Low-temperature environment preheating-free welding 460mpa grade steel plate and manufacturing method

Abstract

The application belongs to the technical field of metal materials, and provides a 460MPa-grade steel plate for preheat-free welding in a low-temperature environment and a manufacturing method.The chemical composition system of the steel plate is low in carbon and manganese, micro-alloy elements such as V-N, Ti and Mo are added to refine grains, the (Ti+V) / N value is accurately controlled to ensure the formation of precipitated phases in the welding process, elements such as La, Ca and Mg are added to improve the purity of molten steel and the quality of continuous casting billets, and fine and dispersed oxide particles are formed in the steel to improve the comprehensive performance of the steel plate in the thickness direction.The manufacturing method comprises smelting, continuous casting, heating in a heating furnace, rolling, online cooling and tempering.The steel plate produced by the application has a structure of acicular ferrite + tempered sorbite, the size of precipitated phases is 40-60nm, the steel plate has excellent low-temperature toughness, preheat-free welding in a-10 DEG C environment can be realized, and the mechanical properties of the welded joint of the steel plate are excellent.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and in particular relates to a method for manufacturing a 460MPa grade steel plate that can be welded without preheating in a low-temperature environment. Background Technology

[0002] As the global shipping industry and marine engineering move towards larger, more efficient, and greener models, ships and marine engineering equipment are widely adopting higher-strength steel plates to reduce structural weight, increase cargo capacity, and improve fuel economy. However, the increase in steel strength is often accompanied by an increase in carbon equivalent, leading to a significant deterioration in weldability, particularly resistance to cold cracking. When welding traditional high-strength ship plates, especially in low-temperature and high-humidity environments, a strict preheating process must be implemented to prevent hydrogen-induced cold cracking.

[0003] While preheating is effective, it presents a series of serious challenges: First, it results in low construction efficiency, significantly extending the work cycle and becoming a bottleneck restricting modular and assembly-line production in shipbuilding. Second, it incurs high energy and environmental costs, consuming large amounts of fuel and increasing carbon emissions. Preheating temperatures for some steel plates reach 80-150°C, and on-site preheating under harsh conditions (such as polar vessels and deep-sea platforms) is extremely difficult. Third, it presents harsh working conditions, with the high-temperature preheating environment severely impacting welders' health and operational precision. Fourth, it complicates quality control, as uneven preheating temperatures can lead to uncontrollable welding stress and deformation. Therefore, there is an urgent need to develop preheat-free welding techniques for high-strength ship plates.

[0004] Patent document "A Preparation Method of Extra-Thick S355MLO Steel for Marine Engineering without Preheating Welding" (Application No.: 202411917870.5) discloses an S355MLO steel plate that can be welded without human intervention. Its chemical composition is: C: 0.04%~0.06%, Si: 0.15%~0.50%, Mn: 1.35%~1.45%, P≤0.008%, S≤0.003%, Ti: 0.012%~0.02%, Al≤0.015%, Ni: 0.15%~0.25%, Cu≤0.18%, Cr≤0.18%, with the remainder being Fe and unavoidable impurities. While the steel plate can be welded without preheating, its post-weld toughness grade is only -40℃, which cannot meet the requirements for use in polar environments.

[0005] Patent document "A Production Method of 420-Grade Preheat-Free Welding Marine Steel" (Application No.: 202411917868.8) discloses a 420-grade preheat-free welding marine steel with the following chemical composition: C: 0.04%~0.06%, Si: 0.15%~0.50%, Mn: 1.45%~1.55%, P≤0.008%, S≤0.003%, Ti: 0.012%~0.02%, Al≤0.010%, Ni: 0.15%~0.25%, Cu: 0.10%~0.18%, Cr: 0.10%~0.18%, with the remainder being Fe and unavoidable impurities. While this steel allows for welding without preheating, its high Mn content easily leads to segregation, affecting the core properties and preventing preheat-free welding at low temperatures.

[0006] Patent document "A 460-grade preheat-free weldable marine steel and its preparation method" (application number: 202411917869.2) discloses a 460-grade preheat-free weldable marine steel with the following chemical composition: C: 0.04%~0.06%, Si: 0.15%~0.50%, Mn: 1.75%~1.85%, P≤0.008%, S≤0.003%, Ti: 0.012%~0.02%, Al≤0.015%, Ni: 0.25%~0.35%, Cu: 0.20%~0.28%, Cr: 0.20%~0.25%, with the remainder being Fe and unavoidable impurities. While this steel plate allows for welding without preheating, it also contains a high Mn content, which can easily cause segregation and affect the core properties of the steel plate, thus failing to achieve preheat-free welding at low temperatures.

[0007] Patent document "Low-Temperature Toughness-Exquisite Preheat-Free Welding Marine Steel and Its Preparation Method" (Application No.: 202511490022.5) discloses a low-temperature toughness-exquisite preheat-free welding marine steel with the following chemical composition: C: 0.03%~0.07%, Si: 0.15%~0.45%, Mn: 1.10%~1.40%, P≤0.012%, S≤0.002%, Ni: 0.80%~1.20%, Cr: 0.20%. The composition is as follows: Nb: 0.02%~0.06%, V: 0.02%~0.05%, Mo: 0.15%~0.35%, Ti: 0.01%~0.025%, Alt≤0.18%, Ca: 0.001%~0.003%, Mg: 0.0005%~0.002%, Ce: 0.010%~0.030%, O≤0.001%, N≤0.007%, with the balance being Fe and unavoidable impurities. This steel plate features high strength, high toughness, and excellent low-temperature toughness, enabling room-temperature welding without preheating. However, the steel plate undergoes two rolling processes, making the manufacturing process complex and limiting it to room-temperature welding only, thus failing to meet the requirements for applications at lower temperatures.

[0008] In summary, the following problems exist in the current production of high-strength ship plates that do not require preheating welding.

[0009] 1) Steel plate production process is complex, with long production cycle and high cost;

[0010] 2) Steel plates can only be welded at room temperature without preheating, and cannot meet the requirements for use at lower temperatures;

[0011] 3) The steel plate has insufficient low-temperature toughness and cannot meet the requirements for low-temperature use. Summary of the Invention

[0012] The purpose of this invention is to overcome the above-mentioned problems and deficiencies and provide a method for manufacturing a 460MPa grade steel plate that can be welded without preheating at room temperature and in a low-temperature environment.

[0013] The objective of this invention is achieved as follows:

[0014] A 460MPa grade steel plate for low-temperature environment preheating welding, wherein the elemental composition of the steel plate by mass percentage is as follows: C: 0.02%~0.07%, Si: 0.03%~0.20%, Mn: 0.80%~1.30%, P≤0.008%, S≤0.002%, V: 0.07%~0.12%, N: 0.030%~0.045%, Cu: 0.25%~0.55%, Ni: 0.90%~1.40%, Mo: 0.25%~0.55%, Ti: 0.02%~0.06%, Als: 0.015%~0.040%, La: 0.025%~0.085%, Ca: 0.0035%~0.0055%, Mg: 0.004%~0.006%, with the balance being Fe and unavoidable impurities.

[0015] Furthermore, the ratio of (V+Ti) / N in the steel plate is 3.1~3.9.

[0016] Furthermore, the microstructure of the steel plate includes ferrite and tempered sorbite, with ferrite accounting for 40%~50% and tempered sorbite accounting for 50%~60%; the average size of the precipitated phases in the steel plate is 40~60 nm.

[0017] Furthermore, the steel plate has a yield strength of 490~540MPa, a tensile strength of 600~650MPa, an elongation after fracture of ≥27.5%, an impact energy of ≥250J at -80℃, a tensile strength of 630~650MPa after welding at -10℃, and an impact energy of ≥160J at -60℃ in the weld heat-affected zone.

[0018] The rationale for the design of the components in this invention is as follows:

[0019] C: An important strengthening element in steel, it forms interstitial solid solutions, effectively improving the strength of steel. It also forms carbide precipitates with microalloying elements, hindering grain growth. Low C content reduces carbide formation, affecting grain refinement during rolling. High C content increases cementite content, significantly raising the brittle transition temperature and negatively impacting the low-temperature toughness, plasticity, and weldability of the steel plate. Therefore, considering cost and performance factors, this invention controls the C content to be between 0.020% and 0.070%.

[0020] Silicon (Si) plays a deoxidizing role in steelmaking. Dissolving in the ferrite matrix, it effectively improves the strength of steel without significantly increasing its carbon equivalent. During welding, it delays the transformation of austenite to proeutectoid ferrite, promoting the formation of finer ferrite structures during preheat-free welding, thus improving the low-temperature toughness of the hard ferrite zone (HAZ). However, excessive Si content can raise the ductile-brittle transition temperature, reduce the low-temperature toughness of the steel plate, increase the weld crack sensitivity coefficient, and affect the surface quality of the steel plate. Considering cost, performance, and other factors, this invention controls the Si content within the range of 0.030% to 0.200%.

[0021] Mn (Mn): An element that expands the austenite phase region, it can lower the temperature of the austenite-ferrite transformation, allowing steel to obtain more fine ferrite under the same cooling conditions, thereby improving the strength and low-temperature toughness of the steel. It forms a substitutional solid solution in steel, which can dissolve extensively in the Fe matrix, improving the strength of the steel through solid solution strengthening; it can delay the transformation of ferrite and pearlite in steel, significantly increasing the hardenability of the steel, lowering the ductile-brittle transition temperature, improving impact toughness, and eliminating the influence of sulfur in the steel, thus improving the hot working properties of the steel. However, excessively high Mn content easily leads to the formation of segregation and banded structures in the steel, adversely affecting both plasticity and toughness, and easily causing temper brittleness, which negatively impacts weldability. Considering all factors, this invention controls the Mn content to be in the range of 0.80%~1.30%.

[0022] Vanadium (V) is a key strengthening and toughening element in this invention. It has a strong affinity for nitrogen and carbon, forming extremely stable carbonitrides. Its key characteristics include high solid solubility in austenite and a strong tendency to precipitate in ferrite. In steel, it enhances strength through grain refinement, precipitation strengthening, and solid solution strengthening. As V content increases, the ductile-brittle transition temperature of the steel decreases. However, excessively high V content can actually increase the ductile-brittle transition temperature. Vanadium carbonitrides can precipitate at lower temperatures, hindering dislocation movement and thus strengthening and toughening the steel, significantly improving the overall mechanical properties of the steel plate. During welding, V interacts with nitrogen to form precipitates, promoting the formation of intragranular ferrite and improving the low-temperature toughness of the hard lattice (HAZ). Considering all factors, this invention controls the V content within the range of 0.070% to 0.120%.

[0023] Nitrogen (N): Another important strengthening and toughening element in this invention. The addition of N promotes the formation of large amounts of V (CN) and Ti (CN) in the steel, thereby refining the grains and improving the steel's plasticity and toughness. Nitrogen-containing steel not only eliminates the cost increase caused by degassing and refining denitrification during steelmaking, but also allows for the fuller utilization of microalloying elements, saving on the amount of alloying elements used, thus significantly reducing production costs. It can optimize the precipitation behavior of V in the steel cross-section, making its properties more uniform. In addition, the addition of N can replace the role of C, forming interstitial solid solutions in the steel to improve its strength. It also reduces the carbon equivalent of the steel without increasing the brittle transition temperature, promoting a more uniform distribution of properties. Considering both performance and cost, this invention controls the range of N to be 0.0300%~0.0450%.

[0024] Cu can improve the stability of austenite in steel, increase the hardenability of steel, and improve the strength, plasticity, and low-temperature toughness of steel when added in appropriate amounts. When dissolved in steel, it will increase the ductile-brittle transition temperature of steel. During low-temperature treatment, it can produce ε-Cu precipitation, thereby increasing the strength of steel. However, if the content is too high, the hot brittleness of steel will deteriorate, and hot cracking will easily occur. In this invention, the Cu content is controlled within the range of 0.25% to 0.55%.

[0025] Ni has no adverse effects on the hardening properties and toughness of the weld heat-affected zone of steel, and can improve the plasticity and low-temperature toughness of steel, significantly reducing the brittle transition temperature of steel. It has a positive effect on the strength of steel without significantly increasing the cold cracking susceptibility coefficient. In addition, the addition of Ni can increase the solid solubility of Cu in steel and prevent Cu segregation at grain boundaries. Taking into account factors such as cost and performance, the range of Ni in this invention is controlled to be 0.90%~1.40%.

[0026] Mo improves the hardenability of steel and enhances the strength of steel plates by promoting acicular ferrite without significantly increasing the risk of cold cracking. Acicular ferrite can be obtained over a wide range of cooling rates during preheating-free welding, thus improving the low-temperature toughness of the HAZ (high-temperature zone). Taking all factors into consideration, the Mo content in this invention is controlled within the range of 0.25% to 0.55%.

[0027] Ti exhibits strong precipitation strengthening, increasing the strength of steel and preventing austenite recrystallization. Simultaneously, it refines grain size, improving the yield strength of the steel. The high formation temperature of Ti's C and N compounds, resulting in TiN and Ti(CN) during billet solidification, effectively inhibits austenite grain growth. Its high remelting temperature during heating further inhibits austenite grain growth, thus refining the grain size of the steel plate, improving its strength and toughness, and lowering its brittle transition temperature. During welding, it inhibits HAZ grain growth, improving low-temperature toughness. Considering all factors, this invention controls the Ti content within the range of 0.020% to 0.050%.

[0028] Al: A strong deoxidizer in steel. Adding a small amount can generate highly fine, ultramicroscopic oxides, which has a beneficial effect on improving the purity of steel and can also improve the uniformity of performance in the thickness direction of the steel plate. Taking all factors into consideration, the Al content in this invention is controlled within the range of 0.015% to 0.040%.

[0029] La (La) has excellent deoxidizing and desulfurizing effects, improves the fluidity of steel, reduces non-metallic inclusions, makes the steel structure denser and purer, and improves the mechanical properties in the thickness direction of thick steel plates, especially low-temperature toughness. It forms dispersed oxides in the steel, which act as nucleation sites for ferrite during welding, thereby improving the low-temperature toughness of the HAZ (high-temperature zone). Taking all factors into consideration, the La content in this invention is controlled within the range of 0.0250% to 0.0850%.

[0030] Ca reacts with Al2O3 inclusions produced during deoxidation to form calcium aluminate compounds, and reacts with MnS to form (Ca,Mn)S composite inclusions, transforming the inclusions into spherical inclusions. This improves the overall properties of the steel, especially during welding, where the fine oxides formed by Ca act as nucleation sites for ferrite, leading to the formation of a large amount of ferrite in the HAZ and improving its low-temperature toughness. However, excessively high Ca content can easily lead to the formation of large, non-deformable inclusions, which become crack initiation sites and reduce the mechanical properties of the steel plate. Considering all factors, this invention controls the Ca content within the range of 0.0035% to 0.0055%.

[0031] Mg has a strong affinity for oxygen and sulfur, forming fine precipitates that are uniformly dispersed in the steel. This avoids stress concentration caused by large oxide particles remaining in the steel, thus improving the steel's plasticity and toughness. Taking all factors into consideration, this invention controls the Mg content within the range of 0.0040% to 0.0060%.

[0032] The second technical solution of the present invention is to provide a method for manufacturing 460MPa grade steel plates that do not require preheating welding in a low-temperature environment, including smelting, continuous casting, heating in a heating furnace, rolling, online cooling, and tempering;

[0033] Smelting: Smelting steel according to the above composition, including converter smelting, ladle refining, and RH treatment;

[0034] a) Converter smelting: During converter smelting, the contents of elements such as C, Si, Mn, P, and S are adjusted to be within the range of this invention, and the basicity of the converter steel is controlled to be R=3.00~4.00.

[0035] b) Ladle refining: Refining the molten steel and adjusting the content of other alloying elements to the range of this invention.

[0036] c) RH treatment: The refined molten steel is subjected to RH treatment for 40-60 minutes. Nitrogen is blown throughout the RH treatment process at a pressure of 660-680 Pa to ensure that the final N content of the steel is within the range of this invention. The [H] content in the steel is controlled to be ≤1.5 ppm and [O] content to be ≤10 ppm. Before the end of smelting, Ca and Mg treatment is performed, and La element is added.

[0037] Continuous casting:

[0038] Molten steel is continuously cast to obtain the required billet. A high superheat (50-70°C) is used in the tundish, with full protective pouring throughout. The casting speed is controlled at 0.70-1.20 m / min, and the secondary cooling water volume is 1.00-1.50 m³ / min. 3 To ensure a high proportion of columnar crystals (≥98.5%) in the continuously cast billet and reduce core segregation, electromagnetic stirring with a current of 550-650A is employed in the later stages of continuous casting, and a light reduction process of 10.0-15.0 mm is used at the end of the casting process. Preferably, to control the grain size of the continuously cast billet, a strong cooling process is used, with an initial cooling temperature of 1050-1150℃ and a final cooling temperature of 400-500℃, after which the billet is heated in a walking beam furnace.

[0039] Reheating:

[0040] The heating temperature of the continuously cast billet is 1120℃~1250℃, the soaking temperature is 1100℃~1200℃, the soaking time is 0.30~0.50min / mm, and the total time in the furnace is 0.50~1.00min / mm.

[0041] Hot-rolled:

[0042] The billet is rolled into hot-rolled steel plate in two stages. The first stage rolling is carried out using a high-temperature fast rolling + large reduction process to fully break down the columnar crystals of the continuously cast billet and prepare for subsequent grain refinement. After descaling, the billet is heated to 1030~1080℃ before rolling begins. The roll speed is controlled at 2.50~3.50m / s, and the reduction rate of the last pass is controlled at ≥16.5%, and the reduction rate of the remaining passes is ≤14.0% to allow the steel plate to recrystallize fully. The final rolling temperature is 970~1020℃, and the thickness of the billet at the waiting temperature is (2.0~3.5)t, where t is the final product thickness. The billet is accelerated to cool during the waiting temperature period to promote the temperature gradient of the billet cross section. The cooling rate is 10.0~15.0℃ / s, and the cooling time is 12.0~17.0s. The second stage rolling starts at a rolling temperature of 780~830℃ and ends at a rolling temperature of 700~750℃.

[0043] Preferably, to eliminate internal stresses formed during steel plate rolling, regulate the precipitated phases in the steel plate, and prepare conditions for subsequent accelerated cooling, the rolled steel plate is relaxed, and straightening is performed during the relaxation process. Cooling:

[0044] The straightened steel plate is cooled using UFC, with an initial cooling temperature of 650~670℃ and a cooling rate of 15.0~20.0℃ / s, and the cooling is stopped when the temperature drops below 200℃.

[0045] Tempering:

[0046] In order to release the internal stress formed in the steel plate during the cooling process and to further form fine precipitates, the cooled steel plate is tempered at a temperature of 550~680℃ and a holding time of 1.50~2.50 min / mm.

[0047] The technical advantages of this invention are as follows:

[0048] (1) The present invention adopts a low carbon and low manganese chemical composition system to reduce the carbon equivalent of steel plate and the segregation tendency of continuous casting billet, and adds micro-alloying elements such as VN, Ti, and Mo to refine grains, accurately control the value of (Ti+V) / N, ensure the formation of precipitates during welding, and improve the purity of molten steel and the quality of continuous casting billet by adding elements such as La, Ca, and Mg, and form fine and dispersed oxide particles in steel to improve the comprehensive performance of steel plate in the thickness direction.

[0049] (2) In the smelting process, a high-yield addition process is adopted for elements such as La, Ca, and Mg. In the continuous casting process, a process of high superheat + strong secondary cooling water + electromagnetic stirring + light pressure is adopted to control the uniformity of the billet and obtain fine initial austenite grains.

[0050] (3) The continuous casting billet adopts a strong cooling + direct loading process to control grain growth and adjust the precipitates of the billet. The rolling process adopts the TMCP process based on two-stage controlled rolling. When the intermediate billet is waiting to be heated, an accelerated cooling process is adopted to reduce the waiting time, prevent grain growth, and form a larger temperature gradient on the billet cross section, so that the rolling deformation can better penetrate into the core of the steel plate. After rolling, the steel plate adopts relaxation + UFC cooling + tempering treatment. The final microstructure of the steel plate includes acicular ferrite and tempered sorbite, with precipitates of 40~60nm. The steel plate has excellent low-temperature toughness and can achieve preheating welding at -10℃. The welded joint of the steel plate has excellent mechanical properties. Detailed Implementation

[0051] The present invention will be further illustrated below through examples.

[0052] According to the component ratio of the technical solution, the embodiments of the present invention carry out smelting, continuous casting, heating in a heating furnace, rolling, online cooling, and tempering.

[0053] Reheating:

[0054] The continuous casting billet heating temperature is 1120℃~1250℃, the soaking temperature is 1100℃~1200℃, the soaking time is 0.30~0.50min / mm, and the total time in the furnace is 0.50~1.00min / mm.

[0055] Hot-rolled:

[0056] The billet is rolled into hot-rolled steel plate in two stages. The first stage of rolling adopts a high-temperature fast rolling + large reduction process. After descaling, the billet is heated to 1030~1080℃ before rolling. The roll speed is 2.50~3.50m / s. The reduction rate of the last pass is controlled to be ≥16.5%, and the reduction rate of the remaining passes is ≤14.0%. The final rolling temperature is 970~1020℃. The thickness of the billet under heating is (2.0~3.5)t, where t is the final product thickness. The second stage of rolling starts at 780~830℃ and ends at 700~750℃.

[0057] cool down:

[0058] The straightened steel plate is cooled using UFC, with an initial cooling temperature of 650~670℃ and a cooling rate of 15.0~20.0℃ / s, until it is cooled to below 200℃.

[0059] Tempering:

[0060] Tempering temperature 550~680℃, holding time 1.50~2.50min / mm.

[0061] Furthermore, after the first stage of rolling is completed, the billet is accelerated to cool while waiting for the temperature to rise, with a cooling rate of 10.0~15.0℃ / s and a cooling time of 12.0~17.0s.

[0062] Furthermore, after the second stage of rolling is completed, the rolled steel plate is relaxed, and straightening is performed during the relaxation process.

[0063] Further; smelting: including converter smelting, ladle refining, and RH treatment;

[0064] a) Converter smelting: Control the basicity of the molten steel in the converter to R = 3.00~4.00;

[0065] b) RH treatment: RH treatment time is 40~60min. Nitrogen is blown throughout the RH treatment process at a pressure of 660~680Pa. The [H] in the steel is controlled to be ≤1.5ppm, [O] to be ≤10ppm, and N to be 0.0300%~0.0450%. Ca and Mg treatments are carried out before the end of smelting, and La is added.

[0066] Further; continuous casting: molten steel is continuously cast to obtain the required billet. The tundish is superheated to 50~70℃, and the entire pouring process is protected. The casting speed is controlled at 0.70~1.20m / min, and the secondary cooling water ratio is 1.00~1.50m³. 3 / t, electromagnetic stirring is used in the later stage of continuous casting with a stirring current of 550~650A, and a light reduction process is used at the end of continuous casting with a reduction of 10.0~15.0mm.

[0067] Furthermore, after continuous casting, the billet is subjected to a strong cooling process, with an initial cooling temperature of 1050~1150℃ and a final cooling temperature of 400~500℃. Subsequently, the continuously cast billet enters a walking beam furnace for reheating.

[0068] The composition of the steel in this embodiment of the invention is shown in Table 1. The main process parameters for smelting and continuous casting of the steel in this embodiment of the invention are shown in Table 2. The main process parameters for cooling and reheating of the steel billet in this embodiment of the invention are shown in Table 3. The main process parameters for the first stage rolling of the steel in this embodiment of the invention are shown in Table 4. The main process parameters for the second stage rolling, cooling, and tempering of the steel in this embodiment of the invention are shown in Table 5. The microstructure of the steel in this embodiment of the invention is shown in Table 6. The mechanical properties of the steel in this embodiment of the invention are shown in Table 7. The weldability of the steel in this embodiment of the invention is shown in Table 8. The results of the oblique Y-shaped breakage test of the steel in this embodiment of the invention are shown in Table 9.

[0069] Table 1. Composition (wt%) of steel in embodiments of the present invention

[0070] C 0.062 0.023 0.031 0.044 0.053 0.049 0.027 0.038 0.058 0.066 Si 0.184 0.057 0.166 0.193 0.149 0.096 0.122 0.048 0.089 0.036 Mn 0.88 1.28 1.17 1.06 0.96 1.04 1.24 1.12 0.93 0.84 P 0.004 0.006 0.007 0.005 0.004 0.006 0.007 0.004 0.007 0.005 S 0.002 0.001 0.001 0.002 0.001 0.002 0.001 0.002 0.001 0.002 V 0.079 0.117 0.108 0.096 0.086 0.094 0.114 0.103 0.082 0.074 N 0.0333 0.0447 0.0438 0.0392 0.0362 0.0376 0.0428 0.0404 0.0347 0.0313 Cu 0.27 0.42 0.54 0.31 0.46 0.39 0.34 0.49 0.37 0.52 Ni 0.92 1.17 1.39 0.96 1.23 1.11 1.03 1.28 1.07 1.32 Mo 0.27 0.42 0.54 0.31 0.44 0.34 0.48 0.37 0.52 0.39 Ti 0.024 0.024 0.024 0.024 0.024 0.024 0.024 0.024 0.024 0.024 Als 0.027 0.018 0.032 0.018 0.033 0.022 0.037 0.024 0.037 0.028 La 0.0378 0.0558 0.0259 0.0604 0.0318 0.0683 0.0442 0.0747 0.0493 0.0769 Ca 0.0042 0.0051 0.0036 0.0054 0.0039 0.0044 0.0046 0.0049 0.0048 0.0052 Mg 0.0052 0.0044 0.0041 0.0054 0.0043 0.0047 0.0046 0.0057 0.0048 0.0059 (V+Ti) / N 3.09 3.15 3.01 3.06 3.04 3.14 3.22 3.14 3.05 3.13

[0071] Table 2 Main process parameters for steel smelting and continuous casting in the embodiments of the present invention.

[0072] 1 3.04 41 679 52 0.72 1.03 579 11.4 2 3.57 53 661 67 1.12 1.42 553 12.7 3 3.12 56 662 64 1.03 1.34 582 14.2 4 3.63 48 664 66 1.06 1.39 557 10.3 5 3.86 52 672 62 0.96 1.28 586 13.1 6 3.24 51 673 54 0.76 1.06 562 10.8 7 3.73 58 666 68 1.16 1.47 593 13.7 8 3.36 47 674 58 0.87 1.17 568 11.9 9 3.91 46 669 56 0.81 1.12 597 14.8 10 3.48 44 677 59 0.92 1.23 574 12.2

[0073] Table 3 Main process parameters for cooling and reheating of steel billets in embodiments of the present invention.

[0074] 1 1074 427 1176 1157 0.37 0.68 2 1092 448 1128 1109 0.48 0.96 3 1058 401 1192 1176 0.34 0.63 4 1107 459 1137 1111 0.46 0.87 5 1068 414 1204 1186 0.32 0.54 6 1113 467 1144 1124 0.43 0.82 7 1126 472 1228 1198 0.36 0.56 8 1134 483 1159 1133 0.41 0.76 9 1082 434 1242 1184 0.47 0.91 10 1146 492 1166 1142 0.39 0.72

[0075] Table 4. Main process parameters for the first stage rolling of steel in the embodiments of the present invention.

[0076] 1 60 1033 2.93 16.6 972 3.3t 10.2 16.8 2 55 1038 2.58 16.7 979 3.1t 10.7 16.3 3 45 1049 3.02 16.8 988 2.1t 11.8 15.3 4 55 1056 3.34 16.9 997 2.9t 12.2 14.1 5 60 1064 2.64 16.6 1004 2.3t 12.6 13.8 6 55 1053 3.11 17.0 992 2.2t 13.2 14.7 7 60 1068 2.73 16.8 1009 2.6t 13.6 13.3 8 45 1072 3.26 16.7 1013 2.7t 14.3 12.6 9 55 1078 2.84 16.9 1017 2.4t 14.8 12.2 10 60 1042 3.47 16.8 983 2.6t 11.3 15.6

[0077] Note: t is the thickness of the final product.

[0078] Table 5. Main process parameters for the second stage rolling, cooling, and tempering of steel in the embodiments of the present invention.

[0079] 1 786 708 652 17.1 618 1.94 2 792 713 664 15.3 607 2.06 3 798 716 657 19.2 678 1.58 4 808 729 669 17.6 594 2.14 5 812 733 666 15.7 626 1.88 6 783 704 654 18.4 578 2.27 7 817 739 659 16.2 644 1.76 8 824 742 668 18.7 566 2.38 9 828 747 661 16.8 659 1.64 10 804 722 663 19.9 553 2.46

[0080] Table 6. Microstructure of steel in embodiments of the present invention

[0081] 1 41.7 58.3 46 2 42.3 57.7 53 3 47.9 52.1 48 4 45.4 54.6 46 5 48.2 51.8 53 6 46.9 53.1 54 7 43.6 56.4 52 8 40.7 59.3 49 9 48.8 51.2 59 10 44.8 55.2 47

[0082] Table 7 Mechanical properties of steel in the embodiments of the present invention

[0083] 1-Horizontal 524 626 29.5 292 269 1-Vertical 508 615 31.0 312 280 2-Horizontal 536 633 31.0 308 268 2-Vertical 527 631 31.5 321 277 3-Horizontal 506 610 30.0 294 256 3-Vertical 498 609 30.5 319 279 4-Horizontal 518 639 28.0 300 262 4-Vertical 507 618 28.5 314 270 5-Horizontal 514 627 27.5 296 258 5-Vertical 496 613 28.0 320 275 6-Horizontal 527 634 27.5 301 261 6-Vertical 514 629 29.0 315 270 7-Horizontal 508 621 29.5 291 268 7-Vertical 497 608 29.5 323 279 8-Horizontal 537 649 27.5 304 263 8-Vertical 523 634 28.0 318 278 9-Horizontal 514 630 29.0 302 256 9-Vertical 502 625 30.5 329 273 10-Horizontal 513 632 28.0 297 262 10-Vertical 498 624 28.5 316 265

[0084] Table 8 Welding properties of the steel in the embodiments of the present invention

[0085] 1-1 637 -10 15 196 166 210 2-1 645 -10 15 194 177 206 3-1 626 -10 15 195 181 210 4-1 642 -10 15 191 171 207 5-1 638 -10 15 201 180 204 6-1 644 -10 15 196 165 205 7-1 637 -10 15 189 170 218 8-1 654 -10 15 194 166 215 9-1 649 -10 15 193 168 213 10-1 636 -10 15 206 179 220 1-2 632 -10 50 207 175 223 2-2 647 -10 50 204 188 219 3-2 628 -10 50 201 179 221 4-2 646 -10 50 199 180 205 5-2 639 -10 50 194 175 210 6-2 641 -10 50 198 173 209 7-2 639 -10 50 205 169 212 8-2 644 -10 50 203 168 214 9-2 648 -10 50 209 166 210 10-2 649 -10 50 206 167 205

[0086] Table 9 Results of the steel oblique Y-shaped break test in the embodiments of the present invention

[0087] 1 -10 0 0 0 2 -10 0 0 0 3 -10 0 0 0 4 -10 0 0 0 5 -10 0 0 0 6 -10 0 0 0 7 -10 0 0 0 8 -10 0 0 0 9 -10 0 0 0 10 -10 0 0 0

[0088] The microstructure of the steel plate produced using this invention comprises ferrite and tempered sorbite, with ferrite comprising 40%~50% and tempered sorbite 50%~60%. The average size of the precipitated phases in the steel plate is 40~60 nm. The yield strength of the steel plate is 490~540 MPa, the tensile strength is 600~650 MPa, the elongation after fracture is ≥27.5%, the impact energy at -80℃ is ≥250 J, the tensile strength of the steel plate after welding at -10℃ is 630~650 MPa, and the impact energy at -60℃ in the weld heat-affected zone is ≥160 J.

[0089] To illustrate the present invention, the present invention has been appropriately and sufficiently described above through embodiments. The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A 460MPa grade steel plate that requires no preheating for welding in a low-temperature environment, characterized in that, The elemental composition of the steel plate, by mass percentage, is as follows: C: 0.02%~0.07%, Si: 0.03%~0.20%, Mn: 0.80%~1.30%, P≤0.008%, S≤0.002%, V: 0.07%~0.12%, N: 0.030%~0.045%, Cu: 0.25%~0.55%, Ni: 0.90%~1.40%, Mo: 0.25%~0.55%, Ti: 0.02%~0.06%, Als: 0.015%~0.040%, La: 0.025%~0.085%, Ca: 0.0035%~0.0055%, Mg: 0.004%~0.006%, with the balance being Fe and unavoidable impurities. In steel plates, the ratio of (V+Ti) / N is 3.1~3.

9. The method for manufacturing a 460MPa grade steel plate that does not require preheating welding in a low-temperature environment includes smelting, continuous casting, heating in a heating furnace, rolling, online cooling, and tempering. Reheating: The continuous casting billet heating temperature is 1120℃~1250℃, the soaking temperature is 1100℃~1200℃, the soaking time is 0.3~0.5min / mm, and the total time in the furnace is 0.5~1min / mm; Hot-rolled: The billet is rolled into hot-rolled steel plate in two stages. The first stage rolling adopts a high-temperature fast rolling + large reduction process. After descaling, the billet is heated to 1030~1080℃ before rolling. The roll speed is 2.5~3.5m / s. The reduction rate of the last pass is controlled to be ≥16.5%, and the reduction rate of the remaining passes is ≤14%. The final rolling temperature is 970~1020℃. The thickness of the billet after heating is (2.0~3.5)t, where t is the final product thickness. The second stage rolling starts at 780~830℃ and ends at 700~750℃. cool down: The straightened steel plate is cooled using UFC, with an initial cooling temperature of 650~670℃, a cooling rate of 15~20℃ / s, and cooling to below 200℃. Tempering: Tempering temperature 550~680℃, holding time 1.5~2.5min / mm.

2. The 460MPa grade steel plate for low-temperature environment preheating welding according to claim 1, characterized in that, The microstructure of the steel plate includes ferrite and tempered sorbite, with ferrite accounting for 40%~50% and tempered sorbite accounting for 50%~60%; the average size of the precipitated phases in the steel plate is 40~60 nm.

3. The 460MPa grade steel plate for low-temperature environment preheating welding according to claim 1, characterized in that, The steel plate has a yield strength of 490~540MPa, a tensile strength of 600~650MPa, an elongation after fracture of ≥27.5%, an impact energy of ≥250J at -80℃, a tensile strength of 630~650MPa after welding at -10℃, and an impact energy of ≥160J at -60℃ in the weld heat-affected zone.

4. The 460MPa grade steel plate for low-temperature environment preheating welding according to claim 1, characterized in that, After the first stage of rolling is completed, the billet is accelerated to cool while waiting for the temperature to rise. The cooling rate is 10~15℃ / s and the cooling time is 12~17s.

5. A 460MPa grade steel plate for low-temperature environment preheating welding according to claim 1, characterized in that, After the second stage of rolling is completed, the rolled steel plate is relaxed and straightened during the relaxation process.

6. A 460MPa grade steel plate for low-temperature environment preheating welding according to claim 1, characterized in that, Smelting: including converter smelting, ladle refining, and RH treatment; a) Converter smelting: Control the basicity of converter steel R=3~4; b) RH treatment: RH treatment time is 40~60min. Nitrogen is blown throughout the RH treatment process at a pressure of 660~680Pa. The [H] in the steel is controlled to be ≤1.5ppm, [O] to be ≤10ppm, and N to be 0.030%~0.045%. Ca and Mg treatments are carried out before the end of smelting, and La is added.

7. A 460MPa grade steel plate for low-temperature environment preheating welding according to claim 1, characterized in that, Continuous casting: Molten steel is continuously cast to obtain the required billet. The tundish is superheated to 50~70℃, and the entire pouring process is protected. The casting speed is controlled at 0.7~1.2m / min, and the secondary cooling water volume is 1~1.5m³ / min. 3 / t, electromagnetic stirring is used in the later stage of continuous casting with a stirring current of 550~650A, and a light reduction process is used at the end of continuous casting with a reduction of 10~15mm.

8. A 460MPa grade steel plate for low-temperature environment preheating welding according to claim 7, characterized in that, After continuous casting, the billet is subjected to a strong cooling process, with an initial cooling temperature of 1050~1150℃ and a final cooling temperature of 400~500℃. The billet is then placed in a walking beam furnace for reheating.