A steel plate for construction in marine environment and its production method

Abstract

The invention discloses a steel plate for construction in a marine environment and a production method thereof. The steel grade comprises C:≤0.02wt%, Si: 0.15-0.3wt%, Mn: 0.4-0.6wt%, V: 0.03-0.05wt%, N: 0.008-0.012wt%, Cu: 0.5-0.8wt%, Ni: 1-2wt%, W: 0.05-0.1wt%, Re: 0.01-0.02wt%, Nb: 0.01-0.02wt%, Cr: 1-1.5wt%, REM: 0.03-0.05wt%, Sn: 0.05-0.1wt%, Ti: 0.001-0.005wt%, P: 0.015-0.025wt%, and S:≤0.005wt%. The production method includes cold charging the steel billet into the furnace at a temperature of ≤200°C, adopting multi-stage heating; the starting rolling temperature is 1110-1140°C, the pass interval is ≤6s, the pass reduction is 10-20%, the final rolling temperature is 910-950°C, and stacking or heat preservation treatment is adopted after air cooling off the line, and the heat preservation temperature is controlled at 300-500°C. The present invention solves the problems of generally low fracture resistance and low safety of weathering steel in the existing marine environment and difficulty in welding of high-strength steel.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material preparation, and particularly relates to a steel plate for construction in a marine environment and a production method thereof. Background Art

[0002] The corrosion of marine steel materials causes nearly 1 trillion yuan of economic losses to the country every year. Taking the selection of materials for infrastructure construction facilities on islands and reefs in the South China Sea as an example, due to the unique near-coastal environment of islands and reefs in the South China Sea, which is extremely corrosive, according to the ISO9223 classification standard, the corrosion level of materials in such high humidity, high salt, and high radiation areas can reach the highest level C5. Compared with other areas, steel structure buildings serving in this environment will suffer from severe corrosion prematurely even if corrosion protection measures are taken. According to statistics, the failure rate of steel structure buildings in service in the South China Sea is three times that of other sea areas and about 10 times that of mainland areas. In addition, for building structures, the safety of the structure itself is also crucial (generally requiring a lower yield strength ratio and fire resistance). At present, the inventions of steel materials related to this environment are mostly focused on improving the corrosion resistance of materials. The invention patent with application number CN201710075154.0 and name "A high corrosion-resistant low-alloy steel suitable for high-temperature coastal environment" has better corrosion resistance than Q235 carbon steel and other weathering steels. Due to the use of a high Ni system (up to 3.5%) and alloying with elements such as Cu and Mo, the problem is that the cost is high, and due to the high alloying and carbon equivalent, it brings difficulties to the selection of welding materials and the guarantee of weldability; the invention patent with application number CN201611097512.X and name "A high-strength weathering steel resistant to high-humidity and heat marine atmosphere environment" and the invention patent with application number CN201611102046.X and name "High-strength weathering steel resistant to high-humidity and heat marine atmosphere environment and preparation method" also use a high-alloy component system based on 3.5% Ni, with high fracture sensitivity, an impact energy of 55J at 30°C, and low impact fracture resistance. In addition, the corrosion resistance of the material is not much improved compared with existing materials.

[0003] At present, the above steel materials cannot solve the structural safety problem required by building structures. Existing weather-resistant and fire-resistant building steels cannot meet the corrosion problem under harsh marine conditions (high salt, high humidity and heat), such as the invention patent with application number CN201810558218.7, named "A Cu precipitation enhanced high-strength fire-resistant and corrosion-resistant steel and its manufacturing method". Therefore, for building steel under harsh marine service conditions, there are problems such as high cost, low fracture resistance, poor safety, and poor weldability. Therefore, there is currently no suitable steel for building structures under harsh marine conditions. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a steel plate for construction in a marine environment and a production method thereof, so as to solve the problems of low fracture resistance, poor safety and weldability of corrosion-resistant steel in the existing harsh marine environment.

[0005] In order to solve the above problems, the technical solution adopted by the present invention is as follows: a steel plate for construction in a marine environment, wherein the steel composition comprises, by weight percentage, C: ≤ 0.02wt%, Si: 0.15-0.3wt%, Mn: 0.4-0.6wt%, V: 0.03-0.05wt%, N: 0.008-0.012wt%, Cu: 0.5-0.8wt%, Ni: 1-2wt%, W: 0.05-0.1wt%, Re: 0.01-0.02wt%, Nb: 0.01-0.02wt%, Cr: 1-1.5wt%, REM: 0.03-0.05wt%, Sn: 0.05 -0.1wt%, Ti: 0.001-0.005wt%, P: 0.015-0.025wt%, S: ≤0.005wt%, the balance is Fe and unavoidable impurities; the average grain size of the steel plate is 18-38μm, containing 50-60% bainite + 20-30% ferrite structure, and the percentage is area percentage; it contains V (C, N) or WC, Nb (C, N), Cr6C, Fe3C nanophases with an average size of 20-30nm dispersed precipitation, and the average spacing of these precipitated phases is 1-2μm; it contains Cu nanophases with an average size of 62-75nm, and the average spacing of the Cu nanophases is 1.5-2μm.

[0006] Furthermore, the dispersed and precipitated V(C, N) or WC, Nb(C, N), Cr6C, Fe3C nanophase size is 10-50nm, and the Cu nanophase size is 50-100nm.

[0007] Furthermore, the yield strength of the steel plate at room temperature is 380-420 MPa, the yield strength ratio is ≤0.8, the impact energy at -50°C is not less than 150 J, the elongation is ≥20%, and the area reduction is ≥70%.

[0008] Furthermore, the yield strength of the steel plate at 600°C is 360-400MPa, the yield strength ratio is ≤0.8, the impact energy at -50°C is not less than 150J, the elongation is ≥20%, and the area reduction is ≥70%.

[0009] Furthermore, under the condition of 60KJ line energy, the tensile strength of the steel plate welded joint is 495-525MPa, and the impact energy at -40℃ is not less than 150J.

[0010] Furthermore, the corrosion rate of the steel plate is less than 0.03 g / m 2 .h.

[0011] The present invention provides a method for producing a steel plate for construction in a marine environment, including smelting, continuous casting, billet heating, controlled rolling and offline processing, the specific contents of which are as follows:

[0012] Billet heating: The billet is cold loaded into the furnace at a temperature of ≤200°C, and multi-stage heating is adopted, wherein the total time at 600-950°C is controlled within 0.1-0.2min / mm, the total time at 1180-1200°C is controlled within ≤0.1min / mm, and the total time at 1150-1180°C is controlled within 0.2-0.4min / mm;

[0013] Controlled rolling: high temperature direct rolling, starting rolling temperature 1110-1140℃, pass interval ≤6s, average pass reduction 10-20%, final rolling temperature 910-950℃, air cooling of the rolled steel plate off the line;

[0014] Off-line treatment: After the steel plate is air-cooled off the line, it is stacked or heat-insulated to regulate the precipitation phase and internal stress, and the insulation control temperature is 300-500℃.

[0015] Furthermore, the steel billet is made by converter smelting + continuous casting, and cooling begins when the surface temperature of the steel billet is 800-850°C, and the cooling rate is controlled at 2-10°C / s, followed by stacking treatment or low-temperature heating treatment, wherein the low-temperature heating temperature is controlled at 180-200°C.

[0016] Furthermore, the steel is smelted in a converter, the weight percentage of Ti element in the molten iron is controlled below 0.005%, and Si and Mn are used for deoxidation.

[0017] The steel plate for construction in marine environment produced according to the above scheme has the following beneficial effects:

[0018] 1. The corrosion resistance of steel plates is greatly improved through the addition and synergistic effect of composite trace elements. The corrosion rate of the on-site hanging piece near the coast of the South China Sea for 4 years is less than 0.03g / m 2 .h, the corrosion resistance is 32% higher than the current best 3.5Ni weathering steel system.

[0019] 2. It has good comprehensive mechanical properties, structural safety and weldability, yield strength 380 ~ 420MPa (room temperature), yield strength 360 ~ 400MPa (under 600℃), yield strength ratio ≤ 0.8, impact energy at -50℃ not less than 150J; elongation ≥ 20%, surface shrinkage ≥ 70%.

[0020] 3. Under the condition of 60KJ line energy, the tensile strength of the welded joint can be controlled at 495~525MPa, and the impact energy at -40℃ is ≥150J. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other examples improved or modified by ordinary technicians in this field belong to the scope of protection of the present invention. It should be understood that the embodiments of the present invention are only used to illustrate the technical effects of the present invention, rather than to limit the scope of protection of the present invention.

[0022] The present invention develops a low-cost solution for 360-400MPa low-alloy steel with good safety service performance and weldability through the micro-alloying compounding effect of elements such as Sn, Re, REM, N, Cr, V, and W, to solve the problems of generally low fracture resistance and low safety of existing harsh environment weathering steels and difficult welding of high-strength steels.

[0023] The steel composition of the present invention will be described in detail below. Unless otherwise specified, the content of each element is expressed in % by weight.

[0024] A steel plate for construction in a marine environment, wherein the steel composition comprises, by weight percentage, C: ≤0.02wt%, Si: 0.15-0.3wt%, Mn: 0.4-0.6wt%, V: 0.03-0.05wt%, N: 0.008-0.012wt%, Cu: 0.5-0.8wt%, Ni: 1-2wt%, W: 0.05-0.1wt%, Re: 0.01-0.02wt%, Nb: 0.01-0.02wt%, Cr: 1-1.5wt%, REM: 0.03-0.05wt%, Sn: 0.05-0.1wt%, Ti: 0.001-0.005wt%, P: 0.015-0.025wt%, S: ≤0.005wt%, and the balance is Fe and unavoidable impurities.

[0025] C: ≤0.02wt%

[0026] The C element is the main phase transformation controlling element for forming a corrosion-resistant structure with 50-60% area percentage of bainite + 20-30% area percentage of ferrite as the matrix, and is an important element for ensuring the strength of the steel grade. Appropriate C promotes the formation of the important tiny cathode phase V (C, N) in the present invention, and controls the precipitation of large carbides of Cr, indirectly improving the corrosion resistance of the steel. Under the component system of the present invention, more C is not good for the corrosion resistance and weldability of the steel, so the C content should be ≤0.02wt%.

[0027] Si: 0.15-0.3wt%

[0028] The Si element plays a certain role in strengthening. In addition, it forms surface oxides with Cu and Sn, effectively improving corrosion resistance. It is one of the important deoxidizers of the present invention. However, too high Si will reduce the density of the rust layer on the surface of the steel, so the Si content is controlled at 0.15-0.3wt%.

[0029] Mn: 0.4-0.6wt%

[0030] The Mn element plays a certain role in strengthening. In the system of the present invention, Mn can be infinitely dissolved with Fe in the austenite state. Too much Mn will reduce the solid solution effect of corrosion-resistant elements such as V and Cu, affecting their scale and distribution control. In addition, Mn is one of the important deoxidizers of the present invention, so the Mn content is controlled at 0.4-0.6wt%.

[0031] Nb: 0.01-0.02wt%

[0032] An appropriate amount of Nb helps to further improve the toughness of steel and promote corrosion resistance, but too much will reduce the alloying effect of the above elements, and it needs to be controlled at 0.01-0.02wt%.

[0033] V: 0.03-0.05wt%

[0034] The V element plays an important role in the toughness and corrosion resistance of steel mainly in the form of precipitation strengthening. The role of V in the present invention is mainly to form V (C, N) with C and N in appropriate proportions. Since the steel material is a multiphase structure formed by multi-element alloying, the control of the cathode ratio in the micro-region is very important. The refined, dispersed, uniform and distributed cathode design is very important for controlling the corrosion resistance of the complex structural system of the steel material. Based on this, the present invention adopts a trace amount of 0.03-0.05wt%. This is mainly because in the component design of the multi-element system, solid solution elements such as Cr that are infinitely soluble in α-Fe are added, so the solid solubility of V is reduced, and it mainly plays a role in controlling the cathode phase. Under the configuration of V, C, N and Cr elements adopted in the present invention, it will promote the formation of 10-50nm (average size 20-30nm) dispersed precipitation V (C, N) and Fe3C in the steel matrix, and the average spacing between these phases is 1-2μm. In addition, the solid solution of V has the effect of compacting the rust layer, which helps to improve the welding process window of the steel and improve the welding performance of the heat affected zone after welding, especially the toughness. Based on the above design, the content of V is 0.03-0.05wt%.

[0035] N: 0.008-0.012wt%

[0036] The N element mainly promotes the precipitation of V (C, N) and Fe3C. In addition, the solid-dissolved N helps to improve the corrosion resistance of the steel. Therefore, the N content of the present invention is controlled at 0.008-0.012 wt%.

[0037] Cu: 0.5-0.8wt%

[0038] Cu is an important corrosion-resistant and toughening element in the present invention. It has the function of compacting the rust layer. When the steel plate surface is initially corroded, a Cu-enriched layer and an oxide layer are formed, which increases the potential of the near-surface matrix and prevents Cl - Intrusion, in addition, a Cu nanophase of 50-100nm (average size 62-75nm) is formed inside the steel plate, and the average spacing between the phases is 1.5-2μm. After the surface rust layer is destroyed, a large number of fine cathode phases are further formed to form a unique cathode size and distribution control system with V (C, N) and Fe3C, which controls the corrosion rate and helps to improve and control the weldability. Excessive Cu is not conducive to corrosion resistance and increases unnecessary costs. Therefore, the Cu content of the present invention is controlled at 0.5-0.8wt%.

[0039] Ni: 1-2wt%

[0040] The main function of Ni is to balance the toughness of weathering steel. In terms of corrosion resistance, it promotes the positive movement of the self-corrosion potential on the steel surface. The present invention adopts a low Mn component design so that Ni can more effectively promote the formation of Fe3O4 oxides, and Ni in the rust layer 2+ It can more effectively occupy the interstitial position of Fe3O4, forming a stable and dense intermetallic compound of Fe and Ni, as well as an enriched layer of Ni, Sn and V, preventing Cl - Diffusion into the matrix reduces acidification and increases the pH value of the electrolyte in the rust layer, so that only 1-2wt% Ni can fully achieve corrosion resistance. Too high Ni will increase the strength of the material and reduce plasticity.

[0041] W: 0.05-0.1wt%

[0042] W: It has the function of compacting rust layer, and WO4 is produced by the anodic reaction of steel 2- Dissolved, WO4 on the rust layer 2- The distribution produces ion selection to resist the corrosion-promoting factor Cl - In addition, W and C generate 10-50nm WC, which helps to improve the low and high temperature stability of the dispersed phase of V and Cu, and helps to improve the fire resistance of steel. Too high W will deteriorate the toughness, so it is controlled at 0.05-0.1wt%.

[0043] Re: 0.01-0.02wt%

[0044] Rhenium is evenly distributed in the dendrite trunk and between dendrites during the solidification process. It is an important solid solution strengthening element with the function of dense rust layer, which can effectively improve the fire resistance of steel. Its corrosion potential is about 0.3V, which can make the corrosion potential positively shift, effectively improve the corrosion potential of the matrix, reduce the corrosion current, and thus improve the corrosion resistance of steel. In addition, the right amount of Re combined with Ni and Cu can effectively promote anode passivation and improve cathode efficiency. Since the anode current in the passivation zone is several orders of magnitude smaller than the current of activation and dissolution, it is very effective to use cathodic elements to improve the corrosion resistance of the alloy. The addition of Re helps to improve the low-temperature and high-temperature stability of the dispersed phase of V and Cu, thereby improving the fire resistance of steel. In addition, the compound addition of Re and V, Ni can effectively control the toughness control problem caused by the addition of elements such as Sn, which helps to improve the welding process window of steel and improve the welding performance of the heat-affected zone after welding, especially the toughness. Therefore, it is controlled at 0.01-0.02wt%.

[0045] Cr: 1-1.5wt%

[0046] Cr; on the one hand, it plays the role of dense rust layer, on the other hand, it forms a passive oxide, which together with other oxides and dense α-FeOOH resists Cl - In the high humidity and heat marine atmosphere environment, the pH value is weakly alkaline, and the Cr oxide can be effectively protected; in addition, Cr is fully dissolved in ferrite and bainite, which indirectly controls the thermodynamic and kinetic changes of V (C, N), and is also beneficial to improving the fire resistance of the material under the alloy system. According to the environmental requirements, the Cr of the present invention is controlled at 1-1.5wt%.

[0047] REM: 0.03-0.05wt%

[0048] REM rare earth elements, on the one hand, can change the size of cathode phases such as V (C, N), increase their dispersion, increase their potential, and reduce their cathode effect. On the other hand, due to their content of 0.03-0.05wt%, they are fully dissolved in the matrix, which plays a role in increasing the matrix potential and directly produces corrosion resistance, which helps to improve the welding process window of steel and improve the welding performance of the heat-affected zone after welding, especially the toughness.

[0049] Sn: 0.05-0.1wt%

[0050] Sn, on the one hand, lowers the energy level of steel in the form of single substance solid solution and weakens the electrochemical activity of steel; it helps to form oxides such as SnO and deposit on the corrosion front, promotes the formation of α-FeOOH, and compacts the oxide layer together with α-FeOOH; when dissolved with Fe, ionic Sn can react with Cl -A certain amount of Sn helps maintain the low temperature toughness of steel and improves its fire resistance, but too much Sn will reduce the impact toughness of the material. According to environmental requirements, the Sn content of the present invention is controlled at 0.05-0.1wt%.

[0051] Ti: 0.001-0.005wt%

[0052] The Ti element helps to control the initial grain size, but too much will consume the N element, affecting the strength and corrosion resistance of the steel. Therefore, the Ti content of the present invention is controlled within 0.001-0.005 wt%.

[0053] P: 0.015-0.025wt%

[0054] The P element is mainly used to reduce the degree of anode polarization, promote the uniform dissolution of steel and accelerate the oxidation rate of iron, promote the formation of non-static protective film, and cooperate with Re, Cu, etc. to resist Cl - However, too much P reduces the weldability of the steel, so the P in the present invention is controlled at 0.015-0.025wt%.

[0055] S: ≤0.005wt%

[0056] Sulfides formed by the sulfur element accelerate corrosion. Too much sulfur has an adverse effect on the toughness of the material, so it needs to be strictly controlled to ≤0.005wt%.

[0057] In addition to the above-mentioned steel components, the balance of the present invention may be Fe and inevitable impurities. Inevitable impurities are impurities that are not artificially mixed in the general steel manufacturing process. They cannot be completely excluded, and the meaning can be easily understood by those skilled in the art of general steel manufacturing. In addition, the present invention does not completely exclude the addition of other components in addition to the above-mentioned steel components.

[0058] The microstructure of the present invention will be described in further detail below.

[0059] The steel plate for construction in marine environment of the present invention has an average grain size of 18-38 μm, contains 50-60% bainite + 20-30% ferrite corrosion-resistant structure, the percentage is area percentage; contains dispersed precipitated V (C, N) / or WC, Nb (C, N), Cr6C, Fe3C nanophases, the size of these precipitated phases is 10-50nm, the average size is 20-30nm, and the average spacing is 1-2 μm; contains dispersed precipitated Cu nanophases, the size is 50-100nm, the average size is 62-75nm, and the average spacing is 1.5-2 μm. The main purpose is to take into account the matching of corrosion resistance, fire resistance and mechanical properties of the material, and the precipitation of the dispersed phase is conducive to the uniform corrosion of the matrix.

[0060] The production process of the present invention is described in further detail below.

[0061] The present invention provides a method for producing a steel plate for construction in a marine environment, including smelting, continuous casting, billet heating, controlled rolling and offline processing, the specific contents of which are as follows:

[0062] Smelting: The steel is smelted in a converter, and Si and Mn are used for deoxidation. The use of Al is strictly controlled because the addition of Al will consume the N element and have a harmful effect on the surface quality of the steel billet. Similarly, the introduction of the Ti element in the molten iron should also be strictly controlled (controlled to below 0.005%), which affects the precipitation effect of V, Nb, W and Cu, and avoids the formation of Ti, Al and other carbonitrides, which is not conducive to corrosion resistance.

[0063] Continuous casting: In order to control the initial surface grain size of the continuous casting billet and the solid distribution of corrosion-resistant elements such as Re and W on the surface, the billet is pre-treated by rapid cooling. The billet surface temperature starts to cool at 800-850℃, and the cooling rate is controlled at 2-10℃ / s. After that, it is not suitable for hot charging, and stacking treatment or low-temperature heating treatment is required, in which the low-temperature heating temperature is controlled at 180-200℃ to control the surface quality and thermal stress distribution of the billet, and control the initiation and expansion of surface cracks and stress cracks on the billet.

[0064] Billet heating: The temperature of the billet cold-charged into the furnace is controlled at ≤200℃, and multi-stage heating is adopted, in which the total time of 600-950℃ is controlled within 0.1-0.2min / mm, the total time of 1180-1200℃ is controlled within 0.1min / mm, and the total time of 1150-1180℃ is controlled within 0.2-0.4min / mm. The purpose is to control the initial distribution of alloy elements before hot working, control the distribution and composition of grains, especially grain boundaries, and regulate mechanical and corrosion resistance.

[0065] Controlled rolling: high temperature direct rolling is adopted, the starting rolling temperature is 1110-1140℃, the interval between passes is ≤6s, the average reduction of each pass is 10-20%, and the final rolling temperature is 910-950℃. The steel plate is air-cooled after rolling and the grain size is controlled at 18-38μm. In this process, 50-60% bainite + 20-30% ferrite is formed in the steel as the matrix corrosion-resistant structure and a part of the dispersed precipitation of V(C, N) (or WC, Nb(C, N)), Cr6C, Fe3C and part of Cu nanophase.

[0066] Off-line treatment: After the steel plate is air-cooled and off-line, the second stage precipitation phase and internal stress are regulated by stacking or heat preservation treatment. The heat preservation temperature is 300-500℃, which promotes the formation of V(C, N) (or WC, Nb(C, N)), Cr6C, Fe3C nanophases with a size of 10-50nm (average size 20-30nm) dispersed precipitation in the steel matrix, and the average spacing of these phases is 1-2μm. At the same time, there are 50-100nm (average size 62-75nm) Cu nanophases in the matrix, and the average spacing of the phases is 1.5-2μm.

[0067] According to the above steel composition and production process, the actual smelting composition of the present invention is shown in Table 1, the actual process parameters and structure of the present invention are shown in Tables 2-4, and the actual properties are shown in Tables 5-9.

[0068] Table 1 Composition of each example / wt%

[0069] C Si Mn V N Cu Ni W Re Cr REM Sn Nb P S Ti 1 0.01 0.15 0.55 0.031 0.011 0.8 1.1 0.07 0.02 1.32 0.03 0.06 0.01 0.015 0.001 0.003 2 0.02 0.16 0.45 0.037 0.008 0.79 1.2 0.09 0.013 1.44 0.04 0.05 0.02 0.018 0.002 0.004 3 0.015 0.15 0.54 0.036 0.009 0.62 1.43 0.1 0.02 1.36 0.04 0.07 0.01 0.02 0.003 0.002 4 0.01 0.29 0.41 0.042 0.012 0.5 2 0.08 0.02 1.5 0.05 0.09 0.02 0.025 0.002 0.005 5 0.02 0.2 0.43 0.05 0.009 0.55 1.9 0.09 0.02 1.1 0.04 0.1 0.02 0.02 0.003 0.003 6 0.005 0.17 0.42 0.032 0.008 0.63 1.75 0.08 0.02 1.27 0.05 0.1 0.01 0.024 0.002 0.004 7 0.02 0.18 0.41 0.04 0.009 0.67 1.82 0.05 0.019 1.33 0.03 0.05 0.02 0.016 0.002 0.003 8 0.02 0.25 0.45 0.032 0.01 0.73 1.22 0.07 0.02 1.46 0.03 0.09 0.01 0.022 0.003 0.002 9 0.01 0.20 0.59 0.041 0.008 0.69 1.34 0.09 0.014 1.47 0.04 0.06 0.02 0.02 0.001 0.001 10 0.005 0.16 0.56 0.032 0.012 0.75 1.56 0.1 0.02 1.5 0.03 0.1 0.02 0.017 0.003 0.004 11 0.005 0.17 0.46 0.035 0.011 0.63 1.72 0.09 0.012 1.45 0.03 0.1 0.01 0.019 0.002 0.005 12 0.01 0.22 0.55 0.04 0.012 0.77 1.21 0.06 0.017 1.3 0.03 0.08 0.02 0.022 0.001 0.003

[0070] Table 2 Billet pretreatment

[0071]

[0072] Table 3 Heating process

[0073]

[0074]

[0075] Table 4 Rolling process

[0076]

[0077] Table 5 Steel plate microstructure ratio

[0078]

[0079] Table 6 Mechanical properties of the examples

[0080]

[0081]

[0082] Table 7 Welding performance of the embodiment (line energy 60KJ, submerged arc welding)

[0083]

[0084] Table 8 Fire resistance performance of the examples

[0085]

[0086] Table 9 Corrosion resistance of the examples

[0087] <![CDATA[Average corrosion rate of coupons in the coastal waters of the South China Sea for 4 years (g / m 2 .h)]]> Comparative Example (3.5Ni system) 0.037 Example 1 0.025 Example 2 0.018 Example 3 0.024 Example 4 0.023 Example 5 0.021 Example 6 0.022 Example 7 0.023 Example 8 0.022 Example 9 0.024 Example 10 0.021 Embodiment 11 0.022 Example 12 0.021

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A steel plate for construction in marine environment, characterized in that: The steel composition includes C:≤0.02wt%, Si: 0.15-0.3wt%, Mn: 0.4-0.6wt%, V: 0.03-0.05wt%, N: 0.008-0.012wt%, Cu: 0.5-0.8wt%, Ni: 1-2wt%, W: 0.05-0.1wt%, Re: 0.01-0.02wt%, Nb: 0.01-0.02wt%, Cr: 1-1.5wt%, REM: 0.03-0.05wt%, Sn: 0.05-0.1wt%, Ti: 0.001-0.005wt%, P: 0.015-0.025wt%, S:≤0.005wt%, and the balance is Fe and unavoidable impurities; The steel plate has an average grain size of 18-38 μm, contains 50-60% bainite + 20-30% ferrite structure, and the percentages are area percentages; contains V (C, N) or WC, Nb (C, N), Cr6C, Fe3C nanophases with an average size of 20-30 nm dispersed precipitation, and the average spacing of these precipitated phases is 1-2 μm; contains Cu nanophases with an average size of 62-75 nm, and the average spacing of the Cu nanophases is 1.5-2 μm.

2. The steel plate for construction in marine environment according to claim 1, characterized in that: The size of the dispersed precipitated V(C, N) or WC, Nb(C, N), Cr6C, Fe3C nanophase is 10-50nm, and the size of the Cu nanophase is 50-100nm.

3. The steel plate for construction in marine environment according to claim 1, characterized in that: The yield strength of the steel plate under room temperature conditions is 380-420MPa, the yield strength ratio is ≤0.8, the impact energy at -50℃ is not less than 150J, the elongation is ≥20%, and the area reduction is ≥70%.

4. The steel plate for construction in marine environment according to claim 1, characterized in that: The yield strength of the steel plate at 600℃ is 360~400MPa, the yield strength ratio is ≤0.8, the impact energy at -50℃ is not less than 150J, the elongation is ≥20%, and the area reduction is ≥70%.

5. The steel plate for construction in marine environment according to claim 1, characterized in that: Under the condition of 60KJ linear energy, the tensile strength of steel plate welded joints is 495~525MPa, and the impact energy at -40℃ is not less than 150J.

6. The steel plate for construction in marine environment according to claim 1, characterized in that: The corrosion rate of steel plate is less than 0.03g / m 2 .h.

7. A method for producing a steel plate for construction in a marine environment according to any one of claims 1 to 6, characterized in that: It includes smelting, continuous casting, billet heating, controlled rolling and offline processing. The specific contents are as follows: Billet heating: The billet is cold loaded into the furnace at a temperature of ≤200°C, and multi-stage heating is adopted, wherein the total time at 600-950°C is controlled within 0.1-0.2min / mm, the total time at 1180-1200°C is controlled within ≤0.1min / mm, and the total time at 1150-1180°C is controlled within 0.2-0.4min / mm; Controlled rolling: high temperature direct rolling, starting rolling temperature 1110-1140℃, pass interval ≤6s, average pass reduction 10-20%, final rolling temperature 910-950℃, air cooling of the rolled steel plate off the line; Off-line treatment: After the steel plate is air-cooled off the line, it is stacked or heat-insulated to regulate the precipitation phase and internal stress, and the insulation control temperature is 300-500℃.

8. The method for producing steel plates for construction in marine environments according to claim 7, characterized in that: The steel billet is made by converter smelting + continuous casting. The steel billet starts to cool when the surface temperature is 800-850°C, and the cooling rate is controlled at 2-10°C / s. Then, stacking treatment or low-temperature heating treatment is adopted, wherein the low-temperature heating temperature is controlled at 180-200°C.

9. The method for producing steel plates for construction in marine environments according to claim 7, characterized in that: The steel is smelted in a converter, the weight percentage of Ti element in molten iron is controlled below 0.005%, and Si and Mn are used for deoxidation.

Images