Low-cost Q345R thick plate and production method thereof

Abstract

The invention discloses a low-cost Q345R thick plate and a production method thereof. The low-cost Q345R thick plate comprises the following chemical components in percentage by mass: 0.14 to 0.17 percent of C, 0.20 to 0.40 percent of Si, 1.50 to 1.70 percent of Mn, less than or equal to 0.017 percent of P, less than or equal to 0.005 percent of S, 0.020 to 0.050 percent of Nb, 0.020 to 0.050 percent of Al, less than or equal to 0.006 percent of N and the balance of Fe and inevitable impurities. The production method comprises the steps of molten iron pretreatment and converter smelting, LF furnace refining and VD vacuum treatment, continuous casting and slow cooling, two-stage controlled rolling and controlled cooling after rolling. According to the method, only niobium microalloy elements are added, normalizing rolling is adopted to replace traditional normalizing heat treatment, it is guaranteed that the yield strength of the Q345R thick plate is larger than or equal to 345 MPa, the impact energy at the temperature of 0 DEG C is larger than or equal to 41 J, the GB / T 713 standard requirement is met, meanwhile, the alloy cost is reduced by 5%-10%, energy consumption and emission are reduced, and the method has the advantages of being low in cost, excellent in performance and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and relates to low-cost Q345R thick plates, as well as a method for producing low-cost Q345R thick plates. Background Technology

[0002] Q345R steel plate, used in boilers and pressure vessels, is widely applied in various reactors, heat exchangers, storage tanks, and other equipment due to its excellent comprehensive mechanical properties. With increasingly stringent market demands for cost control, how to further reduce production costs while ensuring steel plate performance, especially low-temperature impact toughness, has become a crucial issue for steel companies. Current technologies typically involve adding expensive alloying elements such as nickel (Ni), vanadium (V), and chromium (Cr) to improve the performance of Q345R steel plate. This is achieved through the precipitation strengthening and grain refinement effects of microalloyed carbonitrides. While this method effectively improves the steel plate's strength and refines the microstructure, it also significantly increases alloy costs, posing a challenge to the economic viability of thick plate production. Alternatively, complex post-rolling heat treatment processes, such as normalizing or normalizing + tempering, can be employed. Although these methods can improve performance to some extent, they significantly increase alloy costs and process energy consumption, weakening the product's market competitiveness.

[0003] In recent years, with the nation's in-depth promotion of energy conservation and carbon reduction initiatives, clear requirements have been put forward for green, low-carbon, and high-quality development in industries such as steel. Against the backdrop of industrial upgrading and transformation, steel companies urgently need to explore new paths to reduce costs and increase efficiency while ensuring product performance meets stringent standards. Therefore, developing a production process that can reduce or optimize the use of microalloying elements and lower production costs, while still ensuring the performance indicators of Q345R thick plates, especially the central mechanical properties and microstructure uniformity, is crucial. This process would overcome the problems of high raw material costs and complex processes caused by excessive reliance on precious metal microalloying such as vanadium and titanium in existing technologies. This would significantly improve the economic efficiency and market competitiveness of products while meeting the stringent performance requirements of pressure equipment, actively responding to the national strategy of energy conservation, carbon reduction, and high-quality development in the steel industry. It is of great positive significance for promoting technological progress in the industry and enhancing the market competitiveness of enterprises. Summary of the Invention

[0004] The purpose of this invention is to provide a low-cost Q345R thick plate, which solves the problems of high raw material costs and complex processes in the prior art.

[0005] Another object of the present invention is to provide a low-cost method for producing Q345R thick plates.

[0006] The technical solution adopted in this invention is a low-cost Q345R thick plate with the following chemical composition by mass percentage: C: 0.14-0.17%, Si: 0.20-0.40%, Mn: 1.50-1.70%, P: ≤0.017%, S: ≤0.005%, Nb: 0.020-0.050%, Al: 0.020-0.050%, N: ≤0.006%, with the balance being Fe and unavoidable impurities.

[0007] The features of this invention are: The thickness of low-cost Q345R thick plates is 80-100mm.

[0008] The low-temperature impact toughness of low-cost Q345R thick plate in the thickness direction meets the following requirement: the average Charpy V-notch impact energy measured at 0℃ by sampling at 1 / 4 thickness position of low-cost Q345R thick plate is ≥142J. The average Charpy V-notch impact energy measured at 0℃ by sampling at half the thickness of a low-cost Q345R thick plate was ≥90J.

[0009] Low-cost Q345R thick plates, in hot-rolled delivery condition, meet the following mechanical properties: yield strength > 365MPa, tensile strength range of 522-549MPa, elongation > 22%, and Charpy V-notch impact energy measured at 0℃ > 90J.

[0010] Another technical solution adopted in this invention is a low-cost production method for Q345R thick plates, comprising the following steps: Step 1: KR hot metal pretreatment and converter smelting. Deoxidation and alloying are carried out during the tapping process, and argon blowing and stirring are performed throughout the tapping process to obtain molten steel. Step 2: The molten steel is fed into the LF furnace for refining, followed by vacuum treatment in the VD furnace. The treated molten steel is then continuously cast to obtain a slab, which is then slowly cooled. Step 3: Heat the slab and use a two-stage rolling process. The first stage rough rolling starts at a temperature >1010℃ and uses large reduction deformation. The second stage finish rolling starts at a temperature of 820-850℃ and rolls in the non-recrystallization zone to obtain the rolled steel plate. Step 4: Accelerate the cooling of the rolled steel plate to obtain low-cost Q345R thick plate.

[0011] The invention is further characterized by: The controlled rolling process employs a two-stage rolling process, including a roughing stage and a finishing stage. The final pass of both the roughing stage and the finishing stage uses a leveling pass.

[0012] Step 1 includes the following steps: Step 101: The sulfur content of the KR molten iron after pretreatment is 0-0.010%; Step 102: The final carbon content of the converter smelting is 0.06%-0.15%, and the tapping temperature is 1580-1620℃; Step 103: During the steel tapping process in the converter, after the molten steel has filled the bottom of the ladle, lime and pre-melted refining slag are added to the ladle. The amount of lime added is 200-400 kg / heat and the amount of pre-melted refining slag added is 100-200 kg / heat. Both are added before the steel tapping volume reaches 1 / 2. The tapping time is ≥4 min. Step 104: Add aluminum blocks, silicon manganese / high carbon ferromanganese, carbon raiser and niobium iron to the ladle in sequence to complete the deoxidation and alloying process. Step 105: Throughout the entire tapping process, argon is blown into the ladle for stirring. After tapping, the molten steel is further treated with argon in the argon station for ≥3 minutes before leaving the station.

[0013] Step 2 includes the following steps: Step 201: Argon is blown throughout the LF furnace refining process, and lime, low-nitrogen slag modifier or aluminum-based slag modifier is added to form white slag within 10 minutes. Then, 0.30-0.50 kg of aluminum particles are added per ton of molten steel, and the white slag state is maintained for ≥10 minutes. Step 202, the LF furnace temperature at the station is 1625-1635℃; Step 203: Transfer the molten steel to a VD furnace for degassing treatment. The vacuum degree after degassing treatment is 67 Pa, the vacuuming time is ≤8 min and maintained for ≥12 min. After the treatment, the hydrogen content in the molten steel is ≤2 ppm and the nitrogen content is ≤50 ppm. Step 204: After vacuum degassing, perform soft argon blowing treatment for ≥10 min. The temperature of the VD process bag is 1560-1570℃.

[0014] Step 3 includes the following steps: Step 301: Heat the slab to 1180-1240℃, with the ratio of heating time to slab thickness ranging from 9.5-11 min / mm, and the soaking time > 60 minutes. Control the slab exit temperature to ≥ 1185℃. Step 302: The initial rolling temperature of the first stage is ≥1010℃. In the roughing stage, a high temperature, low speed and large reduction process is adopted. The rolling speed is 0.9-1.2m / s, the maximum reduction per pass is >27mm, and the average reduction rate of the last three passes of roughing is >15%. A 150mm thick intermediate billet is rolled out. Step 303: The initial rolling temperature in the second stage is 820-850℃, the average reduction rate in the last three passes of finishing rolling is >10%, and the final rolling temperature is 780-820℃.

[0015] The accelerated cooling process specifically involves controlling the initial cooling temperature after rolling to 790-820℃ and the reheating temperature at the end of cooling to 600-640℃.

[0016] The beneficial effects of this invention are: The low-cost Q345R thick plate of this invention, firstly, by abandoning the expensive microalloying elements such as vanadium and titanium in traditional production, and optimizing the alloying scheme with the synergistic effect of low-content niobium and aluminum, significantly reduces the alloy cost per ton of steel by 5%-10% while ensuring the core mechanical properties of the steel plate. This meets the cost reduction and efficiency improvement needs of production enterprises and enhances the market competitiveness of the products.

[0017] Secondly, by precisely designing key components such as carbon and manganese, the drawbacks of insufficient strength due to low carbon and deterioration of weldability due to high carbon are avoided. Furthermore, through niobium-manganese synergistic strengthening and the grain-refining effect of aluminum, the thick plate products are ensured to have excellent strength and toughness matching. The yield strength of the produced Q345R thick plate is stable at ≥345MPa, and the impact energy at 0℃ is ≥41J, which fully meets the strict requirements of standards such as GB / T 713 for steel used in pressure equipment. The product has good performance. At the same time, this method can be directly implemented on existing conventional production lines without the need for additional major equipment modifications. It has strong process adaptability and is easy to promote and apply.

[0018] Finally, by simplifying the types of alloys added and optimizing the amount of elements used, not only is the consumption of alloy resources reduced from the source, but also the energy consumption and potential pollutant emissions caused by adding and smelting multiple alloys are reduced. This technical approach actively responds to the national policy guidance on energy conservation and carbon reduction in the steel industry, and provides a feasible technical solution for producing high-performance, low-cost, and low-environmental-impact steel products. It is in line with the concept of green and low-carbon development and achieves a synergistic improvement in economic value and ecological benefits. Attached Figure Description

[0019] Figure 1 This is a metallographic microstructure image of a 1 / 4 thickness section of the low-cost Q345R thick plate of this invention; Figure 2 This is a metallographic microstructure image of the 1 / 2 thickness of the low-cost Q345R thick plate of this invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0021] Example 1 Low-cost Q345R thick plate, chemical composition by mass percentage: C: 0.14-0.17%, Si: 0.20-0.40%, Mn: 1.50-1.70%, P: ≤0.017%, S: ≤0.005%, Nb: 0.020-0.050%, Al: 0.020-0.050%, N: ≤0.006%, balance is Fe and unavoidable impurities.

[0022] The thickness of low-cost Q345R thick plates is 80-100mm.

[0023] Example 2 Based on the low-cost Q345R thick plate provided in Example 1, this example provides a low-cost Q345R thick plate with low-temperature impact toughness in the thickness direction that satisfies the following: the average Charpy V-notch impact energy measured at 0°C when a sample is taken at 1 / 4 thickness of the low-cost Q345R thick plate is ≥142J. The average Charpy V-notch impact energy measured at 0℃ by sampling at half the thickness of a low-cost Q345R thick plate was ≥90J.

[0024] Example 3 Based on the low-cost Q345R thick plate provided in Example 2, this example provides a low-cost Q345R thick plate with the following mechanical properties in the hot-rolled delivery state: yield strength > 365MPa, tensile strength range of 522-549MPa, elongation > 22%, and Charpy V-notch impact energy measured at 0℃ > 90J.

[0025] Example 4 This embodiment provides a low-cost Q345R thick plate production method for producing any of the low-cost Q345R thick plates in Embodiments 1-3, including the following steps: Step 1: KR hot metal pretreatment and converter smelting. Deoxidation and alloying are carried out during the tapping process, and argon blowing and stirring are performed throughout the tapping process to obtain molten steel. Step 2: The molten steel is fed into the LF furnace for refining, followed by vacuum treatment in the VD furnace. The treated molten steel is then continuously cast to obtain a slab, which is then slowly cooled. Step 3: Heat the slab and use a two-stage rolling process; Step 4: Accelerate the cooling of the rolled steel plate to obtain low-cost Q345R thick plate.

[0026] The controlled rolling process employs a two-stage rolling process, including a roughing stage and a finishing stage. The final pass of both the roughing stage and the finishing stage uses a leveling pass.

[0027] Example 5 Based on the low-cost Q345R thick plate production method provided in Example 4, the specific operation steps of the low-cost Q345R thick plate production method provided in this example are as follows: Step 1: The blast furnace hot metal undergoes KR mechanical stirring desulfurization pretreatment, with the final sulfur content controlled at 0.005%. The desulfurized hot metal is then transferred to a 120-ton nominal capacity converter for smelting, employing a high-carbon-pulling process, with the final carbon content controlled at 0.08%. The tapping temperature is 1650℃. The tapping time is 4.5 minutes. After tapping begins, when the molten steel covers the bottom of the ladle, slag-forming materials are immediately added for pre-slag formation. The specific amounts added are: 350 kg of lime and 150 kg of pre-melted refining slag, all added before half of the steel has been tapped. After pre-slag formation, when approximately one-quarter of the steel has been tapped, aluminum blocks, ferrosilicon, carbon raiser, and ferroniobium are added sequentially, with all alloys added when three-quarters of the steel has been tapped. Throughout the tapping process, the ladle is subjected to strong argon stirring to promote slag-metal reaction, homogenization of composition, and flotation of inclusions.

[0028] Step 2: The molten steel is hoisted to the LF furnace station, with argon blowing throughout. Based on the slag foundation created during tapping, slag-forming and alloying materials are added to precisely adjust the composition and slag system. The specific addition amounts are: 50 kg calcium carbide, 227 kg silicon manganese, 130 kg aluminum granules, 1253 kg lime, 117 kg slag-forming agent, 60 kg silicon carbide, and 182 kg ferrosilicon. The mixture is heated for 22 minutes to fully melt the slag and rapidly form white slag within 10 minutes. The steel temperature is then precisely adjusted to the target value. The LF furnace treatment is complete, and the outlet temperature is 1643℃. The ladle is then transferred to the VD station. The total argon blowing time is 43 minutes. The vacuum pump is started, and the vacuum level is rapidly reduced to ≤60 Pa. This vacuum level is maintained for ≥12 minutes to deeply remove hydrogen and nitrogen from the steel. After vacuum breaking, the hydrogen content of the molten steel was measured to be 1.8 ppm, reaching an ultra-low hydrogen level. The temperature of the molten steel after VD treatment was 1565℃. The refined molten steel was then fed into an arc-shaped continuous casting machine for casting, with the superheat of the molten steel in the tundish controlled at 36℃, and a typical tundish temperature of 1549℃. Large slabs with cross-sectional dimensions of 300mm (thickness) × 2280mm (width) were cast. After the slabs came off the production line, they were immediately placed in a slow cooling pit or covered with an insulation cover for slow cooling for no less than 72 hours to fully eliminate internal stress in the slabs and prevent hydrogen-induced cracking.

[0029] Step 3: Load the slowly cooled slab into a walking beam furnace. Set the slab soaking zone temperature to 1220℃, and the total furnace time (including preheating, heating, and soaking) to 282 minutes to ensure complete austenitization and uniform temperature in the slab core, with an exit surface temperature ≥1185℃. A two-stage rolling process is employed. The first stage (roughing / recrystallization zone rolling): After high-pressure water descaling, the slab is rolled on a roughing mill at an initial temperature of 1015℃. A high-temperature, low-speed, high-reduction process is used, with a rolling speed of 0.9 m / s and a maximum reduction of 30 mm per pass. The average reduction rate of the last three roughing passes reaches 16%, and leveling passes are used to improve the slab shape, resulting in an intermediate slab with a thickness of 150 mm. The second stage (finishing / rolling in the non-recrystallization zone): After the intermediate billet enters the cooling zone and cools to the target temperature, it begins rolling on the finishing mill at an initial rolling temperature of 843℃. The average reduction rate for the last three passes of finishing rolling is 11%, and the final rolling temperature is strictly controlled at 781℃. The rolled steel sheet immediately enters the laminar flow cooling system, with the initial cooling temperature controlled at 806℃ and a suitable cooling rate employed. Phase transformation control during the cooling process is completed when the steel sheet's reddening temperature is controlled to 635±15℃.

[0030] Example 6 Based on the production method of low-cost Q345R thick plate provided in Example 5, this example provides performance testing of the low-cost Q345R thick plate produced by this method. Samples of 80-100mm low-cost Q345R thick plates produced according to the above process were taken, and comprehensive performance tests were conducted according to GB / T713-2023 "Steel Plates and Strips for Pressure Equipment" standard. The test results of the mechanical properties of the low-cost Q345R thick plate are shown in Table 1: Table 1. Performance Test Results of Mechanical Properties of Low-Cost Q345R Thick Plates

[0031] According to the data in Table 1, the mechanical properties of the low-cost Q345R thick plate disclosed in this invention are as follows: lower yield strength of 365-401 MPa, tensile strength of 522-549 MPa, and elongation after fracture of 22.3-29.5%, which fully meet the standard requirements. The transverse impact performance test results of the low-cost Q345R thick plate are shown in Table 2. Table 2 Impact Test Results of Low-Cost Q345R Thick Plates

[0032] According to the data in Table 2, the transverse impact performance of the low-cost Q345R thick plate disclosed in this invention is as follows: Samples taken at 1 / 4 thickness and measured at 0℃ show an average Charpy V-notch impact energy ≥142J; samples taken at 1 / 2 thickness and measured at 0℃ show an average Charpy V-notch impact energy ≥90J, both far exceeding the standard requirement of ≥41J, demonstrating excellent core toughness. The Z-axis performance test results of the low-cost Q345R thick plate are shown in Table 3 below: Table 3. Performance Test Results of Low-Cost Q345R Thick Plate in the Z-Direction

[0033] According to the data in Table 3, the low-cost Q345R thick plate disclosed in this invention exhibits excellent Z-direction performance. The average reduction of area (R&A) of all tested thick plates ranges from 52% to 68%, fully meeting and significantly exceeding the requirement of ≥35% for the Z35 level in GB / T 5313 standard. The highest average R&A value was 68% for the 100mm thick plate and 60% for the 80mm thick plate, indicating outstanding resistance to lamellar tearing in the low-cost Q345R thick plate. The data from each sample showed low dispersion, and the performance of the same plate material was stable and uniform. The experimental results fully demonstrate that the composition and process system of this invention, while significantly reducing costs, effectively ensures the thickness-direction mechanical properties of the low-cost Q345R thick plate, fully meeting the stringent requirements of high-end pressure-bearing equipment for material isotropy and welding safety.

[0034] In addition, metallographic examination was performed on low-cost Q345R thick plates, such as... Figure 1 and Figure 2 As shown, the microstructure at both 1 / 4 and 1 / 2 thickness points is dominated by fine ferrite and pearlite, with consistent microstructure types. No obvious Widmanstätten structure, banded segregation, or abnormally large grains were observed. This indicates that through the compositional design and the "normalizing rolling + controlled cooling" process of this invention, a uniform and refined room-temperature microstructure was successfully obtained across the entire thickness section of the steel plate. Figure 1 As shown, the microstructure at 1 / 4 thickness is finer, with uniform ferrite grain size and well-dispersed pearlite clusters. This is due to the sufficient deformation penetration and relatively fast cooling rate at this location during rolling and cooling, resulting in a significant microstructure refinement effect after phase transformation. Figure 2 As shown, the microstructure at 1 / 2 thickness remains fine, although it is slightly coarser than at 1 / 4 thickness. However, the grain size is still far superior to that of steel plates of the same specification produced by conventional processes. This indicates that the high-temperature, low-speed, high-reduction rough rolling and non-recrystallization zone finishing rolling process of the present invention effectively promotes the flattening and accumulated strain of the austenite in the core, providing a large number of nucleation particles for subsequent phase transformation. Even under the condition of slow cooling in the core, a refined ferrite and pearlite microstructure is still obtained.

[0035] Metallographic analysis shows that this invention, through optimized processes and a low-cost composition system, achieves uniform and refined microstructure across the entire thickness of a Q345R extra-thick plate cross-section. This microscopically confirms the source of its high strength, high toughness, and excellent Z-axis properties, achieving the goals of high performance, low cost, and green manufacturing.

Claims

1. A low-cost Q345R thick plate, characterized in that, The chemical composition in terms of mass percentage is: C: 0.14-0.17%, Si: 0.20-0.40%, Mn: 1.50-1.70%, P: ≤0.017%, S: ≤0.005%, Nb: 0.020-0.050%, Al: 0.020-0.050%, N: ≤0.006%, and the balance is Fe and inevitable impurities.

2. The low-cost Q345R thick plate according to claim 1, characterized in that, The thickness of the low-cost Q345R thick plate is 80-100 mm.

3. The low-cost Q345R thick plate according to claim 1, characterized in that, The low-cost Q345R thick plate has a low-temperature impact toughness in the thickness direction, which satisfies: the average value of Charpy V-notch impact energy measured at 0 DEG C is ≥142 J at the 1 / 4 thickness position of the low-cost Q345R thick plate; The average value of Charpy V-notch impact energy measured at 0 DEG C is ≥90 J at the 1 / 2 thickness position of the low-cost Q345R thick plate.

4. The low-cost Q345R thick plate according to claim 1, characterized in that, The low-cost Q345R thick plate has mechanical properties in the hot-rolled delivery state, which satisfy: yield strength >365 MPa, tensile strength range is 522-549 MPa, elongation >22%, and Charpy V-notch impact energy at 0 DEG C >90 J.

5. A method for producing a low-cost Q345R thick plate for producing a low-cost Q345R thick plate as claimed in any one of claims 1 to 4, characterized in that, The method comprises the following steps: Step 1, KR molten iron pretreatment and converter smelting, deoxidization and alloying are performed when the converter is tapped, and argon blowing and stirring are performed throughout the tapping process to obtain molten steel; Step 2, the molten steel is sent to an LF furnace for refining, then VD furnace vacuum treatment is performed, and the treated molten steel is continuously cast to obtain a slab and the slab is slowly cooled; Step 3, the slab is heated, and a two-stage rolling process is adopted, the first-stage rough rolling open rolling temperature >1010 DEG C, and large reduction deformation is adopted; the second-stage finish rolling open rolling temperature is 820-850 DEG C, and non-recrystallization zone rolling is performed to obtain a rolled steel plate; Step 4, the rolled steel plate is accelerated cooled to obtain a low-cost Q345R thick plate.

6. The method for producing a low-cost Q345R thick plate according to claim 5, characterized by, The control rolling adopts two-stage rolling, including a rough rolling stage and a finish rolling stage, and a flattening pass is adopted at the end of the rough rolling stage and the last pass of the finish rolling stage.

7. The method of producing a low-cost Q345R thick plate according to claim 5, characterized by, The step 1 comprises the following steps: Step 101, the sulfur content after the KR molten iron pretreatment ends is 0-0.010%; Step 102, the end-point carbon content of the converter smelting is 0.06%-0.15%, and the tapping temperature is 1580-1620 DEG C; Step 103, during the converter tapping process, lime and premelted refining slag are added to the ladle after the molten steel covers the bottom of the ladle, the addition amount of the lime is 200-400 kg / furnace, the addition amount of the premelted refining slag is 100-200 kg / furnace, and both are added before the tapping amount reaches 1 / 2, and the tapping time is ≥4 min; Step 104, aluminum blocks, silicon manganese / high-carbon ferromanganese, carbon additive and niobium iron are sequentially added to the ladle to complete deoxidization and alloying; Step 105, during the whole tapping process, argon blowing and stirring are performed throughout the ladle, and after the molten steel is tapped, the molten steel is continuously treated by argon blowing in the argon station for ≥3 min before leaving the station.

8. The method of producing a low-cost Q345R thick plate according to claim 5, wherein The step 2 comprises the following steps: Step 201, argon blowing is performed in the whole refining process of the LF furnace, and lime, low-nitrogen slagging agent or aluminum-based slagging agent is added, white slag is formed within 10 min, then aluminum particles are added at a dosage of 0.30-0.50 kg per ton of molten steel, and the white slag state is maintained for ≥10 min; Step 202, the off-site temperature of the LF furnace is 1625-1635℃; Step 203, the molten steel is transferred into the VD furnace for degassing treatment, the vacuum degree after the degassing treatment is 67 Pa, the vacuum extraction time is ≤8 min, and the molten steel is maintained for ≥12 min, the hydrogen content in the molten steel after the treatment is ≤2 ppm, and the nitrogen content is ≤50 ppm; Step 204, after vacuum degassing, soft argon blowing treatment is performed, the soft blowing time is ≥10 min, and the VD process ladle temperature is 1560-1570℃.

9. The method of producing a low-cost Q345R thick plate according to claim 5, characterized by, The step 3 comprises the following steps: Step 301, the slab is heated to 1180-1240℃, the ratio of heating time to slab thickness is in the range of 9.5-11 min / mm, the soaking time is >60 min, and the slab out-of-furnace temperature is controlled to be ≥1185℃; Step 302, the first stage rolling temperature is ≥1010℃, the high-temperature low-speed large reduction process is adopted in the rough rolling stage, the rolling speed is 0.9-1.2 m / s, the single pass maximum reduction is >27 mm, and the average reduction rate of the last three passes of rough rolling is >15%, and a 150 mm thick intermediate billet is obtained; Step 303, the second stage rolling temperature is 820-850℃, the average reduction rate of the last three passes of finish rolling is >10%, and the finish rolling temperature is 780-820℃.

10. The method of producing a low-cost Q345R thick plate according to claim 5, characterized by, The accelerated cooling process is specifically: the open cooling temperature after rolling is controlled to be 790-820℃, and the re-red temperature at the end of cooling is 600-640℃.

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