A 1200mpa grade marine environment fatigue-resistant steel plate for conveying mineral pipelines and a production method thereof

Abstract

The application belongs to the field of metal materials, and provides a 1200MPa-grade marine environment fatigue-resistant mine pipeline steel plate and a production method thereof.The composition of the steel plate is as follows in terms of percentage by weight: C: 0.13%-0.17%, Si: 0.51%-0.80%, Mn: 1.21%-1.50%, P≤0.015%, S≤0.001%, Cr: 0.80%-1.20%, Mo: 0.25%-0.45%, Al: 0.010%-0.050%, Nb: 0.08%-0.12%, V: 0.11%-0.20%, Ti: 0.005%-0.025%, Ni: 0.51-0.70%, Ce: 0.01-0.06%, and the balance of Fe and inevitable impurities.The production method comprises smelting, continuous casting, heating, rolling, accelerated cooling and slow cooling.The steel plate produced by the application has excellent comprehensive mechanical properties, the yield strength is 1250-1350MPa, the tensile strength is 1300-1500MPa, the elongation is greater than or equal to 10%, the steel plate impact energy at-20 DEG C is greater than or equal to 110J, the 10 7 cycle fatigue strength is greater than or equal to 220MPa, the hardness is greater than or equal to 420HBW, and the abrasion rate in the simulated marine environment is only 40% or less of that of Q460C steel.Each performance meets the technical requirements of the 1200MPa-grade mine pipeline in the marine environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal materials, and particularly relates to a 1200MPa-grade steel plate for an anti-fatigue ore-conveying pipeline in a marine environment and a production method thereof. BACKGROUND

[0002] Deep sea contains a large number of important mineral resources needed for the development of human society, and its wide distribution, high grade and large reserves far exceed those on land. With the exhaustion of land mineral resources due to long-term exploitation, deep sea mining will become an important part of future mineral resource development. The pipeline lifting type deep sea mining system has been proven to be the most promising in commercial prospect through multiple sea trials. The ore-conveying riser is an indispensable equipment for deep sea mining engineering, which conveys the mixture of seabed ore and seawater at a certain speed and concentration from the mining equipment to the sea surface. In addition to the requirements of wear resistance, seawater corrosion resistance, anti-clogging and other characteristics, the ore-conveying pipeline also needs to overcome the influence of complex marine environment such as waves and currents in the range from the sea surface to several hundred meters below the sea surface, and has excellent anti-fatigue performance.

[0003] The demand for mineral resources in China is increasing year by year. Mineral resources, as an important material basis to support the development process of the country, affect more than 90% of energy supply and more than 80% of industrial raw material supply in China. Deep sea crust contains a variety of mineral resources, and China has multiple deep sea mining areas with exclusive exploration rights and preferential mining rights, which have extremely high resource abundance and economic value. The pipeline lifting type mining system has the advantages of continuous operation, high mining efficiency and relatively low energy consumption ratio, and is currently recognized as the most promising commercial deep sea mining and ore-conveying technology in the world. The ore-conveying riser is an indispensable equipment for deep sea mining engineering, which conveys the mixture of seabed ore and seawater at a certain speed and concentration from the mining equipment to the sea surface. In addition to the requirements of wear resistance, seawater corrosion resistance, anti-clogging and other characteristics, the ore-conveying pipeline also needs to overcome the influence of complex marine environment such as waves and currents in the range from the sea surface to several hundred meters below the sea surface, and has excellent anti-fatigue performance.

[0004] The patent document with application number 202311812963.7 discloses "High-strength plastic rare earth treated complex microstructure wear-resistant steel and its production method". Its chemical composition is: C: 0.10%-0.30%; Si: 0.30%-1.5%; Mn: 1.0%-3.5%; Mo: 0.10%-0.50%; Nb: 0.01%-0.05%; Ti: 0.01%-0.10%; Al: 0.030%-0.070%; Ce: 0.01%-0.05%; P≤0.008%; S≤0.005%; B: 0.0010%-0.0050%; O≤0.0020%; N≤0.0020%, the balance being Fe. By adding 0.0010%-0.0050% B and a high content of Mn, more than 50% martensite is obtained, significantly improving wear resistance. However, such a high content of martensite is not conducive to fatigue resistance, and the addition of a certain amount of B and a high content of Mn can cause segregation at the grain boundary, making the grain boundary brittle, which also worsens the fatigue resistance.

[0005] The patent document with application number 201710182924.1 discloses "Super-high strength steel plate with excellent seawater corrosion resistance, fatigue resistance and environmental brittleness resistance and manufacturing method thereof". Its chemical composition is: C 0.025%-0.055%, Si≤0.10%, Mn 0.45%-0.85%, P≤0.013%, S≤0.0050%, Cr 11%-16%, Mo 0.85%-1.25%, Ni 4.50%-6.50%, Nb 0.05%-0.08%, Ti 0.008%-0.018%, Ca 0.0015%-0.0040%, the balance being iron and unavoidable impurities. By high Cr, high Mo, and high Ni composition design, a super-high strength steel plate with excellent fatigue resistance and environmental brittleness resistance is obtained. However, the alloy content exceeds 16%, which not only increases the cost of alloy, but also is not conducive to the formability and weldability of the steel plate.

[0006] The patent document with application number 202211106045.8 discloses "HB500 grade high cold bending type wear-resistant steel and production method". Its chemical composition is: C 0.15%-0.30%, Si 0-0.08%, Mn 1.0%-4.0%, P≤0.015%, S≤0.005%, Al 0.03%-0.06%, Ti 0.005%-0.030%, Cr 0.4%-1.0%, Mo 0-0.3%, the balance being Fe and impurities. By achieving an ultra-high cooling speed of more than 100 ℃ / s, a martensite structure is obtained, making the steel plate have good wear resistance. However, this design does not have seawater corrosion resistance and is not suitable for strong abrasive environments containing seawater minerals, and cannot meet the harsh service conditions of deep-sea mineral transportation.

[0007] In summary, the production of the steel for the ore transport riser mainly has the following problems:

[0008] (1) The material wear-resistant and fatigue-resistant comprehensive performance is not matched according to the characteristics of the mineral transportation and the marine service conditions, is not suitable for the strong abrasive environment of the mineral transportation, and cannot meet the severe service conditions of the deep sea mineral transportation.

[0009] (2) The alloy content is high, the total addition amount of Cr, Ni and other alloy elements is more than 16%, which is not conducive to the formability and weldability of the steel plate, and greatly increases the alloy cost. SUMMARY

[0010] The purpose of the present application is to overcome the above problems and deficiencies and provide a 1200MPa grade marine environment fatigue-resistant ore transport pipeline steel plate suitable for the strong abrasive environment of mineral transportation and meeting the severe service conditions of deep sea mineral transportation and a production method thereof.

[0011] The purpose of the present application is achieved as follows:

[0012] A 1200MPa grade marine environment fatigue-resistant ore transport pipeline steel plate, the composition of the steel plate is as follows in terms of weight percentage: C: 0.13%~0.17%, Si: 0.51%~0.80%, Mn: 1.21%~1.50%, P≤0.015%, S≤0.001%, Cr: 0.80%~1.20%, Mo: 0.25%~0.45%, Al: 0.010%~0.050%, Nb: 0.08%~0.12%, V: 0.11%~0.20%, Ti: 0.005%~0.025%, Ni: 0.51~0.70%, Ce: 0.01~0.06%, the balance being Fe and inevitable impurities.

[0013] Further, Cr+Mo≥1.20% in the steel plate.

[0014] Further, Nb / Ce≥1.8 in the steel plate.

[0015] Further, V / Ce≥2.2 in the steel plate.

[0016] The microstructure of the steel plate is a mixed structure of lower bainite+ lath martensite+ nanoscale V-containing precipitated phase; wherein, in terms of volume percentage: lower bainite 10%~30%, nanoscale precipitated phase 2.0%~3.0%, more than 90% of the precipitated phase has a size ≤30nm and is in a dispersed distribution.

[0017] The yield strength of the steel plate is 1250~1350MPa, the tensile strength is 1300~1500MPa, and the elongation is ≥10%. The steel plate-20℃ impact energy is ≥110J, 10 7The fatigue strength per week is greater than or equal to 220 MPa, the hardness is greater than or equal to 420 HBW, and the abrasion rate in the simulated marine environment is only 40% or less of that of Q460C steel.

[0018] The component design reasons of the application are as follows:

[0019] C: the basic strengthening element in steel, which is the main element for ensuring strength and hardness in the technical scheme of the application. The appropriate amount of C can significantly improve the strength and hardness of the steel plate. C can also form fine granular precipitates by combining with V and Nb, further improving the strength and toughness of the steel. However, too much C is not conducive to the welding, toughness and plasticity of the steel plate. Therefore, considering the cost, performance and other factors, the range of C in the application is controlled to be 0.13% to 0.17%.

[0020] Si: Si is a necessary element for deoxidization in the steelmaking process, and can improve the strength and hardness of the steel plate through solid solution strengthening, and has the effects of improving the hardenability, wear resistance and corrosion resistance of the material. The appropriate amount of Si added to the steel can also inhibit the precipitation of cementite, and at the same time, Si will enrich around the carbide, hinder the growth of the carbide, and make the carbide become fine and dispersedly distributed in the matrix, thereby improving the fatigue resistance of the steel. However, higher content of Si will make the steel tend to graphitize, and make the steel brittle, reduce the plasticity and deteriorate the toughness. The content of Si in the application is controlled to be 0.51% to 0.80%.

[0021] Mn: a common strengthening element in steel, which can be largely solid-solved in the Fe matrix to improve the strength through solid solution strengthening. Manganese can reduce the critical cooling rate of the steel, promote the formation of martensite, greatly improve the hardenability, and significantly reduce the brittle transition temperature of the steel, thereby improving the impact toughness and refining the microstructure of the steel. However, too high content of Mn will easily form segregation in the steel, which is not conducive to the fatigue and corrosion performance of the steel. Therefore, the range of Mn in the application is controlled to be 1.21% to 1.50%.

[0022] Cr, Mo: which can improve the hardenability and bainite tendency of the steel, effectively improve the strength, hardness and fatigue strength of the steel, and obtain good wear resistance and fatigue resistance. The addition of a certain amount of Cr and Mo in the steel can also effectively fill the voids formed by the point corrosion caused by chloride ions in the marine environment, form a dense protective film, and prevent the development of the point corrosion, thereby playing a role in corrosion resistance in the marine environment. The range of Cr in the application is controlled to be 0.80% to 1.20%, the content of Mo is controlled to be 0.25% to 0.45%, and preferably Cr+Mo is greater than or equal to 1.20%.

[0023] Nb: is a grain refining element, undissolved Nb carbon, nitride particles distributed on the austenite grain boundary when heating, can hinder the growth of austenite grain when heating; can effectively delay the recrystallization of deformed austenite, prevent the growth of austenite grain, refine ferrite grain, can improve the impact toughness of the steel and reduce the brittle transition temperature. Nb can also increase the solid solution amount of Ce and other rare earths in the steel, thereby improving the corrosion resistance of the steel. The appropriate amount of Nb can further improve the non-recrystallization temperature window of the steel, realize non-recrystallization rolling at a higher temperature, and reduce the rolling load of the rolling mill. The Nb content in the application is controlled at 0.08%~0.12%, preferably Nb / Ce≥1.8.

[0024] V: V is a strong carbide forming element. Vanadium mainly exists in the form of carbide in steel, and a large amount of vanadium carbide is precipitated at low temperature, which has obvious precipitation strengthening and refining effect, thereby improving the fatigue crack initiation and propagation resistance of the steel, and improving the strength, toughness and fatigue resistance of the steel. During welding, V combines with C and N to form second phase particles, which can ensure the strength of the heat affected zone of the steel. Under certain C content, the composite addition of V and Nb can form dispersed nanoscale carbide particles in the steel, which can significantly improve the strength and hardness of the steel without deteriorating the toughness, thereby improving the wear resistance of the steel. V can also increase the solid solution amount of Ce and other rare earth elements in the steel, thereby improving the corrosion resistance of the steel. The content of V in the application is controlled at 0.11~0.20%, preferably V / Ce≥2.2.

[0025] Ti: is a strong solid N element, the addition of trace Ti in Al-containing steel can significantly reduce the corrosion rate, and Ti can preferentially combine with N in the steel to reduce the amount of AlN in the steel and improve weldability. However, when the Ti content exceeds a certain value, TiN particles will coarsen, causing deterioration of low temperature toughness. Therefore, the Ti content in the application is selected as 0.010%~0.025%.

[0026] Al: is usually used as a deoxidizer in steel, and if the aluminum content is too low, the deoxidization will not be sufficient, and Ti and other easily oxidized elements will form oxides; if the aluminum content is too high, the amount of aluminum oxide inclusions will increase, reducing the cleanliness of the steel and adversely affecting the fatigue resistance. Therefore, the Al content in the application is controlled in the range of 0.010%~0.050%.

[0027] Ni: can improve the strength of the steel, reduce the critical cooling temperature, improve the microstructure control and grain refinement, and improve the low temperature toughness and fatigue resistance. However, Ni is relatively expensive and should not be added too much. The Ni content in the application is controlled at 0.51%~0.70%.

[0028] Ce: can be in the steel-making process with O and S chemical reaction to form stable oxides and sulfides, MnS inclusions into strip-shaped into spherical, and promote the full floating of these compounds in the liquid steel, more conducive to the removal of inclusions, thereby reducing the generation of large inclusions, reduce the irregular inclusions and large inclusions on the matrix of the splitting effect, achieve the effect of purifying molten iron, and significantly improve the fatigue resistance. In the process of solidification of molten steel, Ce can also be as a nucleation core to increase the number of crystal nucleus, thereby refining the grain, further improve the strength and toughness of the steel and fatigue resistance. The content of Ce is controlled to be 0.01% to 0.06% in the application.

[0029] P, S: as impurity elements, phosphorus and sulfur significantly deteriorate the toughness, plasticity and weldability of steel, so the content of P and S in the steel should be reduced as much as possible, and the content of P and S is required to be controlled to P≤0.015% and S≤0.001% respectively in the application.

[0030] The second technical scheme of the application provides a production method of a 1200MPa-grade marine environment fatigue-resistant mine conveying pipeline steel plate, which comprises smelting, continuous casting, heating, rolling, accelerated cooling and slow cooling.

[0031] Heating: the slab adopts a multi-stage stepped temperature heating mode, wherein the high-temperature heating section temperature is 1200-1250 DEG C, the soaking section temperature is 1180-1220 DEG C, and the high-temperature heating section + soaking section time is not less than 120 min.

[0032] The design of the heating process is mainly to ensure the solid solution of Mn, Cr, Mo, Ni, Cu, Nb, V and other elements, so that they can play a role in subsequent rolling and accelerated cooling, and at the same time, effectively control the growth of austenite grains; the heating time can ensure the heating effect and temperature uniformity.

[0033] Rolling: the steel plate rolling is divided into two stages of rough rolling and finish rolling, wherein the rough rolling stage end temperature is greater than or equal to 1050 DEG C, the single pass reduction rate of the last two passes of rough rolling is greater than or equal to 14%, so that the original austenite grains are fully broken and refined. The intermediate billet thickness in the finish rolling stage is 3.5-4.0t, wherein t is the thickness of the finished steel plate (12-20mm), the opening rolling temperature is 850-900 DEG C, the single pass reduction rate of the first three passes before finish rolling is greater than or equal to 13%, and the finish rolling temperature is 780-820 DEG C.

[0034] The rolling temperature design mainly considers reducing the deformation resistance in the rough rolling and finish rolling processes, achieving greater deformation, fully penetrating the rolling effect in the thickness direction, obtaining excellent thickness direction microstructure uniformity, and then improving the fatigue resistance, while promoting the formation of nanoscale precipitates, pinning grain boundaries and dislocations, and refining the grains. A larger single pass reduction rate is used to fully break and flatten the austenite grains, and a relatively low finish rolling temperature is used to increase the dislocation density in the steel, thereby improving the strength and toughness through grain refinement and dislocation strengthening.

[0035] accelerated cooling: after the steel plate is rolled, accelerated cooling is performed, and the accelerated cooling is divided into two stages. The first stage is 760-800℃, the cooling rate is 5-10℃ / s, and the cooling time is 8-10s; the second stage cooling speed is 20-25℃ / s, and the final cooling temperature is 300-370℃.

[0036] After the steel plate is rolled, accelerated cooling is performed, and the accelerated cooling is divided into two stages. The first stage is 760-800℃, the cooling rate is 5-10℃ / s, and the cooling time is 8-10s. The purpose of this stage cooling process is to suppress the transformation of austenite to ferrite, and to obtain granular bainite structure of the steel plate at a proper cooling rate. The second stage cooling has no obvious time and distance interval with the first stage, and the cooling rate is increased to 20-25℃ / s, and the final cooling temperature is 300-370℃. The purpose is to suppress the formation of lamellar martensite structure and promote the formation of short and small lath-shaped martensite structure by proper cooling rate and final cooling temperature, and finally obtain a mixed structure of lower bainite+ lath-shaped martensite+ nanoscale V-containing precipitates. The content of lower bainite is 10%-30%, and the proportion of nanoscale precipitates is 2.0%-3.0%, of which more than 90% of the precipitates are ≤30nm and are dispersedly distributed. The lower bainite and short and small lath-shaped martensite in the final microstructure can play a good role in coordinating strain, can effectively deal with the tensile stretching of the steel pipe caused by the movement of the float, can reduce the stress concentration caused by the periodic reciprocating deformation of the material, and can effectively resist fatigue crack cracking. At the same time, it can also effectively absorb the energy of the crack after cracking and continue to expand, hinder the further expansion of the crack, and improve the crack arrest performance. The lath-shaped martensite can improve the strength and wear resistance of the steel plate. The martensite as a hard phase structure is surrounded by bainite, which not only improves the strength of the steel, but also does not deteriorate the fatigue resistance. The dispersedly distributed nanoscale V-containing precipitates as hard phase points not only significantly improve the wear resistance of the steel, but also can maintain the dispersed precipitation state during welding, ensure the strength of the heat affected zone, significantly improve the softening of the heat affected zone, improve the performance uniformity of the steel pipe, and then improve the fatigue fracture resistance of the steel pipe. The cooled steel plate is stacked and slowly cooled to room temperature to fully release the internal stress of the steel plate.

[0037] Slow cooling: after the steel plate is finished with accelerated cooling, slow cooling is carried out in a stacking mode, and the cooling rate is ≤0.2℃ / s, and the steel plate is cooled to room temperature. The purpose is to slowly release the internal stress in the steel, and to avoid cracking caused by the rapid increase of stress due to the dramatic change of the structure of the steel after accelerated cooling due to the high C and Cr, Mo, and Mo strong quenching elements.

[0038] The beneficial effects of the present application are:

[0039] (1) The present application adds appropriate amounts of Cr, Mo, Ni, Nb and V alloying elements on the basis of C and Mn elements, and through the interaction between the elements, and with appropriate heating, rolling and cooling processes, a mixed structure of lower bainite + lath martensite + nanoscale V-containing precipitates is finally obtained. Compared with the prior art, the present application is targeted for component design and microstructure design to improve the fatigue resistance and corrosion resistance of the steel plate, and the produced steel plate has good strength and toughness, corrosion resistance and excellent fatigue resistance.

[0040] (2) The steel plate has excellent comprehensive mechanical properties, with a yield strength of 1250-1350MPa, a tensile strength of 1300-1500MPa, and an elongation of ≥10%. The steel plate has an impact energy of ≥110J at -20℃, a 10 7 cycle fatigue strength of ≥220MPa, a hardness of ≥420HBW, and an abrasion rate in a simulated marine environment of only 40% or less of that of Q460C steel. The various properties meet the technical requirements of 1200MPa grade mine pipeline in a marine environment. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a microstructure metallographic photograph of Example 1 of the present application.

[0042] Figure 2 is a nanoscale precipitate characteristic map of Example 1 of the present application. DETAILED DESCRIPTION

[0043] The present application will be further described below through examples.

[0044] According to the component ratio of the technical scheme, the example of the present application is smelted, continuously cast, heated, rolled, accelerated cooled and slowly cooled.

[0045] Heating:

[0046] The slab is heated in a multi-stage stepped temperature mode, wherein the high-temperature heating section temperature is 1200-1250℃, the soaking section temperature is 1180-1220℃, and the high-temperature heating section + soaking section time is not less than 120min.

[0047] Rolling: the steel plate rolling is divided into two stages of rough rolling and finish rolling, wherein the rough rolling stage ends at a temperature of more than or equal to 1050 DEG C, the single pass reduction rate of the last two passes of the rough rolling is more than or equal to 14%; the intermediate blank thickness in the finish rolling stage is 3.5-4.0t, wherein t is the finished steel plate, the open rolling temperature is 850-900 DEG C, the single pass reduction rate of the first three passes before finish rolling is more than or equal to 13%, and the finish rolling temperature is 780-820 DEG C;

[0048] Accelerated cooling: after the steel plate rolling is completed, accelerated cooling is carried out, and the accelerated cooling is divided into two stages. The first stage open cooling temperature range is 760-800 DEG C, the cooling speed is 5-10 DEG C / s, and the cooling time is 8-10s; the second stage cooling speed is 20-25 DEG C / s, and the final cooling temperature is 300-370 DEG C.

[0049] Slow cooling: after the steel plate completes the accelerated cooling, slow cooling is carried out in a stacking manner, the cooling speed is less than or equal to 0.2 DEG C / s, and the cooling is to room temperature.

[0050] The composition of the steel in the embodiment and the embodiment is shown in Table 1. The main process parameters of the steel heating in the embodiment and the embodiment are shown in Table 2. The main process parameters of the steel rolling in the embodiment and the embodiment are shown in Table 3. The main process parameters of the steel cooling in the embodiment and the embodiment are shown in Table 4. The performance of the steel in the embodiment and the steel in the embodiment is shown in Table 5. The structure of the steel in the embodiment and the steel in the embodiment is shown in Table 6.

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057] The steel plate produced by the application has excellent comprehensive mechanical properties, the yield strength is 1250-1350 MPa, the tensile strength is 1300-1500 MPa, the elongation is greater than or equal to 10%, the steel plate impact energy at -20 DEG C is greater than or equal to 110J, the 10 7 The fatigue strength of each pass is greater than or equal to 220 MPa, the hardness is greater than or equal to 420 HBW, and the abrasion rate in the simulated marine environment is only 40% or less of that of Q460C steel. The performance meets the technical requirements of the 1200 MPa grade mine pipeline in the marine environment.

[0058] For the purpose of illustrating the present application, the best mode for the same will be described in the above embodiments with reference to the accompanying drawings. The embodiments are presented herein for purposes of illustration and description and are not intended to limit the scope of the present application. The skilled person in the art, without departing from the spirit and scope of the present application, can make various changes and modifications, and any modification, equivalent replacement, improvement, etc. made should be included in the protection scope of the present application. The patent protection scope of the present application should be defined by the claims.

Claims

1. A 1200MPa grade marine environment fatigue-resistant steel plate for ore transportation pipelines, characterized in that, The composition of the steel plate by weight percentage is as follows: C: 0.13%~0.17%, Si: 0.51%~0.80%, Mn: 1.21%~1.50%, P≤0.015%, S≤0.001%, Cr: 0.80%~1.20%, Mo: 0.25%~0.45%, Al: 0.010%~0.050%, Nb: 0.08%~0.12%, V: 0.11%~0.20%, Ti: 0.005%~0.025%, Ni: 0.51~0.70%, Ce: 0.01~0.06%, with the balance being Fe and unavoidable impurities.

2. The steel plate for ore transportation pipelines with 1200MPa grade marine environment fatigue resistance according to claim 1, characterized in that, The steel plate contains Cr+Mo≥1.20%.

3. The steel plate for ore transportation pipelines with 1200MPa grade marine environment fatigue resistance according to claim 1, characterized in that, The Nb / Ce ratio in the steel plate is ≥1.

8.

4. The steel plate for ore transportation pipelines with 1200MPa grade marine environment fatigue resistance according to claim 1, characterized in that, The V / Ce ratio in the steel plate is ≥2.

2.

5. The steel plate for ore transportation pipelines with 1200MPa grade marine environment fatigue resistance according to claim 1, characterized in that, The microstructure of the steel plate is a mixture of lower bainite, lath martensite, and nanoscale V-containing precipitates; wherein, by volume percentage: lower bainite 10%~30%; nanoscale precipitates 2.0%~3.0%, of which more than 90% of the precipitates are ≤30nm in size and are diffusely distributed.

6. The steel plate for ore transportation pipelines with 1200MPa grade marine environment fatigue resistance according to claim 1, characterized in that, The steel plate has a thickness of 12~20mm, a yield strength of 1250~1350MPa, a tensile strength of 1300~1500MPa, and an elongation of ≥10%. The impact energy of the steel plate at -20℃ is ≥110J, 10 7 Cycle fatigue strength ≥220MPa, hardness ≥420HBW.

7. A method for producing a 1200MPa grade marine environment fatigue-resistant ore transport pipeline steel plate as described in any one of claims 1-6, comprising smelting, continuous casting, heating, rolling, accelerated cooling, and slow cooling; characterized in that: heating: The slab adopts a multi-stage stepped temperature heating method, in which the high temperature heating section temperature is 1200~1250℃, the soaking temperature is 1180~1220℃, and the time of the high temperature heating section + soaking section is not less than 120min. Rolling: Steel plate rolling is carried out in two stages: roughing and finishing. The finishing temperature of the roughing stage is ≥1050℃, and the single-pass reduction rate of the last two passes of roughing is ≥14%. The intermediate billet thickness of the finishing stage is 3.5~4.0t, where t is the finished steel plate. The initial rolling temperature is 850~900℃, the single-pass reduction rate of the first three passes of finishing is ≥13%, and the final rolling temperature is 780~820℃. Accelerated cooling: After the steel plate is rolled, accelerated cooling is carried out in two stages. The first stage starts with a cooling temperature range of 760~800℃, a cooling rate of 5~10℃ / s, and a cooling time of 8~10s. The second stage cools at a cooling rate of 20~25℃ / s and a final cooling temperature of 300~370℃. Slow cooling: After the steel plates have completed accelerated cooling, they are slowly cooled by stacking, with a cooling rate of ≤0.2℃ / s, until they reach room temperature.

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