Anti-collision steel in marine environment and production method thereof

Abstract

The invention discloses anti-collision steel under marine environment and a production method thereof. The steel plate comprises C0.02-0.04%, Si0.3-0.5%, Mn0.2-0.4%, V0.03-0.05%, N0.007-0.01%, Cu0.7-1%, Ni0.8-1.2%, Mo0.05-0.1%, W0.1-0.2%, Re0.01-0.02%, Cr1-1.5%, REM0.03-0.05%, Sn0.05-0.1%, Ti: 0.001-0.005wt%, P0.01-0.02%, and S≤0.005%. The production method includes the following steps: the temperature of the steel billet entering the furnace is ≤100°C, multi-stage heating is adopted, the final rolling temperature is controlled to be above 1000°C in the first stage, the pass reduction is 10-20%, the final rolling temperature in the second stage is 915-950°C, the pass reduction is 15-25%, the cooling rate between the two rollings is 0.5-2°C / s, the steel plate is relaxed to 500-550°C after rolling and then cooled, and the cooling rate is 2-4°C / s; the heat preservation treatment is adopted for control, and the heat preservation control temperature is 300-500°C. The steel grade of the present invention takes into account strength, toughness, corrosion resistance and good anti-collision performance at the same time, and effectively solves the anti-collision risk problem faced by marine equipment.

Description

Technical Field

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

[0002] International offshore wind power projects are showing a trend of development from nearshore to offshore. The demand for the construction of floating wind power will continue to increase in the future. The service environment of floating wind power is more severe than that of traditional marine structural steel. The floating wind power foundation structure is subjected to alternating stresses such as wind and waves at sea for a long time, and is at risk of being hit by the hull and marine floating objects. This puts forward higher requirements on the impact resistance and pitting corrosion resistance of structural steel. Similar scenarios also include various floating and fixed marine platforms and ocean-going ships in the deep sea. The stress corrosion problems caused by these offshore equipment and welding nodes cannot be ignored.

[0003] my country's South China Sea is the sea area with the richest offshore wind resources and is the direction of my country's medium- and long-term development of offshore wind power resources. However, this sea area is also one of the sea areas with the worst marine environment in the world. According to the ISO9223 classification standard, in this high-humidity, high-salt, and high-irradiation area, the corrosion level of materials can reach the highest level C5. Compared with other regions, surface ships, ground buildings, equipment and facilities, and offshore floating platforms serving in this environment will suffer from severe corrosion prematurely even if corrosion protection measures are taken. According to statistics, the failure rate of equipment and facilities serving in the South China Sea is three times that of other sea areas and about 10 times that of the mainland. It can be said that a material that adapts to the service requirements of the South China Sea environment can basically meet the material needs of all sea areas in my country, and how to balance cost and performance is an important proposition.

[0004] 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. However, due to the use of a high Ni system and alloying with elements such as Cu and Mo, the problem is that the cost is relatively high, and due to the high alloying and carbon equivalent, there are problems with welding performance. In addition, this system steel has stress corrosion problems, and as the strength increases, the hydrogen-induced cracking problem of the steel structure becomes prominent, there are major safety hazards, and the elongation is low, only about 15%. Similar cases include 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”.

[0005] The invention patent with application number CN202010044231.8 and the name of "A weathering steel resistant to high temperature, high humidity and high salt fog marine atmospheric environment" adopts a low Ni and high Cr composition formula, with a low elongation of only about 12%, which cannot meet the technical requirements of marine anti-collision. The above studies are all aimed at improving the corrosion resistance of materials in the South China Sea environment, and there are high costs, poor weldability, and low elongation, especially the uniform elongation that is crucial for anti-collision performance. There is no solution to the anti-collision performance of offshore floating structures represented by offshore wind power in the complex waters of the South China Sea.

[0006] For the anti-collision steel with high ductility, the invention patent with application number 201910999129.0, named "EH32 grade marine engineering steel with high ductility and method for manufacturing steel plate", adopts a three-stage rolling process to control the ratio of ferrite and pearlite, and the process is complicated. Application number 201810320311.4, named "A high ductility EH40 grade ship plate steel and its preparation method", also adopts a multi-stage rolling and multi-stage water cooling process, which is complex and difficult to implement in industry; in addition, the above patents do not have the ability to resist atmospheric corrosion in marine environments. Summary of the invention

[0007] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a collision-resistant steel and a production method for marine environment. Through a new component system design and corresponding production process, the developed steel plate takes into account strength, toughness, corrosion resistance and good collision resistance, effectively solving the collision risk problem faced by marine equipment.

[0008] In order to solve the above problems, the technical solution adopted by the present invention is as follows: an anti-collision steel for marine environment, the steel plate composition includes C: 0.02-0.04wt%, Si: 0.3-0.5wt%, Mn: 0.2-0.4wt%, V: 0.03-0.05wt%, N: 0.007-0.01wt%, Cu: 0.7-1wt%, Ni: 0.8-1.2wt%, Mo: 0.05-0.1wt%, W: 0.1-0.2wt%, Re: 0.01-0.02wt%, Cr: 1-1.5wt%, REM: 0.03-0.05wt%, Sn: 0.05-0. 1wt%, Ti: 0.001-0.005wt%, P: 0.01-0.02wt%, S: ≤0.005wt%, the remainder is Fe and other inevitable impurities; the average grain size of the steel plate is 25-35μm, containing 20-25% low carbon bainite + 40-50% blocky ferrite + 20-25% acicular ferrite structure, and the percentage is the area percentage; it contains spherical V (C, N), WC, Mo2C, Fe3C nanophases with an average size of 15-25nm dispersedly precipitated, and the average spacing of these precipitated phases is 1-1.5μm; it contains Cu nanophases with an average size of 43-65nm, and the average spacing of the phases is 2-3μm.

[0009] Furthermore, the dispersed and precipitated V (C, N), WC, Mo2C, and Fe3C nanophases have a size of 5-30 nm, and the Cu nanophase has a size of 30-80 nm.

[0010] Furthermore, the average grain size of the surface layer -1 / 8 thickness of the steel plate is 15-22 μm.

[0011] Furthermore, the yield strength of the steel is 360-400 MPa, the yield strength ratio is ≤0.74, the impact energy at -60°C is not less than 130 J, the elongation is ≥32%, and the uniform elongation is ≥20%.

[0012] Furthermore, the tensile strength of the welded joint is controlled at 495-525MPa under 50KJ line energy conditions, and the impact energy at -60°C is not less than 130J.

[0013] Furthermore, a cyclic immersion test was conducted in a simulated South China Sea seawater splash zone, and the corrosion resistance was 67-80% relative to that of 3Ni system steel.

[0014] The present invention provides a method for producing anti-collision steel in a marine environment, including smelting, continuous casting, billet heating, controlled rolling and controlled cooling, and offline processing, the specific contents of which are as follows:

[0015] Billet heating: The billet is cold loaded into the furnace at a temperature of ≤100°C, and multi-stage heating is adopted, wherein the total time at 650-1000°C is controlled within 0.2-0.3min / mm, the total time at 1230-1240°C is controlled within 0.1min / mm, and the total time at 1200-1220°C is controlled within 0.2-0.4min / mm;

[0016] Controlled rolling and controlled cooling: In the first stage, the final rolling temperature is controlled at above 1000℃, and the pass reduction is controlled at 10-20%. In the second stage, the final rolling temperature is controlled at 915-950℃, and the pass reduction is 15-25%. Cooling is used as a transition between the two rolling passes, and the cooling rate is 0.5-2℃ / s. After rolling, the steel plate is relaxed to 500-550℃ and then cooled down at a cooling rate of 2-4℃ / s.

[0017] Off-line treatment: After the steel plate is off the line, the second stage precipitation phase and internal stress are regulated by insulation treatment, and the insulation regulation temperature is 300-500℃.

[0018] Furthermore, the steel plate 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.

[0019] 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 3-11°C / s, followed by low-temperature heating treatment at a heating temperature of 200-360°C.

[0020] The anti-collision steel plate produced in the marine environment according to the above scheme has the following beneficial effects:

[0021] 1. Through the addition and synergistic effect of composite trace elements, a low-cost composition design is proposed, which can greatly improve the corrosion resistance of steel plates. Combined with the two-stage controlled rolling and controlled cooling process, it has the advantages of industrial production.

[0022] 2. Using a simulated South China Sea seawater splash zone immersion test, the corrosion resistance is 20-33% higher than the relative corrosion rate (64d) of 3Ni system steel, which is 67-80%.

[0023] 3. It has good mechanical properties and weldability, yield strength of 360-400Mpa, yield strength ratio ≤0.74, and impact energy of not less than 130J at -60℃.

[0024] 4. Elongation ≥32%, uniform elongation ≥20%, which is more than 35% higher than the existing low alloy steel.

[0025] 5. Under the condition of 50KJ line energy, the tensile strength of the welded joint can be controlled at 495~525MPa, and the impact energy at -60℃ is ≥130J. DETAILED DESCRIPTION

[0026] 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.

[0027] The present invention proposes a low-cost component design through the addition and synergistic effect of composite trace elements, which can greatly improve the corrosion resistance of steel plates. Combined with the two-stage controlled rolling and controlled cooling process, it has the advantage of industrial production. Under the corrosion conditions of the marine environment, the steel plate takes into account the mechanical properties and corrosion properties of the steel, and has a good comprehensive performance of mechanical-corrosion resistance matching. While meeting the -60℃ impact toughness requirements, the corrosion resistance is 10-20% higher than the existing 3Ni system with the highest resistance to marine atmosphere, and has good anti-collision performance, and the elongation is more than 35% higher than the existing ordinary carbon steel, and can effectively solve the anti-collision risk problem faced by deep-sea equipment in the marine environment.

[0028] 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.

[0029] Disclosed is a collision-resistant steel for use in a marine environment. The steel plate comprises, by weight percentage, C: 0.02-0.04wt%, Si: 0.3-0.5wt%, Mn: 0.2-0.4wt%, V: 0.03-0.05wt%, N: 0.007-0.01wt%, Cu: 0.7-1wt%, Ni: 0.8-1.2wt%, Mo: 0.05-0.1wt%, W: 0.1-0.2wt%, Re: 0.01-0.02wt%, Cr: 1-1.5wt%, REM: 0.03-0.05wt%, Sn: 0.05-0.1wt%, Ti: 0.001-0.005wt%, P: 0.01-0.02wt%, S: ≤0.005wt%, and the balance is Fe and other inevitable impurities.

[0030] C: 0.02-0.04wt%

[0031] The C element is the main phase change controlling element for forming the corrosion-resistant and collision-resistant structure of 20-25% low-carbon bainite + 40-50% massive ferrite and 20-25% acicular ferrite, and is an important element for ensuring the strength of the steel plate. Appropriate C promotes the formation of important tiny cathode phases V (C, N), WC, Mo2C, and Fe3C in the present invention, and controls the precipitation of large carbides of Cr. These phases help to improve the corrosion resistance of the steel. However, 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 0.02-0.04wt%.

[0032] Si: 0.3-0.5wt%

[0033] The Si element plays a certain role in strengthening and improving ductility. In addition, it forms surface oxides with Cr, 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 plate. Appropriate Si can effectively increase the ferrite content, so the Si content is controlled at 0.3-0.5wt%.

[0034] Mn: 0.2-0.4wt%

[0035] The Mn element plays a certain role in strengthening and is one of the important deoxidizers of the present invention. Too much Mn will reduce the corrosion resistance of the steel and affect the solid solution effect of the corrosion-resistant elements in the steel. In addition, Mn is an austenite stabilizing element. Too high Mn is not conducive to the formation of a stable ferrite phase region. Therefore, the Mn content is controlled at 0.2-0.4wt%.

[0036] V: 0.03-0.05wt%

[0037] The V element plays an important role in the toughness and corrosion resistance of steel mainly in the form of precipitation strengthening. It is also an important ferrite stabilizing element. 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 to give full play to its excellent precipitation effect. The electrochemical impedance spectrum shows that after full precipitation, the surface inductive arc of the steel plate is greatly weakened, indicating that the pitting phenomenon is effectively suppressed. It mainly plays the role of controlling the cathode phase. Under the configuration of V, C, N and Cr elements adopted in the present invention, it will promote the dispersion and generation of 10-30nm spherical V (C, N) in the steel matrix, with an average spacing of 1-1.5μm, which can further prevent the expansion of fatigue cracks. Based on the above design, the content of V is 0.03-0.05wt%.

[0038] N: 0.007-0.01wt%

[0039] The N element mainly promotes the precipitation of fine particles of V (C, N) and Fe3C. In addition, the solid-dissolved N helps to improve the corrosion resistance of the steel and is beneficial to control the ratio of bainite and ferrite. The N in the present invention is controlled at 0.007-0.01wt%.

[0040] Cu: 0.7-1wt%

[0041] Cu is an important corrosion-resistant and toughening element in the present invention. On the one hand, in the early stage of corrosion, when the surface is initially corroded, an enrichment layer and an oxide layer are formed. In addition, a Cu nanophase of 30-80nm (average size 43-65nm) is formed inside the steel plate, and the average spacing between the phases is 2-3μm. 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), Fe3C, and VN, which controls the corrosion rate and helps to improve weldability. Appropriate Cu can promote the formation of high ductility ferrite, so the Cu of the present invention is controlled at 0.7-1wt%.

[0042] Ni: 0.8-1.2wt%

[0043] 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. In addition, too high Ni is not conducive to the formation of high ductility ferrite structure, so Ni is controlled at 0.8-1.2wt%.

[0044] Mo: 0.05-0.1wt%

[0045] Mo element can make the rust layer dense, and when combined with Si, Cu, etc., the oxide film formed is effective against initial corrosion. In addition, along with the anodic reaction of steel, MoO4 2- Dissolved, MoO4 on the rust layer 2- distribution, producing ion selection, resisting the corrosion promoting factor Cl - In addition, the addition of Mo helps to improve the low and high temperature stability of the V and Cu dispersion phases, while precipitating 10-30nm Mo2C, improving its corrosion resistance and slip control ability. Too high is not good for plasticity, so it is controlled at 0.05-0.1wt%.

[0046] W: 0.1-0.2wt%

[0047] W element accompanies the anode reaction of steel, WO4 2- Dissolved, WO4 on the rust layer 2- distribution, producing ion selection, resisting the corrosion promoting factor Cl - In addition, the addition of W helps to improve the low and high temperature stability of the V and Cu dispersion phases, balance the phase ratio, and precipitate 10-30nm WC, thereby improving the overall performance of the steel. Too high W will deteriorate the toughness, so it is controlled at 0.1-0.2wt%.

[0048] Re: 0.01-0.02wt%

[0049] 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 the dispersed phases of V and Cu. In addition, the compound addition of Re, V, and Ni can effectively control the problem of reduced toughness caused by the addition of elements such as Sn, so it is controlled at 0.01-0.02wt%.

[0050] Cr: 1-1.5wt%

[0051] 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; In addition, in the composition design of the multi-component system of the present invention, Cr and other solid solution elements are fully dissolved in the matrix, which reduces the solid solubility of V and improves its precipitation behavior, indirectly controlling the thermodynamic and kinetic changes of V (C, N), and after the composite effect of Cr, V and other elements forms a stable rust layer, the inductive impedance effect tends to completely disappear, indicating that the material's fatigue resistance and pitting resistance have reached the best match. According to environmental requirements, the Cr of the present invention is controlled at 1-1.5wt%.

[0052] REM: 0.03-0.05wt%

[0053] 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. 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. The RE absorbed by grain boundaries, subgrain boundaries, precipitate mismatches and other positions plays a role in balancing the segregation of elements such as Cr and Cu, reducing intergranular and interphase corrosion caused by segregation.

[0054] Sn: 0.05-0.1wt%

[0055] On the one hand, Sn element can reduce the energy level of steel and weaken the electrochemical activity of steel in the form of single substance solid solution. In addition, it helps to form oxides such as SnO and deposit on the corrosion front, promote the formation of α-FeOOH, and compact the oxide layer together with α-FeOOH. When dissolved with Fe, ionic Sn can react with Cl - In combination, the local pH value is increased to control the acceleration of the corrosion process. According to environmental requirements, the Sn content of the present invention is controlled at 0.05-0.1wt%.

[0056] Ti: 0.001-0.005wt%

[0057] 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%.

[0058] P: 0.01-0.02wt%

[0059] 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 the invasion of Cl-. However, too much P reduces the weldability of steel. Taking the converter smelting process as an example, no special control is required. Therefore, the P of the present invention is controlled at 0.01-0.02wt%.

[0060] S: ≤0.005wt%

[0061] 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%.

[0062] 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.

[0063] The microstructure of the present invention will be described in further detail below.

[0064] The invention discloses a collision-resistant steel for use in a marine environment, wherein the steel has an average grain size of 25-35 μm (the average grain size of the steel plate surface layer - 1 / 8 of the thickness is 15-22 μm), contains corrosion-resistant and collision-resistant structures of 20-25% low-carbon bainite + 40-50% blocky ferrite and 20-25% acicular ferrite, wherein the percentages are area percentages; contains dispersed precipitated spherical V (C, N), WC, Mo2C, Fe3C nanophases, wherein the sizes of the precipitated phases are 5-30 nm, the average size is 15-25 nm, and the average spacing is 1-1.5 μm; contains dispersed precipitated Cu nanophases, wherein the sizes are 30-80 nm, the average size is 43-65 nm, and the average spacing between the phases is 2-3 μm.

[0065] The production process of the present invention is described in further detail below.

[0066] The present invention provides a method for producing anti-collision steel in marine environment, including smelting, continuous casting, billet heating, rolling and offline processing, the specific contents of which are as follows:

[0067] Smelting: The steel plate 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 and Cu and avoids the formation of Ti, Al and other carbonitrides, which are not good for corrosion resistance and mechanical properties.

[0068] 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 begins to cool when it is 800-850℃, and the cooling rate is controlled at 3-11℃ / s. After that, it is not suitable for hot charging. Low-temperature heating treatment is required, with a heating temperature of 200-360℃, to control the surface quality and thermal stress distribution of the billet.

[0069] Billet heating: The temperature of the billet cold-charged into the furnace is controlled at ≤100℃, and multi-stage heating is adopted, in which the total time of 650-1000℃ is controlled within 0.2-0.3min / mm, the total time of 1230-1240℃ is controlled within 0.1min / mm, and the total time of 1200-1220℃ is controlled within 0.2-0.4min / mm. The purpose is to control the initial distribution of Re, W, Mo, Cu, Ni, and Cr elements before hot processing, so as to play the role of dense rust layer. Since the distribution and composition of grains, especially grain boundaries, have a great influence on corrosion, they need to be reasonably controlled.

[0070] Controlled rolling and controlled cooling: rolling begins as soon as the billet leaves the furnace. High-temperature controlled rolling is used to control the grain size from the surface to the core of the steel plate. The final rolling temperature in the first stage is controlled to be above 1000°C, and the pass reduction is controlled to be 10-20%. The final rolling temperature in the second stage is controlled to be 915-950°C. Cooling is used as a transition between the two rolling passes, and the cooling rate is 0.5-2°C / s, so that the steel plate does not produce mixed crystals, and the single pass reduction of the second stage of rolling is controlled to be 15-25%. After rolling, the steel plate adopts a relaxation process to control the grain structure and phase ratio, and the average grain size is controlled to 25-35μm. Relax to 500-550°C and start cooling, and quickly cool down the line at a cooling rate of 2-4°C / s. The average grain size of the steel plate surface layer - 1 / 8 thickness is controlled at 15-22μm. Too fine grain size is not conducive to anti-collision performance. In addition, the above process also helps to increase the composition of corrosion-resistant elements in the steel by supercooling to stably control the precipitation process and reduce the control deviation of the precipitation phase. In this process, a corrosion-resistant and anti-collision structure with 20-25% low-carbon bainite + 40-50% blocky ferrite + 20-25% acicular ferrite as the matrix is ​​formed in the steel.

[0071] Off-line treatment: After the steel plate is off the line, the second stage precipitation phase and internal stress are regulated by insulation treatment. The insulation temperature is 300-350℃, which plays a certain role in improving the comprehensive performance matching of the steel plate, especially the surface corrosion resistance.

[0072] After regulation, V (C, N), WC, and Mo2C with a size of 5-30nm (average size 15-25nm) are dispersed and precipitated in the matrix of the steel to form a complex with the Fe3C phase in the steel. The average spacing between these phases is 1-1.5μm. At the same time, there are also Cu nanophases with a size of 30-80nm (average size 43-65nm) in the matrix, and the average spacing between the phases is 2-3μm.

[0073] According to the above steel plate 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 2-4, and the actual properties are shown in Tables 5-9.

[0074] Table 1 Composition of each example / wt%

[0075]

[0076] Table 2 Pretreatment of blanks

[0077] Example Billet cooling temperature, ℃ Cooling rate of ingot, ℃ / s Heating temperature, °C 1 827 10 270 2 816 6 292 3 815 3 229 4 820 7 232 5 828 6 239 6 819 4 281 7 836 9 279 8 847 8 360 9 846 11 221 10 810 9 320

[0078] Table 3 Heating process

[0079]

[0080]

[0081] Table 4 Rolling process

[0082]

[0083] Table 5 Steel plate structure

[0084]

[0085] Table 6 Steel plate structure

[0086]

[0087] Table 7 Mechanical properties of the examples

[0088]

[0089] It can be seen from the examples and comparative examples that the elongation of the present invention is ≥32%, and the uniform elongation is ≥20%, which is more than 35% higher than that of the existing low alloy steel.

[0090] Table 8 Welding performance of the embodiment (heat input 50KJ, submerged arc welding)

[0091]

[0092] Table 9 Corrosion resistance of the examples (g / m 2 .h)

[0093]

[0094] 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 collision-resistant steel for use in marine environments, characterized in that: The steel plate composition includes C: 0.02-0.04wt%, Si: 0.3-0.5wt%, Mn: 0.2-0.4wt%, V: 0.03-0.05wt%, N: 0.007-0.01wt%, Cu: 0.7-1wt%, Ni: 0.8-1.2wt%, Mo: 0.05-0.1wt%, W: 0.1-0.2wt%, Re: 0.01-0.02wt%, Cr: 1-1.5wt%, REM: 0.03-0.05wt%, Sn: 0.05-0.1wt%, Ti: 0.001-0.005wt%, P: 0.01-0.02wt%, S: ≤0.005wt%, and the balance of Fe and other inevitable impurities; The average grain size of the steel plate is 25-35μm, containing 20-25% low-carbon bainite + 40-50% blocky ferrite + 20-25% acicular ferrite structure, and the percentage is the area percentage; it contains spherical V (C, N), WC, Mo2C, Fe3C nanophases with an average size of 15-25nm dispersed and precipitated, and the average spacing of these precipitated phases is 1-1.5μm; it contains Cu nanophases with an average size of 43-65nm, and the average spacing of the phases is 2-3μm.

2. The anti-collision steel for marine environment according to claim 1, characterized in that: The dispersed precipitated V (C, N), WC, Mo2C, Fe3C nanophase size is 5-30nm, and the Cu nanophase size is 30-80nm.

3. The anti-collision steel for marine environment according to claim 1, characterized in that: The average grain size of the steel plate surface layer - 1 / 8 thickness is 15-22μm.

4. The anti-collision steel for marine environment according to claim 1, characterized in that: The yield strength of the steel is 360~400Mpa, the yield strength ratio is ≤0.74, the impact energy at -60℃ is not less than 130J, the elongation is ≥32%, and the uniform elongation is ≥20%.

5. The anti-collision steel for marine environment according to claim 1, characterized in that: Under the condition of 50KJ line energy, the tensile strength of the welded joint is controlled at 495~525MPa, and the impact energy at -60℃ is not less than 130J.

6. The anti-collision steel for marine environment according to claim 1, characterized in that: Using a simulated South China Sea seawater splash zone immersion test, the corrosion resistance is 67-80% relative to 3Ni system steel.

7. A method for producing anti-collision steel in marine environment according to any one of claims 1 to 6, characterized in that: It includes smelting, continuous casting, billet heating, controlled rolling and cooling, and off-line processing. The specific contents are as follows: Billet heating: The billet is cold loaded into the furnace at a temperature of ≤100°C, and multi-stage heating is adopted, wherein the total time at 650-1000°C is controlled within 0.2-0.3min / mm, the total time at 1230-1240°C is controlled within 0.1min / mm, and the total time at 1200-1220°C is controlled within 0.2-0.4min / mm; Controlled rolling and controlled cooling: In the first stage, the final rolling temperature is controlled at above 1000℃, and the pass reduction is controlled at 10-20%. In the second stage, the final rolling temperature is controlled at 915-950℃, and the pass reduction is 15-25%. Cooling is used as a transition between the two rolling passes, and the cooling rate is 0.5-2℃ / s. After rolling, the steel plate is relaxed to 500-550℃ and then cooled down at a cooling rate of 2-4℃ / s. Off-line treatment: After the steel plate is off the line, the second stage precipitation phase and internal stress are regulated by insulation treatment, and the insulation regulation temperature is 300-500℃.

8. The method for producing anti-collision steel in marine environment according to claim 7, characterized in that: The steel plate 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.

9. The method for producing anti-collision steel in marine environment 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 3-11°C / s. It is then subjected to low-temperature heating treatment at a heating temperature of 200-360°C.

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