CN109536846B - High-toughness hot-rolled steel plate with yield strength of 700MPa and manufacturing method thereof - Google Patents
High-toughness hot-rolled steel plate with yield strength of 700MPa and manufacturing method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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Abstract
The invention discloses a high-toughness hot-rolled steel plate with 700MPa of yield strength and a manufacturing method thereof, and solves the technical problems of low toughness and high manufacturing cost of the conventional high-toughness hot-rolled steel plate with 700MPa of yield strength. The invention provides a high-toughness hot-rolled steel plate with yield strength of 700MPa, which comprises the following chemical components in percentage by weight: 0.06-0.10% of C, less than or equal to 0.10% of Si, 1.20-1.80% of Mn, less than or equal to 0.012% of P, less than or equal to 0.006% of S, less than or equal to 0.0040% of N, 0.015-0.040% of Al, 0.10-0.30% of Mo, 0.06-0.12% of Ti, and the balance of iron and inevitable impurities. The-40 ℃ impact power value Akv of the hot rolled steel plate with the thickness of 1.5-14.0 mm is more than or equal to 120J. The method can be used in the fields of engineering machinery, automobiles, railways, pipelines, containers and the like.
Description
Technical Field
The invention relates to a high-strength hot-rolled steel plate, in particular to a high-toughness hot-rolled steel plate with the yield strength of 700MPa and a manufacturing method thereof, and belongs to the technical field of iron-based alloys.
Background
The hot-rolled high-strength steel can play the roles of high strength and thinning, equipment dead weight reduction and energy consumption reduction, and is widely applied to the industries of engineering machinery, automobiles, railways, pipelines, containers and the like. The general hot-rolled low-alloy steel high-strength steel mainly adopts single or composite addition of micro alloy elements such as Nb, V, Ti and the like to improve the strength, and often needs to further add alloy elements such as Cr, Ni, Mo, B and the like to improve the strength in steel with yield strength of more than 700MPa, and along with the increase of the types and the contents of the alloy elements, the toughness, especially the low-temperature impact toughness, can be reduced while the strength of the steel is improved. In the production process of the high-strength steel, besides the conventional controlled rolling and controlled cooling process, the controlled rolling and controlled cooling and tempering process (TMCP and tempering process) and the controlled rolling and tempering process are also common. From the aspects of process control and cost, the method has the advantages of adopting less alloy and procedures and reducing the manufacturing cost. Therefore, on the premise of adding less alloy elements, the controlled rolling and controlled cooling process is used, the strength of the steel plate is ensured, and meanwhile, the plasticity and toughness indexes can be ensured, so that the method is a technical problem for iron and steel enterprises to research and develop new low-cost high-toughness high-strength steel plates.
The Chinese patent application publication No. CN105200332A discloses a 700 MPa-level thin-specification high-strength steel strip and a production method thereof, and the components are Nb (less than or equal to 0.065%), Ti (0.045-0.06%) and Cr (0.25-0.5%) in design, the alloy cost is relatively low, but an annealing process is added, the thickness of a finished product is only 1.2-2.5mm, and obviously, the components are only suitable for thin specifications.
Chinese patent application publication No. CN106591714A discloses a steel plate for engineering machinery with yield strength of 700MPa and a preparation method thereof, and the steel plate is formed by microalloying Nb (0.055-0.065%), Ti (0.095-0.105%) and Mo (0.1-0.15%) in component design. No specific applicable thickness range is described, only 6 mm, 8mm and 10mm are mentioned in the examples, the toughness of the steel plate is not described, the steel plate needs to be put into a coiling furnace after being coiled, and the alloy and the process cost are high.
The Chinese patent application publication No. CN104018087A discloses a steel for an automobile beam with yield strength of more than 700MPa and a manufacturing method thereof, wherein the steel is formed by microalloying Nb (0.03-0.06%), Ti (0.06-0.2%), Cr (0.35-0.55) and Mo (less than or equal to 0.25%) in component design, the thickness is 2-8 mm, the yield ratio is less than 0.9, the toughness condition is not mentioned, and three-stage cooling is required for laminar cooling.
The application publication number CN106756564A of Chinese patent application discloses a steel strip with yield strength of 700MPa and a production method thereof, the steel strip adopts Nb (0.05-0.07%) and Ti (0.08-0.13%) microalloying design, and TMCP technology is adopted in production, obviously, the alloy cost is low, the technology is simple, but the thickness of the product is 1.2-4.0 mm, and the steel strip is only suitable for thin products.
The application publication No. CN102226250A discloses a hot-rolled steel plate with yield strength of 700MPa and a preparation method thereof, wherein the hot-rolled steel plate is formed by microalloying Nb (0.06-0.08%), Ti (0.09-0.12%) and B (0.0008-0.005), the Si content is (0.15-0.3%), the thickness is 5.0-10.0 mm, and the half-size-60 ℃ impact energy is more than 79. Since a certain amount of B is added to the steel sheet, it is obvious that there is a problem that the impact power value fluctuates greatly.
The Chinese patent application with application publication number CN103014539A discloses a high-strength and high-toughness steel plate with yield strength of 700MPa grade and a manufacturing method thereof, the impact work value of the prepared steel plate at-60 ℃ is more than 150J, the prepared steel plate has high toughness, but the component design adopts the composite addition of various alloys such as Ti (0.01-0.25%), Cr (0.3-0.75%), Mo (0.1-0.3%), Ni (0.1-0.4%) and the like, the alloy cost is also high, and in addition, the tempering treatment is adopted in the process.
The Chinese patent application publication No. CN104694822A discloses a high-strength hot-rolled steel plate with a yield strength of 700MPa and a manufacturing method thereof, and the high-strength hot-rolled steel plate adopts a microalloying design of Nb (0.024-0.07%) and Ti (0.08-0.15%), adopts a TMCP (thermal mechanical control processing) process in production, has the advantage of low alloy cost, has a low-temperature impact energy of more than or equal to 80J at the temperature of-40 ℃, and is applicable to a thickness of 3.0-12 mm.
Therefore, most of the technical schemes disclosed in the prior art for hot-rolled high-strength steel plates with yield strength of 700MPa mainly adopt Nb-Ti micro-alloys, one or more of alloy elements such as V, Cr, Mo, Ni and the like are properly added to improve the strength, the alloy addition is large, the resource consumption is large, and the manufacturing cost is high. A few parts of Nb-Ti micro-alloys are hot rolled steel plates with the yield strength of 700MPa, and the problems of low toughness or thin applicable thickness exist. In addition, a part of hot rolled steel with the yield strength of 700MPa is produced in more processes, so that the manufacturing cost is higher.
Disclosure of Invention
The invention aims to provide a high-toughness hot-rolled steel plate with 700MPa of yield strength and a manufacturing method thereof, solves the technical problems of low toughness and high manufacturing cost of the conventional high-toughness hot-rolled steel plate with 700MPa of yield strength, and meets the requirements of industries such as engineering machinery, automobiles, railways, pipelines, containers and the like on the low-cost high-toughness high-strength hot-rolled steel plate.
The technical idea of the invention is that the low-temperature impact toughness of the hot-rolled steel plate is improved by adopting a proper amount of Mo-Ti micro-alloying and combining proper components and hot rolling process design on the premise of ensuring the material strength.
The technical scheme adopted by the invention is that a high-toughness hot-rolled steel plate with the yield strength of 700MPa comprises the following chemical components in percentage by weight: 0.06-0.10% of C, less than or equal to 0.10% of Si, 1.20-1.80% of Mn, less than or equal to 0.012% of P, less than or equal to 0.006% of S, less than or equal to 0.0040% of N, 0.015-0.040% of Al, 0.10-0.30% of Mo, 0.06-0.12% of Ti, and the balance of iron and inevitable impurities.
The metallographic structure of the high-toughness hot-rolled steel plate with the yield strength of 700MPa is fine-grained ferrite and a very small amount of pearlite, the grain size of the ferrite in the metallographic structure is 10-13 grades, and the upper yield strength R of the hot-rolled steel plate with the thickness of 1.5-14.0 mm iseHNot less than 700MPa, tensile strength Rm750MPa or more, 18 percent or more of elongation A after fracture, 120J or more of impact power Akv at minus 40 ℃, and qualified d-a in a 180-degree bending test.
The reason why the chemical composition of the high toughness hot rolled steel sheet having a yield strength of 700MPa according to the present invention is limited to the above range is as follows:
carbon: the carbon content is favorable for improving the strength, but too high carbon content can form more large and thick brittle carbide particles in steel, is unfavorable for plasticity and toughness, can form a segregation zone in the center of a steel plate, is unfavorable for bending performance, and increases the welding carbon equivalent by the too high carbon content, and is unfavorable for welding processing. And a large amount of alloy must be added to improve the strength when the carbon content is too low, so that the cost is high, and the C content set by the invention is 0.06-0.10%.
Silicon: silicon solid solution in a steel plate matrix has an obvious strengthening effect, but the plasticity and toughness of the steel plate are unfavorable due to the excessively high silicon content, and meanwhile, a severe rust red iron sheet which is difficult to remove is formed on the surface of a hot rolled plate, so that the appearance of the product and the subsequent surface treatment are influenced. The invention limits Si to be less than or equal to 0.10 percent.
Manganese: on one hand, manganese can play a role in solid solution strengthening, can improve the hardenability of the material, is one of important elements for improving the strength of the material, and can expand a gamma region, reduce the gamma → alpha transition temperature and expand a rolling process window. However, the Mn content is high, segregation is easily generated, the toughness of the material is reduced, the performance is deteriorated, the carbon equivalent is increased, welding is not facilitated, and the alloy cost is further increased. The invention limits the Mn content to 1.20-1.80%.
Sulfur and phosphorus: too high a sulfur and phosphorus element may adversely affect the toughness and plasticity of the material. Therefore, the invention limits that S is less than or equal to 0.006 percent and P is less than or equal to 0.012 percent.
Aluminum: the aluminum plays a role in deoxidation in the present invention, and is a strong oxidizing forming element, and forms Al with oxygen in steel2O3Is removed during steel making. Too high an aluminum content can lead to excessive Al formation2O3Inclusion and the continuous casting are easy to block the casting nozzle. The Al content is limited to be 0.015-0.040%.
Molybdenum: molybdenum is the main alloy element of the invention, and the molybdenum can be dissolved in ferrite in the steel to play a role in solid solution strengthening, and can also form carbide with carbon to play a role in precipitation strengthening, thereby improving the strength of the steel. In addition, molybdenum remarkably increases the hardenability and hardenability of the steel, refines the microstructure and can remarkably improve the toughness of the steel. The content of Mo is limited to be 0.10-0.30%.
Titanium: titanium is an important microalloy element in the invention, forms TiN precipitated phase at high temperature to effectively refine austenite grains, forms TiC precipitated phase at low temperature, easily obtains fine and dispersed precipitated phase, can effectively improve strength, and can obtain obvious strengthening effect by using a very small amount of Ti. Too much Ti content is detrimental to the impact toughness of the steel sheet, and is particularly likely to cause cracking during bending. The invention limits the Ti content to 0.06-0.12%.
Nitrogen: too high a nitrogen content can seriously deteriorate the plasticity and toughness of the material, especially for Ti microalloyed high strength steel, since N combines with Ti at high temperature to produce TiN with larger size, on the one hand, the toughness of the material is affected, and on the other hand, the effective titanium content of steel grade combining with C to produce fine TiC is reduced, thereby causing the strength to be reduced. In view of the adverse effect of N on toughness, the present invention defines N.ltoreq.0.0040%.
A manufacturing method of a high-toughness hot-rolled steel plate with yield strength of 700MPa comprises the following steps:
continuously casting molten steel to obtain a continuous casting slab, wherein the molten steel comprises the following chemical components in percentage by weight: 0.06-0.10% of C, less than or equal to 0.10% of Si, 1.20-1.80% of Mn, less than or equal to 0.012% of P, less than or equal to 0.006% of S, less than or equal to 0.0040% of N, 0.015-0.040% of Al, 0.10-0.30% of Mo, 0.06-0.12% of Ti, and the balance of iron and inevitable impurities;
heating the continuous casting plate blank at 1230-1270 ℃ for 150-240 min, and then carrying out hot rolling, wherein the hot rolling is a two-stage rolling process, the rough rolling is 6-pass continuous rolling, the rolling is carried out at a temperature above the austenite recrystallization temperature, and the finish temperature of the rough rolling is 1050-1100 ℃; the thickness of the intermediate blank is 34-55 mm, the finish rolling is 7-pass continuous rolling, the inlet temperature of the finish rolling is 1020-1060 ℃, and the finish rolling finishing temperature is 810-880 ℃; after finish rolling, the thickness of the steel plate is controlled to be 1.5-14.0 mm, front-end cooling is adopted for laminar cooling, the laminar cooling speed is 50-100 ℃/s, and when the coiling temperature is 520-600 ℃, the hot rolled steel coil is coiled.
The reason of the hot rolling process system adopted by the invention is as follows:
1. setting of heating temperature and heating time of continuous casting slab
The heating temperature and time of the continuous casting slab are set to ensure the dissolution of coarse TiN, TiC and other particles in the continuous casting slab, and because a certain amount of Ti exists, the TiN, TiC and other particles can be separated out in the cooling process of the continuous casting slab. In the heating process of the plate blank, large TiN, TiC and other particles need to be fully dissolved, the sufficient amount of dispersed fine TiC and other particles can be precipitated in the cooling process after rolling, and the precipitation strengthening effect of Ti is effectively exerted, so the heating temperature is very important for the technical scheme of the invention, the large original TiN, TiC and other particles in the continuous casting plate blank cannot be fully dissolved due to too low temperature or too short heating time, the temperature is too high, the heating time is too long, the original structure of the plate blank is large, the surface oxidation and decarburization are serious, the final performance and the surface quality of the steel plate are not facilitated, and energy is also consumed. The heating temperature of the continuous casting plate blank is set to be 1240-1270 ℃, and the heating time is set to be 150-240 min.
2. Roughing finish temperature setting
The rough rolling process is controlled to be rolled above the austenite recrystallization temperature, so that uniform and fine austenite grains are ensured to be obtained. Therefore, the rough rolling finishing temperature is set to be 1050-1100 ℃.
3. Intermediate billet thickness and finish rolling entry temperature settings
In order to obtain good impact toughness, particularly for hot continuous rolled steel sheets with a thickness of 8mm or more, it is necessary to control the effective reduction ratio at the finish rolling stage. The effective reduction rate is the reduction rate of deformation occurring in the temperature range of the austenite non-recrystallization region in the finish rolling stage, and is related to the thickness and temperature of the intermediate billet at the finish rolling inlet. Therefore, the thickness of the intermediate blank is set to be 34-55 mm, and the finish rolling inlet temperature is set to be 1020-1060 ℃.
4. Finish rolling finish temperature setting
The final rolling temperature is set to have two functions, on one hand, flat austenite grains with deformation zones inside are obtained through rolling in an austenite non-recrystallization region, and are converted into fine ferrite grains in the subsequent laminar cooling process, so that the fine grain strengthening function is exerted. On the other hand, the finish rolling temperature is set so as to prevent most of particles such as TiC from precipitating in the deformed austenite in advance, so that re-precipitation in the ferrite is reduced and the function of precipitation strengthening cannot be exerted. In order to ensure the low-temperature toughness of thick specifications, the invention sets the finish rolling temperature to be related to the thickness of the final finished product of the hot continuous rolling steel plate. Therefore, the finish rolling finishing temperature is set to be 810-880 ℃.
5. Laminar cooling rate setting
The set laminar cooling speed after finish rolling is very critical, and the rapid cooling speed is adopted to inhibit the growth of ferrite grains and the precipitation of TiC at a high-temperature stage. The rapid cooling makes it possible to precipitate fine and dispersed particles of TiC and the like in the ferrite at a lower temperature. The cooling speed is too slow, and the advance precipitation of TiC in high-temperature deformation austenite cannot be inhibited; too fast cooling may adversely affect the toughness of the steel plate and may also have a significant impact on the plate shape. The laminar cooling adopts a front-section cooling mode, and the cooling speed is 50-100 ℃/s.
6. Coiling temperature setting
The coiling temperature mainly affects the structure and performance of the strip steel. Too high or too low coiling temperature is not favorable for the precipitation of particles such as TiC and the like, and the precipitation strengthening effect cannot be well exerted. Comprehensively, the hot rolling coiling temperature is set to be 520-600 ℃.
The metallographic structure of the high-toughness hot-rolled steel plate with the yield strength of 700MPa produced by the method is fine-grained ferrite and a very small amount of pearlite, the grain size of the ferrite in the metallographic structure is 10-13 grades, and the upper yield strength R of the hot-rolled steel plate with the thickness of 1.5-14.0 mmeHNot less than 700MPa, tensile strength Rm750MPa or more, 18 percent or more of elongation A after fracture, 120J or more of impact power Akv at minus 40 ℃, and qualified d-a in a 180-degree bending test.
Compared with the prior art, the invention has the following positive effects: 1. the invention adopts the microalloying component design of low carbon, high Mn, Mo and Ti, and alloy elements such as Cr, Ni, Nb, V, B and the like are not added, so that the obtained steel plate has lower carbon equivalent; according to the thickness of the intermediate blank, the finish rolling and the coiling temperature designed according to different thickness grades, the controlled rolling control process is fully utilized, and the functions of fine grain strengthening and precipitation strengthening are exerted; the produced hot rolled steel plate has good processing and welding performance and low manufacturing cost. 2. The hot rolled steel plate with the yield strength of 700MPa has excellent impact toughness, and the-40 ℃ impact work value Akv of the hot rolled steel plate with the thickness of 1.5-14.0 mm is more than or equal to 120J; and (4) passing a 180-degree bending test when d is equal to a.
Drawings
FIG. 1 is a photograph of a metallographic structure of a hot-rolled steel sheet according to example 4 of the invention.
Detailed Description
The present invention is further described below with reference to examples 1 to 5, which are shown in tables 1 to 3.
Table 1 shows the chemical composition (in weight percent) of the steels of the examples of the invention, with the balance being iron and unavoidable impurities.
Table 1 chemical composition of the steels of the examples of the invention, in units: and (4) weight percentage.
Smelting in a converter, carrying out Ar blowing treatment in an LF ladle refining furnace refining procedure, carrying out vacuum cycle degassing treatment in an RH furnace, finely adjusting components to obtain molten steel meeting the component requirements, and continuously casting to obtain a continuous casting slab. The thickness of the continuous casting plate blank is 210-230 mm, the width is 900-1600 mm, and the length is 8000-11700 mm (long blank), or 4700-5300 mm (short blank).
And (3) conveying the fixed-length plate blanks produced in the steelmaking process to a heating furnace for heating, discharging and descaling, and conveying to a hot continuous rolling unit for rolling. And controlling rolling by a rough rolling and finish rolling continuous rolling unit, coiling after laminar cooling, and carrying out front-section cooling on the laminar cooling to produce a qualified hot-rolled steel coil. The thickness of the hot rolled steel plate is 1.5-14.0 mm. The hot rolling process control parameters are shown in Table 2.
TABLE 2 Hot Rolling Process control parameters of the inventive examples
Referring to FIG. 1, the hot rolled steel sheet obtained by the method has a metallographic structure comprising fine-grained ferrite and a very small amount of pearlite, wherein the grain size of the ferrite in the metallographic structure is 10 to 13 grades, and the upper yield strength R of the hot rolled steel sheet with a thickness of 1.5 to 14.0mmeHNot less than 700MPa, tensile strength Rm750MPa or more, 18 percent or more of elongation A after fracture, 120J or more of impact power Akv at minus 40 ℃, and qualified d-a in a 180-degree bending test.
The hot rolled steel plate obtained by the invention is sampled, a transverse sample is obtained by tensile and bending tests, a longitudinal sample is obtained by impact tests, and the tensile test is carried out according to the part 1 of the GB/T228.1-2010 metal material tensile test: room temperature test method for tensile test; performing a bending test according to GB/T232-2010 bending test method for metal materials; the impact test is carried out according to GB/T229-2007 method for testing charpy pendulum impact of metal materials, and the mechanical properties are shown in Table 3.
TABLE 3 mechanical Properties of Hot rolled Steel sheets according to examples of the present invention
As seen from Table 3, the hot rolled steel sheet obtained by the present invention has the advantages of high strength and high toughness, and also has good cold-bending formability.
In addition to the above embodiments, the present invention may have other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.
Claims (3)
1. A high-toughness hot-rolled steel plate with yield strength of 700MPa comprises the following chemical components in percentage by weight: c: 0.06-0.10%, Si is less than or equal to 0.10%, Mn: 1.20-1.80%, P is less than or equal to 0.012%, S is less than or equal to 0.006%, N is less than or equal to 0.0040%, Al:0.015 to 0.040%, Mo: 0.10-0.30%, Ti: 0.06-0.12% of iron and inevitable impurities as the rest; the metallographic structure of the hot-rolled steel plate is fine-grained ferrite and a very small amount of pearlite, and the grain size of the ferrite in the structure is 10-13 grades; upper yield strength R of hot rolled steel plate with thickness of 1.5 mm-14.0 mmeHNot less than 700MPa, tensile strength Rm750MPa or more, elongation A after fracture is 18% or more, and impact work value Akv at minus 40 ℃ is 120J or more.
2. A manufacturing method of a high-toughness hot-rolled steel plate with 700MPa of yield strength is characterized by comprising the following steps:
continuously casting molten steel to obtain a continuous casting slab, wherein the molten steel comprises the following chemical components in percentage by weight: c: 0.06-0.10%, Si is less than or equal to 0.10%, Mn: 1.20-1.80%, P is less than or equal to 0.012%, S is less than or equal to 0.006%, N is less than or equal to 0.0040%, Al:0.015 to 0.040%, Mo: 0.10-0.30%, Ti: 0.06-0.12% of iron and inevitable impurities as the rest;
heating the continuous casting plate blank at 1230-1270 ℃ for 150-240 min, and then carrying out hot rolling, wherein the hot rolling is a two-stage rolling process, the rough rolling is 6-pass continuous rolling, the rolling is carried out at a temperature above the austenite recrystallization temperature, and the finish temperature of the rough rolling is 1050-1100 ℃; the thickness of the intermediate blank is 34-55 mm, the finish rolling is 7-pass continuous rolling, the intermediate blank is rolled in an austenite non-recrystallization temperature area, the inlet temperature of the finish rolling is 1020-1060 ℃, and the finish rolling finishing temperature is 810-880 ℃; and after finish rolling, performing front-stage cooling by adopting laminar cooling, wherein the laminar cooling speed is 50-100 ℃/s, and the hot-rolled steel coil is obtained by coiling when the coiling temperature is 520-600 ℃.
3. The method for manufacturing a high toughness hot rolled steel sheet having a yield strength of 700MPa according to claim 2, wherein the thickness of the steel sheet after finish rolling is controlled to be 1.5 to 14.0 mm.
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