A wire rod for 1960mpa grade steel strand and a preparation method, steel wire and steel strand

Abstract

The application provides a 1960MPa-grade steel wire rod for steel strand, a preparation method, a steel wire and a steel strand, and belongs to the field of steel preparation.The chemical composition of the steel wire rod comprises, in mass fraction, C: 0.78% to 0.84%, Si: 0.17% to 0.35%, Mn: 0.50% to 0.90%, Cr: 0.10% to 0.20%, V: 0.04% to 0.08%, P: 0.015% or less, S: 0.010% or less, N: 0.0035% or less, and the balance of Fe and inevitable impurities; the metallographic structure of the steel wire rod is pearlite, and the lamellar spacing of the pearlite is 80nm to 100nm.The chemical composition of the steel wire rod is reasonably designed, the strength of the original steel wire rod is controlled at 1220MPa to 1260MPa by adding V and using the solid solution strengthening of V and the post-rolling water mist strong cooling, Cr is added to use Cr as a medium-strong carbide precipitation element, the starting and ending temperatures of the steel wire rod during the phase transformation from austenite to pearlite are reduced, and the permeability of the steel is increased.A 1960MPa steel wire rod with a specification of Φ15.24mm is successfully developed, the ton steel cost is only increased by about 100 yuan on the basis of 82B, and the production cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel production, in particular to a 1960MPa-grade wire rod for steel strand, a preparation method thereof, a steel wire and a steel strand. BACKGROUND

[0002] In order to improve the safety factor of buildings such as bridges, dams and mines, in recent years, the 1960MPa steel strand with a specification of Φ15.24mm has gradually been in demand. Compared with the 1860MPa steel strand with a specification of Φ15.24mm, the 1960MPa steel strand can improve the span and strength of the building and save steel materials.

[0003] At present, the basic composition of the wire rod for the 1960MPa steel strand developed at home and abroad is 82B. Most manufacturers adopt the method of adding 0.08%-0.12%V on the basis of the composition system of the national standard 82B. A few southern enterprises also develop the wire rod through the method of adding a proper amount of V (about 0.04%) on the basis of 82B and through offline salt bath. The method of adding 0.08-0.12%V on the basis of 82B increases the cost of per ton of steel by about 200-300 yuan. The method of adding a small amount of V on the basis of 82B and through salt bath heat treatment increases the cost by 500-600 yuan. In the current unfavorable environment of the steel industry, the high cost of the designed product is not conducive to product development and market development. Therefore, how to reduce the production cost of the wire rod for the 1960MPa steel strand is a technical problem to be solved at present. SUMMARY

[0004] The present application provides a 1960MPa-grade wire rod for steel strand, a preparation method thereof, a steel wire and a steel strand to solve the following technical problem: a wire rod for the 1960MPa steel strand is successfully developed through continuous casting of a small square billet, and the production cost thereof is reduced.

[0005] In a first aspect, the present application provides a 1960MPa-grade wire rod for steel strand. The chemical composition of the wire rod, in terms of mass fraction, comprises: C: 0.78%-0.84%, Si: 0.17%-0.35%, Mn: 0.50%-0.90%, Cr: 0.10%-0.20%, V: 0.04%-0.08%, P≤0.015%, S≤0.010%, N≤0.0035%, and the balance being Fe and unavoidable impurities. The metallographic structure of the wire rod is pearlite, and the interlamellar spacing of the pearlite is 80nm-100nm.

[0006] Optionally, the diameter of the wire rod is 12.5mm-13mm.

[0007] Optionally, the wire rod satisfies the following performance: tensile strength is 1220MPa-1260MPa, the tensile strength fluctuation value of the wire rod head and tail is ≤40MPa, and the tensile strength fluctuation value of the wire rod same circle is ≤30MPa.

[0008] In a second aspect, the application provides a preparation method of the wire rod in any one of the embodiments of the first aspect, and the method comprises:

[0009] The molten steel with the chemical composition is continuously cast to obtain a casting blank with a set C segregation index and a set porosity and shrinkage hole level;

[0010] The casting blank is heated, rolled and cooled to obtain the wire rod.

[0011] Optionally, the cooling mode is the combination of air mist cooling and air cooling.

[0012] Optionally, the superheat degree of the molten steel is 10℃-20℃.

[0013] Optionally, the set C segregation index of the casting blank is ≤1.05, and the set porosity and shrinkage hole level of the casting blank is ≤1.0 level.

[0014] In a third aspect, the application provides a steel wire, and the raw material of the steel wire is the wire rod in any one of the embodiments of the first aspect.

[0015] Optionally, the diameter of the steel wire is 5.05mm-5.25mm, and the tensile strength of the steel wire is ≥1960MPa.

[0016] In a fourth aspect, the application provides a steel strand, and the composition of the steel strand comprises the steel wire in the embodiment of the third aspect.

[0017] The above technical solutions provided by the embodiments of the application have the following advantages compared with the prior art:

[0018] The application provides a wire rod for 1960MPa steel strand, which comprises the following components in mass fraction: C: 0.78%-0.84%, Si: 0.17%-0.35%, Mn: 0.50%-0.90%, Cr: 0.10%-0.20%, V: 0.04%-0.08%, P≤0.015%, S≤0.010%, N≤0.0035%, and the balance of Fe and inevitable impurities; the metallographic structure of the wire rod is pearlite, and the lamellar spacing of the pearlite is 80nm-100nm. The chemical composition of the wire rod is reasonably designed, the strength of the original wire rod is controlled at 1220MPa-1260MPa by adding V and using the solid solution strengthening of V and post-rolling water mist strong cooling; Cr is added, Cr is a medium-strong carbide precipitation element, and the addition of high-carbon steel can reduce the start and end temperature of the wire rod during the transformation from austenite to pearlite, and increase the permeability of the steel. In combination with the post-rolling air mist cooling mode, the wire rod for 1960MPa steel strand with a specification of Φ15.24mm is successfully developed, the ton steel cost is only increased by about 100 yuan on the basis of 82B, and the production cost is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0019] The drawings incorporated into the specification and forming a part thereof, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required to be used in the embodiments or the prior art description will be briefly introduced. Obviously, those skilled in the art can obtain other drawings according to these drawings without any creative effort.

[0021] Figure 1 The edge metallographic structure diagram of the wire rod provided by the embodiments of the present application;

[0022] Figure 2 The core metallographic structure diagram of the wire rod provided by the embodiments of the present application;

[0023] Figure 3 The flowchart of the preparation method of the wire rod provided by the embodiments of the present application. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will be combined with the accompanying drawings for the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0025] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a hard limit on the scope of the present application; therefore, it should be considered that the described range has been specifically disclosed all possible sub-ranges and single values in 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 in the 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 application, it refers to any cited number (fraction or integer) in the indicated range.

[0026] In addition, in the description of the present application, the terms "include", "contain" and the like mean "include but not limited to". In the present application, 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 application, "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can represent the cases of A alone, A and B together, and B alone. Wherein A, B can be singular or plural. In the present application, "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 single item or any combination of 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, wherein a, b, c can be single or multiple.

[0027] Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0028] At present, there are two methods for developing the Φ15.24 mm specification 1960 MPa steel wire rod in China, one is directly adding 0.08-0.12% V on the basis of Φ12.5 mm 82B; the other method is to strengthen through on-line or off-line salt bath treatment while adding 0.04-0.08% V. Both of the two methods lead to high cost, especially the second method, although the organization form control is good, but the cost is high by 400-500 yuan / ton. The present application successfully develops the Φ15.24 mm specification 1960 MPa steel wire rod by adding a small amount of V in the composition of the steel, and the cooling mode of air mist cooling combined with air cooling after rolling, the ton steel cost increases by about 100 yuan based on the basis of 82B, reduces the production cost, and improves the market competitiveness of the product.

[0029] The present application provides a 1960 MPa grade steel wire rod, the chemical composition of the wire rod comprises, in mass fraction: C: 0.78%-0.84%, Si: 0.17%-0.35%, Mn: 0.50%-0.90%, Cr: 0.10%-0.20%, V: 0.04%-0.08%, P≤0.015%, S≤0.010%, N≤0.0035%, the balance being Fe and unavoidable impurities; the metallographic structure of the wire rod is pearlite, and the interlamellar spacing of the pearlite is 80 nm-100 nm.

[0030] In the embodiment of the present application, the positive effect of controlling the content of C to be 0.78%-0.84%: carbon is the most important element to determine the mechanical properties of steel. When the carbon content of the steel is increased, although the hardness continues to increase, the strength begins to decrease, and the plasticity and toughness decrease even more. Specifically, the content of C can be 0.78%, 0.79%, 0.81%, 0.83%, 0.84%, etc.

[0031] The positive effect of controlling the content of Si to be 0.17%-0.35%: silicon element plays an important role in steelmaking, and the molten steel needs to be deoxidized during steelmaking, silicon element has good affinity with oxygen, and can produce silicon dioxide to achieve the purpose of deoxidization. Adding silicon in steel can improve the strength and toughness. Specifically, the content of Si can be 0.17%, 0.23%, 0.28%, 0.32%, 0.35%, etc.

[0032] The positive effect of controlling the content of Mn to be 0.50%-0.90%: manganese can increase the strength and hardness of steel, especially in the later drawing process, it can improve the work hardening rate of steel wire. Specifically, the content of Mn can be 0.50%, 0.60%, 0.70%, 0.80%, 0.90%, etc.

[0033] The positive effect of controlling the content of Cr to be 0.10% to 0.20%: Cr is a medium carbide precipitation element, and adding Cr to high carbon steel can reduce the start and end temperatures of the wire rod during the phase transition from austenite to pearlite, and increase the permeability of the steel. By adding Cr and controlling cooling with water mist and air cooling on the air cooling line, the difference between the surface and core structure of the large-size wire rod during air cooling can be solved. If the content of Cr is too high, the cooling intensity will be too large to some extent, and the over-cooled structure that affects drawing will easily occur; if the content of Cr is too low, the cooling intensity will be small to some extent, and coarse pearlite structure will occur after the phase transition of the wire rod. Specifically, the content of Cr can be 0.10%, 0.12%, 0.15%, 0.18%, 0.20%, etc.

[0034] The positive effect of controlling the content of V to be 0.04% to 0.08%: V can improve the tensile strength of the wire rod through solid solution strengthening in high carbon steel. If the content of V is too high, the strength of the wire rod will be too high to some extent, which will lead to a high wire breakage rate during drawing and a high strength of the finished twisted wire; if the content of V is too low, the strength of the wire rod will be lower than 1220 MPa, which cannot meet the minimum requirement of 1860 MPa for the steel wire after drawing by the user. Specifically, the content of V can be 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, etc.

[0035] The positive effect of controlling the content of P to be ≤0.015%: Phosphorus in steel will reduce the cold workability of the steel, cause cold brittleness, and reduce the plasticity of the steel, especially for materials used for deep drawing, the content of P should be controlled as low as possible in the invention. Specifically, the content of P can be 0.007%, 0.009%, 0.008%, 0.010%, 0.011%, 0.015%, etc.

[0036] The positive effect of controlling the content of S to be ≤0.010%: S is a harmful element in steel, which reduces the ductility and toughness of the steel, damages the corrosion resistance of the steel, and has adverse effects on welding, etc. The content of S should be controlled as low as possible in the invention. Specifically, the content of S can be 0.010%, 0.008%, 0.006%, 0.004%, 0.005%, etc.

[0037] The positive effect of controlling the content of N to be ≤0.0035%: the addition of N in the steel can strengthen the hardness and strength, but also directly cause the plasticity and ductility of the steel to be significantly reduced, and the deformation aging over time, causing the plasticity and ductility of the steel to be further reduced, even significantly reduced, and in severe cases, the low alloy steel can crack and have micro pores, which should be controlled to be lower in the application. Specifically, the content of N can be 0.0035%, 0.0030%, 0.0025%, 0.0023%, 0.0020%, 0.0018%, etc.

[0038] The positive effect of controlling the interlamellar spacing of pearlite to be 80nm-100nm: compared with the pearlite with an interlamellar spacing greater than 100nm, the strength is higher, and compared with the troostite with an interlamellar spacing lower than 80nm, the drawing performance is better. The designed wire rod needs to meet the tensile strength of 1220-1260MPa or more, and also needs to meet the drawing performance of being directly drawn from Φ12.5 / 13mm to Φ5.05 / 5.25mm, and the interlamellar spacing of the wire rod needs to be controlled to be 80nm-100nm. Specifically, the interlamellar spacing of the wire rod can be 80nm, 85nm, 90nm, 95nm, 100nm, etc. Figure 1 The edge metallographic structure diagram of the wire rod provided in the embodiments of the application; Figure 2 The core metallographic structure diagram of the wire rod provided in the embodiments of the application. In combination with Figure 1 and Figure 2 It can be seen that the uniformity of the organization of the Φ12.5mm wire rod is good.

[0039] In the embodiments, the diameter of the wire rod is 12.5mm-13mm.

[0040] The positive effect of controlling the diameter of the wire rod to be 12.5mm-13mm: the drawing process of the wire rod is a work hardening process, and the tensile strength of the finished steel wire depends on the superposition of the tensile strength of the original wire rod and the work hardening strength in the drawing process, and the work hardening strength is directly related to the reduction ratio generated in the drawing process. In order to obtain a steel wire strength of 1220MPa or more, the diameter of the original wire rod should be controlled to be 12.5mm or more. Specifically, the diameter of the wire rod can be 12.5mm, 12.6mm, 12.7mm, 12.8mm, 12.9mm, 13mm, etc.

[0041] In the embodiments, the wire rod needs to meet the following performance requirements: the tensile strength is 1220MPa-1260MPa, the tensile strength fluctuation value of the head and tail of the wire rod is ≤40MPa, and the tensile strength fluctuation value of the same circle of the wire rod is ≤30MPa.

[0042] In the above embodiment, the tensile strength of the finished steel wire depends on the drawing work hardening strength and the original strength, and when the original wire rod with a specification of 12.5-13 mm is drawn to 5.05-5.25 mm, the strength needs to reach 1960 MPa, and the original wire rod should be controlled to be above 1220 MPa. The tensile strength of the wire rod can be 1220 MPa, 1255 MPa, 1260 MPa, etc. The tensile strength fluctuation of the wire rod head and tail is controlled within 40 MPa, and the tensile strength of the same circle is controlled within 30 MPa. The wire rod should not be scratched or have other behaviors that damage the surface quality of the wire rod during the bundling and transportation process.

[0043] Figure 3 A flowchart of a wire rod preparation method provided in the embodiment of the present application.

[0044] Please refer to Figure 3 The present application provides a wire rod preparation method as described in any one of the above embodiments, and the method comprises:

[0045] S1, continuously casting molten steel with the chemical composition to obtain a casting blank with a set C segregation index and a set porosity and shrinkage hole level;

[0046] S2, heating, rolling and cooling the casting blank to obtain a wire rod.

[0047] In the embodiment, the cooling mode is a combination of air mist cooling and air cooling.

[0048] In the above embodiment, the interlamellar spacing of the wire rod pearlite is controlled to be 80-100 nm by combining air mist cooling and air cooling on the post-rolling air cooling line, and the tensile strength of the wire rod after being offline is improved through microstructure strengthening.

[0049] In the embodiment, the superheat degree of the molten steel is 10-20℃.

[0050] In the embodiment, the set C segregation index of the casting blank is ≤1.05, and the set porosity and shrinkage hole level of the casting blank is ≤1.0 level.

[0051] Before step S1, the molten iron is subjected to converter smelting; the molten iron after converter smelting is subjected to refining to obtain the above molten steel, and the positive effect of controlling the process parameters of the above continuous casting is to ensure that the wire rod does not break during drawing and to ensure the surface quality of the wire rod.

[0052] The product prepared by the wire rod preparation method is the above wire rod, and the chemical composition and microstructure of the wire rod prepared by the wire rod preparation method can refer to the above embodiments. Since the wire rod preparation method adopts part or all of the technical solutions of the wire rod embodiments, it at least has all the beneficial effects brought by the technical solutions of the wire rod embodiments, which will not be repeated here.

[0053] Based on one general inventive concept, the application provides a steel wire, raw material of which is the wire rod according to any one of the above embodiments.

[0054] In an embodiment, the diameter of the steel wire is 5.05-5.25 mm, and the tensile strength of the steel wire is ≥1960 MPa.

[0055] In the embodiments of the application, the wire rod is directly drawn without heat treatment to obtain a steel wire with a diameter of 5.05-5.25 mm and a tensile strength of 1960-2060 MPa, which is lower in cost than the current domestic production mode. Specifically, the diameter of the steel wire can be 5.05 mm, 5.10 mm, 5.15 mm, 5.20 mm, 5.25 mm, etc., and the tensile strength of the steel wire can be 1960 MPa, 1970 MPa, 1980 MPa, 2000 MPa, 2050 MPa, 2060 MPa, etc.

[0056] Based on one general inventive concept, the application provides a steel strand, which is composed of the steel wire according to the above embodiments.

[0057] The Φ15.24 mm 1960 MPa steel strand produced by the method has a lower cost.

[0058] The application will be further described in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the application and not to limit the scope of the application. The experimental methods not specified in the following embodiments are generally determined according to the industry standards. If there is no corresponding industry standard, the general international standards, conventional conditions, or the conditions suggested by the manufacturers are used.

[0059] In the embodiments of the application, the full process route of the wire rod is as follows:

[0060] Industrial molten iron, scrap steel → 90 tons of converter smelting → LF furnace refining → continuous casting of 160 mm square billet → billet heating → rough rolling → medium rolling → water cooling (primary controlled cooling) → finish rolling (controlled rolling) → water cooling (secondary controlled cooling) → wire drawing → air mist cooling + air cooling (tertiary controlled cooling) → coil collecting → PF line transportation → bundling → packaging and transportation. The chemical composition of the wire rod can be seen in Table 1, the preparation process can be seen in Table 2, and the performance of the wire rod and the steel wire can be seen in Table 3.

[0061] Table 1 Chemical composition of the wire rod (wt%)

[0062] No. C Si Mn P S N V Cr Example 1 0.81 0.22 0.80 0.014 0.004 0.0026 0.04 0.15 Example 2 0.82 0.23 0.84 0.008 0.005 0.0028 0.05 0.18 Example 3 0.82 0.22 0.85 0.011 0.003 0.0028 0.06 0.17 Example 4 0.84 0.23 0.78 0.012 0.005 0.0032 0.07 0.20 Example 5 0.79 0.17 0.83 0.009 0.006 0.0028 0.06 0.15 Example 6 0.83 0.23 0.81 0.007 0.005 0.0026 0.06 0.18 Comparative Example 1 0.80 0.18 0.80 0.011 0.005 0.0028 -- --

[0063] Table 2 Preparation process parameters of the wire rod

[0064] No. Superheat °C Casting Billet C Segregation Index Porosity, Shrinkage Level / Grade Example 1 20 1.05 0.5 Example 2 18 1.02 0.5 Example 3 20 1.05 1.0 Example 4 18 1.05 0.5 Example 5 19 1.04 1.0 Example 6 20 1.03 0.5 Comparative Example 1 32 1.08 2.5

[0065] Table 3 Properties of wire rod and steel wire

[0066]

[0067] From Tables 1-3, it can be seen that the 1960 MPa steel strand and steel wire can be successfully obtained by the scheme of the present application, meeting the needs of users.

[0068] The above description is merely that of the specific embodiments of the present application, to enable a person skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein but will be accorded the widest scope consistent with the principles and novel features described herein.

Claims

1. A type of wire rod for 1960MPa grade steel strand, characterized in that, The chemical composition of the wire rod, by mass fraction, includes: C: 0.78%~0.84%, Si: 0.17%~0.35%, Mn: 0.50%~0.90%, Cr: 0.10%~0.15%, V: 0.04%~0.08%, P≤0.015%, S≤0.010%, N≤0.0035%, with the balance being Fe and unavoidable impurities; the metallographic structure of the wire rod is pearlite, and the interlamellar spacing of the pearlite is 80nm~100nm; the preparation process of the 1960MPa grade steel strand wire rod includes heating, rolling, and cooling the billet, wherein the cooling method is a combination of air mist cooling and air cooling.

2. The wire rod according to claim 1, characterized in that, The diameter of the wire rod is 12.5mm~13mm.

3. The wire rod according to claim 2, characterized in that, The wire rod meets the following performance requirements: tensile strength of 1220MPa~1260MPa, tensile strength fluctuation at the beginning and end of the wire rod ≤40MPa, and tensile strength fluctuation within the same coil of the wire rod ≤30MPa.

4. A method for preparing wire rod according to any one of claims 1 to 3, characterized in that, The method includes: Molten steel with the aforementioned chemical composition is continuously cast to obtain a billet with a set C segregation index and a set porosity and shrinkage level. The cast billet is heated, rolled, and cooled to obtain wire rod; The C segregation index of the billet is set to ≤1.05, and the porosity and shrinkage level is set to ≤1.

0.

5. The method according to claim 4, characterized in that, The superheat of the molten steel is 10℃~20℃.

6. A steel wire, characterized in that, The raw material for the steel wire is the wire rod described in any one of claims 1 to 3.

7. The steel wire according to claim 6, characterized in that, The diameter of the steel wire is 5.05mm~5.25mm, and the tensile strength of the steel wire is ≥1960MPa.

8. A type of steel strand, characterized in that, The steel strand comprises the steel wire as described in claim 6 or 7.

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