500MPa-grade radiation-proof weather-proof bridge steel and preparation method thereof

Abstract

The invention provides 500MPa-grade radiation-proof weather-proof bridge steel and a preparation method thereof. The steel comprises the following chemical components in percentage by mass: less than or equal to 0.12% of C, 0.5%-0.8% of Cr, 0.25%-0.45% of Ni, 0.1%-0.3% of Mo, 0.2%-0.4% of Cu, 0.8%-1.4% of Mn, 0.3%-0.5% of Si, 0.01%-0.03% of Ti, 0.02%-0.04% of Nb, less than or equal to 0.006% of P, less than or equal to 0.005% of S and the balance of Fe and inevitable impurities. The process comprises the following steps: smelting according to the given mass percent of the element components, LF-RH refining, continuous casting and controlled rolling, and temperature-controlled cooling. The prepared bridge steel has excellent radiation resistance and weather resistance, the use performance is met, meanwhile, the manufacturing cost is low, and the stable performance is achieved in a bridge structure in the highland and other intense ultraviolet radiation environments.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to 500MPa-grade radiation-resistant and weather-resistant bridge steel and a preparation method thereof. Background Art

[0002] With the rapid development of the economy, bridges, as an important part of transportation, have also developed rapidly. Bridge steel is widely used in key bridge construction projects such as railways, cross-river and cross-sea bridges. Traditional bridge steel has disadvantages such as poor weather resistance and high maintenance costs, and can no longer fully meet the increasingly harsh service environment. The comprehensive performance requirements for bridge steel have changed from high strength to excellent comprehensive performance, mainly manifested in high strength and toughness, high fracture resistance, high corrosion resistance and good welding performance.

[0003] China is actively promoting the construction of the western region. The Sichuan-Tibet Railway, cross-river and cross-canyon complex geological areas have put forward higher requirements for the service performance of bridges. The plateau environment has the characteristics of difficult transportation, high cold, large temperature difference, strong ultraviolet rays, etc., requiring steel to be lightweight, easy to form and weather-resistant. At present, the research and development of weather-resistant bridge steel is mainly focused on 400Mpa grade weather-resistant bridge steel. The service environment mainly involves marine atmospheric corrosion, industrial waste gas pollution corrosion, etc. There are few studies on radiation-resistant weather-resistant bridge steel for plateau environment. Therefore, it is urgent to develop a higher level of radiation-resistant weather-resistant bridge steel to meet the major needs of bridge construction in harsh plateau environment, reduce the cost of construction enterprises on the basis of ensuring the safety of bridge structure, and have important practical significance for extending the service life of bridges, reducing maintenance costs, and promoting energy conservation and emission reduction in related industries. Summary of the invention

[0004] The present invention aims to provide a 500MPa grade radiation-resistant and weather-resistant bridge steel for plateau environment and a preparation method thereof. The produced steel can meet the performance requirements of bridge steel in harsh plateau environment and reduce the production cost of the steel as much as possible.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: A 500MPa grade radiation-resistant weathering bridge steel, wherein the chemical composition of the steel is C≤0.12%, Cr=0.5%~0.8%, Ni=0.25%~0.45%, Mo=0.1%~0.3%, Cu=0.2%~0.4%, Mn=0.8%~1.4%, Si=0.3%~0.5%, Ti=0.01%~0.03%, Nb=0.02%~0.04%, P≤0.006%, S≤0.005%, and the rest is Fe and unavoidable impurities; the steel has a yield strength of ≥500MPa, a tensile strength of ≥640MPa, an elongation after fracture A≥20%, an impact energy of ≥140J at -40℃, and a high ultraviolet radiation intensity of 1.0~1.5W / m2 Under the conditions, the corrosion rust layer is dense and the corrosion rate of the substrate is 0.45-0.60 mm / y after 384h of corrosion.

[0006] A method for preparing 500MPa grade radiation-resistant and weather-resistant bridge steel comprises the following key steps: S1 smelting: smelting is carried out according to the established chemical composition mass percentage, after pre-desulfurization of molten iron, and composite blowing at the top and bottom of the converter; slag washing and full bottom argon blowing process are adopted during steel tapping, and deoxidizer, high carbon ferromanganese, ferrosilicon and ferrochrome are added to the ladle to complete the initial deoxidation and alloying, and the steel tapping temperature is 1620-1640℃; S2 LF-RH refining: In the LF furnace, argon gas flow rate of 80-120 L / min is used for bottom blowing throughout the process, and alloy elements Cr, Mn, Ni, Mo and Cu are added. After the alloy is melted and homogenized, deoxidation, desulfurization and inclusion removal are carried out; the molten steel is further alloyed in the RH furnace, and the content of each element is controlled within the set range; when the vacuum degree is less than 2 mbar, a net circulation treatment of more than 10 minutes is carried out, and the tapping temperature is controlled at 1560-1600℃; S3 continuous casting and controlled rolling: the molten steel from the RH furnace refining process is cast into continuous casting billets through a continuous casting machine under the protective casting conditions of carbon-free protective slag or ultra-low carbon protective slag. The temperature is controlled at 1520-1560℃ during the continuous casting process; the billet is heated to 1100-1200℃ in the heating furnace for 3-4h; the rough rolling temperature is 950-1100℃, the start rolling temperature of the finishing rolling is 800-850℃, the final rolling temperature is 760-810℃, and the cumulative reduction amount of the finishing rolling is 65%-70%; S4 cooling: After rolling, the rolled piece is cooled to 500-560°C by laminar flow, and the cooling rate is 20-25°C / s.

[0007] The mechanism of action of each alloy component in the radiation-resistant and weather-resistant bridge steel of the present invention is as follows: C affects the comprehensive properties of steel. When the C content in steel is too high, C atoms precipitate in the form of carbides on the grain boundaries, which significantly increases the strength. However, too high a carbon content will not only reduce the steel's plastic toughness and welding performance, but the carbides formed at the grain boundaries will also have an adverse effect on the corrosion resistance, increase the electrochemical corrosion sensitivity of the grain boundaries, and induce the occurrence of intergranular corrosion. Therefore, in order to improve the utilization efficiency of matrix alloy elements, the C content in the matrix must be strictly controlled to remain at a low level during the development of weather-resistant steel grades.

[0008] Si is mainly dissolved in steel to play a role in solid solution strengthening. However, too high Si content will reduce the toughness and welding performance of the steel.

[0009] Mn is a solid solution strengthening element that can improve the stability of austenite and is beneficial to low temperature transformation of the structure. However, too high a Mn content will produce banded segregation and affect the uniformity of the structure.

[0010] Cr can significantly improve hardenability and is widely used in the production of corrosion-resistant steel because it significantly improves corrosion resistance.

[0011] Cu can improve the hardenability of steel and play a role in solid solution strengthening and precipitation strengthening in steel. It is not only beneficial to improve weather resistance, but also to improve the low temperature toughness of steel.

[0012] Mo can improve the hardenability and strength of steel, and also promote the transformation of bainite. However, too high Mo content will deteriorate the low temperature toughness and weld joint performance. In terms of corrosion resistance, Mo can improve pitting resistance, but it will increase the cost.

[0013] Ni can improve hardenability, has a certain solid solution strengthening effect, and can significantly improve the low temperature toughness of steel. In addition, Ni can significantly improve the weather resistance of steel, but Ni will increase production costs.

[0014] Ti is a strong nitride-forming element. Ti nitride can effectively pin austenite grain boundaries and help control the growth of austenite grains.

[0015] Nb can increase the austenite recrystallization temperature and make the deformed austenite in an unrecrystallized state to obtain a very fine grain size. At the same time, Nb is a strong carbonitride forming element and can play a role in precipitation strengthening in steel.

[0016] P and S: P reduces the plasticity and toughness of steel. From the perspective of corrosion, P is an anode depolarizer that can accelerate the uniform dissolution of steel and Fe 2+ The oxidation rate of S can significantly improve the corrosion resistance of weathering steel. The presence of S will increase the sensitivity to hot and cold cracks and reduce the ability to resist hydrogen embrittlement. In addition, P and S are prone to form component segregation, and inclusions containing P and S elements will induce local corrosion such as pitting corrosion.

[0017] The inevitable impurity elements mainly refer to O, H and harmful elements such as Pb, Sn, As, Sb, and Bi.

[0018] The present invention designs and develops micro-alloyed radiation-resistant and weather-resistant bridge steel by adding Cr, Mn, Ni, Mo and Cu elements, and reduces the cost as much as possible under the condition of meeting the performance of the radiation-resistant and weather-resistant bridge steel for harsh plateau environments.

[0019] Compared with the prior art, the present invention has the following beneficial effects: the 500MPa grade radiation-resistant and weather-resistant bridge steel for plateau environment has excellent ultraviolet radiation resistance, and the stable and dense rust layer can well delay corrosion and has excellent weather resistance. In addition, the preparation process is relatively simple, efficient and energy-saving, and it is a corrosion-resistant steel bar for marine building structures with good corrosion resistance and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the organizational diagram of the 500MPa grade radiation-resistant and weather-resistant bridge steel produced in Example 1.

[0021] Figure 2 It is a process flow chart of the present invention. DETAILED DESCRIPTION Example 1

[0022] A 500MPa grade radiation-resistant and weather-resistant bridge steel, the chemical composition weight percentage of the steel is shown in Table 1, and the rest is Fe and unavoidable impurities; the process steps include: S1 smelting: smelting is carried out according to the established chemical composition mass percentage, after pre-desulfurization of molten iron, and composite blowing at the top and bottom of the converter; slag washing and bottom argon blowing are used during steel tapping, and deoxidizer, high carbon ferromanganese, ferrosilicon and ferrochrome are added to the ladle to complete the initial deoxidation and alloying, and the steel tapping temperature is 1620℃; S2 LF-RH refining: In the LF furnace, argon gas flow rate of 80L / min is used for bottom blowing throughout the whole process, and the alloy elements Cr, Mn, Ni, Mo and Cu required in the steel are added to ensure the melting and homogenization of the alloy in the ladle, and deoxidation, desulfurization, and removal of inclusions are carried out to reduce secondary oxidation and nitrogen increase in the refining process; the molten steel is further alloyed and regulated in the RH furnace to control the content of each element within the appropriate range; when the vacuum degree is less than 2mbar, a net circulation treatment is carried out for 10min, and the tapping temperature is controlled at 1560℃; S3 continuous casting and controlled rolling: the molten steel from the RH furnace refining process is cast into continuous casting billets through a continuous casting machine under the protective casting conditions of carbon-free protective slag or ultra-low carbon protective slag, and the temperature is controlled at 1520℃ during the continuous casting process; the rolling process includes rough rolling and finishing rolling, the billet is heated in the heating furnace at a temperature of 1100℃ for 3h; the rough rolling temperature is 950℃, the start rolling temperature of finishing rolling is 800℃, the final rolling temperature is 760℃, and the cumulative reduction amount of finishing rolling is 65%; S4 cooling: After rolling, the rolled piece is cooled to 500°C by laminar flow at a cooling rate of 20°C / s. Example 2

[0023] A 500MPa grade radiation-resistant and weather-resistant bridge steel, the chemical composition weight percentage of the steel is shown in Table 1, and the rest is Fe and unavoidable impurities; the process steps include: S1 smelting: smelting is carried out according to the established chemical composition mass percentage, after pre-desulfurization of molten iron, and composite blowing at the top and bottom of the converter; slag washing and argon blowing at the bottom are used during steel tapping, and deoxidizer, high carbon ferromanganese, ferrosilicon and ferrochrome are added to the ladle to complete the initial deoxidation and alloying, and the steel tapping temperature is 1640℃; S2 LF-RH refining: In the LF furnace, argon gas flow rate of 120L / min is used for bottom blowing throughout the whole process, and the alloy elements Cr, Mn, Ni, Mo and Cu required in the steel are added to ensure the melting and homogenization of the alloy in the ladle, and deoxidation, desulfurization, and removal of inclusions are carried out to reduce secondary oxidation and nitrogen increase in the refining process; the molten steel is further alloyed and regulated in the RH furnace to control the content of each element within the appropriate range; when the vacuum degree is less than 2mbar, a net circulation treatment is carried out for 15min, and the tapping temperature is controlled at 1600℃; S3 continuous casting and controlled rolling: the molten steel from the RH furnace refining process is cast into continuous casting billets through a continuous casting machine under the protective casting conditions of carbon-free protective slag or ultra-low carbon protective slag, and the temperature is controlled at 1560℃ during the continuous casting process; the rolling process includes rough rolling and finishing rolling, the billet is heated in the heating furnace at a temperature of 1200℃ for 4h; the rough rolling temperature is 1100℃, the start rolling temperature of the finishing rolling is 850℃, the final rolling temperature is 810℃, and the cumulative reduction amount of the finishing rolling is 70%; S4 cooling: After rolling, the rolled piece is cooled to 560°C by laminar flow at a cooling rate of 25°C / s.

[0024] The radiation resistance and weather resistance test of Examples 1 and 2 was carried out by placing the samples in a UV weathering test box and setting the UV irradiation for 8 h (the irradiation intensity of Example 1 was 1 W / m 2 , the irradiation intensity of Example 2 is 1.5W / m 2 )+4h dark environment as one cycle, the test temperature is 40℃, the test humidity is 80 RH, and the solution used in the accelerated cycle experiment is 3.5wt.% NaCl solution. After the test, rust removal liquid (500mlHCl+3.5g hexamethylenetetramine+950ml deionized water), supersaturated NaHCO3 solution, deionized water and alcohol are used for chemical rust removal, and finally dried, and the corrosion weight loss is calculated according to the weight loss method.

[0025] The strength, plasticity and corrosion resistance test results of the radiation-resistant weather-resistant bridge steel produced in the embodiment are shown in Table 2.

[0026] The test results show that the comprehensive mechanical properties of Examples 1 and 2 are good. By analyzing the morphology of the radiation-resistant weathering bridge steel prepared in Examples 1 and 2 of the present invention, the organization is bainite + ferrite, the organization is uniform, and there is no obvious inclusion. 2 and 1.5 W / m 2Under high irradiation conditions, the corrosion rates after 32 cycles were 0.46 mm / y and 0.53 mm / y respectively, and the corrosion rates were kept at a low level. The developed corrosion-resistant steel has low sensitivity to high ultraviolet radiation corrosion.

[0027] In summary, within the composition range and process range designed by the present invention, the solution can achieve the expected effect.

[0028] Table 1 Chemical composition of examples (wt%) .

[0029] Table 2 Mechanical properties and weather resistance of Examples 1 and 2 .

Claims

1. A 500MPa grade radiation-resistant and weather-resistant bridge steel, characterized in that: The chemical composition of the steel is C≤0.12%, Cr=0.5%~0.8%, Ni=0.25%~0.45%, Mo=0.1%~0.3%, Cu=0.2%~0.4%, Mn=0.8%~1.4%, Si=0.3%~0.5%, Ti=0.01%~0.03%, Nb=0.02%~0.04%, P≤0.006%, S≤0.005%, and the rest is Fe and unavoidable impurities; the yield strength of the steel is ≥500 MPa, the tensile strength is ≥640 MPa, the elongation after fracture A is ≥20%, the impact energy at -40℃ is ≥140 J, and the steel has a high ultraviolet radiation intensity of 1.0~1.5W / m 2 Under the conditions, the corrosion rust layer is dense and the corrosion rate of the substrate is 0.45-0.60 mm / y after 384h of corrosion.

2. A method for preparing 500MPa grade radiation-resistant and weather-resistant bridge steel, characterized in that The key steps include: S1 smelting: smelting is carried out according to the established chemical composition mass percentage, after pre-desulfurization of molten iron, and composite blowing at the top and bottom of the converter; slag washing and full bottom argon blowing process are adopted during steel tapping, and deoxidizer, high carbon ferromanganese, ferrosilicon and ferrochrome are added to the ladle to complete the initial deoxidation and alloying, and the steel tapping temperature is 1620-1640℃; S2 LF-RH refining: In the LF furnace, argon gas flow rate of 80-120 L / min is used for bottom blowing throughout the process, and alloy elements Cr, Mn, Ni, Mo and Cu are added. After the alloy is melted and homogenized, deoxidation, desulfurization and inclusion removal are carried out; the molten steel is further alloyed in the RH furnace to control the content of each element within the set range; when the vacuum degree is less than 2 mbar, a net circulation treatment of more than 10 minutes is carried out, and the tapping temperature is controlled at 1560-1600℃; S3 continuous casting and controlled rolling: the molten steel from the RH furnace refining process is cast into continuous casting billets through a continuous casting machine under the protective casting conditions of carbon-free protective slag or ultra-low carbon protective slag. The temperature is controlled at 1520-1560℃ during the continuous casting process; the billet is heated to 1100-1200℃ in the heating furnace for 3-4h; the rough rolling temperature is 950-1100℃, the start rolling temperature of the finishing rolling is 800-850℃, the final rolling temperature is 760-810℃, and the cumulative reduction amount of the finishing rolling is 65%-70%; S4 cooling: After rolling, the rolled piece is cooled to 500-560°C by laminar flow, and the cooling rate is 20-25°C / s.

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