High-strength marine engineering steel with high ductility and resistance to marine atmospheric corrosion and method for manufacturing the same

Abstract

The invention provides a high-strength marine engineering steel with high ductility and resistance to marine atmospheric corrosion and a manufacturing method thereof, wherein C: 0.035%-0.065%, Si: 0.15%-0.25%, Mn: 1.0%-1.40%, Cr: 0.70%-1.20%, Ni: 0.70%-1.20%, Cu: 0.20%-0.50%, Sn: 0.05%-0.15%, Nb: 0.02%-0.04%, Ti: 0.005%-0.025%, Ca: 0.002%-0.005%, P: ≤0.01%, S: ≤0.002%, Als: 0.02%-0.05%, and the rest is Fe and unavoidable impurities. The manufacturing method comprises smelting, continuous casting, primary rolling and secondary rolling; the steel plate produced by the present invention has a yield strength of ≥360MPa, a tensile strength of 490-630MPa, an elongation after fracture of ≥33%, a Charpy impact energy of ≥250J at -40°C, and a zero plastic transition temperature NDTT of ≤-50°C.

Description

Technical Field

[0001] The present invention belongs to the field of metal materials, and in particular relates to a high-strength marine engineering steel with high ductility and resistance to marine atmospheric corrosion and a manufacturing method thereof. Background Art

[0002] The particularity of the application environment of marine engineering has always placed high requirements on the service safety of marine equipment and structural materials. In recent years, as the offshore industry is gradually transforming and upgrading to the marine industry, the service environment of marine equipment has become increasingly complex and harsh. Not only does it require marine engineering steel to have good strength, but it also specifically requires steel plates to have high ductility and ultra-low temperature toughness to cope with sudden accidents and operational safety in severe sea conditions that ships and marine engineering equipment may encounter. The American ABS classification society has currently incorporated high ductility performance indicators into the relevant specifications "Material requirements for higher-ductility hull structural steel plates and sections". Its purpose is to allow the steel plate to absorb the energy of the collision when the ship, marine engineering equipment and structure collide, so that it is not easy to cause structural instability, thereby improving the service safety of the equipment. Japan's Nippon Steel and Sumitomo Metal have developed such marine engineering steel plates with high ductility and anti-collision functions ("NSafe-Hull" series), which are currently in the application stage. At present, my country has not formed a systematic research and large-scale application of such steel plates. On the other hand, since the marine atmospheric environment is characterized by high humidity, high salt fog, and high solar radiation intensity compared to the inland atmospheric environment, conventional steel grades are extremely susceptible to corrosion damage in this environment, seriously affecting the long-term service stability of marine engineering equipment and structures.

[0003] For a long time, the design and manufacturing of marine engineering steel have focused more on strength and toughness indicators, and less on the ductility and corrosion properties of the materials. However, with the deepening of human exploration of marine resources, marine engineering applications are developing towards the deep sea and offshore. The long-term service safety and stability brought by high ductility and resistance to marine atmospheric corrosion will become an inevitable trend in the future demand for marine engineering steel.

[0004] Public reports of related patents:

[0005] The invention patent with publication number CN110846554A discloses a method for manufacturing a high-ductility EH32 grade marine engineering steel and steel plate. The patent adopts a composition design scheme with alloy reduction, does not add high-priced metals and micro-alloying elements, and achieves high ductility and low-temperature toughness of the steel plate through a three-stage controlled rolling + controlled cooling TMCP process. However, since the three-stage rolling process requires two intermediate billets to be heated, the process is relatively cumbersome and the production efficiency is low. The corrosion performance of the steel plate was not evaluated.

[0006] The invention patent with publication number CN108517462A proposes a high-ductility EH40 grade ship plate steel and its preparation method. The patent is designed with low carbon and micro-alloy strengthening components, and adopts two-stage rolling plus water cooling-air cooling-water cooling three-stage cooling. The production process of this technology is complex, the control capability of the cooling equipment is high, and the process window is narrow. The corrosion performance of the steel plate has not been evaluated.

[0007] The invention patent with publication number CN110714171A discloses a high-ductility EH420 grade ship plate steel and its production method. The patent uses the TMCP method of low carbon plus Nb and Ti microalloy strengthening combined with two-stage rolling and two-stage cooling, and uses ultra-fast cooling technology with a cooling rate of 60℃ / s to obtain a composite structure of soft phase ferrite and hard bainite. However, this technology is difficult and it is difficult to achieve the required cooling rate conditions in actual industrial production, and there are limitations on the thickness of the steel plate. The corrosion performance of the steel plate was not evaluated.

[0008] The invention patent with publication number CN104046898A discloses a high-performance marine climate resistant steel plate and its manufacturing method. It adopts a low-alloy weathering steel composition design of ultra-low C-low Mn-high Als-low N-(Cu+high Ni) alloying-Nb micro-alloying-ultra-micro Ti treatment, and combines it with a two-stage controlled rolling + controlled cooling process in the austenite single-phase zone to obtain ferrite + pearlite (controlled rolling) or ferrite + bainite (TMCP) structure, and obtains a 355Mpa grade steel plate with resistance to marine atmospheric corrosion and a yield strength of less than 0.8. The tensile elongation of the steel plate is in the range of 30% to 35%.

[0009] The invention patent with publication number CN109136752A discloses a 420MPa grade low yield ratio marine atmospheric corrosion resistant bridge steel and its production method. It adopts a composition design of adding Cu and Ni corrosion resistant elements and combining Nb and Ti micro-alloying, combined with the process route of TMCP+low temperature tempering heat treatment, to obtain a steel plate with marine atmospheric corrosion resistance and a yield strength lower than 0.85, and the steel plate tensile elongation after fracture ranges from 28.5% to 33.5%.

[0010] The invention patent with publication number CN108004488A discloses a high-toughness bridge steel plate resistant to marine climate and its production method. Ca is used to control the number and shape of inclusions in the steel, and Sb, Cu, Ni, Cr, and Mo are added to improve the corrosion resistance of the steel. Through the TMCP post-tempering process, a 690Mpa grade steel plate with resistance to marine atmospheric corrosion and a yield strength of less than 0.86 is obtained, and the tensile elongation of the steel plate ranges from 25% to 28%.

[0011] The invention patent with publication number CN111014292A discloses a method for improving the production efficiency of thick plates in a single-stand rolling mill, which is to directly cool the intermediate billet after the first heating and rolling, and then heat and roll it again, and then directly roll it to the finished product thickness after the second heating to the target temperature. The method of directly cooling the intermediate billet and then heating and rolling it again saves the cooling time of the intermediate billet, which can significantly improve the efficiency of the rolling mill and thus greatly increase the mill hourly output. However, this method increases the consumption of energy and industrial water due to the increase in the heating and cooling process in the process path, and the extent of the improvement in production efficiency remains to be discussed. Summary of the invention

[0012] The object of the present invention is to overcome the above problems and shortcomings and to provide a high-strength marine engineering steel with high ductility, resistance to marine atmospheric corrosion, and a method for manufacturing the same, having a tensile elongation after break ≥33%, an impact energy ≥220J at -40°C, and an NDTT temperature ≤-50°C.

[0013] The object of the invention is achieved in this way:

[0014] The present invention adopts the composition design of low C + "Cr-Ni-Cu-Sn" alloying + Nb microalloying, combines the secondary heating controlled rolling and controlled cooling process to control the microstructure and grain size of the steel plate, and obtains a 360Mpa grade steel plate with high yield rate, stable strength and toughness, especially resistance to marine atmospheric corrosion and high ductility. Compared with the above-mentioned public patents, the present invention prepares a marine engineering steel plate with resistance to marine atmospheric corrosion, high ductility and low temperature toughness suitable for the field of marine engineering. Its comprehensive performance can meet the long-term service conditions of marine engineering equipment, with a tensile elongation of ≥33%, an impact energy of ≥220J at -40℃, and an NDTT temperature of ≤-50℃.

[0015] A high-strength marine engineering steel with high ductility and resistance to marine atmospheric corrosion, the components of the steel are as follows by weight percentage: C: 0.035%-0.065%, Si: 0.15%-0.25%, Mn: 1.0%-1.40%, Cr: 0.70%-1.20%, Ni: 0.70%-1.20%, Cu: 0.20%-0.50%, Sn: 0.05%-0.15%, Nb: 0.02%-0.04%, Ti: 0.005%-0.025%, Ca: 0.002%-0.005%, P: ≤0.01%, S: ≤0.002%, Als: 0.02%-0.05%, and the rest is Fe and unavoidable impurities.

[0016] The offshore steel plate has a yield strength of ≥360MPa, a tensile strength of 490-630MPa, an elongation after fracture of ≥33%, a Charpy impact energy at -40°C of ≥250J, a zero plastic transition temperature NDTT of ≤-50°C, and a thickness of 20-50mm.

[0017] The marine engineering steel microstructure is mainly composed of ferrite and bainite, wherein the volume percentage of ferrite is 85% to 95%, and the average grain size of ferrite is 10.0 to 18.0 μm.

[0018] The reasons for the composition design of the present invention are as follows:

[0019] C: is a necessary element to ensure strength. It has a significant effect on improving the strength of steel through solid solution strengthening and precipitation strengthening. However, too high C content has a negative impact on the ductility, low temperature toughness and fracture toughness, weldability and corrosion resistance of steel. Too low C content will lead to high austenite crystal mobility, affect the uniform refinement of the TMCP process, and easily form mixed crystal structure. Therefore, from the perspective of product performance, it is preferred that the C content be controlled at C: 0.035-0.065%.

[0020] Si: It is the main deoxidizing component in the steelmaking process. In order to obtain a sufficient deoxidation effect, it must contain more than 0.10%. However, too high an upper limit will reduce the toughness of the base material and the weld. Si in the form of solid solution will increase the strength while also reducing plasticity and increasing the ductile-brittle transition temperature. Therefore, the preferred Si content is 0.15-0.25%.

[0021] Mn: Mn is an essential element to ensure the strength and toughness of steel. With the increase of Mn content, the strength of steel increases significantly. 1% Mn can increase the tensile strength by about 100MPa. In addition to improving strength and toughness, it also has the effect of expanding the austenite phase, reducing the temperature of Ac1, Ac3, Ar1, Ar3 points, and refining ferrite grains. However, Mn is easy to segregate in steel, and it is easy to segregate at 1 / 4 and 1 / 2 thickness of medium and thick steel plates, resulting in a strong decrease in low-temperature toughness and even impact fracture delamination. More importantly, with the increase of Mn content, the corrosion resistance of the steel plate will drop sharply. Therefore, considering the material mechanics and corrosion resistance, it is preferred that the Mn content be controlled in the range of 1.0% to 1.40%.

[0022] Cr: Cr is an effective element for improving the corrosion resistance of steel. It can form a dense passivation layer containing Cr that is closely bonded to the substrate. This relatively stable structure can improve the corrosion resistance of steel. In addition, Cr is also an effective element for improving the strength of steel plates. However, excessive Cr can cause a decrease in welding performance. Therefore, the present invention controls the Cr content to 0.70% to 1.20%.

[0023] Ni: Ni has a solid solution strengthening effect, which can improve the strength and toughness of steel. It has the characteristics of reducing the Ar3 point and minimizing the increase in carbon equivalent or cold crack sensitivity coefficient Pcm. Ni is also one of the key alloying elements to improve the marine atmospheric corrosion resistance of steel plates. Adding Ni to steel can promote the formation of a stable, dense, chloride ion-resistant amorphous layer on the surface of the steel plate, inhibit the permeability of chloride ions and oxygen atoms, and improve the marine atmospheric corrosion resistance of the steel plate; secondly, the amorphous oxide amorphous layer with a high pH value inhibits electrochemical reactions and improves the marine atmospheric corrosion resistance of the steel plate, but the cost of adding Ni is relatively high, so the Ni content is controlled in the range of 0.70% to 1.10%.

[0024] Cu: Cu is an essential element for resisting marine atmospheric corrosion. During the corrosion process of steel, it will be enriched in the inner rust layer in the form of CuO, which can well isolate corrosive media, reduce the promoting effect of chloride ions on corrosion, and increase the polarization resistance of steel, resulting in enhanced protection of the rust layer, thereby improving the marine atmospheric corrosion resistance of steel. In terms of mechanical properties, Cu can improve the strength of steel plates and has little effect on the low-temperature toughness of steel plates; but when too much Cu is added, fine and dispersed ε-Cu precipitation will occur during hot rolling and normalizing treatment (the solid solubility of Cu in ferrite is about 0.45%), which will damage the low-temperature toughness of the steel plate, and may also cause copper embrittlement, ingot cracks, liquid precipitation and other defects. Therefore, considering the material mechanics and corrosion resistance, it is preferred that the Cu content range is controlled within 0.20% to 0.50%.

[0025] Sn: Sn can increase the corrosion potential of steel itself, reduce the self-corrosion current density, increase the double layer resistance, inhibit ion exchange, and slow down the corrosion rate, thereby improving its corrosion resistance. After the rust layer is formed, the presence of SnO2 in the rust layer can inhibit the further dissolution of steel and reduce the corrosion rate. There is also a synergistic effect between Sn and Cu, forming a continuous film layer containing tin oxide and copper oxide on the surface of steel, which improves the corrosion resistance of steel. However, too high Sn content will damage the toughness of steel and increase the risk of local acid pitting, so its content is controlled at 0.05% to 0.15%.

[0026] Nb: Nb has a strong affinity with C, N, and O, and forms corresponding extremely stable compounds with them. Nb can refine the grains of steel and reduce the overheating sensitivity of steel. Under certain conditions, it can improve the strength and toughness of steel, especially under the conditions of induction heating with a high heating rate, and precipitates fine Nb carbonitrides to refine austenite grains. The Nb content of the present invention is controlled at 0.02% to 0.04%.

[0027] Ti: Ti can not only improve the strength of steel, refine grains, reduce aging sensitivity and cold brittleness, but also improve welding performance in small amounts. Ti works in the form of TiN. When it is less than 0.005%, the effect is small, and when it exceeds 0.04%, it is easy to form large particles of TiN and lose the effect. Therefore, the preferred Ti content is 0.005% to 0.025%.

[0028] Ca: Ca treatment is performed on molten steel to purify the molten steel. The Ca element can spheroidize the MnS inclusions and disperse their size, preventing the MnS inclusions from forming long strip plastic shapes during the rolling process, and forming dispersed spherical shapes, and refining the size of sulfide inclusions, inhibiting the hot brittleness of S, improving the impact toughness and Z-direction performance of the steel plate, and improving the anisotropy of the impact toughness of the steel plate. The amount of Ca added depends on the S content in the steel. If the Ca addition is too low, the treatment effect is not great; if the Ca addition is too high, the size of Ca(O,S) is too large, the brittleness is also increased, and it can become the starting point of the fracture crack, reducing the low-temperature toughness of the steel, while also reducing the purity of the steel and polluting the molten steel. The present invention controls the Ca element content to 0.002% to 0.005%.

[0029] P: P can segregate in the center of the slab and gather at the grain boundaries, and is an element that has an adverse effect on the low-temperature toughness, ductility and weldability of the steel plate. Although P has the effect of improving the marine atmospheric corrosion resistance of the steel plate, considering the damage of P to the mechanical properties of the steel plate, P cannot be used to improve the marine atmospheric corrosion resistance of the steel plate. The present invention requires that the P content be controlled to be no higher than 0.01%.

[0030] S: S can combine with Mn in steel to form MnS inclusions. During hot rolling, MnS extends along the rolling direction to form a MnS inclusion band along the rolling direction, which becomes a crack source and seriously damages the transverse low-temperature impact toughness and Z-direction properties of the steel plate. The content of S in the material of the present invention is controlled to be no higher than 0.002%.

[0031] Als: As a deoxidation and grain refinement element that must be added in the present invention, the added content is above 0.01%, but when it exceeds 0.08%, hot cracks of the casting are likely to occur, and the toughness of the steel is reduced. The Als content is controlled at 0.01% to 0.05%.

[0032] The second technical solution of the present invention is to provide a method for manufacturing high-strength marine engineering steel with high ductility and resistance to marine atmospheric corrosion, including smelting, continuous casting, primary rolling, and secondary rolling;

[0033] (1) Smelting and continuous casting: Smelting is carried out according to the composition range of the present invention, and a continuous casting billet is obtained after smelting and continuous casting. The LF and RH refining furnace treatments each require 20 to 40 minutes, the superheat of the molten steel in the tundish is ≤25°C, and the casting is protected throughout the process; the A, B, C, and D inclusions in the steel meet the requirements of A≤0.5, B≤0.5, C≤0.5, and D≤0.5.

[0034] One-step rolling process:

[0035] The heating temperature is 1150-1190°C, the rolling temperature is in the austenite recrystallization temperature zone of 1000-1060°C, and the average single-pass reduction rate is above 10%, so as to fully carry out the dynamic recrystallization process of austenite and refine the austenite grain size; after the first rolling, a rapid laminar cooling system with an average cooling rate of 10-20°C / s is used to quickly cool the intermediate billet to room temperature, complete the austenitization pretreatment of the intermediate billet, and obtain a fine martensite / bainite structure;

[0036] Secondary rolling process:

[0037] The intermediate billet cooled to room temperature is heated up to 900-950°C for the second time, the start rolling temperature of the second rolling is 780-830°C, the average single-pass reduction rate reaches 15%-20%, and the final rolling temperature is 760-800°C; after the steel plate is relaxed to 700-730°C, it is rapidly cooled at an average cooling rate of 5-10°C / s, the red-return temperature is 550-600°C, and then the steel plate is slowly cooled to room temperature.

[0038] The intermediate billet cooled to room temperature is heated up to 900-950℃ for the second time to re-austenize the intermediate billet. The pre-treatment structure after one rolling and cooling is a fine martensite / bainite structure. This non-steady-state structure has a high internal energy storage. A large number of crystal defects such as dislocations and interfaces can provide a large number of recrystallization nucleation points during the secondary heating austenitization process, and a finer austenite structure can be obtained; on the other hand, the secondary heating is equivalent to the normalizing treatment, which is conducive to the uniform distribution of corrosion-resistant solid solution elements in the steel. The opening temperature of the secondary rolling is 780-830℃ in the austenite / proeutectoid ferrite two-phase region, the average single-pass reduction rate reaches 15-20%, and the final rolling temperature is 760-800℃. The purpose is to fully deform the austenite grains, provide energy storage and position for the phase deformation nucleus, increase the phase deformation nucleus rate, and further reduce the ferrite grains in the two-phase region, and finally achieve the purpose of grain refinement.

[0039] After the post-rolling relaxation phase transformation, the steel plate enters the cooling system. The specific control process of the post-rolling relaxation phase transformation is: by adjusting the cooling temperature to control the relaxation time of the α / γ two-phase region, and then adjust the ratio and morphology of the F / B two-phase structure of the steel plate. The steel plate is relaxed to 700-730℃ before entering the cooling system. The purpose is to increase the relaxation time in the α / γ two-phase region after final rolling, which is conducive to the full nucleation of the proeutectoid ferrite and ensure that the proportion of the ferrite structure of the final structure is greater than 85%. During relaxation, the carbon element in the supercooled austenite develops from uniform distribution to aggregation, and the area where carbon migrates out forms proeutectoid ferrite, that is, the long-range diffusion of carbon expulsion from the proeutectoid ferrite to the austenite. Therefore, the longer the steel plate relaxes before the cooling, the more fully this phase transformation and carbon diffusion process proceeds, the higher the degree of C element aggregation in the austenite area around the proeutectoid ferrite, and bainite is formed in the subsequent laminar rapid cooling process. Therefore, the present invention requires that the C content is less than 0.065%, which can effectively reduce the carbon enrichment phenomenon of the surrounding austenite during the nucleation and growth of proeutectoid ferrite, which is beneficial to the dispersion distribution of bainite and avoids local stress concentration during the deformation process;

[0040] After the steel plate relaxes to 700-730℃, it enters a rapid laminar cooling system with an average cooling rate of 5-10℃ / s. The red-return temperature is controlled at 550-600℃. The purpose is to control the phase change structure and size. The steel plate is then slowly cooled to room temperature, and the slow cooling time is ≥20h.

[0041] The beneficial effects of the present invention are:

[0042] (1) The present invention improves the purity of steel by controlling the sulfur and phosphorus content in pure steel smelting, and improves the steel quality by treating spheroidized inclusions with Ca. The chemical composition of the steel plate is rationally designed, and a low C content is used and Cr, Cu, Ni, and Sn are added to improve the marine atmospheric corrosion resistance of the steel. The addition of a small amount of Sn plays a synergistic role with other corrosion-resistant elements, and reduces the amount of Cu, Cr, and Ni high-valent alloy elements to a certain extent. The combination of other elements such as Si, Mn, and Nb microalloying ensures the toughness of the steel. Through the interaction between the elements, the steel plate has excellent marine atmospheric corrosion resistance, elongation, and low-temperature impact performance.

[0043] (2) An innovative method of secondary heating rolling and controlled cooling is adopted. The intermediate billet is heated again after rapid cooling. The non-steady-state structure with high energy storage releases energy and provides a large number of nucleation sites during the re-austenitization process, which refines the austenite grain size of the intermediate billet. At the same time, it is beneficial to the good organization and composition uniformity of the steel plate in the second stage of rolling, which is beneficial to the improvement of the plastic toughness of the product and provides a guarantee for the service safety of marine engineering.

[0044] (3) The steel plate prepared by the present invention has resistance to marine atmospheric corrosion, high strength (yield strength ≥360MPa, tensile strength 490-630MPa), high ductility (elongation after fracture ≥33%) and low-temperature impact toughness (-40℃ Charpy impact energy ≥250J, zero plastic transition temperature (NDTT) ≤-50℃). The product thickness ranges from 20 to 50mm.

[0045] (4) The microstructure of the steel of the present invention is mainly composed of ferrite + bainite, wherein the ferrite content ranges from 85 to 95%, and the average ferrite grain size is 10.0 to 18.0 μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a metallographic microstructure diagram of Example 1 of the present invention. DETAILED DESCRIPTION

[0047] The present invention will be further described below by way of examples.

[0048] The embodiment of the present invention performs smelting, continuous casting, primary rolling and secondary rolling according to the component ratio of the technical solution;

[0049] One-pass rolling:

[0050] The heating temperature is 1150-1190°C, the rolling temperature is in the austenite recrystallization temperature zone of 1000-1060°C, and the average single-pass reduction rate is above 10%; after one rolling, the intermediate billet is quickly cooled to room temperature, and the cooling rate is 10-20°C / s;

[0051] Secondary rolling:

[0052] The intermediate billet cooled to room temperature is heated up to 900-950°C for the second time, the start rolling temperature of the second rolling is 780-830°C, the average single-pass reduction rate reaches 15%-20%, and the final rolling temperature is 760-800°C; after the steel plate is relaxed to 700-730°C, it is rapidly cooled at an average cooling rate of 5-10°C / s, the red return temperature is 550-600°C, and then the steel plate is slowly cooled to room temperature.

[0053] Furthermore, the microstructure of the steel plate after one rolling is martensite / bainite.

[0054] Further; smelting and continuous casting: smelting is carried out according to the composition range of the present invention, and a continuous casting billet is obtained after smelting and continuous casting. The LF and RH refining furnace treatments each require 20 to 40 minutes, the superheat of the molten steel in the middle package is ≤25°C, and the casting is protected throughout the process; A, B, C, and D inclusions in the steel meet the requirements of A≤0.5, B≤0.5, C≤0.5, and D≤0.5.

[0055] The composition of the steel of the embodiment of the present invention is shown in Table 1. The main process parameters of the steel of the embodiment of the present invention are shown in Table 2. The main process parameters of the controlled rolling and controlled cooling of the steel of the embodiment of the present invention are shown in Table 3. The mechanical properties and NDTT temperature of the steel of the embodiment of the present invention are shown in Table 4. The marine atmospheric corrosion resistance rate of the steel of the embodiment of the present invention and the comparative example is shown in Table 5. The microstructure of the steel of the embodiment of the present invention is shown in Table 6.

[0056] Table 1 Composition of steel according to the present invention (wt%)

[0057] Example C Si Mn Cr Ni Cu Sn Nb Ti Ca Als 1 0.046 0.25 1.36 0.77 0.72 0.26 0.067 0.036 0.012 0.002 0.035 2 0.057 0.17 1.24 0.82 0.75 0.35 0.089 0.035 0.011 0.003 0.023 3 0.049 0.23 1.27 0.75 0.83 0.34 0.085 0.033 0.013 0.003 0.034 4 0.053 0.24 1.19 0.91 0.98 0.28 0.094 0.038 0.012 0.004 0.041 5 0.056 0.16 1.25 0.96 1.02 0.40 0.121 0.030 0.012 0.005 0.029 6 0.042 0.23 1.38 1.12 0.81 0.44 0.091 0.031 0.010 0.002 0.027 7 0.063 0.2 1.26 1.03 1.03 0.39 0.107 0.034 0.012 0.003 0.043 8 0.058 0.21 1.33 0.99 1.08 0.47 0.112 0.031 0.013 0.004 0.031 Comparative Example 0.093 0.16 1.48 0.02 0.03 ＜0.005 ＜0.005 0.033 0.013 0.002 0.035

[0058] Note: P: ≤0.01%, S: ≤0.002%

[0059] Table 2 Main process parameters for steel smelting in the embodiment of the present invention

[0060]

[0061] Table 3 Main process parameters of controlled rolling and controlled cooling of steel in the embodiment of the present invention

[0062]

[0063] Table 4 Mechanical properties and NDTT temperature of steel according to the present invention

[0064]

[0065] Table 5 Marine atmospheric corrosion resistance rate of steels in the embodiments of the present invention and comparative examples (g / m 2 h)

[0066] Example 168h 360h 1 0.7533 0.7083 2 0.7322 0.7029 3 0.7026 0.6851 4 0.6941 0.6516 5 0.6582 0.6227 6 0.6795 0.6394 7 0.6326 0.5348 8 0.6068 0.5120 Comparative Example 0.9754 0.8906

[0067] Note: The corrosion resistance test experiment adopts the laboratory salt spray accelerated corrosion test to simulate the marine atmosphere environment, and the accelerated corrosion test is carried out on the embodiment of the present invention, and a 50mm thick EH36 steel plate is introduced as a comparative example. The test solution is 3.5% NaCl solution, the temperature in the salt spray chamber is controlled at 35±2℃, and the salt spray settling speed is 80cm / s. 2 The area settles 1.5 to 2 ml per hour. The corrosion cycle nodes are set at 168h and 360h. After accelerated corrosion, the weight loss method is used to measure and calculate the average corrosion rate (g / m 2 h) Evaluate the corrosion resistance of the steel plate.

[0068] Table 6 Microstructure of steel in the embodiment of the present invention

[0069] Example Ferrite / Vol% Average ferrite grain size μm 1 85.3 14.6 2 86.1 15.2 3 88.2 15.3 4 86.5 12.4 5 91.4 13.1 6 92.7 12.8 7 89.6 16.4 8 90.5 15.5

[0070] The marine engineering steel plate produced by the present invention has a yield strength of ≥360MPa, a tensile strength of 490-630MPa, an elongation after fracture of ≥33%, a Charpy impact energy of ≥250J at -40°C, a zero plastic transition temperature NDTT ≤-50°C, and a steel plate thickness of 20-50mm.

[0071] In order to describe the present invention, the present invention is appropriately and fully illustrated by the examples in the above. The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made should be included in the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A high-strength marine engineering steel with high ductility and resistance to marine atmospheric corrosion, characterized in that: The steel has the following components by weight percentage: C: 0.035%-0.065%, Si: 0.15%-0.25%, Mn: 1.0%-1.40%, Cr: 0.70%-1.20%, Ni: 0.70%-1.20%, Cu: 0.20%-0.50%, Sn: 0.05%-0.15%, Nb: 0.02%-0.04%, Ti: 0.005%-0.025%, Ca: 0.002%-0.005%, P: ≤0.01%, S: ≤0.002%, Als: 0.02%-0.05%, and the remainder is Fe and unavoidable impurities; The method for manufacturing a high-strength marine engineering steel with high ductility and resistance to marine atmospheric corrosion comprises smelting, continuous casting, primary rolling and secondary rolling; One-pass rolling: The heating temperature is 1150-1190°C, the rolling temperature is in the austenite recrystallization temperature zone of 1000-1060°C, and the average single-pass reduction rate is above 10%; after one rolling, the intermediate billet is quickly cooled to room temperature, and the cooling rate is 10-20°C / s; Secondary rolling: The intermediate billet cooled to room temperature is heated up to 900-950°C for the second time, the start rolling temperature of the second rolling is 780-830°C, the average single-pass reduction rate reaches 15%-20%, and the final rolling temperature is 760-800°C; after the steel plate is relaxed to 700-730°C, it is rapidly cooled at an average cooling rate of 5-10°C / s, the red return temperature is 550-600°C, and then the steel plate is slowly cooled to room temperature.

2. The high-strength marine engineering steel with high ductility and resistance to marine atmospheric corrosion according to claim 1, characterized in that: The marine engineering steel has a microstructure of ferrite+bainite, wherein the volume percentage of ferrite is 85% to 95%, and the average grain size of ferrite is 10.0 to 18.0 μm.

3. The high-strength marine engineering steel with high ductility and resistance to marine atmospheric corrosion according to claim 1, characterized in that: The offshore steel plate has a yield strength of ≥360MPa, a tensile strength of 490-630MPa, an elongation after fracture of ≥33%, a Charpy impact energy at -40°C of ≥250J, a zero plastic transition temperature NDTT of ≤-50°C, and a thickness of 20-50mm.

4. A high-strength marine engineering steel with high ductility and resistance to marine atmospheric corrosion according to claim 3; characterized in that: The microstructure of the steel plate after one rolling is martensite / bainite.

5. The high-strength marine engineering steel with high ductility and resistance to marine atmospheric corrosion according to claim 3; characterized in that: Smelting and continuous casting: Smelting is carried out according to the composition range of steel. After smelting and continuous casting, continuous casting billets are obtained. The LF and RH refining furnace treatments each require 20 to 40 minutes. The superheat of the molten steel in the tundish is ≤25°C, and the casting is protected throughout the process. The A, B, C, and D inclusions in steel meet the requirements of A≤0.5, B≤0.5, C≤0.5, and D≤0.5.

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