CN114836694B - A marine anti-seawater corrosion fatigue ultra-high-strength steel and its manufacturing method - Google Patents

Abstract

A marine anti-seawater corrosion fatigue ultra-high-strength steel and its manufacturing method, the chemical components in the steel are C0.030%-0.080%, Si0.25%-0.60%, Mn0.95%-1.50%, Nb0.030%-0.050%, V0.040%～0.070%, Cu0.30%～0.70%, N0.0120%～0.0160%, Ni0.40%～0.80%, P0.010%～0.030%, S≤0.005%, Sb0.10%～ 0.50%, Sn0.30%-0.45%, Cr0.50%-1.00%, Mo0.15%-0.40%, La 0.0040%-0.0060%, Als0.015%-0.035%, and the balance is Fe and impurities. The invention can produce ultra-high-strength steel plates with reasonable composition design, high strength, good low-temperature toughness and excellent corrosion fatigue performance.

Description

A kind of ultra-high strength steel for ship that resists seawater corrosion fatigue and its manufacturing method

Technical Field

The invention relates to the field of metal material preparation, and in particular to a marine seawater corrosion fatigue resistant ultra-high strength steel and a manufacturing method thereof.

Background Art

Corrosion fatigue is one of the key factors causing failure of engineering structures, in which the maximum loading stress amplitude is often less than the material yield limit, and there is no sign before the damage. In the corrosion fatigue process, there are two basic fatigue damage modes, one is fatigue damage caused by alternating loads; the other is corrosion damage caused by corrosive media. These two types of damage are often not simply superimposed, but there is an obvious coupling effect between the two, that is, they promote and compete with each other. When ships serve in the marine environment, especially in the ice environment, they are subjected to the alternating influence of low temperature, chloride ions, dry-wet cycles, wind and waves, and sea ice loads in the ocean for a long time, and the above damage failure is more significant. In order to cope with the service environment in the ice area, it is necessary to improve the strength and low-temperature toughness of ship construction materials while making the steel have good resistance to seawater corrosion fatigue.

For a long time, in the design and manufacture of engineering steel, more attention has been paid to high strength and high toughness, and less attention has been paid to corrosion, fatigue and corrosion fatigue. However, with the development of steel material research, its corrosion, fatigue and other properties have received more and more attention. The patent document entitled "A yield 345MPa grade high fatigue structural steel and its manufacturing method", application number: 201910712227.1, discloses a yield strength 345MPa grade high fatigue structural steel, whose chemical composition is: C 0.13%~0.16%, Mn 1.30%~1.60%, Nb 0.020%~0.050%, Alt 0.020%~0.030%, Ti≤0.010%, Si≤0.12%, P≤0.010%, S≤0.005%, the remainder is iron and unavoidable impurities. By adopting a large reduction + controlled cooling process, the obtained steel plate has good comprehensive mechanical properties and good surface quality. However, the corrosion fatigue performance of the steel plate was not evaluated, and the impact toughness of the steel plate was only evaluated at -20°C, which is far from meeting the use requirements. The patent document entitled "High-strength hot-rolled steel plate with excellent fatigue resistance and its manufacturing method", application number: 201180044623.3, discloses a high-strength hot-rolled steel plate with excellent fatigue resistance, whose chemical composition is: C 0.05-0.15%, Si 0.2-1.2%, Mn 1.0-2.0%, P less than 0.03%, S less than 0.0030, Al 0.005-0.10%, N less than 0.006%, and the remaining elements also contain one or more of Ti 0.03-0.13%, Nb 0.02-0.10%, and V 0.02-0.15. By adopting a controlled rolling and controlled cooling process, the strength of the obtained steel plate is above 780MPa, and the fatigue strength under 2 million cycles is above 580MPa. The corrosion fatigue performance of the steel plate is also not evaluated, and the low-temperature toughness of the steel plate is not evaluated. The patent document entitled "A high crack arrest and fatigue strength thick steel plate and its preparation method", application number: 201810007814.6, discloses a high crack arrest and fatigue strength thick steel plate, whose chemical composition is: C 0.05-0.07%, Si 0.10-0.20%, Mn 1.40-1.60%, Nb 0.04-0.06%, Ti 0.01-0.02%, Cu 0.30-0.35%, Cr 0.27-0.31%, Ni0.4-0.5%, Al 0.01-0.04%, Mo 0.06～0.11%, P≤0.020%, S≤0.010%, the remainder is iron and impurities. The yield strength of the invented steel is not less than 500MPa, the impact absorption energy at -60℃ is greater than 250J, and the fatigue strength of 2 million times is greater than 160J. Its fatigue strength is low, which affects the service performance of the steel plate, and the corrosion fatigue performance is not evaluated. The patent document named "TMCP type high-strength and high-toughness weather-resistant bridge steel plate and preparation method", application number: 201810783890.6, discloses a high-fatigue bridge steel plate, whose chemical composition is: C 0.05-0.08%, Si 0.12-0.18%, Mn 1.4-1.6%, Nb 0.045-0.058%, Ti 0.01-0.02%, Cu 0.30-0.35%, Cr 0.22-0.30%, Ni0.45-0.55%, Al 0.02-0.04%, Mo 0.05-0.12%, P≤0.009%, S≤0.005%, and the rest are Fe and other inevitable impurities; the fatigue strength of the steel is not less than 170MPa after 10 million times, and its fatigue strength is low, which is not conducive to the service performance of the steel plate. The patent document entitled "A Corrosion-Resistant Fatigue Steel for Engineering and Its Preparation Method", application number: 202110068169.0, discloses a corrosion-resistant fatigue steel for engineering. Based on the main elements of E690 steel (C 0.04-0.07%, Si 0.20-0.26%, Mn 1.45-1.60%, P≤0.01%, S≤0.015%, Cr 0.44-0.50%), the steel is elementally regulated and characteristic elements are added, including Cu 0.28-0.66%, Ni 0.76-1.55%, Sb 0.03-0.12%, and the rest are Fe and unavoidable impurities. The corrosion fatigue strength of the steel can be increased by up to 52%, but the low-temperature toughness of the steel is not evaluated.

In summary, the current production of high-strength marine steel plates mainly has the following problems.

1) The low temperature toughness of the steel plate is insufficient and cannot meet the use requirements.

2) The fatigue performance of the steel plate is relatively low, which affects the service performance of the steel plate.

3) The steel plate’s resistance to seawater corrosion fatigue is insufficient and cannot meet the long-term service requirements of ships.

Summary of the invention

The present invention provides a marine seawater corrosion fatigue resistant ultra-high strength steel and a manufacturing method thereof, the purpose of which is to produce a marine ultra-high strength steel plate with reasonable component design, high strength, good low temperature toughness and excellent corrosion fatigue performance.

In order to achieve the above object, the present invention adopts the following technical solutions:

A seawater corrosion fatigue resistant ultra-high strength steel for ships, wherein the chemical components of the steel are as follows by weight percentage: C 0.030%-0.080%, Si 0.25%-0.60%, Mn 0.95%-1.50%, Nb 0.030%-0.050%, V 0.040%-0.070%, Cu 0.30%-0.70%, N 0.0120%-0.0160%, Ni 0.40%-0.80%, P 0.010%-0.030%, S≤0.005%, Sb 0.10%-0.50%, Sn 0.30%-0.45%, Cr 0.50%-1.00%, Mo 0.15%-0.40%, La 0.0040% to 0.0060%, Als 0.015% to 0.035%, and the balance Fe and unavoidable impurities.

The functions of each chemical component in the present invention are described in detail below.

C: basic strengthening element in steel, it is the main element to ensure strength and hardness in the technical solution of the present invention; when its content is low, the amount of carbides etc. generated will be reduced, affecting the effect of grain refinement during rolling. When the content is high, the cementite content in the steel increases, which is unfavorable to the low temperature toughness, welding performance and corrosion performance of the steel plate. Therefore, considering the cost, performance and other factors, the present invention controls the range of C to be 0.030%-0.080%.

Si: An essential element for steelmaking deoxidation, with strong solid solubility in steel, can improve the elastic limit, yield strength and fatigue strength of steel, but when the content is too high, it has an adverse effect on the low temperature toughness and surface quality of steel. The present invention controls Si in the range of 0.25%-0.60%.

Mn: forms substitutional solid solution in steel and can be dissolved in Fe matrix in large quantities. It can delay the transformation of ferrite and pearlite in steel, greatly increase the hardenability of steel, reduce the brittle transition temperature of steel, and improve impact toughness. However, if the Mn content is too high, it is easy to form segregation in steel, which has an adverse effect on the plasticity, toughness, fatigue and corrosion properties of steel. Taking all factors into consideration, the present invention controls the range of Mn to be 0.95%-1.50%.

Nb: Grain refining element. When heated, the carbon and nitride particles of Nb that are not dissolved are distributed on the austenite grain boundaries, which can hinder the growth of austenite grains when the steel is heated; it can effectively delay the recrystallization of deformed austenite, prevent the growth of austenite grains, refine the ferrite grains, improve the impact toughness of steel and reduce its brittle transition temperature. The present invention controls the range of Nb to be 0.030%-0.050%.

V: A strong carbide-forming element, which has little effect on austenite recrystallization. At low temperatures, V carbon and nitrides precipitate in large quantities, and the precipitates have a specific orientation relationship with ferrite, which has obvious precipitation strengthening and microstructure refinement effects, thereby improving the resistance of steel to fatigue crack initiation and expansion. The present invention controls V in the range of 0.040%-0.070%.

Cu: When added in an appropriate amount, it improves the strength, low temperature toughness and corrosion resistance of steel, and has no adverse effect on the hardenability and toughness of the welding heat affected zone. However, when the content is too high, the hot brittleness of the steel deteriorates and hot cracks are easily generated. The present invention controls the range of Cu to be 0.30%-0.70%.

N: An important strengthening element of the present invention. In the steel, N mainly exists in two states: free state and compound. The existence of the former is not good for the toughness of the steel plate, while the existence of the latter has a positive effect on the comprehensive performance of the steel plate. For steel containing V, when there is a lack of nitrogen in the steel, most of the V does not fully exert its precipitation strengthening effect. Nitrogen-containing steel not only eliminates the cost increase caused by degassing and refining and denitrification during the steelmaking process, but also the increase of nitrogen in the steel can give full play to the role of micro-alloying elements, saving the amount of alloying elements, thereby greatly reducing production costs. At the same time, the precipitation of V (C, N) in the steel has a specific orientation relationship with the ferrite, which has a beneficial effect on improving the fatigue performance of the steel of the present invention. In addition, the addition of N can fix dislocations, inhibit the movement of dislocations to form a cellular structure, and delay the occurrence of fatigue cracks. The present invention controls N in the range of 0.0120%-0.0160%.

Ni: has no adverse effect on the hardenability and toughness of the welding heat affected zone of steel, and can improve the toughness of steel, and also has a beneficial effect on improving the fatigue strength and corrosion resistance of steel. In addition, the addition of Ni can also reduce the tendency of thermal cracking when the Cu content is high. Considering the cost, performance and other factors comprehensively, the present invention controls the range of Ni to be 0.40%-0.80%.

P: It can form various composite salts with Cu element, making the grains of the inner rust layer fine and dense, resisting the damage of Cl-, and reducing the corrosion rate of steel. However, when the content is too high, it is easy to form serious segregation, which is unfavorable to the low-temperature toughness and welding performance of steel. The present invention controls P in the range of 0.010%-0.030%.

Sb: Generally, it has an adverse effect on the mechanical properties of steel, reducing the strength of steel and increasing its brittleness. However, if a certain amount of antimony is added to steel, the corrosion resistance and wear resistance of steel will be improved to varying degrees. When added in combination with Sn, Sn enrichment and uniform distribution of Sb appear in the rust layer of steel, and a _SnO2 - _Sb2O5 corrosion-resistant oxide film is formed on the surface of steel, which can improve the ability to block Cl- penetration, thereby further improving the corrosion resistance of steel. The present invention controls the range of Sb to be 0.10 _% -0.50%.

Sn: Similar to Sb, adding a proper amount of Sn can improve the corrosion resistance of steel. When added in combination with Sb, the corrosion resistance of steel can be further improved. The present invention controls the range of Sn to be 0.30%-0.45%.

Cr: Increases the hardenability of steel and improves its toughness. A small amount of Cr can effectively delay the initial corrosion of the steel plate, but when the Cr content is too high, the corrosion resistance of the steel will be reduced as the corrosion time in the acidic environment increases. The present invention controls the Cr content to be in the range of 0.50% to 1.00%.

Mo: improves the hardenability of steel, forms fine carbides in steel, can effectively improve the strength and fatigue strength of steel, and can improve the corrosion resistance of steel plates when combined with elements such as Ni and Cu. The present invention controls the range of Mo to be 0.15%-0.40%.

La: Rare earth element. A small amount of La can improve the fluidity of steel, has a good desulfurization effect, reduces non-metallic inclusions in steel, makes the steel structure dense and pure, and has a positive effect on improving the fatigue strength and low-temperature toughness of steel. At the same time, it can increase the corrosion potential of steel in seawater, thereby improving the corrosion resistance of steel. The present invention controls La in the range of 0.0040% to 0.0060%.

Al: a strong deoxidizer, which produces highly fine and ultra-micro oxides in steel, plays a role in refining grains and can improve the strength and fatigue strength of steel. The present invention controls the range of Als to be 0.015%-0.035%.

The steel plate has a yield strength of 550-620 MPa, a tensile strength of >630 MPa, an elongation after fracture of >20.0%, and an impact absorption energy of -60°C of >150 J.

The corrosion fatigue performance of the steel plate was tested with reference to ISO 11782-Ⅰ-2017 “Corrosion of metals and alloys - Corrosion fatigue tests Part 1: Cyclic failure tests”. Under the test conditions of stress ratio of -1 and loading frequency of 1HZ, the corrosion fatigue strength in the simulated seawater environment was ≥306MPa.

A method for manufacturing seawater corrosion fatigue resistant ultra-high strength steel for ships, comprising smelting, continuous casting, heating in a heating furnace and rolling, including the following steps:

1) Smelt the steel according to the above composition:

a) During converter smelting, the contents of elements such as C, Si, Mn, P, and S are adjusted to be within the scope of the present invention, and other alloy components are added as required for smelting.

b) refining the molten steel and adjusting the contents of other alloy elements within the scope of the present invention.

c) subjecting the refined molten steel to RH treatment for a period of ≥30 min, with nitrogen blowing throughout the RH treatment to ensure that the final nitrogen content of the steel is 0.0120% to 0.0160%, and that [H] in the steel is controlled to be ≤2.0ppm and [O] ≤18ppm;

2) The molten steel obtained in step 1) is continuously cast to obtain the required ingot. In order to improve the center segregation of the ingot, the superheat of the tundish is controlled to be ≤30°C; the pouring is protected throughout, and electromagnetic stirring and light pressure are applied, and the electromagnetic stirring: I≥450A.

3) In order to regulate the internal stress of the continuous casting billet, promote the precipitation of C/N compounds, and prevent abnormal grain growth of the continuous casting billet, the billet obtained in step 2) is stacked and slowly cooled, and the stacking time is ≥36h.

4) The ingot is heated to 1150°C to 1250°C. The steel of the present invention has a high alloy content and poor thermal conductivity. In order to control the heating quality of the continuous casting ingot, a segmented heating process is used for heating. Below 700°C, slow heating is used to alleviate excessive thermal stress caused by poor thermal conductivity. The heating rate is 8 to 12°C/min. Above 700°C, a rapid heating process is used to prevent abnormal growth of austenite grains. The heating rate is 15 to 20°C/min and the holding time is 0.5 to 3.5h.

5) The ingot is rolled into a hot-rolled steel plate through three stages. In order to fully crush the austenite grains of the ingot, the first stage adopts a low-speed and high-reduction rolling process, the starting rolling temperature is 1050-1150°C, the roller speed is 8.0-12.0r/min, the first pass reduction is ≥50mm, the ingot is rolled to a thickness of 3.0-4.0 times the thickness of the finished product and then waits for warming, the second stage adopts a recrystallization zone rolling + high-reduction rolling process, the starting rolling temperature is 950-1000°C, the roller speed is 14.0-16.0r/min, the pass reduction rate is 15%-35%, the ingot is rolled to 1.5-2.0 times the thickness of the finished product and then waits for warming, the third stage adopts a high-speed + low-temperature and high-reduction process to further refine the grain size of the steel plate, the starting rolling temperature is 800-850°C, the roller speed is 18.0-25.0r/min, and the final rolling temperature is 780-830°C;

6) After rolling, the steel plate is cooled at an accelerated rate to prevent the grain size from growing and further maintain the refined grains. The cooling temperature is 700-730°C, the cooling rate is 6-15°C/s, and the red-return temperature is 500-550°C;

7) In order to release the internal stress formed during the rolling and cooling process and further form fine precipitates, the steel plates are stacked and slowly cooled at a stacking temperature of 400-480°C and a stacking time of ≥20h.

Compared with the prior art, the present invention has the following beneficial effects:

1) The present invention adopts low carbon and adds alloy elements such as Cu, P, Ni, Cr, Mo, Sb, Sn to improve the corrosion resistance of steel, improves the fatigue performance of steel by adding elements such as Si, Nb, V-N, etc., cancels the addition of Ti elements and other elements that are easy to form polyhedral precipitation phases, adds rare earth elements to improve the purity of steel, and inhibits the initiation and expansion of steel corrosion fatigue cracks through the interaction between the elements. The rolling adopts a three-stage rolling process of low speed and large reduction in the first stage, recrystallization zone rolling + large reduction in the second stage, and high speed + low temperature and large reduction in the third stage, and cooperates with the subsequent rapid cooling process + stacking slow cooling. The final steel plate structure is ultrafine ferrite + bainite structure, the ferrite content is 20.0-40.0%, the grain size is ≤10.0μm, and spherical Nb and V precipitation phases are dispersed on the ferrite matrix, the size is 10-25nm, and the bainite content is 60.0-80.0%. The steel plate has good resistance to seawater corrosion fatigue. Its corrosion fatigue strength is over 306MPa, which is 1.6 times that of conventional steel plates, and its corrosion fatigue ratio is >0.48.

2) The steel plate has excellent comprehensive mechanical properties, with a yield strength of 550-620MPa, a tensile strength of >630MPa, an elongation after fracture of >20.0%, and an impact absorption energy of -60°C at a low temperature of >150J.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a typical metallographic structure photograph of Example 4.

DETAILED DESCRIPTION

The present invention is described in more detail below by way of examples. These examples are merely descriptions of the best mode for carrying out the present invention and do not impose any limitation on the scope of the present invention.

According to the chemical composition range designed by the present invention, smelting is carried out, and the chemical composition is shown in Table 1. The obtained molten steel is subjected to continuous casting-heating-rolling-cooling to obtain the steel plate of the present invention. The smelting process and heating process are shown in Table 2, the rolling process is shown in Table 3, and the cooling process is shown in Table 4.

Table 1 Smelting process and chemical composition of steel in the embodiment of the present invention (wt%)

serial number C Si Mn Nb V Cu N Ni P S Sb Sn Cr Mo La Als 1 0.033 0.48 1.47 0.048 0.043 0.33 0.0132 0.42 0.023 0.003 0.13 0.32 0.52 0.37 0.0042 0.018 2 0.037 0.52 1.34 0.042 0.047 0.38 0.0138 0.49 0.029 0.002 0.18 0.38 0.96 0.17 0.0059 0.033 3 0.058 0.33 1.08 0.039 0.056 0.49 0.0151 0.61 0.012 0.004 0.29 0.36 0.93 0.21 0.0048 0.029 4 0.046 0.39 1.42 0.031 0.068 0.44 0.0158 0.53 0.018 0.001 0.31 0.37 0.88 0.29 0.0054 0.021 5 0.069 0.27 1.19 0.033 0.064 0.68 0.0144 0.79 0.027 0.002 0.47 0.39 0.82 0.32 0.0056 0.022 6 0.062 0.36 1.11 0.036 0.061 0.62 0.0146 0.73 0.026 0.003 0.38 0.44 0.64 0.36 0.0053 0.026 7 0.044 0.43 1.36 0.049 0.054 0.54 0.0129 0.63 0.016 0.002 0.43 0.34 0.69 0.33 0.0047 0.016 8 0.052 0.59 1.24 0.047 0.058 0.59 0.0153 0.69 0.014 0.001 0.49 0.41 0.58 0.34 0.0046 0.019 9 0.071 0.41 0.96 0.046 0.053 0.52 0.0155 0.64 0.028 0.004 0.18 0.43 0.74 0.39 0.0052 0.032 10 0.079 0.34 1.02 0.044 0.049 0.49 0.0147 0.58 0.013 0.003 0.22 0.42 0.77 0.36 0.0051 0.028

Table 2 Steel smelting and heating process of the present invention embodiment

Table 3 Rolling process of steel according to the present invention

Table 4 Cooling process of steel in the embodiment of the present invention

serial number Cooling temperature/℃ Cooling speed/℃/s Red return temperature/℃ Stacking temperature/℃ Stacking time/h 1 719 12 536 419 27 2 714 10 521 442 32 3 712 9 546 436 29 4 726 13 512 464 36 5 703 11 509 476 28 6 712 10 526 473 35 7 724 8 518 432 twenty four 8 728 7 531 469 twenty two 9 716 14 522 456 33 10 711 12 533 452 34

Conventional mechanical property tests were performed on the steel of the present invention, and the results are shown in Table 5.

Table 5 Mechanical properties of steel according to the present invention

The corrosion fatigue performance of the steel of the embodiment of the present invention and the comparative steel was tested. The corrosion fatigue life curve was determined by the axial stress control method with reference to ISO 11782-Ⅰ-2017 "Corrosion of Metals and Alloys - Corrosion Fatigue Test Part 1 Cyclic Failure Test". Stress ratio -1, loading frequency 1HZ. The corrosion solution for corrosion fatigue simulated seawater according to ASTM D1141-98 standard configuration, and the pH value was adjusted to 8.2 using a dilute NaOH solution. The test results are shown in Table 6.

Table 6 Corrosion fatigue properties of steel according to the present invention

Claims (5)

1. A marine seawater corrosion fatigue resistant ultra-high strength steel, characterized in that the chemical composition of the steel is calculated by weight percentage: C 0.030%-0.080%, Si 0.25%-0.60%, Mn 0.95%-1.50%, Nb 0.030%-0.050%, V0.040%-0.070%, Cu 0.30%-0.70%, N 0.0120%-0.0160%, Ni 0.40%-0.80%, P 0.010%-0.030%, S≤0.005%, Sb 0.31%-0.50%, Sn 0.32%-0.45%, Cr 0.64%-1.00%, Mo 0.32%-0.40%, La 0.0040%-0.0048%, Als 0.015%～0.035%, the balance is Fe and unavoidable impurities; The method for manufacturing seawater corrosion fatigue resistant ultra-high strength steel for ships comprises the following steps: 1) The refined molten steel is subjected to RH treatment for a period of ≥30 min. Nitrogen is blown throughout the RH treatment to ensure that the final N content of the steel is 0.0120% to 0.0160%, and that [H] in the steel is ≤2.0ppm and [O] ≤18ppm; 2) The molten steel obtained in step 1) is continuously cast to obtain the required ingot, and the superheat of the tundish is controlled to be ≤30°C; 3) Heat the ingot to 1150℃～1250℃, using a segmented heating process. Below 700℃, the heating rate is 8～12℃/min, above 700℃, the heating rate is 15～20℃/min, and the holding time is 0.5～3.5h; 4) The ingot is rolled into a hot-rolled steel plate in three stages. The first stage rolling temperature is 1050-1150°C, the roller speed is 8.0-12.0r/min, the first pass reduction is ≥50mm, the ingot is rolled to a thickness of 3.0-4.0 times the thickness of the finished product and then kept warm. The second stage rolling temperature is 950-1000°C, the roller speed is 14.0-16.0r/min, the pass reduction rate is 15%-35%, the ingot is rolled to a thickness of 1.5-2.0 times the thickness of the finished product and then kept warm. The third stage rolling temperature is 800-850°C, the roller speed is 18.0-25.0r/min, and the final rolling temperature is 780-830°C. 5) After rolling, the steel plate is cooled at an accelerated rate of 700-730°C, a cooling rate of 6-15°C/s, and a red-return temperature of 500-550°C; 6) Stack the steel plates for slow cooling, with the stacking temperature at 400-480°C and the stacking time ≥20h. 2. The ultra-high strength steel for marine use that resists seawater corrosion fatigue according to claim 1 is characterized in that the steel plate has a yield strength of 550-620 MPa, a tensile strength of >630 MPa, an elongation after fracture of >20.0%, and an impact absorption energy of -60°C at low temperature of >150 J. 3. The marine seawater corrosion fatigue resistant ultra-high strength steel according to claim 1 is characterized in that the corrosion fatigue performance of the steel plate is tested with reference to ISO11782-Ⅰ-2017 "Corrosion of metals and alloys - Corrosion fatigue test Part 1 Cyclic failure test", and under the test conditions of a stress ratio of -1 and a loading frequency of 1 Hz, the corrosion fatigue strength in a simulated seawater environment is ≥306 MPa. 4. The marine seawater corrosion fatigue resistant ultra-high strength steel according to claim 1 is characterized in that the step 2) is poured with full protection, and electromagnetic stirring and light pressure are applied, and the electromagnetic stirring: I≥450A. 5. The seawater corrosion fatigue resistant ultra-high strength steel for ships according to claim 1, characterized in that the ingots obtained in step 2) are stacked and slowly cooled, and the stacking time is ≥36 hours.

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