Rare earth microalloyed weather-proof bridge steel as well as preparation method and application thereof

Abstract

The invention provides rare earth microalloyed weather-resistant bridge steel as well as a preparation method and application thereof, and belongs to the technical field of corrosion-resistant steel. The rare earth La or Ce is introduced for microalloying treatment on the basis of the component standard of the weather-proof bridge steel, the mechanical property of the obtained bridge steel meets the requirements of the standard GB / T714-2015, the strength and plasticity are improved compared with those of traditional 345 MPa-grade weather-proof bridge steel, the corrosion resistance has obvious advantages, and the weather-proof bridge steel has the advantages of being good in corrosion resistance in the simulated industrial atmospheric environment. Compared with traditional weather-proof bridge steel, the weather-proof bridge steel has the advantages that the corrosion rate can be reduced by 30-60%, the coating-free application potential is achieved, the bridge construction and later maintenance cost can be greatly reduced, and remarkable economic and social benefits are generated.

Description

Technical Field

[0001] The present invention relates to the technical field of corrosion-resistant steel, and in particular to a rare earth microalloyed weather-resistant bridge steel and a preparation method and application thereof. Background Art

[0002] Structural steel for bridges is a typical type of low-alloy high-strength steel, mainly used to manufacture large box-girder highway bridges and welded railway bridges. In recent years, with the rapid development of bridge construction towards large spans, heavy loads, long life, environmental protection and aesthetics, the performance requirements for bridge steel have been further improved. Not only are bridge steels required to have good strength and toughness, low yield ratio and excellent low-temperature toughness, but they are also required to have better corrosion resistance to meet the requirements of paint-free use. According to the design concept of micro-alloying and corrosion-resistant steel, the current domestic production of bridge steel mostly uses the addition of precious elements such as Ni, Cr, Cu and Mo, which has complex processes and high production costs. Therefore, reducing the alloy cost of such steel is of great significance to improving the economic benefits of enterprises.

[0003] Therefore, providing a bridge steel with low precious element content, excellent mechanical properties and excellent corrosion resistance has become a technical problem that needs to be urgently solved in this field. Summary of the invention

[0004] The purpose of the present invention is to provide a rare earth microalloyed weathering resistant bridge steel and a preparation method and application thereof. The mechanical properties of the rare earth microalloyed weathering resistant bridge steel provided by the present invention meet the performance requirements of Q345qNH in the relevant technical conditions of the national standard GB / T714-2015 "Structural Steel for Bridges", and at the same time have excellent corrosion resistance.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a rare earth microalloyed weather-resistant bridge steel, which comprises the following chemical composition by mass percentage: C: 0.06-0.1%, Si: 0.15-0.3%, Mn: 1-1.3%, Nb: 0.02-0.06%, V: 0.01-0.06%, Ti: 0.006-0.03%, Al: 0.01-0.07%, Cr: 0.4-0.7%, Ni: 0.3-0.4%, Cu: 0.25-0.5%, Mo≤0.15%, La or Ce: 0.001-0.1% and the balance Fe.

[0007] Preferably, the rare earth microalloyed weathering bridge steel comprises the following chemical composition, measured by mass percentage: C: 0.06-0.1%, Si: 0.2-0.3%, Mn: 1-1.2%, Nb: 0.02-0.06%, V: 0.01-0.02%, Ti: 0.01-0.02%, Al: 0.015-0.05%, Cr: 0.4-0.7%, Ni: 0.3-0.4%, Cu: 0.25-0.5%, Mo≤0.15%, La or Ce: 0.001-0.1% and the balance Fe.

[0008] Preferably, the rare earth microalloyed weathering resistant bridge steel comprises the following chemical composition, by mass percentage: C: 0.079%, Si: 0.28%, Mn: 1.15%, Nb: 0.02%, V: 0.02%, Ti: 0.027%, Al: 0.03%, Cr: 0.42%, Ni: 0.32%, Cu: 0.32%, Mo: 0.11%, Ce: 0.074% and the balance Fe.

[0009] Preferably, the structure of the rare earth microalloyed weather-resistant bridge steel is a multiphase composite structure of fine-grained ferrite and granular bainite.

[0010] The present invention provides a method for preparing the rare earth microalloyed weathering bridge steel described in the above technical solution, comprising the following steps:

[0011] (1) The raw materials of bridge steel other than La or Ce are sequentially smelted and LF refined, then vacuum cycle degassing and refining is performed and La or Ce is added, and finally casting is performed to obtain a cast billet;

[0012] (2) The ingot obtained in step (1) is sequentially rolled in the austenite recrystallization zone and in the austenite non-recrystallization zone to obtain rare earth micro-alloyed weather-resistant bridge steel.

[0013] Preferably, in the step (1), the vacuum degree of the vacuum cycle degassing refining is ≤100 Pa, the processing time of the vacuum cycle degassing refining is ≥20 min, and the atmosphere of the vacuum cycle degassing refining is argon.

[0014] Preferably, in the step (2), the ingot is heated before rolling in the austenite recrystallization zone; the heating holding temperature is 1200° C., and the heating holding time is 1.5 to 2.5 h.

[0015] Preferably, in step (2), the starting rolling temperature of the austenite recrystallization zone rolling is ≥1100°C, and the cumulative reduction ratio of the austenite recrystallization zone rolling is ≥50%.

[0016] Preferably, in step (2), the starting rolling temperature of the austenite non-recrystallization zone rolling is ≥930°C, the cumulative reduction rate of the austenite non-recrystallization zone rolling is ≥60%, and the final rolling temperature of the austenite non-recrystallization zone rolling is 830-850°C.

[0017] The present invention provides the rare earth microalloyed weather-resistant bridge steel described in the above technical solution or the rare earth microalloyed weather-resistant bridge steel prepared by the preparation method described in the above technical solution, which is applied to large box girder structure highway bridges and welded structure railway bridges.

[0018] The invention provides a rare earth microalloyed weather-resistant bridge steel, which comprises the following chemical composition by mass percentage: C: 0.06-0.1%, Si: 0.15-0.3%, Mn: 1-1.3%, Nb: 0.02-0.06%, V: 0.01-0.06%, Ti: 0.006-0.03%, Al: 0.01-0.07%, Cr: 0.4-0.7%, Ni: 0.3-0.4%, Cu: 0.25-0.5%, Mo≤0.15%, La or Ce: 0.001-0.1% and the balance Fe. The present invention introduces rare earth La or Ce to carry out micro-alloying treatment on the basis of the weather-resistant bridge steel composition standard, and the mechanical properties of the obtained bridge steel meet the requirements of standard GB / T714-2015. Not only are the strength and plasticity improved compared with the traditional 345MPa grade weather-resistant bridge steel, but the corrosion resistance has obvious advantages. In a simulated industrial atmospheric environment, the corrosion rate can be reduced by 30-60% compared with the traditional weather-resistant bridge steel. It has the potential for painting-free application, can greatly reduce the cost of bridge construction and subsequent maintenance, and produce significant economic and social benefits. At the same time, the content of precious metals such as Ni, Cr, Cu and Mo in the bridge steel is low, which effectively reduces the production cost of the bridge steel. The results of the embodiments show that the bridge steel provided by the present invention has a yield strength of ≥345MPa, a tensile strength of ≥490MPa, and an elongation of ≥20%. The mechanical properties of the steel plate meet the performance requirements of Q345qNH in the relevant technical conditions of the national standard GB / T714-2015 "Structural Steel for Bridges", and the yield strength ratio reaches below 0.7, which is much lower than that of traditional weather-resistant bridge steels, and has excellent comprehensive mechanical properties. At the same time, the weather-resistant bridge steel that has been micro-alloyed with rare earths has excellent corrosion resistance in a simulated industrial atmospheric environment. After 30 days, the average corrosion rate is significantly reduced compared with the bridge steel of the control example, reaching up to 60%, and has a significant corrosion resistance advantage. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The microstructure morphology of the bridge steel provided in Example 1;

[0020] Figure 2 The microstructure morphology of the bridge steel provided in Example 2;

[0021] Figure 3 The microstructure morphology of the bridge steel provided in Example 3;

[0022] Figure 4 The microstructure morphology of the bridge steel provided in Example 4;

[0023] Figure 5 The microstructure morphology of the bridge steel provided in Example 5;

[0024] Figure 6 Microstructure morphology of bridge steel provided for comparative example;

[0025] Figure 7 Stress-strain curves of bridge steel provided for Experimental Examples 1 to 5 and Comparative Example;

[0026] Figure 8 A comparison chart of the corrosion rates of bridge steel provided for Experimental Examples 1 to 3 and the comparative example. DETAILED DESCRIPTION

[0027] The invention provides a rare earth microalloyed weather-resistant bridge steel, which comprises the following chemical composition by mass percentage: C: 0.06-0.1%, Si: 0.15-0.3%, Mn: 1-1.3%, Nb: 0.02-0.06%, V: 0.01-0.06%, Ti: 0.006-0.03%, Al: 0.01-0.07%, Cr: 0.4-0.7%, Ni: 0.3-0.4%, Cu: 0.25-0.5%, Mo≤0.15%, La or Ce: 0.001-0.1% and the balance Fe.

[0028] In terms of mass percentage, the rare earth microalloyed weathering bridge steel provided by the present invention includes C: 0.06-0.10%. In the present invention, C, as a common strengthening element in steel, can improve the strength and hardness of bridge steel through solid solution strengthening, but too high a carbon content will reduce the plasticity and weldability of steel. In order to ensure the strength and weldability of bridge steel, the present invention adopts a low-carbon component design and controls the C content within the range of 0.06-0.10%. As an embodiment of the present invention, the mass percentage of C can be 0.06%, 0.07%, 0.08%, 0.09% or 0.1%.

[0029] The rare earth microalloyed weathering bridge steel provided by the present invention includes Si in an amount of 0.15-0.3% by mass. In the present invention, Si is a good deoxidizer, and the addition of Si can play a role in deoxidation and solid solution strengthening of molten steel, and is beneficial to increasing the tempering stability of steel. As an embodiment of the present invention, the mass percentage of Si can be 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28% or 0.3%.

[0030] In terms of mass percentage, the rare earth microalloyed weather-resistant bridge steel provided by the present invention includes Mn: 1-1.3%. In the present invention, Mn has the functions of deoxidation and desulfurization, and improving the hardenability and toughness of steel. However, if the Mn content is too high, the strength of the steel will be too high, the plasticity and weldability will be reduced, and it will easily lead to the center segregation of the continuous casting billet. Therefore, the present invention controls the Mn content within the range of 1-1.3%. As an embodiment of the present invention, the mass percentage of Mn can be 1%, 1.1%, 1.2% or 1.3%.

[0031] In terms of mass percentage, the rare earth microalloyed weathering bridge steel provided by the present invention includes Nb: 0.02-0.06%. In the present invention, a trace amount of Nb can form a NbC nano-precipitation phase, which pins the austenite grain boundary during the high-temperature rolling stage, hinders the grain growth, and delays the austenite recrystallization, thereby refining the grains of the bridge steel, improving the microstructure of the bridge steel, and thus improving its strength and toughness. However, Nb is a precious microalloying element, and excessive content will lead to increased costs. Therefore, the present invention controls the content of Nb within the range of 0.02-0.06%. As an embodiment of the present invention, the mass percentage of Nb can be 0.02%, 0.03%, 0.04%, 0.05% or 0.06%.

[0032] In terms of mass percentage, the rare earth microalloyed weathering bridge steel provided by the present invention includes V: 0.01-0.06%. In the present invention, a trace amount of V can refine the structure and grains of the bridge steel, and can form VC nano-precipitation phases in the low-temperature rolling stage, which can play a role in hydrogen resistance and secondary hardening, thereby improving the yield strength and tensile strength of the bridge steel. V is also a precious microalloying element, so the present invention controls the content of V within the range of 0.01-0.06%. As an embodiment of the present invention, the mass percentage of V can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05% or 0.06%.

[0033] In terms of mass percentage, the rare earth microalloyed weathering bridge steel provided by the present invention includes Ti: 0.006-0.03%. In the present invention, Ti has a strong affinity with nitrogen, oxygen and carbon, and can play a role in deoxidation and fixation of nitrogen and carbon. It can effectively prevent grain growth during the high-temperature rolling stage, thereby refining the grain size, improving the microstructure, and improving the strength and toughness of the bridge steel. As an embodiment of the present invention, the mass percentage of Ti can be 0.006%, 0.008%, 0.01%, 0.012%, 0.014%, 0.016%, 0.018%, 0.02%, 0.022%, 0.024%, 0.026%, 0.028% or 0.03%.

[0034] In terms of mass percentage, the rare earth microalloyed weathering bridge steel provided by the present invention includes Al: 0.01-0.07%. In the present invention, Al as a deoxidizer can effectively reduce the oxygen content in the bridge steel and refine the grains, thereby improving the mechanical properties of the bridge steel. As an embodiment of the present invention, the mass percentage of Al can be 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, 0.055%, 0.06%, 0.065% or 0.07%.

[0035] In terms of mass percentage, the rare earth microalloyed weathering bridge steel provided by the present invention includes Cr: 0.4-0.7%. In the present invention, Cr can improve the hardenability and corrosion resistance of the bridge steel, and Cr can also significantly improve the strength, hardness and wear resistance of the metal material. As an embodiment of the present invention, the mass percentage of Cr can be 0.4%, 0.41%, 0.42%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65% or 0.7%.

[0036] In terms of mass percentage, the rare earth microalloyed weather-resistant bridge steel provided by the present invention includes Ni: 0.3-0.4%. In the present invention, Ni is mainly used to improve the toughness and corrosion resistance of bridge steel, while improving the low-temperature toughness of bridge steel in low-temperature environments. However, the price of Ni element is relatively high. In order to ensure the balance between corrosion resistance and economy of bridge steel, the present invention controls the Ni content within the range of 0.3-0.4%. As an embodiment of the present invention, the mass percentage of Ni can be 0.3%, 0.32%, 0.34%, 0.36%, 0.38% or 0.4%.

[0037] In terms of mass percentage, the rare earth microalloyed weather-resistant bridge steel provided by the present invention includes Cu: 0.25-0.5%. In the present invention, Cu can improve the ability of bridge steel to resist atmospheric corrosion, thereby improving the weather resistance of bridge steel; at the same time, Cu can also improve the strength and toughness of bridge steel. However, if the Cu content is too high, it is easy to cause hot brittleness and reduce weldability. Therefore, the present invention controls the Cu content within the range of 0.25-0.5%. As an embodiment of the present invention, the mass percentage of Cu can be 0.25%, 0.3%, 0.35%, 0.4%, 0.45% or 0.5%.

[0038] In terms of mass percentage, the rare earth microalloyed weather-resistant bridge steel provided by the present invention includes Mo≤0.15%. In the present invention, Mo can refine the grains and eliminate or reduce the temper brittleness caused by other alloying elements, thereby improving the impact toughness of the bridge steel, and can also cooperate with Ni / Cr alloying elements to improve the corrosion resistance of the bridge steel. However, the Mo element is a precious alloying element. In order to ensure the economy of the invented weather-resistant bridge steel, the present invention controls the Mo content to ≤0.15%. As an embodiment of the present invention, the mass percentage of Mo can be 0.1%, 0.11%, 0.12%, 0.13%, 0.14% or 0.15%.

[0039] In terms of mass percentage, the rare earth microalloyed weather-resistant bridge steel provided by the present invention includes La or Ce: 0.001-0.1%. The present invention performs microalloying treatment on the bridge by adding rare earth elements La / Ce, which can not only make the strength of the bridge steel reach 345MPa level, and the mechanical properties meet the requirements of standard GB / T714-2015, but also significantly improve the corrosion resistance of the bridge steel. In a simulated industrial atmospheric environment, the corrosion rate can be reduced by 30-60% compared with traditional weather-resistant bridge steel, and has the potential for non-painting application, which can greatly reduce the cost of bridge construction and later maintenance, and produce significant economic and social benefits. As an embodiment of the present invention, the mass percentage of La or Ce can be 0.001%, 0.005%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09% or 0.1%.

[0040] In terms of mass percentage, the rare earth microalloyed weathering bridge steel provided by the present invention requires N≤0.008%. In the present invention, N as an impurity element can form hard and brittle TiN with Ti, which reduces the mechanical properties of the bridge steel, especially the low-temperature impact toughness. The dissolved N element also increases the strain aging sensitivity, thereby increasing the tendency of the bridge steel to brittle fracture, so its content needs to be controlled at 0.008% or less.

[0041] In terms of mass percentage, the rare earth microalloyed weathering bridge steel provided by the present invention preferably also includes P≤0.007%. In the present invention, P as an impurity element in steel will reduce the mechanical properties of bridge steel, especially low temperature impact toughness, so its content needs to be controlled at 0.007% or less.

[0042] In terms of mass percentage, the rare earth microalloyed weathering bridge steel provided by the present invention preferably also includes S≤0.006%. In the present invention, S as an impurity element will reduce the mechanical properties and corrosion resistance of the bridge steel, so its content needs to be controlled at 0.006% or less.

[0043] In terms of mass percentage, the rare earth microalloyed weathering bridge steel provided by the present invention includes a balance of Fe. In the present invention, Fe is a matrix element of the bridge steel.

[0044] In the present invention, the structure of the rare earth microalloyed weather-resistant bridge steel is preferably a multiphase composite structure of fine-grained ferrite and granular bainite.

[0045] The present invention introduces rare earth La or Ce to carry out micro-alloying treatment on the basis of the composition standard of weather-resistant bridge steel. The mechanical properties of the obtained bridge steel meet the requirements of standard GB / T714-2015. Not only are the strength and plasticity improved compared with traditional 345MPa grade weather-resistant bridge steel, but the corrosion resistance has obvious advantages. In a simulated industrial atmospheric environment, the corrosion rate can be reduced by 30-60% compared with traditional weather-resistant bridge steel. It has the potential for painting-free application, can greatly reduce the cost of bridge construction and subsequent maintenance, and produce significant economic and social benefits.

[0046] The present invention also provides a method for preparing the rare earth microalloyed weathering bridge steel described in the above technical solution, comprising the following steps:

[0047] (1) The raw materials of bridge steel other than La or Ce are sequentially smelted and LF refined, then vacuum cycle degassing and refining is performed and La or Ce is added, and finally casting is performed to obtain a cast billet;

[0048] (2) The ingot obtained in step (1) is sequentially rolled in the austenite recrystallization zone and in the austenite non-recrystallization zone to obtain rare earth micro-alloyed weather-resistant bridge steel.

[0049] The present invention sequentially smelts and LF refines the raw materials of bridge steel other than La or Ce, then performs vacuum cycle degassing and refining, adds La or Ce, and finally performs casting to obtain a cast billet.

[0050] The present invention has no special limitation on the specific type and source of the raw material for the bridge steel, as long as the chemical composition of the rare earth microalloyed weather-resistant bridge steel meets the requirements.

[0051] The present invention has no particular limitation on the temperature and time of the smelting, as long as the raw materials can be mixed, melted and mixed uniformly.

[0052] The present invention preferably controls the composition of the smelted molten steel. The present invention has no special limitation on the specific operation of the composition control, and the molten steel can be properly supplemented with components according to the chemical composition of the required rare earth microalloyed weathering bridge steel.

[0053] In the present invention, the LF refining is preferably carried out in an LF refining furnace. The present invention has no particular limitation on the specific operation of the LF refining, and the LF refining well known to those skilled in the art can be used. The present invention has no particular limitation on the specific model and source of the LF refining furnace, and the commercially available LF refining furnace well known to those skilled in the art can be used.

[0054] In the present invention, the vacuum degree of the vacuum cycle degassing refining (RH refining) is preferably ≤100Pa; the treatment time of the vacuum cycle degassing refining is preferably ≥20min; the atmosphere of the vacuum cycle degassing refining is preferably argon. The present invention can remove gas and inclusions in molten steel, adjust and make uniform the composition and temperature of molten steel, and reduce the burnout of rare earth elements through vacuum cycle degassing refining.

[0055] The present invention preferably adds La or Ce after the treatment time of vacuum cycle degassing refining is ≥15min. The present invention preferably performs electromagnetic stirring for 3 to 5min after adding La or Ce. The present invention has no special limitation on the rate of the electromagnetic stirring, which can be determined according to the technical common sense of those skilled in the art to ensure that the melt does not splash and the rare earth elements are evenly mixed.

[0056] In the present invention, the vacuum cycle degassing refining is preferably carried out in an RH furnace. The present invention has no particular limitation on the specific model and source of the RH furnace, and a commercially available RH furnace well known to those skilled in the art can be used.

[0057] The present invention has no special limitation on the specific operation of the casting, and the casting can be performed by a casting method well known to those skilled in the art.

[0058] The present invention has no special limitation on the size and shape of the ingot, which can be adjusted according to the technical knowledge and technical needs of those skilled in the art.

[0059] After obtaining the ingot, the present invention sequentially performs austenite recrystallization zone rolling and austenite non-recrystallization zone rolling on the ingot to obtain rare earth micro-alloyed weather-resistant bridge steel.

[0060] The present invention preferably heats the ingot before rolling in the austenite recrystallization zone. In the present invention, the holding temperature of the heating is preferably 1200°C; the holding time of the heating is preferably 1.5 to 2.5 hours, more preferably 2 hours. The present invention can fully homogenize the composition and structure of the ingot by heating, and the temperature reaches the austenite recrystallization zone, thereby facilitating hot rolling.

[0061] In the present invention, the starting rolling temperature of the austenite recrystallization zone rolling is preferably ≥1100°C; the cumulative reduction rate of the austenite recrystallization zone rolling is preferably ≥50%. The present invention can fully refine the original austenite grains through austenite recrystallization zone rolling. As an embodiment of the present invention, the starting rolling temperature of the austenite recrystallization zone rolling can be 1100-1200°C, or 1100-1150°C; the cumulative reduction rate of the austenite recrystallization zone rolling can be 50-60%, or 50-55%.

[0062] In the present invention, the starting rolling temperature of the austenite non-recrystallization zone rolling is preferably ≥930°C; the cumulative reduction rate of the austenite non-recrystallization zone rolling is preferably ≥60%; the final rolling temperature of the austenite non-recrystallization zone rolling is preferably 830-850°C. The present invention can fully crush the austenite, refine the grains, and further refine the structure during the phase transformation process by rolling in the austenite non-recrystallization zone. As an embodiment of the present invention, the starting rolling temperature of the austenite non-recrystallization zone rolling can be 930-950°C, or 937-940°C; the cumulative reduction rate of the austenite non-recrystallization zone rolling can be 60-70%, or 60-65%; the final rolling temperature of the austenite non-recrystallization zone rolling can be 839-840°C.

[0063] The present invention does not have any special limitation on the cooling method after rolling of the austenite non-recrystallization zone, which can be determined according to the technical common sense of those skilled in the art. As an embodiment of the present invention, the cooling method after rolling of the austenite non-recrystallization zone is preferably natural cooling or air cooling. The present invention adopts natural cooling after rolling, which avoids the plate shape problem caused by uneven cooling due to accelerated cooling, can save process and energy, has a simple overall production process, and is highly operable. It can be implemented in general metallurgical enterprises and steel structure manufacturers, and can be promoted on a large scale in industry.

[0064] The present invention has no special limitation on the thickness of the rare earth microalloyed weathering bridge steel, which can be controlled according to the technical common sense and technical requirements of those skilled in the art. As an embodiment of the present invention, the thickness of the rare earth microalloyed weathering bridge steel can be 12 to 20 mm.

[0065] The present invention can reduce the oxygen content in the melt through LF refining and RH refining processes, and control the vacuum degree and the adding time of rare earth elements in the RH refining process, so that the recovery rate of rare earth can reach more than 50%. The higher recovery rate of rare earth ensures that the multi-phase composite structure of fine-grained ferrite + granular bainite can be obtained during hot rolling of the ingot. The strain hardening rate and uniform elongation of the steel are increased through the sequential and coordinated deformation of the soft ferrite and the hard phase bainite. While ensuring that the yield strength reaches 345MPa, the tensile strength of the steel is greatly improved, thereby greatly reducing the yield strength ratio of the steel.

[0066] The present invention also provides the rare earth microalloyed weather-resistant bridge steel described in the above technical solution or the rare earth microalloyed weather-resistant bridge steel prepared by the preparation method described in the above technical solution, which is applied to large box girder structure highway bridges and welded structure railway bridges.

[0067] The present invention has no particular limitation on the specific manner of the application, and the application may be performed according to the technical common sense and actual needs of those skilled in the art.

[0068] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0069] Example 1

[0070] A method for preparing rare earth microalloyed weather-resistant bridge steel is as follows:

[0071] (1) After smelting bridge steel raw materials other than Ce, LF refining is performed in an LF refining furnace, and then vacuum cycle degassing refining is performed in an RH furnace, and after vacuum cycle degassing refining for 15 minutes, 0.003% Ce by mass percentage of the alloy melt is added, electromagnetic stirring is performed for 5 minutes, and finally casting is performed to obtain a cast billet; the vacuum degree of the vacuum cycle degassing refining is 100 Pa, the processing time of the vacuum cycle degassing refining is 20 minutes, and the atmosphere of the vacuum cycle degassing refining is argon;

[0072] (2) The ingot obtained in step (1) is heated to 1200° C. and kept warm for 2 h, and then rolled in the austenite recrystallization zone and the austenite non-recrystallization zone in turn, and finally air-cooled to room temperature to obtain rare earth microalloyed weathering bridge steel; the starting rolling temperature of the austenite recrystallization zone rolling is 1100° C., and the cumulative reduction rate of the austenite recrystallization zone rolling is 50%; the starting rolling temperature of the austenite non-recrystallization zone rolling is 950° C., the cumulative reduction rate of the austenite non-recrystallization zone rolling is 60%, and the final rolling temperature of the austenite non-recrystallization zone rolling is 845° C.

[0073] The chemical composition of the rare earth microalloyed weathering bridge steel provided in Example 1 is shown in Table 1.

[0074] The microstructure morphology of the rare earth microalloyed weathering bridge steel provided in Example 1 is as follows: Figure 1 As shown. Figure 1 It can be seen that the structure of the rare earth microalloyed weather-resistant bridge steel provided in Example 1 is a multiphase composite structure of fine-grained ferrite + granular bainite.

[0075] Example 2

[0076] A method for preparing rare earth microalloyed weather-resistant bridge steel is as follows:

[0077] (1) After smelting bridge steel raw materials other than Ce, LF refining is performed in an LF refining furnace, and then vacuum cycle degassing refining is performed in an RH furnace, and after vacuum cycle degassing refining for 15 minutes, 0.02% Ce by mass percentage of the alloy melt is added, electromagnetic stirring is performed for 5 minutes, and finally casting is performed to obtain a cast billet; the vacuum degree of the vacuum cycle degassing refining is 100 Pa, the processing time of the vacuum cycle degassing refining is 20 minutes, and the atmosphere of the vacuum cycle degassing refining is argon;

[0078] (2) The ingot obtained in step (1) is heated to 1200°C and kept warm for 2 hours, and then rolled in the austenite recrystallization zone and the austenite non-recrystallization zone in turn, and finally air-cooled to room temperature to obtain rare earth micro-alloyed weathering bridge steel; the starting rolling temperature of the austenite recrystallization zone rolling is 1120°C, and the cumulative rolling reduction rate of the austenite recrystallization zone rolling is 50%; the starting rolling temperature of the austenite non-recrystallization zone rolling is 930°C, the cumulative rolling reduction rate of the austenite non-recrystallization zone rolling is 60%, and the final rolling temperature of the austenite non-recrystallization zone rolling is 830°C.

[0079] The chemical composition of the rare earth microalloyed weathering bridge steel provided in Example 2 is shown in Table 1.

[0080] The microstructure morphology of the rare earth microalloyed weathering bridge steel provided in Example 2 is as follows: Figure 2 As shown. Figure 2 It can be seen that the structure of the rare earth microalloyed weather-resistant bridge steel provided in Example 2 is a multiphase composite structure of fine-grained ferrite + granular bainite.

[0081] Example 3

[0082] A method for preparing rare earth microalloyed weather-resistant bridge steel is as follows:

[0083] (1) After smelting bridge steel raw materials other than Ce, LF refining is performed in an LF refining furnace, and then vacuum cycle degassing refining is performed in an RH furnace, and after vacuum cycle degassing refining for 15 minutes, 0.1% Ce by mass percentage of the alloy melt is added, electromagnetic stirring is performed for 5 minutes, and finally casting is performed to obtain a cast billet; the vacuum degree of the vacuum cycle degassing refining is 100 Pa, the processing time of the vacuum cycle degassing refining is 20 minutes, and the atmosphere of the vacuum cycle degassing refining is argon;

[0084] (2) The ingot obtained in step (1) is heated to 1200°C and kept warm for 2 hours, and then rolled in the austenite recrystallization zone and the austenite non-recrystallization zone in turn, and finally air-cooled to room temperature to obtain rare earth micro-alloyed weathering bridge steel; the starting rolling temperature of the austenite recrystallization zone rolling is 1125°C, and the cumulative reduction rate of the austenite recrystallization zone rolling is 50%; the starting rolling temperature of the austenite non-recrystallization zone rolling is 950°C, the cumulative reduction rate of the austenite non-recrystallization zone rolling is 60%, and the final rolling temperature of the austenite non-recrystallization zone rolling is 850°C.

[0085] The chemical composition of the rare earth microalloyed weathering bridge steel provided in Example 3 is shown in Table 1.

[0086] The microstructure morphology of the rare earth microalloyed weathering bridge steel provided in Example 3 is as follows: Figure 3 As shown. Figure 3 It can be seen that the structure of the rare earth microalloyed weather-resistant bridge steel provided in Example 3 is a multiphase composite structure of fine-grained ferrite + granular bainite.

[0087] Example 4

[0088] A method for preparing rare earth microalloyed weather-resistant bridge steel is as follows:

[0089] (1) After smelting the raw materials of bridge steel other than La, LF refining is performed in an LF refining furnace, and then vacuum cycle degassing refining is performed in an RH furnace, and after vacuum cycle degassing refining for 15 minutes, 0.1% La by mass percentage of the alloy melt is added, electromagnetic stirring is performed for 5 minutes, and finally casting is performed to obtain a cast billet; the vacuum degree of the vacuum cycle degassing refining is 100 Pa, the processing time of the vacuum cycle degassing refining is 20 minutes, and the atmosphere of the vacuum cycle degassing refining is argon;

[0090] (2) The ingot obtained in step (1) is heated to 1200° C. and kept warm for 2 h, and then rolled in the austenite recrystallization zone and rolled in the austenite non-recrystallization zone in sequence, and finally air-cooled to room temperature to obtain rare earth microalloyed weathering bridge steel; the starting rolling temperature of the austenite recrystallization zone rolling is 1150° C., and the cumulative reduction rate of the austenite recrystallization zone rolling is 50%; the starting rolling temperature of the austenite non-recrystallization zone rolling is 937° C., the cumulative reduction rate of the austenite non-recrystallization zone rolling is 60%, and the final rolling temperature of the austenite non-recrystallization zone rolling is 840° C.

[0091] The chemical composition of the rare earth microalloyed weathering bridge steel provided in Example 4 is shown in Table 1.

[0092] The microstructure morphology of the rare earth microalloyed weathering bridge steel provided in Example 4 is as follows: Figure 4 As shown. Figure 4 It can be seen that the structure of the rare earth microalloyed weather-resistant bridge steel provided in Example 4 is a multiphase composite structure of fine-grained ferrite + granular bainite.

[0093] Example 5

[0094] A method for preparing rare earth microalloyed weather-resistant bridge steel is as follows:

[0095] (1) After smelting the raw materials of bridge steel other than La, LF refining is performed in an LF refining furnace, and then vacuum cycle degassing refining is performed in an RH furnace, and after vacuum cycle degassing refining for 15 minutes, 0.15% La by mass percentage of the alloy melt is added, electromagnetic stirring is performed for 5 minutes, and finally casting is performed to obtain a cast billet; the vacuum degree of the vacuum cycle degassing refining is 100 Pa, the processing time of the vacuum cycle degassing refining is 20 minutes, and the atmosphere of the vacuum cycle degassing refining is argon;

[0096] (2) The ingot obtained in step (1) is heated to 1200° C. and kept warm for 2 h, and then rolled in the austenite recrystallization zone and rolled in the austenite non-recrystallization zone in sequence, and finally air-cooled to room temperature to obtain rare earth microalloyed weathering bridge steel; the starting rolling temperature of the austenite recrystallization zone rolling is 1145° C., and the cumulative reduction rate of the austenite recrystallization zone rolling is 50%; the starting rolling temperature of the austenite non-recrystallization zone rolling is 930° C., the cumulative reduction rate of the austenite non-recrystallization zone rolling is 60%, and the final rolling temperature of the austenite non-recrystallization zone rolling is 839° C.

[0097] The chemical composition of the rare earth microalloyed weathering bridge steel provided in Example 5 is shown in Table 1.

[0098] The microstructure morphology of the rare earth microalloyed weathering bridge steel provided in Example 5 is as follows: Figure 5 As shown. Figure 5It can be seen that the structure of the rare earth microalloyed weather-resistant bridge steel provided in Example 5 is a multiphase composite structure of fine-grained ferrite + granular bainite.

[0099] Comparative Example

[0100] A method for preparing bridge steel is as follows:

[0101] (1) After smelting the raw material of bridge steel, LF refining is performed in an LF refining furnace, and then vacuum cycle degassing refining is performed in an RH furnace, and finally casting is performed to obtain a casting billet; the vacuum degree of the vacuum cycle degassing refining is 100 Pa, the processing time of the vacuum cycle degassing refining is 20 minutes, and the atmosphere of the vacuum cycle degassing refining is argon;

[0102] (2) The ingot obtained in step (1) is heated to 1200°C and kept warm for 2 hours, and then rolled in the austenite recrystallization zone and the austenite non-recrystallization zone in turn, and finally air-cooled to room temperature to obtain bridge steel; the starting rolling temperature of the austenite recrystallization zone rolling is 1100°C, and the cumulative reduction rate of the austenite recrystallization zone rolling is 50%; the starting rolling temperature of the austenite non-recrystallization zone rolling is 937°C, the cumulative reduction rate of the austenite non-recrystallization zone rolling is 60%, and the final rolling temperature of the austenite non-recrystallization zone rolling is 840°C.

[0103] The chemical composition of the bridge steel provided by the comparative example is shown in Table 1.

[0104] The microstructure morphology of the bridge steel provided by the comparative example is as follows Figure 6 As shown. Figure 6 It can be seen that the structure of the bridge steel provided in the comparative example is a multiphase composite structure of fine-grained ferrite + pearlite + a small amount of granular bainite.

[0105] Table 1 Chemical composition (wt%) of bridge steels prepared in Examples 1 to 5 and Comparative Examples

[0106] Comparative Example Example 1 Example 2 Example 3 Example 4 Example 5 C 0.078 0.079 0.077 0.079 0.079 0.060 Si 0.28 0.23 0.27 0.28 0.28 0.28 Mn 1.11 1.09 1.15 1.15 1.14 1.17 Nb 0.02 0.02 0.02 0.02 0.02 0.02 V 0.025 0.02 0.02 0.02 0.02 0.02 Ti 0.012 0.013 0.020 0.027 0.021 0.011 Al 0.019 0.017 0.014 0.030 0.025 0.063 Cr 0.43 0.41 0.42 0.42 0.41 0.42 Ni 0.32 0.31 0.31 0.32 0.31 0.32 Cu 0.31 0.31 0.32 0.32 0.32 0.32 Mo 0.11 0.11 0.11 0.11 0.1 0.1 P 0.007 0.007 0.006 0.006 0.006 0.004 S 0.005 0.006 0.004 0.003 0.003 0.002 Ce - 0.002 0.012 0.074 - - La - - - - 0.052 0.07 Fe margin margin margin margin margin margin

[0107] It can be seen from Table 1 that although the content of rare earth elements in the rare earth microalloyed weathering bridge steels provided in Examples 1 to 5 of the present invention is lower than the added amount, the yield of rare earth elements is basically around 50%, indicating that the preparation method provided by the present invention can improve the yield of rare earth elements.

[0108] The mechanical properties of the bridge steels provided in Examples 1 to 5 and the comparative example were tested. The test results of the mechanical properties at room temperature are shown in Table 2. The stress-strain curves of the bridge steels are shown in Table 2. Figure 7 shown.

[0109] Table 2 Mechanical properties of bridge steels prepared in Examples 1 to 5 and Comparative Examples

[0110]

[0111]

[0112] From Table 2 and Figure 7 It can be seen that although the yield strength and yield strength ratio of the bridge steel provided by Examples 1 to 2 of the present invention are slightly lower than those of the comparative example, the tensile strength is significantly improved, and the yield strength ratio is lower, which generally meets the requirements of GB / T714-2015; the yield strength, tensile strength and elongation of Examples 3 to 5 are significantly higher than those of the comparative example, indicating that the present invention can significantly improve the mechanical properties of bridge steel by introducing rare earth elements for rare earth microalloying and adjusting the preparation process; and according to the comparison of the performance of the bridge steel prepared in Examples 1 to 5, the optimal value of the rare earth content in the bridge steel is selected as 0.01% to 0.1%.

[0113] According to the TB / T2375-1993 "Cyclic Immersion Corrosion Test Method for Weathering Steel for Railways", the bridge steel provided in Examples 1 to 3 and the comparative example was subjected to a cyclic immersion accelerated corrosion test in a simulated industrial atmospheric environment. The experimental method is:

[0114] (1) Twelve pieces of 60×40×2 mm hanging specimens were processed from each of the bridge steels prepared in Examples 1 to 3 and the comparative example by wire cutting. The specimens were then polished step by step using 400#, 1000# and 2000# SiC water-based sandpapers. After being washed and dried with deionized water and alcohol, the specimens were weighed and their dimensions were measured.

[0115] (2) Twelve coupons of each steel were subjected to accelerated corrosion tests in a weekly immersion accelerated test chamber. The corrosive medium used was a 0.01 mol / L NaHSO3 solution. The test cycles were 5d, 10d, 20d and 30d, respectively. The corrosive solution in the weekly immersion chamber was replaced every 5d. After each test cycle, three coupons were taken out for ultrasonic rust removal, washed with anhydrous ethanol, dried and weighed. The rust removal solution was 500mLH2O+500mL HCl+3.5g hexamethylenetetramine. The annual corrosion rates of the steel plates were calculated according to Formula I:

[0116]

[0117] In Formula I, R corr is the corrosion rate, in mm / y; m0 is the original weight of the sample, in g; m1 is the weight of the sample after the rust layer is removed, in g; S is the exposed area of ​​the sample, in cm 2 ; ρ is the density of steel, which is 7.8g / cm 3 ; t is the exposure time, unit is d.

[0118] The corrosion rate results of bridge steel of Experimental Examples 1 to 3 and Comparative Example are shown in Tables 3 and Figure 8 As shown:

[0119] Table 3 Corrosion rates of bridge steels in Experimental Examples 1 to 3 and Comparative Examples

[0120]

[0121]

[0122] From Table 3 and Figure 8 It can be seen that although the corrosion rate of the bridge steel provided by Examples 1 to 2 is slightly higher than that of the comparative example when the corrosion time is 5 days, when the corrosion time reaches more than 10 days, the corrosion rate of the bridge steel provided by Examples 1 to 3 is significantly lower than that of the comparative example, and when the corrosion time reaches 30 days, the corrosion rate of the bridge steel provided by the present invention is much lower than that of the comparative example, indicating that the technical solution of the present invention can significantly improve the corrosion resistance of bridge steel.

[0123] Since La-microalloyed Examples 4-5 have similar properties and corrosion resistance effects to Ce-microalloyed Examples 1-3.

[0124] From the above analysis, it can be seen that the yield strength of the bridge steel prepared by the present invention is ≥345MPa, the tensile strength is ≥490MPa, the elongation is ≥20%, and the mechanical properties of the steel plate meet the performance requirements of Q345qNH in the relevant technical conditions of the national standard GB / T714-2015 "Structural Steel for Bridges", and the yield strength ratio reaches below 0.7, which is much lower than that of traditional weather-resistant bridge steels, and has excellent comprehensive mechanical properties; at the same time, the weather-resistant bridge steel after rare earth micro-alloying has excellent corrosion resistance in a simulated industrial atmospheric environment. After 30 days, the average corrosion rate is significantly reduced compared with the control bridge steel, up to 60%, and has a significant corrosion resistance advantage.

[0125] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A rare earth microalloyed weathering bridge steel, comprising the following chemical composition, by mass percentage: C: 0.06-0.1%, Si: 0.15-0.3%, Mn: 1-1.3%, Nb: 0.02-0.06%, V: 0.01-0.06%, Ti: 0.006-0.03%, Al: 0.01-0.07%, Cr: 0.4-0.7%, Ni: 0.3-0.4%, Cu: 0.25-0.5%, Mo≤0.15%, La or Ce: 0.001-0.1% and the balance Fe.

2. The rare earth microalloyed weathering bridge steel according to claim 1, characterized in that: By mass percentage, it includes the following chemical compositions: C: 0.06~0.1%, Si: 0.2~0.3%, Mn: 1~1.2%, Nb: 0.02~0.06%, V: 0.01~0.02%, Ti: 0.01~0.02%, Al: 0.015~0.05%, Cr: 0.4~0.7%, Ni: 0.3~0.4%, Cu: 0.25~0.5%, Mo≤0.15%, La or Ce: 0.001~0.1% and the balance Fe.

3. The rare earth microalloyed weathering bridge steel according to claim 1, characterized in that: By mass percentage, it includes the following chemical compositions: C: 0.079%, Si: 0.28%, Mn: 1.15%, Nb: 0.02%, V: 0.02%, Ti: 0.027%, Al: 0.03%, Cr: 0.42%, Ni: 0.32%, Cu: 0.32%, Mo: 0.11%, Ce: 0.074% and the balance Fe.

4. The rare earth microalloyed weathering bridge steel according to any one of claims 1 to 3, characterized in that: The structure of the rare earth microalloyed weather-resistant bridge steel is a multiphase composite structure of fine-grained ferrite and granular bainite.

5. The method for preparing the rare earth microalloyed weathering bridge steel according to any one of claims 1 to 4, comprising the following steps: (1) The raw materials of bridge steel other than La or Ce are sequentially smelted and LF refined, then vacuum cycle degassing and refining is performed and La or Ce is added, and finally casting is performed to obtain a cast billet; (2) The ingot obtained in step (1) is sequentially rolled in the austenite recrystallization zone and in the austenite non-recrystallization zone to obtain rare earth micro-alloyed weather-resistant bridge steel.

6. The preparation method according to claim 5, characterized in that: In the step (1), the vacuum degree of the vacuum cycle degassing refining is ≤100 Pa, the processing time of the vacuum cycle degassing refining is ≥20 min, and the atmosphere of the vacuum cycle degassing refining is argon.

7. The preparation method according to claim 5, characterized in that: In the step (2), the ingot is heated before rolling in the austenite recrystallization zone; the heating holding temperature is 1200° C., and the heating holding time is 1.5 to 2.5 hours.

8. The preparation method according to claim 5, characterized in that: In the step (2), the starting rolling temperature of the austenite recrystallization zone rolling is ≥1100°C, and the cumulative reduction rate of the austenite recrystallization zone rolling is ≥50%.

9. The preparation method according to claim 5, characterized in that: In the step (2), the starting rolling temperature of the austenite non-recrystallization zone rolling is ≥930°C, the cumulative reduction rate of the austenite non-recrystallization zone rolling is ≥60%, and the final rolling temperature of the austenite non-recrystallization zone rolling is 830-850°C.

10. The rare earth microalloyed weather-resistant bridge steel described in any one of claims 1 to 4 or the rare earth microalloyed weather-resistant bridge steel prepared by the preparation method described in any one of claims 5 to 9 is used in large box girder structure highway bridges and welded structure railway bridges.

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