural steel also includes the following chemical components in percentage by mass: C≤0.20%, Si: 0.05~0.60%, Mn: 0.80~1.5%, P≤0.015%, S≤0.015%, and the balance is Fe and unavoidable impurities.

3. The corrosion-resistant building structural steel according to claim 2, characterized in that: The building structural steel includes the following chemical components in mass percentage: C: 0.05-0.18%, Si: 0.20-0.50%, Mn: 1.00-1.20%, P≤0.015%, S≤0.01%, Cr: 0.30-0.50%, Cu: 0.30-0.50%, Ti: 0.02-0.04%, Nb: 0.02-0.04%, and the balance is Fe and unavoidable impurities.

4. The corrosion-resistant building structural steel according to any one of claims 1 to 3, characterized in that: The mass proportion of Fe3O4 in the surface oxide layer of the building structural steel is ≥60%, the thickness of the surface oxide layer is 8~15μm, and the bonding strength between the surface oxide layer and the substrate is ≥15MPa; the yield strength of the building structural steel is ≥600MPa, and the elongation after fracture is ≥20%.

5. The method for preparing the corrosion-resistant building structural steel according to any one of claims 1 to 4, characterized in that: The following steps are involved: Converter smelting, LF refining, continuous casting, heating, rolling, cooling, and coiling; the heating process includes a preheating section, a heating section, and a soaking section; the preheating section is carried out in a weak reducing atmosphere, and the weak reducing atmosphere includes 5-8% by volume of H2O, 2-3% by volume of CO, and the rest is N2.

6. The preparation method according to claim 5, characterized in that: The temperature of the preheating section is 850-950°C, and the heating time is 30-40 minutes; the temperature of the soaking section is 1150-1200°C, and the heating time is 80-90 minutes. The concentration of O2 in the controlled environment is 1-1.5%.

7. The preparation method according to claim 5, characterized in that: The rolling process includes: Use 18~20MPa high pressure dephosphorization water to remove phosphorus before rough rolling; Finish rolling is performed after secondary dephosphorization; in the secondary dephosphorization, the dephosphorization water contains CuSO4, and the concentration of CuSO4 in the dephosphorization water is 0.1~0.35w / v%.

8. The preparation method according to claim 7, characterized in that: During the rough rolling process, the starting rolling temperature is 1100-1190° C., and the pass reduction ratio is ≥15%; during the finish rolling process, the final rolling temperature is 850-900° C., and the last two passes reduction ratios are ≤10%.

9. The preparation method according to claim 7, characterized in that: The cooling process adopts segmented laminar cooling, with the front section cooled to 740-760°C and the middle section cooled to 600°C; the cooling rate of the front section is 40-50°C / s, and the cooling rate of the middle section is 20-30°C / s; the middle section cooling is carried out in hot and humid air with a humidity of 80-90%.

10. The preparation method according to any one of claims 5 to 9, characterized in that: In the coiling process, the coiling temperature is 550-600°C.

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