Thin-gauge high-strength low-density weathering steel free of painting, and preparation method and application thereof

Abstract

The application provides a thin-gauge high-strength low-density weather-resistant steel and a preparation method and application thereof; the thin-gauge high-strength low-density weather-resistant steel comprises, in percentage by mass, 0.06-0.12% of carbon, 0.15-0.40% of silicon, 1.25-1.6% of manganese, ≤0.015% of sulfur, ≤0.018% of phosphorus, 0.025-0.035% of niobium, 0.10-0.13% of titanium, 0.5-1.0% of chromium, 4.0-4.5% of aluminum and ≤0.0060% of nitrogen; the rest is Fe and other inevitable impurity elements. The yield strength of the weather-resistant steel is greater than 690 MPa, the tensile strength is 770-940 MPa, the elongation is greater than 18%, and the density is close to or less than 7.4 g / cm 3 The corrosion loss of thickness in the marine atmospheric environment is only one third of that of the existing Corten-A, and the weather-resistant steel can be used without coating.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, specifically relating to a thin-gauge, high-strength, low-density, paint-free weathering steel, its preparation method, and its application. Background Technology

[0002] Corten-A steel is a type of Corten steel with excellent weather resistance. It belongs to the category of low-alloy, high-strength, atmospheric corrosion-resistant structural steels, and is also known as weathering steel. Compared to ordinary carbon steel, weathering steel exhibits superior corrosion resistance in the atmosphere. Currently, Corten-A steel is widely used in the welding and manufacturing of structural components for locomotives and rolling stock, ships, sculptures, environmental protection equipment, gardens and factories, landscaping projects, road and bridge lighthouses, harbor structures, boiler pipes, coal mining equipment, chemical and textile equipment, construction machinery, towers, and other applications.

[0003] Compared to ordinary steel, Corten-A steel is more corrosive; however, in marine environments, the corrosion of Corten-A steel will also be significantly aggravated over a long period of time, which means that the performance of Corten-A steel in marine environments needs to be further improved.

[0004] Therefore, it is necessary to provide a thin-gauge, high-strength, low-density, paint-free weathering steel, its preparation method, and its application, in order to solve or at least alleviate the technical defects of the aforementioned existing steel grades in terms of poor corrosion resistance in marine environments. Summary of the Invention

[0005] The main objective of this invention is to provide a thin-gauge, high-strength, low-density, paint-free weathering steel, its preparation method, and its application, aiming to solve the technical problem of poor corrosion resistance of the aforementioned existing steel grades in marine environments.

[0006] To achieve the above objectives, the present invention provides a thin-gauge, high-strength, low-density, paint-free weathering steel, comprising, by weight percentage: 0.06-0.12% carbon, 0.15-0.40% silicon, 1.25-1.6% manganese, ≤0.015% sulfur, ≤0.018% phosphorus, 0.025-0.035% niobium, 0.10-0.13% titanium, 0.5-1.0% chromium, 4.0-4.5% aluminum, and ≤0.0060% nitrogen; the remainder being Fe and other unavoidable impurity elements.

[0007] Furthermore, the thickness of the weathering steel is no more than 6 mm.

[0008] Furthermore, the microstructure of the weathering steel includes ferrite.

[0009] Furthermore, MC-type second-phase precipitates are precipitated between the ferrite matrix.

[0010] Furthermore, the second phase precipitates with a particle size in the range of 20-64 nm account for 20-25% of the total mass of the second phase precipitates.

[0011] Furthermore, the second phase precipitate comprises TiC and NbC.

[0012] The present invention also provides a method for preparing thin-gauge, high-strength, low-density, uncoated weathering steel as described above, comprising: smelting molten iron and casting it into a slab, hot rolling the slab into a steel coil, and subjecting the steel coil to recrystallization annealing and aging strengthening in sequence to obtain the weathering steel.

[0013] Furthermore, the holding temperature for the recrystallization annealing is 820±20℃, and the holding time is 24±2h.

[0014] Furthermore, the aging strengthening includes: cooling the steel coil after recrystallization annealing to 620±20℃ and holding it at 620±20℃ for 1-3 hours.

[0015] The present invention also provides an application of thin-gauge, high-strength, low-density, uncoated weathering steel as described above in marine engineering.

[0016] Compared with the prior art, the present invention has at least the following advantages:

[0017] The high-strength, low-density, uncoated weathering steel provided by this invention has a yield strength greater than 690 MPa, a tensile strength of 770-940 MPa, an elongation greater than 18%, and an impact energy greater than 60 J for KV2 type steel at -40℃. Its density is close to or less than 7.4 g / cm³. 3 Furthermore, the steel grade provided by this invention has a corrosion loss of only one-third that of the existing Corten A in a marine atmospheric environment, and can be used without coating in a marine environment.

[0018] The high-strength, low-density, paint-free weathering steel provided by this invention has a specific element compounding method; for example, its constituent elements do not contain precious metals such as Cu, Ni, and Mo alloys, but instead use more economical Al to replace Cu, Ni, Mo and other alloying elements, which significantly reduces manufacturing costs while ensuring the corrosion resistance of the steel; for another example, the addition of an appropriate amount of Ti can form a TiC precipitate strengthening phase of about 10-20 nm, which significantly increases the strength increment; the addition of a small amount of Nb can refine the grains, control the polygonal grain morphology, and ensure isotropic mechanical properties.

[0019] Furthermore, the present invention performs recrystallization annealing on the steel coil at 820±20℃, which ensures the equiaxed structure of the hot-rolled state; subsequently, the present invention performs aging strengthening on the steel coil at 620±20℃, which allows the MC phase to be fully precipitated, ensuring that the weathering steel has high strength mechanical properties and uniformity. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 This is a metallographic diagram of the steel coil obtained in step S2 of Embodiment 1 of the present invention. The coordinate scale in the diagram is 200 μm.

[0022] Figure 2 The image shows the metallographic structure of the steel obtained in Example 1 of this invention. The scale bar in the image is 200 μm.

[0023] Figure 3 This is a grain size distribution diagram of the MC phase of the steel obtained in Example 1 of the present invention;

[0024] Figure 4 The corrosion rate curves are for the steel grades obtained in each embodiment and comparative example of the present invention.

[0025] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0028] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0029] It should be noted that the smelting temperature and heating temperature in the embodiments of the present invention are only target values. In actual operation, the temperature will fluctuate to some extent. In Embodiment 1 of the present invention, the heating temperature of the slab is lower than the furnace exit temperature because the heating temperature is a target value and will fluctuate to some extent.

[0030] This invention provides a thin-gauge, high-strength, low-density, paint-free weathering steel, comprising, by mass percentage: 0.06-0.12% carbon, 0.15-0.40% silicon, 1.25-1.6% manganese, ≤0.015% sulfur, ≤0.018% phosphorus, 0.025-0.035% niobium, 0.10-0.13% titanium, 0.5-1.0% chromium, 4.0-4.5% aluminum, and ≤0.0060% nitrogen; the remainder being Fe and other unavoidable impurity elements.

[0031] In this invention, the thickness of the weathering steel may not exceed 6 mm; further, the thickness of the weathering steel may be 3-5 mm.

[0032] The metallographic structure of the weathering steel may include or be ferrite; MC-type second phase precipitates are precipitated between the matrix of the ferrite; the second phase precipitates may include or be TiC and NbC.

[0033] The particle size of the second phase precipitate can include multiple ranges such as 8-20 nm and 20-64 nm; among them, the second phase precipitate with a particle size of 20-64 nm accounts for the highest mass proportion of the total second phase precipitate, which is 20-25%.

[0034] As a supplementary explanation, in this invention, the mass content of oxygen and hydrogen elements is usually no more than 0.0015%, and the content of acid-soluble aluminum is usually 0.015-0.035%.

[0035] The design routes for each component in this invention include:

[0036] Carbon: In this invention, the carbon content is selected to be 0.06-0.12%. Carbon is an effective and economical element for improving the strength of steel. When the carbon content is higher than 0.12%, the strength of steel increases, but the elongation decreases, and the weldability and corrosion resistance decrease. Therefore, the carbon content is controlled at 0.06-0.12%.

[0037] Silicon: Silicon can be deoxidized during the smelting process, but if its content is too high, it will affect weldability and toughness. Its content should be controlled between 0.15-0.40%.

[0038] Manganese: Manganese is beneficial to the high-temperature toughness of steel, and can improve both strength and toughness. Its content should be controlled at 1.25-1.6%.

[0039] Sulfur: Sulfur easily forms MnS inclusions in steel. MnS inclusions are detrimental to impact toughness, corrosion resistance and weldability. Therefore, its content should be ≤0.015%.

[0040] Phosphorus: Excessive phosphorus can cause grain boundary segregation, increasing the brittleness of steel. A small amount of phosphorus can improve the weather resistance of steel. The phosphorus content should be controlled at ≤0.018%.

[0041] Niobium: Niobium is a carbide-forming element that can increase the recrystallization temperature of austenite, allowing austenite to be rolled at higher rolling temperatures. In addition, Nb strengthens the austenite grains by controlling precipitation during continuous cooling during rolling. The strain-induced precipitation of Nb carbonitrides can pin the austenite grains, refine the austenite grains, and improve the strength and isotropic properties. However, excessively high Nb content makes it difficult to control the yield strength ratio, while excessively low Nb content does not have a significant grain-refining effect. Therefore, it is preferable to control the niobium content to be 0.025-0.035%.

[0042] Titanium: During continuous casting solidification, titanium combines with nitrogen to form TiN, reducing the influence of nitrogen on boron. The presence of TiN can inhibit grain coarsening in the weld heat-affected zone. Maintaining a certain amount of Ti allows for the precipitation of nano-sized TiC second-phase particles during medium-temperature aging. These fine TiC particles exhibit significant precipitation strengthening and grain refinement strengthening effects, which are beneficial for improving the strength of the steel plate. However, excessive Ti content can lead to the formation of coarse, square TiN precipitates. Under stress, the stress will concentrate near the TiN particles, becoming a nucleation and growth source for microcracks, thus reducing the fatigue performance of the steel plate. Furthermore, the low solid solubility product of TiC makes it difficult for Ti to dissolve during the continuous casting heating process, rendering it ineffective. Therefore, to ensure sufficient carbonitride precipitation and achieve a yield strength of over 690 MPa, the Ti content in this invention is controlled within the range of 0.10-0.13%.

[0043] Chromium: A chromium content greater than 0.2% can improve corrosion resistance and enhance the uniformity of steel cooling. However, excessively high chromium content can easily cause performance fluctuations. A chromium content controlled between 0.5% and 1.0% can provide basic weather resistance for steel.

[0044] Aluminum: The density of metallic aluminum is 2.7 g / cm³. 3 Metallic solutions in steel readily combine with oxygen to form Al₂O₃. Adding a certain amount of aluminum can reduce the specific gravity of the steel, decrease the electrical conductivity of the steel matrix, slow down electrochemical reactions, and improve weather resistance. However, excessive aluminum increases the recrystallization driving force of the steel, leading to the formation of banded ferrite structures during hot rolling, making it difficult to achieve isotropic properties in the hot-rolled state. Therefore, the preferred aluminum content in the composition system and process of this invention is set to Al 4.0-4.5%.

[0045] It is important to understand that this invention solves the problems of corrosion performance and specific gravity in high-strength, low-density weather-resistant steel. This invention possesses the same strength as traditional high-strength steel, while having a density 6% lower than traditional high-strength weather-resistant steel plates. Its constituent elements do not contain precious metals such as Cu, Ni, and Mo alloys. It uses Al, which has a lower density and is more economical, to replace Cu, Ni, Mo, and other precious alloying elements, improving the steel's weather resistance and significantly reducing manufacturing costs. The addition of an appropriate amount of Ti forms a TiC nano-precipitate phase of approximately 10-20 nm, significantly increasing the strength increment. The addition of a small amount of Nb refines the grains, controls the polygonal grain morphology, and ensures isotropic mechanical properties.

[0046] In this invention, the yield strength R of weathering steel el Greater than 690MPa, tensile strength R m Its strength is 770-940 MPa, elongation A is greater than 18%, impact energy of KV2 type at -40℃ is greater than 60 J, and density is close to or less than 7.4 g / cm³. 3 The density can specifically range from 7.350 to 7.415 g / cm³. 3 In marine atmospheric environments, the corrosion loss is one-third that of the existing Corten-A, allowing for bare application. The corrosion loss rate on a single surface is less than 0.15 mm / a over 10 years, making it suitable for applications such as marine photovoltaic supports and marine engineering steel structures.

[0047] To obtain the aforementioned weathering steel, the present invention also provides a method for preparing thin-gauge, high-strength, low-density, uncoated weathering steel as described above, comprising: smelting molten iron and casting it into a slab, hot rolling the slab into a steel coil, and sequentially subjecting the steel coil to recrystallization annealing and aging strengthening to obtain the weathering steel.

[0048] The process of smelting molten iron and casting it into slabs may include: sequentially subjecting the molten iron to KR desulfurization (molten iron pretreatment), converter smelting, LF refining and RH vacuum treatment, then continuously casting it into slabs (thin slabs), and then stacking the slabs to cool to room temperature.

[0049] The process of hot rolling slabs into steel coils includes: heating the slabs in a furnace, then performing rough rolling and finish rolling in sequence (5 passes of rough rolling on a single stand, followed by 7 passes of finish rolling on a mill), then entering a laminar flow cooling system for microstructure control, and finally coiling the steel coils by strip.

[0050] The specific steps can be carried out as follows:

[0051] KR desulfurization: The sulfur content must be reduced to below 0.010% before molten iron can be fed into the furnace.

[0052] Converter smelting: After converter smelting, the steel ladle is blown with argon, and the final temperature of the argon station is controlled to be greater than 1537℃.

[0053] LF refining: The inlet temperature is greater than 1522℃, the outlet temperature is 1585-1605℃, the refining time is 40-45min, the LF refining and composition fine-tuning are carried out to the target composition, and when the molten steel temperature is greater than 1538℃, it is transferred to RH for vacuum treatment.

[0054] RH vacuum treatment: vacuum degree requirement ≤133MPa, RH cycle time 22-30min; specifically, in the implementation of this invention, the vacuum degree requirement is less than 130MPa, and the RH cycle time is 22-30min.

[0055] Continuous casting: The continuous casting speed is controlled at 1.2-1.7 m / min, and the continuous casting adopts a light reduction mode; specifically, in the implementation of this invention, the continuous casting speed is controlled at 1.4-1.6 m / min.

[0056] Slab loading and heating: The slab heating temperature is 1170-1200℃, and the heating time is 150-250min, preferably 180-240min; wherein, the solution treatment time is 20-30min, specifically 20min.

[0057] Roughing, finishing, laminar flow cooling, and strip coiling: The initial rolling temperature of roughing is 1150-1180℃, the final rolling temperature of roughing is 1120-1160℃, the initial rolling temperature of finishing is 980-1060℃, the final rolling temperature is 780-850℃, the hot-rolled thickness is not greater than or less than 6mm, laminar flow cooling is performed after finishing, the cooling rate is 20-30℃ / s, and the strip is coiled after final cooling to 750-770℃.

[0058] Recrystallization annealing and aging strengthening (heat treatment process): The whole coil of steel is fed into the bell-type annealing furnace for recrystallization annealing. The recrystallization annealing can be carried out under the protection of hydrogen (protective gas) atmosphere. The holding temperature of recrystallization annealing is 820±20℃ and the holding time is 24±2h. After that, the steel coil is cooled with the furnace to 620±20℃ and held for 1-3h (aging strengthening). Then, it is air-cooled with the bell-type furnace to 340±20℃ and taken out of the furnace.

[0059] The design basis of the above preparation method includes:

[0060] Hot rolling is based on metal deformation and phase transformation processes. Under specified deformation and temperature conditions, it completes hardening measures such as solid solution strengthening, precipitation strengthening, dislocation strengthening, and grain refinement strengthening to obtain steel plates with excellent comprehensive properties. It reduces the use of precious alloys, lowers manufacturing costs, and makes full use of the rolling and heat treatment control capabilities of continuous rolling mills. It utilizes high-temperature austenite deformation recrystallization, low-temperature non-recrystallized austenite deformation, and high-temperature annealing recrystallization and medium-temperature aging strengthening processes after hot rolling.

[0061] In this invention, the heat treatment process for steel employs high-temperature recrystallization annealing combined with medium-temperature aging precipitation strengthening (aging strengthening). Specifically, annealing is performed at 820±20℃ to ensure complete recrystallization of the fibrous structure of the hot-rolled plate, guaranteeing isotropic mechanical properties of the matrix. Aging treatment is then performed at 620±20℃ to precipitate a large amount of MC-type TiC and NbC second-phase precipitates between the ferrite matrix, thereby improving the strength properties of the material.

[0062] Because the weathering steel obtained in this invention has excellent comprehensive properties and strong corrosion resistance, this invention also provides an application of the weathering steel as described above in marine engineering.

[0063] The following are specific examples of the present invention:

[0064] Example 1

[0065] The specific implementation process of this embodiment includes the following steps:

[0066] S1, after the molten iron is desulfurized by KR (the sulfur content is reduced to below 0.010%), it is smelted in a 210-ton converter, and then successively undergoes ladle argon blowing, LF furnace refining, RH vacuum treatment, and then continuously cast into 230mm slabs. The slabs are stacked and cooled for 48 hours. The final temperature of the argon station for ladle argon blowing is controlled at 1570℃.

[0067] During the LF furnace refining process, the inlet temperature is 1565℃, the outlet temperature is 1600℃, the refining time is 40 minutes, the LF refining and composition fine-tuning are carried out to the target composition, and the molten steel is transferred to RH for vacuum treatment when the temperature reaches 1550℃.

[0068] S2 involves heating the slab at 1180℃ for 4 hours and then removing it from the furnace. After removing it from the furnace, it undergoes five roughing passes, followed by finishing rolling on a 7-stand 2250 continuous rolling mill. After finishing rolling, it is cooled by laminar flow and the steel strip is coiled to obtain a steel coil of the corresponding thickness.

[0069] S3, the steel coil is subjected to recrystallization annealing and age hardening in sequence; specifically, the whole coil of steel is fed into a bell-type annealing furnace and heated to the recrystallization annealing temperature, and the annealing is carried out under the protection of a hydrogen atmosphere; then the steel coil is cooled to the age hardening temperature by cooling method one; and after age hardening, the steel coil is cooled by cooling method two to obtain weathering steel.

[0070] 1. In this embodiment, the mass percentage content of the chemical composition of the weathering steel is as follows:

[0071] element C Si Mn S P content 0.07 0.28 1.58 ≤0.005 ≤0.015 element Nb Ti Cr Al N content 0.028 0.126 0.68 4.15 0.0050

[0072] 2. In this embodiment, the steel thickness, as well as the process parameters for rolling, laminar flow cooling, and coiling, are as follows:

[0073]

[0074]

[0075] 3. In this embodiment, the process parameters for recrystallization and aging strengthening are as follows:

[0076]

[0077] 4. In this embodiment, the thickness, mechanical properties, and density of the obtained weathering steel are as follows:

[0078]

[0079] 5. In this embodiment, the metallographic structure (hot-rolled state) of the steel coil is as follows: Figure 1 As shown, the metallographic structure of the obtained weathering steel is as follows: Figure 2 As shown.

[0080] 6. In this embodiment, the MC phase grain size distribution of the obtained weathering steel is as follows: Figure 3 As shown; among them, the proportion of the 20-64nm particle size range in the total mass of the MC phase is between 20-25%; the proportion of the 8-20nm particle size range in the total mass of the MC phase is between 10-15%.

[0081] Example 2

[0082] The specific implementation process of this embodiment includes the following steps:

[0083] S1, after the molten iron is desulfurized by KR (the sulfur content is reduced to below 0.010%), it is smelted in a 210-ton converter, and then successively undergoes ladle argon blowing, LF furnace refining, RH vacuum treatment, and then continuously cast into 230mm slabs. The slabs are stacked and cooled for 48 hours. The final temperature of the argon station for ladle argon blowing is controlled at 1570℃.

[0084] During the LF furnace refining process, the inlet temperature is 1565℃, the outlet temperature is 1600℃, the refining time is 40 minutes, the LF refining and composition fine-tuning are carried out to the target composition, and the molten steel is transferred to RH for vacuum treatment when the temperature reaches 1550℃.

[0085] S2 involves reheating the slab at 1180℃ for 4 hours before removing it from the furnace. After removal, the slab undergoes five roughing passes, followed by finishing rolling on a 7-stand 2250 continuous rolling mill. After finishing, the slab is cooled in laminar flow and the steel strip is coiled to obtain a steel coil of the corresponding thickness.

[0086] S3, the steel coil is subjected to recrystallization annealing and age hardening in sequence; specifically, the whole coil of steel is fed into a bell-type annealing furnace and heated to the recrystallization annealing temperature, and the annealing is carried out under the protection of a hydrogen atmosphere; then the steel coil is cooled to the age hardening temperature by cooling method one; and after age hardening, the steel coil is cooled by cooling method two to obtain weathering steel.

[0087] 1. In this embodiment, the mass percentage content of the chemical composition of the weathering steel is as follows:

[0088] element C Si Mn S P content 0.063 0.33 1.52 ≤0.005 ≤0.012 element Nb Ti Cr Al N content 0.032 0.128 0.72 4.28 0.0053

[0089] 2. In this embodiment, the steel thickness, as well as the process parameters for rolling, laminar flow cooling, and coiling, are as follows:

[0090]

[0091] 3. In this embodiment, the process parameters for recrystallization and aging strengthening are as follows:

[0092]

[0093] 4. In this embodiment, the thickness, mechanical properties, and density of the obtained weathering steel are as follows:

[0094]

[0095] Comparative Example 1

[0096] Corten-A steel was used as a comparison steel.

[0097] Analysis example 1

[0098] The steel grades obtained in each embodiment and comparative example were subjected to marine atmospheric corrosion tests at the Wanning Marine Atmospheric Test Station in accordance with GB / T19292.1-2018 "Corrosion of metals and alloys - Atmospheric Corrosion - Part 1".

[0099] The corrosion rate curves of the steel grades obtained in each embodiment and comparative example at the Wanning Marine Atmospheric Test Station are shown in the figure. Figure 4 As shown. Those skilled in the art will understand that, Figure 4 The unit of the vertical axis is mm / a (millimeters per year), which represents the average annual loss thickness within the corresponding time period; Figure 4 The vertical axis is normalized to the parameters of the month, consistent with the horizontal axis for the month; Figure 4 The curves in the table represent: the number of months before 24 months corresponds to the measured values ​​of corrosion data, and the time period from 24 to 120 months is based on the relationship between rust layer thickness and the curve C = At. n The thickness loss curve obtained by extrapolation calculation.

[0100] The results of the marine atmospheric corrosion test are as follows:

[0101] 1. The corrosion loss rate of the weathering steels obtained in Examples 1 and 2 is only about one-third of that of the comparative steel Corten-A, and the corrosion resistance is excellent.

[0102] 2. The 10-year single-sided corrosion thickness loss rate of the weathering steel obtained in Examples 1 and 2 is less than 0.15 mm / a (mm / year), which is only close to 0.15 mm / a; where the 10-year single-sided corrosion thickness loss rate refers to the average annual thickness loss of the exposed surface after 10 years of service.

[0103] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A thin-gauge, high-strength, low-density, paint-free weathering steel, characterized in that, By mass percentage, it includes: carbon 0.06-0.12%, silicon 0.15-0.40%, manganese 1.25-1.6%, sulfur ≤0.015%, phosphorus ≤0.018%, niobium 0.025-0.035%, titanium 0.10-0.13%, chromium 0.5-1.0%, aluminum 4.0-4.5%, nitrogen ≤0.0060%; the remainder is Fe and other unavoidable impurity elements. The microstructure of the weathering steel includes ferrite, and MC-type second phase precipitates are precipitated between the matrix of the ferrite. The second phase precipitates with a particle size in the range of 20-64 nm account for 20-25% of the total mass of the second phase precipitates. The second phase precipitates include TiC and NbC.

2. The weathering steel according to claim 1, characterized in that, The thickness of the weathering steel is no more than 6 mm.

3. A method for preparing thin-gauge, high-strength, low-density, paint-free weathering steel as described in claim 1 or 2, characterized in that, include: The molten iron is smelted and cast into slabs, the slabs are hot-rolled into steel coils, and the steel coils are successively subjected to recrystallization annealing and aging strengthening to obtain the weathering steel.

4. The preparation method according to claim 3, characterized in that, The holding temperature for recrystallization annealing is 820±20℃, and the holding time is 24±2h.

5. The preparation method according to claim 4, characterized in that, The aging strengthening process includes: cooling the steel coil after recrystallization annealing to 620±20℃ and holding it at 620±20℃ for 1-3 hours.

6. The application of thin-gauge, high-strength, low-density, uncoated weathering steel as described in claim 1 or 2 in marine engineering.

Images