Steel, wire rod for high-strength and long fatigue life cable, and method for producing the same

Abstract

The present invention discloses a high-strength, long-fatigue-life steel for cables containing, in addition to Fe, the following chemical elements in mass percentages: C: 0.90-1.00%, Si: 0.90-1.50%, Mn: 0.25-0.58%, Cr: 0.20-1.00%, V: 0.03-0.12%, and Ca: 0.0008-0.0025%. Furthermore, the present invention discloses a wire rod obtained using the high-strength, long-fatigue-life steel for cables, and a method for producing the wire rod.

Description

Technical Field

[0001] The present invention relates to a kind of steel type, wire rod and its manufacturing method, and particularly relates to steel for cable, wire rod and its manufacturing method.

Background Art

[0002] Suspension bridges and cable-stayed bridges are currently preferred forms for the design of long bridges crossing bays, canyons, and large rivers. With the development of society and technology, the spans of suspension bridges and cable-stayed bridges are constantly increasing. The span of the suspension bridges built in the world is nearly 2000 meters, and the span of the cable-stayed bridges exceeds 1000 meters. With the increase in the spans of these bridges, higher performance requirements are put forward for galvanized steel wires, which are the main raw materials for bridge cables. The research on galvanized steel wires for bridge cables with ultra-high strength of 2000 MPa or more and high torsional performance has attracted attention.

[0003] Wire rod is the raw material for manufacturing steel wires for high-strength bridge cables. Large wire rods are processed into cable wires through processes such as wire drawing, galvanizing, and stabilization. However, in order to complete the wire drawing process of steel wires with a large area reduction rate, first, the wire rod needs to have good drawability. In recent years, with the continuous improvement of the strength level of bridge cable steel wires, the strength of wire rods has also been continuously improved. Among them, alloy strengthening and refinement of the microstructure are the two most effective means to improve the strength of wire rods.

[0004] Regarding the method of alloy strengthening of wire rods, many advanced steel companies around the world are conducting a series of research. For example, the KKP wire rod developed by Japanese companies adds a small amount of chromium based on the conventional SWRS82B, and after Stelmor cooling, a high-strength sorbite wire rod with good performance can be obtained. By further increasing the carbon content of the wire rod to 0.87% and simultaneously adding trace amounts of microalloying elements, a wire rod with high strength and little variation is manufactured, which is called super KKP wire rod. Of course, in Europe, there are also many companies manufacturing wire rods for high-strength bridge cables by this method, but the strength of the steel wires processed from this wire rod is still very low. In response to this, domestic researchers mainly adopt low-silicon alloy composition design, increase the C element and Mn element of the wire rod to improve the material strength, develop steel with a carbon content of 0.87%, and can improve the strength of the wire rod and steel, but can only meet the processing requirements of 1860MPa steel wires, and the strength level of the steel wires is still low.

[0005] In addition, making high-carbon wire rods into high-sorbite structures to achieve refinement of the structure is also an important means to improve wire rod strength. Currently, the high-sorbite of wire rods is mainly realized by controlled cooling after rolling. Currently, 95% of wire rod production in China adopts the Stelmor air cooling process, that is, continuous tissue transformation of sorbite is realized in the air cooling section after the wire rod after final rolling is water cooled. The Stelmor cooling process has problems such as insufficient cooling capacity and poor temperature uniformity when manufacturing large wire rods, which affects the further improvement of material properties. Nippon Steel Corporation in Japan has developed an on-line salt bath isothermal treatment DLP process that meets the requirements of sorbite transformation of wire rods, but there are still problems such as large equipment investment and high maintenance costs.

[0006] In addition to the requirement of high strength for the zinc-plated steel wire for bridge cables, it is necessary to maintain high ductility and high torsional performance under high strength. Currently, the mainly adopted method is to control the contents of P and S in the material within a specific range. In particular, the content of P in the alloy is controlled to be 0.02% or less to prevent segregation during solidification and reduce the significant damage of P to the torsional performance of the steel wire. By adding 10 - 500 ppm of Zr, fine ZrO2 particles are formed to improve the compositional segregation at the core of the wire rod. By adding 9 - 60 ppm of B, the microstructure of the high-carbon steel wire rod is improved. The B element dissolved in high-temperature austenite segregates at the grain boundaries, preventing the formation of primary ferrite during cooling and promoting the precipitation of cementite at the same time. Although the optimization of the microstructure improves the torsional performance, all are limited to a certain range of strength.

[0007] It should be noted that long-span bridges have a long construction period and require huge investments, so long service life, high safety and reliability are required. To extend the service life of the bridge, special attention is also needed for the fatigue life of the zinc-plated steel wire of the bridge cable.

[0008] In the existing technology, the current high-carbon wire rods can well meet the processing requirements of high-strength and high-torsion zinc-plated steel wires for bridge cables with strengths of 1670 MPa, 1770 MPa or 1860 MPa, and the strength of some steel wires can reach up to 2000 MPa. Although the strength of the steel wire reaches the standard, the torsional performance and fatigue life of the steel wire still need to be further improved.

[0009] Based on this, in order to solve the above problems, the present invention hopes to obtain steel, wire rods and their manufacturing methods for high-strength long-fatigue-life cables. The steel for high-strength long-fatigue-life cables not only ensures high strength but also has good plasticity and fatigue life, so it can be used in the manufacture of wire rods. The wire rods are drawn and zinc-plated steel wires can effectively meet the production requirements of long-span and long-life bridge cables.

Summary of the Invention

Problems to be Solved by the Invention

[0010] One of the objectives of the present invention is to provide a steel for high-strength and long fatigue life cables. The steel for high-strength and long fatigue life cables ensures the performance of the steel plate through a reasonable chemical composition design. The characteristics of the steel for high-strength and long fatigue life cables are very beneficial. While ensuring high strength, it has good plasticity and fatigue life, can be effectively used in the manufacture of wire rods, and the wire rods drawn and zinc-plated can effectively meet the production requirements of large-span and long-life bridge cables, with good application prospects and application value.

Means for Solving the Problems

[0011] To achieve the above objective, in addition to Fe, the present invention provides a steel for high-strength and long fatigue life cables containing the following chemical elements by mass percentage: C: 0.90 - 1.00%; Si: 0.90 - 1.50%; Mn: 0.25 - 0.58%; Cr: 0.20 - 1.00%; V: 0.03 - 0.12%; Ca: 0.0008 - 0.0025% And provides a steel for high-strength and long fatigue life cables.

[0012] Furthermore, in the steel for high-strength and long fatigue life cables of the present invention, the mass percentages of the chemical elements are: C: 0.90 - 1.00%; Si: 0.90 - 1.50%; Mn: 0.25 - 0.58%; Cr: 0.20 - 1.00%; V: 0.03 - 0.12%; Ca: 0.0008 - 0.0025%, and the balance is Fe and other inevitable impurities.

[0013] In the technical solution of the present invention, the design principles of the chemical elements are specifically as follows.

[0014] C: In the steel for high-strength and long fatigue-life cables of the present invention, element C is a chemical composition necessary to ensure the high strength of the steel. The content of element C in the steel determines the volume fraction of cementite in the sorbite structure of the cable steel. Increasing the content of C element in the steel helps to form more cementite sheets and fine sorbite sheet structures. Therefore, the steel can obtain better deformation characteristics and work hardening characteristics, which is helpful for improving the strength of the steel wire in subsequent processing. Therefore, in order to ensure the quality of the steel, it is necessary to control the content of C element in the steel of the present invention to be 0.90% or more. However, it should be noted that the content of C element in the steel should not be too high. With the increase of the content of C element in the steel, it becomes difficult to control segregation during the smelting and continuous casting processes, especially to form reticular cementite precipitated along the grain boundaries, resulting in a significant decrease in the plasticity and toughness of the material. Therefore, in the steel for high-strength and high fatigue-life cables of the present invention, the mass percentage of C element is controlled to be 0.90 - 1.00%.

[0015] Si: In the steel for high-strength and long fatigue-life cables of the present invention, element Si is often added to the steel as a deoxidizer in the smelting process. Si element dissolved in the ferrite phase significantly improves the strength of the steel. Also, during the cooling phase transformation process of the steel, Si element is enriched at the interface between the ferrite phase and the cementite phase. In the process of degreasing by lead bath and hot-dip galvanizing of the steel wire drawn with a large reduction ratio, the enrichment of Si element at the phase interface can delay the decomposition of the largely deformed cementite sheets and effectively reduce the strength loss of the steel. In order to ensure the high strength of the wire rod and the higher strength of the steel wire after wire drawing, it is necessary to control the content of Si element in the steel to exceed 0.9%. However, if the content of Si element in the steel is too high, the plasticity of the steel will be significantly reduced and the material will become brittle. Therefore, in the steel for high-strength and long fatigue-life cables of the present invention, the mass percentage of Si element is controlled to be 0.90 - 1.50%.

[0016] Of course, in some preferred implementation methods, in order to obtain better implementation effects, the mass percentage of Si element can be controlled to be 1.0 - 1.4%.

[0017] Mn: In the steel for high-strength and long fatigue-life cables of the present invention, the Mn element is often added to the steel as a deoxidizer in the steelmaking process. At the same time, the Mn element easily combines with the harmful element S in the steel to form MnS, and its harm can be reduced. Also, Mn is a common strengthening element of steel, mainly playing a role in solid solution strengthening. Since the formed alloy cementite has higher strength, it is necessary to control the content of the Mn element in the steel to exceed 0.25%. However, it should be noted that the content of the Mn element in the steel should not be too high. If the content of the Mn element in the steel is too high, the grain size of the material tends to coarsen during the heating process. Especially when the contents of C and Si in the material are high, the Mn element also easily promotes the segregation of residual elements. Therefore, it is necessary to control the content of the Mn element in the steel to be less than 0.58%. From this, in the steel for high-strength and long fatigue-life cables of the present invention, the mass percentage of the Mn element is controlled to be 0.25 - 0.58%.

[0018] Cr: In the steel for high-strength and long fatigue-life cables of the present invention, the addition of the Cr element is beneficial for refining the sorbite lamellar structure of the steel and can increase the strength of cementite, thereby effectively improving the strength and plasticity of the material. To enable the Cr element to effectively exert its advantages, it is necessary to make the content of the Cr element in the steel higher than 0.20%. Correspondingly, to prevent the occurrence of abnormal martensite structure and reduce the difficulty of tissue control, it is necessary to control the Cr content in the steel to be less than 1.00%. Therefore, in the steel for high-strength and long fatigue-life cables of the present invention, the mass percentage of the Cr element is controlled to be 0.20 - 1.00%. In some embodiments, the mass percentage of the Cr element is controlled to be 0.30 - 1.00%, and the Cr in Example 10 is adjusted to 0.2%.

[0019] Of course, in some preferred embodiments, in order to obtain better implementation effects, the mass percentage of the Cr element can be controlled to be 0.2 - 0.7%.

[0020] V: In the steel for high-strength and long fatigue life cables according to the present invention, the V element can perform microalloy strengthening. The precipitation of V element in the form of nanoscale carbonitrides with a size of 5 - 50 nm can help refine the structure of the cable steel, promote the pinning of dislocations, improve the strength and plasticity of the material, and not overly affect the torsional properties of the product steel. Furthermore, the addition of the V element also helps to suppress the formation of grain boundary network cementite. However, if the content of the V element in the steel is too high, it will lead to coarsening of the carbonitrides and an increase in material cost. Therefore, in the steel for high-strength and long fatigue life cables of the present invention, the mass percentage of the V element is controlled to be 0.03 - 0.12%.

[0021] Ca: In the steel for high-strength and long fatigue life cables according to the present invention, the Ca element is beneficial for improving the plasticity of inclusions in the steel, thereby increasing the aspect ratio of inclusions in the product cable steel and further improving the performance of the steel. Therefore, in the steel for high-strength and long fatigue life cables of the present invention, the mass percentage of the Ca element is controlled to be 0.0008 - 0.0025%.

[0022] Also, in the steel for high-strength and long fatigue life cables according to the present invention, the mass content ratio of each element satisfies at least one of Si: 1.0 - 1.4% and Cr: 0.2 - 0.7%.

[0023] Also, in the steel for high-strength and long fatigue life cables according to the present invention, the total content of other inevitable impurities is 0.1% or less, preferably 0.08% or less, more preferably 0.05% or less, and the content of each impurity element satisfies at least one of Cu ≤ 0.05%, Al ≤ 0.004%, Ti ≤ 0.003%, P ≤ 0.015%, S ≤ 0.010%, O ≤ 0.0025%, and N ≤ 0.0045%.

[0024] In the above technical solution, the elements Cu, Al, Ti, P, S, O, and N are all impurity elements in the steel. If technical conditions permit, in order to obtain steel with better performance and quality, it is necessary to reduce the content of impurity elements in the steel as much as possible.

[0025] Here, if the content of P and S elements in the steel is too high, especially when segregation occurs, the brittleness of the steel increases. Therefore, in the steel for high-strength long fatigue life cables according to the present invention, it is necessary to control the content of P and S elements so that P ≤ 0.015% and S ≤ 0.010%.

[0026] Also, it should be noted that if the Al content in the steel is too high, the plasticity of the inclusions decreases, and the performance and fatigue life of the steel wire decrease. Therefore, in the steel for high-strength long fatigue cables, the Al content of the impurity element is controlled to Al ≤ 0.004%.

[0027] In some embodiments, in the steel for high-strength long fatigue life cables according to the present invention, the content by mass percentage of Cu is 0.005 - 0.05%, the content by mass percentage of Al is 0.0001 - 0.004%, and the content by mass percentage of Ti is 0.0005 - 0.003%.

[0028] Furthermore, the steel for high-strength long fatigue life cables according to the present invention also contains at least one of the following chemical elements.

[0029] Mo: 0.10 - 0.80%; B: 0.0008 - 0.0012%; Re: 0.0005 - 0.008%.

[0030] In the technical solution of the present invention, in order to obtain better implementation effects and obtain steel with better quality and performance, elements of Mo, B, and Re can also be added to the steel for high-strength long fatigue life cables of the present invention.

[0031] Here, the addition of Mo and B elements to the steel further improves the hardenability of the material, helps to improve the sorbite structure of the steel, and helps to improve the plasticity, toughness, and torsional performance while increasing the strength of the material. When the Re element is added to the steel, the purity of the steel is effectively improved, the number and size of the inclusions decrease, and the influence of the inclusions on the fatigue life and torsional performance of the steel wire decreases.

[0032] In addition, since the addition of the above elements increases the material cost, in the technical solution of the present invention, it is preferable to add at least one of the above elements in consideration of performance and cost management.

[0033] In addition, in the steel for high-strength long fatigue life cable of the present invention, its microstructure is mainly a refined sorbite structure, the phase ratio (volume ratio) of sorbite is ≧ 95%, and there is no obvious grain boundary network cementite and martensite structure in the microstructure, that is, the phase ratio of grain boundary network cementite and martensite structure is ≦ 0.5%.

[0034] In addition, in the steel for high-strength long fatigue life cable of the present invention, the average value of the interlamellar spacing of the sorbite structure is 40 - 260 nm.

[0035] In addition, in the steel for high-strength long fatigue life cable according to the present invention, the carbon segregation in the core is less than 1.08.

[0036] In addition, in the steel for high-strength long fatigue life cable according to the present invention, the microstructure also has V carbonitride precipitates with a size of 5 - 50 nm.

[0037] In addition, in the steel for high-strength long fatigue life cable according to the present invention, the size of the inclusions is < 35 μm, and the aspect ratio of the inclusions is > 2.

[0038] In addition, in the steel for high-strength long fatigue life cable according to the present invention, the tensile strength is ≧ 1430 MPa. In some embodiments, the tensile strength of the steel for high-strength long fatigue life cable is 1445 - 1560 MPa.

[0039] Accordingly, another object of the present invention is to provide a wire rod with excellent performance and good strength-plasticity matching ability, which can meet the processing requirements of wire drawing and zinc plating of high-strength steel wire, and has a tensile strength of ≧ 1430 MPa and a reduction of area of > 30%. In a preferred embodiment, the tensile strength of the wire rod of the present invention is 1445 - 1560 MPa, and the reduction of area is 32 - 40%.

[0040] After the wire rod is drawn, zinc-plated, and stabilized, the steel wire obtained has a tensile strength of ≥2000 MPa, a torsional value of >8 times for a 100D gauge sample, and a fatigue life of >2.4 million cycles under the condition of a maximum stress of 0.45σ b This can effectively meet the production requirements of long-span and long-life bridge cables. In a preferred embodiment, the steel wire obtained after the wire rod is drawn, zinc-plated, and stabilized has a tensile strength of 2020-2100 MPa, a torsional value of 12-24 times for a 100D gauge sample, and a fatigue life of 2.49-4.2 million cycles under the condition of a maximum stress of 0.45σ b The chemical elements of the steel wire and the mass percentage of each element are the same as those of the steel for high-strength long-fatigue-life cables of the present invention.

[0041] To achieve the above object, the present invention provides a wire rod obtained by using the above steel for high-strength long-fatigue-life cables. The chemical elements of the wire rod and the mass percentage of each element are the same as those of the steel for high-strength long-fatigue-life cables of the present invention.

[0042] In addition, the wire rod of the present invention satisfies at least one of the following performance requirements: tensile strength ≥1430 MPa, reduction of area >30%, tensile strength of the steel wire after drawing and zinc plating ≥2000 MPa, torsional value >8 times, and fatigue life >2.4 million cycles under the condition of a maximum stress of 0.45σ b In a preferred embodiment, the performance of the wire rod satisfies tensile strength ≥1430 MPa, reduction of area >30%, tensile strength of the steel wire after drawing and zinc plating ≥2000 MPa, torsional value >8 times, and fatigue life >2.4 million cycles. In a more preferred embodiment, the performance of the wire rod is such that the tensile strength is 1445-1560 MPa, the reduction of area is 32-40%, the tensile strength of the steel wire after drawing and zinc plating is 2020-2100 MPa, the torsional value of a 100D gauge sample is 12-24 times, and the fatigue life under the condition of a maximum stress of 0.45σ b is 2.49-4.2 million cycles.

[0043] Furthermore, the present invention also provides a steel wire obtained by drawing, zinc plating, and stabilizing treatment of the wire rod described herein. The above drawing, zinc plating, and stabilizing treatment are all conventional techniques in the art. The diameter of the steel wire is 4 - 8 mm. The steel wire of the present invention has a tensile strength of ≧2000 MPa or more, a torsion value of >8 times, and a fatigue life of >2.4 million times. Preferably, the tensile strength is 2020 - 2100 MPa, the torsion value of a 100D gauge sample is 12 - 24 times, and the fatigue life under the condition of a maximum stress of 0.45σ b is 2.49 - 4.2 million times.

[0044] Also, another object of the present invention is to provide a manufacturing method of the above wire rod. The manufacturing method is simple in production, the obtained wire rod has excellent performance, good strength-plasticity matching ability, and can meet the requirements of wire drawing and zinc plating processing of high-strength steel wire.

[0045] To achieve the above object, the present invention provides a manufacturing method of the wire rod including the following steps.

[0046] (1) Smelting and casting; (2) Rough rolling; (3) High-speed wire rod rolling; (4) Stelmor controlled cooling; (5) Isothermal treatment: The austenite heating temperature is 890 - 1050 °C, the holding time is 6 - 20 minutes, and the isothermal treatment temperature is 530 - 600 °C.

[0047] In the technical solution according to the present invention, in step (1), smelting can be carried out by an electric furnace or a converter, and then refining can be carried out outside the furnace. In the case of refining outside the furnace, an LF furnace + VD or RH degassing treatment process can be used. The composition and addition amount of the synthetic slag can be adjusted in the smelting process, the content of impurity elements in the steel can be controlled, and the vacuum degassing time is controlled to be >20 minutes.

[0048] Also, in the manufacturing method according to the present invention, in step (1), the vacuum degassing time is controlled to be >20 minutes during the smelting process, and the carbon segregation in the billet core is controlled to be less than 1.08 during the casting process.

[0049] In the above technical solution, in step (1), during the casting process, a billet can be cast using a bloom continuous casting machine. In order to ensure the quality and performance of the billet, it is preferable to control the carbon segregation in the billet core to be less than 1.08.

[0050] In the above step (2), a two-time firing and forming process can be used. The continuously cast billet is roughly rolled and block-rolled into billets with a size of 150 - 250 mm square at a temperature of 1100 - 1250 °C. After the billets are subjected to ultrasonic flaw detection, magnetic particle flaw detection, grinding die correction, auxiliary magnetic particle flaw detection, and die correction, they are put into a heating furnace for heating, and the heating temperature is controlled to 960 - 1150 °C, and the holding time is controlled to 1.5 - 2.5 hours.

[0051] In the above step (3), the rolling speed is controlled to 20 - 60 m / s. Also, the inlet temperature of the finishing rolling mill is controlled to 920 - 990 °C, the inlet temperature of the drawing and sizing machine is controlled to 920 - 990 °C, and the wire spitting temperature is controlled to 880 - 950 °C.

[0052] It should be noted that in step (4), by adjusting the air volume of the Stelmor line fan, the transformation of the wire rod structure can be controlled, the wire rod structure can be optimized, and a wire rod with better performance can be obtained. Preferably, the wire rod size specification is rolled to φ10 - 15 mm. Preferably, the air volume adjustment range of 14 Stelmor fans is such that the air volume of F1 - F8 fans is 80 - 100%, the air volume of F9 - F12 fans is 75 - 100%, and the air volume of F13 - F14 fans is 0 - 45%.

[0053] It should be noted that in step (5), the isothermal treatment of the wire rod can be carried out by methods such as a lead bath or a salt bath.

Advantages of the Invention

[0054] The high-strength long fatigue life cable steel, wire rod, and its manufacturing method according to the present invention have the following advantages and beneficial effects compared with the prior art: The steel for high-strength and long fatigue-life cables according to the present invention ensures the performance of the steel plate through a reasonable chemical composition design. The characteristics of the steel for high-strength and long fatigue-life cables have good plasticity and fatigue life while ensuring high strength, can be used in the manufacture of wire rods, and the steel wires after the wire rods are drawn and zinc-plated can effectively meet the production requirements of large-span and long-life bridge cables, showing good application prospects and application values.

[0055] The wire rods made of the steel for high-strength and long fatigue-life cables according to the present invention also have excellent performance and good strength-plasticity matching ability, can meet the processing requirements of wire drawing and zinc plating of high-strength steel wires, with a tensile strength of ≧1430 MPa and a reduction of area of >30%. The steel wires obtained after the wire rods are drawn, zinc-plated and stabilized treatment have a tensile strength of ≧2000 MPa, a torsional value of >8 times for 100D gauge samples, and a fatigue life of >2.4 million cycles under the condition of a maximum stress of 0.45σ b which can effectively meet the production requirements of long-span and long-life bridge cables.

[0056] Accordingly, the manufacturing method of the present invention is simple in production, the obtained wire rods have excellent performance, good strength-plasticity matching ability, and can meet the requirements of wire drawing and zinc plating processing of high-strength steel wires.

Embodiments for Carrying Out the Invention

[0057] Hereinafter, the steel for high-strength and long fatigue-life cables, wire rods and their manufacturing methods of the present invention will be further interpreted and explained using specific examples, but these interpretations and explanations do not unduly limit the technical solutions of the present invention.

[0058] Examples 1 to 11 and Comparative Examples 1 to 3 The wire rods of Examples 1 to 11 are all manufactured by adopting the following steps: (1) Smelting and casting according to the chemical composition shown in Table 1: After smelting in an electric furnace or a converter, secondary refining is carried out. The secondary refining adopts an LF furnace + VD or RH degassing treatment process. During smelting, the composition and addition amount of the synthetic slag are adjusted, and here the vacuum degassing time during smelting is controlled to be >20 minutes. A bloom continuous casting machine is used to cast square billets, and in the casting process, by adjusting the parameters of the casting speed, cooling, and final reduction in the continuous casting process, the carbon segregation in the billet core is controlled to be less than 1.08.

[0059] (2) Rough rolling: Using a two-pass firing and forming process, the continuously cast billet is rough rolled at a temperature of 1100 - 1250°C and block-rolled into billets with a square cross-section of 150 - 250 mm. After the billets are subjected to ultrasonic flaw detection, magnetic particle flaw detection, grinding die modification, auxiliary magnetic particle flaw detection, and die modification, they are put into a heating furnace and heated, with the heating temperature controlled at 960 - 1150°C and the holding time controlled at 1.5 - 2.5 hours.

[0060] (3) High-speed wire rolling: The rolling speed is controlled at 20 - 60 m / s, the inlet temperature of the finishing rolling mill is controlled at 920 - 990°C, the inlet temperature of the drawing and sizing mill is controlled at 920 - 990°C, and the coiling temperature is controlled at 880 - 950°C.

[0061] (4) Stelmor controlled cooling: The wire rod is rolled to a dimensional specification of φ10 - 15 mm. After the wire rod is rolled, by adjusting the air volume of the Stelmor line fans, the transformation of the wire rod structure is controlled to optimize the wire rod structure. The air volume adjustment range of the 14 Stelmor fans is such that the air volume of fans F1 - F8 is 80 - 100%, the air volume of fans F9 - F12 is 75 - 100%, and the air volume of fans F13 - F14 is 0 - 45%.

[0062] (5) Isothermal treatment: The isothermal treatment is carried out on the wire rod in a lead bath or a salt bath, where the austenite heating temperature is 890 - 1050°C, the holding time is 6 - 20 minutes, and the isothermal treatment temperature is 530 - 600°C.

[0063] It should be noted that all the wire rods of Examples 1 to 11 according to the present invention are manufactured by the above-mentioned processes, and their chemical compositions and related process parameters all meet the control requirements of the design specifications of the present invention. On the other hand, the comparative wire rods of Comparative Examples 1 to 3 adopt the same processes of smelting and casting, rough rolling, high-speed wire rod rolling, Stelmor controlled cooling and isothermal treatment, but there are parameters in their chemical compositions and related process parameters that do not meet the design requirements of the present invention.

[0064] Also, it should be noted that the wire rods of Examples 1 to 11 all use the high-strength long fatigue life cable steel according to the present invention. Correspondingly, the comparative wire rods of Comparative Examples 1 to 3 are also manufactured from their corresponding comparative steels.

[0065] Table 1 lists the mass percentage compositions of each chemical element in the high-strength long fatigue life cable steel of Examples 1 to 11 and the comparative steels of Comparative Examples 1 to 3.

[0066]

Table 1

[0067] Table 2 lists the specific process parameters of the wire rods of Examples 1 to 11 and the comparative wire rods of Comparative Examples 1 to 3 in the above-mentioned processes.

[0068]

Table 2

[0069] The wire rods of Examples 1 to 11 and the comparative wire rods of Comparative Examples 1 to 3 obtained were sampled, observed, analyzed, and respective performance tests were conducted. The obtained observation results and performance test results are shown in Table 3 and Table 4 respectively.

[0070] The observation results of the wire rods of Examples 1 to 11 and the comparative wire rods of Comparative Examples 1 to 3 are shown in Table 3.

[0071]

Table 3

[0072] It should be noted that, as shown in Table 3, all the wire rods according to the present invention are obtained by using the high-strength long fatigue life cable steel according to the present invention. Correspondingly, in Examples 1 to 11, the microstructure of the high-strength long fatigue life cable steel for manufacturing the wire rods of Examples 1 to 11 is mainly a refined sorbite structure, and the phase ratio of sorbite is all ≧95%, and there is no obvious grain boundary network cementite and martensite structure in the microstructure. Furthermore, in Examples 1 to 11 of the present invention, the lamellar spacing of the sorbite structure is all 40 to 260 nm, and the carbon segregation in the core part is all less than 1.08.

[0073] Also, it should be noted that in the high-strength long fatigue life cable steel according to Examples 1 to 11 of the present invention, the microstructure also has V carbonitride precipitates with a size of 5 to 50 μm.

[0074] In addition, in the high-strength long fatigue life cable steel of Examples 1 to 11 according to the present invention, the size of the inclusions in the steel is <35 μm, and the aspect ratio of the inclusions is >2.

[0075] Table 4 lists the performance test results of the wire rods of Examples 1 to 11 and the comparative wire rods of Comparative Examples 1 to 3. Here, the test methods for the tensile strength and reduction of area are the normal temperature tensile test method for metallic materials of GB / T 228.1-2010.

[0076]

Table 4

[0077] It should be noted that the sampled wire rods of Examples 1 to 11 and the comparative wire rods of Comparative Examples 1 to 3 can obtain steel wires with better performance and quality after 6 to 9 passes of wire drawing, zinc plating of steel wires, and stabilization treatment. Various performance tests related to the obtained steel wires of Examples 1 to 11 and the comparative steel wires of Comparative Examples 1 to 3 were carried out, and the obtained performance test results are shown in Table 5.

[0078] Table 5 lists the performance test results of the steel wires of Examples 1 to 11 and the comparative steel wires of Comparative Examples 1 to 3. Here, the test method for tensile strength is the room temperature tensile test method of metallic materials of GB / T 228.1-2010, the test method for torsion value is the unidirectional torsion test method of GB / T 239.1-2012, metallic materials wire rod part 1, and the fatigue test method is the axial force control method of GB / T 3075-200, metallic materials fatigue test.

[0079] [Table 5]

[0080] From Tables 4 and 5, it can be seen that the comparative wires of Comparative Examples 1 to 3 and the steel wires produced therefrom are clearly inferior in performance to those of Examples 1 to 11. In the present invention, the wires of Examples 1 to 11 all have good properties, and their tensile strengths are all ≧1430 MPa, and their reduction in area is all >30%.

[0081] The steel wires obtained from the above wire rods after drawing and galvanizing all have tensile strengths of ≥2000MPa, the torsion values ​​of 100D gauge samples are all >8 times, and the maximum stress is 0.45σ. b The fatigue lives under these conditions are all >2.4 million cycles, which can effectively meet the production requirements of long-span and long-life bridge cables.

[0082] Therefore, it can be seen that the wire rod according to the present invention can be used to manufacture bridge cable steel wire with a strength of 2000MPa or more after wire drawing and galvanizing. At present, the span of cable-stayed bridges is over 1000 meters, and the span of suspension bridges is also close to 2000 meters. With the increase in bridge span, it is necessary to use galvanized steel wire cables with high strength levels to improve the service life of bridges in order to reduce construction costs and save materials. The market prospects of the wire rod according to the present invention are very broad, with high popularization and application value, which can bring huge economic benefits.

[0083] In addition, the combination of each technical feature in the present disclosure is not limited to the combination described in the claims of the present disclosure or the combination described in the specific embodiments. All the technical features described in the present disclosure can be freely combined or arbitrarily combined as long as they do not conflict with each other.

[0084] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications added thereto can be directly obtained by those skilled in the art from the disclosure of the present invention or can be easily recalled, and all should belong to the protection scope of the present invention.

Claims

1. A wire made of high-strength long fatigue life cable steel containing the following chemical elements by mass percentage: C: 0.90 - 1.00%; Si: 0.90 - 1.50%; Mn: 0.25 - 0.58%; Cr: 0.20 - 1.00%; V: 0.03 - 0.12%; Ca: 0.0008 - 0.0025%, with the balance being Fe and other inevitable impurities, and the tensile strength of the high-strength long fatigue life cable steel is ≥ 1430 MPa, and the tensile strength of the wire is ≥ 1430 MPa, and the performance of the wire satisfies at least one of the following: reduction area > 30%, tensile strength of the drawn and zinc-plated steel wire ≥ 2000 MPa, torsional value > 8 times, fatigue life > 2.4 million times under the condition of maximum stress 0.45σb.

2. The wire according to Claim 1, wherein the mass percentage of each chemical element satisfies at least one of Si: 1.0 - 1.4% and Cr: 0.2 - 0.7%.

3. The total content of other inevitable impurities is 0.10% or less, and the content of each impurity element satisfies at least one of Cu ≤ 0.05%, Al ≤ 0.004%, Ti ≤ 0.003%, P ≤ 0.015%, S ≤ 0.010%, O ≤ 0.0025%, and N ≤ 0.0045%. The wire according to Claim 1.

4. The following chemical elements: Mo: 0.10 - 0.80%; B: 0.0008 - 0.0012%; Re: 0.0005 - 0.008%, The wire according to Claim 1, containing at least one of them.

5. The wire according to Claim 1, wherein the microstructure is mainly refined sorbite structure, the phase ratio of sorbite is ≥ 95%, and the phase ratio of grain boundary network cementite and martensite structure is ≤ 0.5%.

6. The wire according to Claim 5, wherein the average value of the interlamellar spacing of the sorbite structure is 40 - 260 nm.

7. The wire according to Claim 5, wherein the microstructure further has V carbonitride precipitates with a size of 5 - 50 nm.

8. The wire according to Claim 5, wherein in the microstructure, the size of inclusions is < 35 μm and the aspect ratio of inclusions is > 2.

9. The wire according to Claim 5, wherein the carbon segregation at the core is less than 1.

08.

10. A steel wire obtained by wire drawing, zinc plating, and stabilization treatment of the wire according to any one of claims 1 to 9, wherein the steel wire has a tensile strength of ≧ 2000 MPa, a torsional value of a 100D gauge sample of > 8 times, and a fatigue life of > 2.4 million times under the condition of a maximum stress of 0.45σb.

11. The steel wire according to claim 10, wherein the steel wire has a tensile strength of 2020 - 2100 MPa, a torsional value of a 100D gauge sample of 12 - 24 times, and a fatigue life of 2.49 - 4.2 million times under the condition of a maximum stress of 0.45σb.

12. The following steps: (1) Smelting and casting; (2) Rough rolling; (3) High - speed wire rolling; (4) Stelmor controlled cooling; (5) Isothermal treatment: The austenite heating temperature is 890 - 1050°C, the holding time is 6 - 20 minutes, and the isothermal treatment temperature is 530 - 600°C. A method for manufacturing a wire according to any one of claims 1 to 9, comprising the above steps.

13. In step (1), during the smelting process, the vacuum degassing time is controlled to be > 20 minutes, and during the casting process, the carbon segregation in the billet core is controlled to be less than 1.

08. The manufacturing method according to claim 12 is characterized by this.

14. In step (2), a two - time firing and forming process is used to rough - roll a continuously cast billet, and it is block - rolled into a billet with an angle of 150 - 250 mm at a temperature of 1100 - 1250°C; then it is put into a heating furnace for heating, and the heating temperature is controlled to be 960 - 1150°C, and the holding time is controlled to be 1.5 - 2.5 hours. The manufacturing method according to claim 12 is characterized by this.

15. In step (3), the rolling speed is controlled to be 20 - 60 m / s. The manufacturing method according to claim 12 is characterized by this.

16. In step (3), the inlet temperature of the finishing rolling mill is controlled to be 920 - 990°C, the inlet temperature of the drawing and sizing machine is controlled to be 920 - 990°C, and the wire - spitting temperature is controlled to be 880 - 950°C. The manufacturing method according to claim 12 is characterized by this.

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