420MPa-grade alkaline soil corrosion resistant steel and preparation method thereof

Abstract

The invention relates to 420 MPa grade alkaline soil corrosion resistant steel and a preparation method, and belongs to the technical field of steel preparation. The alkali soil corrosion resistant steel comprises the following chemical components in percentage by mass: 0.03%-0.12% of C, 0.2%-0.6% of Si, 0.5%-2.0% of Mn, 0.6%-3.5% of Cr, 0.6%-1.2% of Al, 0.001%-0.3% of Mo, 0.001%-0.5% of Ni, 0.001%-0.5% of Cu, less than or equal to 0.008% of P, less than or equal to 0.006% of S, less than or equal to 0.1% of Sn, less than or equal to 0.1% of Sb and a matrix element Fe. Specific chemical components including C, Si, Mn, Cr, Al, Mo, Ni, Cu and other alloy elements are designed, the content range of all the elements is strictly controlled, through the composite effect of all the elements, the steel can form a compact oxidation film in a corrosion environment, corrosion of a corrosion medium is effectively resisted, and therefore the corrosion resistance of the steel is improved, the service life of the steel is prolonged, and the service life of the steel is prolonged. And a powerful guarantee is provided for long-term application of the steel structure in the northwest alkaline soil environment, and wide application prospects are achieved.

Description

Technical Field

[0001] This application relates to the technical field of steel preparation, and particularly to a 420MPa grade steel resistant to alkaline soil corrosion and its preparation method. Background Art

[0002] The corrosion problem of materials in the soil environment is not only an important topic in the field of corrosion science research, but also a practical problem that urgently needs to be solved in underground engineering applications. Soil is composed of moisture, gas, microorganisms and various granular minerals, and has ionic conductivity, biological activity, colloidal properties, etc., and is a special electrolyte. The corrosivity of soil is closely related to factors such as soil resistivity, water content, soluble salts, pH value, etc. The soil corrosion of metal materials is usually faster than that of atmospheric corrosion. With the development of the western region of China, the major engineering construction in the west urgently needs to develop corrosion-resistant steels that meet the soil environment in the northwest region.

[0003] In the northwest region, the soil has alkaline characteristics and contains various corrosive components, and has strong corrosivity to steel structure materials. Traditional carbon steels have a short service life in this environment and are prone to corrosion failure problems. Summary of the Invention

[0004] This application provides a 420MPa grade steel resistant to alkaline soil corrosion and its preparation method to solve the following technical problems: how to improve the service life of steel structures in the alkaline soil environment in the northwest.

[0005] In the first aspect, an embodiment of this application provides a 420MPa grade steel resistant to alkaline soil corrosion. In terms of mass fraction, the chemical composition of the steel resistant to alkaline soil corrosion includes: C: 0.03% - 0.12%, Si: 0.2% - 0.6%, Mn: 0.5% - 2.0%, Cr: 0.6% - 3.5%, Al: 0.6% - 1.2%, Mo: 0.001% - 0.3%, Ni: 0.001% - 0.5%, Cu: 0.001% - 0.5%, P ≤ 0.008%, S ≤ 0.006%, Sn ≤ 0.1%, Sb ≤ 0.1%, and the matrix element Fe.

[0006] Optionally, in terms of mass fraction, the chemical composition of the steel resistant to alkaline soil corrosion includes: Mo: 0.1% - 0.3%, Ni: 0.1% - 0.5%, Cu: 0.2% - 0.5%, Cr: 1.0% - 3.0%, Sb: 0.05% - 0.1%.

[0007] Optionally, the steel resistant to alkaline soil corrosion meets at least one of the following properties: yield strength ≥ 420MP, tensile strength ≥ 500MPa, elongation after fracture ≥ 25%, impact toughness at -40°C ≥ 60J.

[0008] Optionally, the thickness of the steel resistant to alkaline soil corrosion is 3 mm to 20 mm.

[0009] Optionally, the steel resistant to alkaline soil corrosion satisfies that in a 30-day full immersion test in a simulated northwest alkaline soil corrosion solution, the corrosion rate is less than 0.5 times the corrosion rate of carbon steel.

[0010] In a second aspect, the present application provides a method for preparing the steel resistant to alkaline soil corrosion described in the first aspect, and the method includes:

[0011] Obtaining a cast slab with the chemical composition;

[0012] Successively heating, rough rolling, finish rolling and cooling the cast slab to obtain the finished steel resistant to alkaline soil corrosion.

[0013] Optionally, the heating temperature is 1150 °C to 1250 °C, and the heating time is 0.5 h to 3 h.

[0014] Optionally, the rough rolling starting temperature is 1100 °C to 1150 °C, and the total reduction ratio of rough rolling is 85% to 90%.

[0015] Optionally, the finish rolling starting temperature is 980 °C to 1050 °C, the finish rolling ending temperature is 850 °C to 920 °C, and the total reduction ratio of finish rolling is 10% to 15%.

[0016] Optionally, the final cooling temperature of the cooling is 550 °C to 620 °C.

[0017] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0018] The embodiment of the present application provides a 420MPa grade alkaline soil corrosion resistant steel. In terms of mass fraction, the chemical composition of the alkaline soil corrosion resistant steel includes: C: 0.03% - 0.12%, Si: 0.2% - 0.6%, Mn: 0.5% - 2.0%, Cr: 0.6% - 3.5%, Al: 0.6% - 1.2%, Mo: 0.001% - 0.3%, Ni: 0.001% - 0.5%, Cu: 0.001% - 0.5%, P≤0.008%, S≤0.006%, Sn≤0.1%, Sb≤0.1%, and the matrix element Fe. By designing a specific chemical composition, including various alloying elements such as C, Si, Mn, Cr, Al, Mo, Ni, Cu, etc., and strictly controlling the content ranges of each element, through the combined effect of each element, a dense oxide film can be formed on the steel in a corrosive environment, effectively resisting the erosion of corrosive media, thereby improving the corrosion resistance of the steel, extending the service life of the steel, providing a strong guarantee for the long-term application of steel structures in the alkaline soil environment in the northwest, and having broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings herein are incorporated into and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 It is a schematic flow chart of a preparation method of a 420MPa grade alkaline soil corrosion resistant steel provided by the embodiment of the present application;

[0022] Figure 2 It is an electron microscope microstructure diagram provided by Embodiment 1 of the present application;

[0023] Figure 3 It is an electron microscope microstructure diagram provided by Comparative Example 1 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present application belong to the scope of protection of the present application.

[0025] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0026] In this text, terms including "comprising" etc. mean "including but not limited to". Relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or" describes the associated relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "a plurality" means two or more; "at least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single items (pieces) or plural items (pieces); for example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. "Part representation methods" such as parts by weight, parts by mass, etc. represent the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0027] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in this text can be obtained through market purchases or can be prepared by existing methods.

[0028] In a first aspect, an embodiment of the present application provides a 420 MPa grade alkaline soil corrosion resistant steel. In terms of mass fraction, the chemical composition of the alkaline soil corrosion resistant steel includes: C: 0.03% to 0.12%, Si: 0.2% to 0.6%, Mn: 0.5% to 2.0%, Cr: 0.6% to 3.5%, Al: 0.6% to 1.2%, Mo: 0.001% to 0.3%, Ni: 0.001% to 0.5%, Cu: 0.001% to 0.5%, P ≤ 0.008%, S ≤ 0.006%, Sn ≤ 0.1%, Sb ≤ 0.1%, and the matrix element Fe.

[0029] C is an important alloying element in steel. The mass fraction of C has a significant influence on the microstructure, mechanical properties, and welding properties of steel. Appropriately increasing the mass fraction of C can promote the formation of pearlite and improve the strength of steel. However, if the mass fraction of C is too high (exceeding 0.12%), it will increase the carbon equivalent, reduce the weldability and toughness. In the embodiment of the present application, the mass fraction of C is limited to be between 0.03% and 0.12%, which can not only ensure sufficient strength but also ensure high toughness and welding properties.

[0030] Si is one of the commonly used deoxidizing elements in steel. It can reduce the O content in steel, improve the purity of molten steel, and improve the quality of continuous casting billets. During the heating process of the billet, an oxide film of Si can be formed, which has a certain protective effect on the burning and oxidation of the billet. In addition, Si can also reduce the diffusion rate of C in austenite, inhibit the formation of pearlite, increase the solid solution amount of C in steel, and improve the strength of steel. However, if the mass fraction of Si is too high (exceeding 0.6%), it will form liquid-phase iron silicate during the heating process of the billet, increase the adhesion force between the scale and the matrix, make the scale difficult to remove, and reduce the surface quality of the steel plate. In addition, during the welding process, Si is prone to form oxides in the molten pool, reducing the weld quality. In the embodiment of the present application, the mass fraction of Si is limited to be between 0.2% and 0.6%, which can not only ensure the quality of the billet but also ensure high strength and toughness and welding properties.

[0031] Mn can be dissolved in austenite and ferrite, improving the strength of steel. At the same time, Mn can improve the hardenability of steel and has a significant impact on welding properties. In addition, Mn will form MnS inclusions with the S element in steel, reducing the corrosion resistance. In the embodiment of the present application, the mass fraction of Mn is limited to be between 0.5% and 2.0%, which can not only ensure the strength and toughness and welding properties of the product but also not reduce the corrosion resistance of the product.

[0032] In the embodiment of the present application, the mass fraction of P is limited to ≤ 0.008% to meet the requirements of the steel for toughness, weldability, and corrosion resistance.

[0033] In the embodiment of the present application, the mass fraction of S is limited to ≤ 0.006% to meet the requirements of the steel for toughness, weldability, and corrosion resistance.

[0034] Cr can significantly affect the mechanical properties, corrosion resistance, high-temperature properties, etc. of steel. Cr forms a dense Cr2O3 passivation film on the steel surface, which can significantly improve the corrosion resistance to the atmosphere, acids, and alkalis. Cr can delay the decomposition of austenite and improve the hardenability of steel. Cr dissolved in ferrite or austenite can increase the strength and hardness of steel. Cr can combine with C to form carbides such as (Fe,Cr)7C3 and (Fe,Cr) 23 C6 to improve wear resistance. In the embodiments of this application, the mass fraction of Cr is limited to 0.6% - 3.5%, which can be compounded with other elements to improve corrosion resistance while ensuring the requirements of the steel for toughness and weldability.

[0035] Al in steel mainly acts as a deoxidizer and grain refiner, while also taking into account corrosion resistance and alloying functions. Aluminum is a powerful deoxidizer. During the steelmaking process, it reacts with oxygen to form Al2O3 (aluminum oxide), reducing the dissolved oxygen in the molten steel and preventing porosity and inclusion defects. Aluminum combines with nitrogen (N) to form AlN precipitation phases, which serve as heterogeneous nuclei for the growth of austenite grains and inhibit grain coarsening. In addition, aluminum forms a dense Al2O3 oxide layer on the surface, which can enhance the atmospheric corrosion resistance. The mass fraction of Al has a promoting effect on the formation of high-temperature ferrite and has a very obvious impact on the hot rolling process. In the embodiments of this application, the mass fraction of Al is limited to 0.6% - 1.2% with the aim of being compounded with other elements to improve corrosion resistance while ensuring the requirements of the steel for toughness and weldability.

[0036] Mo in steel mainly acts as a strengthener and corrosion inhibitor, and improves strength, high-temperature properties, and corrosion resistance through mechanisms such as solid-solution strengthening, secondary hardening, and grain refinement. Mo can increase the resistance to dislocation movement by dissolving in ferrite, thereby increasing the matrix strength. In addition, Mo can inhibit the growth of austenite grains, improve the uniformity of the ferrite / bainite structure, and enhance the comprehensive mechanical properties. However, Mo is expensive, and a trade-off between performance improvement and economy is required. In the embodiments of this application, the mass fraction of Mo is limited to 0.001% - 0.3% with the aim of being compounded with other elements to improve corrosion resistance while ensuring the requirements of the steel for strength, toughness, and weldability.

[0037] The core role of Ni in steel is to stabilize austenite, enhance corrosion resistance and low-temperature toughness, while also improving the comprehensive mechanical properties. Ni is a powerful austenite stabilizing element, which can lower the critical phase transformation temperature (Ar3) of steel, expand the austenite phase region, and improve the corrosion resistance of steel to media such as acids, alkalis, and salts. Especially in cooperation with chromium (Cr), it can enhance the stability of the passivation film. Ni dissolved in ferrite can increase the matrix strength (but weaker than elements such as carbon and molybdenum), refine grains, and reduce the resistance to dislocation movement, significantly improving the impact toughness of steel. In the embodiments of this application, the mass fraction of Ni is limited to 0.001% - 0.5%.

[0038] Cu mainly acts as a corrosion inhibitor and precipitation strengthening element in steel. Cu forms a dense oxide layer on the steel surface, which can prevent further oxidation and significantly improve the atmospheric corrosion resistance. An appropriate amount of Cu (0.001% - 0.5%) can refine the ferrite grains and increase the strength of the steel. When the mass fraction of Cu is too high (>0.5%) and contains P, it is easy to form a Cu-P brittle phase, resulting in hot working cracking. In the embodiments of this application, the mass fraction of Cu is limited to 0.001% - 0.5%.

[0039] Sn mainly acts as a deoxidizer, corrosion inhibitor and weldability improver in steel, but the mass fraction of Sn needs to be strictly controlled. Sn can react with oxygen in the molten steel to form SnO2 or SnO, reducing the mass fraction of dissolved oxygen, reducing the risk of pores and inclusions, and can also form a dense SnO2 oxide film on the steel surface to delay corrosion. Excessive Sn (>0.1%) is easy to combine with phosphorus (P) to form a Sn-P brittle phase, resulting in cold brittleness and hot working cracking.

[0040] Sb mainly acts as a deoxidizer, refiner and wear resistance enhancer in steel, but the mass fraction of Sb needs to be strictly controlled. Sb can react with oxygen in the molten steel to form oxides, reducing the mass fraction of dissolved oxygen, reducing the risk of pores and inclusions, and can also combine with sulfur to form Sb2S3, reducing sulfide inclusions, improving the cleanliness of the steel, and can cooperate with Cu and Cr to form a dense oxide film to enhance the atmospheric corrosion resistance.

[0041] In some embodiments, by mass fraction, the chemical composition of the alkaline soil corrosion resistant steel includes: Mo: 0.1% - 0.3%, Ni: 0.1% - 0.5%, Cu: 0.2% - 0.5%, Cr: 1.0% - 3.0%, Sb: 0.05% - 0.1%.

[0042] In some embodiments, the alkaline soil corrosion resistant steel meets at least one of the following properties: yield strength ≥ 420MP, tensile strength ≥ 500MPa, elongation after fracture ≥ 25%, impact toughness at -40°C ≥ 60J.

[0043] Yield strength ≥ 420MPa and tensile strength ≥ 500MPa ensure that the steel can withstand large loads without plastic deformation or fracture when stressed, which is crucial for ensuring the safety and stability of the structure. Elongation after fracture ≥ 25% reflects the extension ability of the steel in the plastic deformation stage. The achievement of this index means that the steel can absorb more energy when subjected to external forces, thereby slowing down the crack propagation and improving the seismic resistance and impact resistance of the structure. Impact toughness at -40°C ≥ 60J indicates that the steel can still maintain good toughness in low-temperature environments, which is particularly important for steel structure materials used in cold regions. It ensures that the steel is not prone to brittle fracture at low temperatures and improves the reliability of the structure.

[0044] The achievement of these performance indicators enables the alkaline soil corrosion-resistant steel to meet the application requirements in different fields and scenarios. For example, in fields such as construction, bridges, and vehicles that require high strength and toughness, this steel can exhibit excellent performance.

[0045] In some embodiments, the thickness of the alkaline soil corrosion-resistant steel is 3 mm to 20 mm.

[0046] Different thickness ranges can adapt to different usage scenarios and requirements. This flexible thickness range enables the alkaline soil corrosion-resistant steel to be widely used in multiple fields such as construction, bridges, and vehicles.

[0047] In some embodiments, the alkaline soil corrosion-resistant steel satisfies: in a 30-day full immersion test in a simulated northwest alkaline soil corrosion solution, the corrosion rate is less than 0.5 times the corrosion rate of carbon steel.

[0048] In a 30-day full immersion test in a simulated northwest alkaline soil corrosion solution, the 420 MPa grade northwest alkaline soil corrosion-resistant steel demonstrated excellent corrosion resistance. According to the test data, the corrosion rate of this steel is less than 0.5 times the corrosion rate of carbon steel, which means that within the same time, the degree of corrosion of the corrosion-resistant steel is much lower than that of ordinary carbon steel. This result indicates that the corrosion-resistant steel has a longer service life and better corrosion resistance in the northwest alkaline soil environment.

[0049] Figure 1 It is a schematic flow chart of a preparation method of a 420 MPa grade alkaline soil corrosion-resistant steel provided by an embodiment of the present application.

[0050] Please refer to Figure 1 , on the second aspect, the present application provides a preparation method of the alkaline soil corrosion-resistant steel described in the first aspect, and the method includes:

[0051] S1. Obtain a billet with the described chemical composition;

[0052] S2. Heat, rough roll, finish roll, and cool the billet in sequence to obtain the finished alkaline soil corrosion-resistant steel.

[0053] In some embodiments, the temperature of the heating is 1150 °C to 1250 °C, and the time of the heating is 0.5 h to 3 h.

[0054] Heating to a high temperature range of 1150°C to 1250°C helps to homogenize the internal structure of the steel. The high temperature enables the alloying elements in the steel to diffuse fully, reducing composition segregation, thereby ensuring the performance consistency of the steel during subsequent processing. At the same time, heating within the temperature range of 1150°C to 1250°C for 0.5 h to 3 h helps to release the internal stress of the steel. During processes such as casting and cooling, the steel accumulates a certain amount of internal stress, and high-temperature heating can cause these stresses to relax, reducing the risk of deformation and cracking of the steel during subsequent processing or use.

[0055] In some embodiments, the starting rolling temperature of the rough rolling is 1100°C to 1150°C, and the total reduction ratio of the rough rolling is 85% to 90%.

[0056] Performing rough rolling within this temperature range, the steel has good plasticity and low deformation resistance, which is beneficial to the smooth progress of the rolling process. The starting rolling temperature of 1100°C to 1150°C can also reduce the temperature gradient during rolling, ensuring the uniformity of the internal structure transformation of the steel and laying a good foundation for subsequent finish rolling and cooling processes.

[0057] A total reduction ratio of 85% to 90% helps the steel to achieve significant thinning and elongation during the rough rolling stage, thereby improving production efficiency. At the same time, a reduction ratio of 85% to 90% can also promote the fragmentation and recrystallization of the internal structure of the steel, refine the matrix structure, and improve the strength and hardness of the steel. In addition, some casting defects such as shrinkage cavities and porosity can be eliminated in advance, improving the density and overall quality of the steel.

[0058] In some embodiments, the starting rolling temperature of the finish rolling is 980°C to 1050°C, the final rolling temperature of the finish rolling is 850°C to 920°C, and the total reduction ratio of the finish rolling is 10% to 15%.

[0059] A starting rolling temperature of 980°C to 1050°C helps the steel to obtain good plasticity and low hardness during finish rolling, making the rolling process smoother. At the same time, the starting rolling temperature of 980°C to 1050°C can also reduce the thermal stress during rolling and improve the dimensional stability of the steel. The final rolling temperature is within the range of 850°C to 920°C, and the strength and hardness of the steel are moderate, which can not only maintain good processing performance but also reduce the internal stress of the steel during cooling and improve the dimensional stability.

[0060] A total reduction ratio of 10% to 15% helps to ensure the plate shape of the steel plate, reduce the residual stress, and at the same time promote the refinement of austenite grains, ensuring the strength and toughness of the final product.

[0061] In some embodiments, the final cooling temperature of the cooling is 550°C to 620°C.

[0062] Within this temperature range, the microstructure transformation of the steel can be better controlled. During the cooling process, the austenite microstructure in the steel will gradually transform into ferrite, bainite, and pearlite microstructures with higher ductility and toughness.

[0063] This application utilizes the combined effect of Cr, Al, Si, Mo, Ni, and Cu elements to reduce the corrosion rate of the matrix in the soil environment. Meanwhile, in combination with the control of heating and rolling processes, a uniform ferrite + bainite duplex phase, or ferrite + bainite + pearlite duplex phase, or bainite + pearlite duplex phase microstructure is obtained. While improving the corrosion resistance of the steel, a high strength-ductility combination is ensured. This steel can be used in fields such as construction, bridges, and vehicles.

[0064] The product prepared by the preparation method of the 420 MPa grade steel resistant to alkaline soil corrosion is the above-mentioned 420 MPa grade steel resistant to alkaline soil corrosion. Since the preparation method of the 420 MPa grade steel resistant to alkaline soil corrosion adopts some or all of the technical solutions of the examples of the 420 MPa grade steel resistant to alkaline soil corrosion, it therefore has at least all the beneficial effects brought by the technical solutions of the examples of the 420 MPa grade steel resistant to alkaline soil corrosion, which will not be elaborated one by one here.

[0065] The following further elaborates this application in combination with specific examples. For the experimental methods without specific conditions indicated in the following examples, they are usually determined according to national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0066] The chemical composition of the continuous casting billet is shown in Table 1.

[0067] Table 1 Chemical composition of continuous casting billets in examples and comparative examples (wt%)

[0068] Group C Si Mn P S Cr Al Mo Ni Cu Sn Sb Example 1 0.05 0.57 0.8 0.006 0.003 3.0 0.6 0.1 0.45 0.39 0.02 0.05 Example 2 0.07 0.33 0.9 0.005 0.004 2.5 0.7 0.2 0.35 0.35 0.08 0.06 Example 3 0.10 0.26 1.3 0.007 0.004 1.5 0.9 0.3 0.29 0.32 0.10 0.10 Example 4 0.15 0.43 1.5 0.006 0.003 1.0 1.0 0.2 0.25 0.25 0.04 0.02 Example 5 0.09 0.38 1.0 0.007 0.005 2.5 0.6 0.1 0.12 0.21 0.03 0.09

[0069] The continuous casting billets of the examples are successively heated, rough rolled, finish rolled, and cooled to obtain the finished steel resistant to alkaline soil corrosion. The main process parameters are shown in Table 2.

[0070] Table 2 Main process parameters

[0071]

[0072] The products obtained from the above examples are subjected to performance tests, and the obtained data are shown in Table 3.

[0073] The finished alkali-resistant soil corrosion-resistant steel obtained from the above embodiments and Q345B steel were processed into corrosion test specimens with dimensions of 50×25×5 mm. There were 5 parallel specimens in each group. A full immersion corrosion test was carried out using a soil simulation solution to analyze their corrosion resistance. The composition of the soil simulation solution was: NaHCO3: 0.146±0.002 g / L, KNO3: 0.216±0.002 g / L, Na2SO4:

[0074] 2.53±0.001 g / L, CaCl2: 0.244±0.002 g / L, NaCl: 3.17±0.01 g / L, MgCl2·6H2O: 0.670±0.005 g / L; the test temperature was 20±5 °C, and the test period was 30 days. The weight changes of the test materials before and after corrosion were compared and analyzed, the corrosion rate was calculated, and the relative corrosion rate was obtained by comparing with plain carbon steel (Q345B steel).

[0075] Table 3

[0076]

[0077] As can be seen from Tables 1 to 3, the chemical compositions and preparation process parameters of the embodiments are all within the required ranges of the present invention, with a yield strength ≥420 MP, a tensile strength ≥500 MPa, an elongation after fracture ≥25%, an impact toughness at -40 °C ≥60 J, and a corrosion rate less than 0.5 times that of carbon steel.

[0078] Appendix Figure 2-3 Detailed description:

[0079] Figure 2 is the electron microscope microstructure diagram provided in Example 1 of this application; as Figure 2 shown, this microstructure is a ferrite + bainite duplex microstructure. The gray polygons are ferrite grains, and the gray and white polygon regions are bainite grains. The white dot-chain particles therein are carbide precipitates.

[0080] Figure 3 is the electron microscope microstructure diagram provided in Comparative Example 1 of this application; as Figure 3 shown, this microstructure is a ferrite + pearlite duplex microstructure. The gray polygon regions are ferrite grains, and the white banded regions are pearlite.

[0081] One or more technical solutions in the embodiments of the present invention at least further have the following technical effects or advantages:

[0082] Due to the significant reduction in the corrosion rate, the service life of the corrosion-resistant steel in the alkaline soil environment in the northwest has been greatly extended. Compared with ordinary carbon steel, the corrosion-resistant steel can maintain the structural integrity and mechanical properties for a longer time, reducing the maintenance and replacement frequency caused by corrosion.

[0083] The low corrosion rate of corrosion-resistant steel means that during long-term use, the maintenance costs caused by corrosion will be significantly reduced. This includes not only direct repair costs, but also indirect losses caused by shutdowns, equipment replacements, etc.

[0084] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but rather to the broadest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A 420MPa grade steel resistant to alkaline soil corrosion. By mass fraction, the chemical composition of the steel resistant to alkaline soil corrosion includes: C： By mass fraction, the chemical composition of the steel resistant to alkaline soil corrosion includes: C: 0.03% - 0.12%, Si: 0.2% - 0.6%, Mn: 0.5% - 2.0%, Cr: 0.6% - 3.5%, Al: 0.6% - 1.2%, Mo: 0.001% - 0.3%, Ni: 0.001% - 0.5%, Cu: 0.001% - 0.5%, P ≤ 0.008%, S ≤ 0.006%, Sn ≤ 0.1%, Sb ≤ 0.1%, and the matrix element Fe.

2. The alkali-resistant soil corrosion-resistant steel according to claim 1, characterized in that, By mass fraction, the chemical composition of the steel resistant to alkaline soil corrosion includes: Mo: 0.1% - 0.3%, Ni: 0.1% - 0.5%, Cu: 0.2% - 0.5%, Cr: 1.0% - 3.0%, Sb: 0.05% - 0.1%.

3. The alkali-resistant soil corrosion-resistant steel according to claim 1, characterized in that, The steel resistant to alkaline soil corrosion meets at least one of the following properties: yield strength ≥ 420 MPa, tensile strength ≥ 500 MPa, elongation after fracture ≥ 25%, impact toughness at - 40 °C ≥ 60 J.

4. The alkali-resistant soil corrosion-resistant steel according to claim 1, characterized in that, The thickness of the steel resistant to alkaline soil corrosion is 3 mm - 20 mm.

5. The alkali-resistant soil corrosion steel according to claim 1, characterized in that The steel resistant to alkaline soil corrosion meets the requirement that in a 30 - day full - immersion test in a simulated northwest alkaline soil corrosion solution, the corrosion rate is less than 0.5 times the corrosion rate of carbon steel.

6. A method for preparing the steel resistant to alkaline soil corrosion according to any one of claims 1 - 5, the method comprising: Obtaining a continuous casting billet with the above - mentioned chemical composition; Successively heating, rough rolling, finish rolling and cooling the continuous casting billet to obtain the finished steel resistant to alkaline soil corrosion.

7. The method according to claim 6, characterized in that, The heating temperature is 1150 °C - 1250 °C, and the heating time is 0.5 h - 3 h.

8. The method according to claim 6, characterized in that, The rough rolling starting temperature is 1100 °C - 1150 °C, and the total reduction ratio of rough rolling is 85% - 90%.

9. The method according to claim 6, wherein The finish rolling starting temperature is 980 °C - 1050 °C, the finish rolling ending temperature is 850 °C - 920 °C, and the total reduction ratio of finish rolling is 10% - 15%.

10. The method according to claim 6, wherein The final cooling temperature of the cooling is 550 °C - 620 °C.

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