High-strength steel with excellent corrosion resistance to neutral water medium, and preparation method and application thereof

Abstract

The application belongs to the technical field of metal materials, and particularly relates to a high-strength steel with excellent corrosion resistance to neutral water medium and a preparation method and application thereof. The steel plate of the application adopts a cheap chemical component design of low carbon, low silicon and medium manganese, and is completely free of precious metal elements such as Cr, Ni and Cu, thereby greatly reducing the material cost. The application does not adopt the traditional Al deoxidization technology, but instead adopts Si or Si-Mn deoxidization, and is supplemented by Zr-Ti composite deoxidization, thereby forming fine, dispersed and uniform composite oxysulfides, greatly reducing the density of corrosion active inclusions, and significantly improving the corrosion resistance to neutral water medium. Through the design of low carbon equivalent, the steel plate has excellent welding performance. Through the composite micro-alloying of Nb, Zr and Ti, and the regulation of TMCP rolling parameters, the steel plate has high strength and good ductility. The steel is particularly suitable for steel used in neutral water medium environment, and can significantly improve the corrosion resistance of the steel to neutral water medium.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials technology, specifically relating to a high-strength steel with excellent resistance to corrosion in neutral aqueous media, its preparation method, and its application. Background Technology

[0002] Currently, most corrosion-resistant steels are mainly focused on resistance to seawater corrosion, atmospheric corrosion, crude oil corrosion, and acid and alkali corrosion. The main technical solutions employed include: first, using elements such as Ni, Cr, Cu, and P to form a dense passivation film; second, using elements such as Cr, Mo, and N for alloying to improve pitting corrosion resistance; third, using special chemical compositions to design a uniform microstructure, eliminating or reducing electrode potential differences between different microstructures; fourth, using rare earth, Si-Ca, Fe-Ca, and Si-Ca-Ba refining technologies to alter the morphology and distribution of inclusions; and fifth, using anti-corrosion coatings and corrosion inhibitors to delay corrosion.

[0003] Human life and activities mostly take place on land, and the vast majority of water on land is freshwater, that is, water with a neutral medium. Like seawater, this water is also a very weak electrolyte and has corrosive properties. The difference is that this water does not contain highly corrosive Cl-. - Structures such as inland rivers, lakes, and reservoirs, as well as dredging vessel pipelines, mine slurry pump bodies and pipelines, common industrial and civil buildings, and fences, are all susceptible to corrosion from neutral aquatic media, even when coated with protective paint. The steel materials used in these neutral aquatic environments typically employ ordinary low-alloy high-strength steel, or utilize the five main technical measures mentioned above—such as forming a dense passivation film with elements like Ni, Cr, Cu, and P—or use corrosion-resistant materials like ordinary stainless steel.

[0004] The above-mentioned technical methods all involve the problem of high alloy costs, and cannot effectively solve the problem of localized corrosion caused by neutral water media. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-strength steel with excellent resistance to corrosion in neutral aqueous media, its preparation method, and its applications. This invention solves the problems of insufficient resistance to corrosion in neutral aqueous media and high alloy costs associated with traditional high-strength steels.

[0006] The technical solution provided by this invention is as follows:

[0007] A high-strength steel with excellent corrosion resistance in neutral water medium, whose chemical composition is as follows by mass percentage: 0.021 < C < 0.059%, 0.11 < Si < 0.29%, 1.35 - 1.55% of Mn, 0.02 < Nb + Ti < 0.05%, 0.01 < Zr < 0.02%, S ≤ 0.0010%, and the rest is Fe and inevitable impurities. At the same time, the above chemical composition must also satisfy the following formulas: by mass percentage, ① Nb / Ti = 1 - 3, ② Ti / Zr = 2 - 4, ③ Ceq ≤ 0.39, ④ Pcm ≤ 0.17. Ceq is the carbon equivalent, and Pcm is the welding crack sensitivity index.

[0008] The above technical solution adopts a low-carbon, low-silicon, medium-manganese cheap chemical composition design, completely free of precious metal elements such as Cr, Ni, and Cu, and greatly reduces the material cost.

[0009] The high-strength steel with excellent corrosion resistance in neutral water medium provided by the above technical solution can form fine, dispersed and uniform composite oxygen sulfides, greatly reducing the density of corrosive active inclusions and significantly improving the corrosion resistance in neutral water medium.

[0010] Through the design of low carbon equivalent in the above technical solution, the steel plate has excellent welding performance.

[0011] The above technical solution adopts the combined microalloying of Nb, Zr, and Ti, and coordinates with the control of TMCP rolling parameters to achieve fine grains, high strength and high toughness of the steel plate.

[0012] The functions of each element in the high-strength steel with excellent corrosion resistance in neutral water medium are as follows:

[0013] Carbon: The addition of C can improve strength. When the content of carbon increases, the hardenability can be increased. However, with the increase of carbon content, the overall corrosion resistance decreases. In addition, since the increase of carbon content promotes the precipitation of carbides and M / A (martensite / austenite), it will also affect the resistance to local corrosion. The carbon content should be reduced to improve the overall corrosion resistance and local corrosion resistance. Moreover, a high carbon content is not conducive to improving the welding performance of the steel. Therefore, the carbon content of the steel in this invention is 0.021 < C < 0.059%.

[0014] Silicon: The Si element can not only play a role in solid solution strengthening, but also has strong deoxidation ability. It exists in an amount of 0.1% or more to act as a deoxidizer and to increase the strength of the steel. In addition, since silicon helps to improve the overall corrosion resistance, it is beneficial to increase the silicon content. However, when the content is 0.30% or more, the low-temperature toughness and weldability may deteriorate, and it is not easy to remove the scale during rolling, causing surface defects. Therefore, the silicon content of the steel in this invention is 0.11 < Si < 0.29%.

[0015] Manganese (Mn) is an important strengthening element in low-alloy high-strength steel. Manganese can effectively improve strength without reducing toughness through solid solution strengthening. However, when the manganese content is too high, the electrochemical reaction rate on the steel surface may increase during corrosion, thereby reducing corrosion resistance; simultaneously, it may form segregation regions in the core of the steel, reducing Z-axis properties and tear resistance. When the manganese content is too low, it is difficult to guarantee the strength of the steel. Therefore, the manganese content of the steel in this invention is 1.35%. <Mn<1.55%。

[0016] Titanium (Ti) is a commonly used microalloying element with strong deoxidizing capabilities. When titanium is added at 0.01% or more, it combines with carbon in the steel to form TiC or Ti(CN), improving strength due to the precipitation strengthening effect. However, when Ti is added at levels greater than 0.05%, the strength improvement effect is not significant, and large TiN inclusions may precipitate, impairing the steel's ductility and toughness. Therefore, the titanium content of the steel in this invention is 0.01-0.05%.

[0017] Niobium (Nb), similar to titanium, is an important microalloying element that combines with carbon in steel to form NbC, thus playing a strengthening role. When Nb is added in amounts of 0.02% or higher, it can effectively improve strength. However, when Nb is added in amounts of 0.05% or higher, the improvement in strength is not significant. Furthermore, high levels of both niobium and carbon will affect the weldability of the steel. Therefore, the niobium content of the steel in this invention is 0.01%. <Ti<0.05%。

[0018] Zirconium: Zr is a strong carbide-forming element, as well as a strong deoxidizing element and a complex oxysulfide-forming element. Adding a small amount of zirconium has degassing, purification, and grain refinement effects, which is beneficial to improving the low-temperature performance of marine engineering steel, improving stamping performance, and significantly improving the hardenability of steel when dissolved in austenite. Therefore, the zirconium content of the marine engineering steel of this invention is 0.01-0.02%.

[0019] Sulfur: S generally exists as an impurity in steel. When the sulfur content exceeds 0.02%, the ductility, impact toughness, and weldability of the steel deteriorate. Sulfur readily reacts with manganese to form elongated inclusions, such as MnS. Furthermore, the voids formed at the ends of these elongated inclusions can be the initiation points for localized corrosion. Because sulfur exists as an impurity and is detrimental to localized corrosion, the upper limit for sulfur content is set at 0.001%, with no separate lower limit.

[0020] Specifically, the microstructure of high-strength steel is a composite microstructure of ferrite and pearlite, with ferrite accounting for ≥85% of the area and pearlite accounting for ≤15% of the area.

[0021] Specifically, the density of corrosion-active inclusions in high-strength steel is ≤10 inclusions / mm².2 .

[0022] Specifically, the saturation current density of high-strength steel at a static electrode potential E = -300mV is ≤7.0mA.

[0023] This invention also provides a method for preparing high-strength steel with excellent resistance to corrosion in neutral aqueous media, comprising the following steps:

[0024] 1) The molten steel is smelted, refined, and vacuum-treated in sequence, and then continuously cast into billets;

[0025] 2) Perform conventional heating and homogenization on the cast billet;

[0026] 3) The billet is continuously rolled into a finished steel plate, and the final rolling temperature is controlled at 750-850℃. After rolling, it is cooled with water to 410-550℃.

[0027] 4) Allow the steel plate to cool naturally to room temperature to obtain the final product.

[0028] Specifically, step 1) of the smelting process includes the following steps: Using a converter or electric arc furnace, molten iron, scrap steel, or molten iron and scrap steel are smelted together, and the temperature and composition of the molten steel are adjusted to achieve a tapping temperature of 1560-1680℃ and a free oxygen content of 121-379ppm. After the molten steel enters the ladle, it is stirred with micro-bubbles for 4-11 minutes. Then, pre-deoxidation is performed in the ladle using Fe-Si alloy or Fe-Si-Mn alloy to adjust the free oxygen content to 21-95ppm. After micro-bubble stirring for 4-7 minutes, final deoxidation is performed using Fe-Zr-Ti alloy to obtain molten steel that meets the stated chemical composition. The Fe-Zr-Ti alloy is added to the molten steel in the form of block alloy or cored wire, with a particle size of 10-20mm. The amount of Fe-Zr-Ti alloy added is 0.41-3.5kg per ton of molten steel.

[0029] The above technical solution does not use the traditional Al deoxidation technology, but instead uses Si or Si-Mn deoxidation, as well as composite deoxidation supplemented by Zr-Ti, to form fine, dispersed and uniform composite oxysulfides, which significantly reduces the density of corrosive inclusions and significantly improves the corrosion resistance to neutral water media; at the same time, due to the use of Nb, Zr and Ti composite microalloying, combined with TMCP (thermomechanical control process) rolling parameter control, the steel plate achieves the effect of fine grains and high strength and toughness.

[0030] Specifically, the refining method involves LF refining followed by VD refining or RH refining, and then the refined molten steel is continuously cast using conventional processes.

[0031] This invention also provides applications of high-strength steel with excellent resistance to corrosion in neutral water media. As steel for neutral water media environments such as marine engineering, shipbuilding, bridges, iron towers, railways, crude oil pipelines rich in mineral water in oil extraction, seawater dredging, river dredging, cement mixer trucks or garbage trucks, it can significantly improve the steel's resistance to corrosion in neutral water media.

[0032] The high-strength steel provided by this invention has excellent resistance to corrosion in neutral water media. It has high resistance to corrosion in neutral water media and high strength and toughness, and can be widely used in the above-mentioned scenarios. Attached Figure Description

[0033] Figure 1 Micrographs of corrosion-active inclusions in steel provided in Example 1;

[0034] Figure 2 Comparison of micrographs of corrosion-active inclusions in Q345 steel;

[0035] Figure 3 Compare the potentiodynamic polarization results of steel Q345 in 3.5% NaCl solution;

[0036] Figure 4 The potentiodynamic polarization results of steel in 3.5% NaCl solution provided in Example 1;

[0037] Figure 5 Compare the AC impedance results of steel Q345 in 3.5% NaCl solution;

[0038] Figure 6 The AC impedance results of the steel provided in Example 1 in 3.5% NaCl solution;

[0039] Figure 7 Compare the potentiostatic polarization results obtained for steel Q345 in the test solution;

[0040] Figure 8 The constant potential polarization results of the steel obtained in the test solution provided in Example 1. Detailed Implementation

[0041] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0042] Example 1

[0043] The chemical composition of a high-strength, easy-to-weld steel with excellent resistance to corrosion in neutral water media, by mass percentage, is as follows: C 0.039%, Si 0.19%, Mn 1.4%, Nb 0.035%, Ti 0.012%, Zr 0.015%, S 0.008%, with the remainder being Fe and unavoidable impurities.

[0044] The smelting and refining method is as follows: After steelmaking in a converter, the temperature and composition of the molten iron are adjusted to achieve a tapping temperature of 1620℃ and a free oxygen content of 170ppm. The molten iron is then stirred with micro-bubbles for 7 minutes in a ladle, followed by pre-deoxidation with an Fe-Si alloy to adjust the free oxygen content to 63ppm. After micro-bubble stirring for 6 minutes, final deoxidation is performed with an Fe-Zr-Ti alloy. The Fe-Zr-Ti alloy is added to the molten steel in block form with a particle size of 15mm. The amount of Fe-Zr-Ti alloy added is 1.9kg per ton of molten steel. The molten steel is then refined using conventional LF and RH processes.

[0045] LF Refining:

[0046] The viscosity of the refining slag was controlled between 1.511 and 1.921 Pa·s to improve the slag system's ability to adsorb inclusions, thereby improving the cleanliness of the molten steel. The basicity of the white slag in the refining furnace was controlled at 5.31 ≤ R ≤ 7.53, which is beneficial to improving the desulfurization rate and the cleanliness of the molten steel, and reducing oxide inclusions in the molten steel. The MI slag index (=CaO / SiO2:Al2O3 ratio) was controlled to be MI > 0.151, which significantly increased the sulfur distribution coefficient, thereby controlling the appropriate fluidity of the refining slag at a certain basicity. The white slag holding time was 14.15 min, the refining cycle was 39.41 min, and the soft blowing time was ensured to be 4.51 min, thereby controlling the [O] content at the outlet.

[0047] RH vacuum treatment:

[0048] The vacuum chamber pressure was evacuated to below 66.61 kPa and maintained for 13.30 min, with a bottom-blown argon flow rate of 14.91 m³ / s. 3 / h, to achieve 4 cycles of molten steel circulation; strict control is required over the type and weight of added alloys, using higher-grade low-carbon ferromanganese, metallic manganese, low-carbon ferrosilicon, ferrotitanium and other alloys to ensure that the composition of the molten steel is completely qualified, and to ensure that the vacuum is maintained for more than 5.17 minutes after the alloy is added, so as to obtain purer molten steel; at the same time, to provide a suitable molten steel temperature for continuous casting, ensuring that the superheat of the tundish is 19.66℃ above the liquidus line.

[0049] The refined molten steel is then continuously cast using conventional processes: the temperature of the tundish is 1541℃ and the casting speed is 1.21 m / s.

[0050] The rolling process is as follows: the billet is heated and held at 1185℃ for 3.5 hours; it is continuously rolled into a product steel plate, and the final rolling temperature is controlled at 810℃. After rolling, it is cooled with water to 480℃; and then naturally cooled to room temperature for use.

[0051] The microstructure of the steel plate obtained by the above process is ferrite + pearlite, with ferrite accounting for 87% of the area and pearlite accounting for 12%. The density of corrosion-active inclusions in the steel plate is 8 inclusions / mm². 2 The saturation current density of the steel plate at a static electrode potential (E = -300mV) is 6.5mA. The yield strength of the steel plate is 380MPa, the tensile strength is 540MPa, and the elongation is 35%.

[0052] Example 2

[0053] The chemical composition of a high-strength, easy-to-weld steel with excellent resistance to corrosion in neutral aqueous media, by mass percentage, is as follows: C 0.058%, Si 0.28%, Mn 1.53%, Nb 0.038%, Ti 0.010%, Zr 0.018%, S 0.0010%, with the remainder being Fe and unavoidable impurities.

[0054] The smelting and refining method is as follows: After steelmaking in a converter, the temperature and composition of the molten iron are adjusted to achieve a tapping temperature of 1670℃ and a free oxygen content of 370ppm. Once the molten iron enters the ladle, it is stirred with micro-bubbles for 10 minutes. Then, Fe-Si alloy is used for pre-deoxidation in the ladle to adjust the free oxygen content to 90ppm. After micro-bubbling for 7 minutes, Fe-Zr-Ti alloy is used for final deoxidation. The Fe-Zr-Ti alloy is added to the molten steel in block form with a particle size of 18mm. The amount of Fe-Zr-Ti alloy added is 3.1kg per ton of molten steel. The molten steel is then refined using conventional LF and RH processes.

[0055] LF Refining:

[0056] The viscosity of the refining slag was controlled between 1.523 and 1.937 Pa·s to improve the slag system's ability to adsorb inclusions, thereby improving the cleanliness of the molten steel. The basicity of the white slag in the refining furnace was controlled at 5.23 ≤ R ≤ 7.47, which is beneficial to improving the desulfurization rate and the cleanliness of the molten steel, and reducing oxide inclusions in the molten steel. The MI slag index (=CaO / SiO2:Al2O3 ratio) was controlled to be MI > 0.153, which significantly increased the sulfur distribution coefficient, thereby controlling the appropriate fluidity of the refining slag at a certain basicity. The white slag holding time was 14.33 min, the refining cycle was 39.43 min, and the soft blowing time was ensured to be 4.54 min, thereby controlling the [O] content at the outlet.

[0057] RH vacuum treatment:

[0058] The vacuum chamber pressure was evacuated to below 66.63 kPa and maintained for 13.35 min, with a bottom-blowing argon flow rate of 14.93 m³ / min. 3 / h, to achieve 5 cycles of molten steel circulation; strict control is required over the type and weight of added alloys, using higher-grade low-carbon ferromanganese, metallic manganese, low-carbon ferrosilicon, ferrotitanium and other alloys to ensure that the composition of the molten steel is completely qualified, and to ensure that the vacuum is maintained for more than 5.33 minutes after the alloy is added, so as to obtain purer molten steel; at the same time, a suitable molten steel temperature is provided for continuous casting, ensuring that the superheat of the tundish is 19.7℃ above the liquidus line.

[0059] The refined molten steel is then continuously cast using conventional processes: the temperature of the tundish is 1543℃ and the casting speed is 1.18 m / s.

[0060] The rolling process is as follows: the billet is heated to 1198℃ and held for 3.4 hours; it is continuously rolled into a product steel plate, and the final rolling temperature is controlled at 840℃. After rolling, it is cooled with water to 540℃; and then naturally cooled to room temperature for use.

[0061] The microstructure of the steel plate obtained by the above process is ferrite + pearlite, with ferrite comprising 88% and pearlite 12%. The density of corrosion-active inclusions in the steel plate is 9 inclusions / mm². 2 The saturation current density of the steel plate at a static electrode potential (E = -300mV) is 6.8mA. The yield strength of the steel plate is 390MPa, the tensile strength is 560MPa, and the elongation is 34%.

[0062] Example 3

[0063] The chemical composition of a high-strength, easy-to-weld steel with excellent resistance to corrosion in neutral water media, by mass percentage, is as follows: C 0.030%, Si 0.15%, Mn 1.48%, Nb 0.030%, Ti 0.015%, Zr 0.012%, S 0.009%, with the remainder being Fe and unavoidable impurities.

[0064] The smelting and refining method is as follows: After steelmaking, the temperature and composition of the molten steel are adjusted in a converter, and the tapping temperature is adjusted to 1610℃, with a free oxygen content of 149ppm. After the molten steel enters the ladle, it is stirred with micro-bubbles for 5 minutes. Then, Fe-Si alloy is used for pre-deoxidation in the ladle to adjust the free oxygen content of the molten steel to 31ppm. After stirring with micro-bubbles for 5 minutes, Fe-Zr-Ti alloy is used for final deoxidation. Fe-Zr-Ti alloy is added to the molten steel in the form of block alloy with a particle size of 12mm. The amount of Fe-Zr-Ti alloy added is 0.81kg per ton of molten steel. Then, the molten steel is refined by LF and RH refining according to conventional processes.

[0065] LF Refining:

[0066] The viscosity of the refining slag is controlled between 1.525 and 1.935 Pa·s to improve the slag system's ability to adsorb inclusions, thereby improving the cleanliness of the molten steel. The basicity of the white slag in the refining furnace is controlled between 5.25 and R, which is beneficial to improving the desulfurization rate and the cleanliness of the molten steel, and reducing oxide inclusions in the molten steel. The MI slag index (=CaO / SiO2:Al2O3 ratio) is controlled to be greater than 0.152, which significantly increases the sulfur distribution coefficient, thereby controlling the appropriate fluidity of the refining slag at a certain basicity. The white slag holding time is 14.35 min, the refining cycle is 39.45 min, and the soft blowing time is 4.55 min, thereby controlling the [O] content at the outlet.

[0067] RH vacuum treatment:

[0068] The vacuum chamber pressure was evacuated to below 66.65 kPa and maintained for 13.31 min, with a bottom-blowing argon flow rate of 14.95 m³ / min. 3 / h, to achieve 6 cycles of molten steel circulation; strict control is required over the type and weight of added alloys, using higher-grade low-carbon ferromanganese, metallic manganese, low-carbon ferrosilicon, ferrotitanium and other alloys to ensure that the composition of the molten steel is completely qualified, and to ensure that the vacuum is maintained for more than 5.35 minutes after the alloy is added, so as to obtain purer molten steel; at the same time, a suitable molten steel temperature is provided for continuous casting, ensuring that the superheat of the tundish is 19.7℃ above the liquidus line.

[0069] The refined molten steel is then continuously cast using conventional processes: the temperature of the tundish is 1545℃ and the casting speed is 1.15 m / s.

[0070] The rolling process is as follows: the billet is heated and held at 1215℃ for 3.3 hours; it is continuously rolled into a product steel plate, and the final rolling temperature is controlled at 770℃. After rolling, it is cooled with water to 450℃; and then naturally cooled to room temperature for use.

[0071] The microstructure of the steel plate obtained by the above process is ferrite + pearlite, with ferrite ≥ 85% and pearlite ≤ 15%. The density of corrosion-active inclusions in the steel plate is 7 inclusions / mm². 2 The saturation current density of the steel plate at a static electrode potential (E = -300mV) is 6.7mA. The yield strength of the steel plate is 400MPa, the tensile strength is 580MPa, and the elongation is 33%.

[0072] Comparative Example 1

[0073] The chemical composition of a conventional Al deoxidation process for easy-to-weld high-strength steel, by mass percentage, is: C 0.038%, Si 0.22%, Mn 1.5%, Nb 0.033%, Ti 0.015%, Al 0.035%, S 0.007%, with the remainder being Fe and unavoidable impurities.

[0074] The smelting and refining method is as follows: after the molten iron is smelted in a converter, the temperature and composition of the molten steel are adjusted, the tapping temperature is adjusted to 1630℃, and the free oxygen content in the molten steel is 180ppm; after the molten steel enters the ladle, it is stirred with micro-bubbles for 7 minutes, and then the pure Al wire is fed into the ladle for final deoxidation. Then the molten steel is refined by LF and RH according to conventional processes.

[0075] LF Refining:

[0076] The viscosity of the refining slag was controlled between 1.527 and 1.939 Pa·s to improve the slag system's ability to adsorb inclusions, thereby improving the cleanliness of the molten steel. The basicity of the white slag in the refining furnace was controlled at 5.27 ≤ R ≤ 7.48, which is beneficial to improving the desulfurization rate and the cleanliness of the molten steel, and reducing oxide inclusions in the molten steel. The MI slag index (=CaO / SiO2:Al2O3 ratio) was controlled to be MI > 0.157, which significantly increased the sulfur distribution coefficient, thereby controlling the appropriate fluidity of the refining slag at a certain basicity. The white slag holding time was 14.37 min, the refining cycle was 39.49 min, and the soft blowing time was ensured to be 4.57 min, thereby controlling the [O] content at the outlet.

[0077] RH vacuum treatment:

[0078] The vacuum chamber pressure was evacuated to below 66.69 kPa and maintained for 13.33 min, with a bottom-blown argon flow rate of 14.98 m³ / min. 3 / h, to achieve 5 cycles of molten steel circulation; strict control is required over the type and weight of added alloys, using higher-grade low-carbon ferromanganese, metallic manganese, low-carbon ferrosilicon, ferrotitanium and other alloys to ensure that the composition of the molten steel is completely qualified, and to ensure that the vacuum is maintained for more than 5.39 minutes after the alloy is added, so as to obtain purer molten steel; at the same time, a suitable molten steel temperature is provided for continuous casting, ensuring that the superheat of the tundish is 19.79℃ above the liquidus line.

[0079] The refined molten steel is then continuously cast using conventional processes: the temperature of the tundish is 1539℃ and the casting speed is 1.25 m / s.

[0080] The rolling process is as follows: the billet is heated and held at 1218℃ for 3.4 hours; it is continuously rolled into a product steel plate, and the final rolling temperature is controlled at 815℃. After rolling, it is cooled with water to 485℃; and then naturally cooled to room temperature for use.

[0081] The microstructure of the steel plate obtained by the above process is ferrite + pearlite, with ferrite accounting for 85% of the area and pearlite accounting for 15%. The density of corrosion-active inclusions in the steel plate is 18 inclusions / mm². 2The saturation current density of the steel plate at a static electrode potential (E = -300mV) is 8.5mA. The yield strength of the steel plate is 370MPa, the tensile strength is 525MPa, and the elongation is 33%.

[0082] The corrosion resistance of the high-strength steel with excellent resistance to neutral aqueous media prepared in Example 1 is analyzed and tested below. The results are as follows:

[0083] 1. Testing Method

[0084] Determination of the density of corrosive inclusions: The sample was cut into 10×10×10mm pieces, and the surface was mechanically ground to 1500 mesh and then polished to a mirror finish. The corrosion reagent was prepared according to the following ratio: each 100mL ethanol solution contained 5.0mL concentrated hydrochloric acid, 0.12g CuCl2, 0.06g SnCl2, and 3.0g FeCl3. The corrosion reagent was dropped onto the sample surface and treated for 8s. The surface was then rinsed with alcohol and dried. The density of corrosive inclusions was then determined under a metallographic microscope at 100× magnification.

[0085] The electrochemical corrosion experiment was conducted at room temperature using a 3.5% NaCl solution to simulate a corrosion environment. A classic three-electrode system was employed. The sample served as the working electrode, a platinum electrode as the auxiliary electrode, and a saturated calomel electrode as the reference electrode (SCE). The electrochemical equipment used was a ZAHNER electrochemical workstation, with parameters set using Thales electrochemical software. The workstation was connected to a computer for data display.

[0086] Electrochemical corrosion experiments were conducted at room temperature to measure the tafel polarization and electrochemical impedance spectroscopy (EIS) curves of small sample pieces. Before testing, the samples were immersed in the etching solution for 40 min to allow the open circuit potential (OCP) to stabilize before performing the EIS and tafel polarization measurements. The sinusoidal transition signal applied to the EIS was 10 mV, and the test scan range was 10 mHz to 10 kHz. The tafel polarization curve scan rate was 0.5 mV / s, and the scan range was -600 mV to 1.2 V. The tafel polarization and EIS curves were fitted using Origin and Zsimpwin software, respectively.

[0087] The AC impedance method perturbs the electrode system with small-amplitude sinusoidal waves of different frequencies. By analyzing the relationship between the electrode system response and the perturbation signal, the equivalent circuit of the electrode can be inferred. By fitting the parameters of each component in the equivalent circuit, the corrosion kinetic parameters of the material can be obtained. This allows for a direct and quantitative analysis of the factors affecting the corrosion resistance of the material, and further understanding of the corrosion behavior of the material.

[0088] All corrosion electrochemical experiments were conducted in a classic three-electrode system. The electrochemical sample to be tested served as the working electrode, the saturated calomel electrode (SCE) as the reference electrode, and a platinum sheet as the counter electrode. The test temperature was room temperature (25℃). For the weld metal in the weld state at room temperature, the sample was first immersed in the corrosion solution to test the open circuit potential (OCP) for 40 minutes. After the open circuit potential stabilized, electrochemical impedance spectroscopy (EIS) testing was performed. The amplitude of the sinusoidal wave applied to the EIS was 10 mV, the scanning frequency range was 10 mHz to 10 kHz, and the scanning time was 40 minutes.

[0089] 2. Test Results and Analysis

[0090] Figure 1 This is a micrograph of the corrosion-active inclusions in the steel provided in Example 1. Measurement results show that the density of corrosion-active inclusions in the steel provided in Example 1 is 5 inclusions / mm². 2 . Figure 2 Micrographs of corrosion-active inclusions in Q345 steel were used for comparison. Measurements showed that the density of corrosion-active inclusions in the comparison steel Q345 was 18 inclusions / mm². 2 The density of corrosion-active inclusions in the steel provided in Example 1 is much lower than that in the comparative steel Q345.

[0091] Figure 3 To compare the potentiodynamic polarization results of steel Q345 in 3.5% NaCl solution. As shown in the figure, the corrosion potential of the comparison steel is -0.5619V, and the corrosion current density is 8.5 × 10⁻⁶ V. -5 A·cm -2 .

[0092] Figure 4 The results show the potentiodynamic polarization of the steel provided in Example 1 in a 3.5% NaCl solution. Figure 4 As can be seen, the corrosion potential of the steel provided in Example 1 is -0.678V, and the corrosion current density is 1.508 × 10⁻⁶. -5 A·cm -2 .

[0093] Figure 5 Table 1 shows the AC impedance test results of Q345 steel in 3.5% NaCl solution. The phase angle exponent 'n' in the table reflects the degree of deviation between the actual capacitance and the ideal capacitance. A larger value of 'n' indicates a smaller deviation from the ideal capacitance. Generally, the 'n' value for the double-layer capacitance of corroded electrodes is between 0.5 and 1. Figure 3 As shown in Table 1, the charge transfer resistance of the comparative steel is 233.7 Ω·cm. -2 .

[0094] Figure 6Table 2 shows the AC impedance test results of the steel provided in Example 1 in 3.5% NaCl solution. Figure 4 As shown in Table 2, the charge transfer resistance of the comparative steel is 956.3 Ω·cm. -2 .

[0095] Table 1 compares the AC impedance fitting results of Q345 steel in 3.5% NaCl solution.

[0096] <![CDATA[R s ,(Ω·cm -2 )]]> <![CDATA[Y0,(S·sec n ·cm -2 )]]> constant phase angle index n <![CDATA[R ct ,(Ω·cm -2 )]]> Comparison with Q345 steel 36.24 0.001118 0.683 233.7

[0097] Table 2 shows the AC impedance fitting results of the steel provided in Example 1 in 3.5% NaCl solution.

[0098] <![CDATA[R s ,(Ω·cm -2 )]]> <![CDATA[Y0,(S·sec n ·cm -2 )]]> constant phase angle index n <![CDATA[R ct ,(Ω·cm -2 )]]> Inventing steel 36.53 0.0008117 0.7775 956.3

[0099] Figure 7 For comparison, the saturation current density obtained from the constant potential polarization test of the Q345 steel sample was 8.5 mA / cm². 2 It is generally believed that 6mA / cm 2 ≤Saturation current density≤8mA / cm 2 It is considered to have good resistance to corrosion in neutral water media.

[0100] Figure 8 The saturation current density of the steel provided in Example 1, obtained by constant potential polarization testing, was 3.93 mA / cm². 2 It is generally considered that the saturation current density is ≤6 mA / cm². 2 It is considered to have excellent resistance to corrosion in neutral water media.

[0101] The results above show that the corrosion current density, from largest to smallest, is: Comparative steel Q345 > Steel provided in Example 1; the charge transfer resistance, from smallest to largest, is: Comparative steel Q345 < Steel provided in Example 1; and the saturation current density, from largest to smallest, is: Comparative steel Q345 > Steel provided in Example 1. This indicates that the steel provided in Example 1 has excellent resistance to corrosion in neutral water media and is significantly better than comparative steel Q345.

[0102] In summary, the steel plate of this invention adopts a low-carbon, low-silicon, and medium-manganese chemical composition design, completely free of precious metal elements such as Cr, Ni, and Cu, significantly reducing material costs. Instead of traditional Al deoxidation technology, this invention uses Si or Si-Mn deoxidation, supplemented by Zr-Ti composite deoxidation, forming fine, dispersed, and uniform composite oxysulfides, significantly reducing the density of corrosive inclusions and substantially improving resistance to corrosion in neutral water media. Through a low-carbon equivalent design, the steel plate exhibits excellent weldability. The use of Nb, Zr, and Ti composite microalloying, combined with TMCP rolling parameter control, achieves high strength and good ductility. This steel grade is particularly suitable for use in neutral water media environments such as marine engineering, shipbuilding, bridge steel, iron tower steel, railway steel, crude oil pipelines in oil extraction rich in mineral water, seawater dredging, river dredging, cement mixer trucks, and garbage trucks, significantly improving the steel's resistance to corrosion in neutral water media.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength steel with excellent resistance to corrosion in neutral aqueous media, characterized in that, The chemical composition in terms of mass percentage is: 0.021 < C < 0.059%, 0.11 < Si < 0.29%, 1.35 < Mn < 1.55%, 0.02 < Nb + Ti < 0.05%, 0.01 < Zr < 0.02%, S <= 0.0010%, the rest is Fe and inevitable impurities, meanwhile the above chemical composition must also satisfy the formula: in terms of mass percentage, ① Nb / Ti = 1-3, ② Ti / Zr = 2-4, ③ Ceq <= 0.39, ④ Pcm <= 0.17, the microstructure type of the high-strength steel is a composite type of ferrite and pearlite, and the area ratio of ferrite is >= 85%, the area ratio of pearlite is <= 15%; the corrosion active inclusion density of the high-strength steel is <= 10 pieces / mm 2 ; the saturation current density of the high-strength steel at electrostatic potential E = -300 mV is <= 7.0 mA.

2. A method for producing a high-strength steel having excellent corrosion resistance to neutral water media according to claim 1, characterized by, The method comprises the following steps: 1) sequentially smelting, refining and vacuum treating the molten steel, and then continuously casting into a slab; 2) performing conventional heating and soaking on the slab; 3) continuously rolling the slab into a product steel plate, and controlling the finish rolling temperature to be 759-859℃, and then performing water cooling to 411-549℃ after rolling; 4) naturally cooling the steel plate to room temperature, and obtaining the product.

3. The preparation method according to claim 2, characterized in that, The smelting of step 1) specifically comprises the following steps: using a converter or an electric arc furnace to smelt molten iron, scrap steel, or molten iron and scrap steel together, adjusting the temperature and composition of the molten steel after steelmaking, adjusting the tapping temperature to be 1560-1680℃, and the free oxygen content in the molten steel to be 121-379ppm; after the molten steel enters a ladle, micro-sub-bubble stirring is performed for 4-11 minutes, then pre-deoxidation is performed in the ladle using Fe-Si alloy or Fe-Si-Mn alloy, the free oxygen content in the molten steel is adjusted to be 21-95ppm, micro-sub-bubble stirring is performed for 4-7 minutes, and then final deoxidation is performed using Fe-Zr-Ti alloy, so as to obtain molten steel satisfying the chemical composition; the Fe-Zr-Ti alloy is added to the molten steel in the form of block alloy or cored wire, the particle size of the Fe-Zr-Ti alloy is 10-20mm, and the addition amount of the Fe-Zr-Ti alloy is 0.41-3.5kg per ton of molten steel.

4. The production method according to claim 2 or 3, characterized by: The refining mode is LF refining followed by VD refining or RH refining, and the refined molten steel is continuously cast according to the conventional process.

5. Use of the high-strength steel having excellent corrosion resistance to neutral water media according to claim 1, characterized by: The steel is used for marine engineering, ship engineering, bridges, towers, rails, oil pipelines rich in mineral water, seawater sand pumping, river water sand pumping, cement mixers or garbage collection trucks.

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