Hot-rolled high-strength steel plate and manufacturing method thereof

Abstract

The invention discloses a hot-rolled high-strength steel plate and a manufacturing method thereof. The hot-rolled high-strength steel plate comprises the following chemical components in percentage by weight: 0.050-0.080% of C; 0.10% to 0.40% of Si; mn: 1.10% to 1.60%; 0.015% to 0.050% of Nb; b: < = 0.0005%. The manufacturing method comprises the following steps of converter smelting, LF + RH refining, continuous casting, heating, rolling, cooling and coiling. According to the hot-rolled high-strength steel plate and the manufacturing method thereof, the alloy component design is simplified, the strengthening approach is fine grain strengthening and solid solution strengthening, the hot-rolled high-strength steel plate has good obdurability matching and performance uniformity, the mechanical property is subjected to rolling and cooling process parameters, particularly, the influence of coiling temperature fluctuation is small, a production process window is relatively large, and the thickness gt is achieved; the impact performance and the uniformity of materials with the thickness of 12 mm are good, and the method is particularly suitable for manufacturing structures such as overhead working truck cantilevers and truck-mounted crane cantilevers which have high requirements for material obdurability and performance uniformity.

Description

Technical Field

[0001] The present invention relates to the technical field of hot-rolled high-strength steel, and in particular to a hot-rolled high-strength steel plate and a manufacturing method thereof. Background Art

[0002] The lightweight development trend in industries such as special-purpose vehicles and construction machinery is becoming increasingly obvious. While the market demand for hot-rolled high-strength steel of grade ≥650MPa is increasing year by year, the comprehensive quality requirements for hot-rolled high-strength steel are becoming increasingly higher, mainly reflected in the requirements for high strength and toughness matching of materials, good performance uniformity and cost-effectiveness.

[0003] In recent years, with the upgrading of ultra-fast cooling equipment and the need for cost reduction of enterprises, Ti microalloying (Ti content 0.030% to 0.20%) has become the mainstream chemical composition design idea for hot-rolled high-strength steel products. The strength of the material can be significantly improved through fine dispersed Ti-containing second phase precipitates. However, there are two problems with Ti microalloyed hot-rolled high-strength steel: 1) The heating temperature, final rolling temperature, coiling process, cooling rate after coiling, etc. will significantly affect the amount of Ti (C, N) solid solution during the heating process and the amount and size of TiC during the coiling and cooling process, which will significantly affect the TiC precipitation strengthening effect, resulting in large fluctuations in the mechanical properties of the material. The strength distribution in the length direction of the hot coil shows the characteristics of "low at the head and tail, high in the middle", and the strength distribution in the width direction of the plate shows the characteristics of "low on both sides, high in the middle". The yield strength and tensile strength fluctuate by as much as 150 to 200 MPa. In order to solve the problem of large fluctuations in the strength of Ti-containing steel through the coil, the Chinese invention patent with application number CN201210567654.3 mainly adopts U-type cooling process to improve the uniformity of the performance in the length direction of the strip. Chinese invention applications with application numbers CN202010860794.4, CN201810631501.8, CN201811133273.8, etc. mainly improve the temperature uniformity and performance uniformity of Ti-containing hot-rolled strip in the length and width directions by adding online insulation cover equipment after the coiler. However, through the above measures, the fluctuation range of the material's through-coil strength is still as high as 90-100MPa, and additional equipment investment is required; 2) The impact performance of thick specifications (thickness > 12mm) fluctuates greatly or even fails to meet the requirements. TiC belongs to a hard phase. The amount, size and distribution uniformity of a large amount of precipitated TiC will significantly affect the impact toughness of the material. At present, the problem of large fluctuations in the impact performance of high-Ti micro-alloyed high-strength steel with a thickness of >12mm has not been solved.

[0004] Therefore, it is urgent to develop a hot-rolled high-strength steel with high strength and toughness matching and good performance uniformity. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned technology, the purpose of the present invention is to provide a hot-rolled high-strength steel plate and a manufacturing method thereof, so as to solve the problem of uneven performance distribution of high-strength steel plates, and obtain hot-rolled high-strength steel with high strength and toughness matching, good mechanical properties and good performance uniformity through reasonable smelting, continuous casting, heating, rolling, cooling and coiling processes.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A hot-rolled high-strength steel plate is special in that it comprises the following chemical components by weight percentage: C: 0.050% to 0.080%; Mn: 1.10% to 1.60%; Nb: 0.015% to 0.050%; B: ≤0.0005%.

[0008] As a preferred embodiment, the hot-rolled high-strength steel plate includes the following chemical components in weight percentage: C: 0.050% to 0.080%; Si: 0.10% to 0.40%; Mn: 1.10% to 1.60%; Nb: 0.015% to 0.050%; Als: 0.015 to 0.050%; B: ≤0.0005%; P: ≤0.010%; S: ≤0.003%; the rest is Fe and unavoidable impurities.

[0009] The present invention also discloses a method for manufacturing a hot-rolled high-strength steel plate, which is special in that it comprises the following steps: converter smelting, LF+RH refining, continuous casting, heating, rolling, cooling and coiling.

[0010] As a preferred solution, in the converter smelting process, alloy auxiliary materials are added during the converter steelmaking process; wherein the alloy auxiliary material Si is high-purity ferrosilicon.

[0011] As a preferred solution, in the heating process, the temperature of the cast billet out of the furnace is 1200-1250° C., and the holding time is 160-210 min.

[0012] As a preferred embodiment, the rolling process includes rough rolling and finish rolling; during the rough rolling process, the final rolling temperature R2DT=1020~1080°C, and the cumulative reduction rate of rough rolling is ≥70%; during the finish rolling process, the final rolling temperature FDT=800~860°C, and the cumulative reduction rate of finish rolling is ≥75%.

[0013] Furthermore, the rolling process adopts a 2-stand roughing and 7-stand finishing hot rolling unit, all the insulation covers between the roughing and finishing units are put into use, and the longitudinal water spraying and bottom water spraying between the finishing rolling F1-F7 stands are closed.

[0014] As a preferred solution, the cooling adopts an ultra-fast cooling process; the ultra-fast cooling process adopts front-end intensive cooling, the cooling rate is ≥100℃ / s, the cooling water flow ratio of the upper and lower surfaces of the strip is 1:1.20~1:1.40, and the side water spraying is symmetrical cross side spraying.

[0015] Furthermore, coiling is directly performed after the front-stage intensive cooling is completed.

[0016] Furthermore, in the coiling process, the coiling temperature CT is 380-500°C, and after the hot coil is coiled, it is placed in a slow cooling pit for air cooling to room temperature, and the air cooling rate is ≤5°C / h.

[0017] The chemical composition and the principle of the main process in the present invention are as follows:

[0018] The chemical composition of the present invention adopts a low C, low Mn, Nb microalloying system, the alloy composition design is simplified, no other alloying elements such as Ti are added, and the residual element B content is controlled (B≤0.0005%), which can effectively avoid the significant adverse effects of rolling, cooling, and coiling process parameter fluctuations on the mechanical properties of high Ti and B microalloyed materials, thereby laying the foundation for expanding the process parameter window of the material under the premise of controlling the uniformity of the material mechanical properties and ensuring the uniformity of the material properties. Among them,

[0019] C: The content is controlled at 0.050% to 0.080%. As a basic element in steel, C plays a very important role in improving the strength of steel. In order to obtain higher strength, the C content must be ≥ 0.050%, but the C content should not be > 0.080%, otherwise it belongs to the category of peritectic steel, which greatly increases the difficulty of hot rolling of the material. At the same time, if the C content is too high, pearlite phase is easily formed during cooling, which is not conducive to the formation of acicular ferrite structure, and then the low-temperature toughness of the material will deteriorate.

[0020] Si: The content is controlled at 0.10% to 0.40%. Si has a strong solid solution strengthening effect and can improve the strength of the material. However, if the Si content is too high, the red rust on the surface of the strip steel is serious and difficult to remove, which is not conducive to the control of the surface quality. The present invention limits the type of alloy auxiliary materials of Si, mainly because the manganese silicon alloy or the silicon iron 75B alloy contains a certain amount of residual alloying element B, and the residual B content in different batches is different. As a typical grain boundary segregation element, when the B content is >0.006%, it will significantly inhibit the nucleation and growth of the recrystallization of the proeutectoid ferrite, thereby significantly improving the strength of the material and increasing the brittleness of the material. Therefore, in order to avoid the adverse effect of the residual B content on the strength, toughness and uniformity of the material, B≤0.0005%.

[0021] Mn: The content is controlled at 1.10% to 1.60%. As a strengthening element of steel, Mn can significantly improve the hardenability of steel and increase the strength of steel. In order to ensure that the tensile strength of the material is ≥650MPa, the Mn content should be controlled above 1.10%. However, too high a Mn content can easily lead to central segregation of the ingot, which is not conducive to the low-temperature impact performance of the material.

[0022] Nb: The content is controlled at 0.015% to 0.050%. Nb mainly refines the ferrite grains by the strong solute dragging effect on the austenite grain boundaries during the heating process and by increasing the recrystallization temperature during the rolling process to refine the austenite grains, thereby ultimately improving the strength and toughness of the material at the same time. In addition, Nb can improve the uniformity of material properties while refining the grains. Considering that the corresponding C content of the present invention is 0.050% to 0.080%, according to the solubility product formula, when the Nb content is greater than 0.060%, the NbC full solution temperature is greater than 1250°C. Given that the heating temperature of the present invention is 1200 to 1250°C, the NbC cannot be completely dissolved in the matrix during the heating process, and the undissolved NbC cannot fully exert the effect of refining the austenite grains and the final ferrite grains.

[0023] Als: The content is controlled at 0.015-0.050%. Als is mainly used as a deoxidizer and can react with N to generate AlN to pin the grain boundaries, thereby refining the grains.

[0024] As impurity elements, P and S will have an adverse effect on the strength, plasticity, formability and other properties of steel. The lower their content, the better. In actual production, P is controlled to be ≤0.010%, S to be ≤0.003%.

[0025] In the heating process design of the present invention, the design of the billet out of the furnace temperature and the time in the furnace is mainly based on the uniform heating of the billet, the rolling stability and the need to control the surface quality of the strip steel. If the heating temperature is too low, it is not conducive to the rolling stability. If the heating temperature is too high, the billet oxide scale is too thick, which is not conducive to the removal of the strip oxide scale and the surface quality control.

[0026] In the rolling process design of the present invention, the rough rolling cumulative reduction rate is ≥70%, the characteristics of high temperature and large deformation are fully utilized in the rough rolling stage to make austenite fully recrystallized, the finishing cumulative reduction rate is controlled to be ≥75%, the cumulative deformation amount of the non-recrystallized zone in the finishing stage is increased and combined with a lower final rolling temperature, which is conducive to generating a larger cumulative strain energy, increasing the nucleation position, and promoting the formation of fine needle-shaped ferrite, thereby improving the strength and toughness of the material. The use of all the insulation covers between the rough rolling and finishing rolling units is conducive to reducing the temperature drop of the intermediate billet and reducing the temperature difference between the head and tail of the hot coil, thereby helping to improve the uniformity of the mechanical properties in the length direction of the hot coil. The longitudinal water spray and bottom water spray between the finishing rolling F1-F7 frames are closed to improve the uniformity of the performance in the width direction of the hot rolled strip. Based on the comprehensive consideration of grain refinement effect, plate shape, and rolling stability, the finishing rolling temperature FDT is controlled in the range of 800-860℃. FDT<800℃ enters the two-phase region, and mixed crystal defects are easily generated in the thickness direction of the material, the uniformity of the material structure and performance is poor, and it is not conducive to the control of low-temperature toughness.

[0027] In the cooling process design, the present invention adopts the front-stage ultra-fast cooling intensive cooling, and the cooling rate is ≥100°C. The main purpose is to increase the cooling rate and "use water instead of gold", so that the temperature of the strip is rapidly reduced from the austenite phase region to the ferrite phase region, and the consistency of phase transformation and performance uniformity in the width and length directions of the strip are improved. In order to control the temperature uniformity of the strip in the ultra-fast cooling section in the width direction, the main measures are to control the upper and lower cooling water ratio, cross-symmetrical side spraying, etc. The purpose of opening less cooling water in the upper cooling water than in the lower cooling water in the ultra-fast cooling section is mainly to avoid excessive upper cooling water remaining on the upper surface of the strip, agglomeration, resulting in uneven temperature distribution in the width direction of the strip, which is not conducive to the uniformity of performance in the width direction of the strip. The invention can obtain good uniformity of mechanical properties under the condition of coiling temperature of 380-500°C and wide coiling temperature range, mainly because: 1) the alloy composition design of the invention is simplified, does not contain other alloys such as Ti, and controls the residual B content (≤0.0005%), which effectively avoids the adverse effect of process parameter fluctuation on the performance of Ti+B microalloyed materials; 2) the strengthening path of the material of the invention is fine grain strengthening + solid solution strengthening, the contribution of solid solution strengthening to strength is mainly determined by the content of C, Si, and Mn elements, and the contribution of fine grain strengthening to strength is mainly determined by the content of alloying element Nb , heating temperature, final rolling temperature and laminar cooling rate. Under the premise of certain Nb content, heating temperature, final rolling temperature and cooling rate, the coiling temperature will only affect the final organization type. Under the premise that the final organization type of the material does not change, the coiling temperature has little effect on the grain size, and thus has little effect on the mechanical properties of the material, which is conducive to the material obtaining good performance uniformity. When the coiling temperature is >500°C, the strength and low-temperature impact toughness of the material decrease significantly. When the coiling temperature is <380°C, it enters the martensitic phase transformation region, which is not the target organization of the present invention, the acicular ferrite organization. The strength of the material is significantly improved, but the low-temperature toughness is poor. In addition, after the hot coil is coiled, it is placed in a slow cooling pit for air cooling to room temperature. The cooling rate of ≤5°C / h is also based on the consideration of material performance uniformity.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The hot-rolled high-strength steel plate and the manufacturing method thereof of the present invention have simplified alloy composition design, and the strengthening approach is fine grain strengthening + solid solution strengthening. The mechanical properties are less affected by rolling and cooling process parameters, especially by coiling temperature fluctuations. The production process window is relatively large, and the performance uniformity is good.

[0030] The hot-rolled high-strength steel plate produced by the present invention has a yield strength of ≥550MPa, a tensile strength of ≥650MPa, an elongation of ≥28%, a low-temperature impact performance Akv of -40°C of ≥200J, and a hot-rolled through-coil yield strength fluctuation range of ≤40MPa, a tensile strength fluctuation range of ≤40MPa, a low-temperature impact work fluctuation range of -40°C of ≤20J, and a hardness fluctuation range of ≤10HV10. The steel plate has good strength-toughness matching, mechanical properties and performance uniformity, wherein the impact performance and uniformity of the material with a thickness of >12mm are also good, and the steel plate is particularly suitable for the manufacture of structures with high requirements on material strength and toughness and performance uniformity, such as aerial work vehicle cantilevers and vehicle-mounted crane arms. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the metallographic structure diagram corresponding to the position of 3m and 1 / 4 plate width of the inner circle of the hot coil in Example 1;

[0032] Figure 2 The metallographic structure diagram corresponding to the middle position of the hot coil and the position of 1 / 4 of the plate width in Example 1;

[0033] Figure 3 This is the metallographic structure diagram corresponding to the 3m and 1 / 4 plate width position of the hot coil outer ring in Example 1. DETAILED DESCRIPTION

[0034] In order to better explain the present invention, the main contents of the present invention are further explained below in conjunction with the drawings and specific embodiments, but the contents of the present invention are not limited to the following embodiments.

[0035] The invention discloses a hot-rolled high-strength steel plate, comprising the following chemical components in percentage by weight: C: 0.050% to 0.080%; Si: 0.10% to 0.40%; Mn: 1.10% to 1.60%; Nb: 0.015% to 0.050%; Als: 0.015% to 0.050%; B: ≤0.0005%; P: ≤0.010%; S: ≤0.003%; the rest is Fe and unavoidable impurities.

[0036] The preparation method of the hot-rolled high-strength steel includes converter smelting, LF+RH refining, continuous casting, heating, rolling, cooling, and coiling processes. Specifically:

[0037] 1) Smelting and continuous casting: the molten steel is smelted in a converter and refined by LF+RH. The alloy auxiliary materials are added to the steel tapped from the converter. The alloy auxiliary material of Si is high-purity ferrosilicon, and manganese silicon alloy or ferrosilicon 75B alloy is not used. The thickness of the ingot is 230 mm.

[0038] 2) Heating: the casting temperature is 1200-1250°C and the holding time is 160-210min.

[0039] 3) Rolling: adopt 2-stand rough rolling and 7-stand finishing hot rolling mill for rolling, the rough rolling final rolling temperature R2DT=1020~1080℃, the rough rolling cumulative reduction rate ≥70%, all the insulation covers between the rough rolling and finishing mills are put into use, the finishing rolling final rolling temperature FDT=800~860℃, the finishing cumulative reduction rate ≥75%, and the longitudinal water spraying and bottom water spraying between the finishing rolling F1-F7 frames are closed.

[0040] 4) Cooling and coiling: After finishing rolling, laminar cooling is carried out, and the front section ultra-fast cooling intensive cooling is adopted, the cooling rate is ≥100℃ / s, the upper and lower cooling water ratio is 1:1.20~1:1.40, the side spray water is symmetrical cross side spray, and the ultra-fast cooling intensive cooling is followed by coiling, and the coiling temperature CT=380~500℃. After the hot coil is coiled, it is placed in a slow cooling pit for air cooling to room temperature, and the cooling rate is ≤5℃ / h.

[0041] The chemical composition and manufacturing method of Examples 1 to 3 adopt the scheme of the present invention, and the difference between Comparative Examples 1 to 7 and the Examples lies in the different chemical composition and its content and the different process parameters. The specific components in Examples 1 to 3 and Comparative Examples 1 to 7 are shown in Table 1, and the rest are Fe and unavoidable impurities. The process parameters of the manufacturing method in Examples 1 to 3 and Comparative Examples 1 to 7 are shown in Tables 2 to 3.

[0042] Table 1: Chemical composition and content (wt%) in Examples and Comparative Examples

[0043] serial number C Si Mn Nb Als B P S Ti Example 1 0.058 0.21 1.55 0.043 0.025 0.0001 0.008 0.002 - Example 2 0.065 0.36 1.42 0.031 0.018 0.0002 0.009 0.002 - Example 3 0.077 0.15 1.18 0.019 0.045 0.0003 0.010 0.001 - Comparative Example 1 0.040 0.20 1.25 0.010 0.025 0.0004 0.010 0.003 - Comparative Example 2 0.070 0.25 0.85 0.028 0.023 0.0003 0.009 0.003 0.085 Comparative Example 3 0.13 0.36 1.42 0.031 0.018 0.0015 0.009 0.002 - Comparative Example 4 0.058 0.33 1.20 0.036 0.020 0.0002 0.009 0.002 - Comparative Example 5 0.065 0.36 1.42 0.031 0.018 0.0002 0.009 0.002 - Comparative Example 6 0.065 0.36 1.42 0.031 0.018 0.0002 0.009 0.002 - Comparative Example 7 0.065 0.36 1.42 0.031 0.018 0.0002 0.009 0.002 -

[0044] Table 2: Heating and rolling process parameters in the examples and comparative examples

[0045]

[0046] Table 3: Cooling and coiling process parameters in the examples and comparative examples

[0047]

[0048] The properties of the high-strength steel product obtained in Example 1 are shown in Table 4. The metallographic structure of the product is as follows: Figures 1 to 3 The properties of the high-strength steel products obtained in Examples 2 to 3 and Comparative Examples 1 to 7 are shown in Tables 5 to 13. In Tables 4 to 13, the outer ring of the hot-rolled coil is the tail of the hot-rolled strip in the length direction, the middle of the hot-rolled coil is the middle of the hot-rolled strip in the length direction, and the inner ring of the hot-rolled coil is the head of the hot-rolled strip in the length direction.

[0049] Among them, the evaluation method of mechanical properties and their fluctuation amplitude is as follows: 3 full-plate width specimens are taken at 3m in the head, middle and tail of the hot-rolled strip in the longitudinal direction, and 5 longitudinal tensile specimens, 5 groups (1 group of 3 pieces) of impact specimens and 5 hardness specimens are cut at equal intervals in the width direction from each full-plate width specimen to ensure that the specimens for each performance test include the middle part and the edge in the width direction. The yield strength, tensile strength and elongation of the material are obtained by room temperature tensile test according to GB / T228.1, the -40℃ low-temperature impact performance index Akv is obtained according to GB / T229, and the Vickers hardness index is obtained according to GB / T4340.1.

[0050] The fluctuation range of the yield strength of hot coil through coil = Max (the yield strength of the tensile specimens at the head 3m, middle and tail 3m) - Min (the yield strength of the tensile specimens at the head 3m, middle and tail 3m).

[0051] The fluctuation range of hot coil tensile strength = Max (tensile strength of tensile specimens at 3m at the head, 3m in the middle and 3m at the tail) - Min (tensile strength of tensile specimens at 3m at the head, 3m in the middle and 3m at the tail).

[0052] The fluctuation range of the impact performance of hot coil through coil = Max (impact performance of the impact specimens at 3m at the head, 3m in the middle and 3m at the tail) - Min (impact performance of the impact specimens at 3m at the head, 3m in the middle and 3m at the tail).

[0053] The fluctuation range of the hardness of the hot coil through the coil = Max (the hardness of the hardness samples at 3m at the head, 3m in the middle and 3m at the tail) - Min (the hardness of the hardness samples at 3m at the head, 3m in the middle and 3m at the tail).

[0054] Table 4: Mechanical properties and fluctuation range of high-strength steel products in Example 1

[0055]

[0056] As shown in Table 4, the yield strength of the high-strength steel product coil at different positions in the embodiment is 625-660MPa, the tensile strength is 686-720MPa, the elongation is 28.9-31.2%, the -40℃ impact energy Akv is 210-228J, and the hardness is 244-254HV10. The fluctuation range is small, indicating that the organization uniformity is good. Figures 1 to 3 It can be seen that Figures 1 to 3 The steel product organization types corresponding to different positions of the steel coil are all acicular ferrite, and the grain size is all 12.5, which shows that the organization uniformity of the steel coil is good.

[0057] Table 5: Mechanical properties and fluctuation range of high-strength steel products in Example 2

[0058]

[0059] Table 6: Mechanical properties and fluctuation range of high-strength steel products in Example 3

[0060]

[0061] Table 7: Mechanical properties and fluctuation range of steel products in Comparative Example 1

[0062]

[0063] Table 8: Mechanical properties and fluctuation range of steel products in comparative example 2

[0064]

[0065] Table 9: Mechanical properties and fluctuation range of steel products in comparative example 3

[0066]

[0067] Table 10: Mechanical properties and fluctuation range of steel products in Comparative Example 4

[0068]

[0069] Table 11: Mechanical properties and fluctuation range of steel products in comparative example 5

[0070]

[0071] Table 12: Mechanical properties and fluctuation range of steel products in Comparative Example 6

[0072]

[0073] Table 13: Mechanical properties and fluctuation range of steel products in comparative example 7

[0074]

[0075] As shown in Tables 1 to 3, the yield strength of the high-strength steel products in Examples 1 to 3 is ≥566MPa, the tensile strength is ≥652MPa, the elongation is ≥28.9%, the -40°C low-temperature impact performance Akv is ≥230J, and the fluctuation range of the hot coil through-coil yield strength is 35MPa, the tensile strength fluctuation range is ≤34MPa, the -40°C low-temperature impact energy fluctuation range is ≤20J, and the hardness fluctuation range is ≤10HV10, which has good strength and toughness matching and performance uniformity. Among them, the finished product thickness in Example 3 is 14mm, the -40°C impact energy Akv is a minimum of 219J and a maximum of 235J, with a fluctuation range of only 17J, good impact performance and uniform performance.

[0076] It can be seen from Tables 1 to 13 that the C content in Comparative Example 1 exceeds the scope of the present invention, and the Nb content is less than the scope of the present invention. The elongation of its product is relatively high, but the yield strength, tensile strength, and -40°C low-temperature impact performance are all low, and the fluctuation range of each performance is relatively large; the Mn content in Comparative Example 2 is relatively low, and the Ti element is added. The yield strength and tensile strength of its product are relatively large, but the elongation and -40°C low-temperature impact performance are relatively low, and the fluctuation range of each performance is larger than that of the embodiment; the C content and B content in Comparative Example 3 far exceed the scope of the present invention, and the yield strength and tensile strength of its product are relatively large, but the elongation and -40°C low-temperature impact performance are relatively low, and the fluctuation range of each performance is larger than that of the embodiment; the chemical composition of Comparative Example 4 is in line with the scope of the present invention, but the cooling rate of the ultra-fast cooling section of Comparative Example 4 is only 85.6°C / s, which does not meet the 100°C / s required by the present invention, and the fluctuation range of each performance of its product is relatively small, and the elongation is high, but the yield The yield strength, tensile strength and -40°C low-temperature impact performance are low; the chemical composition of comparative examples 5 to 7 is the same as that of embodiment 2, but the final rolling temperature FDT in comparative example 5 is only 776°C, which does not reach the 800-860°C range of the present invention, and the slow cooling pit is not used for cooling after hot rolling, and the cooling rate exceeds 5°C / h, resulting in a large fluctuation in the yield strength and tensile strength of the product. The cooling rate of the ultra-fast cooling section of comparative example 6 is only 78.1°C / s, which does not meet the requirement of 100°C / s of the present invention, and the coiling temperature is 537°C, which exceeds the scope of the present invention. The fluctuation range of various properties of the product is small, but the yield strength, tensile strength and -40°C low-temperature impact performance are low; the coiling temperature of comparative example 7 is 331°C, which does not meet the requirements of the scope of the present invention, and the slow cooling pit is not used for cooling after hot rolling, and the cooling rate exceeds 5°C / h, resulting in a low elongation, a low -40°C low-temperature impact energy and a large fluctuation in performance.

[0077] Therefore, the high-strength steel product obtained by using the chemical composition and process parameters of the present invention has the advantages of uniform mechanical properties and a large production process window while taking into account high strength and high toughness. The impact performance and uniformity of materials with a thickness greater than 12 mm are good.

[0078] Other parts not described belong to the prior art.

Claims

1. A hot-rolled high-strength steel plate, characterized in that: The invention comprises the following chemical components in percentage by weight: C: 0.050% to 0.080%; Si: 0.10% to 0.40%; Mn: 1.10% to 1.60%; Nb: 0.015% to 0.050%; B: ≤0.0005%.

2. The hot-rolled high-strength steel plate according to claim 1, characterized in that: The hot-rolled high-strength steel plate comprises the following chemical components by weight percentage: C: 0.050% to 0.080%; Si: 0.10% to 0.40%; Mn: 1.10% to 1.60%; Nb: 0.015% to 0.050%; Als: 0.015~0.050%; B：≤0.0005％； P ：≤0.010％； S: ≤0.003%; the rest is Fe and unavoidable impurities.

3. A method for manufacturing the hot-rolled high-strength steel plate according to claim 1 or 2, characterized in that: The following steps are involved: Converter smelting, LF+RH refining, continuous casting, heating, rolling, cooling and coiling.

4. The manufacturing method according to claim 3, characterized in that: In the converter smelting process, alloy auxiliary materials are added during the converter steelmaking process; wherein the alloy auxiliary material Si is high-purity ferrosilicon.

5. The manufacturing method according to claim 3, characterized in that: In the heating process, the temperature of the cast billet out of the furnace is 1200-1250° C., and the holding time is 160-210 minutes.

6. The manufacturing method according to claim 3, characterized in that: The rolling process includes rough rolling and finish rolling; during the rough rolling process, the final rolling temperature R2DT=1020-1080°C, and the cumulative reduction rate of rough rolling is ≥70%; during the finish rolling process, the final rolling temperature FDT=800-860°C, and the cumulative reduction rate of finish rolling is ≥75%.

7. The manufacturing method according to claim 6, characterized in that: The rolling process adopts a 2-stand roughing and 7-stand finishing hot rolling unit, all the insulation covers between the roughing and finishing units are put into use, and the longitudinal water spray and bottom water spray between the finishing rolling F1-F7 stands are closed.

8. The manufacturing method according to claim 3, characterized in that: The cooling adopts an ultra-fast cooling process; the ultra-fast cooling process adopts front-end intensive cooling, the cooling rate is ≥100°C / s, the cooling water flow ratio of the upper and lower surfaces of the strip is 1:1.20 to 1:1.40, and the side water spraying is symmetrical cross side spraying.

9. The manufacturing method according to claim 8, characterized in that: After the front-stage intensive cooling is completed, the coiling is carried out directly.

10. The manufacturing method according to any one of claims 3 to 9, characterized in that: In the coiling process, the coiling temperature CT is 380-500° C., and after the hot coil is coiled, it is placed in a slow cooling pit for air cooling to room temperature, and the air cooling rate is ≤5° C. / h.

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