Steel for grating type pavement structure for frozen soil environment and production method of steel

Abstract

The invention relates to steel for a grating type pavement structure in a frozen soil environment. 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 0.02% of P, less than or equal to 0.005% of S, 0.10%-0.80% of Cr, less than or equal to 0.30% of Cu, less than or equal to 0.03% of Nb, 0.01%-0.03% of Ti, 0.01%-0.05% of Al, 0.005%-0.015% of Ag and the balance of Fe and inevitable impurities. Compared with the prior art, the steel plate has the beneficial effects that the design thought of low-carbon microalloyed steel is adopted in component design, a small amount of alloy elements such as Cr and Cu are added, and it is guaranteed that the steel plate has high-performance indexes such as good obdurability matching, easy welding and excellent corrosion resistance. The steel plate has good strength and toughness matching, the yield strength is 355 MPa or above, the tensile strength is 470-630 MPa, the percentage elongation after fracture is larger than 20%, and the KV2 impact absorbing energy value at the temperature of-40 DEG C is larger than 100 J. And various performance indexes can meet the requirements of technical indexes.

Description

Technical Field

[0001] The invention belongs to the field of structural steel, and in particular relates to a grid-type pavement structure steel for a frozen soil environment and a production method thereof. Background Art

[0002] The existing application and research of assembled pavement structures are mainly aimed at temporary roads and special roads, and they pay more attention to strength and ease of assembly and disassembly, but pay less attention to stiffness and durability, and are mainly based on concrete pavement structures. Both the assembled pavement structure and the materials used under plateau permafrost conditions are brand-new concepts. There are no related reports at home and abroad, and the development of materials belongs to independent innovation. Frozen soil contains ice, which has high strength when frozen and completely loses its bearing capacity when melted. The solid and liquid phase changes of water in frozen soil cause drastic changes in the volume of the soil, resulting in certain frost heave and thaw deformation of the soil, and the engineering structures built on it are deformed accordingly. At the same time, infrastructure steel under plateau permafrost environment also faces problems such as low temperature, resistance to plateau atmospheric environment and soil corrosion. Therefore, the research and development of materials must meet the basic mechanical performance indicators of structural steel, and also have certain anti-deformation performance, excellent low-temperature toughness, weldability and certain corrosion resistance, so as to provide a new material for the design and construction of pavement structures in permafrost areas of the plateau.

[0003] Due to the plateau permafrost environment, the soil freezes and thaws, resulting in uneven roadbeds. Therefore, it is necessary to select a special prefabricated road structure with a ventilation and heat dissipation structure. Steel used in permafrost environments is in direct contact with soil and concrete during application and is susceptible to soil erosion. Soil freeze-thaw erosion refers to the soil erosion caused by the process of freezing and thawing of the soil in winter or spring. There are two main mechanisms of soil freeze-thaw erosion. One is physical erosion caused by soil freezing, and the other is chemical erosion caused by soil melting. Physical erosion caused by soil freezing refers to the freezing of water in the soil when it encounters cold temperatures in winter or spring. When water freezes, it expands, causing the particles in the soil to diffuse and move, pushing the soil layer to a farther place. Once the water in the soil begins to melt, it flows rapidly and carries the soil particles downward. This process causes soil collapse and loss. Chemical erosion caused by soil melting refers to the downward penetration of dissolved minerals and organic matter in the soil under the action of water flow and interacting with solid matter in the soil layer. During this process, solid matter will combine with negative ions in the water to form ion complexes, which will flow rapidly in the soil layer and cause the inorganic and organic matter in the soil to dissolve.

[0004] Concrete contains a high content of calcium oxide, which will be converted into calcium hydroxide under hydration, thus creating an alkaline environment with a pH as high as about 13.5. In this highly alkaline environment, a passivation film with a thickness of 5 to 10 nm will form on the surface of ordinary carbon steel, the main components of which are FeO and Fe 2 O 3 The stable existence of the passive film can protect the steel plate from corrosion, but the carbonization of concrete and the erosion of frozen soil will cause the passive film to rupture. CO in the air 2 When diffusing into the concrete structure through the pores, alkaline substances will be consumed, which will in turn induce a decrease in the pH value of the concrete. The minimum pH value for maintaining a stable passive film on the steel bars is about 11.5, and carbonization can even reduce the pH value to below 10. When the passive film is stable, its dissolution and growth processes are in dynamic equilibrium. When chloride ions in the environment gradually penetrate into the vicinity of the steel with the aqueous solution, the chloride ions can be adsorbed on the oxygen ion vacancies in the passive film structure, inhibiting the formation of the passive film, causing it to gradually thin until local rupture occurs.

[0005] Chinese invention patent application number CN 113584980A discloses a reusable assembled concrete pavement structure and its method, which has a reasonable and ingenious design, a simple construction method, good use effect, high safety, and reduces the probability of pavement problems. However, the disadvantage of this invention patent application is that the initial cost of making concrete bricks is high, and the joints of bricks need to be glued and the maintenance cost is high.

[0006] The study "Study on the Corrosion Behavior of Q235 Steel in Frozen Soil Environment" compared the corrosion behavior of Q235 steel in soil media with different moisture contents in frozen soil environments. The soil is more corrosive to Q235 steel at medium moisture content, while it is less corrosive at low and high moisture contents. However, the strength of Q235 grade steel is low and cannot meet the requirements of steel for steel grid pavement structures.

[0007] In summary, the existing technology is still insufficient in the research of steel for steel grid pavement structure in frozen soil environment. Both concrete pavement structure and ordinary steel plate cannot meet the coupling requirements of high strength, toughness, corrosion resistance and low cost. Summary of the invention

[0008] The present invention provides a steel for a grid-type pavement structure for use in a frozen soil environment and a method for manufacturing the same. The steel has high performance indicators such as good strength-toughness matching, easy welding and excellent corrosion resistance.

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

[0010] A steel for a grid-type pavement structure for use in a frozen soil environment, wherein the chemical composition of the steel is, by weight percentage, C: 0.05%-0.15%, Si: 0.10%-0.50%, Mn: 1.00%-1.80%, P: ≤0.02%, S≤0.005%, Cr: 0.10%-0.80%, Cu: ≤0.30%, Nb: ≤0.03%, Ti: 0.01%-0.03%, Al: 0.01%-0.05%, Ag: 0.005%-0.015%, and the balance is Fe and unavoidable impurities.

[0011] The steel grid type pavement structure steel for frozen soil environment of the present invention adopts the design concept of low carbon micro alloy steel. In order to ensure the strength and corrosion resistance of the steel plate, other alloy elements should be added in appropriate amounts: Mn, Cr, Cu and other elements can produce solid solution strengthening effect, make up for the strength loss of steel due to low carbon, and have good corrosion resistance. The precipitation of fine carbonitrides formed by Nb and Ti elements has an inhibitory effect on the expansion of fatigue cracks, which can improve the fatigue performance of steel. Ag element can effectively resist the erosion of microorganisms in frozen soil.

[0012] C: It is an indispensable element for improving the mechanical strength of steel, but too high a C content will deteriorate the welding performance and low-temperature toughness of the steel plate. The present invention believes that it is more appropriate to control C to 0.05% to 0.15%.

[0013] Si: It is used as an important reducing agent for deoxidation in the steelmaking process. It also has a strong solid solution strengthening effect, which can improve the corrosion resistance and oxidation resistance of 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 to 0.10% to 0.50%.

[0014] Mn: the most common alloying element in steel, and the steel of the present invention uses it as one of the deoxidation and solid solution strengthening elements. Too high a content of Mn will lead to structural segregation, and the manganese content in the steel of the present invention is in the range of 1.00% to 1.80%.

[0015] P: It is the most effective and cheapest element to improve the atmospheric corrosion resistance of steel. When added in combination with Cu, the weather resistance will be further improved. However, increasing the P content will easily cause structural segregation. The present invention considers that the P content in the steel is ≤ 0.02%.

[0016] S: It is a harmful element under normal circumstances. It will make steel hot brittle, reduce the toughness and ductility of steel, and cause cracks during forging and rolling. S is not conducive to welding performance and will reduce the corrosion resistance of steel. Sulfide inclusions in steel will induce pitting and stress corrosion, so the S content must be controlled to maintain the corrosion resistance of steel. In the present invention, the S content is controlled to ≤0.005%.

[0017] Cr: can significantly improve the strength of steel. The addition of Cr can promote the compactness of the rust layer and good protection. It is a relatively cheap and effective element for improving strength and corrosion resistance. However, excessive Cr content will reduce its plasticity and toughness. In the present invention, the Cr content is controlled at 0.10% to 0.80%.

[0018] Cu: Combined with P element to form various composite salts, it is the core of FeOOH crystallization, which can refine the inner rust layer to reduce the ion channel and anode area, and reduce Fe 3 O 4 The formation of Cu can reduce the conductivity of the inner rust layer. Cu can also effectively inhibit the growth and attachment of microorganisms in the soil, especially in the corrosive environment of buried soil, but a high Cu content deteriorates the surface performance of the steel plate. An appropriate amount of Cu element is beneficial to the strength and hot workability of the steel plate, effectively reduces the tendency of hot-rolled edge cracking of the steel plate, and significantly improves the surface quality of the steel plate. Cu also has the effect of reducing work hardening, improving the plasticity of the steel plate, and greatly improving the low-temperature toughness. Therefore, in the present invention, the Cu content is controlled at 0% to 0.30%.

[0019] Nb: It can effectively increase the recrystallization temperature of austenite, prevent the growth of austenite grains, refine the grains, and improve the strength and toughness of steel; Nb is a strong carbonitride forming element, which can combine with carbon and nitrogen to form stable and fine carbonitrides, playing a significant precipitation strengthening role. Therefore, in the present invention, the Nb content is controlled to 0% to 0.03%.

[0020] Ti: It is a carbonitride-forming element and can also fix harmful element S, improving the purity and high-temperature performance of steel. Ti can inhibit the formation of unstable phase β-FeOOH in rust and improve the corrosion resistance of steel. The present invention believes that the Ti content is more suitable at 0.01% to 0.03%.

[0021] Al: Aluminum is a strong deoxidizing element in steel, which can combine with nitrogen to form aluminum nitride, which can play a role in refining austenite grains. The aluminum content in the steel of the present invention is controlled in the range of 0.01% to 0.05%.

[0022] Ag: The ecosystem in plateau areas is fragile and has strict environmental protection requirements. After the frozen soil melts, there are a large number of microorganisms, which cause corrosion to steel. However, conventional anti-corrosion technologies that affect the ecosystem, such as anti-corrosion coatings, cannot be used. Only the anti-corrosion ability of the material itself can be enhanced. Silver ions can destroy the integrity of microbial cell membranes, causing the outflow of substances in the cells, thereby effectively preventing microbial erosion, but the addition of silver elements will inevitably lead to an increase in costs. The silver content in the steel of the present invention is controlled in the range of 0.005% to 0.015%.

[0023] The thickness of the structural steel plate is 10 to 25 mm.

[0024] The yield strength of steel is ≥355MPa, the tensile strength is 470~630MPa, the elongation after fracture is >20%, -40℃ KV 2 Impact absorption energy value>100J.

[0025] The structure of structural steel is ferrite + pearlite + bainite.

[0026] The structural steel and Q355B steel were processed into corrosion samples, and corrosion resistance tests were carried out in soil leaching solution in a frozen soil environment. Taking the corrosion rate of Q355B steel as 100% as a benchmark, the corrosion rate of the structural steel was ≤78.5%.

[0027] A method for manufacturing steel for a grid-type pavement structure for use in a frozen soil environment comprises smelting, casting, heating, rolling and laminar cooling. The smelting is performed by converter or electric furnace smelting. The casting is performed by continuous casting or die casting. The continuous casting billet or ingot is loaded into a heating furnace for uniform heating. The heating temperature is 1200-1250°C and the temperature is kept for 1-3 hours. The rolling process adopts a two-stage controlled rolling process. The first stage of rolling is a rough rolling stage with a start rolling temperature of 1050-1100°C. The second stage of rolling is a finishing rolling stage with a start rolling temperature of 850-890°C and a final rolling temperature of 800-840°C. The compression ratio of the finishing rolling stage is not less than 3. The water cooling temperature range of the steel plate after rolling is 730-780°C and the red-returning temperature range is 580-630°C.

[0028] Rolling at the austenite recrystallization zone temperature in the rough rolling stage can allow the austenite to fully recrystallize and obtain refined austenite grains; rolling at the austenite non-recrystallization zone temperature in the finishing rolling stage can flatten the austenite grains, and a large number of deformation substructures will accumulate inside the flattened austenite grains, which increases the number of nucleations during the austenite cooling phase transformation and inhibits the growth of austenite grains, thereby further refining the grains and structure after the low-temperature phase transformation.

[0029] The present invention adopts a relatively low final rolling temperature, which can generate a large number of deformed grains during the rolling process, creating favorable conditions for refining the grain structure. The carbonitride formed by the added Nb element disperses and precipitates at low temperatures, strongly pins the grain boundaries, and further inhibits the growth of grains. The relatively low final rolling temperature cooperates with solid solution strengthening elements such as Cr to effectively improve the strength of the material.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention adopts the design concept of low-carbon microalloy steel in the composition design, adding a small amount of Cr, Cu and other alloy elements to ensure that the steel plate has good strength and toughness matching, easy welding and excellent corrosion resistance and other high performance indicators. It has good strength and toughness matching, yield strength above 355MPa, tensile strength between 470 and 630MPa, elongation after fracture greater than 20%, -40℃ KV 2 The impact absorption energy value is greater than 100 J. All performance indicators can meet the technical index requirements.

[0032] The present invention can meet the service requirements of the plateau frozen soil environment in terms of the selection of various elements and the control of their contents, such as the anti-deformation performance and the soil corrosion resistance, and can achieve a good match of various comprehensive properties such as corrosion resistance, easy welding, and low-temperature toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the metallographic structure diagram of the steel used for the grid-type pavement structure for frozen soil environment of the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the specific implementation methods of the present invention are further described below in conjunction with embodiments. The following embodiments are used to specifically illustrate the contents of the present invention. These embodiments are only general descriptions of the contents of the present invention and do not limit the contents of the present invention.

[0035] Table 1 lists the chemical composition of the example steel; Table 2 lists the manufacturing process parameters and structure of the example steel; Table 3 lists the mechanical properties and relative corrosion rate of the example steel. Figure 1 , the grains are fine.

[0036] Table 1 Chemical composition of example steel, wt%

[0037]

[0038]

[0039] Table 2 Process parameters and structure of steel in the embodiment of the present invention

[0040]

[0041] Table 3 Mechanical properties and relative corrosion rates of steel examples of the present invention

[0042]

[0043] The steel grid type pavement structure steel for frozen soil environment of the above embodiment and ordinary Q355B steel were processed into corrosion specimens, and corrosion resistance tests were carried out in soil leachate of frozen soil environment. The test medium parameters of soil leachate are shown in Table 4. Taking the corrosion rate of ordinary Q355B steel as 100% as the standard, the test results of the embodiment of the present invention are shown in Table 3.

[0044] Table 4 Circular immersion corrosion test parameters of 355MPa grade light corrosion resistant structural steel for highway guardrail

[0045] Media Name Parameters (mg / L) <![CDATA[Ca 2+ ]]> 15.15 <![CDATA[Mg 2+ ]]> 11.58 <![CDATA[F - ]]> 0.57 <![CDATA[Cl - ]]> 1.83 <![CDATA[SO 4- ]]> 3.16 pH 7.44 Microbial community Psychrophilic bacteria, anaerobic bacteria, etc. .

Claims

1. A steel for grid-type pavement structure for frozen soil environment, characterized in that: The chemical composition of the steel by weight percentage is: C: 0.05% ~ 0.15%, Si: 0.10% ~ 0.50%, Mn: 1.00% ~ 1.80%, P: ≤ 0.02%, S ≤ 0.005%, Cr: 0.10% ~ 0.80%, Cu: ≤ 0.30%, Nb: ≤ 0.03%, Ti: 0.01% ~ 0.03%, Al: 0.01% ~ 0.05%, Ag: 0.005% ~ 0.015%, and the balance is Fe and unavoidable impurities.

2. The grid-type pavement structure steel for frozen soil environment according to claim 1, characterized in that: The thickness of the structural steel plate is 10 to 25 mm.

3. The grid-type pavement structure steel for frozen soil environment according to claim 1, characterized in that: The yield strength of the steel is ≥355MPa, the tensile strength is 470-630MPa, the elongation after fracture is >20%, and the -40℃ KV2 impact absorption energy value is >100J.

4. The steel for grid-type pavement structure for frozen soil environment according to claim 1, characterized in that: The structure of structural steel is ferrite + pearlite + bainite.

5. The steel for grid-type pavement structure for frozen soil environment according to claim 1, characterized in that: The structural steel and Q355B steel were processed into corrosion samples, and corrosion resistance tests were carried out in soil leaching solution in a frozen soil environment. Taking the corrosion rate of Q355B steel as 100% as a benchmark, the corrosion rate of the structural steel was ≤78.5%.

6. A method for manufacturing steel for grid-type pavement structure for frozen soil environment according to any one of claims 1 to 5, comprising smelting, casting, heating, rolling, and laminar cooling; characterized in that: The heating temperature is 1200-1250℃, and the insulation time is 1-3h. A two-stage controlled rolling process is adopted, the first stage of rolling is the rough rolling stage, and the start rolling temperature is 1050-1100℃; the second stage of rolling is the finishing rolling stage, and the start rolling temperature is 850-890℃, and the final rolling temperature is 800-840℃; the water cooling temperature range of the steel plate after rolling is 730-780℃, and the red return temperature range is 580-630℃.

7. The method for manufacturing steel for grid-type pavement structure for frozen soil environment according to claim 6, characterized in that: The finishing compression ratio is not less than 3.

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