Short-process weathering steel and preparation method

Abstract

Short-process weathering steel. The short-process weathering steel comprises the following chemical components in percentage by mass: C: 0.03%-0.06%, Si: 0.40%-0.80%, Mn: 0.20%-0.6%, Cr: 1.05%-1.49%, Cu: 0.10%-0.60%, P: 0.07%-0.15%, S≤0.005%, Ti: 0.10%-0.25%, N≤0.006%, Ca: 0.0010%-0.0025%, and the balance being Fe and inevitable impurities.

Description

A short-process weathering steel and a preparation method thereof Cross-reference to Related Applications

[0001] This application claims priority to Chinese Patent Application No. 202410856271.0, filed on June 28, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present disclosure relates to the technical field of steel production, and in particular, to a short-process weathering steel and a preparation method thereof. BACKGROUND

[0003] Weathering steel has been widely used in the production of steel structures such as containers, railway vehicles, and bridges that require corrosion resistance in outdoor applications. Its production and application have a history of several decades. In recent years, with the increasing demand for green, low-carbon, and environmental protection, the application scenarios of weathering steel are also expanding. In the application scenarios of photovoltaic supports and outdoor structures, people can take advantage of the corrosion resistance of weathering steel to replace some surface corrosion protection processes of steel, such as pre-galvanizing, zinc-aluminum-magnesium, and post-galvanizing, to achieve the naked use of steel, thereby reducing energy consumption and pollution problems caused by coating processes, and reducing maintenance costs for later corrosion maintenance and renovation. Short-process manufacturing is increasingly attracting attention because of its simple, efficient, and energy-saving manufacturing process, and the products manufactured have high dimensional accuracy and high performance uniformity. According to the difference in production line layout, short-process manufacturing can be divided into CSP (Compact Strip Production), ESP (Endless Strip Production), and MCCR (Multi-mode Continuous Casting & Rolling plant), etc. However, in essence, the essence of short-process manufacturing is continuous casting and rolling.

[0004] In related technologies, current weathering steel is mainly used for railway vehicles, containers, and bridges, and the product service life is ≤10 years. Although some weathering steels consider high-strength design, their weather resistance requirements and design are still at a general level of weathering performance, which limits the application scenarios of weathering steel. Therefore, the corrosion resistance of short-process weathering steel cannot meet the application scenarios of longer product service life, which is a technical problem that needs to be solved at present. SUMMARY

[0005] By utilizing one or more embodiments of the present disclosure, a short-process weathering steel and a preparation method thereof are provided to solve the problem that the corrosion resistance of short-process weathering steel cannot meet the application scenarios of longer product service life.

[0006] According to a first aspect of the present disclosure, a short-process weathering steel is provided, the chemical composition of the short-process weathering steel includes, in mass fraction: C: 0.03% to 0.06%, Si: 0.40% to 0.80%, Mn: 0.20% to 0.6%, Cr: 1.05% to 1.49%, Cu: 0.10% to 0.60%, P: 0.07% to 0.15%, S≤0.005%, Ti: 0.10% to 0.25%, N≤0.006%, Ca: 0.0010% to 0.0025%, and the balance being Fe and inevitable impurities.

[0007] According to a second aspect of the present disclosure, a preparation method of the short-process weathering steel according to any one of the embodiments of the first aspect is provided, including: continuously casting molten steel having the chemical composition of the short-process weathering steel to obtain a slab; rapidly heating and finish rolling the slab to obtain a hot-rolled steel; and stage cooling and coiling the hot-rolled steel to obtain the short-process weathering steel. BRIEF DESCRIPTION OF DRAWINGS

[0008] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present disclosure and serve to explain the principles of the present disclosure together with the specification.

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the related art, the accompanying drawings needed to be used in the embodiments or the related art description will be briefly introduced here. Obviously, for those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

[0010] FIG. 1 shows a flowchart of a preparation method of a short-process weathering steel according to some embodiments of the present disclosure;

[0011] FIG. 2 shows a metallographic structure diagram of a short-process weathering steel prepared by a preparation method of a short-process weathering steel disclosed in Embodiment 2 of the present disclosure; and

[0012] FIG. 3 shows a metallographic structure diagram of a short-process weathering steel prepared by a preparation method of a short-process weathering steel disclosed in Embodiment 6 of the present disclosure. DETAILED DESCRIPTION

[0013] In order to make the objects, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be described clearly and completely below with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only some of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skill in the art without any creative effort fall within the scope of protection of the present disclosure.

[0014] Various embodiments of the present disclosure can exist in a range of forms; it should be understood that the description in a range form is merely for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present disclosure; therefore, it should be considered that the described range has specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the described range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in the present disclosure, it refers to any cited number (fraction or integer) within the indicated range.

[0015] In addition, in the description of the present disclosure, the terms "include", "contain" and the like mean "include but not limited to". In the present disclosure, the relationship terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. In the present disclosure, "and / or" describes the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can represent the cases of A alone, A and B together, and B alone. Wherein A and B can be singular or plural. In the present disclosure, "one or more" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of the items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0016] Unless otherwise specifically stated, the various raw materials, reagents, instruments and equipment, etc. used in the present disclosure can be purchased from the market or can be prepared by existing methods.

[0017] A short-process weathering steel according to some embodiments of the present disclosure has a chemical composition including, in mass fraction, C: 0.03% to 0.06%, Si: 0.40% to 0.80%, Mn: 0.20% to 0.6%, Cr: 1.05% to 1.49%, Cu: 0.10% to 0.60%, P: 0.07% to 0.15%, S≤0.005%, Ti: 0.10% to 0.25%, N≤0.006%, Ca: 0.0010% to 0.0025%, and the balance being Fe and inevitable impurities.

[0018] The reasons for limiting the chemical composition of the short-process weathering steel according to some embodiments of the present disclosure are as follows:

[0019] C is an effective strengthening element in steel, which can form nanoscale second-phase precipitated particles with micro-alloy elements such as Ti and Nb, in addition to solid solution strengthening, to play the role of precipitate strengthening and refining the structure. Meanwhile, in the chemical composition system of high-Cr steel, C can be converted into bainite or martensite hard phase at a lower critical cooling rate, which can also significantly improve the tensile strength of the steel. However, excessive C can form more carbides in the steel, which can reduce the toughness and formability of the steel, and also can reduce the corrosion resistance of the steel due to the galvanic effect, and also can reduce the welding performance of the steel. Meanwhile, considering that the C content in the steel can affect the peritectic reaction occurring in the high-speed continuous casting process, which has a certain influence on the surface quality of the casting blank, in order to ensure the surface quality of the casting blank, the C content in the steel needs to be strictly controlled. Therefore, in the chemical composition of the short-process weathering steel according to some embodiments of the present disclosure, the designed mass fraction of C can be 0.03% to 0.06%. For example, the mass fraction of C can be 0.03%, 0.04%, 0.045%, 0.05%, and 0.06%, etc.

[0020] Si is a commonly used deoxidizing element in steel, which also has a solid solution strengthening effect on the steel and can improve the corrosion resistance of the steel, but excessive Si content can reduce the welding performance of the steel and cause deterioration of the toughness of the weld heat-affected zone. Therefore, in the chemical composition of the short-process weathering steel according to some embodiments of the present disclosure, the designed mass fraction of Si can be 0.40% to 0.80%. For example, the mass fraction of Si can be 0.40%, 0.50%, 0.60%, 0.70%, and 0.80%, etc.

[0021] Mn is an important toughening element in steel, which has the effect of solid solution strengthening, and can also reduce the transformation temperature of supercooled austenite, reduce the ferrite phase transformation temperature, benefit the refinement of the structure, and improve the strength and toughness of the steel. However, excessive Mn content will inhibit the transformation of ferrite, promote the transformation of the structure to bainite, and reduce the plasticity and cold forming performance of the steel. Therefore, in the chemical composition of the short process weathering steel of some embodiments of the present disclosure, the designed mass fraction of Mn can be 0.2% to 0.6%. For example, the mass fraction of Mn can be 0.2%, 0.3%, 0.4%, 0.5%, and 0.6%, etc.

[0022] Cr is an important element for improving the weather resistance of steel. On the one hand, Cr can increase the corrosion potential of the matrix in the steel, reduce the corrosion rate by increasing the electrochemical impedance; more importantly, Cr can promote the formation of a dense rust layer on the surface of the steel to physically block the corrosion medium, and change the corrosion environment of the matrix in the steel. Therefore, in the chemical composition of the short process weathering steel of some embodiments of the present disclosure, the designed mass fraction of Cr can be 1.05% to 1.49%. For example, the mass fraction of Cr can be 1.05%, 1.10%, 1.15%, 1.20%, 1.30%, 1.40%, 1.45%, and 1.49%, etc.

[0023] Cu is also one of the important elements for improving the weather resistance (corrosion resistance) of steel, and the effect is more obvious when added together with Cr. Cu can promote the formation of a dense rust layer on the surface of the steel, and the addition of 0.10% or more of Cu can significantly improve the corrosion resistance of the steel. However, Cu is a metal with a relatively low melting point. When the steel is heated in the form of a strip, due to the problem of selective oxidation, the copper-rich phase with a relatively low melting point is easy to accumulate on the surface of the matrix in the steel, and in the process of forming hot-rolled steel after heating the strip, the copper-rich phase with a relatively low melting point is also easy to form copper brittle network cracks and skin defects on the surface of the strip, which deteriorates the surface quality of the formed hot-rolled steel. That is, if the content of Cu in the steel is too high, more copper-rich phases with a relatively low melting point will be formed in the steel; and more copper-rich phases with a relatively low melting point will deteriorate the surface quality of the hot-rolled steel.

[0024] In addition, since Cu is also a valuable element, excessive Cu content in the steel will increase the cost of the steel. Therefore, in the chemical composition of the short process weathering steel of some embodiments of the present disclosure, the designed mass fraction of Cu can be 0.10% to 0.60%, in order to avoid the defects of surface quality deterioration or cost increase caused by excessive Cu in the short process weathering steel. For example, the mass fraction of Cu can be 0.10%, 0.20%, 0.30%, 0.40%, 0.50%, and 0.60%, etc.

[0025] P can promote the formation of a protective rust layer on the surface of the steel material, effectively improving the corrosion resistance of the steel material, but P is also a harmful impurity element in steel, which is easy to segregate in the center of the thickness during the continuous casting of the steel billet. Therefore, in the chemical composition of the short process weathering steel of some embodiments of the present disclosure, the mass fraction of P is designed to be 0.07% to 0.15%. For example, the mass fraction of P can be 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.14% and 0.15%, etc.

[0026] S is a common harmful impurity element in steel, which has adverse effects on weather resistance, low temperature toughness, welding performance and cold forming performance, etc. Therefore, in the chemical composition of the short process weathering steel of some embodiments of the present disclosure, the content of S is required to be ≤0.005% or less. For example, the mass fraction of S can be 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, etc.

[0027] Ti is a strong carbonitride forming element, which can precipitate in the form of extremely fine TiC or Ti(C, N) second phase particles, and can significantly improve the strength of the steel material. Compared with Nb and other micro-alloy elements, Ti is relatively inexpensive, so in the chemical composition of the short process weathering steel of some embodiments of the present disclosure, Ti can be added as an important strengthening element. At the same time, the precipitation of TiC can significantly reduce the free C to form larger carbides or pearlite, thereby reducing the galvanic effect of heterogeneous phases during corrosion, improving the intergranular corrosion resistance of the steel material, and making the corrosion on the surface of the steel material more inclined to uniform corrosion. Therefore, a dense rust layer can be formed on the surface of the steel material by uniform corrosion and the quality of the rust layer can be improved to physically block the corrosion medium and change the corrosion environment of the position where the matrix in the steel material is located. That is, Ti can improve the strength of the steel material while also improving the corrosion resistance of the steel material. However, with the increase of the addition amount of Ti, the precipitation strengthening effect of Ti will gradually weaken, and will begin to significantly affect the low temperature toughness of the steel material. Therefore, in the chemical composition of the short process weathering steel of some embodiments of the present disclosure, the mass fraction of Ti is designed to be 0.10% to 0.25%. For example, the mass fraction of Ti can be 0.10%, 0.12%, 0.15%, 0.18%, 0.20%, 0.22% and 0.25%, etc.

[0028] N is an impurity element in the steel material, N can combine with Ti to form TiN inclusions with larger size when the steel material is formed in molten steel, which can reduce the effective content of Ti on one hand, and the TiN inclusions can also significantly damage the toughness of the steel material on the other hand, so the content of N should be reduced as much as possible, and therefore the mass fraction of N in the chemical composition of the short process weathering steel in some embodiments of the present disclosure can be required to be ≤0.006%. For example, the mass fraction of N can be 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, and 0.006%, etc.

[0029] Ca can form CaS in a spherical dispersed distribution with S, reduce the generation of sulfide inclusions such as MnS and FeS in irregular shapes, that is, the addition of Ca can improve the distribution of sulfide inclusions in the steel material, so that the sulfide inclusions have better dispersibility and lower stress concentration effect. On the one hand, the spherical dispersed CaS reduces the enrichment opportunity of corrosion medium on the surface of the steel material, so that the corrosion of the steel material surface is more uniform, and the risk of pitting corrosion is reduced; at the same time, the distribution of sulfide inclusions is improved, and the local corrosion caused by the aggregation of inclusions is reduced; and then the uniform corrosion of the surface of the steel material is improved. On the other hand, the spherical CaS reduces the stress concentration, so that the steel material is less likely to crack when stressed, that is, the adverse effects of sulfide inclusions on the plasticity and toughness of the steel material are improved, and the overall toughness of the steel material is improved. Therefore, in the chemical composition of the short process weathering steel in some embodiments of the present disclosure, the mass fraction of Ca can be generally limited to 0.0005% to 0.0025%. For example, the mass fraction of Ca can be 0.0010%, 0.0012%, 0.0015%, 0.0018%, 0.0020%, and 0.0025%, etc.

[0030] In some embodiments, the chemical composition satisfies the following relationship: [C]+[Mn] / 6+[Cr] / 10+[Cu] / 5+[P] / 15≤0.50, wherein [C] represents the mass fraction of C before the numerical value, [Mn] represents the mass fraction of Mn before the numerical value, [Cr] represents the mass fraction of Cr before the numerical value, [Cu] represents the mass fraction of Cu before the numerical value, and [P] represents the mass fraction of P before the numerical value.

[0031] The positive effect of controlling the chemical composition of the short process weathering steel to satisfy [C]+[Mn] / 6+[Cr] / 10+[Cu] / 5+[P] / 15≤0.50 is that, in the manufacturing process of the short process weathering steel, the influence of the peritectic reaction occurring in the high speed continuous casting process on the surface quality of the casting blank in the manufacturing process can be considered, while the strengthening effect and corrosion resistance of C, Mn and Cr on the steel can be fully utilized. Mn and Cr both have the effect of improving the hardenability of the short process weathering steel, so that the short process weathering steel can form bainite or martensite at a lower critical cooling rate, thereby making the short process weathering steel obtain higher strength and lower yield ratio. However, too high Mn or Cr content will cause Mn or Cr to enter the peritectic zone, which will cause the surface shrinkage of the blank shell in the short process high speed continuous casting process, form surface crack defects, and even cause blank shell cracking to cause a leakage accident. Exemplarily, the value of [C]+[Mn] / 6+[Cr] / 10+[Cu] / 5+[P] / 15 can be 0.25, 0.28, 0.30, 0.35, 0.38, 0.40, 0.45 and 0.50, etc.

[0032] In some embodiments, the chemical composition of the short process weathering steel also satisfies the following relationship: I = 26.01[Cu]+1.20[Cr]+1.49[Si]+17.28[P]-33.29[Cu] 2 ≥8, wherein I represents the weathering resistance index, [Cu] represents the mass fraction % of Cu in front of the numerical value, [Cr] represents the mass fraction % of Cr in front of the numerical value, [Si] represents the mass fraction % of Si in front of the numerical value, and [P] represents the mass fraction % of P in front of the numerical value.

[0033] Controlling the chemical composition of the short process weathering steel to satisfy I = 26.01[Cu]+1.20[Cr]+1.49[Si]+17.28[P]-33.29[Cu] 2Positive effect ≥ 8: The weather resistance index formula is an index used to evaluate the weather resistance of steel under different environmental conditions, which can predict the durability of steel exposed to natural environment for a long time, and provide a basis for the selection and engineering design of steel. In some embodiments of the present disclosure, by reasonably designing the mass fraction of Cu, Cr, Si and P in the chemical composition of the short-process weathering steel, the weather resistance of the short-process weathering steel can be improved; Cu is one of the important corrosion resistance elements, and the effect is more obvious when Cu and Cr are added together; Si is a commonly used deoxidizing element in steel, which also has a solid solution strengthening effect on steel and can improve the corrosion resistance of steel. At the same time, the high mass fraction of P and Cr in the chemical composition of the short-process weathering steel can promote the formation of uniform and dense rust layer on the steel, significantly improve the corrosion potential and electrochemical impedance, and interrupt the continuous corrosion of the matrix in the steel, so that the short-process weathering steel can obtain ultra-high corrosion resistance. For example, the value of I can be 8, 8.05, 8.10, 8.20, 8.30, 8.40, 8.50, etc.

[0034] In some embodiments, the metallographic structure of the short-process weathering steel includes, in volume fraction: ferrite: 70% to 90%, martensite-austenite island: 5% to 25%, and the balance is pearlite or carbide; wherein, fine Ti(C, N) precipitates are dispersedly distributed on the ferrite matrix in the steel.

[0035] In some embodiments of the present disclosure, by stage cooling, a short-process weathering steel with ferrite and martensite-austenite island as the main metallographic structure can be obtained, realizing a lower yield ratio of the short-process weathering steel, so that the short-process weathering steel obtains higher forming performance. For example, the volume fraction of ferrite can be 70%, 72%, 75%, 80%, 85%, 86%, 90%, etc., and the volume fraction of martensite-austenite island can be 5%, 8%, 10%, 15%, 20%, 22%, 25%, etc.

[0036] In some embodiments, the short-process weathering steel satisfies at least one of the following performances: relative corrosion rate ≤ 30% compared with structural steel Q355B, corrosion depth ≤ 0.1 mm in 25 years, yield strength ≥ 620 MPa, tensile strength ≥ 750 MPa, yield ratio ≤ 0.80, fracture elongation ≥ 18%, impact energy at -20°C ≥ 60 J, cold bending performance satisfies d = 1t, and 180° bending is qualified, wherein d is the bending diameter, and t is the thickness of the steel plate.

[0037] In some embodiments of the present disclosure, the use of high mass fraction of P and Cr in the chemical composition of the short-process weathering steel can promote the formation of a uniform and dense rust layer on the surface of the short-process weathering steel, significantly increase the corrosion potential and electrochemical impedance of the short-process weathering steel, and interrupt the continuous occurrence of corrosion, thereby obtaining a short-process weathering steel with ultra-high corrosion resistance, which has a relative corrosion rate of ≤30% compared to structural steel Q355B, and the weather resistance is more than three times that of structural steel Q355B; compared to ordinary weathering steel, the weather resistance of the short-process weathering steel is also more than doubled; the corrosion rate of the short-process weathering steel rapidly decays over time, and the corrosion depth in 25 years is ≤0.1 mm. The presence of a large amount of ferrite in the short-process weathering steel can make the short-process weathering steel have very high plasticity and low-temperature toughness, so that the short-process weathering steel has a fracture elongation of ≥18%, a -20°C impact energy of ≥60 J, and a yield strength of ≤0.8, so that the short-process weathering steel has good cold forming performance. There are also fine and dispersed Ti(C, N) precipitates on the ferrite matrix in the steel, which realize precipitation strengthening and make the short-process weathering steel have a high strength performance of a yield strength of ≥620 MPa and a tensile strength of ≥750 MPa.

[0038] FIG. 1 shows a flowchart of a preparation method of a short-process weathering steel according to some embodiments of the present disclosure.

[0039] Referring to FIG. 1, to obtain the above-mentioned microstructure and performance of the short-process weathering steel, the preparation method of the short-process weathering steel according to some embodiments of the present disclosure includes:

[0040] S1, continuously casting molten steel having the chemical composition of the short-process weathering steel to obtain a slab;

[0041] S2, rapidly heating and finish rolling the slab to obtain a hot-rolled steel; and

[0042] S3, stage cooling and coiling the hot-rolled steel to obtain the short-process weathering steel.

[0043] In some embodiments, the continuously casting molten steel having the chemical composition of the short-process weathering steel in step S1 to obtain a slab can be: casting molten steel having the chemical composition of the short-process weathering steel obtained by smelting and refining into a slab in a continuous casting machine at a casting speed of ≥3.8 m / min, and performing light reduction of the slab exiting the continuous casting machine at a light reduction rate of ≥20%, so as to obtain a slab that can be directly sent to a soaking furnace.

[0044] wherein the temperature of the molten steel is ≤ the liquidus temperature + 15℃; soft reduction refers to a process method of applying a small pressure to the casting blank during continuous casting. In some embodiments, the continuous casting in step S1 satisfies the following parameters: a casting speed ≥ 3.8 m / min, a superheat of the molten steel ≤ 15℃, and a soft reduction rate of the slab ≥ 20%.

[0045] In some embodiments, the rapid heating satisfies the following parameters: an entry temperature ≥ 900℃, a soaking time in the soaking furnace of 20 min to 30 min, and an exit temperature of 1200℃ to 1250℃.

[0046] In some embodiments of the present disclosure, the rapid heating process can be performed in a soaking furnace, and in the rapid heating process, a high-temperature fast heating process can be used to quickly pass through a sensitive temperature range and a low plasticity stage of the slab that causes copper embrittlement in order to reduce the copper embrittlement effect. For example, the entry temperature can be 900℃, 902℃, 904℃, 906℃, 908℃, 910℃, 912℃, and 915℃, etc., the soaking time in the furnace can be 20 min, 22 min, 24 min, 26 min, 28 min, and 30 min, etc., and the exit temperature can be 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, and 1250℃, etc.

[0047] In some embodiments, the cumulative deformation rate of the finish rolling is ≥ 94%, and the finish rolling temperature is 870℃ to 930℃.

[0048] In the above embodiments, the slab is subjected to finish rolling by a finish rolling mill to achieve a cumulative deformation rate of the finish rolling ≥ 94% by the finish rolling mill. Alternatively, the thickness of the slab entering the finish rolling mill can be 62 mm to 72 mm, and the thickness of the slab exiting the finish rolling mill can be 1.5 mm to 4 mm. That is, the thickness of the slab can be 62 mm to 72 mm, and the thickness of the hot-rolled steel obtained after the finish rolling of the slab can be 1.5 mm to 4 mm.

[0049] In some embodiments, the hot-rolled steel is subjected to stage cooling and coiling to obtain a short-process weathering steel, including: subjecting the hot-rolled steel to first-stage cooling, and after the hot-rolled steel reaches a final cooling temperature of the first-stage cooling, the hot-rolled steel is kept for a set time; the cooling rate of the first-stage cooling is ≥ 120℃ / s, the final cooling temperature of the first-stage cooling is 640℃ to 660℃, and the set time is 3 s to 5 s; and subjecting the hot-rolled steel kept for the set time to second-stage cooling, and after the hot-rolled steel reaches a final cooling temperature of the second-stage cooling, the hot-rolled steel is coiled to obtain the short-process weathering steel; the cooling rate of the second-stage cooling is ≥ 20℃ / s, the final cooling temperature of the second-stage cooling is 560℃ to 640℃, and the coiling temperature is 560℃ to 640℃.

[0050] In some embodiments of the present disclosure, by two-stage staged cooling, a short-process weathering steel with a microstructure mainly composed of ferrite and martensite islands can achieve a lower yield ratio, thereby obtaining a short-process weathering steel with high forming performance. For example, the cooling rate of the first stage cooling can be 120℃ / s, 130℃ / s, 140℃ / s, 150℃ / s, and 160℃ / s, etc., the final cooling temperature of the first stage cooling can be 640℃, 645℃, 650℃, 655℃, and 660℃, etc., the setting time can be 3s, 3.5s, 4s, 4.5s, and 5s, etc., the cooling rate of the second stage cooling can be ≥20℃ / s, 22℃ / s, 24℃ / s, 26℃ / s, 28℃ / s, 30℃ / s, and 32℃ / s, etc., and the final cooling temperature of the second stage cooling is the coiling temperature, which can be 560℃, 570℃, 580℃, 590℃, 620℃, and 640℃, etc.

[0051] The product prepared by the preparation method of the short-process weathering steel is the short-process weathering steel described above. The chemical composition and microstructure of the short-process weathering steel prepared by the preparation method of the short-process weathering steel can refer to the above embodiments. Since the preparation method of the short-process weathering steel adopts part or all of the technical solutions of the short-process weathering steel embodiments, it at least has all the beneficial effects brought by the technical solutions of the short-process weathering steel embodiments, which will not be repeated here.

[0052] The present disclosure will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present disclosure and not to limit the scope of the present disclosure. The experimental methods not specified in the following examples are generally determined according to the industry standards. If there is no corresponding industry standard, it is determined according to the general international standards, conventional conditions, or according to the conditions suggested by the manufacturer.

[0053] In the present disclosure, the molten iron is subjected to converter smelting and refining to prepare the molten steel of Examples 1-8 and Comparative Example 1 and to prepare short-process weathering steel. The chemical composition of the short-process weathering steel is shown in Table 1.

[0054] Table 1 Chemical composition of short-process weathering steel (wt%), the rest is Fe and unavoidable impurities

[0055] Based on the chemical composition of the short-process weathering steel described above, the preparation method of the short-process weathering steel according to some embodiments of the present disclosure includes:

[0056] S1, continuously casting the molten steel with the chemical composition of the short-process weathering steel to obtain a slab;

[0057] S2, rapidly heating and finish rolling the slab to obtain a hot-rolled steel; and,

[0058] S3, the hot-rolled steel is subjected to staged cooling and coiling to obtain the short-process weathering steel. The process parameters of the preparation method of each embodiment are shown in Table 2.

[0059] Table 2 Process parameters of the preparation method of the short-process weathering steel

[0060] The short-process weathering steels prepared in Examples 1 to 8 are subjected to performance testing, and the relevant performances are shown in Table 3. According to the “Periodic Immersion Corrosion Test Method for Weathering Steel for Railway” disclosed in TB / T2375, the short-process weathering steels prepared in Examples 1 to 8 and the 450NQR1 steel material of Comparative Example 1 are subjected to performance testing, and the corrosion rates of the short-process weathering steels prepared in Examples 1 to 8 and the 450NQR1 steel material of Comparative Example 1 relative to the structural steel Q355B are shown in Table 3.

[0061] Table 3 Performance of the short-process weathering steel

[0062] Note: The impact energy of the examples with a thickness of ≥2.5 mm is converted from the results of 2.5 mm x 10 mm x 55 mm samples by 4 times.

[0063] Figure 2 shows the metallographic structure diagram of the short-process weathering steel prepared according to the preparation method of the short-process weathering steel disclosed in Example 2 of the present disclosure; and Figure 3 shows the metallographic structure diagram of the short-process weathering steel prepared according to the preparation method of the short-process weathering steel disclosed in Example 6 of the present disclosure. As shown in Figure 2, the metallographic structure of the short-process weathering steel prepared in Example 2 is: 73% ferrite, 25% martensite-austenite islands, and the balance of carbides. As shown in Figure 3, the metallographic structure of the short-process weathering steel prepared in Example 6 is: 85% ferrite, 8% martensite-austenite islands, and the balance of carbides.

[0064] In addition, one or more technical solutions in the embodiments of the present disclosure have at least the following technical effects or advantages:

[0065] (1) In the embodiments of the present disclosure, the prepared short-process weathering steel has ultra-high corrosion resistance, the weather resistance index I of the prepared short-process weathering steel is ≥8, the relative corrosion rate of the prepared short-process weathering steel to the structural steel Q355B is ≤30%, the weather resistance of the prepared short-process weathering steel is more than three times that of the structural steel Q355B, and the weather resistance of the prepared short-process weathering steel is also improved by more than one time compared with ordinary weathering steel; the corrosion rate of the prepared short-process weathering steel rapidly decays with time, and the corrosion depth of the prepared short-process weathering steel in 25 years is ≤0.1 mm.

[0066] (2) In the embodiments of the present disclosure, the prepared short-process weathering steel has high strength and forming performance. The yield strength of the prepared short-process weathering steel is greater than or equal to 620 MPa, the tensile strength is greater than or equal to 750 MPa, the yield strength ratio is less than or equal to 0.80, the elongation at break is greater than or equal to 18%, the cold bending performance can meet d = 1t, and the 180° bending is qualified (d is the bending diameter, and t is the thickness of the steel plate), and the low-temperature impact toughness at -20°C can reach more than 60 J.

[0067] (3) In the embodiments of the present disclosure, the mass fraction of high P and high Cr in the chemical composition of the short-process weathering steel can promote the formation of a uniform and dense rust layer on the surface of the prepared short-process weathering steel, significantly improve the corrosion potential and electrochemical impedance, and interrupt the continuous occurrence of corrosion, so that the short-process weathering steel has super-high corrosion resistance. Through the rolling and controlled cooling process, the short-process weathering steel has high strength, high plasticity and high toughness by using the high plasticity of ferrite and TiC precipitation strengthening mechanism. The two-stage staged cooling can obtain a metallographic structure mainly composed of ferrite and martensite islands, so as to realize low yield strength ratio and high forming performance of the short-process weathering steel.

[0068] It should be noted that in the embodiments of the present disclosure, the descriptions of the high Cr steel chemical composition system, the mass fraction of high P and high Cr, the super-high corrosion resistance, the low yield strength ratio and the high forming performance are all relative to the structural steel Q355B.

[0069] Compared with related art, the short-process weathering steel according to some embodiments of the present disclosure has the following advantages:

[0070] According to some embodiments of the present disclosure, a short-process weathering steel includes, in mass fraction, C: 0.03% to 0.06%, Si: 0.40% to 0.80%, Mn: 0.20% to 0.6%, Cr: 1.05% to 1.49%, Cu: 0.10% to 0.60%, P: 0.07% to 0.15%, S≤0.005%, Ti: 0.10% to 0.25%, N≤0.006%, Ca: 0.0010% to 0.0025%, and the balance being Fe and unavoidable impurities. The short-process weathering steel has high corrosion resistance and good mechanical properties by reasonably designing the chemical composition of the short-process weathering steel. Among them, Cu and Cr are important corrosion resistance elements in the chemical composition of the short-process weathering steel, and the simultaneous addition and appropriate addition of Cu and Cr in the short-process weathering steel can make the corrosion resistance effect of the short-process weathering steel more obvious.

[0071] In addition, Si is a commonly used deoxidizing element in steel, and the appropriate addition of Si in the short-process weathering steel has a solid solution strengthening effect on the steel, and can also improve the corrosion resistance of the steel.

[0072] In addition, the high P and high Cr mass fraction in the chemical composition of the short-process weathering steel can promote the generation of a uniform and dense rust layer on the surface of the short-process weathering steel, significantly improve the corrosion potential and electrochemical impedance, interrupt the continuous occurrence of corrosion, and thus improve the corrosion resistance of the short-process weathering steel.

[0073] The above description is merely a specific implementation of the present disclosure, which enables those skilled in the art to understand or implement the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A short process weathering steel, the short process weathering steel comprising, in mass fraction: C： 0.03%~0.06%, Si: 0.40%~0.80%, Mn: 0.20%~0.6%, Cr: 1.05%~1.49%, Cu: 0.10%~0.60%, P: 0.07%~0.15%, S≤0.005%, Ti: 0.10%~0.25%, N≤0.006%, Ca: 0.0010%~0.0025%, and, the balance being Fe and unavoidable impurities.

2. The short-cycle weathering steel of claim 1, wherein, The chemical composition satisfies the following relationship: [C]+[Mn] / 6+[Cr] / 10+[Cu] / 5+[P] / 15≤0.50, In the formula, [C] represents the mass fraction % of C in front of the numerical value, [Mn] represents the mass fraction % of Mn in front of the numerical value, [Cr] represents the mass fraction % of Cr in front of the numerical value, [Cu] represents the mass fraction % of Cu in front of the numerical value, and [P] represents the mass fraction % of P in front of the numerical value.

3. The short-cycle weathering steel of claim 2, wherein, The chemical composition also satisfies the following relationship: I = 26.01 [Cu] + 1.20 [Cr] + 1.49 [Si] + 17.28 [P] - 33.29 [Cu] 2 ≥ 8, In the formula, I represents the weather resistance index, [Cu] represents the mass fraction % of Cu in front of the numerical value, [Cr] represents the mass fraction % of Cr in front of the numerical value, [Si] represents the mass fraction % of Si in front of the numerical value, and [P] represents the mass fraction % of P in front of the numerical value.

4. The short process weathering steel of claim 1, wherein, The short-process weathering steel has a metallographic structure including, in volume fraction: ferrite: 70%~90%, martensite-austenite island: 5%~25%, and the balance being pearlite or carbide; wherein fine Ti(C, N) precipitates are dispersedly distributed on the ferrite matrix.

5. The short process weathering steel of claim 1, wherein, The short-process weathering steel satisfies at least one of the following properties: relative corrosion rate ≤30% compared with ordinary structural steel Q355B, corrosion depth ≤0.1mm in 25 years, yield strength ≥620MPa, tensile strength ≥750MPa, yield strength ratio ≤0.80, fracture elongation ≥18%, impact energy at -20℃ ≥60J, cold bending performance satisfying d=1t, and 180° bending is qualified; wherein d is the bending diameter, and t is the thickness of the steel plate.

6. A preparation method of the short-process weathering steel according to any one of claims 1~5, comprising: continuously casting molten steel having the chemical composition to obtain a slab; rapidly heating and finish rolling the slab to obtain a hot-rolled steel; and, staging cooling and coiling the hot-rolled steel to obtain the short-process weathering steel.

7. The method of claim 6, wherein, The staging cooling and coiling the hot-rolled steel to obtain the short-process weathering steel comprises: first-stage cooling the hot-rolled steel, and stopping for a set time after the hot-rolled steel reaches the final cooling temperature of the first-stage cooling; the cooling rate of the first-stage cooling is ≥120℃ / s, the final cooling temperature of the first-stage cooling is 640℃~660℃, and the set time is 3s~5s; and, The hot-rolled steel after staying for the set time is subjected to second stage cooling, and is coiled after the hot-rolled steel reaches the final cooling temperature of the second stage cooling, to obtain the short-process weathering steel; the cooling rate of the second stage cooling is ≥20℃ / s, the final cooling temperature of the second stage cooling is 560℃-640℃, and the coiling temperature is 560℃-640℃.

8. The method of claim 6, wherein, The rapid heating satisfies the following parameters: furnace entry temperature ≥900℃, furnace soaking time of 20min-30min, and furnace exit temperature of 1200℃-1250℃.

9. The method of claim 6, wherein, The cumulative deformation rate of the finish rolling is ≥94%, and the finish rolling final rolling temperature is 870℃-930℃.

10. The method of claim 6, wherein, The continuous casting satisfies the following parameters: casting speed ≥3.8m / min, molten steel superheat ≤15℃, and slab soft reduction rate ≥20%.

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