Ultrahigh-strength hot-rolled wire rod having 1600 MPA tensile strength grade and manufacturing method therefor

Abstract

The present invention relates to an ultrahigh-strength hot-rolled wire rod having 1600 MPa tensile strength grade and a manufacturing method therefor. A C-Si-Mn-Al-Cr-V-Mo composition design is used for the hot-rolled wire rod. The manufacturing method comprises performing an online molten salt cooling treatment on a wire rod resulting from high-speed wire rolling and wire laying, wherein the temperature of a molten salt in the online molten salt cooling treatment is 480-540ºC, the isothermal holding time is 100-190 s, and the cooling rate of the wire rod is greater than or equal to 42ºC / s. The wire rod obtains a mixed microstructure composed of predominantly fine and uniform sorbite and containing a small amount of ferrite and dispersively distributed carbide precipitate phase. The wire rod can achieve a net-shaped carbide grade of 0, a sorbite microstructure interlamellar spacing of 60-80 nm, a tensile strength of greater than or equal to 1610 MPa, and a section shrinkage rate of greater than or equal to 30%. The wire rod is used in application fields such as manufacturing ultrahigh-strength bridge cables and steel strands, meets ultrahigh strengthening and lightweight requirements, and has good market application prospects.

Description

[0001] The present disclosure belongs to the technical field of alloys, and specifically relates to an ultra-high-strength hot-rolled wire rod with a 1,600 MPa grade tensile strength and a manufacturing method thereof. BACKGROUND

[0002] Hot-rolled steel wire rods used in fields such as ultra-high-strength bridge cables are generally of high-carbon steel grades. Molten iron is made into molten steel through electrosmelting and refining, and then made into a wire rod through continuous casting, rolling, and spinning. The conventional hot-rolled wire rods of high-speed wires produced after spinning usually pass through the Stelmor air-cooling line for final structure and performance control. However, the Stelmor air-cooling line has an inadequate controlled cooling capacity. For example, the patent CN102352469B discloses an ultra-high-strength vanadium-titanium composite microalloyed high-carbon steel wire rod and a manufacturing method thereof This patent has C-Mn-Si-V-Ti composition, medium-high temperature spinning, and Stelmor air-cooling line-based controlled cooling process designs. Even if the air-cooling line adopts quick cooling before the pearlitic transformation, a cooling rate can only reach 14°C / s, and a product has a tensile strength Rm of 1,330 MPa to 1,410 MPa and a section shrinkage rate Z of greater than or equal to 32%. The unsatisfactory strength and plasticity are due to the following factors: 1. The increase of the carbon content can improve the strength of a steel grade, but the high carbon content will aggravate the precipitation risk of reticulated carbides. During the cooling process of the wire rod, the time required for passing through a reticulated carbide-sensitive zone is still long, such that reticulated carbides are precipitated, which will cause a strength loss, especially aggravate the deterioration of strength and plasticity of the wire rod. 2. Grains in the cast structure are relatively coarse. Although the addition of alloying elements such as V and Ti in the patent can play a role in inhibiting the growth of austenite grains during hot rolling. However, the coarsening of VC particles caused by improper controlled cooling will weaken the precipitation strengthening effect. The more and the coarser the VC particles precipitated, the more significant the reduction of strength and plasticity of the wire rod. The reduction of plasticity will lead to the fracture of the wire rod during the wire drawing process. Moreover, the small content of sorbite structures and the increase of an interlamellar spacing that are caused by improper controlled cooling will further reduce the strength of the wire rod. The insufficient controlled cooling capacity of the air-cooling line and the uneven cooling rates of windward and leeward sides of a wire rod will also increase the performance fluctuation of a wire rod.

[0003] There is a method of replacing air cooling with on-line water-bath cooling after spinning in the prior art. For example, the patent CN114369760B discloses a wire rod for a stress-corrosion-resistant ultra-high-strength steel strand and a manufacturing method of the steel strand. This patent has C-Mn-Si-Cr-V-B composition, high-temperature spinning, and on-line water-bath controlled cooling process designs. In this patent, the cooling rate can reach 15°C / s or more, and the product has a tensile strength Rm of 1,360 MPa to 1,450 MPa and a section shrinkage rate Z of 20% to 25%. However, the cooling rate is still insufficient, resulting in limited improvement for strength and plasticity. Moreover, bubbles formed on the surface of the wire rod heated by the water bath are easy to cause the uneven cooling of the wire rod and increase the fluctuation of mechanical properties of the wire rod.

[0004] In addition, for example, the patent CN112176258A discloses a wire rod for a 2,500 MPa steel strand and a manufacturing method of the wire rod. This patent has C-Mn-Si-Cr-V-Ti composition, Stelmor cooling, coiling, and salt-bath cooling process designs. The salt-bath cooling is used to alleviate the solidification segregation and improve the material uniformity, such that the wire rod has a tensile strength Rm of 1,610 MPa to 1,660 MPa and a section shrinkage rate Z of greater than or equal to 28%. However, after the coiling, the re-coiling needs to be conducted through decoding, heating, and off-line salt-bath heat treatment, resulting in many procedures and large energy consumption. SUMMARY

[0005] The present disclosure is intended to solve at least one of the above-mentioned technical problems to some extent and provide an ultra-high-strength hot-rolled wire rod with a 1,600 MPa grade tensile strength and a manufacturing method thereof. The present disclosure achieves the development of ultra-high-strength and lightweight hot-rolled wire rods, and has a promising market prospect.

[0006] The present disclosure provides the following technical solutions to solve the technical problems: A manufacturing method of an ultra-high-strength hot-rolled wire rod with a 1,600 MPa grade tensile strength is provided. The hot-rolled wire rod includes the following chemical components in mass percentages: C: 0.90% to 1.10%, Si: 0.60% to 1.10%, Mn: 0.50% to 0.90%, Al: 0.10% to 0.30%, P: less than or equal to 0.020%, S: less than or equal to 0.008%, Cr: 0.10% to 0.50%, V: 0.030% to 0.070%, Mo: 0.10% to 0.40%, and Fe and unavoidable impurities: a balance. The manufacturing method includes: subjecting a wire rod produced after high-speed wire rolling and spinning to on-line molten-salt cooling with a molten-salt temperature of 480°C to 540°C, an isothermal time of 100 s to 190 s, and a wire-rod cooling rate of greater than or equal to 42°C / s.

[0007] Design bases for the chemical components and the mass percentages thereof of the hot-rolled wire rod include: (1) Carbon: C is the most basic and economical strengthening element in the steel. C is added to produce a sufficient amount of a carbide strengthening phase to significantly enhance a strength of the material and ensure a satisfactory strength grade of the steel, which is conducive to improving a strength grade of the wire rod after drawing when used in bridge cables, strands, and other fields. However, an excessively high C content will increase the segregation during continuous casting and reduce the plasticity of the wire rod, resulting in fractures during drawing or twisting. Therefore, the mass percentage of C is controlled at 0.90% to 1.10%.

[0008] (2) Silicon and aluminum: Si and Al have similar effects, can play a solid-solution strengthening role in the steel, and can expand the range of ferrite generation. The enrichment of Si and Al at a ferrite / cementite interface is conducive to inhibiting the generation of cementite and improving the thermal stability during processing, thereby improving the plasticity of the wire rod. However, an excessively high Si content will cause the decarburization and reduce the surface quality of the wire rod. An excessively high Al content will cause the nozzle nodulation in a continuous casting process and accelerate the decarburization. Therefore, the mass percentage of Si is controlled at 0.60% to 1.10%, and the mass percentage of Al is controlled at 0.10% to 0.30%.

[0009] (3) Manganese: Mn can expand an austenite phase zone, which is conducive to the refinement of phase change structures and the regulation of a matrix structure content. Moreover, the solid-solution Mn element can improve a strength of the steel to ensure a strength grade of the steel. However, an excessively high Mn content is easy to promote the segregation of residual elements, and will increase the overheating sensitivity of the steel and the control difficulty for the controlled cooling of a structure. Therefore, the mass percentage of Mn is controlled at 0.50% to 0.90%.

[0010] (4) Chromium: Cr is a medium-high carbide-producing element, and can significantly improve the hardenability of the steel and enhance the matrix. However, an excessively high Cr content will lead to the generation of low-temperature structures, which is not conducive to the structure control and can reduce the plasticity and toughness. Therefore, the mass percentage of Cr is controlled at 0.10% to 0.50%.

[0011] (5) Vanadium: Amain function of the V microalloying element is to produce a dispersed precipitated strengthening phase in a middle-temperature isothermal zone, strengthen the matrix, and reduce the hydrogen-induced cracking sensitivity of the wire rod, such that the wire rod has excellent hydrogen embrittlement resistance. However, an excessively high V content will lead to an excessively high material cost and reduced plasticity. Therefore, the mass percentage of V is controlled at 0.030% to 0.070%.

[0012] (6) Molybdenum: Mo can improve the thermal stability of a microalloy carbide, inhibit the precipitation and coarsening of Cr and the coarsening tendency of a carbide including VC, is conducive to playing the roles of Cr and V, and can improve the strength of the material. However, an excessively high Mo content will increase the risks of decarburization and ferrite and brittle phases, resulting in reduced plasticity. Therefore, the mass percentage of Mo is controlled at 0.10% to 0.40%.

[0013] (7) Phosphorus and sulfur: P will cause the grain coarsening, such that the plasticity and toughness of the steel will be significantly reduced. S will increase the harmful impurities in the steel grade to cause hot shortness. Therefore, the mass percentage of P is limited to less than or equal to 0.020%, and the mass percentage of S is limited to less than or equal to 0.008%.

[0014] On the basis of the design of V, Al, and Mo components and the design of adding appropriate Cr and Si alloying elements, the above manufacturing method adopts a process of directly conducting on-line molten-salt cooling after spinning: On the one hand, a cooling rate for the wire rod is significantly higher than cooling rates of the Stelmor air-cooling line and the on-line water-bath treatment. Under the action of ultra-fast cooling, the wire rod with a high carbon content can quickly pass by a harmful reticulated carbide-precipitating temperature range to prevent a secondary cementite from precipitating from an austenite, growing along a grain boundary, and distributing in a reticulated manner before the phase transformation of the austenite, such that the secondary cementite can quickly enter a sorbite phase region to precipitate fine and uniform sorbite, which improves the strength of the wire rod and especially the plasticity of the wire rod.

[0015] On the other hand, the high-temperature wire rod produced after spinning is quickly cooled to a molten-salt temperature through on-line molten-salt cooling, such that the phase transformation of a structure of the wire rod is driven by a temperature while a dispersed precipitated strengthening phase is formed in a middle-temperature isothermal zone. The higher the molten-salt temperature, the longer the isothermal time, and the lower the cooling rate, the greater the coarsening tendency of VC precipitated, the lower the content of sorbite transformed from austenite, the higher the ferrite content, and the larger the interlamellar spacing of sorbite, which reduces the strength of the wire rod. However, if the molten-salt temperature is too high and the isothermal time is too long, the strength of the wire rod will be reduced due to the continuous coarsening of VC, especially the plasticity will be significantly reduced. On the contrary, the lower the molten-salt temperature, the shorter the isothermal time, and the higher the cooling rate, the finer and more uniformly dispersed the VC precipitated, the higher the content of sorbite transformed from austenite, the lower the ferrite content, and the lower the interlamellar spacing of sorbite, which increases the strength of the wire rod and decreases the plasticity. However, if a molten-salt temperature is too low, the abnormal bainite structure will occur, which will cause the plasticity of the wire rod to decrease significantly. If the isothermal time is too short, the structure is not fully transformed, which will cause the strength of the wire rod to decrease. Thus, on the basis of inhibiting the coarsening of Cr and VC precipitated by Mo, the molten-salt temperature and the isothermal time can be further controlled to make the wire rod have fine and uniform sorbite structures and diffusely distributed carbides, so as to enhance the strength of the hot-rolled wire rod and achieve the excellent hydrogen embrittlement resistance and the strong plasticity matching.

[0016] Preferably, the manufacturing method includes: conducting high-speed wire rolling on a continuous casting billet. The continuous casting billet is produced through continuous casting of molten steel and has a carbon segregation index of less than or equal to 1.04. For the continuous casting, a superheat degree of a continuous casting tundish is controlled at 10°C to 30°C. The carbon segregation of the high-carbon steel is improved by reducing the supercooling degree. A fluctuation of a molten steel level in a crystallizer is controlled within ±3 mm to allow pouring at a stable speed. Electromagnetic stirring at a head end is conducted at a current of 200 Ato 400 A and a frequency of 1 Hz to 5 Hz. Electromagnetic stirring at a tail end is conducted at a current of 350 A to 550 A and a frequency of 9 Hz to 12 Hz. The use of electromagnetic stirring makes the impurities float up to enable a prominent internal quality of the casting billet, promotes the formation of an equiaxed crystal solidification structure, and avoids the uneven structures caused by segregation to affect the quality of the product.

[0017] Preferably, an oxide scale on a surface of the continuous casting billet is removed with high-pressure descaling water before the initial rolling during the high-speed wire rolling. A pressure of the high-pressure descaling water is greater than or equal to 16 MPa. This operation is intended to prevent the oxide scale from being pressed into a surface of a wire during a rolling process to affect the surface quality.

[0018] Preferably, the high-speed wire rolling includes low-temperature rolling with a heavy-duty pre-finishing mill, a heavy-duty finishing mill, and a heavy-duty reducing and sizing mill at a temperature lower than or equal to 860°C, and a final rolling reduction of the high-speed wire rolling is 7% to 11%. When the wire rod passes through the pre-finishing mill, the finishing mill, and the reducing and sizing mill successively, grains are refined through low-temperature heavy-duty large-reduction rolling, such that a wire grain size is less than or equal to 18 pm. The strain energy accumulation inside grains and the fine prior austenite grains provide a prominent phase-transformation basic structure for the on-line molten-salt cooling, are conducive to further refining the interlamellar spacing, and improve the sorbite rate and the material strength.

[0019] Preferably, the spinning is low-temperature spinning at a temperature lower than or equal to 860°C. When the controlled cooling is conducted with the conventional Stelmor air-cooling line, high-temperature spinning is required to avoid the precipitation of reticulated carbides during spinning or reduce the reticulated carbides precipitated in an air-cooling zone after spinning. Because the present disclosure adopts on-line molten-salt cooling directly after spinning to improve the reticulated carbon problem. Therefore, the use of low-temperature spinning can further reduce the growth tendency of austenite grains and lead to fine and rich austenite grains, which is convenient for the subsequent decomposition of fine austenite grains into fine sorbite structures and thus improves the sorbite rate and the material strength.

[0020] Preferably, the on-line molten-salt cooling is conducted with a molten-salt circulating rate of 230 t / h to 280 t / h. The higher the molten-salt circulating rate, the higher the molten-salt temperature accuracy, but the higher the energy consumption cost. The molten-salt temperature accuracy is generally controlled within ±3°C, such that the wire rod undergoes a rapid heat exchange with the molten salt to ensure a transition temperature of a phase-transformation process of the wire rod. The wire-rod cooling rate is preferably lower than or equal to 50°C / s, such that the wire rod undergoes full phase transformation and the strength and plasticity of the wire rod are further improved.

[0021] An ultra-high-strength hot-rolled wire rod with a 1,600 MPa grade tensile strength is provided. The hot-rolled wire rod is manufactured by the manufacturing method of an ultra-high-strength hot-rolled wire rod with a 1,600 MPa grade tensile strength described above.

[0022] Preferably, the hot-rolled wire rod has a sorbite structure with a volume percentage of greater than or equal to 96% and a balance of a mixed structure composed of a ferrite and a dispersed precipitated phase. The sorbite structure has a high strength and excellent plasticity, and the sorbite rate is high. There is no residual austenite phase and bainite abnormal structure. The diffused precipitation of fine and uniform VC particles significantly increases the strength of the wire rod, and makes the wire rod have excellent plasticity. It is suitable for the wire rod to be drawn into a high-strength steel wire.

[0023] Preferably, the sorbite structure has a fine interlamellar spacing of 60 nm to 80 nm, and thus the wire rod has a high strength.

[0024] Preferably, a reticulated carbide grade of the hot-rolled wire rod is less than 0.5 and can reach 0.

[0025] Preferably, the hot-rolled wire rod has a diameter of 12.5 mm to 15.0 mm, a tensile strength of greater than or equal to 1,610 MPa, and a section shrinkage rate of larger than or equal to 30%, such that the large-size hot-rolled wire rod has excellent strong plasticity matching. The present disclosure allows a comparable strong plasticity level to the off-line salt-bath treatment, and features of significantly reduced process steps, low energy consumption, and prominent industrial production adaptability.

[0026] Preferably, when passing through a molten salt, the wire rod can undergo a quick and uniform heat exchange, which does not involve a cold side or a non-cold side compared with the Stelmor air-cooling line and does not undergo bubble interference compared with the on-line water-bath cooling. Therefore, the cooling and the microstructural evolution are uniform. A same-circle mechanical fluctuation of the hot-rolled wire rod is smaller than or equal to 24 MPa.

[0027] A use of the ultra-high-strength hot-rolled wire rod with a 1,600 MPa grade tensile strength is provided, including a use in manufacturing a bridge cable and a steel strand. The bridge cable and the steel strand include a bridge cable and a steel strand of 2,100 MPa or more.

[0028] Compared with the prior art, the present disclosure has the following advantages: (1) In view of the problems that the existing hot-rolled wire rods have an insufficient strength grade, cannot be developed to have an ultra-high strength and a light weight, and cannot meet the market use needs, the manufacturing method of the present disclosure has a C-Si-Mn-Al-Cr-V-Mo composition design and an on-line rapid salt-bath treatment design directly after spinning. The ultra-fast cooling quickly passes by a harmful reticulated carbide-precipitating temperature range, and achieves a reticulated carbide grade of 0. On the basis of inhibiting by Mo the coarsening of Cr and VC precipitated, a molten-salt temperature and an isothermal time can be controlled to inhibit the coarsening of VC particles, improve the content of sorbite, reduce the interlamellar spacing of sorbite, and avoid the bainite abnormal structure while enabling the isothermal phase transformation in a middle-temperature zone and the precipitation of a VC strengthening phase. As a result, a wire rod that mainly includes fine and uniform sorbite structures and further includes a small amount of a mixed structure composed of a ferrite and a dispersed carbide precipitated phase can be obtained, the sorbite structure has an interlamellar spacing of 60 nm to 80 nm, and the excellent hydrogen embrittlement resistance and the strong plasticity matching are achieved. The chemical composition characteristics of steel + low-temperature heavy-duty + low-temperature spinning + on-line rapid cooling technology can be further used to further refine grains with the fine prior austenite grains to improve the strength of the wire rod. The present disclosure has prominent industrial production adaptability.

[0029] (2) The present disclosure has successfully developed a hot-rolled wire rod with a 1,600 MPa grade tensile strength. The hot-rolled wire rod has a tensile strength of greater than or equal to 1,610 MPa, a section shrinkage rate of greater than or equal to 30%, and a same-circle mechanical fluctuation of smaller than or equal to 24 MPa. The hot-rolled wire rod can be used in manufacturing ultra-high-strength bridge cables, steel strands, etc., can meet the ultra-high strength and light weight requirements, and has a promising market prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and / or additional aspects and advantages of the present disclosure will become apparent and easy to understand from the description of embodiments in conjunction with the following accompanying drawings. FIG. 1 is an image of a metallurgical structure of Example 1 of the present disclosure; FIG. 2 is an image of a metallurgical structure of Comparative Example 1 of the present disclosure; FIG. 3 is an image of a metallurgical structure of Example 2 of the present disclosure; FIG. 4 is an image of a metallurgical structure of Comparative Example 2 of the present disclosure; FIG. 5 is an image of a metallurgical structure of Example 3 of the present disclosure; FIG. 6 is an image of a metallurgical structure of Comparative Example 3 of the present disclosure; and FIG. 7 is an image of a metallurgical structure of Example 4 of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The examples described below with reference to the accompanying drawings are illustrative merely for explanation, and are not intended to limit the description of the features and characteristics of the present disclosure. These examples propose the best way to implement the present disclosure, are intended to explain the present disclosure, are sufficient to make a person skilled in the art implement the present disclosure, and shall not be construed as limiting the scope of the present disclosure in any way. The scope of the present disclosure is limited only by the appended claims. Example 1

[0032] A preferred embodiment of the manufacturing method of an ultra-high-strength hot-rolled wire rod with a 1,600 MPa grade tensile strength in the present disclosure was provided. The hot-rolled wire rod included the following chemical components in mass percentages: C: 0.9%, Si: 1.1%, Mn: 0.78%, Al: 0.26%, P: 0.02%, S: 0.008%, Cr: 0.25%, V: 0.05%, Mo: 0.4%, and Fe and unavoidable impurities: a balance. The manufacturing method had a process flow of continuous casting —> heating furnace —> high-speed wire rolling —» spinning —> on-line molten-salt cooling, and was specifically as follows: The continuous casting process was as follows: high-temperature molten steel produced through molten iron pretreatment, converter smelting, ladle furnace (LF) refining, and vacuum degassing (VD) was made into a continuous casting billet by a continuous casting machine. A superheat degree of a continuous casting tundish was controlled at 10°C to 15°C. A fluctuation of a molten steel level in a crystallizer was controlled within ±3 mm to allow stable pouring. Electromagnetic stirring was adopted. Electromagnetic stirring at a head end was conducted at a current of 300 A and a frequency of 2 Hz and electromagnetic stirring at a tail end was conducted at a current of 500 A and a frequency of 10 Hz, such that impurities floated up to achieve a prominent internal quality of the continuous casting billet. The continuous casting billet had a Carbon segregation index of 1.03, and was a square billet with a size of 160 mm * 160 mm.

[0033] The heating furnace procedure was intended to heat the continuous casting billet by a heating furnace to produce a high-temperature red steel with rollable plasticity. The high-speed wire rolling procedure was intended to roll the high-temperature red steel into a wire through hot rolling of a rolling line. The red steel produced after the continuous casting billet was treated in the heating furnace had an oxide scale on a surface due to oxidation. The oxide scale on the surface of the continuous casting billet was removed with high-pressure descaling water before initial rolling. A pressure of the high-pressure descaling water was 17 MPa. The rolling line adopted low-temperature rolling with a heavy-duty pre-finishing mill at 860°C, a heavy-duty finishing mill at 852°C, and a heavy-duty reducing and sizing mill at 840°C sequentially, and a final rolling reduction was 8.5%. A wire grain size was less than or equal to 17 pm. The strain energy accumulation inside grains and the fine prior austenite grains provided a prominent phase-transformation basic structure for the on-line molten-salt cooling.

[0034] The spinning procedure was intended to manufacture a wire from the rolling line into a wire rod through a spinning mechanism. Low-temperature spinning was conducted at 851 °C, which further reduced the growth tendency of austenite grains. The wire rod had a diameter of 12.5 mm.

[0035] The on-line molten-salt cooling procedure was conducted in a salt-bath tank filled with a molten salt. When passing through the salt-bath tank, a wire rod produced after spinning underwent a heat exchange with the molten salt and thus was quickly cooled to a molten-salt temperature. A high-temperature molten salt heated by the wire rod in the salt-bath tank was continuously circulated with a molten salt of a relatively low temperature outside the salt-bath tank to control the temperature rise of the molten salt in the salt-bath tank. A molten-salt circulating rate was 230 t / h to 250 t / h, the molten-salt temperature was controlled at 508°C, a molten-salt temperature accuracy was controlled within ±3°C, an isothermal time was 135 s, and a wire-rod cooling rate was 45°C / s. As a result, the wire rod had fine and uniform sorbite structures, diffusely distributed carbides, and fine and evenly dispersed VC particles precipitated, which could enhance the strength of the hot-rolled wire rod and achieve the strong plasticity matching. A wire rod from the salt-bath tank was cleaned, transported along a track for air cooling and coiling, and then transported along a line for finishing, packaging, and stocking to produce a finished coil of the hot-rolled wire rod. A metallurgical structure of the hot-rolled wire rod was shown in FIG. 1.

[0036] Comparative Example 1 A manufacturing method of a hot-rolled wire rod was provided, which was different from Example 1 in that: The manufacturing method had a process flow of continuous casting —> heating furnace —» high-speed wire rolling —► spinning —> Stelmor air-cooling. A rolling line of high-speed wire rolling adopted a heavy-duty pre-finishing mill at 965°C, a heavy-duty finishing mill at 944°C, and a heavy-duty reducing and sizing mill at 936°C sequentially. The spinning was conducted at 952°C. The Stelmor air-cooling was conducted as follows: a wire rod produced after spinning was allowed to pass through a Stelmor air-cooling line to produce the hot-rolled wire rod, where insulation covers for the Stelmor line all were covered, a speed of a roller table was 1.1 m / s, first fans No. 1 to No. 13 all were turned on by 100%, a total air volume of each fan was 260,000 m3t / h, and an average cooling rate for the wire rod was 13°C / s. A metallurgical structure of the hot-rolled wire rod was shown in FIG. 2. Example 2

[0037] A preferred embodiment of the manufacturing method of an ultra-high-strength hot-rolled wire rod with a 1,600 MPa grade tensile strength in the present disclosure was provided. The hot-rolled wire rod included the following chemical components in mass percentages: C: 0.97%, Si: 0.6%, Mn: 0.9%, Al: 0.22%, P: 0.018%, S: 0.007%, Cr: 0.32%, V: 0.046%, Mo: 0.1%, and Fe and unavoidable impurities: a balance. The manufacturing method had a process flow of continuous casting —► heating furnace —► high-speed wire rolling —> spinning —> on-line molten-salt cooling, and was specifically as follows: The continuous casting process was as follows: high-temperature molten steel produced through molten iron pretreatment, converter smelting, LF refining, and VD was made into a continuous casting billet by a continuous casting machine. A superheat degree of a continuous casting tundish was controlled at 12°C to 20°C. A fluctuation of a molten steel level in a crystallizer was controlled within ±3 mm to allow stable pouring. Electromagnetic stirring was adopted. Electromagnetic stirring at a head end was conducted at a current of 250 A and a frequency of 4 Hz and electromagnetic stirring at a tail end was conducted at a current of 400 A and a frequency of 10 Hz, such that impurities floated up to achieve a prominent internal quality of the continuous casting billet. The continuous casting billet had a Carbon segregation index of 1.01, and was a square billet with a size of 160 mm x 160 mm.

[0038] The heating furnace procedure was intended to heat the continuous casting billet by a heating furnace to produce a high-temperature red steel with rollable plasticity. The high-speed wire rolling procedure was intended to roll the high-temperature red steel into a wire through hot rolling of a rolling line. The red steel produced after the continuous casting billet was treated in the heating furnace had an oxide scale on a surface due to oxidation. The oxide scale on the surface of the continuous casting billet was removed with high-pressure descaling water before initial rolling. A pressure of the high-pressure descaling water was 18 MPa. The rolling line adopted low-temperature rolling with a heavy-duty pre-finishing mill at 850°C, a heavy-duty finishing mill at 842°C, and a heavy-duty reducing and sizing mill at 829°C sequentially, and a final rolling reduction was 9%. A wire grain size was less than or equal to 16 pm. The strain energy accumulation inside grains and the fine prior austenite grains provided a prominent phase-transformation basic structure for the on-line molten-salt cooling.

[0039] The spinning procedure was intended to manufacture a wire from the rolling line into a wire rod through a spinning mechanism. Low-temperature spinning was conducted at 840°C, which further reduced the growth tendency of austenite grains. The wire rod had a diameter of 13 mm.

[0040] The on-line molten-salt cooling procedure was conducted in a salt-bath tank filled with a molten salt. When passing through the salt-bath tank, a wire rod produced after spinning underwent a heat exchange with the molten salt and thus was quickly cooled to a molten-salt temperature. A high-temperature molten salt heated by the wire rod in the salt-bath tank was continuously circulated with a molten salt of a relatively low temperature outside the salt-bath tank to control the temperature rise of the molten salt in the salt-bath tank. A molten-salt circulating rate was 250 t / h to 270 t / h, the molten-salt temperature was controlled at 536°C, a molten-salt temperature accuracy was controlled within ±3°C, an isothermal time was 182 s, and a wire-rod cooling rate was 43°C / s. As a result, the wire rod had fine and uniform sorbite structures, diffusely distributed carbides, and fine and evenly dispersed VC particles precipitated, which could enhance the strength of the hot-rolled wire rod and achieve the strong plasticity matching. A wire rod from the salt-bath tank was cleaned, transported along a track for air cooling and coiling, and then transported along a line for finishing, packaging, and stocking to produce a finished coil of the hot-rolled wire rod. A metallurgical structure of the hot-rolled wire rod was shown in FIG. 3. Pal in FIG. 3 indicated a measured interlamellar spacing of 10 sorbites.

[0041] Comparative Example 2 A manufacturing method of a hot-rolled wire rod was provided, which was different from Example 2 in that: The on-line molten-salt cooling was conducted with a molten-salt temperature of 576°C, an isothermal time of 234 s, and a wire-rod cooling rate of 39°C / s to produce the hot-rolled wire rod. A metallographic structure of the hot-rolled wire rod was shown in FIG. 4. Pal in FIG. 4 indicated a measured interlamellar spacing of 10 sorbites. Example 3

[0042] A preferred embodiment of the manufacturing method of an ultra-high-strength hot-rolled wire rod with a 1,600 MPa grade tensile strength in the present disclosure was provided. The hot-rolled wire rod included the following chemical components in mass percentages: C: 1.1%, Si: 0.88%, Mn: 0.5%, Al: 0.3%, P: 0.018%, S: 0.008%, Cr: 0.47%, V: 0.033%, Mo: 0.33%, and Fe and unavoidable impurities: a balance. The manufacturing method had a process flow of continuous casting —> heating furnace —» high-speed wire rolling —> spinning —> on-line molten-salt cooling, and was specifically as follows: The continuous casting process was as follows: high-temperature molten steel produced through molten iron pretreatment, converter smelting, LF refining, and VD was made into a continuous casting billet by a continuous casting machine. A superheat degree of a continuous casting tundish was controlled at 14°C to 22°C. A fluctuation of a molten steel level in a crystallizer was controlled within ±3 mm to allow stable pouring. Electromagnetic stirring was adopted. Electromagnetic stirring at a head end was conducted at a current of 400 A and a frequency of 2 Hz and electromagnetic stirring at a tail end was conducted at a current of 500 A and a frequency of 9 Hz, such that impurities floated up to achieve a prominent internal quality of the continuous casting billet. The continuous casting billet had a Carbon segregation index of 0.98, and was a square billet with a size of 160 mm * 160 mm.

[0043] The heating furnace procedure was intended to heat the continuous casting billet by a heating furnace to produce a high-temperature red steel with rollable plasticity. The high-speed wire rolling procedure was intended to roll the high-temperature red steel into a wire through hot rolling of a rolling line. The red steel produced after the continuous casting billet was treated in the heating furnace had an oxide scale on a surface due to oxidation. The oxide scale on the surface of the continuous casting billet was removed with high-pressure descaling water before initial rolling. A pressure of the high-pressure descaling water was 18 MPa. The rolling line adopted low-temperature rolling with a heavy-duty pre-finishing mill at 822°C, a heavy-duty finishing mill at 814°C, and a heavy-duty reducing and sizing mill at 807°C sequentially, and a final rolling reduction was 11%. A wire grain size was less than or equal to 16 pm. The strain energy accumulation inside grains and the fine prior austenite grains provided a prominent phase-transformation basic structure for the on-line molten-salt cooling.

[0044] The spinning procedure was intended to manufacture a wire from the rolling line into a wire rod through a spinning mechanism. Low-temperature spinning was conducted at 824°C, which further reduced the growth tendency of austenite grains. The wire rod had a diameter of 14 mm.

[0045] The on-line molten-salt cooling procedure was conducted in a salt-bath tank filled with a molten salt. When passing through the salt-bath tank, a wire rod produced after spinning underwent a heat exchange with the molten salt and thus was quickly cooled to a molten-salt temperature. A high-temperature molten salt heated by the wire rod in the salt-bath tank was continuously circulated with a molten salt of a relatively low temperature outside the salt-bath tank to control the temperature rise of the molten salt in the salt-bath tank. A molten-salt circulating rate was 260 t / h to 280 t / h, the molten-salt temperature was controlled at 486°C, a molten-salt temperature accuracy was controlled within ±3°C, an isothermal time was 119 s, and a wire-rod cooling rate was 47°C / s. As a result, the wire rod had fine and uniform sorbite structures, diffusely distributed carbides, and fine and evenly dispersed VC particles precipitated, which could enhance the strength of the hot-rolled wire rod and achieve the strong plasticity matching. A wire rod from the salt-bath tank was cleaned, transported along a track for air cooling and coiling, and then transported along a line for finishing, packaging, and stocking to produce a finished coil of the hot-rolled wire rod. A metallurgical structure of the hot-rolled wire rod was shown in FIG. 5. Pal in FIG. 5 indicated a measured interlamellar spacing of 10 sorbites.

[0046] Comparative Example 3 A manufacturing method of a hot-rolled wire rod was provided, which was different from Example 3 in that: The on-line molten-salt cooling was conducted with a molten-salt temperature of 435°C, an isothermal time of 95 s, and a wire-rod cooling rate of 53°C / s to produce the hot-rolled wire rod. A metallographic structure of the hot-rolled wire rod was shown in FIG. 6. Example 4

[0047] A preferred embodiment of the manufacturing method of an ultra-high-strength hot-rolled wire rod with a 1,600 MPa grade tensile strength in the present disclosure was provided. The hot-rolled wire rod included the following chemical components in mass percentages: C: 1.04%, Si: 0.93%, Mn: 0.83%, Al: 0.1%, P: 0.016%, S: 0.006%, Cr: 0.14%, V: 0.062%, Mo: 0.26%, and Fe and unavoidable impurities: a balance. The manufacturing method had a process flow of continuous casting —>■ heating furnace —> high-speed wire rolling —> spinning —> on-line molten-salt cooling, and was specifically as follows: The continuous casting process was as follows: high-temperature molten steel produced through molten iron pretreatment, converter smelting, LF refining, and VD was made into a continuous casting billet by a continuous casting machine. A superheat degree of a continuous casting tundish was controlled at 20°C to 30°C. A fluctuation of a molten steel level in a crystallizer was controlled within ±3 mm to allow stable pouring. Electromagnetic stirring was adopted. Electromagnetic stirring at a head end was conducted at a current of 400 A and a frequency of 4 Hz and electromagnetic stirring at a tail end was conducted at a current of 350 A and a frequency of 12 Hz, such that impurities floated up to achieve a prominent internal quality of the continuous casting billet. The continuous casting billet had a Carbon segregation index of 1.03, and was a square billet with a size of 160 mm * 160 mm.

[0048] The heating furnace procedure was intended to heat the continuous casting billet by a heating furnace to produce a high-temperature red steel with rollable plasticity. The high-speed wire rolling procedure was intended to roll the high-temperature red steel into a wire through hot rolling of a rolling line. The red steel produced after the continuous casting billet was treated in the heating furnace had an oxide scale on a surface due to oxidation. The oxide scale on the surface of the continuous casting billet was removed with high-pressure descaling water before initial rolling. A pressure of the high-pressure descaling water was 18 MPa. The rolling line adopted low-temperature rolling with a heavy-duty pre-finishing mill at 830°C, a heavy-duty finishing mill at 821°C, and a heavy-duty reducing and sizing mill at 819°C sequentially, and a final rolling reduction was 8%. A wire grain size was less than or equal to 18 pm. The strain energy accumulation inside grains and the fine prior austenite grains provided a prominent phase-transformation basic structure for the on-line molten-salt cooling.

[0049] The spinning procedure was intended to manufacture a wire from the rolling line into a wire rod through a spinning mechanism. Low-temperature spinning was conducted at 840°C, which further reduced the growth tendency of austenite grains. The wire rod had a diameter of 14 mm.

[0050] The on-line molten-salt cooling procedure was conducted in a salt-bath tank filled with a molten salt. When passing through the salt-bath tank, a wire rod produced after spinning underwent a heat exchange with the molten salt and thus was quickly cooled to a molten-salt temperature. A high-temperature molten salt heated by the wire rod in the salt-bath tank was continuously circulated with a molten salt of a relatively low temperature outside the salt-bath tank to control the temperature rise of the molten salt in the salt-bath tank. A molten-salt circulating rate was 245 t / h to 275 t / h, the molten-salt temperature was controlled at 522°C, a molten-salt temperature accuracy was controlled within ±3°C, an isothermal time was 174 s, and a wire-rod cooling rate was 44°C / s. As a result, the wire rod had fine and uniform sorbite structures, diffusely distributed carbides, and fine and evenly dispersed VC particles precipitated, which could enhance the strength of the hot-rolled wire rod and achieve the strong plasticity matching. A wire rod from the salt-bath tank was cleaned, transported along a track for air cooling and coiling, and then transported along a line for finishing, packaging, and stocking to produce a finished coil of the hot-rolled wire rod. A metallurgical structure of the hot-rolled wire rod was shown in FIG. 7. Pal in FIG. 7 indicated a measured interlamellar spacing of 10 sorbites.

[0051] Comparative Example 4 A manufacturing method of a hot-rolled wire rod was provided, which was different from Example 4 in that: For the continuous casting process, a superheat degree of a continuous casting tundish was controlled at 25°C to 35°C. A fluctuation of a molten steel level in a crystallizer was controlled within ±5 mm to allow stable pouring. Electromagnetic stirring was adopted, where electromagnetic stirring at a tail end was conducted at a current of 600 A and a frequency of 4 Hz. The continuous casting billet had a Carbon segregation index of 1.16. The hot-rolled wire rod was produced.

[0052] Comparative Example 5 A manufacturing method of a hot-rolled wire rod was provided, which was different from Example 4 in that: A rolling line of the high-speed wire rolling procedure adopted low-temperature rolling with a heavy-duty pre-finishing mill at 920°C, a heavy-duty finishing mill at 945°C, and a heavy-duty reducing and sizing mill at 904°C sequentially, and a final rolling reduction was 3%. A wire grain size was less than or equal to 28 pm. The spinning procedure was conducted at 925°C to produce the hot-rolled wire rod.

[0053] The hot-rolled wire rods obtained in the above examples and comparative examples each were subjected to structure and performance tests: A test method of a same-circle mechanical fluctuation range was as follows: 2 wire rods were taken at 5 m away from an end of a coil. With a position of a lap zone as a base point, each wire rod was divided into 8 segments equally, and 1 tensile sample was taken from each segment. A strength difference obtained after a tensile test of tensile samples was a same-circle difference of a wire rod. The tensile test was conducted according to "GB-T228.1-2021 Metal Materials - Tensile Test Part 1: Room-Temperature Test Method" to obtain a tensile strength and a section shrinkage rate. The structure test was conducted according to the metal microstructure test method in the GB / T13298 standard. Resulting comparison results were shown in Table 1 below: Table 1 Comparison results of structures and properties of hot-rolled wire rods manufactured with different compositions and manufacturing methods Example Tensile Section Same-circle Micro structures Interlamellar Reticulated strength / MPa shrinkage rate / % mechanical fluctuation / MPa spacing of a sorbite structure / nm carbide / grade Example 1 1625 35 21 97% of a sorbite structure and the balance of a ferrite and a dispersed precipitated phase 65 0 Comparative Example 1 1054 20 82 84% of a sorbite structure and the balance of a ferrite and a residual austenite 215 3 Example 2 1611 38 22 96% of a sorbite structure and the balance of a ferrite and a dispersed precipitated phase 77 0 Comparative Example 2 1329 24 24 90% of a sorbite structure and the balance of a ferrite and a dispersed precipitated phase 130 0 Example 3 1640 33 24 98% of a sorbite structure and the balance of a ferrite and a dispersed precipitated phase 60 0 Comparative Example 3 1699 10 48 83% of a sorbite structure and the balance of a ferrite, a residual austenite, and a bainite 67 0 Example 4 1632 36 23 97% of a sorbite structure and the balance of a ferrite and a dispersed precipitated phase 74 0 Comparative Example 4 1546 21 52 95% of a sorbite structure and the balance of a ferrite and a dispersed precipitated phase 76 0.5 Comparative 1469 27 26 92% of a sorbite 96 0 Example 5 structure and the balance of a ferrite and a dispersed precipitated phase

[0054] According to the comparison results of Examples 1 to 4 and Comparative Example 1: In view of the problems that the existing hot-rolled wire rods have an insufficient strength grade, cannot be developed to have an ultra-high strength and a light weight, and cannot meet the market use needs, on the basis of a design of a V, Al, and Mo-containing composition and a design of adding appropriate Cr and Si alloying elements, the present disclosure adopts the process of conducting on-line molten-salt cooling directly after spinning. Compared with the conventional Stelmor air-cooling line, the present disclosure can quickly pass by a harmful reticulated carbide-precipitating temperature range under the action of ultra-fast cooling, which can effectively improve the reticulated carbon precipitation problem.

[0055] Moreover, a molten-salt temperature and an isothermal time can be controlled, such that the wire rod can have fine and uniform sorbite structures and diffusely distributed carbides, and includes a sorbite structure in a volume percentage of greater than or equal to 96% and a balance of a mixed structure composed of a ferrite and a dispersed precipitated phase. An interlamellar spacing of the sorbite structure reaches 60 nm to 80 nm. The wire rod of the present disclosure has a higher sorbite rate, a finer precipitated phase, and a finer sorbite-structure interlamellar spacing than the hot-rolled wire rod from the conventional Stelmor air-cooling line, which achieves the excellent hydrogen embrittlement resistance and strong plasticity matching and effectively improves the strength of the wire rod. The hot-rolled wire rod has a diameter of 12.5 mm to 15.0 mm, a tensile strength of greater than or equal to 1,610 MPa, and a section shrinkage rate of greater than or equal to 30%. The present disclosure can achieve the considerable levels to the off-line salt-bath treatment, but involves reduced procedures and small energy consumption. Because the wire rod can undergo a uniform heat exchange with a molten salt, the same-circle mechanical properties of the wire rod are effectively controlled, and the same-circle mechanical fluctuation is smaller than or equal to 24 MPa. The hot-rolled wire rod can be used in manufacturing ultra-high-strength bridge cables, steel strands, etc., can meet the ultra-high strength and light weight requirements, and has a promising market prospect.

[0056] According to the comparison results of Example 2 and Comparative Example 2: In the present disclosure, if the molten-salt temperature is too high and the isothermal time is too long, there will be a strength loss due to the decrease of a sorbite rate and the increase of a sorbite interlamellar spacing, and the strength of the wire rod will be further reduced and especially the plasticity will be significantly reduced due to the continuous coarsening of VC. According to the comparison results of Example 3 and Comparative Example 3: In the present disclosure, when the molten-salt temperature is too low, the bainite abnormal structure will occur, resulting in the significant decrease in plasticity of the wire rod. When the isothermal time is too short, a structure will not fully transformed, resulting in the decline of a sorbite rate. The significant decrease in plasticity is manifested as the sharp decrease in the section shrinkage rate, indicating that the hot-rolled wire rod is easy to break, and is not suitable for drawing applications even at a high strength. Therefore, in the present disclosure, a dispersed precipitated strengthening phase is formed in a middle-temperature isothermal zone while the phase transformation of a structure of the wire rod is driven by a temperature, which can avoid the occurrence of abnormal structures such as bainite and residual austenite and can further achieve the strong plasticity matching of the wire rod.

[0057] It can be seen from the comparison results of Example 4 and Comparative Example 4 that the segregation can cause the uneven structures and thus affect the quality of a product. It can be seen from the comparison results of Example 4 and Comparative Example 5 that the present disclosure adopts the chemical composition characteristics of steel + low-temperature heavy-duty + low-temperature spinning + on-line rapid cooling technology to further refine grains with fine prior austenite grains to improve the strength of the wire rod. The present disclosure has prominent industrial production adaptability.

[0058] The series of detailed description listed above are only specific illustrations of feasible embodiments of the present disclosure, and are not intended to limit the claimed scope of the present disclosure. When molten steel for a continuous casting billet is smelted with a converter, blowing can be conducted in a top / bottom combined blowing manner to improve the fluidity of the molten steel and reduce the impurity elements such as P and S in the molten steel. All equivalent embodiments or changes made without departing from the technical spirit of the present disclosure should be included in the claimed scope of the present disclosure.

Claims

1. A manufacturing method of an ultra-high-strength hot-rolled wire rod with a 1,600 MPa grade tensile strength, characterized in that the ultra-high-strength hot-rolled wire rod with the 1,600 MPa grade tensile strength comprises the following chemical components in mass percentages: C: 0.90% to 1.10%, Si: 0.60% to 1.10%, Mn: 0.50% to 0.90%, Al: 0.10% to 0.30%, P: less than or equal to 0.020%, S: less than or equal to 0.008%, Cr: 0.10% to 0.50%, V: 0.030% to 0.070%, Mo: 0.10% to 0.40%, and Fe and unavoidable impurities: a balance; and the manufacturing method comprises: conducting high-speed wire rolling on a continuous casting billet, wherein the continuous casting billet is produced through continuous casting of molten steel and has a Carbon segregation index of less than or equal to 1.04, a final rolling reduction of the high-speed wire rolling is 7% to 11%, and a wire grain size is less than or equal to 18 pm; and subjecting a wire rod produced after the high-speed wire rolling and spinning to on-line molten-salt cooling with a molten-salt temperature of 480°C to 540°C, an isothermal time of 100 s to 190 s, and a wire-rod cooling rate of greater than or equal to 42°C / s; wherein the ultra-high-strength hot-rolled wire rod with the 1,600 MPa grade tensile strength has a sorbite structure with a volume percentage of greater than or equal to 96% and a balance of a mixed structure composed of a ferrite and a dispersed precipitated phase; the sorbite structure has an interlamellar spacing of 60 nm to 80 nm and a section shrinkage rate of greater than or equal to 30%; and the ultra-high-strength hot-rolled wire rod with the 1,600 MPa grade tensile strength has a reticulated carbide grade of less than 0.5.

2. The manufacturing method of the ultra-high-strength hot-rolled wire rod with the 1,600 MPa grade tensile strength according to claim 1, characterized in that, for the continuous casting, a superheat degree of a continuous casting tundish is controlled at 10°C to 30°C; a fluctuation of a molten steel level in a crystallizer is controlled within ±3 mm; electromagnetic stirring at a head end is conducted at a current of 200 A to 400 A and a frequency of 1 Hz to 5 Hz; and electromagnetic stirring at a tail end is conducted at a current of 350 Ato 550 A and a frequency of 9 Hz to 12 Hz.

3. The manufacturing method of the ultra-high-strength hot-rolled wire rod with the 1,600 MPa grade tensile strength according to claim 1, characterized in that the high-speed wire rolling comprises low-temperature rolling with a heavy-duty pre-finishing mill, a heavy-duty finishing mill, and a heavy-duty reducing and sizing mill at a temperature lower than or equal to 860°C.

4. The manufacturing method of the ultra-high-strength hot-rolled wire rod with the 1,600 MPa grade tensile strength according to claim 1, characterized in that the spinning is low-temperature spinning at a temperature lower than or equal to 860°C.

5. The manufacturing method of the ultra-high-strength hot-rolled wire rod with the 1,600 MPa grade tensile strength according to claim 1, characterized in that the on-line molten-salt cooling is conducted with a molten-salt circulating rate of 230 t / h to 280 t / h and a molten-salt temperature accuracy controlled within ±3°C.

6. An ultra-high-strength hot-rolled wire rod with a 1,600 MPa grade tensile strength manufactured by the manufacturing method of the ultra-high-strength hot-rolled wire rod with the 1,600 MPa grade tensile strength according to any one of claims 1 to 5.

7. The ultra-high-strength hot-rolled wire rod with the 1,600 MPa grade tensile strength according to claim 6, characterized in that the ultra-high-strength hot-rolled wire rod with the 1,600 MPa grade tensile strength has a diameter of 12.5 mm to 15.0 mm, a tensile strength of greater than or equal to 1,610 MPa, and a same-circle mechanical fluctuation of smaller than or equal to 24 MPa.

8. A use of the ultra-high-strength hot-rolled wire rod with the 1,600 MPa grade tensile strength according to claim 6, characterized by comprising a use in manufacturing a bridge cable and a steel strand.A. CLASSIFICATION OF SUBJECT MATTERC22C38 / 24(2006.01)i; C22C38 / 22(2006.01)i; C22C38 / 02(2006.01)i; C22C38 / 04(2006.01)i; C22C38 / 06(2006.01)i;C22C38 / 12(2006.01)i; C21D8 / 06(2006.01)i; C21Dl / 46(2006.01)i; C21D9 / 52(2006.01)iAccording to International Patent Classification (IPC) or to both national classification and IPCB.FIELDS SEARCHEDMinimum documentation searched (classification system followed by classification symbols) IPC:C22C C21DDocumentation searched other than minimum documentation to the extent that such documents are included in the fields searchedElectronic data base consulted during the international search (name of data base and, where practicable, search terms used)CNABS, CNTXT, DWPI, CNKI: ft], ft, ft, ft, ft, ft, <<lift, fttL SiftAluminium, Chromium, Manganese, Molybdenum, Phosphorus, silicon, Sulfur, Vanadium, sorbit, pearlite, molten, salt, bathC.DOCUMENTS CONSIDERED TO BE RELEVANTCategory* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. PX CN 117987742 A (JIANGSU YONGGANG GROUP CO., LTD.) 07 May 2024 (2024-05-07) description, paragraphs 5-29 1-8 Y CN 114075639 A (BAOSHAN IRON &STEEL CO., LTD.) 22 February 2022 (2022-02-22) description, paragraphs 10-71 1-8 Y JP H03271322 A (NIPPON STEEL CORP.) 03 December 1991 (1991-12-03) 1-8 description, page 2, lower left column, last line to page 4, upper right column, line 17 Y CN 113748224 A (NIPPON STEEL CORP.) 03 December 2021 (2021-12-03) description, paragraphs 24-240 1-8 Y CN 114032372 A (ZHANGJIAGANG RONGSHENG SPECIAL STEEL CO., LTD. et al.) 11 February 2022 (2022-02-11) description, paragraphs 6-33 1-8 Y CN 102719650 A (GUIZHOU UNIVERSITY) 10 October 2012 (2012-10-10) description, paragraphs 3-8 1-8| | Further documents are listed in the continuation of Box C. | J | See patent family annex.* Special categories of cited documents: “T” later document published after the international filing date or priority “A” document defining the general state of the art which is not considered date and not in conflict with the application but cited to understand the to be of particular- relevance principle or theory underlying the invention “D” document cited by the applicant in the international application “X” document of particular- relevance; the claimed invention cannot be “E” earlier application orpatent but published on or after the international considered novel or cannot be considered to involve an inventive step filing date when the document is taken alone “L” document which may throw doubts on priority claim(s) or which is “Y” document of particular relevance; the claimed invention cannot be cited to establish the publication date of another citation or other considered to involve an inventive step when the document is special reason (as specified) combined with one or more other such documents, such combination “O” document referring to an oral disclosure, use, exhibition or other being obvious to a person skilled in the art means document member of the same patent family “P” document published prior to the international filing date but later than the priority date claimed Date of the actual completion of the international search 16 December 2024 Date of mailing of the international search report 01 January 2025 Name and mailing address of the ISA / CN China National Intellectual Property Administration (ISA / CN) China No. 6, Xitucheng Road, Jimenqiao, Haidian District, Beijing 100088 Authorized officer Telephone No.C. DOCUMENTS CONSIDERED TO BE RELEVANTCategory* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. A US 2018327889 Al (NIPPON STEEL &SUMITOMO METAL CORP.) 15 November 2018 (2018-11-15) entire document 1-8 A CN 116145036 A (JIANGYIN XINGCHENG ALLOY MATERIAL CO., LTD. et al.) 23 May 2023 (2023-05-23) entire document 1-8INTERNATIONAL SEARCH REPORT Information on patent family membersPCT / CN2024 / 109201Patent document cited in search report Publication date (day / month / year) Patent family member, s) Publication date (day / month / year) CN 117987742 A 07 May 2024 None CN 114075639 A 22 February 2022 None JP H03271322 A 03 December 1991 JPH 079037 B2 01 February 1995 CN 113748224 A 03 December 2021 WO 2020256140 Al 24 December 2020 JPWO 2020256140 A1 24 December 2020 JP 7226548 B2 21 February 2023 EP 3988678 Al 27 April 2022 EP 3988678 A4 06 July 2022 EP 3988678 Bl 06 December 2023 CN 114032372 A 11 February 2022 None CN 102719650 A 10 October 2012 None US 2018327889 Al 15 November 2018 CA 3001966 Al 27 April 2017 KR 20180053388 A 21 May 2018 KR 102059046 Bl 24 December 2019 US 10597748 B2 24 March 2020 TW 201718907 A 01 June 2017 TWI 614351 B 11 February 2018 JPWO 2017069207 Al 30 August 2018 JP 6481770 B2 13 March 2019 BR 112018007711 A2 23 October 2018 EP 3366802 A1 29 August 2018 EP 3366802 A4 15 May 2019 WO 2017069207 Al 27 April 2017 MX 2018004711 A 20 June 2018 CN 116145036 A 23 May 2023 None

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