High-strength 460mpa-grade hot-rolled pickled low-alloy high-strength steel and preparation method thereof

Abstract

The present application relates to the technical field of steel material preparation, in particular to a high-strength 460MPa-grade hot-rolled pickling low-alloy high-strength steel and a preparation method thereof.The chemical composition of the steel material contains elements such as C, Si, Mn, Nb, Ti, Cu and Ni, and satisfies Ti / N = 3.2-4.8, (Nb+Ti) / C = 0.45-0.75 and Cu / Ni = 2.5-3.5.The preparation method comprises molten iron pretreatment, converter smelting, LF+RH refining, continuous casting, slab heating, hot rolling, controlled cooling, coiling, flattening and pickling.The present application obtains fine-grained ferrite+pearlite structure through Ti-Nb-Cu-Ni composite micro-alloying and slab low-temperature heating process, and the product has high strength, excellent formability and good surface quality, while the energy consumption and cost are reduced.

Description

Technical Field

[0001] This invention relates to the field of steel material preparation technology, specifically to a high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel and its preparation method. Background Technology

[0002] Low-alloy high-strength steel, due to its excellent strength, good formability, and relatively low cost, has been widely used in automotive structural components, construction machinery, and logistics transportation. With the increasing urgency of global energy conservation, emission reduction, and lightweighting in manufacturing, higher requirements are being placed on the strength level, formability, and surface quality of low-alloy high-strength steel. Hot-rolled and pickled products eliminate the need for cold rolling and annealing processes, offering significant advantages in low production costs and short delivery cycles, and have become one of the important directions for the development of high-strength steel products. Among them, 460MPa grade hot-rolled and pickled low-alloy high-strength steel, due to its excellent comprehensive performance, has broad application prospects in components such as commercial vehicle beams and body structural parts.

[0003] To achieve a strength of 460 MPa while maintaining formability, existing technologies mainly employ two approaches: one is to use solid solution strengthening or increase pearlite content by adding higher amounts of elements such as carbon and manganese; the other is to use microalloying elements such as niobium, titanium, and vanadium, combined with controlled rolling and cooling processes, to achieve fine grain strengthening and precipitation strengthening.

[0004] For example, Chinese patent application CN201710191992.4 discloses a low-silicon titanium-containing acid-washed steel sheet with a yield strength of 460 MPa and its preparation method. Its chemical composition is C: 0.06%–0.09%, Mn: 0.20%–0.60%, and Ti: 0.025%–0.06%. It is prepared using steps including converter smelting, LF refining, RH vacuum treatment, hot continuous rolling, laminar flow cooling, coiling, and acid washing. While it contains a relatively high amount of titanium, this high titanium content can easily lead to unstable mechanical properties during continuous coiling, affecting the final use by the user. Simultaneously, the high heating temperature of the slab increases process energy consumption and production costs.

[0005] Chinese patent application CN202410972989.6 discloses an ultra-thick high-manganese, high-carbonate steel sheet and its production method. The sheet's chemical composition is C: 0.28%–0.65%, Mn: 0.89%–1.85%, and V: 0.08%–0.12%, and it is produced using a continuous pickling line. While it can produce products with a yield strength of 460 MPa, the high carbon and manganese content significantly deteriorates the steel's formability and weldability, making it difficult to meet the processing requirements of complex structural components.

[0006] Chinese patent application CN201911331759.7 discloses a vanadium-containing hot-rolled pickled sheet and its pickling method. Its chemical composition is C: 0.180%–0.250%, Mn: 0.150%–0.250%, and V: 0.035%–0.060%. Due to its high carbon content, it also suffers from poor formability and weldability; furthermore, the high vanadium content significantly increases the alloy cost.

[0007] Furthermore, the aforementioned existing technologies typically employ high slab heating temperatures (e.g., exceeding 1200℃) during production to ensure sufficient solid solution of microalloying elements. However, this not only increases energy consumption but also exacerbates the formation of iron oxide scale, intensifies subsequent pickling loads, and may adversely affect surface quality. Simultaneously, existing technologies lack sufficient control over steel purity (such as the content of impurities like sulfur, phosphorus, oxygen, and nitrogen), leaving room for improvement in the product's transverse toughness, fatigue resistance, and weld stability. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, this invention provides a high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel and its preparation method. While ensuring the 460MPa grade strength, it further reduces production costs, simplifies the process, improves forming and welding performance, and enhances the stability of product performance.

[0009] To achieve the above objectives, the present invention employs the following technical solution: A high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel is composed of the following chemical composition by weight percentage: C: 0.05%~0.09%, Si: 0.15%~0.35%, Mn: 1.10%~1.40%, P: ≤0.020%, S: ≤0.012%, Als: 0.030%~0.065%, Nb: 0.015%~0.035%, Ti: 0.015%~0.035%, Cu: 0.20%~0.30%, Ni: 0.07%~0.12%, RE: ≤0.0020%, O: ≤0.0050%, N: ≤0.0055%, with the remainder being Fe and unavoidable impurities. It also satisfies the following conditions: Ti / N = 3.2–4.8, (Nb+Ti) / C = 0.45–0.75, Cu / Ni = 2.5–3.5. Its microstructure consists of ferrite and pearlite, with the average grain size of the ferrite being 4.0–6.0 μm and the area percentage of the pearlite being 5%–10%.

[0010] The effect of selecting the above alloying elements and their contents: C: As the main interstitial solid solution strengthening element, its content is controlled within the low carbon range of 0.05% to 0.09%. This design aims to maximize the excellent weldability, low-temperature toughness, and formability of the steel while providing the necessary basic strength, and to avoid the increase of brittle phases and deterioration of formability due to excessive carbon content.

[0011] Silicon (Si): As an inexpensive solid solution strengthening element, it can effectively improve the strength of ferrite. Simultaneously, silicon is an important deoxidizer, preferentially combining with oxygen during steelmaking, helping to reduce iron oxide inclusions in steel and purify the molten steel. Its content is controlled at a low level of 0.15% to 0.35%, mainly to prevent adverse effects on surface quality.

[0012] Mn: As a core alloying element, its content ranges from 1.10% to 1.40%. Manganese significantly improves the strength and hardness of steel through solid solution strengthening, while also lowering the γ→α phase transformation temperature and refining the ferrite grains after the phase transformation. In addition, manganese can combine with sulfur to form MnS, fixing the harmful element sulfur, thereby improving the hot working properties and toughness of steel.

[0013] P: Phosphorus is a harmful element that is very prone to segregation in steel, which significantly worsens the cold brittleness, weldability and secondary processing performance of steel. Strictly controlling its content at a low level of ≤0.020% is to prevent its enrichment at grain boundaries and ensure that the product has uniform and stable mechanical properties.

[0014] S: Sulfur is also a major harmful element, easily forming low-melting-point FeS, which leads to hot brittleness. Strictly limiting it to ≤0.012% is to reduce the quantity and size of sulfide inclusions, which is crucial for improving the transverse toughness, fatigue performance, and anisotropy of steel.

[0015] Als: Aluminum is a strong deoxidizer, with a content of 0.030% to 0.065%. It is mainly used for deep deoxidation during the refining process to form fine Al2O3 inclusions, promoting the purity of molten steel. In addition, acid-soluble aluminum (Als) can refine grains and fix free nitrogen in steel, which helps to improve the cold forming properties of steel.

[0016] Niobium (Nb) is a grain-refining element, with a content of 0.015% to 0.035%. Some Nb dissolves in austenite under low-temperature heating of the slab. During rolling, these dissolved Nb particles form nanoscale Nb(C,N) precipitates at defects such as dislocations through a strain-induced precipitation mechanism, resulting in a strong precipitation strengthening effect and further preventing recrystallization, thus refining the grains.

[0017] Ti: Titanium is a grain-refining element, with a content of 0.015% to 0.035%. At high temperatures, titanium forms extremely stable TiN particles with N. During continuous casting and low-temperature heating of slabs, these fine TiN particles can effectively pin the austenite grain boundaries and strongly inhibit the abnormal growth of austenite grains, laying the foundation for obtaining fine phase transformation structures in the future.

[0018] Ti / Nb synergy: By precisely controlling the content of Ti and N, it is ensured that after the formation of sufficient and fine TiN, a certain amount of solid-dissolved N still binds with Nb. This design avoids the excessive binding of Nb with N to form coarse compounds, ensuring the precipitation enhancement potential of Nb.

[0019] Cu: Copper is an effective substitutional solid solution strengthening element, and its content is controlled at 0.20%–0.30%. On the one hand, its solid solution strengthening in ferrite and precipitation hardening during aging can stably improve the strength of steel; on the other hand, copper can significantly improve the atmospheric corrosion resistance of steel. Its upper limit needs to be strictly controlled to avoid excessive copper accumulation at grain boundaries during hot working, which could lead to "copper embrittlement" defects, thus ensuring thermoplasticity and surface quality.

[0020] Ni: Nickel is an important element for toughness and process compatibility, with its content controlled between 0.07% and 0.12%. Its main role is to form a synergistic effect with copper: nickel can increase the solubility of copper in austenite, effectively suppressing the tendency for high-temperature brittleness caused by copper addition, and ensuring the smooth operation of continuous casting and hot rolling processes. At the same time, nickel itself also has the beneficial effects of mild solid solution strengthening and improving low-temperature toughness.

[0021] RE (Rare Earth): Rare earth elements, the content of which is controlled at ≤0.0020%. The trace amounts of rare earth elements remaining in steel can modify sulfides, transforming long strip-shaped MnS into spherical rare earth sulfides, thereby significantly improving the transverse impact toughness and fatigue resistance of steel, and reducing banded segregation.

[0022] Oxygen (O): Oxygen is the main impurity gaseous element in steel, and its content is limited to ≤0.0050%. On the one hand, extremely low oxygen content can significantly reduce the number and size of brittle inclusions such as Al2O3, fundamentally improving the fatigue life, toughness, and isotropy of steel. On the other hand, it provides a clean steelmaking environment for subsequent control of trace rare earth elements, allowing trace rare earth elements to be more effectively used for modified residual sulfides rather than being consumed by large amounts of primary oxides. Ultra-low oxygen and trace rare earth elements are key chemical characteristics for achieving high purity steel and high toughness in products.

[0023] Nitrogen (N) is an interstitial element, and its content is limited to ≤0.0055%. This is to prevent age embrittlement caused by free nitrogen atoms and to ensure the ductility and toughness of the steel. On the other hand, it is to ensure that it combines with sufficient amounts of microalloying elements such as titanium and niobium and is completely transformed into beneficial carbonitride precipitates, thus avoiding the waste of alloying elements.

[0024] The yield strength of the above-mentioned high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel is 488-535MPa, the tensile strength is 565-610MPa, the elongation is 22.0%-30.5%, and the hole expansion rate is 70%-90%.

[0025] The preparation method of the above-mentioned high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel specifically includes the following steps: 1) Hot metal pretreatment; 2) Converter smelting; 3) LF+RH refining; 4) Continuous casting; 5) Slab heating: The heating temperature is 1145~1165℃, and the holding time is 1~3h; 6) Hot rolling: including roughing and finishing rolling, wherein the initial rolling temperature of the roughing rolling is ≥1100℃ and the total reduction rate of the roughing rolling is ≥75%; the initial rolling temperature of the finishing rolling is 1000~1050℃ and the final rolling temperature is 840~880℃, and the total reduction rate of the finishing rolling is ≥75%; high-density dislocations and deformation bands are introduced into the austenite to provide nucleation sites for strain-induced precipitation of Nb(C,N).

[0026] 7) Controlled cooling: After final rolling, cool to 610-640℃ at a cooling rate of ≥28℃ / s, then air cool for 2-7s; 8) Winding: Winding temperature is 570-600℃; then air cool to room temperature; 9) Leveling: Leveling elongation is 1.0% to 1.3%, and the surface roughness of the work roll is Ra 1.2 to 1.6 μm; 10) Pickling: The acid concentration is 12% to 18%, the pickling temperature is 75 to 85℃, and the pickling speed is 80 to 180 m / min.

[0027] Furthermore, in step 1), the KR mechanical stirring method is used to control the mass ratio of magnesium powder to lime powder to be 1:3.5 to 4.5, the final temperature of the pretreatment is ≥1300℃, and the final S content of the pretreatment is ≤0.003%, so as to achieve extremely low sulfur content in the subsequent process and ensure the efficient transformation of rare earth elements into inclusions.

[0028] Furthermore, in step 2), the final carbon content is 0.06% to 0.10%, the tapping temperature is 1620 to 1650°C, and the tapping process is protected by argon gas sealing throughout to prevent nitrogen and oxygen enrichment.

[0029] Furthermore, in step 3), the LF furnace produces high-basicity white slag with an basicity R≥8, a white slag holding time≥25min, and a soft argon blowing time≥15min; this promotes the full flotation and removal of inclusions.

[0030] The RH furnace vacuum degree is ≤100Pa, the deep degassing time is ≥18min, the final H content is ≤2ppm, the final O content is ≤0.0035%, and the final N content is ≤0.0045%. During this stage, the final fine-tuning of alloying elements such as Ti, Nb, Cu, and Ni is completed, and the element ratios are ensured to be within the target range.

[0031] Furthermore, in step 4), low superheat casting is used, with a superheat of 10-20°C.

[0032] Furthermore, in step 7), the cooling rate is 29-35°C / s, and after cooling to 615-630°C, it is air-cooled for 2.5-4.5s.

[0033] Furthermore, in step 8), the winding temperature is 576–594°C.

[0034] Furthermore, in step 9), the leveling elongation is 1.05% to 1.28%, and the surface roughness of the work roll is Ra 1.38 to 1.55 μm.

[0035] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention achieves a significant improvement in both strength-ductility ratio and porosity. Firstly, it employs low carbon and low pearlite area fraction, resulting in a balanced hard-brittle phase ratio, thus avoiding porosity cracking caused by excessive pearlite. Secondly, by rapidly cooling at ≥28℃ / s to 610–640℃ after final rolling, followed by air cooling for 2–7s, and then coiling at 570–600℃, fine-grained ferrite with an average grain size of 4.0–6.0 μm is obtained, providing a good balance of strength and ductility. Thirdly, by using ultra-low oxygen and trace amounts of rare earth elements to transform elongated MnS into fine spherical rare earth sulfides, crack initiation is eliminated, hindering crack propagation during porosity expansion and significantly improving flanging formability.

[0036] 2. Low-temperature heating of slabs significantly reduces energy consumption and oxidation loss. First, the invention utilizes ultra-stable TiN particles (Ti / N = 3.2–4.8) formed by Ti and N to effectively pin austenite grain boundaries and suppress grain coarsening during the low-temperature heating stage. Simultaneously, some Nb forms nanoscale Nb(C,N) in subsequent hot rolling as unsolvable or strain-induced precipitation, compensating for the precipitation strengthening effect lost due to low-temperature heating. This ensures both strength and energy saving.

[0037] 3. A cooling path combining rapid cooling, short-duration air cooling, and medium-temperature coiling achieves both high strength and good plasticity. This invention first suppresses premature proeutectoid ferrite formation through rapid cooling after final rolling; air cooling causes nano-Nb(C,N) to disperse and precipitate along dislocation lines, resulting in significant precipitation strengthening; coiling at 570–600℃ not only yields fine-grained ferrite to improve plasticity, but this temperature range also coincides with the ideal temperature range for the dispersed precipitation of Nb(C,N). The large number of nano-sized precipitates compensates for the strength loss caused by low carbon content, achieving a synergistic effect of "fine-grained plasticization" and "dispersion strengthening," resulting in a final yield strength of 488–535 MPa and a tensile strength of 565–610 MPa.

[0038] 4. This invention ensures the ultra-high purity of molten steel through extremely low P, S, ultra-low oxygen, and trace rare earth treatment, eliminating banded structures and long strip-shaped sulfides, thus significantly improving the fatigue life of the material under dynamic load; the low carbon design and low carbon equivalent avoid the hardening tendency of the weld heat-affected zone, resulting in excellent welding performance.

[0039] 5. This invention adopts a low-carbon and low-manganese composition design, which avoids the problem of deterioration in forming and welding performance caused by excessive carbon and manganese content, while reducing alloy cost. Attached Figure Description

[0040] Figure 1 This is a metallographic diagram of Embodiment 1 of the present invention. Detailed Implementation

[0041] This invention discloses a high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel and its preparation method. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the same result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0042] The chemical composition of the steel in this embodiment is shown in Table 1. The weight ratios of Ti / N, (Nb+Ti) / C, and Cu / Ni of the steel in this embodiment are shown in Table 2. The hot metal pretreatment process in this embodiment is shown in Table 3. The converter smelting and LF refining process in this embodiment is shown in Table 4. The RH refining and continuous casting process in this embodiment is shown in Table 5. The slab heating and hot rolling process in this embodiment is shown in Table 6. The controlled cooling and coiling process in this embodiment is shown in Table 7. The leveling and pickling process in this embodiment is shown in Table 8. The mechanical properties of the finished steel plate in this embodiment are shown in Table 9.

[0043] Table 1. Chemical composition (wt%) of steel in the embodiments of the present invention: Table 2. Weight ratios of Ti / N, (Nb+Ti) / C, and Cu / Ni in the steel chemical composition of the embodiments of the present invention: Table 3. Iron pretreatment parameters in the embodiments of the present invention: Table 4. Converter smelting parameters and LF refining parameters of the embodiments of the present invention: Table 5. RH refining parameters and continuous casting parameters of the embodiments of the present invention: Table 6. Slab heating parameters and hot rolling parameters in the embodiments of the present invention: Table 7. Cooling and winding parameters in embodiments of the present invention: Table 8. Leveling parameters and pickling parameters of the embodiments of the present invention: Table 9. Test results of mechanical properties of finished steel plates according to embodiments of the present invention: The microstructure of the finished product in Example 1 is shown below. Figure 1 The microstructure consists of ferrite and a small amount of pearlite, with a ferrite area percentage of 93% and a ferrite grain size of 5.4 μm.

[0044] Based on the mechanical performance test results shown in Table 9 and Figure 1 As shown in the typical microstructure photographs, the 460MPa grade finished steel plates prepared in Examples 1-5 all exhibit a microstructure consisting of a fine equiaxed ferrite matrix with an average grain size of 4.0-6.0 μm, and uniformly distributed pearlite with an area fraction of 5%-10%. This microstructure was obtained through a Ti-Nb-Cu-Ni composite microalloying composition design, coupled with a coordinated design of low-temperature heating and hot rolling processes for the slab. Compared to lower strength grades, higher alloy content, stronger cooling, and lower coiling temperature significantly enhance the contributions of nano-carbonitride precipitation strengthening and pearlite second-phase strengthening. Simultaneously, the control over purity (ultra-low S, O, P, and RE treatment) and microstructure uniformity throughout the entire process ensures that the material maintains good plasticity and excellent flanging formability.

[0045] Comparative Example 1: This comparative example provides a low-alloy high-strength steel with the following chemical composition by mass percentage: C: 0.072%, Si: 0.25%, Mn: 1.20%, P: 0.015%, S: 0.006%, Als: 0.052%, Nb: 0%, Ti: 0.045%, Cu: 0.22%, Ni: 0.075%, RE: 0%, O: 0.0045%, N: 0.0065%, with the remainder being Fe and unavoidable impurities. Calculations show that Ti / N = 6.92, (Nb+Ti) / C = 0.63, and Cu / Ni = 2.93.

[0046] The production method of this comparative example is basically the same as that of Example 1, except that: the slab heating temperature is 1200℃ (higher than the 1145~1165℃ limited by this invention), the final rolling temperature is 890℃ (higher than the 840~880℃ limited by this invention), and the coiling temperature is 620℃ (higher than the 570~600℃ limited by this invention).

[0047] The mechanical properties of Comparative Example 1 were tested as follows: yield strength 465 MPa, tensile strength 540 MPa, elongation 18.5%, and porosity 52%.

[0048] A comparison of Comparative Example 1 and Example 1 shows that Comparative Example 1 did not add Nb, and its Ti content exceeded the upper limit of this invention. Furthermore, its slab heating temperature, final rolling temperature, and coiling temperature were all higher than the range of this invention. Its mechanical properties exhibited lower yield strength and tensile strength, and significantly reduced elongation and porosity, indicating a poor match between its strength and formability. In addition, due to the higher heating temperature, the iron oxide scale thickened, increasing the subsequent pickling load and affecting surface quality.

[0049] Comparative Example 2: This comparative example provides a low-alloy high-strength steel with the following chemical composition by mass percentage: C: 0.12%, Si: 0.20%, Mn: 1.50%, P: 0.018%, S: 0.008%, Als: 0.045%, Nb: 0.010%, Ti: 0.010%, Cu: 0%, Ni: 0%, RE: 0%, O: 0.0055%, N: 0.0060%, with the remainder being Fe and unavoidable impurities. Calculations show Ti / N = 1.67, (Nb+Ti) / C = 0.17, and Cu / Ni is not applicable (no Cu or Ni added).

[0050] The production method of this comparative example is basically the same as that of Example 1, except that the slab heating temperature is 1180℃, the finishing rolling temperature is 820℃, and the coiling temperature is 550℃.

[0051] The mechanical properties of Comparative Example 2 were tested as follows: yield strength 492 MPa, tensile strength 585 MPa, elongation 16.0%, and porosity 45%.

[0052] A comparison of Comparative Example 2 and Example 1 shows that Comparative Example 2 uses a high-carbon, high-manganese composition design, without adding Cu or Ni, and the Ti / N and (Nb+Ti) / C ratios are both lower than the lower limits of this invention. Although the yield strength and tensile strength meet the 460MPa requirement, the elongation and porosity are significantly lower, indicating poor formability. Furthermore, due to the high carbon and manganese content, welding performance tests show increased hardness and decreased toughness in the weld heat-affected zone, making it difficult to meet the welding requirements of complex structural parts.

[0053] Comparative Example 1, due to the absence of Nb, excessively high Ti content, and excessively high heating temperature, resulted in insufficient strength and poor formability. Comparative Example 2, due to the use of high carbon and high manganese, the absence of Cu / Ni, and a low key ratio, achieved the required strength but significantly deteriorated plasticity and porosity. In contrast, Examples 1-5 of the present invention, while maintaining a strength of 460 MPa, all achieved elongation of over 22.0% and porosity of over 70%, demonstrating excellent comprehensive mechanical and formability properties.

[0054] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel, characterized in that, The high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel has the following chemical composition by weight percentage. composition: C: 0.05%~0.09%, Si: 0.15%~0.35%, Mn: 1.10%~1.40%, P: ≤0.020%, S: ≤0.012%, Als: 0.030%~0.065%, Nb: 0.015%~0.035%, Ti: 0.015%~0.035%, Cu: 0.20%~0.30%, Ni: 0.07%~0.12%, RE: ≤0.0020%, O: ≤0.0050%, N: ≤0.0055%, with the remainder being Fe and unavoidable impurities; And it satisfies Ti / N = 3.2~4.8, (Nb+Ti) / C = 0.45~0.75, Cu / Ni = 2.5~3.5; Its microstructure consists of ferrite and pearlite, with the average grain size of the ferrite being 4.0–6.0 μm and the area percentage of the pearlite being 5%–10%. The preparation method specifically includes the following steps: 1) Hot metal pretreatment; 2) Converter smelting; 3) LF+RH refining; 4) Continuous casting; 5) Slab heating: The heating temperature is 1145~1165℃, and the holding time is 1~3h; 6) Hot rolling: including roughing and finishing rolling, wherein the initial rolling temperature of the roughing rolling is ≥1100℃ and the total reduction rate of the roughing rolling is ≥75%; the initial rolling temperature of the finishing rolling is 1000~1050℃ and the final rolling temperature is 840~880℃, and the total reduction rate of the finishing rolling is ≥75%. 7) Controlled cooling: After final rolling, cool to 610-640℃ at a cooling rate of ≥28℃ / s, then air cool for 2-7s; 8) Winding: Winding temperature is 570~600℃; 9) Leveling: Leveling elongation is 1.0% to 1.3%, and the surface roughness of the work roll is Ra 1.2 to 1.6 μm; 10) Pickling: The acid concentration is 12% to 18%, the pickling temperature is 75 to 85℃, and the pickling speed is 80 to 180 m / min.

2. The method for preparing high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel according to claim 1, characterized in that, The high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel has a yield strength of 488-535MPa, a tensile strength of 565-610MPa, an elongation of 22.0%-30.5%, and a hole expansion rate of 70%-90%.

3. The method for preparing high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel according to claim 1, characterized in that, In step 1), the KR mechanical stirring method is used to control the mass ratio of magnesium powder to lime powder to be 1:3.5 to 4.5, the final temperature of the pretreatment is ≥1300℃, and the final S content of the pretreatment is ≤0.003%.

4. The method for preparing high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel according to claim 1, characterized in that, In step 2), the final carbon content is 0.06% to 0.10%, the tapping temperature is 1620 to 1650℃, and the tapping process is protected by argon gas sealing throughout.

5. The method for preparing high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel according to claim 1, characterized in that, In step 3), the LF furnace produces high-alkalinity white slag with an alkalinity R≥8, a white slag holding time≥25min, and a soft argon blowing time≥15min; the RH furnace has a vacuum degree≤100Pa, a deep degassing time≥18min, an endpoint H content≤2ppm, an endpoint O content≤0.0035%, and an endpoint N content≤0.0045%.

6. The method for preparing high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel according to claim 1, characterized in that, In step 4), low superheat casting is used, with a superheat of 10-20°C.

7. The method for preparing high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel according to claim 1, characterized in that, In step 7), the cooling rate is 29-35°C / s, and after cooling to 615-630°C, it is air-cooled for 2.5-4.5s.

8. The method for preparing high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel according to claim 1, characterized in that, In step 8), the winding temperature is 576–594°C.

9. The method for preparing high-strength 460MPa grade hot-rolled pickled low-alloy high-strength steel according to claim 1, characterized in that, In step 9), the leveling elongation is 1.05% to 1.28%, and the surface roughness of the work roll is Ra 1.38 to 1.55 μm.

Images