690MPa quenched and tempered high-strength steel and manufacturing method thereof

Abstract

The invention relates to the technical field of steel smelting, and provides 690MPa quenched and tempered high-strength steel and a manufacturing method thereof. The invention relates to 690 MPa quenched and tempered high-strength steel which is composed of the following components in percentage by weight: 0.15%-0.17% of C, 0.15%-0.30% of Si, 1.50%-1.65% of Mn, less than 0.018% of P, less than 0.008% of S, 0-0.30% of Cr, 0-0.20% of Ni, 0-0.25% of Mo, 0-0.04% of Nb, 0-0.12% of V, 0-0.04% of Ti, 0-0.0025% of B, 0.01%-0.03% of Al and the balance of Fe and inevitable impurities, and the ratio of (C + Cr + Ti) to Mn is (1-5): 10. According to the technical scheme, the problem that the strength of 690 MPa quenched and tempered steel is low in the related technology is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of steel smelting, and specifically, to a 690 MPa quenched and tempered high-strength steel and a manufacturing method thereof. Background Art

[0002] From the large steel beams of building structures to the key components of bridge construction, from the body skeletons of construction machinery to the safety components of automobile manufacturing, high-strength steel plays an indispensable role in ensuring the structural safety and stability by virtue of its excellent mechanical properties. Especially the 690 MPa quenched and tempered high-strength steel, due to its high yield strength and tensile strength, is widely used in scenarios with strict strength requirements, such as the structural components of deep-sea drilling platforms in offshore engineering, which can withstand huge water pressure and wind and wave impacts; the key transmission components of large mining machinery, which can tolerate heavy loads and wear.

[0003] After years of tracking and researching the application markets of construction machinery, coal mining machinery, and port machinery, the annual demand for construction machinery, coal mines, and port machinery has been continuously increasing. According to statistics, the domestic demand for plates in construction machinery, coal mines, and port machinery is more than 12.5 million tons, among which the steel plates with a strength series of 690 MPa account for about 10%, and the proportion is very low and urgently needs to be increased. Technologically, an upgrade and replacement are necessary.

[0004] However, there are still some problems with the 690 MPa steel in terms of strength. Some existing 690 MPa steels are difficult to maintain a stable high strength under complex working conditions, and their strength decays to varying degrees under the influence of factors such as long-term alternating loads and harsh corrosion environments. Low strength will bring many hazards. In the construction field, it may cause the structural instability of buildings under natural disasters such as earthquakes and strong winds, endangering the safety of life and property; in mechanical manufacturing, mechanical components are prone to deformation and fracture, reducing the service life of equipment, increasing maintenance costs and downtime, and seriously affecting production efficiency. Therefore, it is necessary to develop a 690 MPa steel with high strength. Summary of the Invention

[0005] The present invention provides a 690 MPa quenched and tempered high-strength steel and a manufacturing method thereof, which solve the problem of low strength of 690 MPa quenched and tempered steel in related technologies.

[0006] The technical solution of the present invention is as follows: The present invention proposes a 690MPa quenched and tempered high-strength steel, which is composed of the following components in weight percentage: C 0.15%~0.17%, Si 0.15%~0.30%, Mn 1.50%~1.65%, P<0.018%, S<0.008%, Cr0~0.30%, Ni 0~0.20%, Mo 0~0.25%, Nb 0~0.04%, V 0~0.12%, Ti 0~0.04%, B 0~0.0025%, Al0.01%~0.03%, and the balance is Fe and unavoidable impurities, wherein (C+Cr+Ti):Mn=1~5:10.

[0007] As a further technical solution, the (C+Cr+Ti):Mn=2~2.2:10, Cr:Ti=7.5:1.

[0008] The present invention also provides a method for manufacturing 690MPa quenched and tempered high-strength steel, comprising the following steps: S1. Mix the materials according to the target composition, deoxidize and refine them after smelting, and continuously cast them into slabs; S2. The slab is heated to 1100-1220°C, and rough rolling, finish rolling, cooling, straightening, peeling, quenching, tempering, and then marked and inspected to obtain 690MPa quenched and tempered high-strength steel.

[0009] As a further technical solution, in step S1, the refining is carried out twice, the first refining is refining in a ladle refining furnace, and the second refining is vacuum refining. The time of the first refining is 15-30 minutes, and the time of the second refining is 15-35 minutes.

[0010] In the present invention, refining is carried out in two steps. In the first refining stage in the ladle refining furnace, the duration is controlled at 15 to 30 minutes. This process can effectively fine-tune the alloy composition and accurately adjust the content of each alloy element to more accurately match the target composition requirements, thereby laying the foundation for subsequent stable and excellent performance.

[0011] In the present invention, vacuum refining is used for the second time for 15 to 35 minutes. Under vacuum environment, the gas in the molten steel can be removed more thoroughly, which greatly reduces internal defects and significantly improves the density and uniformity of the steel plate.

[0012] As a further technical solution, in step S1, the refining includes the following steps: transferring the deoxidized molten steel into a ladle refining furnace, fine-tuning the alloy composition, and performing the first refining; after the first refining, vacuum degassing, bottom blowing argon, feeding calcium wire, and performing the second refining.

[0013] In the present invention, when the deoxidized molten steel is transferred to the ladle furnace for the first refining, by precisely controlling the alloy composition, the contents of various alloy elements meet the design requirements, strengthening the synergistic effect between elements.

[0014] In the present invention, the measure of bottom blowing argon can form a strong stirring flow inside the molten steel. On the one hand, it accelerates the collision and aggregation of inclusions, making them easier to float and remove; on the other hand, it promotes the uniform distribution of the molten steel composition and temperature, avoiding local composition segregation and temperature unevenness, and ensuring the uniform and stable performance of the steel plate.

[0015] In the present invention, feeding the calcium wire is a key step in the refining process. Calcium can react with harmful elements such as sulfur and phosphorus to form compounds with low melting points and easy to float, effectively reducing the content of harmful elements and reducing the erosion and weakening of grain boundaries by impurities. At the same time, calcium can also improve the morphology of inclusions, changing them from long strip and flake shapes to spherical shapes, reducing the damage of inclusions to the continuity of the steel plate matrix, and comprehensively improving the strength of the steel plate.

[0016] As a further technical solution, the protective atmosphere for continuous casting is argon, and the drawing speed for continuous casting is 0.75 - 1.0 m / min.

[0017] In the present invention, argon is used as the protective atmosphere isolation gas for continuous casting. As an inert gas, argon has stable chemical properties and does not react with the molten steel. During continuous casting, it can form an effective protective barrier on the surface of the molten steel, preventing harmful gases such as oxygen and nitrogen in the air from contacting the molten steel, ensuring the stability of the molten steel composition, reducing internal defects caused by gas pollution, and thus improving the quality and performance of the steel plate.

[0018] In the present invention, the continuous casting drawing speed is controlled within the appropriate range of 0.75 - 1.0 m / min. The appropriate drawing speed can ensure that the molten steel has sufficient time to solidify and crystallize in the mold, forming a uniform and dense billet tissue structure. If the drawing speed is too fast, the molten steel does not have enough time to fully solidify, which may lead to defects such as cracks and bulges on the surface of the billet, and the internal structure will also become loose, affecting the strength and toughness of the steel plate; if the drawing speed is too slow, the production efficiency will be reduced and the production cost will be increased. The drawing speed range of the present invention can not only ensure the production efficiency, but also enable inclusions in the molten steel to have enough time to float to the surface of the molten steel and be removed during the solidification process of the billet, further improving the purity of the billet. In addition, the stable drawing speed also helps to ensure the dimensional accuracy and surface quality of the billet, providing a good billet basis for subsequent rough rolling, finish rolling and other processing operations.

[0019] As a further technical solution, in step S2, the heating time is 3.5 - 4.5 h.

[0020] As a further technical solution, in step S2, the starting rolling temperature of the rough rolling is 1070 - 1180 °C, the final rolling temperature of the rough rolling is 970 - 1080 °C, the starting rolling temperature of the finish rolling is 900 - 950 °C, and the final rolling temperature of the finish rolling is 800 - 850 °C.

[0021] In the present invention, the starting rolling temperature of the rough rolling is set to 1070 - 1180 °C. This temperature range can ensure that the slab has good plasticity, is easy to deform, avoid work hardening phenomenon caused by too low temperature, prevent defects such as cracks in the steel plate, and ensure the internal quality and processing performance of the steel plate.

[0022] In the present invention, the starting rolling temperature of the finish rolling is set to 900 - 950 °C, which is beneficial to controlling the deformation resistance during rolling, and ensuring the stability of the rolling process and the dimensional accuracy of the product.

[0023] In the present invention, the final rolling temperature of the finish rolling is set to 800 - 850 °C. This temperature helps to promote the formation of a uniform and dense structure, effectively improving the comprehensive mechanical properties of the steel plate.

[0024] As a further technical solution, in step S2, the quenching temperature is 890 - 920 °C, and the quenching process method is roll - press water - jet quenching.

[0025] In the present invention, the quenching temperature is set to 890 - 920 °C, and the roll - press water - jet quenching method is adopted to improve the surface quality of the steel plate, reduce surface defects, make the steel plate surface more flat and smooth, and provide guarantee for subsequent tempering treatment and finished product quality.

[0026] As a further technical solution, in step S2, the tempering is carried out in two times. The temperatures and times of the first tempering and the second tempering are different. The temperature of the first tempering > the temperature of the second tempering, and the time of the first tempering < the time of the second tempering.

[0027] In the present invention, at the initial stage of tempering, there are a large number of quenching residual stresses in the steel plate. These stresses will significantly reduce the toughness of the material and increase the risk of brittle fracture at low temperatures. The higher temperature during the first tempering can quickly relax some internal stresses, which helps to improve the toughness of the steel plate and lay a foundation for further optimizing the structure during the subsequent second tempering.

[0028] In the present invention, the second tempering at a relatively low temperature and for a long time makes the microstructure inside the steel plate more uniform, reduces the performance differences between microscopic regions, further optimizes the structure, and significantly improves the low - temperature impact resistance of the steel plate.

[0029] In the present invention, the first tempering creates a good organizational basis for the second tempering, and the second tempering further optimizes the structure on the basis of the first tempering. This combination of tempering processes, with high temperature for a short time first and then low temperature for a long time, enables the steel plate to have a synergistic effect in eliminating internal stress and refining the structure, effectively improving the toughness of the steel plate, significantly enhancing the low-temperature impact resistance of the 690 MPa quenched and tempered high-strength steel, enabling it to reliably withstand impact loads in low-temperature environments, and broadening its application range in cold regions or under low-temperature working conditions.

[0030] As a further technical solution, the temperature of the first tempering is 610 °C and the time is 1 - 1.5 h, and the temperature of the second tempering is 560 °C and the time is 2 - 2.5 h.

[0031] In the present invention, during the two tempering processes, the diffusion and redistribution of alloying elements are more sufficient, further strengthening the effects such as solid solution strengthening, and at the same time improving the states of grain boundaries and phase boundaries, thereby enhancing the toughness of the steel plate.

[0032] As a further technical solution, in step S2, the equipment used for straightening is a nine-roll straightening machine.

[0033] As a further technical solution, in step S2, the method of descaling is shot peening.

[0034] The working principle and beneficial effects of the present invention are as follows: In the present invention, the carbon content is precisely controlled. As a strengthening element, the appropriate presence of carbon can effectively enhance the solid solution strengthening effect of the steel plate, providing a basic guarantee for the strength of the steel. The extremely low contents of harmful elements phosphorus and sulfur greatly reduce the damage of impurities to the crystal structure of the steel plate, effectively avoiding the weakening of grain boundaries caused by impurity segregation, and thus ensuring the stability and reliability of the steel plate strength. By limiting the element contents of carbon, manganese, chromium, and titanium, each element can fully play its strengthening role in the steel, forming an effective strengthening mechanism and further enhancing the strength characteristics of the steel. Specific Embodiments

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

[0036] Example 1 A 690MPa quenched and tempered high-strength steel, composed of the following components in weight percentage: C 0.15%, Si 0.15%, Mn 1.50%, P 0.010%, S 0.003%, Al 0.01%, and the balance Fe and unavoidable impurities; A method for manufacturing 690MPa quenched and tempered high-strength steel, comprising the following steps: S1. Mix the materials according to the target composition, deoxidize after smelting, transfer the deoxidized molten steel into the ladle refining furnace, fine-tune the alloy composition, and perform the first refining for 15 minutes. After the first refining, vacuum degassing, bottom blowing argon, feeding calcium wire, and performing the second refining for 35 minutes, and continuously casting to form slabs. During the continuous casting process, argon protection is used throughout the process, and the casting speed is 0.75m / min. S2. Heat the slab to 1100°C for 3.5h, raise the temperature to 1070°C for rough rolling, finish the rough rolling at 970°C, perform finish rolling at 900°C, finish the finish rolling at 800°C, straighten it with a nine-roll straightening machine after cooling, remove the iron oxide scale from the steel plate by shot peening, quench it with a roller water jet at 890°C, temper it at 610°C for 3h, and after marking and inspection, obtain 690MPa tempered high-strength steel with a thickness of 40mm.

[0037] Example 2 A 690MPa quenched and tempered high-strength steel, composed of the following components in weight percentage: C 0.16%, Si 0.22%, Mn 1.55%, P 0.012%, S 0.005%, Cr 0.15%, Ni 0.10%, Mo 0.15%, Nb 0.02%, V 0.06%, Ti 0.02%, B 0.0015%, Al 0.02%, and the balance is Fe and unavoidable impurities; A method for manufacturing 690MPa quenched and tempered high-strength steel, comprising the following steps: S1. Mix the materials according to the target composition, deoxidize after smelting, transfer the deoxidized molten steel into the ladle refining furnace, fine-tune the alloy composition, and perform the first refining for 20 minutes. After the first refining, vacuum degassing, bottom blowing argon, feeding calcium wire, and performing the second refining for 25 minutes, and continuously casting to form slabs. During the continuous casting process, argon protection is used throughout the process, and the casting speed is 0.9 m / min. S2. Heat the slab to 1150°C for 4 hours, raise the temperature to 1120°C for rough rolling, finish the rough rolling at 1020°C, perform finish rolling at 925°C, finish the finish rolling at 825°C, straighten it with a nine-roll straightening machine after cooling, remove the steel plate oxide scale by shot peening, quench it with a roller water jet at 905°C, temper it at 610°C for 3 hours, and after marking and inspection, obtain 40mm thick 690MPa quenched and tempered high-strength steel.

[0038] Example 3 A 690 MPa quenched and tempered high-strength steel consists of the following components by weight percentage: C 0.17%, Si 0.30%, Mn 1.65%, P 0.017%, S 0.007%, Cr 0.30%, Ni 0.20%, Mo 0.25%, Nb 0.04%, V 0.12%, Ti 0.04%, B 0.0025%, Al 0.03%, and the balance is Fe and unavoidable impurities; A manufacturing method of a 690 MPa quenched and tempered high-strength steel includes the following steps: S1. After batching according to the target composition and mixing, deoxidize after melting, transfer the molten steel after deoxidation treatment into a ladle refining furnace, finely adjust the alloy composition, conduct the first refining, the refining time is 30 min. After the first refining is completed, conduct vacuum degassing, bottom-blow argon, feed in calcium wire, conduct the second refining, the refining time is 15 min, continuously cast to form a slab, and protect with argon throughout the continuous casting process, and the casting speed is 1.0 m / min; S2. Heat the slab to 1220 °C, the heating time is 4.5 h, raise the temperature to 1180 °C for rough rolling, finish rough rolling at 1080 °C, conduct finish rolling at 950 °C, finish finish rolling at 850 °C, after cooling, straighten with a nine-high straightening machine, remove the scale on the steel plate by shot blasting, after quenching with a roll-type water jet at 920 °C, temper at 610 °C for 3 h, and then through marking and inspection, a 690 MPa quenched and tempered high-strength steel with a thickness of 40 mm is obtained.

[0039] Example 4 Compared with Example 2, the difference in Example 4 is that the addition amount of Mn is 1.65%.

[0040] Example 5 Compared with Example 2, the difference in Example 5 is that the addition amount of Mn is 1.50%.

[0041] Example 6 Compared with Example 2, the difference in Example 6 is that step S2 is different. S2 in this example includes the following steps: S2. Heat the slab to 1150 °C, the heating time is 4 h, raise the temperature to 1120 °C for rough rolling, finish rough rolling at 1020 °C, conduct finish rolling at 925 °C, finish finish rolling at 825 °C, after cooling, straighten with a nine-high straightening machine, remove the scale on the steel plate by shot blasting, after quenching with a roll-type water jet at 905 °C, temper at 610 °C for 1 h for the first time, and then temper at 560 °C for 2 h for the second time, and then through marking and inspection, a 690 MPa quenched and tempered high-strength steel is obtained.

[0042] Example 7 Compared with Example 2, the difference in Example 7 lies in that step S2 is different. S2 in this example includes the following steps: S2. Heat the slab to 1150°C for 4 hours, raise the temperature to 1120°C for rough rolling, finish rough rolling at 1020°C, perform finish rolling at 925°C, finish finish rolling at 825°C, after cooling, straighten it using a nine-roll straightening machine, remove the steel plate scale by shot blasting, perform roll-press water jet quenching at 905°C, perform primary tempering at 560°C for 2 hours, perform secondary tempering at 610°C for 1 hour, and after identification and inspection, obtain the 690 MPa quenched and tempered high-strength steel.

[0043] Example 8 Compared with Example 2, the difference in Example 8 lies in that step S2 is different. S2 in this example includes the following steps: S2. Heat the slab to 1150°C for 4 hours, raise the temperature to 1120°C for rough rolling, finish rough rolling at 1020°C, perform finish rolling at 925°C, finish finish rolling at 825°C, after cooling, straighten it using a nine-roll straightening machine, remove the steel plate scale by shot blasting, perform roll-press water jet quenching at 905°C, perform primary tempering at 610°C for 2 hours, perform secondary tempering at 560°C for 1 hour, and after identification and inspection, obtain the 690 MPa quenched and tempered high-strength steel.

[0044] Example 9 Compared with Example 2, the difference in Example 9 lies in that step S2 is different. S2 in this example includes the following steps: S2. Heat the slab to 1150°C for 4 hours, raise the temperature to 1120°C for rough rolling, finish rough rolling at 1020°C, perform finish rolling at 925°C, finish finish rolling at 825°C, after cooling, straighten it using a nine-roll straightening machine, remove the steel plate scale by shot blasting, perform roll-press water jet quenching at 905°C, perform primary tempering at 560°C for 1 hour, perform secondary tempering at 610°C for 2 hours, and after identification and inspection, obtain the 690 MPa quenched and tempered high-strength steel.

[0045] Example 10 Compared with Example 2, the difference in Example 10 lies in that step S2 is different. S2 in this example includes the following steps: S2. Heat the slab to 1150°C for 4 hours, raise the temperature to 1120°C for rough rolling, finish rough rolling at 1020°C, perform finish rolling at 925°C, finish finish rolling at 825°C, after cooling, straighten it using a nine-roll straightening machine, remove the steel plate scale by shot blasting, perform roll-press water jet quenching at 905°C, perform tempering at 560°C for 3 hours, and after identification and inspection, obtain the 690 MPa quenched and tempered high-strength steel.

[0046] Example 11 Compared with Example 2, Example 11 is different in that step S2 is different. S2 in this example includes the following steps: S2. Heat the slab to 1150°C for 4 hours, raise the temperature to 1120°C for rough rolling, finish rough rolling at 1020°C, perform finish rolling at 925°C, finish finish rolling at 825°C, straighten using a nine-high straightening machine after cooling, remove the steel plate scale by shot peening, perform roll-type water jet quenching at 905°C, perform primary tempering at 610°C for 1.5 hours, perform secondary tempering at 560°C for 1.5 hours, and obtain the 690 MPa quenched and tempered high-strength steel after identification and inspection.

[0047] Comparative Example 1 Compared with Example 2, Comparative Example 1 is different in that the addition amount of Mn is 1.8%.

[0048] Comparative Example 2 Compared with Example 2, Comparative Example 2 is different in that the addition amount of Mn is 1.2%.

[0049] Experimental Example 1 For the 690 MPa quenched and tempered high-strength steels prepared in Examples 1 to 5 and Comparative Examples 1 to 2, according to the test method specified in GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", the yield strength of the test samples was tested.

[0050] The test results are shown in Table 1: Table 1 Performance test results of 690 MPa quenched and tempered high-strength steels prepared in Examples 1 to 5 and Comparative Examples 1 to 2

[0051] Compared with Comparative Examples 1 and 2, the yield strength of Examples 1 to 5 is better than that of Comparative Examples 1 and 2, indicating that when the element content satisfies (C + Cr + Ti):Mn = 1 to 5:10, the strength of the steel plate can be improved, and when (C + Cr + Ti):Mn = 2 to 2.2:10 and Cr:Ti = 7.5:1, the strength of the steel plate is better.

[0052] Experimental Example 2 For the 690 MPa quenched and tempered high-strength steels prepared in Example 2 and Examples 6 to 11, according to the test method specified in GB / T 229-2020 "Metallic materials - Charpy pendulum impact test method", the impact energy of the test samples was tested. The specimen size was 10×10 mm, at a quarter of the plate thickness, and the temperature was -20°C.

[0053] The test results are shown in Table 2: Table 2 Performance test results of 690 MPa quenched and tempered high-strength steels prepared in Example 2 and Examples 6 to 11

[0054] Compared with Example 6, the impact energy of Example 6 is higher than that of Example 2 and Examples 7 to 11, indicating that when tempering is carried out in two steps, the temperature of the first tempering > the temperature of the second tempering, and the time of the first tempering < the time of the second tempering, the low-temperature impact resistance of the steel plate can be improved.

[0055] Experimental Example 3 The 690 MPa quenched and tempered high-strength steel prepared in Example 2 was tested according to the following method: 1. Tensile strength: The tensile strength of the test sample was tested according to the test method specified in GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature".

[0056] 2. Elongation: The elongation of the test sample was tested according to the test method specified in GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature".

[0057]

[0058] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A 690MPa quenched and tempered high-strength steel, characterized in that: It is composed of the following components in weight percentage: C 0.15%~0.17%, Si 0.15%~0.30%, Mn 1.50%~1.65%, P<0.018%, S<0.008%, Cr 0~0.30%, Ni 0~0.20%, Mo 0~0.25%, Nb 0~0.04%, V 0~0.12%, Ti 0~0.04%, B 0~0.0025%, Al 0.01%~0.03%, and the balance is Fe and unavoidable impurities, wherein (C+Cr+Ti):Mn=1~5:

10.

2. The 690MPa quenched and tempered high-strength steel according to claim 1, characterized in that: The (C+Cr+Ti):Mn=2~2.2:10, Cr:Ti=7.5:

1.

3. The method for manufacturing 690MPa quenched and tempered high-strength steel according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1. Mix the materials according to the target composition, deoxidize and refine them after smelting, and continuously cast them into slabs; S2. The slab is heated to 1100-1220°C, and rough rolling, finish rolling, cooling, straightening, peeling, quenching, tempering, and then marked and inspected to obtain 690MPa quenched and tempered high-strength steel.

4. The method for manufacturing 690MPa quenched and tempered high-strength steel according to claim 3, characterized in that: In step S1, the refining is carried out twice, the first refining is refining in a ladle refining furnace, and the second refining is vacuum refining. The time of the first refining is 15-30 minutes, and the time of the second refining is 15-35 minutes.

5. The method for manufacturing 690MPa quenched and tempered high-strength steel according to claim 4, characterized in that: In step S1, the refining includes the following steps: transferring the deoxidized molten steel into a ladle refining furnace, fine-tuning the alloy composition, and performing the first refining. After the first refining is completed, vacuum degassing, bottom blowing argon, feeding calcium wire, and performing the second refining.

6. The method for manufacturing 690MPa quenched and tempered high-strength steel according to claim 3, characterized in that: In step S1, the protective atmosphere of the continuous casting is argon, and the casting speed of the continuous casting is 0.75-1.0 m / min.

7. The method for manufacturing 690MPa quenched and tempered high-strength steel according to claim 3, characterized in that: In step S2, the starting rolling temperature of the rough rolling is 1070-1180°C, the final rolling temperature of the rough rolling is 970-1080°C, the starting rolling temperature of the finish rolling is 900-950°C, and the final rolling temperature of the finish rolling is 800-850°C.

8. The method for manufacturing 690MPa quenched and tempered high-strength steel according to claim 3, characterized in that: In step S2, the quenching temperature is 890-920°C, and the quenching process is roller-type water jet quenching.

9. The method for manufacturing 690MPa quenched and tempered high-strength steel according to claim 3, characterized in that: In step S2, the tempering is performed twice, the temperature and time of the first tempering are different from those of the second tempering, the temperature of the first tempering is greater than the temperature of the second tempering, and the time of the first tempering is less than the time of the second tempering.

10. The method for manufacturing 690MPa quenched and tempered high-strength steel according to claim 9, characterized in that: The temperature of the first tempering is 610° C., and the time is 1 to 1.5 h. The temperature of the second tempering is 560° C., and the time is 2 to 2.5 h.

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