355MPa-grade corrosion-resistant structural steel for highway guardrail and manufacturing method of 355MPa-grade corrosion-resistant structural steel

Abstract

The invention relates to 355MPa-grade corrosion-resistant structural steel for highway guardrails. The steel comprises the following chemical components in percentage by weight: 0.05%-0.15% of C, 0.10%-0.50% of Si, 1.00%-1.80% of Mn, less than or equal to 0.03% of P, less than or equal to 0.02% of S, 0.20%-1.00% of Cr, 0.01%-0.03% of Ti, 0.01%-0.05% of Al, less than or equal to 0.008% of N, 0.05%-0.20% of Sn, 0.02%-0.10% of Sb and the balance of Fe. And the balance of Fe and inevitable impurities. The design thought of low-alloy high-strength steel is adopted in component design, a small amount of Cr, Sn, Sb and other alloy elements are added, it is guaranteed that the steel has good corrosion resistance, and the cost is low; the steel has good toughness matching, the yield strength is 355 MPa or above, the tensile strength is 470-630 MPa, the ductility is larger than 20%, and all performance indexes can meet the requirements of steel for highway guardrails.

Description

Technical Field

[0001] The present invention belongs to the field of structural steel, and particularly relates to a 355MPa grade corrosion-resistant structural steel for highway guardrails and a manufacturing method thereof. Background Art

[0002] In order to strengthen the safety guarantee of driving, guardrails need to be installed on both sides of the road. Due to the complex and harsh climate in alpine regions, adverse weather such as long periods of rain, snow, ice, severe seasonal temperature changes, and large temperature drops between day and night occurs frequently. And after snow, "chloride salt" type snow melting agents are generally used for road snow removal, which seriously corrodes the steel used for guardrails. The harsh service environment poses extremely high requirements for the comprehensive mechanical properties and corrosion resistance of the steel used for guardrails.

[0003] Currently, 235MPa grade steel with galvanized coating is generally used as the steel structure material for guardrails. The existing guardrail steel has low strength level, large steel consumption, poor safety performance, and low service life. At the same time, anti-corrosion treatment methods such as hot-dip galvanizing and spraying after galvanizing are required, which not only have a relatively high cost but also bring a large number of environmental pollution sources. Weathering steel has excellent strength and toughness, corrosion resistance, and welding performance, and its weather resistance is 2 to 8 times that of ordinary carbon steel. Using low-alloy high-strength weathering steel as the construction material for highway guardrails can effectively reduce the amount of steel used while improving the safety of guardrails, make full use of the characteristics of weathering steel that can be anti-corrosive without galvanizing (or painting) treatment, reduce the maintenance cost of guardrails, extend the service life, and reduce the environmental pollution caused by anti-corrosion treatment, which has good economic benefits and environmental protection effects. However, weathering steel generally has the characteristics of many alloy components, high content, and high production cost. For example: In addition to adding a certain amount of Cr element, Q355NH steel also needs to add a large amount of Cu and Ni elements, or rare and precious elements Mo and Zr.

[0004] The composition design of "A Low-Alloy High-Strength and High-Weather-Resistant Structural Steel for Highway Guardrails and Its Preparation Method" disclosed in Chinese Patent Application No. CN 112647018 A is: C≤0.12%, Si≤0.65%, Mn≤1.20%, P 0.07% - 0.12%, S≤0.030%, Cu 0.20% - 0.55%, Cr 0.30% - 1.25%, Ni 0.12% - 0.65%, Nb≤0.03%, Al≤0.05%. This structural steel can have a certain weather resistance while ensuring strength, but in terms of composition design, there are many alloy types and high contents, resulting in relatively high smelting costs; in terms of application and promotion, this structural steel is smelted in a 25kg vacuum induction furnace and cast into ingots, which is somewhat different from industrial mass production, and the actual industrial promotion remains to be verified.

[0005] The Chinese invention patent application number CN 114411041 A discloses a method for producing 800MPa high-strength weathering steel for highway guardrails. Its composition is designed as follows: C is 0.035% to 0.045%, Si is 0.30% to 0.50%, Mn is 1.0% to 1.3%, P≤0.020%, S≤0.003%, Als≤0.050%, Cr is 0.30% to 1.25%, Ni is 0.12% to 0.30%, Cu is 0.20% to 0.55%, Ti is 0.080% to 0.150%, N≤0.0060%, and Ca is 0.0010% to 0.0020%. The products produced by this technology have the characteristics of high strength, good toughness and plasticity, strong corrosion resistance, and excellent machinability, meeting the requirements of steel for highway guardrails. However, the large number of alloy types and high content lead to high smelting costs; ultra-low S smelting is difficult, requires high quality of molten iron, and has average economic efficiency.

[0006] The Chinese invention patent application number CN 114606447 A discloses "a low alloy high strength and high weathering resistant structural steel for highway guardrails and its preparation method", and its composition is designed as: C ≤ 0.2%, Mn: 1.0% ~ 1.6%, Si ≤ 0.55%, P ≤ 0.045%, S ≤ 0.03%, V: 0.03% ~ 0.07%, N: 0.09% ~ 0.018%, Ti: 0.02 ~ 0.2%, Al ≥ 0.015%, and the balance is Fe. The products produced by this technology have the performance characteristics of high strength, good toughness and plasticity, and meet the mechanical performance requirements of highway guardrail steel. However, there is no evaluation of corrosion resistance, and the actual industrial promotion needs to be verified.

[0007] In summary, the existing technology is still insufficient in the research of low-alloy high-strength weather-resistant structural steel for highway guardrails, and most guardrail steels cannot meet the coupling requirements of high strength and toughness, corrosion resistance and low cost. Summary of the invention

[0008] The present invention provides a 355MPa grade corrosion-resistant structural steel for highway guardrails and a manufacturing method thereof. The steel has the performance indicators of high strength and toughness, easy welding and good corrosion resistance, and has the advantages of excellent comprehensive performance and low production cost.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A 355MPa grade corrosion-resistant structural steel for highway guardrails, the chemical components in the steel are by weight percentage: C: 0.05% - 0.15%, Si: 0.10% - 0.50%, Mn: 1.00% - 1.80%, P: ≤0.03%, S ≤0.02%, Cr: 0.20% - 1.00%, Ti: 0.01% - 0.03%, Al: 0.01% - 0.05%, N: ≤0.008%, Sn: 0.05% - 0.20%, Sb: 0.02% - 0.10%; the balance is Fe and unavoidable impurities.

[0011] The yield strength of the corrosion-resistant structural steel ≥355MPa, the tensile strength is 470 - 630MPa, and the elongation > 20%.

[0012] The structure of the corrosion-resistant structural steel is ferrite + pearlite.

[0013] Using the corrosion method recommended in the national standard GB / T 23851-2009 for the full immersion corrosion test, the relative corrosion rate ≤85.5%.

[0014] The corrosion-resistant structural steel for highway guardrails of the present invention adopts the design concept of low-alloy high-strength steel. In order to ensure the strength of the steel, alloying elements such as Mn, Si, and Ti are added in appropriate amounts; in order to ensure that the steel has a certain corrosion resistance, Sn and Sb are added in appropriate amounts, and they form SnO 2 and Sb 2 O 5 oxide film on the steel surface, which inhibits the anodic dissolution of Fe.

[0015] The reasons for the design of the alloy composition in the steel of the present invention are as follows:

[0016] Carbon (C): It has a significant solid solution strengthening effect and directly affects the mechanical properties such as the strength and toughness of the steel. Excessive C content will deteriorate the welding performance of the steel plate. The steel of the present invention adopts a low-carbon composition design, and the carbon content range is controlled at 0.05% - 0.15%.

[0017] Silicon (Si): It is used as an important reducing agent for deoxidation during steelmaking, and at the same time has a strong solid solution strengthening effect, which can improve the corrosion resistance and oxidation resistance of the steel. If the Si content is too high, it will accelerate high-temperature delamination and deteriorate the toughness and welding performance of the steel. The present invention controls the Si content range at 0.10% - 0.50%.

[0018] Manganese (Mn): The most common alloying element in steel. The steel of the present invention uses it as one of the deoxidation and solid solution strengthening elements. The manganese content range in the steel of the present invention is 1.00% - 1.80%.

[0019] Phosphorus (P): It is beneficial to the atmospheric corrosion resistance of steel. However, an increase in the P content is likely to cause segregation in the microstructure, reducing the plasticity, toughness, and weldability of the steel. In the present invention, it is considered appropriate to control the P content in the steel within 0.03%.

[0020] Sulfur (S): An impurity element in steel, which is usually a harmful element. It causes hot brittleness in steel, reducing the toughness and ductility of the steel and leading to cracks easily during forging and rolling processes. Sulfide inclusions in steel can induce pitting corrosion and stress corrosion. Therefore, its content should be as low as possible without significantly increasing costs. In the present invention, the S content is controlled within 0.02%.

[0021] Chromium (Cr): A common alloying element in steel that can significantly improve the strength of the steel. Cr is a relatively inexpensive and effective element for improving corrosion resistance. Cr can form a dense rust layer on the surface of the steel, providing good protection. However, an excessive Cr content will reduce its plasticity and toughness. In the present invention, the Cr content is controlled within the range of 0.20% - 1.00%.

[0022] Titanium (Ti): The steel in the present invention has been micro - titanium treated. Ti mainly combines with nitrogen to form nano - sized titanium nitride particles, refining the austenite grains during the heating process of the continuous casting billet. The nitrogen content in the steel of the present invention does not exceed 0.008%. According to the ideal chemical ratio of titanium nitride, the addition of titanium content generally does not exceed 0.03%. Excessive titanium is likely to form coarser titanium nitride, which is not conducive to refining austenite grains and will instead damage the toughness and plasticity of the steel. In the present invention, the Ti content is preferably within the range of 0.01% - 0.03%.

[0023] Aluminum (Al): A strong deoxidizing element in steel, which can combine with nitrogen to form aluminum nitride and play a role in refining austenite grains. In the steel of the present invention, the aluminum content range is controlled within 0.01% - 0.05%.

[0024] Tin (Sn) and antimony (Sb) can form a SnO 2 , Sb 2 O 5 corrosion - resistant oxide film on the steel surface. They can also form precipitates of Sn / Sb hydroxides through hydrolysis, attaching to and filling corrosion cracks or cavities, improving the ability of the rust layer to block the penetration of erosive ions and the proportion of α - FeOOH with a protective effect in the rust layer, and inhibiting the generation of β - FeOOH that is unfavorable to the protection of the rust layer. In the steel of the present invention, the Sn content is 0.05% - 0.20%, and the Sb content is 0.02% - 0.10%.

[0025] A manufacturing method of 355MPa grade corrosion-resistant structural steel for highway guardrails, including hot metal pretreatment, converter smelting, secondary refining (ANS / LF), slab continuous casting, heating, rolling, and coiling; the heating furnace temperature is 1180 - 1250 °C; two-stage controlled rolling process is adopted for rolling; the rolling temperature in the first stage is 1050 - 1200 °C; the starting rolling temperature in the second stage is 1000 - 1100 °C, and the finishing rolling temperature is 850 - 900 °C; the coiling temperature of the rolled steel plate is 550 - 650 °C.

[0026] During the rolling process, the rolling temperature is basically above the recrystallization temperature. At this time, Ti elements form carbonitrides with elements such as carbon and nitrogen in the steel. These compounds will be dispersed at the grain boundaries and, like "obstacles", strongly hinder the migration of grain boundaries, making it difficult for grains to grow, thus refining the grain structure. The addition of Ti elements will also increase the degree of lattice distortion during the deformation of the steel, increasing the dislocation density. These high dislocation density regions provide more nucleation sites for recrystallization, promoting recrystallization nucleation and facilitating the formation of a large number of fine recrystallized grains, further refining the grains. The refined grains can significantly improve the comprehensive mechanical properties such as the strength and toughness of the material.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] In the composition design of the present invention, the design concept of low-alloy high-strength steel is adopted, and a small amount of alloying elements such as Cr, Sn, and Sb are added to ensure that the steel has good corrosion resistance and relatively low cost; it has good strength-ductility matching, with a yield strength above 355MPa, a tensile strength of 470 - 630MPa, and an elongation greater than 20%, and all performance indicators can meet the requirements of steel for highway guardrails. Description of the Drawings

[0029] Figure 1 The metallographic structure of the 355MPa grade corrosion-resistant structural steel for highway guardrails in Example 1. Specific Embodiments

[0030] In order to make the purpose, technical solutions, and advantages of the present invention clearer, the following further illustrates the specific embodiments of the present invention in conjunction with examples. The following examples are used to specifically illustrate the content of the present invention. These examples are only general descriptions of the content of the present invention and do not limit the content of the present invention.

[0031] Table 1 lists the chemical compositions of the steel in the examples; Table 2 lists the manufacturing process parameters and structures of the steel in the examples; Table 3 lists the mechanical properties and relative corrosion rates of the steel in the examples. The metallographic structure of Example 1 is shown in Figure 1 , with fine grains and a grain size grade above 10.

[0032] Table 1 Chemical Compositions of the Steel in the Examples, wt%

[0033]

[0034]

[0035] Table 2 Process parameters and microstructure of the steel in the embodiments of the present invention

[0036]

[0037] Table 3 Mechanical properties and relative corrosion rates of the steel in the embodiments of the present invention

[0038]

[0039]

[0040] The corrosion specimens were processed from the 355 MPa grade corrosion-resistant structural steel for highway guardrails in the above embodiments and ordinary Q345B steel. The full immersion corrosion test was carried out using the corrosion method recommended in the national standard GB / T 23851-2009 to simulate the service environment of highway guardrails immersed in snowmelt salts. The parameters of the full immersion corrosion test are shown in Table 4. Taking the corrosion rate of ordinary Q345B steel as 100%, the test results of the embodiments of the present invention are shown in Table 3.

[0041] Table 4 Parameters of the full immersion corrosion test for the 355 MPa grade corrosion-resistant structural steel for highway guardrails

[0042] Item Parameter Temperature 40℃ Cycle time 30d Corrosive medium 20% NaCl solution 。

Claims

1. A 355MPa grade corrosion-resistant structural steel for highway guardrails, characterized in that: The chemical composition of the steel is calculated by weight percentage: C: 0.05% ~ 0.15%, Si: 0.10% ~ 0.50%, Mn: 1.00% ~ 1.80%, P: ≤ 0.03%, S ≤ 0.02%, Cr: 0.20% ~ 1.00%, Ti: 0.01% ~ 0.03%, Al: 0.01% ~ 0.05%, N: ≤ 0.008%, Sn: 0.05% ~ 0.20%, Sb: 0.02% ~ 0.10%; The balance is Fe and inevitable impurities.

2. The 355MPa grade corrosion-resistant structural steel for highway guardrail according to claim 1, characterized in that: The yield strength of corrosion-resistant structural steel is ≥355MPa, the tensile strength is 470~630MPa, and the elongation is >20%.

3. The 355MPa grade corrosion-resistant structural steel for highway guardrail according to claim 1, characterized in that: The structure of corrosion-resistant structural steel is ferrite + pearlite.

4. The 355MPa grade corrosion-resistant structural steel for highway guardrail according to claim 1, characterized in that: The full immersion corrosion test was carried out using the corrosion method in the national standard GB / T 23851-2009, and the relative corrosion rate was ≤85.5%.

5. A method for manufacturing 355MPa grade corrosion-resistant structural steel for highway guardrails as claimed in any one of claims 1 to 4, comprising molten iron pretreatment, converter smelting, refining outside the furnace, slab continuous casting, heating, rolling and coiling; characterized in that: The heating furnace temperature is 1180~1250℃; the rolling adopts a two-stage controlled rolling process; the rolling temperature in the first stage is 1050~1200℃; the starting rolling temperature in the second stage is 1000~1100℃, and the final rolling temperature is 850~900℃; the coiling temperature of the steel plate after rolling is 550~650℃.

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