Corrosion-fatigue-resistant ultrahigh-strength marine steel and preparation method thereof

Abstract

The invention provides corrosion-fatigue-resistant ultrahigh-strength maritime work steel and a preparation method thereof, and relates to the technical field of maritime work steel manufacturing. The maritime work steel comprises the following components in percentage by mass: 0.04 to 0.07 percent of C, 0.20 to 0.26 percent of Si, 1.45 to 1.60 percent of Mn, less than or equal to 0.01 percent of P, less than or equal to 0.015 percent of S, 1.44 to 1.52 percent of Cr, 1.44 to 1.52 percent of Ni, 0.88 to 0.96 percent of Cu, 0.08 to 0.12 percent of Nb, 0.08 to 0.12 percent of Sb and the balance of Fe and inevitable impurities. The corrosion-fatigue-resistant ultrahigh-strength maritime work steel is prepared through raw material smelting and casting, austenitizing heat treatment, multi-pass hot rolling and cooling and temperature control. The corrosion resistance, the fatigue resistance and the corrosion fatigue resistance of the ultrahigh-strength maritime work steel are remarkably improved while the mechanical property of the ultrahigh-strength maritime work steel is improved, and the ultrahigh-strength maritime work steel has great significance in guaranteeing safe and stable operation of ocean engineering.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of offshore steel manufacturing, and particularly relates to an anti-corrosion fatigue type ultrahigh-strength offshore steel and a preparation method thereof. BACKGROUND

[0002] The high-strength offshore steel is always subjected to the strong coupling of various harsh factors such as a complex marine environment, a load and corrosion during long-term service, and is prone to failure due to corrosion fatigue and the like. In particular, the corrosion fatigue increasingly causes damage to marine engineering structures and failure of marine engineering equipment, and has become a key problem restricting the long service life of major marine engineering structures.

[0003] Micro-alloying, microstructure regulation and process optimization are the current regulation and technical researches for improving the strength and toughness and corrosion resistance of offshore steel. Compared with microstructure regulation (transformation control, grain refinement, etc.) and process optimization (controlled rolling and controlled cooling, heat treatment, etc.), micro-alloying has unique advantages in improving the comprehensive performance of offshore steel. Firstly, the synergistic regulation of microstructure improves the strength and toughness: nano-precipitation strengthening, grain boundary pinning effect and grain refinement not only improve the strength of offshore steel, but also ensure the toughness. Secondly, the essential improvement of corrosion resistance: the stability of corrosion product film is enhanced, and the density of irreversible hydrogen traps is improved, which not only slows down the enrichment of erosive ions, but also inhibits the diffusion and aggregation of hydrogen, thereby improving the resistance of offshore steel to hydrogen-induced cracking. Thirdly, the unique mechanism of corrosion fatigue resistance: crack propagation path regulation and electrochemical-mechanical coupling inhibit corrosion fatigue, on the one hand, the submicron precipitates change the crack propagation path and slow down the crack propagation, and on the other hand, the inhibition of cathodic reaction and anodic dissolution inhibits the initiation and propagation of corrosion fatigue cracks, thereby improving the corrosion fatigue resistance of offshore steel. Therefore, the development of high-strength offshore steel not only focuses on the engineering comprehensive performance such as strength and toughness and corrosion resistance, but also focuses on the design and development of long-life corrosion fatigue resistant ultrahigh-strength offshore steel for complex marine environments.

[0004] For example, Chinese patent CN116043105A discloses a corrosion-resistant ultrahigh-strength steel for offshore platforms and a preparation method thereof, which only focuses on the improvement of corrosion resistance, and does not focus on the synergistic improvement of fatigue resistance and fatigue corrosion resistance and strength; in particular, the strength values in Tables 1-3 prove this point, and the lower strength-plasticity product of the prepared steel than that of the present application also indicates that the strength-plasticity performance of the prepared steel is poorer than that of the present application.

[0005] Chinese patent CN117660837A discloses an anti-seawater corrosion fatigue ultrahigh-strength marine steel with high ductility and its manufacturing method. Although the strength of the prepared steel plate is improved, the maximum tensile strength does not exceed 1100MPa, the maximum yield strength does not exceed 920MPa, the preparation process is complex, the cost is high, the efficiency is low, and the corrosion fatigue life is lower than that of the present application. Chinese patent CN113549825A is also the same.

[0006] Chinese patent CN114990433A discloses a corrosion-resistant steel suitable for high-humidity marine environment and its preparation method. The content of Mn and Cr is low, and the content of Cu and Sb is high in the component selection. The prepared corrosion-resistant steel cannot be synergistically improved in strength, corrosion resistance and fatigue resistance by quenching and tempering treatment after hot rolling and air cooling.

[0007] Therefore, it is urgent to develop an anti-corrosion fatigue type ultrahigh-strength marine steel and its preparation method. SUMMARY

[0008] The present application is to solve the technical problems of the prior art that the strength, ductility, fatigue resistance and fatigue corrosion resistance of traditional marine steel cannot be synergistically improved, and the preparation cost is high, the process is complex, the efficiency is low, the product quality is poor, the product quality is unstable, and it is not conducive to industrial large-scale production and promotion. Therefore, an anti-corrosion fatigue type ultrahigh-strength marine steel and its preparation method are proposed to solve the above problems.

[0009] An anti-corrosion fatigue type ultrahigh-strength marine steel, the steel plate thickness of the anti-corrosion fatigue type ultrahigh-strength marine steel is 10-12mm, and the components are as follows in terms of mass percentage: C 0.04-0.07%, Si 0.20-0.26%, Mn 1.45-1.60%, P≤0.01%, S≤0.015%, Cr 1.44-1.52%, Ni 1.44-1.52%, Cu 0.88-0.96%, Nb 0.08-0.12%, Sb 0.08-0.12%, and the balance is Fe and unavoidable impurities.

[0010] Optionally, the microstructure of the anti-corrosion fatigue type ultrahigh-strength marine steel is lath and granular bainite.

[0011] Optionally, the performance of the anti-corrosion fatigue type ultrahigh-strength marine steel is as follows: yield strength≥880MPa, tensile strength≥1000MPa, yield strength ratio≤0.90, elongation≥14%, and strength plastic product reaches 15GPa%.

[0012] The corrosion rate of the ultrahigh-strength marine steel after immersion in simulated seawater for 150d is less than 0.05mm / a.

[0013] The axial fatigue test in air at room temperature is carried out at a stress ratio of 0.1, a loading frequency of 10 Hz, and a loading waveform of a sine wave, and the fatigue limit of the super-high-strength marine steel is 828.73 MPa.

[0014] Alternatively, the solution composition of the simulated seawater is 24.53 g / L of NaCl, 5.20 g / L of MgCl2, 4.09 g / L of Na2SO4, 1.16 g / L of CaCl2, 0.695 g / L of KCl, 0.201 g / L of NaHCO3, 0.101 g / L of KBr, 0.027 g / L of H3BO3, 0.025 g / L of SrCl2, and 0.003 g / L of NaF.

[0015] A preparation method of the anti-corrosion fatigue type super-high-strength marine steel, the preparation method comprising the following steps:

[0016] S1, raw material smelting and casting: the raw materials are weighed and matched according to the component content of the anti-corrosion fatigue type super-high-strength marine steel, then a vacuum induction furnace is used for smelting to obtain a molten steel, and then the molten steel is cooled to obtain a marine steel ingot;

[0017] S2, austenitizing heat treatment: the marine steel ingot obtained in S1 is heated to an austenitizing temperature and is kept for a certain time, and then the austenitizing steel ingot is obtained after complete austenitization;

[0018] S3, multi-pass hot rolling: the austenitizing steel ingot obtained in S2 is furnace-cooled to a rolling temperature and is kept for a certain time, and then multi-pass rolling is performed to obtain a hot-rolled marine steel plate;

[0019] S4, controlled cooling and temperature control: the hot-rolled marine steel plate obtained in S3 is sent to a water flow area for cooling, and then is cooled to room temperature in air to obtain an anti-corrosion fatigue type super-high-strength marine steel plate.

[0020] Alternatively, the austenitizing temperature in S2 is 1190-1210℃, and the holding time is 1.5-2h.

[0021] Alternatively, the rolling temperature in S3 is 990-1010℃, the holding time is 1.5-2.5h, the number of passes of the multi-pass rolling is 10-12, the reduction per pass is 1mm, and the finish rolling temperature is 870-890℃.

[0022] Alternatively, the cooling rate in S4 is 20-25℃ / s, and the water outlet temperature is ensured to be between 420-440℃.

[0023] Alternatively, the anti-corrosion fatigue type super-high-strength marine steel plate obtained in S4 has a fatigue life of 107 The steel does not break due to fatigue for several weeks, and the fatigue strength is increased by more than 28%; under the same peak stress load, the corrosion fatigue life is increased by more than 60%.

[0024] Technical principle of the application:

[0025] The application selects the above alloying elements and their contents based on the principles of improving the strength, toughness, corrosion resistance and fatigue resistance of the steel for marine engineering as follows:

[0026] Effect of C: C is one of the most basic elements in steel and one of the best alloying elements for strengthening. When the C content in the steel increases, cracks are easily generated during heat treatment, and too high carbon content also deteriorates the welding performance of the steel. Therefore, the application adopts ultra-low carbon design to improve the tensile strength and yield strength of the marine steel through grain refinement and nano precipitates, and the C content in the application is set to 0.04-0.07%.

[0027] Effect of Si: Si is a necessary element for deoxidization in steelmaking and has a certain solid solution strengthening effect in steel, and appropriate Si is also beneficial to the refinement of alpha-FeOOH, thereby reducing the overall corrosion rate of the steel. In combination with other elements such as Cr, Cu, etc., the corrosion resistance of the steel can be effectively improved. However, too high Si content in the steel will reduce the critical cooling rate of martensite transformation, seriously damaging the low temperature toughness, elongation and weldability of the ultra-high strength steel plate. Si not only promotes the formation of M-A islands, but also forms relatively coarse M-A islands with uneven distribution, reducing the toughness of the heat affected zone. Considering the above, the Si content in the application is set to 0.20-0.26%.

[0028] Effect of Mn: Mn mainly plays a solid solution strengthening role and is an important element for significantly improving strength and toughness, with very low cost, being the main added element in steel. When the C content is low, higher Mn content can improve the strength of the steel plate through organization refinement and promotion of bainite transformation, and also has benefits for improving corrosion resistance. Mn expands the austenite region and promotes grain growth, so it is necessary to add grain refinement elements such as Nb, Sb, V and Ti to promote grain refinement and improve the fatigue performance of the steel. However, too high Mn content in the steel can easily form Mn segregation, which not only affects the toughness of the steel, but also easily leads to H2S corrosion cracking. Therefore, the Mn content in the application is set to 1.45-1.60%.

[0029] Effect of Cr: Cr can improve the strength and hardness of the steel. Cr is a ferrite forming element, which can increase the ferrite content in the steel and improve the low temperature toughness of the steel. In addition, Cr can effectively improve the corrosion resistance of the steel. Cr has an accelerated film forming effect, which can promote the formation of α-FeOOH to improve the density and stability of the rust layer, inhibit the initiation of local corrosion and fatigue cracks. In addition, Cr can have good corrosion resistance in an environment with a pH value of > 4. Therefore, the content of Cr in the present application is set to 0.48-1.52%.

[0030] Effect of Cu: Cu is the most important and most commonly used alloying element in corrosion-resistant steel. When a proper amount of Cu is added to the steel, not only can the cathodic reaction be inhibited, but also the anodic passivation can be promoted to slow down the corrosion; in addition, Cu can form a dense and strongly adherent intermediate layer in the corrosion products during corrosion, which can effectively alleviate the corrosion of the steel. Especially when used in combination with P, the corrosion resistance of the steel in various atmospheric corrosion environments and seawater environments can be significantly improved. However, excessive Cu content can cause "copper brittleness", which seriously affects the quality of the steel. Therefore, the content of Cu in the present application is set to 0.28-0.92%.

[0031] Effect of Ni: Ni can strengthen ferrite and refine pearlite in the steel to improve the strength of the steel. At the same time, the addition of Ni can greatly increase the self-corrosion potential of the material in a chloride ion environment, enhance the corrosion resistance, and in addition, can improve the corrosion product layer, and by promoting the formation of α-FeOOH, the density of the corrosion product layer can be improved. However, Ni is expensive, and considering the overall situation, the content of Ni in the present application is set to 0.79-1.52%.

[0032] Effect of Nb: Nb is an important factor in controlled rolling and controlled cooling steel. The addition of Nb can effectively improve the comprehensive mechanical properties and corrosion resistance. The addition of trace amounts (<0.1%) of Nb to low alloy steel can effectively refine the grains by precipitating nanometer Nb(C,N) particles, thereby significantly improving the comprehensive mechanical properties of the steel. Nb forms a dense product on the surface of the matrix, mainly Nb oxides, which can inhibit anodic dissolution and alleviate the occurrence of local corrosion. Therefore, the content of Nb in the present application is set to 0.08-0.12%.

[0033] Effect of Sb: Sb precipitates along the prior austenite grain boundaries below the austenite temperature, thereby inhibiting the precipitation of MnS inclusions; at the same time, Sb can refine the structure of the steel to improve toughness and fatigue resistance. In addition, the content of Sb in the steel is usually not more than 0.12%, which can improve the corrosion resistance of low alloy steel. Sb not only forms a protective Sb2O5 oxide film on the surface, but also forms a compound with Cu that has high corrosion resistance, thereby further inhibiting the electrochemical anodic and cathodic reactions, reducing the corrosion current density, and effectively inhibiting the anodic dissolution process of the steel in the marine environment. Therefore, the content of Sb element in the present application is set to 0.08-0.12%.

[0034] In addition, the control of P and S is also very important. P is easy to form serious segregation, and high P content will affect the mechanical properties and weldability of the material, so the P content should be controlled below 0.04%. The addition of S is easy to form dangerous inclusions such as MnS. Therefore, P and S in the steel need to be controlled as low as possible, so the content of P and S in the present application is controlled as P≤0.01%, S≤0.02%.

[0035] The present application adopts low carbon design, controls the composite addition of alloying elements to improve the strength of the steel, and at the same time ensures that the steel plate has excellent corrosion resistance and fatigue resistance. The strength of the steel is ensured by fine grain strengthening, dislocation strengthening, solid solution strengthening and second phase strengthening. The composite addition of alloying elements Cu, Cr, Ni, Sb and Nb can effectively reduce the electrochemical activity of the ultra-high strength marine steel in the simulated seawater solution, on the one hand, inhibit the anodic activation dissolution process, alleviate the formation and development of local corrosion, especially the formation and development of corrosion pits, inhibit the crack initiation process, on the other hand, inhibit the cathodic hydrogen evolution reaction, reduce the hydrogen permeation rate to weaken the effect of hydrogen in the corrosion fatigue process, at the same time, reduce the corrosion fatigue sensitivity, inhibit the anodic dissolution and hydrogen embrittlement to inhibit the initiation and propagation of corrosion fatigue cracks. The fatigue resistance of the steel is improved by fine and dispersed second phase and element segregation control.

[0036] The above technical scheme has at least the following beneficial effects compared with the prior art:

[0037] The above scheme, the present application proposes an anti-corrosion fatigue type ultra-high strength marine steel and a preparation method, which can solve the technical problems of the prior art, such as the inability of traditional marine steel to simultaneously improve strength, plasticity, fatigue resistance and fatigue corrosion resistance, high preparation cost, complex process, low efficiency, poor product quality, unstable product quality, and being not conducive to industrial large-scale production and promotion.

[0038] The application significantly improves the precipitation strengthening effect through the synergistic effect between alloy elements, thereby improving the yield strength and tensile strength of the offshore steel. The synergistic effect of the high Cr / Ni / Cu ternary alloying significantly improves the corrosion fatigue resistance by refining the bainite lath, promoting the precipitation of composite nano precipitates, and increasing the dislocation density.

[0039] The mechanical properties of the anti-corrosion fatigue type ultrahigh strength offshore steel of the application are as follows: yield strength ≥ 880 MPa, tensile strength ≥ 1000 MPa, yield strength ratio ≤ 0.90, elongation ≥ 14%, and strength plastic product reaches 15 GPa%.

[0040] The corrosion rate of the ultrahigh strength offshore steel after being immersed in simulated seawater for 150 days is less than 0.05 mm / a.

[0041] The fatigue limit of the ultrahigh strength offshore steel in air at room temperature, stress 0.1, loading frequency 10 Hz, and loading waveform sine wave is as high as 800 MPa.

[0042] The application significantly improves the mechanical properties, corrosion resistance, fatigue resistance and corrosion fatigue resistance of the ultrahigh strength offshore steel, which is of great significance to the safe and stable operation of offshore engineering.

[0043] In summary, compared with the traditional aluminum alloy composite material preparation method, the anti-corrosion fatigue type ultrahigh strength offshore steel can be prepared by raw material melting and casting, austenitizing heat treatment, multi-pass hot rolling and controlled cooling and temperature control. The method has the advantages of short preparation process, simple operation, low preparation cost, high efficiency, good uniformity of organization and performance, high yield, and synergistic improvement of mechanical properties, corrosion resistance, fatigue resistance and corrosion fatigue resistance, which is beneficial to industrial large-scale production and promotion. BRIEF DESCRIPTION OF DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0045] Figure 1 is a process schematic diagram of the preparation method of the anti-corrosion fatigue type ultrahigh strength offshore steel of the application;

[0046] Figure 2 is a metallographic structure diagram of the anti-corrosion fatigue type ultrahigh strength offshore steel of embodiment 1 of the application;

[0047] Figure 3is a metallographic structure diagram of an anti-corrosion fatigue type super-high-strength marine steel of Example 2 of the present application;

[0048] Figure 4 is a metallographic structure diagram of a high-strength marine steel prepared in Comparative Example 1 of the present application;

[0049] Figure 5 is a metallographic structure diagram of an anti-corrosion fatigue type super-high-strength marine steel of Comparative Example 2 of the present application;

[0050] Figure 6 is a metallographic structure diagram of an anti-corrosion fatigue type super-high-strength marine steel of Comparative Example 3 of the present application;

[0051] Figure 7 is a metallographic structure diagram of an anti-corrosion fatigue type super-high-strength marine steel of Comparative Example 4 of the present application;

[0052] Figure 8 is a metallographic structure diagram of an anti-corrosion fatigue type super-high-strength marine steel of Comparative Example 5 of the present application;

[0053] Figure 9 is a metallographic structure diagram of an anti-corrosion fatigue type super-high-strength marine steel of Comparative Example 6 of the present application;

[0054] Figure 10 is a metallographic structure diagram of an anti-corrosion fatigue type super-high-strength marine steel of Comparative Example 7 of the present application;

[0055] Figure 11 is a comparison diagram of corrosion rates of marine steels prepared in Comparative Examples 1-7 and Examples 1-2 in simulated seawater;

[0056] Figure 12 is a comparison diagram of S-N curves of marine steels prepared in Comparative Examples 1-7 and Examples 1-2 in simulated seawater. DETAILED DESCRIPTION

[0057] The technical solutions in the present application will be described below with reference to the drawings.

[0058] In the embodiments of the present application, the words such as "example", "for example" are used to represent as an example, illustration or description. Any embodiment or design scheme described as "example" in the present application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. Rather, the word "example" is intended to present the concept in a specific manner. In addition, in the embodiments of the present application, the meaning expressed by "and / or" can be both, or can be one of the two.

[0059] In the embodiments of the present application, "image" and "picture" can be used interchangeably at times. It should be pointed out that when the distinction is not emphasized, the meanings expressed are consistent.

[0060] In the embodiments of the present application, sometimes the subscript such as W1 can be written in the form of non-subscript such as W1, and the meanings expressed thereby are consistent when the difference is not emphasized.

[0061] To make the technical problems, technical solutions and advantages to be solved by the present application clearer, specific embodiments will be described in detail below with reference to the drawings.

[0062] An anti-corrosion fatigue type ultra-high strength marine steel, the steel plate thickness of the anti-corrosion fatigue type ultra-high strength marine steel is 10-12mm, the components are as follows in terms of mass percentage: C 0.04-0.07%, Si 0.20-0.26%, Mn 1.45-1.60%, P≤0.01%, S≤0.015%, Cr 1.44-1.52%, Ni 1.44-1.52%, Cu 0.88-0.96%, Nb 0.08-0.12%, Sb 0.08-0.12%, and the balance is Fe and inevitable impurities.

[0063] In particular, the microstructure of the anti-corrosion fatigue type ultra-high strength marine steel is lath and granular bainite.

[0064] In particular, the performance of the anti-corrosion fatigue type ultra-high strength marine steel is as follows: yield strength≥880MPa, tensile strength≥1000MPa, yield ratio≤0.90, elongation≥14%, and the product of strength and plasticity reaches 15GPa%.

[0065] The corrosion rate of the ultra-high strength marine steel after being immersed in the simulated seawater for 150d is less than 0.05mm / a.

[0066] At room temperature, the loading frequency of the axial fatigue test in air is 10Hz, the loading waveform is a sine wave, and the fatigue limit of the ultra-high strength marine steel is 828.73MPa when the stress ratio is 0.1.

[0067] In particular, the solution composition of the simulated seawater is as follows: 24.53g / L of NaCl, 5.20g / L of MgCl2, 4.09g / L of Na2SO4, 1.16g / L of CaCl2, 0.695g / L of KCl, 0.201g / L of NaHCO3, 0.101g / L of KBr, 0.027g / L of H3BO3, 0.025g / L of SrCl2, and 0.003g / L of NaF.

[0068] A preparation method of the anti-corrosion fatigue type ultra-high strength marine steel, the preparation method of the anti-corrosion fatigue type ultra-high strength marine steel is combined with Figure 1 The preparation method comprises the following steps:

[0069] S1, raw material smelting and casting: the raw materials are weighed according to the component content of the anti-corrosion fatigue type ultra-high strength marine steel, and then smelted by a vacuum induction furnace to obtain a molten steel, and then the molten steel is cooled to obtain a marine steel ingot;

[0070] S2, austenitizing heat treatment: the marine steel ingot obtained in S1 is heated to an austenitizing temperature and kept for a certain time, and then an austenitized steel ingot is obtained after complete austenitizing;

[0071] S3, multi-pass hot rolling: the austenitized steel ingot obtained in S2 is furnace-cooled to a rolling temperature and kept for a certain time, and then multi-pass rolled to obtain a hot-rolled marine steel plate;

[0072] S4, controlled cooling and temperature: the hot-rolled marine steel plate obtained in S3 is sent to a water flow area for cooling, and then cooled to room temperature in air to obtain an anti-corrosion fatigue type ultra-high strength marine steel plate.

[0073] In particular, the austenitizing temperature in S2 is 1190-1210℃, and the holding time is 1.5-2h.

[0074] In particular, the rolling temperature in S3 is 990-1010℃, the holding time is 1.5-2.5h, the number of passes of multi-pass rolling is 11-12, the reduction of each pass is 1mm, and the final rolling temperature is 870-890℃.

[0075] In particular, the cooling rate in S4 is 20-25℃ / s, and the water outlet temperature is ensured to be between 420-440℃.

[0076] In particular, the anti-corrosion fatigue type ultra-high strength marine steel plate obtained in S4 has a fatigue life of 10 7 times under a cyclic stress of 0.8-0.9 times the yield strength, and the steel does not fatigue fracture, and the fatigue strength is increased by more than 28%; under the same peak stress load, the corrosion fatigue life is increased by more than 60%.

[0077] Example 1

[0078] An anti-corrosion fatigue type ultra-high strength marine steel, the thickness of the steel plate of the anti-corrosion fatigue type ultra-high strength marine steel is 12mm, and the components are as follows in terms of mass percentage: C 0.08%, Si 0.25%, Mn 1.62%, P≤0.01%, S≤0.03%, Cr 1.41%, Cu 0.90%, Ni 1.46%, Nb 0.10%, Sb 0.10%, and the balance is Fe and unavoidable impurities.

[0079] A preparation method of the anti-corrosion fatigue type ultra-high strength marine steel, the preparation method of the anti-corrosion fatigue type ultra-high strength marine steel comprises the following steps:

[0080] S1, raw material smelting and casting: the raw materials are weighed according to the component content of the anti-corrosion fatigue type ultra-high strength marine steel, and then smelted by a vacuum induction furnace to obtain a molten steel, and then the molten steel is cooled to obtain a marine steel ingot with a certain size;

[0081] S2, austenitizing heat treatment: the marine steel ingot obtained in S1 is heated to an austenitizing temperature and kept for 2 hours, and the austenitizing temperature is 1190-1210℃, and after complete austenitizing, an austenitized steel ingot is obtained;

[0082] S3, multi-pass hot rolling: the austenitized steel ingot obtained in S2 is furnace-cooled to a rolling temperature and kept for 2 hours, and the rolling temperature is 990-1010℃, and the number of passes of multi-pass rolling is 12, and the reduction of each pass is 1mm, and the final rolling temperature is 870-890℃, and a hot-rolled marine steel plate with a thickness of 12mm is obtained;

[0083] S4, controlled cooling and temperature: the hot-rolled marine steel plate obtained in S3 is sent to a water flow area for cooling, and the cooling rate is 20-25℃ / s, and the water outlet temperature is ensured to be between 420-440℃, and then cooled to room temperature in air, and an anti-corrosion fatigue type ultra-high strength marine steel plate is obtained.

[0084] As shown in Figure 2 , the microstructure of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the embodiment is granular bainite.

[0085] The room temperature tensile test is carried out according to ASTM E8 / E8M "Standard Test Methods of Tensile Testing of Metallic Materials at Room Temperature". The performance of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the embodiment is: yield strength 889.64MPa, tensile strength 1015.66MPa, yield strength ratio 0.88, elongation 15.40%, and strength plastic product 15.64GPa%.

[0086] The electrochemical test is carried out according to the method of GB / T 40299-2021 "Corrosion of Metals and Alloys - General Guidelines for Electrochemical Measurements for Corrosion Testing". The corrosion solution for electrochemical test is simulated seawater prepared according to ASTM D1141-98(2021) standard, and the solution composition is as follows.

[0087] The composition of the simulated seawater solution is (g / L): 24.53 NaCl, 5.20 MgCl2, 4.09 Na2SO4, 1.16 CaCl2, 0.695 KCl, 0.201 NaHCO3, 0.101 KBr, 0.027 H3BO3, 0.025 SrCl2 and 0.003 NaF. The pH of the solution is adjusted to 8.2 using diluted 0.1M NaOH solution.

[0088] As Figure 11 shown in the figure, the corrosion rate of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the embodiment is less than 0.05 mm / a after being soaked in the simulated seawater for 150 d;

[0089] The ultra-high strength marine steel is subjected to fatigue life and corrosion fatigue life tests at room temperature, with a stress of 0.1, a loading frequency of 10 Hz and 2 Hz in air and simulated seawater respectively, and a sine wave as the loading waveform. The fatigue limit is obtained to be 828.73 MPa in air by using the ascending and descending method, and the corrosion fatigue life in the simulated seawater is shown in the figure. Figure 12

[0090] Embodiment 2

[0091] An anti-corrosion fatigue type ultra-high strength marine steel, the steel plate thickness of the anti-corrosion fatigue type ultra-high strength marine steel is 12 mm, and the components are as follows in terms of mass percentage: C 0.06%, Si 0.24%, Mn 1.53%, P≤0.01%, S≤0.03%, Cr 1.46%, Cu 0.89%, Ni 1.48%, Nb 0.09%, Sb 0.09%, and the balance is Fe and unavoidable impurities.

[0092] A preparation method of the anti-corrosion fatigue type ultra-high strength marine steel, the preparation method of the anti-corrosion fatigue type ultra-high strength marine steel comprises the following steps:

[0093] S1, raw material smelting and casting: the raw materials are weighed and matched according to the component content of the anti-corrosion fatigue type ultra-high strength marine steel, and then smelted by using a vacuum induction furnace to obtain a molten steel, and then the molten steel is cooled to obtain a marine steel ingot with a certain size;

[0094] S2, austenitizing heat treatment: the marine steel ingot obtained in S1 is heated to an austenitizing temperature and kept for 2 h, the austenitizing temperature is 1190-1210℃, and after complete austenitizing, an austenitized steel ingot is obtained;

[0095] S3, multi-pass hot rolling: the austenitized steel ingot obtained in S2 is furnace-cooled to a rolling temperature and kept for 2 h, the rolling temperature is 990-1010℃, the number of passes of multi-pass rolling is 12, the reduction of each pass is 1 mm, and the final rolling temperature is 870-890℃, so as to obtain a hot-rolled marine steel plate with a thickness of 12 mm;

[0096] S4, controlled cooling and temperature control: the hot-rolled marine steel plate obtained in S3 is sent to a water flow area for cooling, the cooling rate is 20-25℃ / s, the water outlet temperature is ensured to be between 420-440℃, and then the plate is cooled to room temperature in air to obtain an anti-corrosion fatigue type ultra-high strength marine steel plate.

[0097] ​As shown in Figure 3 The microstructure of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the embodiment is granular bainite.

[0098] The room temperature tensile test was carried out according to ASTM E8 / E8M "Standard Test Methods of Tensile Testing of Metallic Materials at Room Temperature". The performance of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the embodiment is: yield strength 911.51 MPa, tensile strength 1037.45 MPa, yield strength ratio 0.88, elongation 14.86%, and strength plastic product 15.42 GPa%.

[0099] The electrochemical test was carried out according to GB / T 40299-2021 "Corrosion of Metals and Alloys - General Guidelines for Electrochemical Measurements for Corrosion Testing". The corrosion solution for the electrochemical test is a simulated seawater prepared according to ASTM D1141-98(2021) standard, and the solution composition is as follows.

[0100] The composition of the simulated seawater solution is (g / L): 24.53 NaCl, 5.20 MgCl2, 4.09 Na2SO4, 1.16 CaCl2, 0.695 KCl, 0.201 NaHCO3, 0.101 KBr, 0.027 H3BO3, 0.025 SrCl2 and 0.003 NaF. The pH of the solution is adjusted to 8.2 using diluted 0.1M NaOH solution.

[0101] As shown in Figure 11 The corrosion rate of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the embodiment after immersion in the simulated seawater for 150 days is less than 0.05 mm / a;

[0102] The fatigue life and corrosion fatigue life of the ultra-high strength marine steel were tested at room temperature, with a stress of 0.1, and the loading frequency in air and simulated seawater was 10 Hz and 2 Hz, respectively. The loading waveform is a sine wave. The fatigue limit in air was obtained by the rise and fall method, and the corrosion fatigue life in simulated seawater is as shown in Figure 12

[0103] Comparative Example 1

[0104] A comparative marine steel, the steel plate thickness of the comparative marine steel is 12 mm, the composition is as follows in terms of mass percentage: C 0.08%, Si 0.24%, Mn 1.57%, P 0.003%, S 0.004%, Cr 0.47%, Ni 0.82%, and the balance is Fe and unavoidable impurities.

[0105] A preparation method based on the comparative marine steel, the preparation method of the comparative marine steel comprises the following steps:​

[0106] S1, raw material smelting and casting: the raw materials are weighed according to the component content of the anti-corrosion fatigue type ultra-high strength marine steel, then smelted by a vacuum induction furnace to obtain a molten steel, and then the molten steel is cooled to obtain a marine steel ingot;

[0107] S2, austenitizing heat treatment: the marine steel ingot obtained in S1 is heated to an austenitizing temperature and kept for 2 hours, the austenitizing temperature is 1190-1210℃, after complete austenitization, an austenitized steel ingot is obtained;

[0108] S3, multi-pass hot rolling: the austenitized steel ingot obtained in S2 is furnace-cooled to a rolling temperature and kept for 2 hours, the rolling temperature is 990-1010℃, the number of passes of multi-pass rolling is 10-12, the reduction of each pass is 1mm, and the final rolling temperature is 870-890℃, thereby obtaining a hot-rolled marine steel plate with a thickness of 12mm;

[0109] S4, controlled cooling and temperature: the hot-rolled marine steel plate obtained in S3 is sent to a water flow area for cooling, the cooling rate is 20-25℃ / s, the water outlet temperature is ensured to be between 420-440℃, and then cooled to room temperature in air, thereby obtaining a comparative marine steel plate.

[0110] As shown in Figure 4 the microstructure of the comparative marine steel prepared in the present comparative example is granular bainite.

[0111] The room temperature tensile test is carried out according to ASTM E8 / E8M "Standard Test Methods of Tensile Testing of Metallic Materials at Room Temperature". The properties of the comparative marine steel prepared in the present comparative example are as follows: the yield strength is 616.42 MPa, the tensile strength is 756.53 MPa, the yield strength ratio is 0.81, the elongation is 15.85%, and the strength-plasticity product is 11.99 GPa%.

[0112] The electrochemical test is carried out according to the method of GB / T 40299-2021 "Corrosion of Metals and Alloys - General Guidelines for Electrochemical Measurements for Corrosion Testing". The corrosion solution for electrochemical test is simulated seawater prepared according to ASTM D1141-98(2021) standard, and the solution composition is as follows.

[0113] The composition of the simulated seawater solution is (g / L): 24.53 NaCl, 5.20 MgCl2, 4.09 Na2SO4, 1.16 CaCl2, 0.695 KCl, 0.201 NaHCO3, 0.101 KBr, 0.027 H3BO3, 0.025 SrCl2 and 0.003 NaF. The pH of the solution is adjusted to 8.2 using a diluted 0.1M NaOH solution.

[0114] As Figure 11 shown, the corrosion rate of the comparative offshore steel prepared in the present application is less than 0.06 mm / a after being immersed in the simulated seawater for 150 d;

[0115] The comparative offshore steel was subjected to fatigue life and corrosion fatigue life tests at room temperature, stress of 0.1, loading frequency of 10 Hz and 2 Hz in air and simulated seawater respectively, and the loading waveform was a sine wave. The fatigue limit in air was obtained by the ascending and descending method, and the corrosion fatigue life in the simulated seawater is shown in Figure 12 .

[0116] Comparative Example 2

[0117] A comparative offshore steel, the thickness of the steel plate of the comparative offshore steel is 12 mm, and the composition is as follows in terms of mass percentage: C 0.05%, Si 0.24%, Mn 1.57%, P 0.003%, S 0.004%, Cr 0.47%, Cu 0.32%, Ni 0.82%, and the balance is Fe and unavoidable impurities.

[0118] A preparation method of the comparative offshore steel, the preparation method of the comparative offshore steel comprises the following steps:

[0119] S1, raw material smelting and casting: the raw materials are weighed and matched according to the composition content of the anti-corrosion fatigue type ultra-high strength offshore steel, and then smelted by a vacuum induction furnace to obtain a molten steel, and then the molten steel is cooled to obtain an offshore steel ingot;

[0120] S2, austenitizing heat treatment: the offshore steel ingot obtained in S1 is heated to an austenitizing temperature and kept for 2 h, the austenitizing temperature is 1190-1210℃, and after complete austenitizing, an austenitized steel ingot is obtained;

[0121] S3, multi-pass hot rolling: the austenitized steel ingot obtained in S2 is furnace-cooled to a rough rolling temperature and kept for 2 h, the rough rolling temperature is 990-1010℃, the number of passes of multi-pass rolling is 10-12, the reduction amount of each pass is 1 mm, and the final rolling temperature is 870-890℃, thereby obtaining a hot-rolled offshore steel plate with a thickness of 12 mm;

[0122] S4, controlled cooling and temperature: the hot-rolled offshore steel plate obtained in S3 is sent to a water laminar flow area for cooling, the cooling rate is 20-25℃ / s, and the water outlet temperature is ensured to be between 420-440℃, and then cooled to room temperature in air, thereby obtaining a comparative offshore steel plate.

[0123] As Figure 5As shown, the microstructure of the comparative marine steel prepared in this comparative example is granular bainite.

[0124] The room temperature tensile test was conducted according to ASTM E8 / E8M, "Metallic materials, tensile testing at room temperature - standard test method". The properties of the comparative marine steel prepared in this comparative example are: yield strength of 708.91 MPa, tensile strength of 869.36 MPa, yield-to-tensile ratio of 0.82, elongation of 17.64%, and strength-ductility product of 15.34 GPa.

[0125] Electrochemical tests were conducted in accordance with GB / T 40299-2021, "Corrosion of Metals and Alloys - Electrochemical Measurement Methods for Corrosion Testing - Applicable Conventions". The corrosion solution used in the electrochemical tests was simulated seawater prepared according to ASTM D1141-98(2021) standard, and its solution composition is shown below.

[0126] The simulated seawater solution composition (g / L) was: 24.53 NaCl, 5.20 MgCl2, 4.09 Na2SO4, 1.16 CaCl2, 0.695 KCl, 0.201 NaHCO3, 0.101 KBr, 0.027 H3BO3, 0.025 SrCl2, and 0.003 NaF. The pH of the solution was adjusted to 8.2 using a diluted 0.1M NaOH solution.

[0127] like Figure 11 As shown, the corrosion rate of the comparative marine steel prepared in this example after immersion in simulated seawater for 150 days is less than 0.06 mm / a.

[0128] Compared to marine engineering steel at room temperature with a stress of 0.1, axial fatigue tests were conducted in air and simulated seawater using loading frequencies of 10Hz and 2Hz, respectively, with a sinusoidal loading waveform. Fatigue life and corrosion fatigue life were tested. The fatigue limit in air using the rise-fall method was 708.91 MPa. The corrosion fatigue life in simulated seawater was as follows... Figure 12 As shown.

[0129] Comparative Example 3

[0130] A comparative marine engineering steel, wherein the steel plate thickness is 12 mm, and the composition by mass percentage is: C 0.05%, Si 0.25%, Mn 1.57%, P 0.003%, S 0.003%, Cr 0.47%, Cu 0.32%, Ni 0.82%, Nb 0.09%, with the balance being Fe and unavoidable impurities.

[0131] A method for preparing the comparative marine steel, comprising the following steps:

[0132] S1, raw material smelting and casting: the raw materials are weighed according to the component content of the anti-corrosion fatigue type ultra-high strength marine steel, then smelted by a vacuum induction furnace to obtain a molten steel, and then the molten steel is cooled to obtain a marine steel ingot;

[0133] S2, austenitizing heat treatment: the marine steel ingot obtained in S1 is heated to an austenitizing temperature and kept for 2h, the austenitizing temperature is 1190-1210℃, after complete austenitization, an austenitized steel ingot is obtained;

[0134] S3, multi-pass hot rolling: the austenitized steel ingot obtained in S2 is furnace-cooled to a rolling temperature and kept for 2h, the rolling temperature is 990-1010℃, the number of passes of multi-pass rolling is 10-12, the reduction of each pass is 1mm, and the final rolling temperature is 870-890℃, thereby obtaining a hot-rolled marine steel plate with a thickness of 12mm;

[0135] S4, controlled cooling and temperature: the hot-rolled marine steel plate obtained in S3 is sent to a water flow area for cooling, the cooling rate is 20-25℃ / s, the water outlet temperature is ensured to be between 420-440℃, and then cooled to room temperature in air, thereby obtaining a comparative marine steel plate.

[0136] As shown in Figure 6 the microstructure of the comparative marine steel prepared in the present comparative example is granular bainite.

[0137] The room temperature tensile test is carried out according to ASTM E8 / E8M "Standard Test Methods of Tensile Testing of Metallic Materials at Room Temperature". The properties of the comparative marine steel prepared in the present comparative example are as follows: yield strength is 686.99 MPa, tensile strength is 909.77 MPa, yield strength ratio is 0.76, elongation is 21.31%, and strength-plasticity product is 19.39 GPa%.

[0138] The electrochemical test is carried out according to GB / T 40299-2021 "Corrosion of Metals and Alloys - General Guidelines for Electrochemical Measurements for Corrosion Testing". The corrosion solution for electrochemical test is simulated seawater prepared according to ASTM D1141-98(2021) standard, and the solution composition is as follows.

[0139] The composition of the simulated seawater solution is (g / L): 24.53 NaCl, 5.20 MgCl2, 4.09 Na2SO4, 1.16 CaCl2, 0.695 KCl, 0.201 NaHCO3, 0.101 KBr, 0.027 H3BO3, 0.025 SrCl2 and 0.003 NaF. The pH of the solution is adjusted to 8.2 using diluted 0.1M NaOH solution.

[0140] AsFigure 11 As shown in Table 1, the corrosion rate of the comparative offshore steel prepared in the present application after immersion in the simulated seawater for 150 days is less than 0.07 mm / a.

[0141] The comparative offshore steel was subjected to axial fatigue test at room temperature, stress of 0.1, loading frequency of 10 Hz and 2 Hz in air and simulated seawater respectively, and loading waveform of sinusoidal wave, to test the fatigue life and corrosion fatigue life. The fatigue limit in air was obtained by the ascending and descending method, and the corrosion fatigue life in simulated seawater was obtained by the descending method. Figure 12 As shown in Table 2.

[0142] Comparative Example 4

[0143] A comparative offshore steel, the steel plate thickness of which is 12 mm, and the composition of which, in terms of mass percentage, is: C 0.07%, Si 0.25%, Mn 1.64%, P 0.002%, S 0.004%, Cr 0.47%, Cu 0.32%, Ni 0.82%, Sb 0.09%, and the balance being Fe and unavoidable impurities.

[0144] A preparation method of the comparative offshore steel, the preparation method comprising the following steps:

[0145] S1, raw material smelting and casting: the raw materials are weighed and matched according to the composition content of the anti-corrosion fatigue type ultra-high strength offshore steel, and then smelted by a vacuum induction furnace to obtain a molten steel, and then the molten steel is cooled to obtain an offshore steel ingot;

[0146] S2, austenitizing heat treatment: the offshore steel ingot obtained in S1 is heated to an austenitizing temperature and kept for 2 h, and the austenitizing temperature is 1190-1210℃, and after complete austenitizing, an austenitized steel ingot is obtained;

[0147] S3, multi-pass hot rolling: the austenitized steel ingot obtained in S2 is furnace-cooled to a rough rolling temperature and kept for 2 h, and the rough rolling temperature is 990-1010℃, and the number of passes of multi-pass rolling is 10-12, and the reduction amount of each pass is 1 mm, and the final rolling temperature is 870-890℃, to obtain a hot-rolled offshore steel plate with a thickness of 12 mm;

[0148] S4, controlled cooling and temperature: the hot-rolled offshore steel plate obtained in S3 is sent to a water laminar flow area for cooling, and the cooling rate is 20-25℃ / s, and the water outlet temperature is ensured to be between 420-440℃, and then cooled to room temperature in air, to obtain a comparative offshore steel plate.

[0149] As shown in Table 1, the corrosion rate of the comparative offshore steel prepared in the present application after immersion in the simulated seawater for 150 days is less than 0.07 mm / a. Figure 7 As shown in Table 3, the microstructure of the comparative offshore steel prepared in the present application is granular bainite.

[0150] The room temperature tensile test was carried out according to ASTM E8 / E8M “Standard Test Methods for Tension Testing of Metallic Materials at Room Temperature”. The properties of the comparative offshore steel prepared in the present comparative example are as follows: yield strength of 692.97 MPa, tensile strength of 920.02 MPa, yield strength ratio of 0.75, elongation of 19.20%, and product of strength and ductility of 17.45 GPa%.

[0151] The electrochemical test was carried out according to GB / T 40299-2021 “Corrosion of Metals and Alloys - Guide to the Corrosion Test - Electrochemical Measurements”. The corrosion solution for the electrochemical test is the simulated seawater prepared according to ASTM D1141-98(2021), and the solution composition is shown as follows.

[0152] The composition of the simulated seawater solution is (g / L): 24.53 NaCl, 5.20 MgCl2, 4.09 Na2SO4, 1.16 CaCl2, 0.695 KCl, 0.201 NaHCO3, 0.101 KBr, 0.027 H3BO3, 0.025 SrCl2, and 0.003 NaF. The pH of the solution is adjusted to 8.2 using diluted 0.1M NaOH solution.

[0153] As shown in Table 1, the corrosion rate of the comparative offshore steel prepared in the present comparative example is less than 0.07 mm / a after immersion in the simulated seawater for 150 days. Figure 11 The fatigue life and corrosion fatigue life of the comparative offshore steel were tested at room temperature, stress of 0.1, and loading frequency of 10 Hz and 2 Hz in air and simulated seawater, respectively. The loading waveform is sinusoidal wave. The fatigue limit in air was obtained by the ascending and descending method, which is 669.79 MPa, and the corrosion fatigue life in the simulated seawater is shown in Table 2.

[0154] Figure 12

[0155] Comparative Example 5

[0156] A comparative offshore steel, the steel plate thickness of which is 12 mm, and the composition of which is as follows in terms of mass percentage: C 0.06%, Si 0.25%, Mn 1.60%, P 0.002%, S 0.004%, Cr 0.47%, Cu 0.32%, Ni 0.82%, Nb 0.09%, Sb 0.09%, and the balance being Fe and unavoidable impurities.

[0157] A preparation method of the comparative offshore steel, the preparation method of the comparative offshore steel comprising the following steps:

[0158] ​​S1. Raw material smelting and casting: The raw materials are weighed according to the composition of the corrosion-resistant fatigue-type ultra-high strength marine engineering steel, and then smelted in a vacuum induction furnace to obtain molten steel. The molten steel is then cooled to obtain marine engineering steel ingots.

[0159] S2, Austenitizing heat treatment: The marine steel ingot obtained from S1 is heated to the austenitizing temperature and held at that temperature. The austenitizing temperature is 1190-1210℃ and the holding time is 2h. After complete austenitization, an austenitized steel ingot is obtained.

[0160] S3, multi-pass hot rolling: The austenitized steel ingot obtained from S2 is furnace cooled to the initial rolling temperature and held at that temperature. The initial rolling temperature is 990-1010℃, the holding time is 2h, the number of passes in the multi-pass rolling is 10-12, the reduction in each pass is 1mm, and the final rolling temperature is 870-890℃ to obtain a hot-rolled marine steel plate with a thickness of 12mm.

[0161] S4. Cooling and temperature control: The hot-rolled marine steel plate obtained in S3 is sent into the laminar flow zone of water for cooling at a rate of 20-25℃ / s to ensure that the outlet water temperature is between 420-440℃. Then it is cooled to room temperature in the air to obtain the comparison marine steel plate.

[0162] like Figure 8 As shown, the microstructure of the comparative marine steel prepared in this comparative example is granular bainite.

[0163] The room temperature tensile test was conducted according to ASTM E8 / E8M, "Metallic materials, tensile testing at room temperature - standard test method". The properties of the comparative marine steel prepared in this comparative example are: yield strength of 715.63 MPa, tensile strength of 873.91 MPa, yield-to-tensile ratio of 0.82, elongation of 22.01%, and strength-ductility product of 19.23 GPa.

[0164] Electrochemical tests were conducted in accordance with GB / T 40299-2021, "Corrosion of Metals and Alloys - Electrochemical Measurement Methods for Corrosion Testing - Applicable Conventions". The corrosion solution used in the electrochemical tests was simulated seawater prepared according to ASTM D1141-98(2021) standard, and its solution composition is shown below.

[0165] The simulated seawater solution composition (g / L) was: 24.53 NaCl, 5.20 MgCl2, 4.09 Na2SO4, 1.16 CaCl2, 0.695 KCl, 0.201 NaHCO3, 0.101 KBr, 0.027 H3BO3, 0.025 SrCl2, and 0.003 NaF. The pH of the solution was adjusted to 8.2 using a diluted 0.1M NaOH solution.

[0166] like Figure 11The corrosion rate of the comparative offshore steel prepared in the present comparative example is less than 0.07 mm / a after being immersed in the simulated seawater for 150 d; the comparative offshore steel is subjected to fatigue life and corrosion fatigue life tests at room temperature, with a stress of 0.1, a loading frequency of 10 Hz and 2 Hz in air and simulated seawater respectively, and a loading waveform of a sine wave. The fatigue limit obtained by the ascending and descending method in air is 644.07 MPa, and the corrosion fatigue life in the simulated seawater is as shown in the table. Figure 12

[0167] Comparative Example 6

[0168] An anti-corrosion fatigue type ultrahigh-strength offshore steel, the steel plate thickness of the anti-corrosion fatigue type ultrahigh-strength offshore steel is 12 mm, and the components are as follows in terms of mass percentage: C 0.06%, Si 0.23%, Mn 1.54%, P 0.002%, S 0.003%, Cr 0.45%, Cu 0.63%, Ni 0.82%, Nb 0.09%, Sb 0.09%, and the balance is Fe and unavoidable impurities.

[0169] A preparation method of the anti-corrosion fatigue type ultrahigh-strength offshore steel, the preparation method of the anti-corrosion fatigue type ultrahigh-strength offshore steel comprises the following steps:

[0170] S1, raw material smelting and casting: the raw materials are weighed according to the component content of the anti-corrosion fatigue type ultrahigh-strength offshore steel, and then smelted by a vacuum induction furnace to obtain a molten steel, and then the molten steel is cooled to obtain an offshore steel ingot;

[0171] S2, austenitizing heat treatment: the offshore steel ingot obtained in S1 is heated to an austenitizing temperature and kept for 2 h, the austenitizing temperature is 1190-1210 ℃, and after complete austenitization, an austenitized steel ingot is obtained;

[0172] S3, multi-pass hot rolling: the austenitized steel ingot obtained in S2 is furnace-cooled to a rolling temperature and kept for 2 h, the rolling temperature is 990-1010 ℃, the number of passes of multi-pass rolling is 12, the reduction of each pass is 1 mm, and the final rolling temperature is 870-890 ℃, thereby obtaining a hot-rolled offshore steel plate with a thickness of 12 mm;

[0173] S4, controlled cooling and temperature: the hot-rolled offshore steel plate obtained in S3 is sent to a water flow area for cooling, the cooling rate is 20-25 ℃ / s, the water outlet temperature is ensured to be between 420-440 ℃, and then cooled to room temperature in air, thereby obtaining an anti-corrosion fatigue type ultrahigh-strength offshore steel plate.

[0174] As Figure 9 ​As shown in Table 1, the microstructure of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the present example is granular bainite.

[0175] The room temperature tensile test was carried out according to ASTM E8 / E8M “Standard Test Methods for Tension Testing of Metallic Materials at Room Temperature”. The properties of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the present example are as follows: yield strength is 676.17 MPa, tensile strength is 827.19 MPa, yield ratio is 0.82, elongation is 22.81%, and the product of strength and ductility is 18.87 GPa%.

[0176] The electrochemical test was carried out according to GB / T 40299-2021 “Corrosion of Metals and Alloys - General Guidelines for Electrochemical Measurements for Corrosion Testing”. The corrosion solution for the electrochemical test is the simulated seawater prepared according to ASTM D1141-98(2021), and the solution composition is shown as follows.

[0177] The composition of the simulated seawater solution is (g / L): 24.53 NaCl, 5.20 MgCl2, 4.09 Na2SO4, 1.16 CaCl2, 0.695 KCl, 0.201 NaHCO3, 0.101 KBr, 0.027 H3BO3, 0.025 SrCl2, and 0.003 NaF. The pH of the solution is adjusted to 8.2 using diluted 0.1M NaOH solution.

[0178] As shown in Table 1, the microstructure of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the present example is granular bainite. Figure 11 As shown in Table 2, the corrosion rate of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the present example is less than 0.07 mm / a after immersion in the simulated seawater for 150 days.

[0179] The fatigue life and corrosion fatigue life of the ultra-high strength marine steel were tested at room temperature, with a stress of 0.1, and the loading frequency in air and simulated seawater was 10 Hz and 2 Hz, respectively. The loading waveform was a sinusoidal wave. The fatigue limit in air was obtained by the ascending and descending method, and the corrosion fatigue life in the simulated seawater is shown in Table 2. Figure 12

[0180] Comparative Example 7

[0181] An anti-corrosion fatigue type ultra-high strength marine steel, the steel plate thickness of the anti-corrosion fatigue type ultra-high strength marine steel is 12 mm, and the composition is as follows in terms of mass percentage: C 0.06%, Si 0.24%, Mn 1.53%, P 0.002%, S 0.003%, Cr 0.45%, Cu 0.91%, Ni 0.83%, Nb 0.09%, Sb 0.09%, and the balance is Fe and unavoidable impurities.

[0182] ​A preparation method of the anti-corrosion fatigue type ultra-high strength marine steel, the preparation method of the anti-corrosion fatigue type ultra-high strength marine steel comprises the following steps:

[0183] S1, raw material smelting and casting: the raw materials are weighed according to the component content of the anti-corrosion fatigue type ultra-high strength marine steel, then a vacuum induction furnace is used for smelting to obtain a molten steel, and then the molten steel is cooled to obtain a marine steel ingot;

[0184] S2, austenitizing heat treatment: the marine steel ingot obtained in S1 is heated to an austenitizing temperature and kept for 2h, the austenitizing temperature is 1190-1210℃, after complete austenitizing, an austenitized steel ingot is obtained;

[0185] S3, multi-pass hot rolling: the austenitized steel ingot obtained in S2 is furnace-cooled to a roughing temperature and kept for 2h, the roughing temperature is 990-1010℃, the number of passes of multi-pass rolling is 11-12, the reduction of each pass is 1mm, and the final rolling temperature is 870-890℃, thereby obtaining a hot-rolled marine steel plate with a thickness of 12mm;

[0186] S4, controlled cooling and temperature: the hot-rolled marine steel plate obtained in S3 is sent to a water flow area for cooling, the cooling rate is 20-25℃ / s, the water outlet temperature is ensured to be between 420-440℃, and then the hot-rolled marine steel plate is cooled to room temperature in air, thereby obtaining an anti-corrosion fatigue type ultra-high strength marine steel plate.

[0187] As shown in Figure 10 the microstructure of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the present example is lath bainite.

[0188] The room temperature tensile test is carried out according to ASTM E8 / E8M "Standard Test Methods of Metallic Materials Tensile Testing at Ambient Temperature". The performance of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the present example is as follows: the yield strength is 725.90MPa, the tensile strength is 969.78MPa, the yield strength ratio is 0.75, the elongation is 23.68%, and the strength plastic product is 22.964GPa%.

[0189] The electrochemical test is carried out according to the method of GB / T 40299-2021 "Corrosion of Metals and Alloys - General Guidelines for Electrochemical Measurements for Corrosion Testing". The corrosion solution for the electrochemical test is a simulated seawater prepared according to the standard of ASTM D1141-98(2021), and the solution composition is as follows.

[0190] The composition of the simulated seawater solution was (g / L): 24.53 NaCl, 5.20 MgCl2, 4.09 Na2SO4, 1.16 CaCl2, 0.695 KCl, 0.201 NaHCO3, 0.101 KBr, 0.027 H3BO3, 0.025 SrCl2, and 0.003 NaF. The pH of the solution was adjusted to 8.2 using dilute 0.1 M NaOH solution.

[0191] As shown in Figure 11 , the corrosion rate of the anti-corrosion fatigue type ultra-high strength marine steel prepared in the comparative example after immersion in simulated seawater for 150 d was less than 0.07 mm / a;

[0192] The ultra-high strength marine steel was subjected to fatigue life and corrosion fatigue life tests at room temperature, with a stress of 0.1, a loading frequency of 10 Hz in air and 2 Hz in simulated seawater, and a loading waveform of a sine wave. The fatigue limit obtained in air using the ascending and descending method was 744.92 MPa, and the corrosion fatigue life in simulated seawater is shown in Figure 12 .

[0193] Comparing the mechanical properties of the marine steels prepared in Examples 1-2 and Comparative Examples 1-7, it can be found that after increasing the content of Cu, Cr, and Ni alloying elements and adding Nb and Sb micro-alloying elements, the yield strength and tensile strength of the marine steel significantly increased, with the yield strength increasing by 37.58% and the tensile strength increasing by 33.63%. The mechanical properties of the marine steel meet the requirements of ultra-high strength marine steel.

[0194] Comparing the electrochemical test fitting data of the marine steels prepared in Examples 1-2 and Comparative Examples 1-7 in simulated seawater, it can be found that after increasing the content of Cu, Cr, and Ni alloying elements and adding Nb and Sb multi-element micro-alloying elements, the corrosion resistance of the marine steel changed significantly, and when Cr was 1.41%, Cu was 0.90%, Ni was 1.46%, Nb was 0.10%, and Sb was 0.10%, the self-corrosion current density of the marine steel decreased significantly and the polarization resistance increased significantly. As can be seen from Figure 7 and Figure 8 , the polarization curve of Example 1-3 moves to the left, and the radius of the electrochemical impedance spectrum increases significantly, indicating that the corrosion resistance of the ultra-high strength marine steel is significantly improved.

[0195] Compared with the corrosion rates of the prepared offshore steels of Examples 1-2 and Comparative Examples 1-7 in simulated seawater, it can be found that the corrosion rate of the offshore steel increases first and then decreases and tends to be stable after the alloying elements Cu, Cr and Ni and the micro-alloying elements Nb and Sb are added in Examples 1-2, and the stable corrosion rate is less than 0.05 mm / a.

[0196] Compared with the axial stress fatigue / corrosion fatigue experimental parameters of the prepared offshore steels of Examples 1-2 and Comparative Examples 1-7 in simulated seawater, it can be found that the fatigue performance of the ultrahigh-strength offshore steels of Examples 1-2 is increased compared with that of the offshore steel of Comparative Example 1-7, and the fatigue strength of Example 1 is increased by 28.04% at most. Figure 9 Figure 9 It can be seen from Table 2 that the corrosion fatigue life of the examples is significantly increased compared with that of the comparative examples, and the corrosion fatigue life is increased by 60% at most under the same peak stress level.

[0197] It can be seen from the test results of Examples 1-7 and Comparative Example 1-2 that the mechanical properties, corrosion resistance, fatigue resistance and corrosion fatigue resistance of the ultrahigh-strength offshore steel are significantly increased by adjusting the content of alloying elements Cu, Cr and Ni and adding micro-alloying elements Nb and Sb, and all meet the requirements of ultrahigh-strength offshore steel on corrosion fatigue resistance.

[0198] The above scheme provides an anti-corrosion fatigue type ultrahigh-strength offshore steel and a preparation method, which can solve the technical problems in the prior art that the strength, ductility, fatigue resistance and fatigue corrosion resistance of the traditional offshore steel cannot be synergistically improved, and the preparation cost is high, the process is complex, the efficiency is low, the quality of the finished product is poor, the quality of the finished product is unstable, and it is not conducive to industrial large-scale production and promotion.

[0199] The present application significantly improves the precipitation strengthening effect through the synergistic effect of alloying elements, thereby improving the yield strength and tensile strength of the offshore steel. The synergistic effect of high Cr / Ni / Cu ternary alloying can significantly improve the corrosion fatigue resistance by refining the bainite lath, promoting the precipitation of composite nano precipitates and increasing the dislocation density.

[0200] The mechanical properties of the anti-corrosion fatigue type ultrahigh-strength offshore steel of the present application are as follows: yield strength ≥ 880 MPa, tensile strength ≥ 1000 MPa, yield strength ratio ≤ 0.90, elongation ≥ 14%, and strength plastic product reaches 15 GPa%;

[0201] The corrosion rate of the ultrahigh-strength offshore steel in simulated seawater after immersion for 150 days is less than 0.05 mm / a;

[0202] ​The axial fatigue test of the super-high-strength marine steel at room temperature, stress 0.1, air, loading frequency 10 Hz, and loading waveform sine wave has a fatigue limit of 800 MPa.

[0203] The application improves the mechanical properties of the super-high-strength marine steel, and significantly improves the corrosion resistance, fatigue resistance and corrosion fatigue resistance of the super-high-strength marine steel, which has great significance for ensuring the safe and stable operation of marine engineering.

[0204] In summary, compared with the traditional preparation method of aluminum alloy composite material, the method can prepare the corrosion fatigue resistant super-high-strength marine steel through raw material melting and casting, austenitizing heat treatment, multi-pass hot rolling and controlled cooling and temperature control; the method has the advantages of short preparation process, simple operation, low preparation cost, high efficiency, good uniformity of microstructure and performance, high yield, and synergistic improvement of mechanical properties, corrosion resistance, fatigue resistance and corrosion fatigue resistance, which is beneficial to industrial large-scale production and promotion.

[0205] It should be understood that the term "and / or" herein merely describes an association relationship of associated objects, and indicates that there can be three relationships, for example, A and / or B can represent three cases of A alone, A and B together, and B alone, wherein A and B can be singular or plural. In addition, the character " / " herein generally represents an "or" relationship between the front and rear associated objects, but can also represent an "and / or" relationship, which can be understood according to the context before and after.

[0206] In the application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or the like means any combination of the items, including any combination of single item or multiple items. For example, at least one of a, b, or c can represent a, b, c, a-b, a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple.

[0207] It should be understood that in various embodiments of the application, the size of the sequence number of the above processes does not mean the order of execution, and the execution order of the processes should be determined according to their functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the application.

[0208] The above is only a specific implementation of the application, but the protection scope of the application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the application, which should be covered within the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

Claims

1. A corrosion-resistant and fatigue-resistant ultra-high-strength marine engineering steel, characterized in that, The corrosion-resistant fatigue-resistant ultra-high strength marine steel has a plate thickness of 10-12 mm and its composition by mass percentage is: C 0.04-0.07%, Si 0.20-0.26%, Mn 1.45-1.60%, P≤0.01%, S≤0.015%, Cr 1.44-1.52%, Ni 1.44-1.52%, Cu 0.88-0.96%, Nb 0.08-0.12%, Sb 0.08-0.12%, with the balance being Fe and unavoidable impurities.

2. The corrosion-resistant fatigue-resistant ultra-high-strength marine steel according to claim 1, characterized in that, The microstructure of the corrosion-resistant fatigue-resistant ultra-high strength marine steel is lath-like and granular bainite.

3. The corrosion-resistant fatigue-resistant ultra-high-strength marine steel according to claim 1, characterized in that, The corrosion-resistant fatigue-resistant ultra-high strength marine steel has the following properties: yield strength ≥ 880 MPa, tensile strength ≥ 1000 MPa, yield-to-tensile ratio ≤ 0.90, elongation ≥ 14%, and strength-ductility product up to 15 GPa%. The corrosion rate of ultra-high strength marine engineering steel after immersion in simulated seawater for 150 days is less than 0.05 mm / a; At room temperature, with a stress ratio of 0.1, and using a loading frequency of 10Hz and a sine wave for the axial fatigue test in air, the fatigue limit of the ultra-high strength marine steel is 828.73MPa.

4. The corrosion-resistant fatigue-resistant ultra-high-strength marine steel according to claim 3, characterized in that, The simulated seawater solution composition is as follows: 24.53 g / L NaCl, 5.20 g / L MgCl2, 4.09 g / L Na2SO4, 1.16 g / L CaCl2, 0.695 g / L KCl, 0.201 g / L NaHCO3, 0.101 g / L KBr, 0.027 g / L H3BO3, 0.025 g / L SrCl2, and 0.003 g / L NaF.

5. A method for preparing corrosion-resistant fatigue-resistant ultra-high-strength marine engineering steel based on claim 1, characterized in that, The preparation method of the corrosion-resistant fatigue-resistant ultra-high strength marine engineering steel includes the following steps: S1. Raw material smelting and casting: The raw materials are weighed according to the composition of the corrosion-resistant fatigue-type ultra-high strength marine engineering steel, and then smelted in a vacuum induction furnace to obtain molten steel. The molten steel is then cooled to obtain marine engineering steel ingots. S2, Austenitizing heat treatment: The marine steel ingot obtained from S1 is heated to the austenitizing temperature and held at that temperature until it is fully austenitized to obtain an austenitized steel ingot. S3, multi-pass hot rolling: The austenitized steel ingot obtained from S2 is cooled to the initial rolling temperature in the furnace and held at that temperature, and then rolled in multiple passes to obtain hot-rolled marine steel plate. S4. Controlled cooling and temperature control: The hot-rolled marine steel plate obtained in S3 is sent into a laminar flow water zone for cooling, and then cooled to room temperature in air to obtain a corrosion-resistant fatigue-resistant ultra-high strength marine steel plate.

6. The method for preparing corrosion-resistant fatigue-resistant ultra-high-strength marine engineering steel according to claim 5, characterized in that, The austenitizing temperature in S2 is 1190-1210℃, and the holding time is 1.5-2h.

7. The method for preparing corrosion-resistant fatigue-resistant ultra-high-strength marine engineering steel according to claim 5, characterized in that, The initial rolling temperature in S3 is 990-1010℃, the holding time is 1.5-2.5h, the number of rolling passes is 11-12, the reduction per pass is 1mm, and the final rolling temperature is 870-890℃.

8. The method for preparing corrosion-resistant fatigue-resistant ultra-high-strength marine engineering steel according to claim 5, characterized in that, The cooling rate in S4 is 20-25℃ / s, ensuring that the outlet water temperature is between 420-440℃.

9. The method for preparing corrosion-resistant fatigue-resistant ultra-high-strength marine engineering steel according to claim 5, characterized in that, The corrosion-resistant, fatigue-resistant ultra-high-strength marine steel plate obtained in S4 achieves a fatigue life of 10 hours under cyclic stress of 0.8-0.9 times the yield strength. 7 The steel does not experience fatigue fracture during the cycle, and its fatigue strength is increased by more than 28%; under the same peak stress load, its corrosion fatigue life is increased by more than 60%.

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