High-strength weathering steel and method for producing the same

Abstract

The application discloses a high-strength weather-resistant steel and a production method thereof. The high-strength weather-resistant steel comprises the following components in percentage by mass: C: 0.03-0.09%, Si: 0.05-0.30%, Mn: 0.4-1.8%, P: 0.04-0.07%, S: ≤0.0050%, Cr: 1.0-4.0%, Cu: 0.20-0.50%, Al: 0.01-0.05%, Ti: 0.05-0.09%, N: ≤0.0060%, and the balance of Fe and other inevitable impurity elements; and the weather resistance index I of the high-strength weather-resistant steel is greater than or equal to 8.0. The high-strength weather-resistant steel product provided by the application has good corrosion resistance on the basis of good processability, and the production method provided by the application also has the above beneficial effects.

Description

Technical Field

[0001] This application belongs to the field of iron and steel smelting technology, specifically relating to a high-strength weather-resistant steel and its production method. Background Technology

[0002] Weathering steel has better atmospheric corrosion resistance than Q235B and Q355B. It is widely used in containers, railway freight vehicles, bridges and construction. However, traditional weathering steel still has problems such as insufficient corrosion resistance and short service life.

[0003] Photovoltaic power generation is a rapidly developing green and environmentally friendly industry. To ensure the corrosion resistance of photovoltaic brackets throughout their 25-year lifespan, galvanized brackets made of Q235 and Q355 steel are currently the primary materials used. However, Q235B and Q355B have poor atmospheric corrosion resistance. Furthermore, the galvanizing process for these products generates significant energy consumption, solid waste, and waste acid pollution. During service, zinc layer detachment or additional carbon emissions and pollution may occur, increasing maintenance workload. Therefore, researching a high-performance atmospheric corrosion-resistant steel that requires no coating is a key research direction. Summary of the Invention

[0004] In view of this, this application provides a high-strength weathering steel and its production method, which enables the high-strength weathering steel product to have good processing performance and good corrosion resistance.

[0005] In a first aspect, embodiments of this application provide a high-strength weather-resistant steel, comprising, by mass percentage:

[0006] C: 0.03%–0.09%, Si: 0.05%–0.30%, Mn: 0.4%–1.8%, P: 0.04%–0.07%, S: ≤0.0050%, Cr: 1.0%–4.0%, Cu: 0.20%–0.50%, Al: 0.01%–0.05%, Ti: 0.05%–0.09%, N: ≤0.0060%, with the balance being Fe and other unavoidable impurity elements; the weathering resistance index I of high-strength weathering steel is ≥8.0.

[0007] According to one embodiment of this application, the microstructure of the high-strength weathering steel is 50% to 80% ferrite and 50% to 80% bainite by volume fraction, and the grain size of the high-strength weathering steel is grade 11 or above.

[0008] According to one embodiment of this application, the mechanical properties of high-strength weather-resistant steel include: yield strength ≥ 550 MPa, tensile strength ≥ 650 MPa, elongation ≥ 16%, and low-temperature impact energy at -40℃ ≥ 60 J.

[0009] Secondly, embodiments of this application provide a method for producing high-strength weather-resistant steel, including:

[0010] A slab is heated to obtain a heated slab. The slab comprises, by mass percentage: C: 0.03%–0.09%, Si: 0.05%–0.30%, Mn: 0.4%–1.8%, P: 0.04%–0.07%, S: ≤0.0050%, Cr: 1.0%–4.0%, Cu: 0.20%–0.50%, Al: 0.01%–0.05%, Ti: 0.05%–0.09%, N: ≤0.0060%, with the balance being Fe and other unavoidable impurity elements; the weathering index I of the high-strength weathering steel is ≥8.0.

[0011] The heated slab is hot-rolled to obtain a hot-rolled plate;

[0012] High-strength weather-resistant steel is produced by cooling and coiling hot-rolled plates. The cooling process includes a first cooling at a rate of 80-200℃ / s to a temperature of 620-700℃, air cooling, and a second cooling at a rate of 80-200℃ / s to a temperature of 520-580℃. The air cooling time is 7-14s.

[0013] According to one embodiment of this application, the slab entering the furnace is at a temperature of 20°C to 550°C or 760°C to 1000°C, and the slab heating rate is 500°C / h to -700°C / h; the slab holding temperature is 1220-1280°C, the holding time is 20-60 min, the total time the slab is in the furnace is 150-350 min, and the slab exiting the furnace is 1200-1260°C.

[0014] According to one embodiment of this application, the slab is heated by a heating furnace, wherein the excess air coefficient of the heating atmosphere inside the furnace is 1.1-1.5.

[0015] According to an embodiment of one aspect of this application, hot rolling includes roughing, the total reduction rate of the roughing is ≥80%, the final pass reduction rate of the roughing is ≥30%, the thickness after the final pass of the roughing is 30-40mm, the rolling speed of the roughing is ≤5.0m / s, the final cooling temperature of the roughing is 1040-1120℃, and the descaling pressure of the roughing body is ≥18MPa.

[0016] According to one embodiment of this application, hot rolling includes finishing rolling, which is carried out in 7-stand continuous rolling. The descaling pressure at the entrance of the finishing rolling mill is ≥18MPa, the initial entry temperature of the finishing rolling mill is 980-1100℃, the reduction rate of the last stand of the finishing rolling mill is ≥8%, and the final cooling temperature of the finishing rolling mill is 800-900℃.

[0017] According to one embodiment of this application, the thickness of the hot-rolled plate and the final rolling temperature of the finishing mill satisfy the following relationship:

[0018] 1) The thickness of the hot-rolled plate is <2.0mm, and the final rolling temperature of the finishing roll is 880-900℃;

[0019] 2) The thickness of the hot-rolled plate is 2.0-3.0 mm, and the final rolling temperature of the finishing roll is 850-870℃;

[0020] 3) The thickness of the hot-rolled plate is greater than 3mm and less than or equal to 4.0mm, and the finishing rolling temperature is 810~840℃;

[0021] 4) The thickness of the hot-rolled plate is >4.0mm, and the final rolling temperature of the finishing roll is 790-810℃.

[0022] According to one embodiment of this application, the winding temperature is 520-580°C; the head and tail of the hot-rolled plate are wound using a U-shaped temperature method; the winding temperature at 20m from both ends of the hot-rolled plate is 580-640°C.

[0023] This application has at least the following beneficial effects:

[0024] The high-strength weathering steel provided in this application has high weather resistance. Compared with Q355B low alloy structural steel, the relative corrosion rate of this high-strength weathering steel is ≤35%. In a general atmospheric environment, the uniform corrosion depth of C1-C3 uncoated service for 25 years is ≤0.1mm. It has high strength and good formability and can replace galvanized products in applications such as photovoltaic brackets and highway guardrails. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0026] Figure 1 A micrograph of the high-strength weathering steel of Embodiment 1 of this application is shown. Detailed Implementation

[0027] To make the purpose, technical solution, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the embodiments described in this specification are merely for explaining this application and are not intended to limit it.

[0028] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0029] In the description of this application, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more.

[0030] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0031] In a first aspect, embodiments of this application provide a high-strength weather-resistant steel, comprising, by mass percentage:

[0032] C: 0.03%–0.09%, Si: 0.05%–0.30%, Mn: 0.4%–1.8%, P: 0.04%–0.07%, S: ≤0.0050%, Cr: 1.0%–4.0%, Cu: 0.20%–0.50%, Al: 0.01%–0.05%, Ti: 0.05%–0.09%, N: ≤0.0060%, with the balance being Fe and other unavoidable impurity elements; the weathering resistance index I of high-strength weathering steel is ≥8.0.

[0033] According to the embodiments of this application, the high-strength weathering steel has high corrosion resistance. Compared with Q355B low alloy structural steel, the relative corrosion rate of the high-strength weathering steel is ≤35%. In a general atmospheric environment, the uniform corrosion depth of C1-C3 uncoated service for 25 years is ≤0.1mm. It has high strength and good formability, and can replace galvanized products in applications such as photovoltaic brackets and highway guardrails.

[0034] The selection principles and design reasons for the content of each element in this application are as follows:

[0035] The composition design avoids the addition of large amounts of precious elements such as Nb, V, Ni, Mo, and W, thus reducing the cost of the alloy.

[0036] C: Carbon (C) is an effective strengthening element in steel, but weathering steel has a high Cr content. When the carbon content is high, martensite is easily formed in the steel, which drastically reduces the steel's ductility and toughness. Furthermore, martensite leads to very high tensile strength, making it prone to forming cracks. C can also form nanoscale precipitates with microalloying elements such as Nb and Ti in steel, exhibiting precipitation strengthening effects. Therefore, to fully utilize the strengthening effect of C and avoid the formation of excessive martensite affecting the microstructure, the C content in this invention is controlled at 0.03–0.09%.

[0037] Si: A commonly used deoxidizing element. Si exists in solid solution in ferrite and austenite to improve the strength of steel and reduce the overall corrosion rate of steel. However, during hot rolling, a high Si content can easily produce obvious red iron oxide scale defects on the surface of the strip steel, which are difficult to remove by descaling and affect the surface quality of the strip steel. Therefore, the Si content of this invention is designed to be 0.05-0.30%.

[0038] Mn: Mn is an important strengthening and toughening element and an austenite stabilizing element. It can expand the austenite region in the iron-carbon phase diagram, promote the transformation of the microstructure at medium temperature, and is beneficial to the refinement of the microstructure and the improvement of the strength and low-temperature toughness of the steel. However, when the Mn content is too high, it will produce serious segregation in the steel and deteriorate the low-temperature toughness of the steel. Therefore, the Mn content in this design is 0.4-1.8%.

[0039] Phosphorus (P): Often added as a corrosion-resistant element in traditional atmospheric corrosion-resistant steels, P promotes the formation of a protective rust layer, effectively improving the steel's atmospheric corrosion resistance. However, P is also a harmful impurity element in steel, easily segregating at the center of the thickness during continuous casting of steel billets. Simultaneously, P tends to agglomerate at grain boundaries, reducing grain boundary bonding energy and decreasing the steel's toughness and plasticity. To fully utilize P's corrosion resistance and suppress the adverse effects of P segregation, this invention designs a P content of 0.04–0.07%.

[0040] S: Sulfur has adverse effects on the corrosion resistance, cold forming performance, low-temperature toughness, and weldability of steel; therefore, in this invention, the value range of S is set to S≤0.005%.

[0041] Cr: Cr forms a dense oxide film on the surface of steel, improving its passivation ability. The effect is particularly pronounced when Cr and Cu are added to steel simultaneously. Increased Cr content is beneficial for refining α-FeOOH, but in areas with high Cl- content, adding Cr is considered detrimental. Furthermore, a higher Cr content can also allow steel to form bainite or martensite at lower cooling rates, significantly improving tensile strength. However, excessively high proportions of bainite or martensite can reduce the steel's processing and formability; therefore, this invention designs the Cr content to be 1.0–4.0%.

[0042] Cu: Copper acts as an active cathode, which can promote anodic passivation of steel under certain conditions, thereby reducing the corrosion rate of steel. Another view is that the enrichment of Cu in the rust layer can improve the protective performance of the rust layer, thereby improving the corrosion resistance of steel. The combined effect of Cu and P promotes the formation of extremely dense amorphous Fe3O4 in the rust layer, thereby preventing oxygen and water from penetrating into the steel matrix. Cu can also react with S to form insoluble compounds that block cracks in the rust layer. The corrosion resistance of steel can be improved by 2 to 3 times by adding only 0.25% Cu. Therefore, the Cu content of this invention is designed to be 0.20 to 0.50%.

[0043] Al: Al is a commonly used deoxidizing element in steel, which refines grains and improves the steel's strength properties. At the same time, Al promotes ferrite formation, inhibits pearlite transformation, and is beneficial to the transformation of ferrite into bainite. Therefore, the Al content in this invention is designed to be 0.01–0.05%.

[0044] Ti: A strong carbonitride forming element that improves the material's resistance to intergranular corrosion. It can also precipitate in the form of nanoscale TiC or Ti(C,N) second-phase particles, which significantly improves the material's strength through precipitation strengthening. Based on the low strength grade, the Ti content in this invention is designed to be 0.05-0.09%.

[0045] N: N is a harmful element in steel, consuming Ti and forming inclusions. The N content needs to be controlled at a low level. In this invention, N is designed to be ≤0.0060%.

[0046] Weather resistance index: The weather resistance index can evaluate the weather resistance performance of steel. Generally, a weather resistance index ≥ 6.0 is sufficient for use without painting. The high-strength weather-resistant steel in this application embodiment can be used without painting for 25 years in C1-C3 environments, and the composition design has a weather resistance index ≥ 8.0.

[0047] The formula for calculating the weather resistance index I is as follows:

[0048] I = 26.01 × Cu content in steel + 3.88 × Ni content in steel + 1.2 × Cr content in steel + 1.49 × Si content in steel + 17.28 × P content in steel - 7.29 × Cu content in steel × Ni content in steel - 9.1 × Ni content in steel × P content in steel - 33.39 × (Cu content in steel) 2

[0049] In this embodiment of the application, molten iron with a certain chemical composition is smelted into molten steel and cast into slabs, the thickness of which can be 230-240mm.

[0050] In some alternative embodiments, the microstructure of the high-strength weathering steel is 50%–80% ferrite and 50%–80% bainite by volume fraction, and the grain size of the high-strength weathering steel is grade 11 or above.

[0051] In the embodiments of this application, the high-strength weather-resistant steel has no pearlite microstructure, but a high proportion of fine ferrite microstructure and very high low-temperature toughness.

[0052] In some alternative implementations, the mechanical properties of high-strength weathering steel include: yield strength ≥550MPa, tensile strength ≥650MPa, elongation ≥16%, and impact energy at -40℃ ≥60J.

[0053] Secondly, embodiments of this application provide a method for producing high-strength weather-resistant steel, including:

[0054] A slab is heated to obtain a heated slab. The slab comprises, by mass percentage: C: 0.03%–0.09%, Si: 0.05%–0.30%, Mn: 0.4%–1.8%, P: 0.04%–0.07%, S: ≤0.0050%, Cr: 1.0%–4.0%, Cu: 0.20%–0.50%, Al: 0.01%–0.05%, Ti: 0.05%–0.09%, N: ≤0.0060%, with the balance being Fe and other unavoidable impurity elements; the weathering index I of the high-strength weathering steel is ≥8.0.

[0055] The heated slab is hot-rolled to obtain a hot-rolled plate;

[0056] High-strength weather-resistant steel is produced by cooling and coiling hot-rolled plates. The cooling process includes a first cooling at a rate of 80-200℃ / s to a temperature of 620-700℃, air cooling, and a second cooling at a rate of 15-45℃ / s to a temperature of 520-580℃. The air cooling time is 7-14s.

[0057] According to the embodiments of this application, the first cooling is a rapid cooling of ultra-fast cooling, which inhibits the transformation of austenite to bainite in the strip. After ultra-fast cooling, the strip enters the ferrite transformation temperature range and is air-cooled for 7-14 seconds to transform austenite into ferrite. The longer the air-cooling time, the higher the proportion of ferrite generated by the transformation. However, if the air-cooling time is too long, the rolling speed will need to be reduced, which will seriously affect the rolling stability of thin strip. After air cooling, the strip undergoes a second stage of cooling. The second stage cooling rate is ≥15℃ / s. After the strip is cooled to 520-580℃, it is coiled. The untransformed austenite is transformed into bainite, so that the strip finally forms a two-phase structure of ferrite + bainite.

[0058] According to the embodiments of this application, a composite weathering composition design using elements such as P, Cu, and Cr is employed. Laminar flow cooling is used, and a specific cooling temperature design ensures that the weathering steel's microstructure forms a high proportion of ferrite and a fine microstructure, improving the steel's low-temperature impact resistance. Appropriate P element addition and good low-temperature toughness effectively utilize inexpensive weathering elements to enhance the steel's weathering resistance while avoiding the deterioration of toughness caused by high P content. A higher Ti element is added to enhance the strength of the weathering steel through precipitation strengthening, while medium-temperature coiling inhibits the precipitation of chromium carbides between Cr and C. This process is employed... By combining different components, the weather resistance and low-temperature toughness of the steel can be improved, resulting in a high-strength weather-resistant steel with a yield strength ≥550MPa, tensile strength ≥650MPa, elongation ≥16%, and impact energy ≥60J at -40℃. Its microstructure is a two-phase structure of ferrite and bainite, with a grain size of grade 11 or higher. The ferrite content is 50-80%, the bainite content is 20-50%, and there is no pearlite structure in the microstructure. The high proportion of fine ferrite structure in the steel and the high low-temperature toughness effectively suppress the adverse effects of P segregation and make full use of the weather resistance properties of P.

[0059] In some optional embodiments, the slab entry temperature is 20°C to 550°C or 760°C to 1000°C, the slab heating rate is 500°C / h to -700°C / h; the slab holding temperature is 1220-1280°C, the holding time is 20-60 min, the total slab time in the furnace is 150-350 min; and the slab exit temperature is 1200-1260°C.

[0060] According to the embodiments of this application, in order to avoid slab cracking caused by charging the slab into the two-phase zone of the furnace, the slab temperature entering the furnace is ≤550℃ or ≥760℃; in order to avoid surface defects caused by Cu liquefaction and grain boundary precipitation during heating, the slab is heated rapidly, with a heating rate ≥500℃ / h and a total furnace time of 150-350min; in order to ensure sufficient solid solution of Ti, the furnace holding temperature is required to be 1220-1280℃ and the holding time is required to be 20-60min.

[0061] According to the embodiments of this application, the heating rate is ≥500℃ / h, which makes the slab temperature rise rapidly, avoids the slab from staying near the melting point of Cu element 1085℃ for a long time, and makes the slab temperature rise to a higher temperature quickly, thereby increasing the solid solubility of Cu in steel, inhibiting Cu liquefaction and precipitation at grain boundaries, and improving the surface quality of steel.

[0062] In some alternative implementations, the slab is heated in a furnace with an excess air coefficient of 1.1-1.5 in the furnace heating atmosphere.

[0063] According to an embodiment of this application, in order to increase the surface burn-off of slabs and remove slab defects through the high-temperature environment of a heating furnace, the superheat coefficient of the heating air is controlled to 1.1-1.5 to improve the burn-off of the slabs in the heating furnace and improve the surface quality of the steel.

[0064] In some alternative embodiments, hot rolling includes roughing, with a total reduction rate of ≥80%, a final pass reduction rate of ≥30%, a final pass thickness of 30-40 mm, a rolling speed of ≤5.0 m / s, a final cooling temperature of 1040-1120 °C, and a descaling pressure of ≥18 MPa.

[0065] In this application, to refine the grain size of the roughing mill, the total reduction rate of the roughing mill is ≥80%, the reduction rate of the last pass of the roughing mill is ≥30%, the thickness after the last pass of the roughing mill is 30-40mm, and the final cooling temperature of the roughing mill is 1040-1120℃; to ensure sufficient recrystallization during the roughing milling process, the roughing milling speed is ≤5.0m / s; the descaling pressure of the roughing mill body is ≥18MPa, and the surface quality of the intermediate billet after roughing milling is improved.

[0066] In some alternative implementations, to increase the rolling deformation capacity and promote the ferrite transformation of the strip after entering the cooling layer, hot rolling includes finishing rolling, which adopts a 7-stand continuous rolling mill, with an inlet descaling pressure ≥18MPa, an inlet temperature of 980-1100℃, a last stand reduction rate ≥8%, and a final cooling temperature of 800-900℃.

[0067] In this application, to refine the strip structure, the reduction rate of the final stand in the finishing mill is ≥8%.

[0068] In some alternative implementations, the thickness of the hot-rolled plate is <2.0 mm, and the finishing rolling temperature is 880-900℃.

[0069] In some alternative embodiments, the thickness of the hot-rolled plate is 2.0 to 3.0 mm, and the finishing rolling temperature is 850-870°C.

[0070] In some alternative embodiments, the thickness of the hot-rolled plate is greater than 3 mm and less than or equal to 4.0 mm, and the finishing rolling temperature is 810–840 °C.

[0071] In some alternative implementations, the thickness of the hot-rolled plate is >4.0 mm, and the finishing rolling temperature is 790-810°C.

[0072] According to the embodiments of this application, by controlling the thickness of the hot-rolled plate and the final rolling temperature of the finishing roll, the rolling deformation capacity can be increased, and the ferrite transformation of the strip after entering the cooling process can be promoted.

[0073] In some alternative embodiments, the winding temperature is 520-580°C; the head and tail of the hot-rolled plate are wound using a U-shaped temperature method; the winding temperature at 20m from both ends of the hot-rolled plate is 580-640°C.

[0074] In this embodiment, the hot-rolled plate is coiled using a U-shaped temperature method at both ends. Since the coiling temperature of the hot-rolled plate is 520-580℃ and the cooling rate of the head and tail of the hot-rolled plate is fast, it is not conducive to the precipitation strengthening of the second phase of TiC. Therefore, the coiling temperature at a distance of 0-20m from the head and tail of the hot-rolled plate is 580-640℃, and the hot-rolled coil unwinding box is slowly cooled to below 250℃ to promote the precipitation strengthening of TiC and improve the performance stability of the steel strip.

[0075] According to the embodiments of this application, a combination of low-temperature final rolling, two-stage cooling, and a relatively low coiling temperature is used to obtain a high proportion of fine ferrite structure, i.e., an appropriate proportion of bainite structure, which improves the low-temperature toughness and strength of the steel. The lower coiling temperature inhibits the precipitation of chromium carbides formed between Cr and C, thereby improving the weather resistance of the steel.

[0076] In some embodiments, slow cooling is performed after winding. Slow cooling in air can promote TiC precipitation strengthening and improve the tensile strength of the steel.

[0077] Example

[0078] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0079] Examples 1-4 and Comparative Examples 1-2

[0080] This application provides a high-strength weather-resistant steel, comprising, by mass percentage:

[0081] C: 0.03%–0.09%, Si: 0.05%–0.30%, Mn: 0.4%–1.8%, P: 0.04%–0.07%, S: ≤0.0050%, Cr: 1.0%–4.0%, Cu: 0.20%–0.50%, Al: 0.01%–0.05%, Ti: 0.05%–0.09%, N: ≤0.0060%, with the balance being Fe and other unavoidable impurities; the weathering resistance index I of high-strength weathering steel is ≥8.0. See Table 1 for details.

[0082] Table 1

[0083]

[0084] The formula for calculating the weather resistance index I in the table above is as follows:

[0085] I=26.01(%Cu)+3.88(%Ni)+1.2(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.1(%Ni)(%P)-33.39(%Cu) 2

[0086] In the formula: (%Cu), (%Ni), (%Cr), (%Si), (%P) are the mass contents of each element.

[0087] The comparative sample was prepared using conventional processes.

[0088] This application provides a method for producing high-strength weather-resistant steel, including:

[0089] A slab is heated to obtain a heated slab. The slab comprises, by mass percentage: C: 0.03%–0.09%, Si: 0.05%–0.30%, Mn: 0.4%–1.8%, P: 0.04%–0.07%, S: ≤0.0050%, Cr: 1.0%–4.0%, Cu: 0.20%–0.50%, Al: 0.01%–0.05%, Ti: 0.05%–0.09%, N: ≤0.0060%, with the balance being Fe and other unavoidable impurity elements; the weathering index I of the high-strength weathering steel is ≥8.0.

[0090] The heated slab is hot-rolled to obtain a hot-rolled plate;

[0091] High-strength weather-resistant steel is produced by cooling and coiling hot-rolled plates. The cooling process includes a first cooling at a rate of 80-200℃ / s to a temperature of 620-700℃, air cooling, and a second cooling at a rate of 80-200℃ / s to a temperature of 520-580℃. The air cooling time is 7-14s.

[0092] The specific process parameters for heating in the embodiment are shown in Table 1.

[0093] Table 1

[0094]

[0095] The hot rolling process parameters of the embodiment are shown in Table 2.

[0096] Table 2

[0097]

[0098]

[0099] The cooling process parameters are shown in Table 3.

[0100] Table 3.

[0101]

[0102] Test section

[0103] The steel plates in the examples were tested using GB / T 13298-2015 "Methods for Examination of Microstructure of Metals". The microstructure of the high-strength weather-resistant steel was found to be 50%–80% ferrite and 50%–80% bainite by volume. According to the grain size classification in GB / T 6394-2017 "Methods for Determination of Average Grain Size of Metals", the grain size of the high-strength weather-resistant steel was found to be above grade 11. The micrograph of Example 1 is shown below. Figure 1 As shown.

[0104] The mechanical properties of the high-strength weathering steels in the comparative examples and examples were tested according to GB / T 228.1-2010 "Metallic materials, tensile testing—Part 1: Test at room temperature". The test results are shown in the table below.

[0105] The corrosion performance of the high-strength weathering steels in the examples and comparative examples was tested according to TB / T2375-93, and the relative corrosion rates were compared with those of ordinary carbon steel Q355B after 72 hours of immersion corrosion. The test results are shown in the table below.

[0106] Table 4

[0107]

[0108] Impact performance tests were not conducted on the steel plates in Examples 1-4 due to their thinness. An impact test was conducted on the steel plate in Example 5.

[0109] Table 4 shows that the mechanical properties of the high-strength weathering steel in the examples include: yield strength ≥ 550 MPa, tensile strength ≥ 650 MPa, elongation ≥ 16%, and low-temperature impact energy at -40℃ ≥ 60 J. Compared with ordinary carbon steel Q355B, the corrosion rate of the steel in the examples is between 30% and 35%. Based on data resources from the National Materials Corrosion and Protection Science Data Center and corrosion kinetic models, the high-strength weathering steel in the examples is predicted to have a uniform single-sided corrosion depth ≤ 0.1 mm over a 25-year service life without coating in a typical atmospheric environment (C1-C3 grade), while the corrosion depth of the comparative steel is approximately 0.15-0.25 mm.

[0110] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for producing high-strength weather-resistant steel, characterized in that, include: A slab is heated to obtain a heated slab, wherein the slab comprises, by mass percentage: C: 0.03%~0.09%, Si: 0.05%~0.30%, Mn: 0.4%~1.8%, P: 0.053%~0.07%, S: ≤0.0050%, Cr: 1.0%-4.0%, Cu: 0.20%-0.50%, Al: 0.023%-0.05%, Ti: 0.05%-0.09%, N: ≤0.0060%, with the balance being Fe and other unavoidable impurity elements; the weathering resistance index I of the high-strength weathering steel is ≥8.0; The heated slab is hot-rolled to obtain a hot-rolled plate, wherein the hot rolling includes finishing rolling, and the thickness of the hot-rolled plate and the final rolling temperature of the finishing rolling satisfy the following relationship: 1) The thickness of the hot-rolled plate is <2.0mm, and the final rolling temperature of the finishing roll is 880-900℃; 2) The thickness of the hot-rolled plate is 2.0~3.0mm, and the final rolling temperature of the finishing roll is 850-870℃; 3) The thickness of the hot-rolled plate is greater than 3 mm and less than or equal to 4.0 mm, and the final rolling temperature of the finishing roll is 810~840℃; 4) The thickness of the hot-rolled plate is >4.0mm, and the final rolling temperature of the finishing roll is 790-810℃; The hot-rolled plate is cooled and coiled to obtain the high-strength weather-resistant steel. The cooling process includes a first cooling at a rate of 80-200℃ / s to a temperature of 620-700℃, air cooling, and a second cooling at a rate of 15-45℃ / s to a temperature of 520-580℃. The air cooling time is 7-14s. The high-strength weathering steel comprises, by mass percentage: C: 0.03%~0.09%, Si: 0.05%~0.30%, Mn: 0.4%~1.8%, P: 0.053%~0.07%, S: ≤0.0050%, Cr: 1.0%-4.0%, Cu: 0.20%-0.50%, Al: 0.023%-0.05%, Ti: 0.05%-0.09%, N: ≤0.0060%, with the balance being Fe and other unavoidable impurity elements; the weathering resistance index I of the high-strength weathering steel is ≥8.

0.

2. The production method according to claim 1, characterized in that, The microstructure of the high-strength weathering steel is 50%–80% ferrite and 50%–80% bainite by volume fraction, and the grain size of the high-strength weathering steel is grade 11 or above.

3. The production method according to claim 1, characterized in that, The mechanical properties of the high-strength weather-resistant steel include: yield strength ≥550MPa, tensile strength ≥650MPa, elongation ≥16%, and impact energy at -40℃ ≥60J.

4. The production method according to claim 1, characterized in that, The slab's furnace entry temperature is 20~550℃ or 760-1000℃, and the slab's heating rate is 500℃ / h to 700℃ / h; the slab's holding temperature is 1220-1280℃, the holding time is 20-60min, and the total furnace time of the slab is 150-350min; the slab's furnace exit temperature is 1200-1260℃.

5. The production method according to claim 1, characterized in that, The slab is heated in a furnace with an excess air coefficient of 1.1-1.5 in the furnace heating atmosphere.

6. The production method according to claim 1, characterized in that, The hot rolling includes roughing, the total reduction rate of the roughing is ≥80%, the final pass reduction rate of the roughing is ≥30%, the thickness after the final pass of the roughing is 30-40mm, the rolling speed of the roughing is ≤5.0m / s, the final cooling temperature of the roughing is 1040-1120℃, and the descaling pressure of the roughing body is ≥18MPa.

7. The production method according to claim 1, characterized in that, The finishing mill adopts a 7-stand continuous rolling mill, the entry descaling pressure of the finishing mill is ≥18MPa, the initial entry temperature of the finishing mill is 980-1100℃, the reduction rate of the last stand of the finishing mill is ≥8%, and the final cooling temperature of the finishing mill is 800-900℃.

8. The production method according to claim 1, characterized in that, The winding temperature is 520-580℃; the head and tail of the hot-rolled plate are wound using a U-shaped temperature method, and the winding temperature at 20m from both ends of the hot-rolled plate is 580-640℃.

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