Steel plate for marine environment coating and production method thereof

Abstract

The invention discloses a steel plate for marine environment coating and a production method thereof. The steel grade comprises C: ≤0.02wt%, Si: 0.3-0.5wt%, Mn: 0.4-0.6wt%, Mg: 0.005-0.01wt%, Ca: 0.008-0.015wt%, V: 0.03-0.05wt%, N: 0.008-0.012wt%, Nb: 0.01-0.02wt%, Cu: 0.3-0.5wt%, Ni: 1-2wt%, Re: 0.02-0.03wt%, Cr: 0.5-1wt%, REM: 0.03-0.05wt%, Sn: 0.15-0.23wt%, Ti: 0.001-0.005wt%, P: 0.01-0.015wt%, and S: ≤0.005wt%. The production method includes cold charging the steel billet into the furnace at a temperature of ≤50°C, adopting multi-stage heating; adopting the direct rolling method after the steel billet is discharged from the furnace, and the final rolling is controlled at 930-970°C; stacking or heat preservation treatment is adopted after air cooling, and the heat preservation temperature is controlled at 300-500°C. The present invention solves the problems of low fracture resistance, poor safety and weldability, high construction cost and reduced service life of the steel-coating system in the existing offshore land environment.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material preparation, and particularly relates to a steel plate for marine environment coating 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 in the South China Sea as an example, due to the unique near-coastal environment of the South China Sea islands and reefs, the corrosion level of materials can reach the highest level C5 in this high-humidity, high-salt, and high-irradiation area according to the ISO9223 classification standard. 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 serving in the South China Sea is 3 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 increased 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, none of the above-mentioned steel materials can solve the structural safety problems required by building structures. The existing weather-resistant and fire-resistant building steels are also unable to meet the corrosion problems 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". In addition, for some extremely harsh coastal building environments, not only is steel required to have good corrosion resistance, but the steel and coating system are also required to play a coupled anti-corrosion role to improve long-term service safety, in order to cope with the failure and corrosion hazards caused by local damage and local aging of the coating. There is no special steel for use in a coating system that is resistant to harsh marine environments. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to propose a steel plate for marine environment coating and a production method thereof, so as to solve the problems of low fracture resistance, poor safety and weldability, high construction cost and reduced service life of steel-coating system of corrosion-resistant steel for coating.

[0005] In order to solve the above problems, the technical solution adopted by the present invention is as follows: a steel plate for marine environment coating, characterized in that the steel composition comprises C: ≤0.02wt%, Si: 0.3-0.5wt%, Mn: 0.4-0.6wt%, Mg: 0.005-0.01wt%, Ca: 0.008-0.015wt%, V: 0.03-0.05wt%, N: 0.008-0.012wt%, N b: 0.01-0.02wt%, Cu: 0.3-0.5wt%, Ni: 1-2wt%, Re: 0.02-0.03wt%, Cr: 0.5-1wt%, REM: 0.03-0.05wt%, Sn: 0.15-0.23wt%, Ti: 0.001-0.005wt%, P: 0.01-0.015wt%, S: ≤0.005wt%, the balance is Fe and unavoidable impurities.

[0006] Furthermore, the steel plate has an average grain size of 25-40 μm, contains a corrosion-resistant structure of 50-60% low-carbon bainite + 35-45% ferrite, 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 1.5-2.5 μm; contains Cu nanophases with an average size of 62-75 nm, and the average spacing of the phases is 1.5-2.5 μm.

[0007] 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.

[0008] Furthermore, the yield strength is 370-420 MPa, the yield strength ratio is ≤0.8, the impact energy at -40°C is not less than 200 J, the elongation is ≥20%, and the area reduction is ≥70%.

[0009] Furthermore, under the condition of 35KJ line energy, the tensile strength of the welded joint can be controlled at 495~535Mpa, and the impact energy at -40℃ is not less than 170J.

[0010] The present invention provides a method for producing a steel plate for marine environment coating, including smelting, continuous casting, billet heating, controlled rolling and offline processing, the specific contents of which are as follows:

[0011] Billet heating: The temperature of the cold billet into the furnace is ≤50℃, and multi-stage heating is adopted, wherein 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;

[0012] Controlled rolling: adopt the direct rolling method, the final rolling temperature is controlled at 930-970℃, and the air cooling method is adopted after rolling.

[0013] 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℃.

[0014] Furthermore, the steel billet is made by converter smelting + continuous casting, and cooling begins when the surface temperature of the steel billet is 795-845°C, and the cooling rate is controlled at 2-10°C / s, followed by low-temperature heating treatment, wherein the low-temperature heating temperature is controlled at 130-200°C.

[0015] Furthermore, the steel is smelted in a converter, the Ti element in the molten iron is controlled below 0.005%, and Si and Mn are used for deoxidation.

[0016] The steel plate for marine environment coating produced according to the above scheme has the following beneficial effects:

[0017] 1. Based on the reasonable combination of traditional corrosion-resistant elements such as Ni, Cu, and Cr, the corrosion resistance of the steel plate coating system is greatly improved by precise control of dispersed precipitates and the synergistic effect of composite trace elements such as Ca, Mg, Re, and Sn, which is 50-100% higher than that of 3.5Ni system steel.

[0018] 2. It has good comprehensive mechanical properties, structural safety and weldability, with yield strength of 370-420Mpa, yield strength ratio ≤0.8, impact energy of not less than 200J at -40℃, elongation ≥20%, and surface shrinkage ≥70%.

[0019] 3. Under the condition of 35KJ line energy, the tensile strength of the welded joint can be controlled at 495~535Mpa, and the impact energy at -40℃ is not less than 170J. DETAILED DESCRIPTION

[0020] 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.

[0021] The present invention is aimed at the steel materials facing high temperature, unstable oxygen, low pH value, high Cl - In a more complex environment, the pH value of the anode area is reduced through the microalloying and compounding of elements such as Sn, Re, REM, N, V, Cr, W, Ca, and Mg, thereby increasing the system potential, reducing the local pH value, and improving the coupled passivation ability of the steel-coating system, so that the steel plate has a good match of mechanical and corrosion resistance, which can minimize the cost of raw material construction of steel structures in the near-coast environment typical of the South China Sea. The application of this formula in the coating system can improve the corrosion resistance of the material under slightly acidic conditions under coating, thereby increasing the coating life. It solves the problems of low fracture resistance, poor safety and weldability, high construction cost, and reduced service life of the steel-coating system in the existing near-shore land environment.

[0022] 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.

[0023] A steel plate for marine environment coating, wherein the steel composition comprises, by weight percentage, C: ≤0.02wt%, Si: 0.3-0.5wt%, Mn: 0.4-0.6wt%, Mg: 0.005-0.01wt%, Ca: 0.008-0.015wt%, V: 0.03-0.05wt%, N: 0.008-0.012wt%, Nb: 0.01-0.02wt%, Cu: 0.3-0.5wt%, Ni: 1-2wt%, Re: 0.02-0.03wt%, Cr: 0.5-1wt%, REM: 0.03-0.05wt%, Sn: 0.15-0.23wt%, Ti: 0.001-0.005wt%, P: 0.01-0.015wt%, S: ≤0.005wt%, and the balance is Fe and unavoidable impurities.

[0024] C: ≤0.02wt%

[0025] The C element is the main phase change controlling element for forming a corrosion-resistant structure with 50-60% low-carbon bainite + 35-45% ferrite as the matrix, and is an important element for ensuring the strength of the steel. Appropriate C promotes the formation of important tiny cathode phases V (C, N) and Nb (C, N) in the present invention, and controls the precipitation of large carbides of Cr, which helps to improve 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 is ≤0.02wt%.

[0026] Si: 0.3-0.5wt%

[0027] The Si element plays a certain role in strengthening and is one of the important deoxidizers of the present invention. It can promote the surface enrichment of Sn and form surface oxides with Cu, Sn, and Cr to effectively improve the corrosion resistance. Appropriate Si helps to improve the potential of the coating system and control the local pH value, so the Si content is controlled at 0.3-0.5wt%.

[0028] Mn: 0.4-0.6wt%

[0029] 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%.

[0030] Mg: 0.005-0.01wt%, Ca: 0.008-0.015wt%

[0031] The Ca and Mg elements are mainly used to reduce the cathode reaction area and the pH value under coating, which plays a passivation role in protecting Cr; in addition, trace amounts of Ca and Mg dissolved in Fe can make Ni, Cu, Cr, Sn and other corrosion-resistant elements relatively enriched after the surface Fe dissolves in the early stage of corrosion, improve corrosion resistance, and reduce the toughness reduction problem caused by the addition of high Sn and other elements. The above elements will also form a coupling effect with Zn in the primer in a weakly acidic environment to improve the corrosion resistance of the steel-coating system. Based on the above design, the content of Ca and Mg elements is controlled at 0.008-0.015wt% and 0.005-0.01wt%, respectively.

[0032] V: 0.03-0.05wt%

[0033] 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 appropriate proportions of C and N. 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% of V. This is mainly due to the addition of solid solution elements such as Cr that are infinitely solid-soluble in α-Fe in the component design of the multi-element system. Therefore, 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 used in the present invention, it will promote the generation of 10-50nm dispersed precipitation of V (C, N) and Fe3C in the steel matrix, and the average spacing of these phases is 1.5-2.5μm. Based on the above design, the content of V is 0.03-0.05wt%.

[0034] N: 0.008-0.012wt%

[0035] The N element mainly promotes the precipitation of V(CN) 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%.

[0036] Nb: 0.01-0.02wt%

[0037] An appropriate amount of Nb can help 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%.

[0038] Cu: 0.3-0.5wt%

[0039] Cu is an important corrosion resistance and toughening agent of the present invention. In the early stage of corrosion, when the surface is initially corroded, an enrichment layer and an oxide layer are formed, which improves the steel plate without significant segregation behavior. In addition, a Cu nanophase with an average size of 62-75nm is formed inside the steel plate, and the average spacing between the phases is 1.5-2.5μm. 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(CN) and Fe3C, which controls the corrosion rate and helps to improve and control the weldability. However, too much Cu is not conducive to further exertion of corrosion resistance and increases unnecessary costs. Therefore, the Cu content of the present invention is controlled at 0.3-0.5wt%.

[0040] Ni: 1-2wt%

[0041] The main function of Ni element 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, 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 the corrosion resistance.

[0042] Re: 0.02-0.03wt%

[0043] The Re element is evenly distributed in the dendrite trunk and between dendrites during the solidification process. It is an important solid solution strengthening element. Its corrosion potential is about 0.3V, which can shift the corrosion potential positively, effectively increase the corrosion potential of the matrix, reduce the corrosion current of the system, and improve the corrosion resistance of steel. In addition, an appropriate 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 dispersed phases such as V and Cu, and improve the combination of steel and coating. In addition, the compound addition of Re, V, and Ni can effectively control the toughness control problem caused by the addition of elements such as Sn, so it is controlled at 0.02-0.03wt%.

[0044] Cr: 0.5-1wt%

[0045] Cr element plays a role in compacting the rust layer, and on the other hand, it forms a passivating oxide, which, together with other oxides and dense α-FeOOH, resists Cl - Intrusion, under the background environment, the pH of the marine atmosphere is weakly alkaline, and Cr oxides 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), but too much Cr is not conducive to the control of pH under coating. According to environmental requirements, the Cr of the present invention is controlled at 0.5-1wt%.

[0046] REM: 0.03-0.05wt%

[0047] On the one hand, REM rare earth elements 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, because the content reaches 0.03-0.05wt%, it is fully dissolved in the matrix, which plays a role in increasing the matrix potential and directly produces corrosion resistance.

[0048] Sn: 0.15-0.23wt%

[0049] On the one hand, the Sn element reduces the energy level of steel and weakens the electrochemical activity of steel in the form of a single substance solid solution. In addition, it helps to form oxides such as SnO and deposit on the corrosion front, promotes the formation of α-FeOOH, and forms a dense oxide layer together with α-FeOOH. When dissolved together with Fe, ionic Sn can combine with Cl- to increase the local pH value, especially for the pH value under coating, which plays a role in controlling the acceleration of the corrosion process. Therefore, according to environmental requirements, the Sn content of the present invention is controlled at 0.15-0.23wt%.

[0050] Ti: 0.001-0.005wt%

[0051] 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%.

[0052] P: 0.01-0.015wt%

[0053] 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 - Considering that too much P reduces the weldability of the coated steel to a certain extent, the P in the present invention is controlled at 0.01-0.015wt%.

[0054] S: ≤0.005wt%

[0055] S: The sulfide formed by the element accelerates corrosion and reduces the toughness of the steel plate, so it needs to be strictly controlled to ≤ 0.005wt%.

[0056] 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.

[0057] The microstructure of the present invention will be described in further detail below.

[0058] The steel plate for marine environment coating of the present invention has an average grain size of 25-40 μm, contains a corrosion-resistant structure of 50-60% bainite + 35-45% ferrite, and the percentage is the 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 1.5-2.5 μm; contains dispersed precipitated Cu nanophases, the size is 50-100nm, the average size is 62-75nm, and the average spacing of the phases is 1.5-2.5 μm.

[0059] The production process of the present invention is described in further detail below.

[0060] The present invention provides a method for producing a steel plate for marine environment coating, including smelting, continuous casting, billet heating, controlled rolling and offline processing, the specific contents of which are as follows:

[0061] Smelting: The steel is smelted in a converter, in which elements such as Re, Cu, Ni, and Cr also play a role in forming a dense rust layer; Si and Mn are used for deoxidation, and the use of Al is strictly controlled because the addition of Al consumes the N element and has a harmful effect on the surface quality of the steel billet. Similarly, the introduction of the Ti element in the molten iron used must also be strictly controlled (controlled to below 0.005%), which affects the precipitation effect of V and Cu and avoids the formation of Ti, Al and other carbonitrides, which is detrimental to the corrosion resistance.

[0062] Continuous casting: The steel billet is made by converter smelting + continuous casting. In order to control the initial surface grain size of the continuous casting billet and the solid distribution of corrosion-resistant elements, rapid cooling is used for pretreatment when the billet is discharged. The billet surface temperature is controlled at 795-845℃ and then begins to cool. The cooling rate is controlled at 2-10℃ / s. After that, it is not suitable for hot loading. Stacking treatment or low-temperature heating treatment is required. The low-temperature heating temperature is controlled at 130-200℃ to control the surface quality and thermal stress distribution of the steel billet.

[0063] Billet heating: The temperature of the cold billet in the furnace is controlled at ≤50℃, and multi-stage heating is adopted. 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 the soaking section 1150-1180℃ is controlled within 0.2-0.4min / mm. The purpose is to control the initial distribution of alloy elements before hot working. Since the distribution and composition of grains, especially grain boundaries, have a greater impact on corrosion, it is necessary to reasonably control the initial grain size.

[0064] Controlled rolling: adopt the direct rolling method out of the furnace, the final rolling is controlled at 930-970℃, and the steel is air-cooled after rolling. In this process, 50-60% bainite + 35-45% ferrite is formed in the steel as the matrix corrosion-resistant structure, and the average grain size is 25-40μm. The purpose is to control the mechanical-corrosion resistance matching under the coating-steel system.

[0065] 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 temperature is regulated at 300-500℃ to promote the formation of V (C, N) and Fe3C with a size of 10-50nm (average size 20-30nm) dispersed precipitation in the steel matrix. The average spacing of these phases is 1.5-2.5μm. At the same time, there is also a Cu nanophase of 50-100nm (average size 62-75nm) in the matrix, and the average spacing of the phases is 1.5-2.5μm.

[0066] According to the above chemical composition and production process, the actual smelting composition of the present invention is shown in Table 1, the actual process parameters of the present invention are shown in Tables 2-5, and the actual properties are shown in Tables 6-8.

[0067] Table 1 Composition of each example, wt%

[0068] C Si Mn Mg Ca V N Nb Cu Ni Re Cr REM Sn P S Ti 1 0.02 0.4 0.57 0.01 0.009 0.047 0.008 0.01 0.49 1.6 0.02 0.86 0.03 0.16 0.014 0.003 0.002 2 0.02 0.31 0.47 0.007 0.011 0.034 0.007 0.02 0.48 1.33 0.026 0.92 0.04 0.16 0.012 0.005 0.005 3 0.01 0.4 0.56 0.008 0.01 0.033 0.01 0.02 0.31 1.24 0.02 0.93 0.03 0.15 0.015 0.001 0.003 4 0.02 0.5 0.6 0.006 0.014 0.039 0.007 0.01 0.49 1.81 0.022 0.7 0.04 0.17 0.015 0.002 0.003 5 0.02 0.45 0.55 0.007 0.008 0.05 0.008 0.02 0.44 2 0.027 1 0.05 0.23 0.014 0.003 0.002 6 0.01 0.42 0.44 0.01 0.012 0.044 0.011 0.01 0.32 1.85 0.03 0.95 0.04 0.22 0.009 0.004 0.004 7 0.01 0.43 0.59 0.008 0.005 0.042 0.008 0.02 0.36 1.78 0.023 0.81 0.03 0.16 0.013 0.003 0.001 8 0.02 0.5 0.47 0.007 0.015 0.034 0.009 0.01 0.42 1.32 0.028 0.94 0.03 0.21 0.012 0.003 0.003 9 0.01 0.39 0.52 0.01 0.01 0.043 0.007 0.02 0.38 1.88 0.025 0.65 0.05 0.22 0.012 0.001 0.001 10 0.01 0.38 0.58 0.009 0.013 0.034 0.011 0.01 0.44 1.65 0.021 0.57 0.03 0.18 0.014 0.002 0.003

[0069] Table 2 Pretreatment of blanks

[0070] Example Ingot cooling temperature, ℃ Cooling rate of ingot, ℃ / s Offline processing method Low temperature heating temperature, ℃ 1 831 7 Low temperature heating treatment 137 2 798 5 Low temperature heating treatment 166 3 822 6 Low temperature heating treatment 146 4 825 4 Low temperature heating treatment 195 5 845 8 Low temperature heating treatment 180 6 814 7 Low temperature heating treatment 182 7 835 10 Low temperature heating treatment 156 8 827 7 Low temperature heating treatment 177 9 830 9 Low temperature heating treatment 170 10 809 4 Low temperature heating treatment 165

[0071] Table 3 Heating process

[0072]

[0073] Table 4 Rolling process and organizational proportion level

[0074] Example Finishing rolling temperature, ℃ Low carbon bainite content, % Ferrite content, % Average grain size, μm 1 946 55 41 40 2 930 54 41 35 3 938 59 35 31 4 945 58 37 27 5 968 53 42 35 6 935 55 40 26 7 951 53 43 38 8 953 59 45 37 9 942 54 39 29 10 965 57 38 37

[0075] Table 5 Steel plate off-line process and organizational proportion level

[0076]

[0077]

[0078] Table 6 Mechanical properties of the examples

[0079]

[0080] Table 7 Welding performance of the embodiment (line energy 35KJ, submerged arc welding)

[0081]

[0082] The test steel and the comparison steel were protected by four layers of Zn-rich primer to make a coated steel accelerated corrosion coupon for the steel-coating accelerated corrosion test. The single test method was as follows:

[0083] 1. 42℃, relative humidity 90%, time 5h;

[0084] 2. An accelerated corrosion test simulating the sea conditions in the South China Sea was used, with a 2% NaCl solution: pH value: PH: 6-6.9, immersion temperature 42±2℃, time 1h;

[0085] 3. Exposure temperature 45±2℃, exposure humidity 60%, time 10h;

[0086] The number of times that 10% coating degradation (peeling of notched parts, blistering, etc.) occurs after corrosion cycles is used as an evaluation of the system's corrosion resistance. The number of corrosion cycles is 50 to 67, and the relative corrosion resistance is 151% to 203%.

[0087] Table 8 Corrosion resistance of the examples

[0088] Corrosion cycles Relative corrosion resistance Comparative Example (3.5Ni Steel) 33 100％ Example 1 50 151％ Example 2 52 158％ Example 3 51 154％ Example 4 59 178％ Example 5 67 203％ Example 6 61 185％ Example 7 54 163％ Example 8 62 188％ Example 9 58 175％ Example 10 53 160％

[0089] 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 marine environment coating, characterized in that: The steel plate composition includes, by weight percentage, C: ≤0.02wt%, Si: 0.3-0.5wt%, Mn: 0.4-0.6wt%, Mg: 0.005-0.01wt%, Ca: 0.008-0.015wt%, V: 0.03-0.05wt%, N: 0.008-0.012wt%, Nb: 0.01-0.02 wt%, Cu: 0.3-0.5wt%, Ni: 1-2wt%, Re: 0.02-0.03wt%, Cr: 0.5-1wt%, REM: 0.03-0.05 wt%, Sn: 0.15-0.23wt%, Ti: 0.001-0.005wt%, P: 0.01-0.015wt%, S: ≤0.005wt%, and the balance is Fe and unavoidable impurities; The steel plate has an average grain size of 25-40 μm, a corrosion-resistant structure containing 50-60% low-carbon bainite + 35-45% ferrite, and the percentages are area percentages; it 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 1.5-2.5 μm; it contains Cu nanophases with an average size of 62-75 nm, and the average spacing of the phases is 1.5-2.5 μm.

2. The steel plate for marine environment coating 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 marine environment coating according to claim 1, characterized in that: Yield strength 370 ~ 420Mpa, yield strength ratio ≤ 0.8, -40 ℃ impact energy not less than 200J, elongation ≥ 20%, area reduction ≥ 70%.

4. The steel plate for marine environment coating according to claim 1, characterized in that: Under the condition of 35KJ line energy, the tensile strength of the welded joint can be controlled at 495~535Mpa, and the impact energy at -40℃ is not less than 170J.

5. A method for producing a steel plate for marine environment coating according to any one of claims 1 to 4, characterized in that: It includes smelting, continuous casting, billet heating, controlled rolling and offline processing. The specific contents are as follows: Billet heating: The temperature of the cold billet into the furnace is ≤50℃, and multi-stage heating is adopted, wherein 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; Controlled rolling: adopt the direct rolling method, the final rolling temperature is controlled at 930-970℃, and the air cooling method is adopted after rolling. 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℃.

6. The method for producing a steel plate for marine environment coating according to claim 5, characterized in that: The steel billet is made by converter smelting + continuous casting. The steel billet starts to cool when the surface temperature is 795-845°C, and the cooling rate is controlled at 2-10°C / s. It is then subjected to low-temperature heating treatment, wherein the low-temperature heating temperature is controlled at 130-200°C.

7. The method for producing a steel plate for marine environment coating according to claim 5, characterized in that: The steel plate is smelted in a converter, the Ti element in the molten iron is controlled at Ti: 0.001-0.005wt%, and Si and Mn are used for deoxidation.

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