Low-cost thick-gauge 460mpa nickel-free weathering steel and method of manufacturing the same

Abstract

The application discloses a low-cost thick-gauge 460MPa nickel-free weather-resistant steel and a manufacturing method thereof. The chemical components of the steel are as follows: C: 0.04-0.07%, Si: 0.55-0.75%, Mn: 0.43-0.63%, P: 0.010-0.014%, S: less than or equal to 0.003%, Cu: 0.3-0.5%, Cr: 0.3-0.5%, Ti: 0.020-0.030%, V: 0.020-0.030%, B: 0.0007-0.0013%, Al: 0.020-0.030%, Zr: 0.0009-0.0015%, and the balance of Fe and other inevitable impurities; and the chemical components need to meet the following conditions simultaneously: a welding crack sensitivity index Pcm is less than or equal to 0.17%; a carbon equivalent CEV is less than or equal to 0.32%; a weather resistance index I is greater than or equal to 6.0; Cu / P+5*Si is greater than or equal to 25; and 0.06% is less than or equal to (Al+Ti+V) and is less than or equal to 0.085%. The obtained weather-resistant steel has the characteristics of high strength and weather resistance, good surface quality, low yield ratio and easy welding without adding Ni, the thickness of the steel can reach 60 mm at most, the use range of the high-strength weather-resistant steel is widened, and the weather-resistant steel can be widely used for manufacturing corrosion-resistant structural parts.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of weathering steel, in particular to a low-cost thick-gauge 460MPa nickel-free weathering steel and a manufacturing method thereof. BACKGROUND

[0002] Weathering steel, i.e. low-alloy atmospheric corrosion-resistant steel, is a low-carbon steel with a small amount of alloying elements Cu, Ni, Cr, P, Mn, Sn, etc. added to improve its atmospheric corrosion resistance. In weathering steel products, 0.2-0.5% of copper must generally be added. However, copper elements are prone to enrichment at the interface between the substrate surface layer and the oxide layer after high-temperature oxidation of the steel, forming "copper brittle" crack defects. Therefore, a high-melting-point copper-nickel compound is generally formed by adding nickel elements to prevent the formation of copper-induced thermal cracks. The amount of nickel added is related to the content of copper, and the nickel-copper ratio is generally required to be close to 1:1. However, the high cost of nickel elements limits the widespread use of weathering steel in economically demanding application fields.

[0003] Chinese patent 202311320781.8 discloses "a 355MPa low-cost weathering steel and a preparation method thereof", the main chemical composition of the steel plate is as follows: C: 0.06-0.08%, Si: 0.3-0.5%, Mn: 0.45-0.55%, P≤0.018%, Cu: 0.2-0.3%, Cr: 0.45-0.50%, Ni: 0.06-0.08%, La: 30-60ppm, and the rest is Fe and unavoidable impurities. On the one hand, this patent adds Ni elements and lanthanum La elements in the composition, greatly increasing the production cost of the steel plate; on the other hand, the insufficient Cu content results in a weathering index I of only 3.0-4.0, insufficient corrosion resistance, and a strength level of only 355MPa. Finally, the thickness specification of the steel plate is relatively narrow, covering only 1.8-3.0mm, which cannot meet the use requirements of domestic large-scale projects such as bridges and railways.

[0004] Chinese patent 202110856859.2 discloses "a 340MPa low-cost weathering steel for cold-rolled automobiles and a manufacturing method thereof", the main chemical composition of the steel plate is as follows: C≤0.10%, Si: 0.10-0.45%, Mn: 0.30-0.60%, P: 0.06-0.13%, Cu: 0.2-0.4%, Ni: 0.1-0.2%, and the balance is Fe and unavoidable impurities. To avoid copper brittleness, this patent also adds Ni elements in the composition, which is relatively high in cost and insufficient in strength.

[0005] Chinese patent 202010769262.X discloses "a 400MPa grade high-silicon weathering steel and its preparation method and application", the main chemical composition of the steel plate is: C≤0.12%, Si: 1.20-2.00%, Mn≤1.50%, P: 0.005-0.030%, Cr: 0.20-0.80%, Ni: 0.10-0.40%, Cu: 0.20-0.60%, the balance is Fe and inevitable impurities. The patent weathering index I reaches 6.0 or more, but the addition of Cr, Ni and other precious metal elements increases the cost, and the high Si content affects the welding performance.

[0006] Chinese patent 202010095562.4 discloses "a method for producing economic weathering steel by using RE-P reinforcement and preparation process", the main chemical composition of the steel plate is: C: 0.01-0.08%, Si: 0.10-0.30%, Mn: 1.30-1.70%, P: 0.06-0.10%, Cu: 0.08-0.20%, Al: 0.015-0.06%, Re: 0.02-0.06%, the balance is Fe and inevitable impurities. Because the amount of Cu element added is very small, the probability of copper brittleness is low, so Ni element is not added, but rare earth Re element is added to refine the grain. Although the alloy cost is not high, the weathering index I is only 1.0-3.0, which reduces the weather resistance.

[0007] With the increasing demand for resource conservation and cost control worldwide, the development of low-cost, high-performance weathering steel has become a research hotspot in the field of materials science. Especially for thick gauge steel, how to achieve 460MPa strength level of high strength and good welding performance, surface quality, while maintaining excellent atmospheric corrosion resistance without using nickel and other expensive alloy elements, is the key challenge of current research. SUMMARY

[0008] The purpose of the present application is to provide a low-cost thick gauge 460MPa nickel-free weathering steel and its manufacturing method. The obtained weathering steel has high strength and weather resistance, good surface quality, low yield ratio and easy welding characteristics without adding Ni, and the thickest steel can reach 60mm, which expands the use range of high-strength weathering steel and can be widely used in the production of corrosion-resistant structural parts. The yield strength of the weathering steel is ≥460MPa, the tensile strength is ≥550MPa, the impact energy at -20℃ is 210-380J, the yield ratio is ≤0.82, and the steel plate surface is free of "copper brittle" cracks.

[0009] In order to achieve the above purpose, the technical scheme provided by the present application is:

[0010] A low-cost thick-gauge 460MPa nickel-free weather-resistant steel, which has the following chemical components by weight percentage: C: 0.04-0.07%, Si: 0.55-0.75%, Mn: 0.43-0.63%, P: 0.010-0.014%, S: ≤0.003%, Cu: 0.3-0.5%, Cr: 0.3-0.5%, Ti: 0.020-0.030%, V: 0.020-0.030%, B: 0.0007-0.0013%, Al: 0.020-0.030%, Zr: 0.0009-0.0015%, and the balance of Fe and other inevitable impurities; and the chemical components need to meet the following conditions simultaneously:

[0011] welding crack sensitivity index Pcm≤0.17%;

[0012] carbon equivalent CEV≤0.32%;

[0013] weathering index I≥6.0;

[0014] Cu / P+5*Si≥25;

[0015] 0.06%≤(Al+Ti+V)≤0.085%.

[0016] wherein, Pcm= %C+ %Si / 30+ %Mn / 20+ %Cu / 20+ %Ni / 60+ %Cr / 20+ %Mo / 15+ %V / 10+5% B;

[0017] CEV= %C+ %Mn / 6+ (%Cr+ %Mo+ %V) / 5+ (%Ni+ %Cu) / 15;

[0018] I=26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.10(%Ni)(%P)-33.39(%Cu) 2 ;

[0019] In the above formula, only the numerical value before the percentage symbol of the corresponding element content is substituted when calculating, for example, the C content is 0.04%, only 0.04 is substituted when calculating.

[0020] The microstructure of the weather-resistant steel is equiaxed ferrite+pearlite+ a small amount of granular bainite; wherein the volume fraction of equiaxed ferrite is 50-70%, the volume fraction of granular bainite is ≤5%, the rest is pearlite, the average grain size is 7-10μm, the grain size is ≥8, and the inclusion level is ≤0.4 level.

[0021] The number density of heterogeneous nucleation particles in the microstructure of the weather-resistant steel is 5.26×10 4~6.58 x 10 4 / mm 3 The number of ferrite heterogeneous nucleation accounts for ≥60%, and the heterogeneous nucleation particles are Ti(C,N) and V(C,N) complex precipitation particles.

[0022] The yield strength of the weathering steel is ≥460MPa, the tensile strength is ≥550MPa, the impact energy at-20℃ is 210-380J, the yield strength ratio is ≤0.82, and the steel plate surface is free of "copper brittle" cracks.

[0023] The steel thickness is 20-60mm.

[0024] In the component design of the weathering steel, the content of each component is as follows:

[0025] C: In the steel, C can stabilize austenite and improve hardenability to improve the strength of the steel plate. However, the increase of C content will increase the brittle phase and carbide, reduce the corrosion resistance, greatly increase the carbon equivalent CEV and the welding crack sensitivity index Pcm, thereby seriously affecting the toughness and weldability of the steel plate, therefore, the C content in the application is controlled to be 0.04-0.07%.

[0026] Si: In the steel, Si can play a similar role as P, and other alloy elements (such as Cu, Cr, P, Ni) can improve the resistivity and corrosion resistance index I value of the steel, enhance the corrosion resistance of the steel under natural conditions, and inhibit the generation of hot cracks in the Cu-containing steel. Therefore, the Si content in the application is controlled to be 0.55-0.75%.

[0027] Mn: In the steel, Mn can improve the strength and hardenability of the steel, and play a solid solution strengthening role, but too high Mn content will lead to serious segregation of the steel and increase the cost, and MnS inclusions are easy to form battery reaction and separate from the matrix to form cavities, thereby reducing the toughness and corrosion resistance of the steel plate. Therefore, the Mn content in the application is controlled to be 0.43-0.63%.

[0028] Cu: In the steel, Cu is the most important corrosion-resistant element in the steel, which can promote the density and stability of the inner rust layer, thereby improving the atmospheric corrosion resistance, but too high content is easy to cause "copper brittle" crack defects. Cu is a valuable alloying element, and the increase of the content will significantly increase the cost of the steel. As can be seen from the I value expression, when the Cu content is 0.39, I has a maximum value, therefore, the Cu content in the application is controlled to be 0.3-0.5%.

[0029] P: In the steel of the present application, P has a strong solid solution strengthening effect, and can greatly improve the corrosion resistance of the steel in cooperation with Cu. Too high P can cause composition segregation to produce hot cracks and worsen the welding performance, while too low P content can increase the steelmaking cost. Therefore, the P content is controlled to be 0.010-0.014% in the present application.

[0030] Cu / P+5*Si≥25: In the steel of the present application, the higher the contents of Cu and Si, the better the weather resistance, but limited by the cost and other mechanical properties, it is necessary to find the minimum addition amount. In addition, P is the most effective element in alloying elements for improving the atmospheric corrosion resistance, which helps to form a uniform rust layer protective film on the surface of the steel, but the presence of P is easy to cause internal and external cracks of the steel, and also worsen the toughness of the steel, especially reduce the low temperature impact toughness of the steel. Controlling Cu / P+5*Si≥25 in the present application aims to ensure that the ratio of copper and phosphorus in the steel is moderate, and the content of silicon is high enough to form an effective protective film. The ratio of copper and phosphorus ensures that copper can form a stable compound with phosphorus, and the content of silicon directly affects the formation and stability of the protective film.

[0031] Cr: In the steel of the present application, Cr is the main corrosion-resistant element in the steel, and increasing the content of Cr can improve the strength and hardenability of the steel, and there is no significant composition segregation in the steel, and too high content has adverse effects on the welding performance. Therefore, the Cr content is controlled to be 0.3-0.5% in the present application.

[0032] Micro Ti-B treatment: In the steel of the present application, B can greatly improve the critical cooling rate of the steel martensite or bainite to improve the hardenability of the steel, but B content exceeding 0.0013% will form carbides at the grain boundary to affect the toughness, therefore, the B content is controlled to be 0.0007-0.0013% in the present application. At the same time, in order to ensure that B element in the steel remains sufficient acid-soluble B form, 0.02-0.03% of Ti is added to fix N in the steel to prevent the formation of BN to ensure effective B content, so that the steel can also guarantee good mechanical properties in the thickness specification of 60 mm. It can also precipitate Ti(C, N) during rolling to refine the grains and improve the strength and toughness of the steel. Therefore, the Ti content is controlled to be 0.02-0.03% in the present application.

[0033] V-Ti treatment: In the steel of the present application, V is used in combination with Ti, which mainly plays a role in refining the grains. In the finishing process, through deformation-induced precipitation of heterogeneous nucleation particles such as Ti(C, N) and V(C, N) complex precipitated particles, the austenite grains are refined, and the precipitated carbonitride also plays a role in precipitation strengthening, so that the room temperature structure is still fine equiaxed grains in the untempered state, thus achieving the effect of La, Re and other elements commonly used in weathering steels; therefore, the V content is controlled to be 0.020-0.030% in the present application.

[0034] Al: In the steel of the present application, the addition of Al can effectively prevent the formation of carbides in the steel, is beneficial to the solid solution of carbon in austenite, improves the stability of austenite during cooling, and is greatly beneficial to the toughness of the steel plate. However, if the aluminum content in the steel is too high, it will lead to the increase of the difficulty of smelting and pouring of the steel, the increase of the manufacturing cost, and the formation of excessive oxides to deteriorate the quality of the steel plate. Therefore, the Al content is controlled at 0.020-0.030%.

[0035] At the same time, the present application controls 0.06%≤(Al+Ti+V)≤0.085%, the number density of Ti(C, N) and V(C, N) heterogeneous nucleation particles formed in the structure is 5.26×10 4 -6.58×10 4 / mm 3 , the proportion of ferrite heterogeneous nucleation is ≥60%, which fully plays the role of improving corrosion resistance, and effectively improves the weather resistance of the steel plate. Too high content may lead to increased cost and adverse effects on other properties (such as weldability), and too low content has no obvious effect on improving corrosion resistance.

[0036] Zr: In the steel of the present application, Zr can replace expensive La and RE to purify the molten steel, reduce hard oxide inclusions, refine grains and uniformize the structure, enhance the polarization resistance of the steel plate, and enrich corrosion-resistant elements (Cu, Cr, etc.) as oxides in the rust layer, forming a shallow zirconium oxide passivation film on the surface of the steel plate, significantly improving the corrosion resistance of the steel, especially in a hydrogen sulfide atmosphere. In addition, Zr is a strong carbide-forming element, which greatly hinders grain growth, ensuring the strength and toughness of thick steel plates. The addition of Zr will move the CCT curve to the right, enhance the stability of supercooled austenite, and enable the formation of fine ferrite and pearlite complex phase structure after the stop-cooling temperature at 440-480℃ is tempered, thereby being beneficial to the reduction of yield strength ratio. Therefore, the Zr content is controlled at 0.0009-0.0015%.

[0037] The application adopts lower C and Si content in component design, improves weather resistance by adding Cu and Zr, adjusts suitable Cu / P and Si ratio (Cu / P+5*Si≥25), and ensures that the weathering steel has better mechanical properties and weather resistance. A small amount of Zr is added to replace expensive La and RE to purify molten steel, reduce hard oxide inclusions, refine grain uniform structure, enhance the polarization impedance of steel plate, and enrich corrosion-resistant elements (Cu, Cr, etc.) as oxides in the rust layer to form a shallow zirconium oxide passivation film on the surface of the steel plate, which significantly improves the corrosion resistance of the steel, especially in a hydrogen sulfide atmosphere. By adding V and Ti at a relatively low cost and controlling 0.06%≤(Al+Ti+V)≤0.085%, the number density of Ti(C, N) and V(C, N) heterogeneous nucleation particles formed in the structure is 5.26×10 4 ~6.58×10 4 / mm 3 , and the proportion of ferrite heterogeneous nucleation is ≥60%, which fully plays the role of improving corrosion resistance and effectively improves the weather resistance of the steel plate.

[0038] The manufacturing method of the low-cost thick-specification 460MPa nickel-free weathering steel according to the application comprises the following steps:

[0039] 1) Smelting and refining

[0040] Smelting, refining and casting into a blank according to the above components;

[0041] 2) Slab heating

[0042] Heating temperature: 1060-1080℃, holding time: 1-2h;

[0043] 3) Rolling

[0044] Coarse rolling opening temperature: 900-1000℃, single pass rolling reduction rate in the coarse rolling stage≥15%;

[0045] Fine rolling opening temperature: 870-890℃, single pass rolling reduction rate in the fine rolling stage≥20%, finish rolling temperature: 840-860℃;

[0046] 4) Cooling

[0047] Opening cooling temperature: 790-830℃, stopping cooling temperature: 440-480℃, cooling speed≥40℃ / s.

[0048] Preferably, in step 4), the cooling adopts water cooling.

[0049] Further, in step 4), the steel plate is air-cooled to room temperature after stopping cooling.

[0050] In the manufacturing method described in the application:

[0051] The slab heating temperature is controlled at 1060-1080 DEG C, which is lower than the melting point of Cu (1083 DEG C). When the Cu element (>=0.2%) in the steel and the temperature is above 1083 DEG C, the CuO+Fe is converted into FeO+Cu due to the surface selective oxidation, the surface Fe content is reduced and the Cu content is increased to form a Cu-rich phase, until the Cu content exceeds the solubility of Cu in Fe, at this time, the Cu-rich phase in the steel is in a molten state and starts to melt, and when the rolling deformation process reaches a certain degree, the surface scale-like cracking occurs, resulting in "copper brittle" crack defects. The present application finds that the heating temperature is controlled below the melting point of copper, so that the dissolution of copper can be avoided, the Cu on the surface of the slab will not be oxidized and converted, and the generation of copper brittleness can be avoided.

[0052] The rolling is divided into rough rolling and finish rolling, the rough rolling opening rolling temperature is 900-1000 DEG C, the single pass rolling reduction rate in the rough rolling stage is >=15%, so that the original austenite grains are fully broken and refined; the finish rolling opening rolling temperature is 870-890 DEG C, the single pass reduction rate in the finish rolling stage is >=20%, large reduction rolling is adopted, the austenite grains are elongated along the rolling direction, and a large amount of deformation bands are introduced into the grains, the grain boundary area is increased, the dislocation density nucleation points in the austenite are increased, the dislocation provides a fast channel for the diffusion of small atoms such as carbon and nitrogen, the carbon and nitrogen atoms are easily aggregated in the dislocation pile-up, and Ti(C, N) and V(C, N) are induced to deform and precipitate in the dislocation pile-up, the dispersed and fine metal carbonitride can more effectively pin the dislocation, further hinder the growth of the grains, ensure that the average grain size of the original austenite in the microstructure is 7-10 mu m, the grain size is >=8, increase the corrosion resistance, produce deformation strengthening, fine-grain strengthening and precipitation strengthening. The finish rolling temperature is controlled at 840-860 DEG C, and the strict control of the finish rolling temperature is beneficial to the fine deformation grains which do not have time to recover and recrystallize, increases the deformation resistance to produce deformation strengthening, so as to improve the strength and toughness of the steel plate at the same time.

[0053] In the cooling process, the opening cooling temperature is controlled at 790-830 DEG C, the cooling speed is greater than the conventional steel plate cooling speed, the supercooling degree of the steel plate during cooling is increased, the cooling speed is controlled at >=40 DEG C / s, and large water volume water cooling is adopted, which is beneficial to increase the nucleation rate and refine the grains, so that the rolling deformation grains are retained in a broken state to room temperature.

[0054] After air cooling at the stop cooling temperature of 440-480℃, the steel plate will be reheated to the pearlite transformation zone, which on the one hand releases the residual stress of the steel plate to achieve the effect of self-tempering, and on the other hand, 440-480℃ is the best precipitation temperature of heterogeneous nucleation particles such as Ti(C,N) and V(C,N) after the reheating of the steel plate, which is beneficial to increase the nucleation rate and prevent the growth of the grains, thereby improving the strength and toughness of the steel plate. Finally, a fine equiaxed ferrite + pearlite + a small amount of granular bainite multiphase structure is obtained, which ensures the strength and toughness while obtaining a lower yield ratio.

[0055] Compared with the prior art, the beneficial effects of the present application are:

[0056] 1、The present application adopts lower C and low Si content in the component design, controls Cu / P+5*Si≥25 through Cu, Zr, V and Ti elements and adjusts the appropriate Cu / P and Si ratio, ensures the mechanical properties and weather resistance of the steel. In addition, combined with the content control of 0.06%≤(Al+Ti+V)≤0.085%, the number density of Ti(C,N) and V(C,N) heterogeneous nucleation particles formed in the structure is 5.26×10 4 ~6.58×10 4 / mm 3 , which fully plays the role of improving corrosion resistance and effectively improves the weather resistance of the steel, ensuring that the weather resistance index I of the steel of the present application is ≥6.0. In the case of low Si content and without adding Ni, Nb and a small amount of Cr, etc. Precious metal elements, the preparation of a steel with high strength, high weather resistance and excellent welding performance is realized.

[0057] 2、On the basis of the component design, the heating temperature is controlled in the lower range of 1060-1080℃, which avoids the surface scale cracking in the subsequent rolling deformation process caused by the oxidation dissolution of the Cu content added in the composition under high temperature oxidation, causing "copper brittle" crack defects. The traditional method to solve the "copper brittle" crack defects in the conventional weathering steel is to add nickel, which solves the surface copper brittle problem caused by the enrichment of Cu element by generating copper-nickel compounds. In the present application, the steel can obtain high weather resistance and good surface quality without adding Ni.

[0058] 3. In the rolling process, this invention employs single-pass high-reduction rolling to increase the dislocation density and nucleation points in austenite. This induces V(C,N) and Ti(C,N) deformation precipitation at dislocation entanglement sites, further hindering grain growth. The average grain size in the microstructure is 7-10 μm, with a grain size ≥8, resulting in deformation strengthening, grain refinement strengthening, and precipitation strengthening. Combined with subsequent rapid cooling, controlling the cooling rate to ≥40℃ / s, and controlling the final rolling temperature and cooling temperature, the rolled deformed grains are retained in a fragmented state at room temperature, fully utilizing the effects of V and Ti to improve the steel's strength. This achieves high strength and weather resistance in a composition system that does not require the addition of precious alloying elements such as La, Re, and Nb. Furthermore, since this invention does not add Nb, it avoids the problem of Nb carbides being unable to dissolve at lower heating temperatures.

[0059] 4. To obtain thick-gauge weathering steel, micro-Ti-B treatment is used in the composition, and the single-pass high reduction and final cooling rate are controlled in the process. This allows the grains to be fully broken down and retained in solid solution, thereby refining the grains in the core of the steel plate. While ensuring the mechanical properties of the material, thick-gauge steel can be produced, with a maximum plate thickness of 60mm. In contrast, the existing technology can only produce weathering steel with a strength level of 460MPa at a maximum thickness of 8mm, which cannot meet the needs of large-scale domestic projects such as bridges and railways. Attached Figure Description

[0060] Figure 1 This is a photograph of the microstructure of the steel plate in Embodiment 1 of the present invention. Detailed Implementation

[0061] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0062] The components of the embodiments and comparative examples of the present invention are shown in Tables 1 and 2, with the balance containing Fe and other unavoidable impurities.

[0063] The process parameters of the embodiments and comparative examples of the present invention are shown in Table 3, and the steel properties of the embodiments and comparative examples of the present invention are shown in Table 4.

[0064] Figure 1 The image shows a microstructure of the steel plate in Example 1 of this invention. As can be seen from the image, the microstructure of the weathering steel obtained by this invention is equiaxed ferrite + pearlite + a small amount of granular bainite; wherein the volume percentage of equiaxed ferrite is 50-70%, the volume percentage of granular bainite is ≤5%, and the remainder is pearlite, with an average grain size of 7-10 μm, a grain size ≥8, and an inclusion grade ≤0.4.

[0065] The steel plate of the embodiment of the present application is tested according to the standard of TB / T-1993 "Railway Weathering Steel Periodic Immersion Corrosion Test Method", and the 3-week immersion corrosion rate of the embodiment and the comparative example is obtained in a 0.01 mol / L sodium bisulfite solution. The corrosion resistance test results are shown in Table 5. The comparative example is a common weathering steel Q460NH purchased, the specific component ratio is shown in Table 1, and the purchased material processing and performance all meet the national standard "GB / T4171 Weathering Structural Steel". The corrosion rates of the embodiments 1-8 are all lower than that of the comparative example, and since the embodiments do not add Ni element, the production cost is greatly reduced.

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[0070]

[0071]

Claims

1. A low-cost, thick-gauge 460MPa nickel-free weathering steel, with the following chemical composition by weight percentage: C: 0.04–0.07%, Si: 0.55–0.75%, Mn: 0.43–0.63%, P: 0.010–0.014%, S≤0.003%, Cu: 0.3–0.5%, Cr: 0.3–0.5%, Ti: 0.020–0.030%, V: 0.020–0.030%, B: 0.0007–0.0013%, Al: 0.020–0.030%, Zr: 0.0009–0.0015%, with the balance including Fe and other unavoidable impurities; and the chemical composition must simultaneously meet the following requirements: The weld crack sensitivity index Pcm ≤ 0.17%; Carbon equivalent (CEV) ≤ 0.32%; Weather resistance index I ≥ 6.0; Cu / P+5*Si≥25; 0.06%≤(Al+Ti+V)≤0.085%.

2. The low-cost, thick-gauge 460MPa nickel-free weathering steel as described in claim 1, characterized in that, The balance consists of Fe and other unavoidable impurities.

3. The low-cost, thick-gauge 460MPa nickel-free weathering steel as described in claim 1 or 2, characterized in that, The microstructure of the weathering steel is equiaxed ferrite + pearlite + a small amount of granular bainite; wherein the volume percentage of equiaxed ferrite is 50-70%, the volume percentage of granular bainite is ≤5%, and the remainder is pearlite, with an average grain size of 7-10 μm, a grain size ≥8, and an inclusion grade ≤0.

4.

4. The low-cost, thick-gauge 460MPa nickel-free weathering steel as described in claim 1, 2, or 3, characterized in that, The number density of heterogeneous nucleated particles in the microstructure of the weathering steel is 5.26 × 10⁻⁶. 4 ~6.58×10 4 / mm 3 The ratio of ferrite heterogeneous nuclei is ≥60%, and the heterogeneous nuclei are Ti(C,N) and V(C,N) composite precipitates.

5. The low-cost, thick-gauge 460MPa nickel-free weathering steel as described in claim 1, 2, 3, or 4, characterized in that, The weathering steel has a yield strength ≥ 460 MPa and a tensile strength ≥ 550 MPa. The impact energy at -20℃ is 210~380J, the yield strength ratio is ≤0.82, and there are no "copper brittleness" cracks on the surface of the steel plate.

6. The low-cost, thick-gauge 460MPa nickel-free weathering steel as described in claim 1, 2, 3, 4, or 5, characterized in that, The thickness of the weathering steel plate is 20-60 mm.

7. The method for manufacturing low-cost, thick-gauge 460MPa nickel-free weathering steel as described in any one of claims 1 to 6, characterized in that, Includes the following steps: 1) Smelting and refining The components described in claim 1 or 2 are smelted, refined, and cast into billets. 2) Slab heating Heating temperature: 1060~1080℃, holding time: 1h~2h; 3) Rolling Roughing rolling start temperature: 900~1000℃, single-pass rolling reduction rate in roughing stage ≥15%; Finishing rolling start temperature: 870~890℃, single-pass rolling reduction rate in the finishing rolling stage ≥20%, finishing rolling temperature: 840~860℃; 4) Cooling Cooling start temperature: 790~830℃, cooling stop temperature: 440~480℃, cooling rate ≥40℃ / s.

8. The manufacturing method as described in claim 7, characterized in that, In step 4), the cooling is achieved by water cooling.

9. The manufacturing method as described in claim 7 or 8, characterized in that, In step 4), the steel plate is air-cooled to room temperature after the cooling process is stopped.

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