700MPa-grade high-corrosion-resistant weathering-resistant steel as well as preparation method and application thereof

Abstract

The invention discloses 700MPa-grade high-corrosion-resistant and weathering-resistant steel as well as a preparation method and application thereof. The invention relates to 700MPa-grade high-strength weathering steel, which comprises the following chemical components in percentage by mass: 0.03 to 0.12 percent of C, 0.05 to 0.40 percent of Si, 1.1 to 1.8 percent of Mn, less than or equal to 0.002 percent of P, less than or equal to 0.0050 percent of S, 0.5 to 1.5 percent of Cr, 0.30 to 0.60 percent of Cu, 0.50 to 1.30 percent of Al, 0.10 to 0.15 percent of Ti, less than or equal to 0.05 percent of Nb, less than or equal to 0.50 percent of Ni, less than or equal to 0.0060 percent of N and the balance of Fe and other inevitable impurities. According to the embodiment of the invention, the low yield ratio and high corrosion resistance can be achieved.

Description

Technical Field

[0001] The present application relates to weathering steel, and in particular to a 700MPa grade high corrosion-resistant weathering steel and a preparation method and application thereof. Background Art

[0002] Weathering steel (atmospheric corrosion resistant steel) refers to a low alloy steel with good atmospheric corrosion resistance made by adding a certain amount of Cu, P, C or Ni, Mo, Nb, Ti and other alloy elements to steel. In industrial and rural atmospheric environments, weathering steel has excellent atmospheric corrosion resistance and other properties because it forms a dense and stable oxide protective film on the surface of its substrate, which hinders the entry of corrosive media. However, the rust layer formed by corrosion on the surface of ordinary carbon steel substrate has a loose structure and micro-cracks, which cannot really protect the substrate steel.

[0003] Weathering steel has better atmospheric corrosion resistance than Q235B and Q355B, so it is widely used in containers, railway freight vehicles, bridges, buildings, etc. However, traditional weathering steel still has problems of insufficient corrosion resistance and mechanical properties. Summary of the invention

[0004] The embodiments of the present application provide a 700MPa grade high corrosion-resistant and weather-resistant steel and a preparation method and application thereof, which can have a low yield strength ratio and high corrosion resistance at the same time.

[0005] In the first aspect, an embodiment of the present application provides a 700MPa grade high-strength weathering steel, whose chemical composition, measured in percentage by mass, includes: C: 0.03%~0.12%, Si: 0.05%~0.40%, Mn: 1.1%~1.8%, P: ≤0.002%, S: ≤0.0050%, Cr: 0.5%~1.5%, Cu: 0.30%~0.60%, Al: 0.50%~1.30%, Ti: 0.10%~0.15%, Nb≤0.05%, Ni≤0.50%, N: ≤0.0060%, and the balance is Fe and other unavoidable impurities.

[0006] In any embodiment of the present application, the metallographic structure of the 700 MPa grade high-strength weathering steel includes ferrite and bainite.

[0007] In any embodiment of the present application, the thickness of the 700 MPa grade high-strength weathering steel is less than or equal to 16 mm.

[0008] In any embodiment of the present application, the yield strength of 700MPa grade high-strength weathering steel is greater than or equal to 700Mpa.

[0009] In any embodiment of the present application, the tensile strength of the 700MPa grade high-strength weathering steel is greater than or equal to 750Mpa.

[0010] In any embodiment of the present application, the elongation A of the 700 MPa grade high-strength weathering steel is greater than 14%.

[0011] In any embodiment of the present application, the corrosion rate of 700 MPa grade high strength weathering steel relative to Q355B is less than or equal to 30%.

[0012] In the second aspect, an embodiment of the present application provides a preparation method of 700MPa grade high-strength weathering steel, comprising: smelting and casting molten iron of a preset composition to obtain a slab; hot rolling the slab to obtain 700MPa grade high-strength weathering steel; wherein the preset composition includes C: 0.03%~0.12%, Si: 0.05%~0.40%, Mn: 1.1%~1.8%, P: ≤0.002%, S: ≤0.0050%, Cr: 0.5%~1.5%, Cu: 0.30%~0.60%, Al: 0.50%~1.30%, Ti: 0.10%~0.15%, Nb≤0.05%, Ni≤0.50%, N: ≤0.0060%, and the remainder is Fe and other inevitable impurities; the hot rolling treatment sequentially includes a heating process, a rolling process, a cooling process and a slow cooling process.

[0013] In any embodiment of the present application, the thickness of the slab is 50-70 mm.

[0014] In any embodiment of the present application, the heating process includes: placing the slab in a heating furnace of a hot rolling line for heating to obtain a heat-treated slab; wherein the heating temperature is 1200-1270°C, the holding time is 8-15min, the total slab time in the furnace is 10-40min, the furnace outlet temperature is 1190-1250°C, and the excess air coefficient of the heating atmosphere in the furnace is 1.1-1.5.

[0015] In any embodiment of the present application, the rolling process includes: placing the heat-treated slab in a multi-stand continuous rolling mill for finish rolling to obtain a strip steel; wherein the descaling pressure at the finishing rolling entrance is greater than or equal to 18 MPa, the temperature at the finishing rolling entrance is 1000-1120°C, the last stand reduction rate is greater than or equal to 8%, and the finishing rolling final rolling temperature is 860-950°C.

[0016] In any embodiment of the present application, the cooling process includes: subjecting the steel strip to laminar cooling to obtain 700MPa grade high-strength weathering steel; wherein the laminar cooling method includes ultra-fast cooling and front-stage concentrated cooling, the cooling rate of ultra-fast cooling is 80 to 200°C / s, and the outlet temperature of ultra-fast cooling is 700 to 780°C; the cooling rate of the front-stage concentrated cooling is greater than or equal to 20°C / s.

[0017] In a third aspect, the embodiments of the present application provide the application of the above-mentioned 700 MPa grade high-strength weathering steel or the 700 MPa grade high-strength weathering steel obtained by the above-mentioned preparation method in railway freight cars, power towers and marine photovoltaic structures under C3-C5 environment.

[0018] The 700MPa grade high corrosion-resistant weathering steel and its preparation method and application in the embodiment of the present application can form a relatively stable and dense rust layer through the interaction between the special ratio of Cu, Cr and Al to improve the corrosion resistance of the weathering steel; and through the interaction between the special ratio of Si, Mn, Nb and Ni, the mechanical properties of the weathering steel are improved. Thus, through the overall composition design, a high-strength weathering steel with a yield strength greater than or equal to 700MPa, a tensile strength greater than or equal to 750MPa, an elongation A greater than 14% and a relative corrosion rate of 30% or less is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solution of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0020] Figure 1 This is the metallographic structure diagram (250X) of the 700MPa high-strength weathering steel in Example 1 of the present application;

[0021] Figure 2 This is the inclusion map (100X) of the 700MPa high-strength weathering steel in Example 1 of the present application. DETAILED DESCRIPTION

[0022] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the scheme of the present application will be further described below. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0023] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present application may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present application, rather than all of the embodiments.

[0024] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0025] If not otherwise specified, all embodiments and optional embodiments of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0026] Unless otherwise specified, all technical features and optional technical features of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0027] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0028] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0029] Unless otherwise specified, this application adopts conventional test methods or test methods recommended by the instrument.

[0030] A 700MPa grade high strength weathering steel

[0031] A 700MPa grade high-strength weathering steel, whose chemical composition, measured by mass percentage, includes: C: 0.03%-0.12%, Si: 0.05%-0.40%, Mn: 1.1%-1.8%, P: ≤0.002%, S: ≤0.0050%, Cr: 0.5%-1.5%, Cu: 0.30%-0.60%, Al: 0.50%-1.30%, Ti: 0.10%-0.15%, Nb≤0.05%, Ni≤0.50%, N: ≤0.0060%, and the balance is Fe and other inevitable impurities.

[0032] C: In this application, the C control range is 0.03% to 0.12%. C is an effective strengthening element in steel, but the Cr content in weathering steel is relatively high. When the carbon content is high, it is very easy to form a martensitic structure in the steel, which sharply reduces the plastic toughness of the steel. In addition, the martensite causes the tensile strength of the steel to be very high, which is easy to cause forming cracks. C can also form nano-scale precipitation phases with micro-alloy elements such as Nb and Ti in steel to exert precipitation strengthening effects. Therefore, in order to make full use of the strengthening effect of C and avoid the formation of a large amount of martensite in the organization to affect the organization, the C component of this application is controlled at 0.03% to 0.12%. Optionally, the mass percentage of C is independently selected from any value of 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, or any range value between the two.

[0033] Si: A commonly used deoxidizing element. Si exists as a solid solution in ferrite and austenite to increase the strength of steel and reduce the overall corrosion rate of steel. However, during the hot rolling process, a higher Si element tends to produce obvious red iron oxide scale defects on the surface of the strip that are difficult to eliminate by descaling, affecting the surface quality of the strip. Therefore, this application designs the Si content to be 0.05% to 0.40%. Optionally, the mass percentage of Si is independently selected from any value among 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.40%, or any range between two thereof.

[0034] Mn: Mn is an important strengthening and toughening element, and is an austenite stabilizing element. It can expand the austenite region in the iron-carbon phase diagram, promote medium-temperature microstructure transformation, and is beneficial to microstructure refinement and improving the strength and low-temperature toughness of steel. However, when Mn is too high, serious segregation occurs in the steel, which deteriorates the low-temperature toughness of the steel. Therefore, the present application designs a Mn content of 1.1% to 1.8%. Optionally, the mass percentage of Mn is independently selected from any value of 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, or any range between the two.

[0035] P: P is a harmful impurity element in steel, which is easy to segregate at the thickness center during continuous casting of steel billets. At the same time, P is easy to segregate at the grain boundaries, reducing the grain boundary binding energy, thereby reducing the toughness and plasticity of the steel. However, it is often used as an added corrosion-resistant element in traditional atmospheric corrosion-resistant steels, which can promote the formation of a protective rust layer on the surface and effectively improve the atmospheric corrosion resistance of the steel. In this application, Cr and Al are used to improve the atmospheric corrosion resistance of steel. In order to minimize the influence of P on the toughness and plasticity of high-strength steel, the P content is designed to be ≤0.002% in this application. Optionally, the mass percentage of P is independently selected from any value of 0.0010%, 0.0011%, 0.0012%, 0.0013%, 0.0014%, 0.0015%, 0.0016%, 0.0017%, 0.0018%, 0.0019%, 0.0020%, or any range value between the two.

[0036] S: sulfur has adverse effects on the corrosion resistance, cold forming performance, low temperature toughness, welding performance and other aspects of steel; therefore, the value range of S in this application is set to S≤0.0050%. Optionally, the mass percentage of S is independently selected from any value of 0.0010%, 0.0020%, 0.0030%, 0.0040%, 0.0050% or any range between the two.

[0037] Cr: When Cr, Cu, and Al are added at the same time, a relatively stable and dense rust layer will be formed to improve the corrosion resistance of weathering steel. Increasing the Cr content is conducive to the refinement of α-FeOOH, but in areas with high Cl- content, adding Cr elements is considered harmful. In addition, a higher Cr content can also allow the steel to form bainite or martensite at a lower cooling rate, significantly improving the tensile strength, but an excessively high proportion of bainite or martensite will reduce the processing and forming properties of the steel. Therefore, the present application designs the Cr content to be 0.5% to 1.5%. Optionally, the mass percentage of Cr is independently selected from any value of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any range between two values.

[0038] Cu: Copper. The enrichment of Cu in the rust layer can improve the protective performance of the rust layer, thereby improving the corrosion resistance of the steel. The Cu content in this application is 0.30% to 0.60%. Optionally, the mass percentage of Cu is independently selected from any value among 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.40%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45%, 0.46%, 0.47%, 0.48%, 0.49%, 0.50%, 0.51%, 0.52%, 0.53%, 0.54%, 0.55%, 0.56%, 0.57%, 0.58%, 0.59%, 0.60%, or any range value between two thereof.

[0039] Al: Al is a commonly used deoxidizing element in steel, which refines the grains and improves the toughness of steel. It also promotes the production of ferrite, inhibits pearlite transformation, and is beneficial to the transformation of ferrite-bainite bidirectional structure. At the same time, Al can react with Cr and Cu to form a relatively stable and dense rust layer to improve the corrosion resistance of weathering steel. Excessive Al content will increase the sensitivity to hot cracks during welding and reduce the quality of the welded joint. Therefore, the Al content is designed in this application to be 0.50% to 1.30%. Optionally, the mass percentage of Al is independently selected from 0.50%, 0.51%, 0.52%, 0.53%, 0.54%, 0.55%, 0.56%, 0.57%, 0.58%, 0.59%, 0.60%, 0.61%, 0.62%, 0.63%, 0.64%, 0.65%, 0.66%, 0.67%, 0.68 %, 0.69%, 0.70%, 0.71%, 0.72%, 0.73%, 0.74%, 0.75%, 0.76%, 0.77%, 0.78%, 0.79%, 0.80%, 0.81%, 0.82%, 0.83%, 0.84%, 0.85%, 0.86%, 0.87%, 0.88%, 0.89%, 0. 90%, 0.91%, 0.92%, 0.93%, 0.94%, 0.95%, 0.96%, 0.97%, 0.98%, 0.99%, 1.00%, 1.01%, 1.02%, 1.03%, 1.04%, 1.05%, 1.06%, 1.07%, 1.08%, 1.09%, 1.10%, 1.11%, Any value among 1.12%, 1.13%, 1.14%, 1.15%, 1.16%, 1.17%, 1.18%, 1.19%, 1.20%, 1.21%, 1.22%, 1.23%, 1.24%, 1.25%, 1.26%, 1.27%, 1.28%, 1.29%, 1.30%, or any range between any two of them.

[0040] Ti: a strong carbonitride-forming element, which improves the material's resistance to intergranular corrosion, and can also precipitate in the form of nano-sized TiC or Ti(C,N) second phase particles, significantly improving the material's strength through precipitation strengthening. The content of Ti in this application is 0.10% to 0.15%. Optionally, the mass percentage of Ti is independently selected from any value among 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, or any range between the two.

[0041] Nb: A strong carbonitride-forming element that can precipitate in the form of nano-scale NbC or Nb(C, N) second phase particles, significantly improving the toughness of the material through precipitation strengthening. Therefore, in the present application, Nb≤0.05%. Optionally, the mass percentage of Nb is independently selected from 0.010%, 0.011%, 0.012%, 0.013%, 0.014%, 0.015%, 0.016%, 0.017%, 0.018%, 0.019%, 0.020%, 0.021%, 0.022%, 0.023%, 0.024%, 0.025%, 0.026%, 0.027%, 0.028%, 0.029%, 0. 0.030%, 0.031%, 0.032%, 0.033%, 0.034%, 0.035%, 0.036%, 0.037%, 0.038%, 0.039%, 0.040%, 0.041%, 0.042%, 0.043%, 0.044%, 0.045%, 0.046%, 0.047%, 0.048%, 0.049%, 0.050%, or any range between any two of them.

[0042] Ni: Ni can inhibit the precipitation of Cu at the grain boundary during heating. Generally speaking, a Ni / Cu ratio of 1 / 3 to 3 / 4 can well inhibit the occurrence of Cu crack defects. Therefore, in the present application, Ni≤0.50%. Optionally, the mass percentage of Ni is independently selected from 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0. Any value among 30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.40%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45%, 0.46%, 0.47%, 0.48%, 0.49%, 0.50%, or any range between two of them.

[0043] N: N is a harmful element in steel, which consumes Ti and forms inclusions. The N content needs to be controlled at a low level. The present application designs N≤0.0060%. Optionally, the mass percentage of N is independently selected from any value of 0.0010%, 0.0020%, 0.0030%, 0.0040%, 0.0050%, 0.0060%, or any range between the two.

[0044] In some embodiments, the metallographic structure of 700 MPa grade high strength weathering steel includes ferrite and bainite. Within this range, weathering steel with a low yield strength ratio can be obtained.

[0045] Ferrite is an interstitial solid solution of carbon dissolved in α-Fe, usually represented by the symbol F. It has a body-centered cubic lattice and its carbon solubility is very low. It can only dissolve 0.0008% of carbon at room temperature, and the maximum carbon solubility is 0.02% at 727°C.

[0046] When austenite is supercooled to a temperature range between below the pearlite transformation temperature and above the martensite transformation temperature, a transformation will occur that is coordinated by shear phase transformation and short-range diffusion, and the transformation product is called bainite or bainite. Bainite in steel is a mixed structure of ferrite and carbide.

[0047] In some embodiments, the thickness of the 700 MPa grade high strength weathering steel is less than or equal to 16 mm.

[0048] In some embodiments, the yield strength of 700MPa grade high strength weathering steel is greater than or equal to 700Mpa.

[0049] In some embodiments, the tensile strength of 700MPa grade high strength weathering steel is greater than or equal to 750MPa.

[0050] In some embodiments, the elongation A of the 700 MPa grade high strength weathering steel is greater than 14%.

[0051] In some embodiments, the corrosion rate of 700MPa high-strength weathering steel is less than or equal to 30% relative to Q355B, wherein Q355B refers to the grade of low-alloy high-strength steel plate, Q refers to yield strength, 335 refers to the value of yield strength in MPa, and B refers to quality grade.

[0052] Preparation method

[0053] A preparation method of 700MPa high-strength weathering steel comprises: S1, smelting and casting molten iron of preset composition to obtain slab; S2, hot rolling the slab to obtain 700MPa high-strength weathering steel; wherein the preset composition comprises C: 0.03%-0.12%, Si: 0.05%-0.40%, Mn: 1.1%-1.8%, P: ≤0.002%, S: ≤0.0050%, Cr: 0.5%-1.5%, Cu: 0.30%-0.60%, Al: 0.50%-1.30%, Ti: 0.10%-0.15%, Nb≤0.05%, Ni≤0.50%, N: ≤0.0060%, and the remainder is Fe and other inevitable impurities; the hot rolling treatment comprises S2.1 heating process, S2.2 rolling process, S2.3 cooling process and S2.4 slow cooling process in sequence.

[0054] In this application, through special composition and rolling process, based on metal deformation and phase transformation, solid solution strengthening, precipitation strengthening, dislocation strengthening and fine grain strengthening are completed under specified deformation and temperature conditions to obtain a steel plate with a thickness of ≤16mm, a yield strength greater than or equal to 700MPa, a tensile strength greater than or equal to 750MPa, an elongation A greater than 14%, suitable for C3-C5 environment, and a high-strength weathering steel with a corrosion rate ≤30% relative to Q355B.

[0055] In some embodiments, the thickness of the slab is 50-70 mm. Optionally, the thickness of the slab is independently selected from any value among 50 mm, 51 mm, 52 mm, 53 mm, 54 mm, 55 mm, 56 mm, 57 mm, 58 mm, 59 mm, 60 mm, 61 mm, 62 mm, 63 mm, 64 mm, 65 mm, 66 mm, 67 mm, 68 mm, 69 mm, 70 mm, or any range value therebetween.

[0056] In some embodiments, step S2.1 includes: placing the slab in a heating furnace of a hot rolling line for heating to obtain a heat-treated slab; wherein the heating temperature is 1200-1270°C, the insulation time is 8-15min, the total slab time in the furnace is 10-40min, the furnace outlet temperature is 1190-1250°C, and the excess air coefficient of the heating atmosphere in the furnace is 1.1-1.5.

[0057] In some embodiments, step S2.2 includes: placing the heat-treated slab in a multi-stand continuous rolling mill for finish rolling to obtain a steel strip; wherein the descaling pressure at the finishing rolling entrance is greater than or equal to 18 MPa, the temperature at the finishing rolling entrance is 1000-1120°C, the last stand reduction rate is greater than or equal to 8%, and the finishing rolling final rolling temperature is 860-950°C.

[0058] In step S2.2, the multi-stand tandem rolling mill may be a 7-stand tandem rolling mill.

[0059] In step S2.2, when the strip thickness is less than 2.0 mm, the final rolling temperature is 910-940°C; when the strip thickness is 2.0-3.0 mm, the final rolling temperature is 900-930°C; when the strip thickness is 3.01-4.0 mm, the final rolling temperature is 890-927°C; when the strip thickness is greater than 4.0 mm, the final rolling temperature is 870-900°C.

[0060] In some embodiments, step S2.3 includes: subjecting the steel strip to laminar cooling to obtain 700MPa grade high-strength weathering steel; wherein the laminar cooling method includes ultra-fast cooling and front-stage concentrated cooling, the cooling rate of ultra-fast cooling is 80-200°C / s, and the outlet temperature of ultra-fast cooling is 700-780°C; the cooling rate of the front-stage concentrated cooling is greater than or equal to 20°C / s.

[0061] In this application, the ultra-fast cooling technology can use tilted nozzles to spray cooling water of a certain pressure onto the surface of the steel plate, so as to achieve full contact between the cooling water and the high-temperature steel plate, thereby improving the cooling speed and cooling uniformity. Front-end centralized cooling refers to the front-end water spray cooling of laminar cooling after the strip exits the finishing mill.

[0062] In step S2.3, ultra-fast cooling can be performed first, and then front-end concentrated cooling can be performed. Ultra-fast cooling is used to quickly cool the strip to inhibit the transformation of austenite structure to bainite; after ultra-fast cooling, the strip enters the ferrite transformation temperature range, and austenite is transformed to ferrite by air cooling for a period of time. 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 be required to be reduced, which will seriously affect the rolling stability of thin-gauge strip steel; after the strip is air-cooled, the front-end concentrated cooling is performed, and the cooling rate of the front-end concentrated cooling is greater than or equal to 20℃ / s. After the strip is cooled to 540-620℃, it is air-cooled to 500-600℃ and then coiled, so that the untransformed austenite is transformed into bainite structure, so that the strip finally forms a two-phase structure of ferrite + bainite.

[0063] In the coiling process, the head and tail of the strip are coiled in a U-shaped temperature method. Because the coiling temperature of the strip is 500-600°C and the cooling speed of the head and tail of the strip is fast, it is not conducive to the second phase precipitation strengthening of TiC. Therefore, the coiling temperature at 0-20m away from the head and tail of the strip is 580-620°C, and the insulation box of the steel coil offline is slowly cooled to below 250°C, which promotes the precipitation strengthening of TiC and improves the performance stability of the entire coil.

[0064] In step S2.4, after the steel coil is off the production line, it can be placed in an insulation box for centralized stack cooling and slowly cooled to a temperature below 350°C.

[0065] application

[0066] The above-mentioned 700MPa grade high-strength weathering steel or the 700MPa grade high-strength weathering steel obtained by the above-mentioned preparation method is used in railway freight cars, power towers and marine photovoltaic structures under C3-C5 environment.

[0067] In the ISO12944-2-2017 standard, six classifications are made for atmospheric corrosion environments: C1 very low corrosiveness, C2 low corrosiveness, C3 medium corrosiveness, C4 high corrosiveness, C5 very high corrosiveness, and CX extreme corrosiveness.

[0068] In this application, typical environments for C5: industrial areas and coastal areas with high humidity and severe weather, buildings and areas where condensation and high pollution continuously occur and exist.

[0069] Example 1-2

[0070] The molten iron is placed in a KR furnace for desulfurization, then placed in a 100-ton converter for smelting, and then argon blowing in a ladle, refined in an LF furnace, and continuously cast into a 60mm slab. The slab is placed in a tunnel furnace for heating, and then thermomechanically controlled rolling and controlled cooling are performed by a 7-stand continuous rolling unit to obtain hot-rolled coils with thickness specifications of 2mm and 6mm.

[0071] Among them, the composition of the weathering steel coils in Example 1 and Example 2 is shown in Table 1, the heating process parameters are shown in Table 2, the controlled rolling and controlled cooling process parameters are shown in Table 3, the mechanical properties are shown in Table 4, and the corrosion resistance is shown in Table 5. ACC controlled cooling is used to cool the steel strip after the rolling process.

[0072] Table 1. Chemical compositions in Examples and Comparative Examples

[0073] element C Si Mn P S Cu Example 1 0.055 0.26 1.30 0.0012 ≤0.003 0.41 Example 2 0.053 0.225 1.27 0.0010 ≤0.003 0.40 Comparative Example 1 0.054 0.24 1.28 0.0010 ≤0.003 0.40 element Cr Ni Ti N Al Nb Example 1 1.20 0.32 0.13 0.048 1.02 0.025 Example 2 1.16 0.31 0.12 0.045 1.00 0.028 Comparative Example 1 1.17 0.31 0.13 0.046 0.03 0.026

[0074] Table 2 Heating process in the embodiments and comparative examples

[0075]

[0076] Table 3 Rolling process in the embodiments and comparative examples

[0077]

[0078] Table 4 Mechanical properties of the embodiments and comparative examples

[0079]

[0080] Note: The impact value is 5mm*10mm*55mm and is not converted.

[0081] Table 5 Corrosion resistance in examples and comparative examples

[0082] serial number Relative corrosion resistance Example 1 28％ Example 2 27％ Comparative Example 1 52％

[0083] The test methods for mechanical properties and corrosion resistance in Table 4 and Table 5 are as follows:

[0084] Corrosion resistance: According to TB / T2375-93, the relative corrosion rate is compared with that of ordinary carbon steel Q355B after 72h immersion corrosion.

[0085] The above is only a specific implementation of the present application. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working processes of the systems, modules and units described above can refer to the corresponding processes in the aforementioned method embodiments, and will not be repeated here. It should be understood that the protection scope of the present application is not limited to this. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in this application, and these modifications or replacements should be included in the protection scope of this application.

Claims

1. A 700MPa grade high-strength weathering steel, characterized in that: Measured by mass percentage, its chemical composition includes: C: 0.03%~0.12%, Si: 0.05%~0.40%, Mn: 1.1%~1.8%, P: ≤0.002%, S: ≤0.0050%, Cr: 0.5%~1.5%, Cu: 0.30%~0.60%, Al: 0.50%~1.30%, Ti: 0.10%~0.15%, Nb≤0.05%, Ni≤0.50%, N: ≤0.0060%, the balance is Fe and other inevitable impurities.

2. The 700MPa grade high strength weathering steel according to claim 1, characterized in that: The metallographic structure of the 700MPa grade high-strength weathering steel includes ferrite and bainite.

3. The 700MPa grade high strength weathering steel according to claim 1, characterized in that: The thickness of the 700MPa grade high-strength weathering steel is less than or equal to 16mm.

4. The 700MPa grade high strength weathering steel according to claim 1, characterized in that: The yield strength of the 700MPa grade high strength weathering steel is greater than or equal to 700Mpa; and / or, The tensile strength of the 700MPa grade high-strength weathering steel is greater than or equal to 750Mpa; and / or, The elongation A of the 700MPa grade high-strength weathering steel is greater than 14%; and / or, The corrosion rate of the 700MPa grade high strength weathering steel is less than or equal to 30% relative to that of Q355B.

5. A method for preparing 700MPa grade high-strength weathering steel, characterized in that: include: The molten iron with a preset composition is smelted and cast to obtain a slab; The slab is hot-rolled to obtain 700MPa grade high-strength weathering steel; Wherein, the preset composition includes C: 0.03%-0.12%, Si: 0.05%-0.40%, Mn: 1.1%-1.8%, P: ≤0.002%, S: ≤0.0050%, Cr: 0.5%-1.5%, Cu: 0.30%-0.60%, Al: 0.50%-1.30%, Ti: 0.10%-0.15%, Nb≤0.05%, Ni≤0.50%, N: ≤0.0060%, and the balance is Fe and other inevitable impurities; The hot rolling process includes a heating process, a rolling process, a cooling process and a slow cooling process in sequence.

6. The preparation method according to claim 5, characterized in that: The thickness of the slab is 50-70 mm.

7. The preparation method according to claim 5, characterized in that: The heating process includes: The slab is placed in a heating furnace of a hot rolling line for heating to obtain a heat-treated slab; Among them, the heating temperature is 1200-1270°C, the holding time is 8-15min, the total slab time in the furnace is 10-40min, the furnace outlet temperature is 1190-1250°C, and the excess air coefficient of the heating atmosphere in the furnace is 1.1-1.

5.

8. The preparation method according to claim 5, characterized in that: The rolling process includes: Placing the heat-treated slab in a multi-stand continuous rolling mill for finish rolling to obtain a steel strip; Among them, the descaling pressure at the finishing rolling entrance is greater than or equal to 18MPa, the temperature at the finishing rolling entrance is 1000-1120°C, the final stand reduction rate is greater than or equal to 8%, and the finishing rolling final rolling temperature is 860-950°C.

9. The preparation method according to claim 5, characterized in that: The cooling process includes: The strip steel is subjected to laminar cooling treatment to obtain the 700MPa grade high-strength weathering steel; Among them, the laminar cooling method includes ultra-fast cooling and front-stage concentrated cooling. The cooling rate of the ultra-fast cooling is 80-200°C / s, and the outlet temperature of the ultra-fast cooling is 700-780°C; the cooling rate of the front-stage concentrated cooling is greater than or equal to 20°C / s.

10. Application of the 700 MPa high-strength weathering steel according to any one of claims 1 to 4 or the 700 MPa high-strength weathering steel obtained by the preparation method according to any one of claims 5 to 9 in railway freight cars, power towers and marine photovoltaic structures under C3-C5 environment.

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