370MPa-grade high-straightness extra-thick bridge steel plate and production method thereof

Abstract

The invention relates to a 370MPa-grade high-straightness extra-thick bridge steel plate and a production method thereof. The bridge steel plate comprises the following components in percentage by weight: 0.08 to 0.135 percent of C, 0.10 to 0.50 percent of Si, 1.35 to 1.55 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.002 percent of S, 0.022 to 0.050 percent of Nb, 0.012 to 0.040 percent of V, 0.010 to 0.025 percent of Ti, 0.010 to 0.045 percent of Als and the balance of Fe and other inevitable impurities. The contents of the components meet the following three relational expressions: (1) 2.2%-6C-1.2 (Cr + Mo + V)-0.5 (Ni + Cu) < = Mn < = 2.4%-6C-1.2 (Cr + Mo + V)-0.5 (Ni + Cu); (2) Nb + V + Ti < = 0.085%; (3) CEV < = 0.40%; the production method comprises the steps of converter smelting, LF refining, RH vacuum refining, continuous casting, slab heating, rolling, straightening, cooling, tempering, inspecting, packaging and finishing. The produced high-straightness extra-thick bridge steel plate has high strength, high toughness, high straightness and excellent welding performance, and can meet the efficient welding and manufacturing requirements of steel structures for bridges, buildings and ocean engineering structures.

Description

Technical Field

[0001] The present invention relates to the technical field of manufacturing extra-thick bridge steel plates, and in particular to a 370MPa-grade high-flatness extra-thick bridge steel plate and a production method thereof, in particular to an extra-thick steel plate with a rolling compression ratio of less than 3. Background Art

[0002] With the accelerated construction of national railway networks such as the Yangtze River High-Speed ​​Railway and the Sichuan-Tibet Railway, there is still a lot of room for infrastructure construction. Large-span steel structure bridges are still important channels across rivers. Structural steel, as an important structural part, requires thick and ultra-thick plates as stress-bearing parts. This requires ultra-thick plates to not only have high strength, high toughness, and resistance to lamellar tearing, but also to ensure excellent uniformity of organizational properties in the thickness direction to ensure the safety of the steel structure.

[0003] At present, the two main methods used in the domestic production of ultra-thick plates are "die casting + normalizing heat treatment" or "continuous casting composite rolling + normalizing heat treatment". Among them, the patent application number "CN200910012823.5" discloses a method for manufacturing ultra-thick anti-laminated tearing steel plates, which is characterized in that a forging process is set between the ingot casting process and the rolling process, the steel ingot is forged into a steel plate blank and subjected to post-forging heat treatment, and the macro defects on the surface of the blank are treated. The initial forging temperature of the forging process is 1225-1250℃, the final forging temperature is 850-900℃, and the compression ratio is not less than 3. This manufacturing method can produce anti-laminated tearing steel plates with a thickness of 130-400mm. Its shortcomings are: the production method adopts die casting and forging, its production efficiency is low, the yield rate is low, and it emphasizes that the compression ratio is not less than 3, which brings great difficulties to domestic medium and thick plate enterprises that only have slab continuous casting machines for the production of ultra-thick plates with a thickness of more than 120mm.

[0004] Patent application number "CN201510996876.0" discloses a high-strength ultra-thick steel plate, whose chemical composition is C: 0.10-0.16%, Si: 0.35%-0.45%, Mn: 1.35%-1.55%, Ni: 0.15-0.50%, Cr: 0.001%-0.25%, P: ≤0.008%, S: ≤0.005%, Al: 0.015%-0.04%, V: 0.06%-0.08%, N: 0.0090%-0.015%, and the balance is Fe; the thickness of the steel plate is 200-400mm, and the normalizing process is air cooling or water cooling after heating at 890-930℃. The 1 / 4 position and the core of the cross section of the steel plate are fine ferrite structure and a small amount of pearlite structure, and the grain size is greater than ASTM grade 8. The disadvantage is that the welding performance of the steel plate is seriously damaged by adding more elements such as C, Mn, V, etc., and normalizing heat treatment is used with high temperature and long time to ensure the straightness of the steel plate. Therefore, the problem of poor plate shape caused by the rolling process is not solved, resulting in high production costs.

[0005] Patent application number "CN201710296107.9" discloses a low-alloy high-strength ultra-thick steel plate S420NL and its production method. The chemical composition and mass percentage of the steel plate are: C: 0.15-0.20%, Si≤0.60%, Mn: 1.00%-1.60%, P≤0.020%, S≤0.010%, Ni: 0.20-0.40%, Nb≤0.040%, V: 0.040-0.050%, Al: 0.020-0.050%, and the rest is Fe and other inevitable impurities. The production method includes steelmaking, rolling, and heat treatment processes. The invention has a reasonable chemical composition design, adopts vacuum carbon deoxidation, and a reasonable heat treatment process, so that the steel plate has good comprehensive performance, meets the high requirements of users for ultra-thick plates, and has broad application prospects. The strength and toughness match well, the yield strength is ≥350MPa, the tensile strength is 540~700MPa, and the longitudinal impact energy at 50℃ is ≥35J. Its disadvantage is that the high content of elements such as C, Mn, and V in the steel seriously damages the welding performance of the steel.

[0006] Patent application number "CN201610955881.1" discloses a thick and ultra-wide Q345E-Z35 steel plate and its production method, wherein the steel plate is composed of the following weight percentage components: 0.15%≤C≤0.17%, 0.10%≤Si≤0.50%, 1.00%≤Mn≤1.25%, P≤0.015%, S≤0.004%, 0.020%≤Al≤0.050%, 0.020%≤Nb≤0.050%, 0.030%≤V≤0.050%, 0.15%≤Cr≤0.25%, and the balance is Fe and unavoidable impurities. The steel plate is produced by smelting, die casting, forging cutting, heating, rolling, hot stacking, normalizing and tempering processes, with a maximum thickness of 350mm, meeting the Class I requirements of GB / T2970; the steel plate has good strength and toughness. The disadvantages are that the production method adopts die casting and forging, which has low production efficiency and low yield rate, and adopts normalizing heat treatment, which has high temperature and long time, resulting in high production cost.

[0007] As can be seen from the above, some of the ultra-thick steel plates produced by the existing technology to ensure excellent low-temperature toughness in the thickness direction have complex production processes, low production efficiency, and low yield, resulting in excessively high production costs. Some have unreasonable component design, resulting in poor welding performance of the steel plates and excessively high production costs. In addition, when rolling medium and thick plates such as TMCP, existing medium and thick plate companies generally have the problem of S-shaped bending at the head and tail, which requires a flattening machine to straighten, which is difficult to correct and has low flattening efficiency. Therefore, a 370MPa-grade high-straightness ultra-thick bridge steel plate is developed to solve the existing S-shaped bending of the head and tail of the rolled ultra-thick steel plate, improve the quality of the ultra-thick plate, facilitate the welding of bridge steel structures, and improve production efficiency. Summary of the invention

[0008] The purpose of the present invention is to provide a 370MPa grade high-straightness extra-thick bridge steel plate and its production method, so as to solve the problems that the extra-thick steel plate with a rolling compression ratio of less than 3 in the prior art has a relatively coarse internal structure, unstable low-temperature work, and S-shaped bending at the head and tail of the steel plate, resulting in poor plate shape and other problems that are difficult to meet user requirements. The steel plate produced by the present invention has a yield strength of ≥370MPa at room temperature, a tensile strength of ≥520MPa, an elongation of ≥22%, a transverse and longitudinal impact energy of the steel plate at -40°C of ≥200J, a ferrite grain size of ≥8.0, and a steel plate straightness of less than 3mm / m. It has high strength, high toughness, high straightness, and excellent welding performance, and can meet the requirements for efficient welding and manufacturing of steel structures for bridges, buildings, and marine engineering structures.

[0009] The present invention discloses a 370MPa grade high flatness extra-thick bridge steel plate, comprising the following components in percentage by weight: C: 0.08-0.135%, Si: 0.10-0.50%, Mn: 1.35-1.55%, P: ≤0.012%, S≤0.002%, Nb: 0.022-0.050%, V: 0.012-0.040%, Ti: 0.010-0.025%, Als: 0.010-0.045%, and the balance is Fe and other inevitable impurities; and the contents of the above components satisfy the following three relationships: (1) 2.2% - 6C -1.2(Cr+Mo+V)-0.5(Ni+Cu) ≤Mn≤2.4% - 6C - 1.2(Cr+Mo+V)- 0.5(Ni+Cu); (2) Nb + V + Ti≤0.06%; (3) CEV=C + Mn / 6 +(Cr+Mo+V) / 5 + (Ni+Cu) / 15 ≤0.40%.

[0010] Preferably, a 370MPa grade high flatness extra-thick bridge steel plate of the present invention comprises the following components in percentage by weight: C: 0.092-0.13%, Si: 0.15-0.38%, Mn: 1.35-1.42%, P: ≤0.012%, S≤0.002%, Nb: 0.025-0.044%, V: 0.016-0.035%, Ti: 0.013-0.017%, Als: 0.027-0.042%, the remainder being Fe and other unavoidable impurities; and the contents of the above components satisfy the following three relationships: (1) 2.2% - 6C -1.2(Cr+Mo+V)-0.5(Ni+Cu) ≤Mn≤2.4% - 6C - 1.2(Cr+Mo+V)- 0.5(Ni+Cu); (2) Nb + V + Ti≤0.06%; (3) CEV= C + Mn / 6 + (Cr+Mo+V) / 5 + (Ni+Cu) / 15 ≤0.40%.

[0011] The finished product thickness of the extra-thick bridge steel plate prepared by the present invention is 120-140 mm, the yield strength of the steel plate at room temperature is ≥370 MPa, the tensile strength is ≥520 MPa, the elongation is ≥22%, the transverse and longitudinal impact energy of the steel plate at -40°C is ≥200 J, the ferrite grain size is ≥8.0, and the straightness of the steel plate is less than 3 mm / m.

[0012] The present invention provides a production method for a 370MPa grade high-straightness extra-thick bridge steel plate, comprising: converter smelting → LF refining → RH vacuum refining → continuous casting → slab heating → rolling → straightening → cooling → tempering → inspection, packaging and finishing; wherein: (1) RH vacuum refining: After RH vacuum refining, ensure that H ≤ 2.0 ppm and N ≤ 40 ppm in molten steel; (2) Continuous casting: The slab continuous casting machine is used to cast a 360 mm thick slab, which is then stacked and slowly cooled to below 200°C. (3) Slab heating: The slab is loaded into the heating furnace for heating, and the temperature of the soaking section is controlled at 1200-1230°C, the soaking time is 35-50 minutes, and the furnace exit temperature is 1160-1190°C; (4) Rolling: A two-stage controlled rolling process of rough rolling and finishing rolling is adopted. Rough rolling is carried out immediately after the slab is descaled after leaving the heating furnace. During the rough rolling stage, the longitudinal rolling pass reduction rate is ensured to be 8-12%, the pass interval time is greater than 10s, the final rolling temperature is greater than 1050℃, and the rough rolling stop thickness is 1.4-1.6 times the thickness of the finished steel plate; the start rolling temperature of finishing rolling is ≤830℃, there is no pause during the finishing rolling stage, and the bite speed of the last two rolling passes is controlled to be lower than 0.8m / s to reduce the problem of inconsistent extension of the upper and lower surfaces of the steel plate during bite. The acceleration time is delayed after bite to avoid the different speeds of the upper and lower rolls aggravating the bending of the head and tail. The last pass of finishing rolling adopts flatness control, and the roll gap compensation is increased within 1m of the head and tail to reduce the problem of excessive thickness of the head and tail of the steel plate due to low temperature and large deformation resistance, resulting in insufficient rolling force or poor plate shape caused by inconsistent extension of the upper and lower surfaces. The final rolling temperature of finishing rolling is 770-800℃; (5) Straightening: After rolling, the pre-straightening machine is used for straightening. The pre-straightening adopts a three-pass straightening process, and the straightening force adopts the principle of increasing the pass; (6) Cooling: The straightened steel plate enters ACC cooling, the initial cooling temperature is 730-760℃, the cooling rate is 5-8℃ / s, the steel plate returns to red temperature at 450-500℃ after cooling, and then is quickly stacked off the line and slowly cooled to room temperature after hot straightening and leveling; (7) Tempering: Tempering at 500℃, tempering time 250~500℃, and air cooling to room temperature after leaving the furnace.

[0013] In the above scheme, preferably, the pre-straightening in step (5) adopts a three-pass straightening process, the straightening force of the first pass is 7-8MN, the second pass is 8-10MN, and the third pass is 10-13MN, and when straightening the same steel plate, the straightening force increases with the pass.

[0014] In the technical solution provided by the present invention, by controlling the composition and optimizing the rolling process, the steel plate grains are refined, the uniformity of the structure is improved, and by optimizing the finishing pass speed and the flattening pass, and gradually increasing the pre-straightening and other methods, a production method for obtaining a super-thick 120-140mm steel plate with high strength and excellent low-temperature impact toughness greater than 200J when the rolling compression ratio is less than 3 is achieved, and the straightness of the steel plate is less than or equal to 3mm / m.

[0015] The chemical composition of the steel plate of the present invention is reasonably designed, which is specifically manifested in: (1) by controlling the Mn content, a relationship between Mn and elements such as C is established, that is, 2.2% - 6C -1.2(Cr+Mo+V)-0.5(Ni+Cu) ≤Mn≤2.4% - 6C - 1.2(Cr+Mo+V)- 0.5(Ni+Cu), on the basis of maintaining a certain strengthening element, the content of the easily segregated elements is reduced to reduce the segregation degree of the ingot, and at the same time, the P content is controlled to reduce its damage to the low-temperature toughness of the steel, and the S content is reduced to reduce the formation of long strip inclusions MnS with Mn after central segregation, thereby improving the uniformity inside the ingot; (2) in order to refine the grains, when adding Nb, V, and Ti elements, the total amount of the above three elements is controlled to be no more than 0.06%; (3) in order to achieve excellent welding performance of the steel plate, the CEV of the steel is required to be C + Mn / 6 + (Cr+Mo+V) / 5 + (Ni+Cu) / 15 ≤0.40%, through the setting of the easy welding strengthening index, the hardenability of the ultra-thick steel plate is improved while ensuring that the steel plate has excellent welding performance and low-temperature impact toughness, while reducing the thickness effect of the steel plate.

[0016] The production method of the steel plate of the present invention achieves the target performance through process optimization, which is specifically manifested in: (1) In the steelmaking stage, the H and N contents in the RH vacuum refining stage are controlled to improve the surface quality of the continuous casting slab and reduce the internal cracks of the slab, thereby providing high-quality materials for the rolling of extra-thick steel plates.

[0017] (2) During the continuous casting stage, the stack of slabs continuously cast into ingots is slowly cooled to below 200°C to reduce the thermal stress of the ingots and allow the hydrogen in the ingots to be fully diffused, thereby improving the uniformity of the ingots.

[0018] (3) In the heating stage, the temperature of the soaking section is controlled at 1200-1230°C and the soaking time is 35-50 min. This can not only ensure that the temperature difference between the upper and lower sections of the slab is less than 15°C but also prevent the austenite grains from being abnormally coarse. The furnace temperature is 1160-1190°C to reduce the rolling load and achieve a large reduction in the rough rolling stage.

[0019] (4) In the rough rolling process, firstly, the longitudinal rolling pass reduction rate is ensured to be greater than 8% and the pass interval time is greater than 10s in the rough rolling stage, so that the austenite grains can recover and fully recrystallize in each rolling gap, and the austenite grains can be refined. Secondly, the longitudinal rolling pass reduction rate is ensured to be less than 12% in the rough rolling stage, so that the number of final rough rolling passes is increased, the number of repeated recovery and recrystallization of austenite grains is increased, and the austenite grains can be further refined. Thirdly, the final rolling temperature is controlled to be greater than 1050℃, so as to ensure that the rough rolling stage is rolled in the austenite recrystallization zone, prevent the austenite grain size from being uneven, and improve the uniformity of the structure. Fourthly, the rough rolling stop thickness is 1.4 to 1.6 times the thickness of the finished product, so as to reserve sufficient cumulative reduction for the finishing rolling stage.

[0020] (5) In the finishing rolling stage, on the one hand, the starting rolling temperature is ≤830℃, and there is no pause in the finishing rolling stage. The final rolling temperature of the finishing rolling is controlled to be 770-800℃, so that the final rolling temperature is close to the Ar3 temperature line. The deformation elongation of austenite without recrystallization is used to form a dislocation substructure, which is beneficial to the grain refinement after phase transformation. At the same time, the deformation is used to induce the ferrite phase transformation, promote the nucleation of ferrite grains, and is beneficial to the refinement of the core structure. On the other hand, the bite speed of the last two rolling passes is controlled to be lower than 0.8m / s, and the acceleration time is delayed after biting. The last pass of the finishing rolling adopts flatness control, and the roll gap compensation is increased within 1m from the head to the tail to reduce the S-shaped bending of the head and tail of the ultra-thick steel plate and improve the flatness of the rolled plate.

[0021] (6) Pre-straightening process after rolling: pre-straightening adopts three-pass straightening process, and the straightening force adopts the principle of increasing pass by pass to further improve the straightness of the steel plate, so that the steel plate reaches the standard range of straightness below 3mm / mm before entering ACC cooling.

[0022] (7) Enter ACC cooling, the initial cooling temperature is 730-760℃, the cooling rate is 5-8℃ / s, and the steel plate returns to red temperature after cooling to 450-500℃, to ensure that the steel plate obtains a relatively fine ferrite + bainite structure, and on the basis of ensuring low-temperature toughness, improve the strength of the steel and reduce the yield strength ratio. After hot straightening and leveling, it is quickly stacked off the line and slowly cooled to room temperature to release the thermal stress of the steel plate and reduce the deformation of the steel plate.

[0023] (8) The steel plate is subjected to tempering heat treatment to further eliminate the stress of the steel plate, so that the internal structure of the steel plate can be further uniformly solidified, and the problem of local stress defects in the steel plate affecting user use can be avoided.

[0024] The extra-thick bridge steel plate prepared by the method of the present invention has a finished steel plate thickness of 120-140 mm, a yield strength of ≥370 MPa, a tensile strength of ≥520 MPa, an elongation of ≥22%, a transverse and longitudinal impact energy of the steel plate at -40°C of ≥200 J, a ferrite grain size of ≥8.0, a steel plate straightness of less than 3 mm / m, high strength, high toughness, and excellent welding performance, and can meet the requirements for efficient welding and manufacturing of steel structures for bridges, buildings, and marine engineering structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The metallographic structure diagram of the steel plate obtained in Example 1 of the present invention is magnified 100 times; Figure 2 This is a metallographic structure diagram of the steel plate obtained in Example 1 of the present invention, magnified 500 times. DETAILED DESCRIPTION

[0026] In order to better explain the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with specific embodiments. The following embodiments are merely illustrative of the technical solution of the present invention and do not limit the present invention in any form.

[0027] Table 1 below is a list of chemical composition values ​​of various embodiments of the present invention; Table 2 below is a list of main mechanical properties test results of various embodiments of the present invention.

[0028] Table 1 List of chemical composition values ​​of various embodiments of the present invention (wt, %)

[0029] Example 1 The chemical composition and weight percentage of a 370MPa grade high flatness extra-thick bridge steel plate of this embodiment are shown in Table 1.

[0030] The production method of a 370MPa grade high-flatness extra-thick bridge steel plate of this embodiment comprises: converter smelting → LF refining → RH vacuum refining → continuous casting → slab heating → rolling → straightening → cooling → tempering → inspection, packaging and finishing; wherein: (1) RH vacuum refining: After RH vacuum refining, the H content in the molten steel is ensured to be 1.5ppm and the N content is 35ppm; (2) Continuous casting: The slab continuous casting machine is used to cast slabs with a continuous casting size of 360 mm × 2000 mm × 2700 mm. The slabs are stacked and slowly cooled to 150°C. (3) Slab heating: The slab is loaded into the heating furnace for heating, and the temperature of the soaking section is controlled at 1210-1220°C, the soaking time is 40 minutes, and the furnace outlet temperature is 1179°C; (4) Rolling: A two-stage controlled rolling process of rough rolling and finishing rolling is adopted. Rough rolling is carried out immediately after the slab is descaled after leaving the heating furnace. During the rough rolling stage, the longitudinal rolling pass reduction rate is ensured to be 8-12%, the pass interval time is greater than 10-15s, the final rolling temperature is 1136℃, and the rough rolling stop thickness is 180mm; the start rolling temperature of finishing rolling is 812℃, and there is no pause in the finishing rolling stage. The bite speeds of the last two passes of rolling are controlled to be 0.72 m / s and 0.76 m / s respectively. The acceleration time is delayed after biting. The last pass of finishing rolling adopts leveling control, the pass reduction is 3.3mm, and the roll gap compensation is increased by 0.2mm within the range of 1m from the head to the tail. The final rolling temperature of finishing rolling is 779℃; (5) Straightening: After rolling, the pre-straightening machine is used for straightening. The pre-straightening adopts a three-pass straightening process. The straightening force adopts the principle of increasing the pass. The straightening forces are 7.88MN, 9.74MN, and 11.2MN respectively. (6) Cooling: The straightened steel plate enters ACC cooling, with the initial cooling temperature of 736°C and the cooling rate of 6.7°C / s. The steel plate returns to a red temperature of 483°C after cooling. After hot straightening and leveling, it is quickly stacked off the line and slowly cooled to room temperature. (7) Tempering: The tempering temperature is 500℃, the tempering time is 250min, and the steel is air-cooled to room temperature after being taken out of the furnace.

[0031] The steel plate manufactured using the chemical composition content and production process steps of this embodiment has a finished steel plate thickness of 124 mm and a steel plate unevenness of 1.0 mm / 1 m. The mechanical property test results of the finished steel plate are shown in Table 2.

[0032] Example 2 The chemical composition and weight percentage of a 370MPa grade high flatness extra-thick bridge steel plate of this embodiment are shown in Table 1.

[0033] The production method of a 370MPa grade high-flatness extra-thick bridge steel plate of this embodiment comprises: converter smelting → LF refining → RH vacuum refining → continuous casting → slab heating → rolling → straightening → cooling → tempering → inspection, packaging and finishing; wherein: (1) RH vacuum refining: After RH vacuum refining, the H content in the molten steel is guaranteed to be 1.2ppm and the N content is 30ppm; (2) Continuous casting: The slab continuous casting machine is used to cast slabs with a continuous casting size of 360 mm × 2200 mm × 3000 mm. The slabs are stacked and slowly cooled to 180°C. (3) Slab heating: The slab is loaded into the heating furnace for heating, and the temperature of the soaking section is controlled at 1218-1227°C, the soaking time is 44 minutes, and the furnace outlet temperature is 1184°C; (4) Rolling: A two-stage controlled rolling process of rough rolling and finishing rolling is adopted. Rough rolling is carried out immediately after the slab is descaled after leaving the heating furnace. During the rough rolling stage, the longitudinal rolling pass reduction rate is ensured to be 8-12%, the pass interval time is greater than 12-15s, the final rolling temperature is 1145℃, and the rough rolling stop thickness is 175mm; the start rolling temperature of finishing rolling is 806℃, and there is no pause in the finishing rolling stage. The bite speeds of the last two passes of rolling are controlled to be 0.82 m / s and 0.78 m / s respectively. The acceleration time is delayed after biting. The last pass of finishing rolling adopts flatness control, the pass reduction is 3.6 mm, and the roll gap compensation is increased by 0.24 mm within the range of 1m from the head to the tail. The final rolling temperature of finishing rolling is 784℃; (5) Straightening: After rolling, the pre-straightening machine is used for straightening. The pre-straightening adopts a three-pass straightening process. The straightening force adopts the principle of increasing the pass. The straightening forces are 7.33MN, 8.99MN, and 10.83MN respectively. (6) Cooling: The straightened steel plate enters ACC cooling, with the initial cooling temperature of 733°C and the cooling rate of 7.2°C / s. The steel plate returns to a red temperature of 457°C after cooling. After hot straightening and leveling, it is quickly stacked off the line and slowly cooled to room temperature. (7) Tempering: The tempering temperature is 500℃, the tempering time is 260min, and the steel is air-cooled to room temperature after being taken out of the furnace.

[0034] The steel plate manufactured using the chemical composition content and production process steps of this embodiment has a finished steel plate thickness of 124 mm and a steel plate unevenness of 1.5 mm / 1 m. The mechanical properties test results of the finished steel plate are shown in Table 2.

[0035] Example 3 The chemical composition and weight percentage of a 370MPa grade high flatness extra-thick bridge steel plate of this embodiment are shown in Table 1.

[0036] The production method of a 370MPa grade high-flatness extra-thick bridge steel plate of this embodiment comprises: converter smelting → LF refining → RH vacuum refining → continuous casting → slab heating → rolling → straightening → cooling → tempering → inspection, packaging and finishing; wherein: (1) RH vacuum refining: After RH vacuum refining, the H content in the molten steel is guaranteed to be 1.8ppm and the N content is 38ppm; (2) Continuous casting: The slab continuous casting machine is used to cast a slab with a continuous casting size of 360 mm × 2200 mm × 3300 mm. The slabs are stacked and slowly cooled to 130°C. (3) Slab heating: The slab is loaded into the heating furnace for heating, and the temperature of the soaking section is controlled at 1202-1214°C, the soaking time is 48 minutes, and the furnace outlet temperature is 1167°C; (4) Rolling: A two-stage controlled rolling process of rough rolling and finishing rolling is adopted. Rough rolling is carried out immediately after the slab is descaled after leaving the heating furnace. During the rough rolling stage, the longitudinal rolling pass reduction rate is ensured to be 8-11%, the pass interval time is greater than 11-14s, the final rolling temperature is 1143℃, and the rough rolling stop thickness is 190mm; the start rolling temperature of finishing rolling is 806℃, and there is no pause in the finishing rolling stage. The bite speeds of the last two passes of rolling are controlled to be 0.77 m / s and 0.65 m / s respectively. The acceleration time is delayed after biting. The last pass of finishing rolling adopts flatness control, the pass reduction is 2.7mm, and the roll gap compensation is increased by 0.22mm within the range of 1m from the head to the tail. The final rolling temperature of finishing rolling is 795℃; (5) Straightening: After rolling, the pre-straightening machine is used for straightening. The pre-straightening adopts a three-pass straightening process. The straightening force adopts the principle of increasing the pass. The straightening forces are 7.78MN, 8.43MN, and 11.65MN respectively. (6) Cooling: The straightened steel plate enters ACC cooling, with the initial cooling temperature of 751°C and the cooling rate of 6.6°C / s. The steel plate returns to a red temperature of 492°C after cooling. After hot straightening and leveling, it is quickly stacked off the line and slowly cooled to room temperature. (7) Tempering: The tempering temperature is 500℃, the tempering time is 270min, and the steel is air-cooled to room temperature after being taken out of the furnace.

[0037] The steel plate manufactured using the chemical composition content and production process steps of this embodiment has a finished steel plate thickness of 124 mm and a steel plate unevenness of 1.5 mm / 1 m. The mechanical properties test results of the finished steel plate are shown in Table 2.

[0038] Example 4 The chemical composition and weight percentage of a 370MPa grade high flatness extra-thick bridge steel plate of this embodiment are shown in Table 1.

[0039] The production method of a 370MPa grade high-flatness extra-thick bridge steel plate of this embodiment comprises: converter smelting → LF refining → RH vacuum refining → continuous casting → slab heating → rolling → straightening → cooling → tempering → inspection, packaging and finishing; wherein: (1) RH vacuum refining: After RH vacuum refining, the H content in the molten steel is guaranteed to be 1.3ppm and the N content is 34ppm; (2) Continuous casting: The slab continuous casting machine is used to cast a slab with a continuous casting size of 360 mm × 2200 mm × 3300 mm. The slab is stacked and slowly cooled to 80°C. (3) Slab heating: The slab is loaded into the heating furnace for heating, and the temperature of the soaking section is controlled at 1215-1225°C, the soaking time is 50 minutes, and the furnace outlet temperature is 1182°C; (4) Rolling: A two-stage controlled rolling process of rough rolling and finishing rolling is adopted. Rough rolling is carried out immediately after the slab is descaled after leaving the heating furnace. During the rough rolling stage, the longitudinal rolling pass reduction rate is ensured to be 8-11%, the pass interval time is greater than 11-14s, the final rolling temperature is 1156℃, and the rough rolling stop thickness is 195mm; the start rolling temperature of finishing rolling is 812℃, and there is no pause in the finishing rolling stage. The bite speeds of the last two passes of rolling are controlled to be 0.75 m / s and 0.64 m / s respectively. The acceleration time is delayed after biting. The last pass of finishing rolling adopts flatness control, the pass reduction is 2.5mm, and the roll gap compensation is increased by 0.20mm within the range of 1m from the head to the tail. The final rolling temperature of finishing rolling is 803℃; (5) Straightening: After rolling, the pre-straightening machine is used for straightening. The pre-straightening adopts a three-pass straightening process. The straightening force adopts the principle of increasing the pass. The straightening forces are 7.98MN, 9.78MN, and 12.44MN respectively. (6) Cooling: The straightened steel plate enters ACC cooling, with the initial cooling temperature of 754°C and the cooling rate of 6.3°C / s. The steel plate returns to a red temperature of 488°C after cooling. After hot straightening and leveling, it is quickly stacked off the line and slowly cooled to room temperature. (7) Tempering: The tempering temperature is 500℃, the tempering time is 285min, and the steel is air-cooled to room temperature after being taken out of the furnace.

[0040] The steel plate manufactured using the chemical composition content and production process steps of this embodiment has a finished steel plate thickness of 135 mm and a steel plate inequality of 2.2 mm / 1 m. The mechanical properties test results of the finished steel plate are shown in Table 2.

[0041] Example 5 The chemical composition and weight percentage of a 370MPa grade high flatness extra-thick bridge steel plate of this embodiment are shown in Table 1.

[0042] The production method of a 370MPa grade high-flatness extra-thick bridge steel plate of this embodiment comprises: converter smelting → LF refining → RH vacuum refining → continuous casting → slab heating → rolling → straightening → cooling → tempering → inspection, packaging and finishing; wherein: (1) RH vacuum refining: After RH vacuum refining, the H content in the molten steel is guaranteed to be 1.4ppm and the N content is 44ppm; (2) Continuous casting: The slab continuous casting machine is used to cast a slab with a continuous casting size of 360 mm × 2000 mm × 3600 mm. The slabs are stacked and slowly cooled to 100 °C. (3) Slab heating: The slab is loaded into the heating furnace for heating, and the temperature of the soaking section is controlled at 1232-1244°C, the soaking time is 49 minutes, and the furnace outlet temperature is 1177°C; (4) Rolling: A two-stage controlled rolling process of rough rolling and finishing rolling is adopted. Rough rolling is carried out immediately after the slab is descaled after leaving the heating furnace. During the rough rolling stage, the longitudinal rolling pass reduction rate is ensured to be 8-11%, the pass interval time is greater than 11-13s, the final rolling temperature is 1157℃, and the rough rolling stop thickness is 200mm; the start rolling temperature of finishing rolling is 786℃, and there is no pause in the finishing rolling stage. The bite speeds of the last two passes of rolling are controlled to be 0.78 m / s and 0.70 m / s respectively. The acceleration time is delayed after biting. The last pass of finishing rolling adopts leveling control, the pass reduction is 2.2mm, and the roll gap compensation is increased by 0.20mm within the range of 1m from the head to the tail. The final rolling temperature of finishing rolling is 775℃; (5) Straightening: After rolling, the pre-straightening machine is used for straightening. The pre-straightening adopts a three-pass straightening process. The straightening force adopts the principle of increasing the pass. The straightening forces are 8.0MN, 9.88MN, and 12.56MN respectively. (6) Cooling: The straightened steel plate enters ACC cooling, with the initial cooling temperature at 760°C and the cooling rate at 6°C / s. The steel plate returns to a red temperature of 477°C after cooling. After hot straightening and leveling, it is quickly stacked off the line and slowly cooled to room temperature. (7) Tempering: The tempering temperature is 500℃, the tempering time is 300min, and the steel is air-cooled to room temperature after being taken out of the furnace.

[0043] The steel plate manufactured using the chemical composition content and production process steps of this embodiment has a finished steel plate thickness of 140 mm and a steel plate inequality of 2.5 mm / 1 m. The mechanical properties test results of the finished steel plate are shown in Table 2.

[0044] Table 2 List of main mechanical properties test results of various embodiments of the present invention

[0045] It can be seen from Table 2 above that the extra-thick bridge steel plate prepared by the method of the present invention has a yield strength of ≥370MPa, a tensile strength of ≥520MPa, an elongation of ≥22%, a transverse and longitudinal impact energy of the steel plate at -40°C of ≥200J, a ferrite grain size of ≥8.0, a steel plate straightness of less than 3mm / m, high strength, high toughness, and excellent welding performance, and can meet the requirements for efficient welding and manufacturing of steel structures for bridges, buildings, and marine engineering structures.

[0046] Figure 1 and Figure 2 This is the metallographic structure diagram of the steel plate obtained in Example 1 of the present invention. It can be seen from the figure that the structure is ferrite + pearlite + a small amount of bainite, the grain size is relatively uniform, and the ferrite grain size is 9.0.

[0047] The above embodiments are only specific examples given by the present invention to explain the present invention, and do not limit the present invention in any form. Any non-substantial changes made by anyone based on the above contents and forms that do not deviate from the protection scope of the claims of the present invention shall be deemed to fall within the protection scope of the claims of the present invention. The present invention is not limited to the above specific implementation examples.

Claims

1. A 370MPa grade high flatness extra thick bridge steel plate, characterized in that The invention comprises the following components in percentage by weight: C: 0.08-0.135%, Si: 0.10-0.50%, Mn: 1.35-1.55%, P: ≤0.012%, S≤0.002%, Nb: 0.022-0.050%, V: 0.012-0.040%, Ti: 0.010-0.025%, Als: 0.010-0.045%, and the balance is Fe and other inevitable impurities; and the contents of the above components satisfy the following three relationships: (1) 2.2% - 6C -1.2(Cr+Mo+V)-0.5(Ni+Cu) ≤Mn≤2.4% - 6C - 1.2(Cr+Mo+V)- 0.5(Ni+Cu); (2) Nb + V + Ti≤0.085%; (3) CEV= C + Mn / 6 + (Cr+Mo+V) / 5 + (Ni+Cu) / 15 ≤0.40%.

2. The 370MPa grade high flatness extra thick bridge steel plate according to claim 1, characterized in that The invention comprises the following components in percentage by weight: C: 0.092-0.13%, Si: 0.15-0.38%, Mn: 1.35-1.42%, P: ≤0.012%, S≤0.002%, Nb: 0.025-0.044%, V: 0.016-0.035%, Ti: 0.013-0.017%, Als: 0.027-0.042%, and the balance is Fe and other unavoidable impurities; and the contents of the above components satisfy the following three relationships: (1) 2.2% - 6C -1.2(Cr+Mo+V)-0.5(Ni+Cu) ≤Mn≤2.4% - 6C - 1.2(Cr+Mo+V)- 0.5(Ni+Cu); (2) Nb + V+ Ti≤0.085%; (3) CEV= C + Mn / 6 + (Cr+Mo+V) / 5 + (Ni+Cu) / 15 ≤0.40%.

3. A 370MPa grade high flatness extra thick bridge steel plate according to claim 1 or 2, characterized in that: The finished product thickness of the extra-thick bridge steel plate is 120-140mm, the yield strength of the steel plate at room temperature is ≥370MPa, the tensile strength is ≥520MPa, the elongation is ≥22%, the transverse and longitudinal impact energy of the steel plate at -40℃ is ≥200J, the ferrite grain size is ≥8.0, and the straightness of the steel plate is less than 3mm / m.

4. A method for producing a 370MPa grade high flatness extra-thick bridge steel plate as claimed in claim 1 or 2, comprising: Converter smelting → LF refining → RH vacuum refining → continuous casting → slab heating → rolling → straightening → cooling → tempering → inspection, packaging and finishing; its characteristics are: (1) RH vacuum refining: After RH vacuum refining, ensure that H ≤ 2.0 ppm and N ≤ 40 ppm in molten steel; (2) Continuous casting: The slab continuous casting machine is used to cast a 360 mm thick slab, which is then stacked and slowly cooled to below 200°C. (3) Slab heating: The slab is loaded into the heating furnace for heating, and the temperature of the soaking section is controlled at 1200-1230°C, the soaking time is 35-50 minutes, and the furnace exit temperature is 1160-1190°C; (4) Rolling: A two-stage controlled rolling process of rough rolling and finishing rolling is adopted. Rough rolling is carried out immediately after the slab is descaled after leaving the heating furnace. During the rough rolling stage, the longitudinal rolling pass reduction rate is ensured to be 8-12%, the pass interval time is greater than 10s, the final rolling temperature is greater than 1050℃, and the rough rolling stop thickness is 1.4-1.6 times the thickness of the finished steel plate; the start rolling temperature of finishing rolling is ≤830℃, there is no pause in the finishing rolling stage, the bite speed of the last two rolling passes is controlled to be less than 0.8m / s, the last pass of finishing rolling adopts flatness control, and the roll gap compensation is increased within 1m from the head to the tail. The final rolling temperature of finishing rolling is 770-800℃; (5) Straightening: After rolling, the pre-straightening machine is used for straightening. The pre-straightening adopts a three-pass straightening process, and the straightening force adopts the principle of increasing the pass; (6) Cooling: The straightened steel plate enters ACC cooling, the initial cooling temperature is 730-760℃, the cooling rate is 5-8℃ / s, the steel plate returns to red temperature at 450-500℃ after cooling, and then is quickly stacked off the line and slowly cooled to room temperature after hot straightening and leveling; (7) Tempering: Tempering at 500℃, tempering time 250~500℃, and air cooling to room temperature after leaving the furnace.

5. The method for producing a 370MPa grade high flatness extra thick bridge steel plate as claimed in claim 4, characterized in that: The pre-straightening in step (5) adopts a three-pass straightening process, wherein the straightening force of the first pass is 7-8 MN, the second pass is 8-10 MN, and the third pass is 10-13 MN. When straightening the same steel plate, the straightening force increases in sequence.

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