460MPa-grade normalized delivery steel plate with good low-temperature toughness and production method of 460MPa-grade normalized delivery steel plate

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to a 460MPa-grade normalized delivery steel plate with good low-temperature toughness and a production method of the 460MPa-grade normalized delivery steel plate. The steel plate comprises the following components in percentage by weight: 0.12 percent to 0.15 percent of C, 0.25 percent to 0.40 percent of Si, 1.40 percent to 1.60 percent of Mn, less than or equal to 0.01 percent of P, less than or equal to 0.003 percent of S, 0.03 percent to 0.05 percent of Nb, 0.045 percent to 0.065 percent of V, 0.015 percent to 0.03 percent of Ti, 0.25 percent to 0.32 percent of Cr, 0.3 percent to 0.4 percent of Ni, 0.015 percent to 0.03 percent of Alt and the balance of Fe and inevitable impurities. According to the invention, through the design of medium and low C content, a small amount of alloy elements Cr and Ni are added to an Nb-V-Ti component system, a high-quality continuous casting billet is obtained through high-purity smelting, and the yield strength of the prepared steel plate is greater than 460MPa, the tensile strength is 580-660MPa, the elongation is greater than or equal to 25%, and the impact energy at-50 DEG C is greater than 150J through the modes of controlled rolling and controlled cooling, stacking after rolling and normalizing treatment.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy, and more particularly to a 460MPa grade normalized steel plate with good low-temperature toughness and its production method. Background Technology

[0002] 460MPa grade steel plates, requiring good low-temperature toughness and yield strength, are widely used in the construction of structural components for large-span buildings, bridges, hydropower, wind power, and marine engineering. 460MPa strength grade structural steel plates are generally produced using TMCP, TMCP+tempering, and quenching-tempering heat treatment processes. However, European structural design requires normalized delivery of this strength grade steel plates (such as S460NL welded structural steel plates), with a yield strength above 460MPa, while ensuring low-temperature impact toughness at -50℃ and an elongation of not less than 19%. While TMCP, TMCP+tempering, and quenching-tempering heat-treated steel plates can easily meet strength requirements through bainitic phase transformation strengthening, normalized delivery steel plates, due to their mixed ferrite and pearlite microstructure, face significant strength challenges. These performance characteristics and supply requirements place high demands on the composition design and process control of this steel grade.

[0003] Currently, most manufacturers use medium to high carbon content in their steel plate designs to ensure performance. While this improves strength, it reduces weldability and low-temperature toughness. On the other hand, when the carbon content is low, the amount of microalloying elements used needs to be increased, which increases the cost of the alloy.

[0004] Patent application number 202110337843.0 discloses a method for producing steel for cryogenic mobile containers. This patent employs a vanadium-nitrogen microalloying design, requiring an N content of 0.008~0.015% and V ≤0.2%, while adding elements such as Nb, Ni, Cu, and Mo. It uses a normalizing + tempering process to ensure a yield strength ≥460MPa, tensile strength 630~725MPa, and impact energy ≥60J at -60℃. The drawbacks are that the high N content easily leads to cracks in continuously cast billets and increases smelting difficulty; the large C content and addition of other alloying elements result in a high carbon equivalent, which is detrimental to the weldability of the steel plate; and the normalizing + tempering heat treatment process is complex and energy-intensive.

[0005] Patent application number 201310108383.X discloses a normalized pressure vessel steel with a yield strength of 460MPa and its manufacturing method. This patent uses a C-Mn-Nb-Ti composition design, requiring 0.04%≤Ti≤0.1%. It produces steel plates with a yield strength ≥460MPa, tensile strength ≥570MPa, and impact energy ≥100J at -40℃ through controlled rolling and cooling followed by normalizing. The drawback is the high Ti content. Due to Ti's high chemical reactivity, it reacts successively with O, N, and S to form TiO2, TiN, and Ti4C2S2. Furthermore, a high Ti content easily leads to more MnS inclusions within the steel plate. This patent lacks any technology for controlling inclusions, resulting in steel plates with poor ductility and toughness.

[0006] Patent application number 202210570629.4 discloses a production method for Q460 grade high corrosion-resistant and high-strength offshore structural steel. This patent employs a low-carbon, low-manganese composition design, combined with the addition of large amounts of Nb, V, Ti, Ni, and Cu elements. Through a TMCP + tempering process, it produces steel plates with a yield strength ≥460MPa, tensile strength ≥570MPa, and impact energy ≥120J at -60℃. However, due to the low C and Mn content, a large amount of Ni and Cu elements are added to ensure the steel plate's strength, resulting in extremely high alloy costs. Furthermore, the TMCP + tempering process does not meet the requirements for delivery in the normalized state.

[0007] Patent application number 202110002563.4 discloses an S460 high-strength low-temperature structural steel and its normalizing rolling preparation method. This patent adds appropriate amounts of Cr, Ni, Mo, and Cu to the C-Mn-Nb-V-Ti composition system. Through a normalizing rolling process, it ensures that the steel plate has a yield strength higher than 460 MPa, a tensile strength of 540~720 MPa, an elongation greater than 18%, and an impact energy greater than 34 J at -50℃. However, due to the high carbon and high manganese composition design, along with the addition of a large amount of alloying elements, especially Ni (0.4%~0.6%), the carbon equivalent and alloy cost of the steel plate increase, which is detrimental to its weldability.

[0008] Patent application number 201210253970.3 discloses a normalized high-strength and high-toughness steel plate with a yield strength of 460MPa and its manufacturing method. This patent employs a vanadium-nitrogen microalloying design, requiring an N content of 0.005%~0.020%, a V content of 0.12%~0.2%, and the addition of 0.15%~0.40% Ni to ensure low-temperature toughness. It uses a controlled rolling + normalizing process to ensure a steel plate with a yield strength ≥460MPa, tensile strength ≥570MPa, and impact energy ≥120J at -60℃. The drawbacks are that the high N content easily leads to cracks in the continuously cast billet and increases the difficulty of smelting, while the high C content is detrimental to the weldability of the steel plate.

[0009] In summary, the production of 460MPa grade normalized steel plates with good low-temperature toughness and yield strength currently has the following defects: (1) The carbon content of 0.15%~0.20% leads to a high carbon equivalent, which is not conducive to welding in the construction process of structural components; (2) When the carbon content is low, the production cost of steel plates increases sharply by adding a large amount of precious metal elements such as Nb, V, Ni, Mo and Cu; (3) When producing steel plates of this strength level, TMCP, TMCP+tempering or TMCP+quenching and tempering process routes are adopted. Such steel plates can easily meet the strength requirements through bainitic phase transformation strengthening, but their production method does not meet the requirements of normalized delivery, and the uniformity of the structure is not as good as that of normalized steel plates. Summary of the Invention

[0010] The purpose of this invention is to provide a normalized steel plate with good low-temperature toughness and a yield strength of 460MPa, and its production method. This invention employs a medium-low carbon design, adding small amounts of alloying elements Cr and Ni to the Nb-V-Ti composition system. High-quality continuously cast billets are obtained through high-purity smelting, and through controlled rolling and cooling, stacking, and normalizing, the normalized steel plate achieves a yield strength >460MPa, a tensile strength of 580~660MPa, an elongation ≥25%, and an impact energy of over 150J at -50℃.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows: This invention provides a 460MPa grade normalized steel plate with good low-temperature toughness. The steel plate contains the following components by weight percentage: C: 0.12%~0.15%, Si: 0.25%~0.40%, Mn: 1.40%~1.60%, P: ≤0.01%, S: ≤0.003%, Nb: 0.03%~0.05%, V: 0.045%~0.065%, Ti: 0.015%~0.03%, Cr: 0.25%~0.32%, Ni: 0.3%~0.4%, Alt: 0.015%~0.03%, with the remainder being Fe and unavoidable impurities.

[0012] The composition of the steel plate provided by this invention, including the function of each component and the control of its content, is as follows: C: Carbon in steel is an economical element that enhances the strength of steel plates through interstitial solid solution. When the carbon content is below 0.08%, it will lead to insufficient yield strength. On the other hand, as the carbon content increases, the low-temperature toughness and weldability of the steel plate will deteriorate. Therefore, this invention sets the carbon content to 0.12%~0.15%.

[0013] Si: Silicon is the most basic deoxidizer in steel. Silicon in steel can exist in the matrix in solid solution form, playing a role in solid solution strengthening. On the other hand, excessive silicon content is not conducive to low-temperature toughness and welding performance. Therefore, the silicon content is set to 0.25%~0.40% in this invention.

[0014] Mn: Manganese is an austenite-forming element in steel. Increasing the manganese content can expand the austenite phase region, improve the stability of austenite, and refine the ferrite grains. However, increasing the manganese content will cause the banded structure of the steel plate to deteriorate the plasticity and toughness of the material. Therefore, this invention controls the manganese content to be between 1.40% and 1.60%.

[0015] P: Phosphorus is an impurity element in steel, which weakens the low-temperature toughness of the steel plate and its welded components. Therefore, this invention controls the phosphorus content to be ≤0.01%.

[0016] S: Sulfur is an impurity element in steel and readily combines with Mn and Ti to form MnS and Ti4C2S. 2， To weaken the low-temperature toughness of the steel plate and its welded components, this invention controls the sulfur content to ≤0.003%.

[0017] Nb: Adding Nb to steel can inhibit austenite recrystallization during rolling, refine ferrite grains during cooling, and provide fine grain preparation for normalizing. At the same time, it combines with C and N to form fine precipitates, which plays a role in precipitation strengthening. Therefore, the present invention controls the Nb content to be 0.03%~0.05%.

[0018] V: Adding vanadium to steel can increase the recrystallization temperature of austenite during rolling. Compared with Nb, the precipitation temperature of V is lower. V can be fully precipitated during the slow cooling process after rolling. During normalizing, it pins the austenite grain boundaries and refines the microstructure. When the V content is higher than 0.03%, VCN precipitates during normalizing and cooling, which plays a precipitation strengthening role. Therefore, this invention controls the V content to be between 0.045% and 0.065%.

[0019] Ti: Adding titanium to steel allows for the precipitation of TiCN during slab heating due to its high precipitation temperature. This precipitates austenite grain boundaries, refining the initial microstructure. Ti in steel can also precipitate in combination with Nb and V, improving the stability of (Nb,V,Ti)CN precipitates. This ensures that a certain amount of (Nb,V,Ti)CN precipitates are present during normalizing to pin austenite grain boundaries and prevent their growth. Furthermore, TiN can improve weldability. However, high Ti content can easily deteriorate low-temperature toughness and plasticity. Therefore, this invention controls the Ti content to be between 0.015% and 0.03%.

[0020] Cr: Chromium can improve the hardenability of steel, and chromium carbides are the smallest compounds in steel, which can be evenly distributed in steel, thereby improving the strength of steel. Stacking of rolled steel plates promotes the precipitation of chromium carbides. At lower normalizing temperatures, the diffusion rate of Cr is slow. In the early stage of normalizing, it can play a role in pinning austenite grain boundaries and refining the microstructure. However, excessive chromium content will reduce the plasticity and toughness of steel. Therefore, this invention controls the Cr content to be between 0.25% and 0.32%.

[0021] Ni: Nickel in steel can expand the austenite phase region and improve the strength of the steel plate. At the same time, it can improve the low-temperature toughness by effectively dispersing the aggregation of carbides. However, Ni is a precious metal element, and excessive addition will lead to increased costs. Therefore, this invention controls the Ni content to be between 0.3% and 0.4%.

[0022] Alt: Aluminum in steel is used as a deoxidizer, and the generated AlN can refine the grain size of the continuously cast billet during heating. It is generally believed that the deoxidation effect is not obvious when the Alt content is below 0.015%, and the Alt content is above 0.03%, which easily generates coarse alumina inclusions and deteriorates the toughness. Therefore, the acid-soluble aluminum content is controlled at 0.015%~0.03%.

[0023] In the above technical solution, the carbon equivalent (CEV) of the steel plate is ≤0.52, and the CEV is calculated according to the following formula: CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15.

[0024] In the above technical solution, the steel plate has a yield strength > 460MPa, a tensile strength of 580~660MPa, an elongation ≥ 25%, an impact energy of -50℃ > 150J, and a grain size ≥ 10.

[0025] In the above technical solution, the microstructure of the steel plate is ferrite + pearlite.

[0026] In the above technical solution, the thickness of the finished steel plate is further 10~40mm.

[0027] Another aspect of the present invention provides a method for producing the above-mentioned 460MPa grade normalized steel plate with good low-temperature toughness, comprising: converter smelting—LF refining—RH vacuum refining—continuous casting—heating—descaling—rolling—cooling—hot straightening—cooling bed—stacking—shot blasting—normalizing; wherein: During the heating process, the total time in the furnace is ≥260 min, of which the temperature of the soaking zone is 1200~1230℃ and the time of the soaking zone is ≥40 min, the temperature of the first heating zone is 1230~1270℃ and the time of the first heating zone is ≥50 min, the temperature of the second heating zone is 1000~1200℃ and the time of the second heating zone is ≥60 min, the temperature of the preheating zone is 600~900℃ and the time of the preheating zone is ≥90 min, and the tapping temperature is 1180~1220℃; In the rolling process, a two-stage controlled rolling process is adopted. During the roughing process, the bite speed of the steel plate during the widening stage is ≤1.0m / s. During the longitudinal rolling of the roughing stage, at least 3 passes with a reduction rate ≥30% are guaranteed. The intermediate billet is cooled by water spray. The initial rolling temperature of the finishing stage is 830~870℃. During the finishing stage, at least two passes with a reduction rate ≥20% are guaranteed. The final rolling temperature of the finishing stage is 760~800℃. In the cooling process, laminar flow cooling is adopted, with a cooling rate of 10~15℃ / s and a reddening temperature of 620~700℃; In the cooling bed process, the steel plate enters the cooling bed for air cooling, with a cooling rate of 5~10℃ / s; During the stacking process, the steel plates are stacked when the temperature drops to 300~450℃, and the stacking time is not less than 16 hours. In the normalizing process, the normalizing temperature is 843~863℃, and the total time in the furnace is t=15+h×(1.0~1.3)min, where h is the thickness of the finished steel plate in mm. After the steel plate is normalized, it is air-cooled on a cooling bed.

[0028] In the above technical solution, the converter smelting process further adopts top and bottom blowing, and argon blowing is used throughout the process. The P content is controlled to be ≤0.01% before leaving the station.

[0029] In the above technical solution, further, in the RH vacuum refining process, RH is vacuum degassed, the deep treatment time is ≥10min, the hydrogen content [H] of the molten steel is ≤2ppm, the composition of the molten steel is controlled according to the target composition, the net circulation time is ≥5min, and after the RH treatment is completed, calcium wire is fed to make the S content of the molten steel ≤0.003%.

[0030] In the above technical solution, furthermore, in the continuous casting process, protective casting is carried out throughout the process, the superheat is less than 20℃, the casting speed is 0.9~1.1m / min, the secondary cooling zone adopts electromagnetic stirring and light pressure reduction technology, the continuous casting billet is stacked and slowly cooled after leaving the line, and the slow cooling time is not less than 16h; the thickness of the continuous casting billet is 240~250mm.

[0031] In the above technical solution, further, in the rolling process, the thickness of the intermediate billet is 2 to 3 times the thickness of the finished steel plate.

[0032] The beneficial effects of this invention are as follows: (1) The present invention adopts a medium-low C design, adds a small amount of Cr and Ni to the Nb-V-Ti composition system, obtains high-quality continuous casting billets through high-purity smelting, and obtains finished steel plates with performance that meet the requirements of S420NL in EN10025-3 through controlled rolling and cooling, stacking and normalizing, with yield strength > 460MPa, tensile strength 580~660MPa, elongation ≥ 25%, and impact energy of -50℃ reaching more than 150J.

[0033] (2) The present invention adopts a medium-low C design, and adds a small amount of alloying elements Cr and Ni to the Nb-V-Ti composition system. The carbon equivalent is low, which is beneficial to the low temperature toughness and welding performance of the steel plate. At the same time, no expensive metal elements such as Mo and Cu are added, which reduces the alloy cost and manufacturing cost, and has both performance advantages and economy.

[0034] (3) By optimizing the tapping temperature, this invention avoids the problem of abnormal grain growth caused by excessively high tapping temperature, and effectively avoids the phenomenon of low remelting rate of (Nb,Ti)C particles and coarsening of unremelted particles when the tapping temperature is too low. It can ensure that the steel grains are small and uniformly distributed when tapping, and at the same time significantly improve the solid solution content of microalloying elements, which is conducive to the uniform precipitation of (Nb,Ti)C particles during subsequent rolling and cooling processes, thereby effectively improving the comprehensive strength and toughness performance of the steel plate.

[0035] (4) The present invention adopts a two-stage controlled rolling process. By precisely limiting the key process parameters of roughing and finishing rolling, it can promote the precipitation of Nb, V, and Ti particles. These precipitates are fine and dispersed, and can exert the synergistic effect of fine grain strengthening and precipitation strengthening at the same time. At the same time, the rapid cooling process after rolling ensures that the steel plate obtains a fine and uniform grain structure and effectively weakens the banded structure, significantly improving the comprehensive mechanical properties of the steel plate. After rapid cooling, by strictly controlling the air cooling and stacking process parameters, it can avoid the formation of coarse cementite in the steel plate, and instead generate fine and dispersed M7C3 and M7C4 particles. 23 C6 alloy carbides have strong stability and can effectively pin austenite grain boundaries in the early stage of normalizing, further refining the microstructure. The microstructure after normalizing is ferrite + pearlite with a grain size ≥10.

[0036] (5) In the converter smelting process of this invention, the top and bottom argon blowing process is adopted to form a bidirectional stirring in the molten pool to achieve uniform mixing of the molten steel throughout the pool, ensuring uniform temperature and composition, promoting the floating of inclusions and improving the purity of the molten steel; by precisely controlling the LF and RH process parameters, the composition is precisely controlled, ultra-deep desulfurization and degassing are achieved, the morphology of inclusions is improved, and the purity of the molten steel is improved; the entire process of protection during casting prevents secondary oxidation and nitrogen absorption of the molten steel, and the parameters of superheat, casting speed, electromagnetic stirring in the secondary cooling zone and light pressure are optimized to suppress columnar crystal growth, reduce central porosity and segregation, refine austenite grains, reduce internal structural defects, etc., to ensure the acquisition of high-quality continuous casting billets.

[0037] (6) The steel plate of the present invention undergoes controlled rolling and cooling, stacking and normalizing treatment, which reduces the strip structure and internal stress of the steel plate. Compared with the steel plate delivered in normalized rolling and TMCP state, the internal structure and properties are more uniform. Attached Figure Description

[0038] Figure 1The microstructures at different tapping temperatures are shown in Figure a, where a represents the grain size at a tapping temperature of 1250℃, and b represents the (Nb,Ti)C particles at a tapping temperature of 1100℃. Figure 2 This represents the relationship between carbide volume fraction and precipitation temperature. Detailed Implementation

[0039] The following embodiments are merely some preferred implementations of the present invention and do not limit the scope and technical means of the invention in any way.

[0040] Table 1 shows the chemical composition of the steel plates in Examples 1-8.

[0041] Table 1 Chemical composition (wt%) of steel plates from Examples 1-8

[0042] The above-mentioned steel plate production methods include: converter smelting—LF refining—RH vacuum refining—continuous casting—heating—descaling—rolling—cooling—hot straightening—cooling bed—stacking—shot blasting—normalizing; wherein: In the converter smelting process, top and bottom blowing is adopted during converter smelting, and argon blowing is used throughout the process. The P content is required to be ≤0.01% before leaving the station. In the LF refining process, slag formation, desulfurization, and composition control are carried out according to the tapping temperature. Bottom blowing argon is used throughout the process, and the slag surface is slightly turned over without exposing the molten steel. In the RH vacuum refining process, RH is vacuum degassing, with a deep treatment time of ≥10 min, and the hydrogen content [H] in the molten steel is ≤2 ppm; the composition of the molten steel is controlled according to the target composition, with a net circulation time of ≥5 min, avoiding oxygen blowing and heating; after RH treatment, calcium wire is fed to improve purity and ensure that the S content is ≤0.003%; During the continuous casting process, protective pouring is carried out throughout, and electromagnetic stirring is used in the secondary cooling zone. The superheat during casting is ≤20℃. The casting speed is 0.9~1.1m / min. Electromagnetic stirring and light reduction technology are used in the secondary cooling zone to reduce segregation. After the continuous casting billet is removed from the line, it is stacked and cooled slowly to avoid rapid cooling that will cause cracks on the surface of the continuous casting billet. The slow cooling time is not less than 16 hours to ensure that the segregation in the core of the continuous casting billet is ≤C1.0. During the heating process, the total time in the furnace is ≥260 min, with the following parameters: soaking zone temperature 1200~1230℃, soaking zone time ≥40 min; first heating zone temperature 1230~1270℃, first heating zone time ≥50 min; second heating zone temperature 1000~1200℃, second heating zone time ≥60 min; preheating zone temperature 600~900℃, preheating zone time ≥90 min; and tapping temperature 1180~1220℃. Figure 1 As shown in Figure a, when the tapping temperature is 1200℃, the grain size is uniform and fine; when the tapping temperature is increased to 1250℃, the austenite grains coarsen and abnormal growth occurs, such as... Figure 1 As shown in b, Figure 2 As shown, the remelting rate of the second phase particles increases significantly when the temperature is above 1180℃. Considering both the austenite grain size and the remelting rate of the second phase, the optimal tapping temperature is 1180~1220℃. In the rolling process, rolling adopts a two-stage control. During the roughing rolling process, the bite speed of the steel plate during the widening stage is ≤1.0m / s. The slower bite speed is conducive to increasing the reduction of each pass during widening, so that widening can be completed in the fewest passes. During the longitudinal rolling of the roughing stage, at least 3 passes with a reduction rate ≥30% are guaranteed. The higher reduction rate per pass is conducive to sufficient recrystallization and grain refinement. The intermediate billet is cooled by water spray and the thickness at the time of heating is 2 to 3 times the thickness of the finished steel plate. The rapid cooling of the intermediate billet can reduce the growth rate of recrystallized grains. In the finishing rolling stage, the initial rolling temperature is 830~870℃, the reduction rate of at least two passes in the finishing rolling stage is ≥20%, and the finishing rolling temperature is 760~800℃. The lower finishing rolling temperature and the higher reduction rate per pass are conducive to increasing the internal energy storage of the rolled steel plate, which is conducive to obtaining fine grains during cooling and enhancing the grain refinement strengthening effect. During the cooling process, the rolled steel plate quickly enters the cooling system for laminar flow cooling at a rate of 10~15℃ / s and a reddening temperature of 620~700℃. Rapid cooling after rolling facilitates the acquisition of fine grains and weakened banded structures. In the cooling bed and stacking process, after laminar flow cooling, the steel plates enter the cooling bed for air cooling at a rate of approximately 5-10°C / s. Stacking is carried out when the steel plate temperature drops to 300-450°C, and the stacking time should not be less than 16 hours. Thermo-Calc calculations show that Fe3C, M7C3, and M... 23 The initial precipitation temperatures of C6 were 698, 406, and 318 °C, respectively. Figure 2 As shown, the purpose of air cooling is to rapidly cool the steel plate below the cementite transformation temperature, reducing the formation of coarse cementite structures; stacking at 300~450℃ is beneficial for alloy carbides such as M7C3 and M 23 C6 precipitation occurs in this type of carbide, which has a high content of Mn and Cr elements and is distributed in a fine and dispersed state. Moreover, the diffusion rate of Mn and Cr elements is much slower than that of Fe elements at high temperatures. Therefore, in the early stage of normalizing, the carbides of this type of alloy cannot be completely dissolved, which can pin the austenite grain boundaries and refine the structure. In the normalizing process, the steel plate undergoes normalizing treatment after shot blasting. The normalizing temperature is 843~863℃, and the total furnace time is t=15+h×(1.0~1.3)min, where h is the thickness of the steel plate. The normalizing temperature is selected to be 10~30℃ above AC3. To prevent grain coarsening and rapid dissolution of carbides, a normalizing temperature of 843~863℃ is chosen, where the calculated temperature of AC3 is 833℃. The calculation method is the following empirical formula:

[0043] After the steel plate is normalized, it is air-cooled on a cooling bed. The slow cooling method is conducive to the precipitation of VC particles, which plays a role in precipitation strengthening. After the steel plate is completely cooled, it is ordered to length and put into storage.

[0044] Table 2 shows the converter smelting, refining, and continuous casting process parameters for the steel plates of Examples 1-8; Table 3 shows the heating process for the steel plates of Examples 1-8; Table 4 shows the rolling and cooling process for the steel plates of Examples 1-8; Table 5 shows the post-rolling stacking and normalizing process for the steel plates of Examples 1-8; and Table 6 shows the properties of the steel plates of Examples 1-8.

[0045] Table 2 Converter smelting, refining and continuous casting processes for steel plates in Examples 1-8

[0046] Table 3 Heating process of steel plates in Examples 1-8

[0047] Table 4 Rolling and cooling processes of steel plates in Examples 1-8

[0048] Table 5 Cooling bed, stacking and normalizing processes for steel plates in Examples 1-8

[0049] Table 6 Properties of steel plates from Examples 1-8

[0050] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A 460 MPa grade normalized as-delivered steel plate with good low temperature toughness, characterized in that, The steel plate comprises the following components in percentage by weight: C: 0.12%~0.15%, Si: 0.25%~0.40%, Mn: 1.40%~1.60%, P: ≤0.01%, S: ≤0.003%, Nb: 0.03%~0.05%, V: 0.045%~0.065%, Ti: 0.015%~0.03%, Cr: 0.25%~0.32%, Ni: 0.3%~0.4%, Alt: 0.015%~0.03%, and the rest is Fe and inevitable impurities.

2. The 460 MPa grade as- normalized delivery steel plate with good low-temperature toughness according to claim 1, characterized in that, The carbon equivalent CEV of the steel plate is ≤0.

52.

3. The 460 MPa grade as- normalized delivery steel plate with good low-temperature toughness according to claim 1, characterized in that, The yield strength of the steel plate is >460 MPa, the tensile strength is 580~660 MPa, the elongation is ≥25%, the impact energy at -50 ℃ is >150 J, and the grain size is ≥10 levels.

4. The 460 MPa grade as- normalized delivery steel plate with good low-temperature toughness according to claim 1, characterized in that, The microstructure of the steel plate is ferrite + pearlite.

5. The 460 MPa grade as- normalized delivery steel plate with good low-temperature toughness according to claim 1, characterized in that, The thickness of the finished steel plate is 10~40 mm.

6. A method of producing a 460 MPa grade normalized as-delivered steel sheet having good low-temperature toughness according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: converter smelting-LF refining-RH vacuum refining-continuous casting-heating-descaling-rolling-cooling-heat straightening-cold bed-piling-marblizing-annealing; wherein: In the heating process, the total time in the furnace is ≥260 min, wherein the soaking section temperature is 1200~1230 ℃, the soaking section time is ≥40 min, the first heating section temperature is 1230~1270 ℃, the first heating section time is ≥50 min, the second heating section temperature is 1000~1200 ℃, the second heating section time is ≥60 min, the preheating section temperature is 600~900 ℃, the preheating section time is ≥90 min, and the tapping temperature is 1180~1220 ℃; In the rolling process, two-stage controlled rolling is adopted, the biting speed of the steel plate is ≤1.0 m / s during the rolling in the spreading stage, at least 3 passes of the longitudinal rolling in the rough rolling stage are ensured to have a reduction rate of ≥30%, the intermediate billet is cooled by water spraying, the opening rolling temperature in the finish rolling stage is 830~870 ℃, at least two passes of the finish rolling stage have a reduction rate of ≥20%, and the finish rolling temperature is 760~800 ℃; In the cooling process, laminar cooling is adopted, and the cooling rate is 10~15 ℃ / s, and the re-red temperature is 620~700 ℃; In the cold bed process, the steel plate enters the cold bed for air cooling, and the cooling rate is 5~10 ℃ / s; In the piling process, the steel plate is piled when the temperature of the steel plate is reduced to 300~450 ℃, and the piling time is not less than 16 h; In the annealing process, the annealing temperature is 843~863 ℃, the total time in the furnace is t=15+h×(1.0~1.3)min, h is the thickness of the finished steel plate, and the unit is mm, and the steel plate is air cooled on the cold bed after annealing.

7. The method of producing a 460 MPa grade normalized as-delivered steel plate with good low-temperature toughness according to claim 6, characterized in that, In the converter smelting process, top and bottom combined blowing is adopted, and argon blowing process is adopted throughout the whole process, and the P content is controlled to be ≤0.01% before leaving the station.

8. The method of producing a 460 MPa grade normalized as-delivered steel plate with good low-temperature toughness according to claim 6, characterized in that, In the RH vacuum refining process, RH vacuum degassing is adopted, the deep treatment time is ≥10 min, the hydrogen content [H] of the molten steel is ≤2 ppm, the composition of the molten steel is controlled according to the target composition, the net circulation time is ≥5 min, and the calcium wire is fed after the RH treatment is completed to make the S content of the molten steel ≤0.003%.

9. The method of producing a 460 MPa grade normalized as-delivered steel plate with good low-temperature toughness according to claim 6, characterized in that, In the continuous casting process, the whole process is protected casting, the superheat is less than 20℃, the drawing speed is 0.9~1.1m / min, the electromagnetic stirring and light pressing down technology are used in the secondary cooling zone, the continuous casting billet is stacked and slowly cooled after being discharged, and the slow cooling time is not less than 16h; the thickness of the continuous casting billet is 240~250mm.

10. The method of producing a 460 MPa grade normalized as-delivered steel plate with good low-temperature toughness according to claim 6, characterized in that, In the rolling process, the thickness of the intermediate billet is 2~3 times of the thickness of the finished steel plate.

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