900mpa grade hot-rolled high-strength steel and method for manufacturing the same

Abstract

The application discloses a 900MPa-grade hot-rolled high-strength steel and a preparation method thereof, and belongs to the technical field of hot-rolled high-strength steel. The chemical components of the hot-rolled high-strength steel are as follows in terms of weight ratio: Si 0.05-0.20%, Mn 1.60-2.00%, Ti 0.090-0.130%, Nb 0.020-0.040%, Zr 0.020-0.040%, Als 0.010-0.060%, P≤0.020%, S≤0.005%, N≤0.0050%, CTi / 4+(Nb+Zr) / 7.6-Ti / 4+(Nb+Zr) / 7.6+0.02%, and the rest is Fe and impurities. While realizing high strengthening, the application solves the common technical problem of controlling the size and quantity of liquid precipitation TiN in the Ti micro-alloyed high-strength steel, and is beneficial to improving the forming performance of the material.

Description

Technical Field

[0001] This invention belongs to the field of hot-rolled high-strength steel technology, and relates to a production method of high-strength hot-rolled steel, specifically to a 900MPa grade hot-rolled high-strength steel and its preparation method. Background Technology

[0002] In recent years, with the improvement of high-purity steelmaking capabilities, Ti microalloying technology has been widely used in steel development. Ti microalloyed steel has advantages such as high precipitation strengthening and low alloy price, but it suffers from the problem of easily forming liquid-precipitated TiN inclusions. Furthermore, Ti's effect on inhibiting austenite recrystallization is not as good as Nb's, resulting in poorer grain uniformity and grain refinement compared to Nb-containing steels. Recent research shows that Zr applied to Ti microalloyed steel can improve TiN morphology, reduce TiN quantity, lower austenite recrystallization temperature, promote grain refinement, and improve grain uniformity. In terms of performance, adding Zr can improve forming cracking problems caused by liquid-precipitated TiN and grain inhomogeneity in Ti microalloyed steel.

[0003] A search revealed that CN 110684930A discloses a low-temperature, high-toughness cerium-zirconium composite-treated FH40 ship plate steel and its preparation method. The chemical composition of the steel, by mass percentage, is: 0.04–0.08% C, 0.2–0.4% Si, 1.4–1.7% Mn, P≤0.012%, S≤0.005%, 0.020–0.055% Nb, 0.01–0.02% Ti, 0.025–0.060% V, 0.20–0.35% Ni, 0.01–0.04% Al, 0.01–0.04% Ce, 0.01–0.03% Zr, with the balance being Fe and unavoidable impurities. The preparation method includes: preparing raw materials and melting them into steel billets; forging to obtain forged billets; rolling; and cooling to form steel. The obtained steel plate has a ferrite-bainite microstructure, a yield strength ≥435MPa, a tensile strength ≥530MPa, an elongation after fracture ≥22.4%, and a low-temperature impact energy of -60℃ ≥244J.

[0004] As can be seen from the above, the existing patents mainly add Zr to steel to improve the purity of molten steel, reduce the activity of O in molten steel, and reduce inclusions. There are no reports on the control of liquid-precipitated TiN and the regulation of microstructure by Zr. Summary of the Invention

[0005] To address the aforementioned technical problems, the purpose of this invention is to provide a 900MPa grade hot-rolled high-strength steel and its preparation method.

[0006] The technical solution adopted by this invention to solve its technical problem is: 900MPa grade hot-rolled high-strength steel, whose chemical composition by weight percentage is: Si 0.05~0.20%, Mn 1.60~2.00%, Ti 0.090~0.130%, Nb 0.020~0.040%, Zr 0.020~0.040%, Als 0.010-0.060%, P≤0.020%, S≤0.005%, N≤0.0050%, C Ti / 4+(Nb+Zr) / 7.6~Ti / 4+(Nb+Zr) / 7.6+0.02%, with the remainder being Fe and unavoidable impurity elements.

[0007] The chemical composition of the aforementioned 900MPa grade hot-rolled high-strength steel, by weight percentage, includes: Si 0.05~0.10%, Mn 1.80~2.00%, Ti 0.100~0.120%, Nb 0.030~0.040%, Zr 0.030~0.040%, Als 0.030~0.050%, P≤0.015%, S≤0.003%, N≤0.0040%, C 0.04~0.06%, with the remainder being Fe and unavoidable impurity elements.

[0008] The aforementioned 900MPa grade hot-rolled high-strength steel has a yield strength ≥800MPa, tensile strength ≥900MPa, and elongation ≥12%. Its microstructure is ferrite, with an average ferrite grain size ≤10μm, an average primary austenite grain size ≤30μm, and a TiN inclusion density of no more than 30 inclusions / mm². 2 The size is no higher than 10μm.

[0009] The preparation method of the above-mentioned 900MPa grade hot-rolled high-strength steel is as follows: the continuous casting billet is obtained by converter smelting-LF refining-RH refining-continuous casting, and then the billet is heated, rough rolled, fine rolled, laminar flow cooled and coiled to obtain the finished steel plate.

[0010] Furthermore, in the RH refining process, after RH vacuum circulation degassing, zirconium iron or sponge zirconium is added, followed by ferrotitanium ilmenite or sponge titanium, and then argon blowing treatment is performed.

[0011] Furthermore, in the continuous casting process, the thickness of the continuously cast billet is 200–250 mm.

[0012] Furthermore, in the slab heating process, the slab heating temperature is 1230–1280℃; even further, the slab heating temperature is 1250–1270℃.

[0013] Furthermore, in the roughing process, 5 to 6 passes of roughing are used, and the thickness of the intermediate billet after roughing is 30 to 60 mm; even further, the thickness of the intermediate billet after roughing is 34 to 58 mm.

[0014] Furthermore, in the finishing rolling process, 6 to 7 rolling passes are used, and the starting temperature of the finishing rolling is not higher than the austenite recrystallization termination temperature T. nr T nr (℃)=887+464C+(6445Nb-644Nb 1 / 2 )+(732V-230V 1 / 2 )+890Ti+363Al-357Si; Furthermore, the finishing rolling temperature is 1030~1060℃.

[0015] Furthermore, in the finishing rolling process, the finishing rolling temperature is not lower than the ferrite initiation transformation temperature A. r3 A r3 (℃)=5 / 9{1670-558[C+(Mn+Mo) / 3.875+Cu / 15.5+Cr / 20.67+Ni / 5.636]+16[(FPT / 25.4)-0.315]-32}, where FPT is the thickness of the steel plate after finishing rolling, which is 2~10mm; furthermore, the finishing rolling temperature is 880~920℃.

[0016] Furthermore, in the winding process, the winding temperature is 570–630℃, and even further, the winding temperature is 580–620℃.

[0017] The beneficial effects of this invention are as follows: The steel provided by this invention achieves high strength while solving the common technical problem of controlling the size and quantity of liquid-precipitated TiN in Ti microalloyed high-strength steel, thus improving the material's formability. The steel provided by this invention, through Ti-Zr-Nb composite microalloying, lowers the austenite recrystallization temperature, refines the austenite grain size, improves the mixed-grain structure of Ti microalloyed steel, and further enhances the material's formability. The Ti-Zr-Nb composite microalloying technology and controlled rolling and cooling technology provided by this invention can be extended to other high-strength steel grades. Attached Figure Description

[0018] Figure 1 The microstructure of the steel in Example 1 of this invention;

[0019] Figure 2 The original austenitic structure of the steel in Example 1 of this invention;

[0020] Figure 3 The liquid-precipitated TiN inclusions in the steel of Example 1 of this invention;

[0021] Figure 4 The microstructure of the steel in Example 2 of this invention;

[0022] Figure 5 The microstructure of the steel in Example 3 of this invention;

[0023] Figure 6 The microstructure of steel in Comparative Example 1 of this invention;

[0024] Figure 7 This is the liquid-precipitated TiN inclusion in the steel of Comparative Example 1 of the present invention;

[0025] Figure 8 The microstructure of steel in Comparative Example 2 of this invention;

[0026] Figure 9 The microstructure of steel in Comparative Example 3 of this invention;

[0027] Figure 10 This is the original austenitic structure of steel in Comparative Example 3 of the present invention. Detailed Implementation

[0028] The technical solution of the present invention can be implemented in the following manner.

[0029] The chemical composition of 900MPa grade hot-rolled high-strength steel by weight percentage is as follows: Si 0.05~0.20%, Mn 1.60~2.00%, Ti 0.090~0.130%, Nb 0.020~0.040%, Zr 0.020~0.040%, Als 0.010-0.060%, P≤0.020%, S≤0.005%, N≤0.0050%, C Ti / 4+(Nb+Zr) / 7.6~Ti / 4+(Nb+Zr) / 7.6+0.02%, with the remainder being Fe and unavoidable impurity elements.

[0030] The chemical composition of the aforementioned 900MPa grade hot-rolled high-strength steel, by weight percentage, includes: Si 0.05~0.10%, Mn 1.80~2.00%, Ti 0.100~0.120%, Nb 0.030~0.040%, Zr 0.030~0.040%, Als 0.030~0.050%, P≤0.015%, S≤0.003%, N≤0.0040%, C 0.04~0.06%, with the remainder being Fe and unavoidable impurity elements.

[0031] The aforementioned 900MPa grade hot-rolled high-strength steel has a yield strength ≥800MPa, tensile strength ≥900MPa, and elongation ≥12%. Its microstructure is ferrite, with an average ferrite grain size ≤10μm, an average primary austenite grain size ≤30μm, and a TiN inclusion density of no more than 30 inclusions / mm². 2 The size is no higher than 10μm.

[0032] The reasons for the restrictions on the main alloying elements in the steel described in this invention are explained below.

[0033] Mn plays a role in solid solution strengthening and improving toughness in steel. Appropriately increasing the Mn content can improve the strength and toughness of steel. However, if the Mn content is too high, it is easy to cause segregation in the billet and affect the uniformity of the microstructure. Therefore, the Mn content is controlled at 1.60 to 2.00%.

[0034] Ti can combine with carbon in steel to form nanoscale TiC precipitates, which can exert a strong precipitation strengthening effect. Simultaneously, Ti inhibits the coarsening of the original austenite structure during slab reheating, which is beneficial for grain refinement. However, the Ti content should not be too high to avoid the formation of large-sized, high-density liquid-precipitated TiN inclusions. Therefore, in this invention, to improve the tensile strength of the steel to above 900 MPa, a relatively high Ti content is added, controlling the Ti content to 0.090–0.130%.

[0035] Nitrogen (Nb) can increase the austenite recrystallization termination temperature, which is beneficial for rolling the non-recrystallization zone of austenite at a higher finishing rolling temperature, thereby promoting austenite flattening and refining the final ferrite structure. In this invention, the Nb content is controlled at 0.020–0.040%.

[0036] Zr is a group element with Ti and is slightly more chemically reactive than Ti. Therefore, adding Zr to steel can form ZrN with N, thereby reducing the size and quantity of liquid-precipitated TiN. Simultaneously, Zr can increase the austenite recrystallization activation energy of Ti microalloyed steel, promoting the refinement of the original austenite structure and mitigating the mixed-grain structure that easily occurs in Ti microalloyed steel. Furthermore, the combination of Zr and C to form nano-sized ZrC particles can also play a precipitation strengthening role. In this invention, the Zr content is controlled at 0.020–0.040%.

[0037] Impurity elements such as P, S, and N can deteriorate the toughness and plasticity of steel and increase the number of inclusions. At the same time, S and N can also form inclusions such as Ti4S2C2 and TiN with Ti. Therefore, in this invention, the contents of P, S, and N are controlled to ≤0.020%, ≤0.005%, and ≤0.0050%, respectively.

[0038] C combines with strong carbide-forming elements such as Nb, Ti, and Zr to form nanoscale MC (NbC, TiC, ZrC) precipitates, which is beneficial for improving the strength of steel. However, when the C content is too high, M3C (alloy cementite) phase will form at higher temperatures and tends to segregate at grain boundaries, which not only affects the toughness and plasticity of the steel but also reduces the number of nanoscale MC precipitates, thus lowering the strength of the steel. Therefore, in this invention, the C content is controlled according to the ideal chemical ratio with Nb, Ti, and Zr, which is Ti / 4+(Nb+Zr) / 7.6 to Ti / 4+(Nb+Zr) / 7.6+0.02%.

[0039] The preparation method of the above-mentioned 900MPa grade hot-rolled high-strength steel is as follows: the continuous casting billet is obtained by converter smelting-LF refining-RH refining-continuous casting, and then the billet is heated, rough rolled, fine rolled, laminar flow cooled and coiled to obtain the finished steel plate.

[0040] Furthermore, after the above-mentioned steel is degassed in an RH vacuum cycle, zirconium iron or sponge zirconium is added, followed by ferrotitanium ilmenite or sponge titanium, and then argon blowing treatment is performed.

[0041] Furthermore, the thickness of the continuously cast steel billet is 200–250 mm.

[0042] Furthermore, the heating temperature of the steel slab is 1230-1280℃, preferably 1250-1270℃.

[0043] Furthermore, the steel slab is subjected to 5 to 6 passes of rough rolling, and the thickness of the intermediate slab after rough rolling is 30 to 60 mm, preferably 34 to 58 mm.

[0044] Furthermore, the above-mentioned steel undergoes 6 to 7 passes of finish rolling, with the initial rolling temperature not exceeding the austenite recrystallization termination temperature T. nr T nr (°C) = 887 + 464C + (6445Nb - 644Nb¹ / ²) + (732V - 230V¹ / ²) + 890Ti + 363Al - 357Si. Preferably, the finishing rolling inlet temperature is 1030–1060°C, and the finishing rolling temperature is not lower than the ferrite initiation transformation temperature A. r3 A r3 (°C) = 5 / 9{1670-558[C+(Mn+Mo) / 3.875+Cu / 15.5+Cr / 20.67+Ni / 5.636]+16[(FPT / 25.4)-0.315]-32}, where FPT is the thickness of the steel plate after finishing rolling, which is 2-10 mm. Preferably, the finishing rolling temperature is 880-920°C.

[0045] Furthermore, the steel is subjected to laminar flow cooling after precision rolling, and the coiling temperature is 570-630℃, preferably 580-620℃.

[0046] The reasons for the limitations in the production process of the steel described in this invention will be explained below.

[0047] As previously mentioned, Zr is more chemically reactive than Ti. In order to control the quantity and size of TiN inclusions in liquid precipitate, Zr and Ti elements should be added after vacuum circulation, with Zr added first and Ti added later, in order to reduce the N content and reduce the amount of TiN in liquid precipitate.

[0048] To promote the full solid solution of microalloying elements such as Mn, Nb, Ti, and Zr and improve the strength of steel, a relatively high slab heating temperature is used. However, excessively high heating temperatures can lead to coarse austenite grains. Therefore, the slab reheating temperature is controlled at 1230-1280℃.

[0049] To ensure austenite grain refinement, the finishing rolling process generally requires a compression ratio ≥5 to ensure sufficient austenite flattening, providing ample nucleation sites for subsequent ferrite phase transformation, thereby refining the grains. In this invention, the finished steel plate thickness after finishing rolling is 2–10 mm. To ensure a compression ratio ≥5, the thickness of the intermediate slab after rough rolling is controlled to be 30–60 mm, depending on the different finished product thicknesses.

[0050] In the finishing rolling process, to refine the grains and improve strength, the rolling of the non-recrystallization zone should be maximized. This requires the finishing rolling temperature to be lower than the austenite recrystallization termination temperature T. nr According to the empirical formula T nr (°C) = 887 + 464C + (6445Nb - 644Nb¹ / ²) + (732V - 230V¹ / ²) + 890Ti + 363Al - 357Si. Substituting the mass percentage of the chemical composition of the steel described in this invention into the formula, we can obtain T. nr The temperature is approximately 1069℃, therefore, the present invention controls the finishing rolling temperature at 1030~1060℃.

[0051] The finishing rolling temperature is generally required to be controlled at the ferrite initiation transformation temperature A. r3 The above is based on empirical formula A. r3 (°C) = 5 / 9{1670-558[C+(Mn+Mo) / 3.875+Cu / 15.5+Cr / 20.67+Ni / 5.636]+16[(FPT / 25.4)-0.315]-32}. Substituting the mass percentage of the chemical composition of the steel described in this invention into the formula, we can obtain A. r3 The temperature is approximately 750℃. Meanwhile, to reduce deformation-induced precipitation during finishing rolling, increase interphase precipitation and ferrite supersaturation precipitation during laminar cooling and coiling, improve the TiC precipitation effect, and increase the steel's strength, the final rolling temperature should be appropriately increased. Therefore, this invention controls the final rolling temperature at 880–920℃.

[0052] The nose point temperature for the supersaturated precipitation of TiC in ferrite is around 600℃. To promote the precipitation of the second phase and improve the strength of the steel, this invention controls the coiling temperature to around 600℃, specifically 570–630℃. The technical solution and effects of this invention will be further illustrated below through practical examples.

[0053] Example

[0054] The 900MPa grade hot-rolled high-strength steel of this invention comprises, by weight percentage: Si 0.05-0.20%, Mn 1.60-2.00%, Ti 0.090-0.130%, Nb 0.020-0.040%, Zr 0.020-0.040%, Als 0.010-0.060%, P≤0.020%, S≤0.005%, N≤0.0050%, C Ti / 4+(Nb+Zr) / 7.6~Ti / 4+(Nb+Zr) / 7.6+0.02%, with the remainder being Fe and unavoidable impurity elements. Table 1 shows the specific chemical composition of Examples 1-3 and Comparative Examples 1-3 of this invention.

[0055] Table 1 Chemical composition / %

[0056] Example 1 0.04 0.16 1.62 0.018 0.002 0.125 0.028 0.035 0.033 0.0035 Example 2 0.05 0.09 1.83 0.009 0.005 0.110 0.030 0.039 0.029 0.0031 Example 3 0.06 0.05 1.95 0.011 0.003 0.095 0.035 0.028 0.040 0.0028 Comparative Example 1 0.05 0.08 1.78 0.010 0.002 0.130 0.021 / 0.032 0.0040 Comparative Example 2 0.10 0.10 1.88 0.015 0.004 0.080 0.035 0.034 0.045 0.0021 Comparative Example 3 0.05 0.12 1.91 0.008 0.003 0.112 / 0.035 0.038 0.0026

[0057] The production process of the embodiments and comparative examples of this invention is as follows: A continuously cast billet is obtained by converter smelting, LF refining, RH refining, and continuous casting; then, it is heated in a slab heating furnace, rough rolled, finish rolled, laminar flow cooled, and coiled to obtain the finished steel plate. Hot rolling process parameters are shown in Table 2.

[0058] Table 2 Process Parameters

[0059] Slab heating temperature / ℃ 1265 1258 1244 1261 1225 1251 Intermediate billet thickness / mm 55 48 40 52 38 45 Finished product thickness / mm 10 6 2 8 3 10 Finishing rolling start temperature / mm 1031 1036 1045 1032 1070 1035 Finishing rolling temperature / ℃ 885 906 914 855 880 895 Winding temperature / ℃ 575 603 618 606 635 590

[0060] Table 3 shows the mechanical properties and microstructure of the steels in the embodiments and comparative examples of the present invention. The finished steel plates have a yield strength greater than 800 MPa, a tensile strength greater than 900 MPa, an elongation greater than 12%, and a ferrite microstructure with an average ferrite grain size ≤10 μm, an average primary austenite grain size ≤30 μm, and a TiN inclusion density not exceeding 30 inclusions / mm². 2 The size is no higher than 10μm.

[0061] Table 3 Mechanical Properties

[0062] Finished product thickness / mm 10 6 2 8 3 10 Yield strength / MPa 836 843 854 792 806 811 Tensile strength / MPa 925 941 948 884 891 903 Elongation / % 20 21 20 18 21 20 Original austenite grain size / μm 15 16 19 18 22 32 Ferrite grain size / μm 8 7 6 11 9 12 Liquid-precipitated TiN number density / mm⁻² 12 11 15 38 22 25

[0063] Appendix Figure 1 ~Attached Figure 3 The images shown are microstructure diagrams, original austenite microstructure diagrams, and liquid-precipitated TiN inclusion morphology diagrams of the test steel corresponding to Example 1. (Attached) Figure 4 Appendix Figure 5 The images show the microstructure of the test steels corresponding to Examples 2 and 3.

[0064] Comparative Example 1 steel did not contain Zr, and its finishing rolling temperature was slightly lower at 855℃ (required to be 880-920℃). All other chemical compositions and hot rolling process parameters met the requirements of this invention. Due to the absence of Zr, the liquid-precipitated TiN density in Comparative Example 1 steel was higher than 30 precipitates / mm², and the precipitated TiN exhibited a distinctly angular morphology. The lower finishing rolling temperature led to increased deformation-induced precipitation and reduced supersaturated ferrite precipitation in the finished steel, resulting in lower yield strength and tensile strength for Comparative Example 1 steel.

[0065] The Ti content in Comparative Example 2 steel is relatively low, the slab heating temperature is relatively low, and the coiling temperature is relatively high. The remaining chemical composition and hot rolling process parameters all meet the requirements of this invention. Due to the low Ti content and low slab heating temperature, the amount of Ti dissolved in the steel is reduced, resulting in less precipitation of the titanium-containing second phase after laminar cooling. Furthermore, the nose point temperature of the second phase precipitation is around 600°C. The higher coiling temperature (635°C) also contributes to the reduction in second phase precipitation. Therefore, the strength of Comparative Example 2 steel is relatively low.

[0066] Comparative Example 3 steel did not contain Nb, had a lower intermediate billet thickness, and all other chemical compositions and hot rolling process parameters met the requirements of this invention. Since Nb can promote rolling of steel in the non-recrystallized austenite region by increasing the austenite recrystallization temperature and promoting austenite flattening, the original austenite grains of Comparative Example 3 steel without Nb are slightly coarser than those of the examples. Simultaneously, due to the lower intermediate billet thickness, the degree of austenite recrystallization in Comparative Example 3 steel is lower than that of the examples. Therefore, the finished microstructure of Comparative Example 3 steel exhibits a mixed-grain structure and coarser grain size compared to the examples.

Claims

1. 900MPa grade hot-rolled high-strength steel, characterized in that, Its chemical composition by weight percentage is: Si 0.05~0.20%, Mn 1.60~2.00%, Ti 0.090~0.130%, Nb 0.020~0.040%, Zr 0.020~0.040%, Als 0.010-0.060%, P≤0.020%, S≤0.005%, N≤0.0050%, C Ti / 4+(Nb+Zr) / 7.6~Ti / 4+(Nb+Zr) / 7.6+0.02%, with the remainder being Fe and unavoidable impurity elements; the hot-rolled high-strength steel is prepared by the following method: The continuous casting billet is obtained by converter smelting, LF refining, RH refining and continuous casting. The billet is then heated, rough rolled, fine rolled, laminar flow cooled and coiled to obtain the finished steel plate. In the RH refining process, zirconium iron or sponge zirconium is added after RH vacuum circulation degassing, followed by the addition of ferrotitanium iron or sponge titanium, and then argon blowing treatment. In the slab heating process, the steel slab heating temperature is 1230~1280℃; The initial rolling temperature for finishing rolling is 1030~1060℃, and the final rolling temperature for finishing rolling is 880~920℃; The hot-rolled high-strength steel has a yield strength ≥800MPa, a tensile strength ≥900MPa, and an elongation ≥12%; its microstructure is ferrite, with an average ferrite grain size ≤10μm, an average original austenite grain size ≤30μm, and a number density of liquid-precipitated TiN inclusions not exceeding 30 inclusions / mm². 2 The size is no higher than 10μm.

2. The 900MPa grade hot-rolled high-strength steel according to claim 1, characterized in that, Its chemical composition by weight percentage is as follows: Si 0.05~0.10%, Mn 1.80~2.00%, Ti 0.100~0.120%, Nb 0.030~0.040%, Zr 0.030~0.040%, Als 0.030~0.050%, P≤0.015%, S≤0.003%, N≤0.0040%, C 0.04~0.06%, with the remainder being Fe and unavoidable impurity elements.

3. The method for preparing 900MPa grade hot-rolled high-strength steel according to claim 1 or 2, characterized in that: The continuous casting billet is obtained by converter smelting, LF refining, RH refining and continuous casting. The billet is then heated, rough rolled, fine rolled, laminar flow cooled and coiled to obtain the finished steel plate. In the RH refining process, zirconium iron or sponge zirconium is added after RH vacuum circulation degassing, followed by the addition of ferrotitanium iron or sponge titanium, and then argon blowing treatment. In the slab heating process, the steel slab heating temperature is 1230~1280℃; The initial rolling temperature for finishing is 1030~1060℃, and the final rolling temperature for finishing is 880~920℃.

4. The method for preparing 900MPa grade hot-rolled high-strength steel according to claim 3, characterized in that: At least one of the following conditions must be met: In the continuous casting process, the thickness of the continuously cast billet is 200~250mm; In the roughing process, 5 to 6 passes of roughing are used, and the thickness of the intermediate billet after roughing is 30 to 60 mm. During the winding process, the winding temperature is 570~630℃.

5. The method for preparing 900MPa grade hot-rolled high-strength steel according to claim 3, characterized in that: The heating temperature of the steel slab is 1250~1270℃.

6. The method for preparing 900MPa grade hot-rolled high-strength steel according to claim 4, characterized in that: The thickness of the intermediate billet after rough rolling is 34~58mm.

7. The method for preparing 900MPa grade hot-rolled high-strength steel according to claim 4, characterized in that: Winding temperature: 580~620℃.

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