A low-cobalt high low-temperature impact energy super-high strength steel for ocean engineering and a preparation method thereof

Abstract

The application provides a kind of marine engineering low cobalt high low temperature impact energy super high strength steel and its preparation method, relate to the technical field of steel material.The chemical composition of the marine engineering low cobalt high low temperature impact energy super high strength steel is as follows in terms of mass percentage: C 0.05-0.07%, Mn 0.6-0.8%, Ni 6.5-7.0%, Cr 0.8-1.0%, V 0.04-0.05%, Nb 0.01-0.02%, Al 0.03-0.05%, Ti 0.008-0.010%, Mo 1.5-2.2%, Co 1.5-3.0%, Si≤0.1%, P≤0.01%, S≤0.002%, and the rest is Fe and inevitable impurities.The method includes smelting, adjusting O, Al and Ti, preparing electroslag ingot, multi-pass hot rolling and quenching + low temperature tempering.The process steps of the application are simple, easy to operate, short processing cycle and easy to control, and the obtained phase structure can well improve the strength and low temperature impact resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel materials, and particularly relates to a low-cobalt high-temperature impact energy super-high-strength steel for marine engineering and a preparation method thereof. BACKGROUND

[0002] In recent years, the demand for oil and rare metals and other resources at home and abroad is increasing, and the ocean, especially the deep-sea resources, is rich in resources, but the development is difficult, which puts forward higher requirements for the strength, toughness and especially low-temperature impact performance of the steel for marine engineering. The preparation idea of the traditional marine engineering steel is "high carbon high alloy + quenching and tempering treatment", which meets the expected strength, but the high carbon content also leads to poor welding performance and poor low-temperature toughness.

[0003] In view of the above problems, the United States has prepared HSLA series steel by reducing the carbon content and adding trace Cu element on the basis of HY series steel. The HSLA series steel compensates for the loss of strength caused by the reduction of carbon content through the precipitation strengthening effect of Cu nanophase precipitated by aging. However, the Cu precipitated phase has a thermal stability problem in the aging process. T. Chairuangsri et al. [T. Chairuangsri, D.V. Edmonds, The precipitation of copper in abnormal ferrite and pearlite in hyper-eutectoid steels, Acta Materialia, 2000.] found that with the change of aging temperature and holding time, the morphology, size and distribution of Cu precipitated phase change significantly, its morphology changes from spherical to short rod or rod, and presents linear distribution in the group and loses the coherent relationship with the matrix, and the Cu precipitated phase becomes coarse at high temperature. The above phenomena will greatly affect the mechanical properties of the material. Therefore, it is of great significance to develop new technologies to realize the strength and toughness of the steel for marine engineering.

[0004] Chinese patent CN103495720A discloses a method for preparing in-situ nanoparticle reinforced Q195 steel, which adds Fe-Ti alloy wire in the process of smelting and pouring, and applies pressure field to the container and stirring flow field to the melt, so as to improve the plasticity and toughness of the steel by forming nano titanium oxide, and further improves the performance by controlling rolling and cooling; obviously, the titanium content used for nano strengthening is relatively high, and the performance improvement is closely related to the controlled rolling and cooling; and the V-notch low-temperature impact energy at-84 DEG C is less than 100J.

[0005] Chinese patent CN113249654A discloses a kind of in-situ nanoparticles enhanced ultra-high strength steel for ocean engineering and preparation method, obviously Al2O3 and Ti3O5 nanoparticles dispersion strengthening are used, but the content of Co added is very high, which leads to the large number of occurrence of twinning in ingot, reduces the plasticity and toughness of ocean engineering steel, and the V notch low temperature impact energy at-84 ℃ is also lower than 100 J.

[0006] Chinese patent CN112048665A discloses a kind of polar ocean engineering steel plate and its preparation method, the required steel plate is obtained by alloy element composition selection and melting hot rolling, the low temperature impact performance of the obtained steel plate is effectively improved, however, the yield strength and tensile strength are low, and the synergistic improvement of strength plasticity and low temperature impact performance cannot be realized.

[0007] Chinese patent CN112779472A discloses a kind of 1GPa grade ocean engineering steel plate with excellent low temperature toughness and its preparation method, the method is to realize the production of steel plate with high strength, low yield ratio and excellent low temperature toughness by designing chemical composition combined with controlled rolling + multi-step heat treatment process; the thickness specification of the steel plate includes medium plate and thick plate, the superheat is low, and the heat treatment method adopted is two-step critical heat treatment, which is difficult to operate; the yield strength of the obtained steel plate does not reach 1200 MPa level, and the yield ratio is close to 1.

[0008] Chinese patent CN106755864A discloses a kind of method for improving the surface low temperature impact toughness of super-high strength ocean engineering steel, which adopts surface ultra-fine grain rolling + quenching and tempering heat treatment process, the rolling method needs to cooperate with temperature control, the operation process is complicated, energy consumption is high, and the efficiency is low; and the steel plate belongs to thick plate, the thickness is greater than 60 mm, the low temperature impact energy at-80 ℃ is more than 100 J, but the yield strength does not reach 1200 MPa level. SUMMARY

[0009] The technical problem to be solved by the present application is that the current ocean engineering steel cannot realize the synergistic improvement of strength plasticity and low temperature impact performance, although some technologies can improve the low temperature impact performance by adding alloy elements and improving the preparation method, many of them have low strength plasticity and high low temperature impact performance, only a small part has high strength plasticity and low low temperature impact performance; it is difficult to obtain ocean engineering steel with yield strength reaching 1200 MPa level and high low temperature impact energy.

[0010] To solve the above technical problems, the technical solutions provided by the present application are as follows:

[0011] The application discloses a low-cobalt high-low-temperature impact energy super-high-strength steel for ocean engineering, and chemical components of the low-cobalt high-low-temperature impact energy super-high-strength steel for ocean engineering are as follows in percentage by mass: C 0.05-0.07%, Mn 0.6-0.8%, Ni 6.5-7.0%, Cr 0.8-1.0%, V 0.04-0.05%, Nb 0.01-0.02%, Al 0.03-0.05%, Ti 0.008-0.010%, Mo 1.5-2.2%, Co 1.5-3.0%, Si≤0.1%, P≤0.01%, S≤0.002%, and the rest is Fe and inevitable impurities.

[0012] The design basis of the above chemical components is as follows:

[0013] C: C can be dissolved in the Fe matrix to form a solid solution, produce solid solution strengthening, and also generate carbides to play the role of second phase strengthening; if the content of C is too low, the strength of the test steel cannot be guaranteed, and if the content of C is too high, brittle structure is easily formed to reduce low-temperature toughness and welding performance; therefore, the content of C is designed to be 0.05-0.07%.

[0014] Si: Si can improve the strength through solid solution strengthening, but if the content of Si is too high, large-size inclusions are generated, and in the use process, the large-size inclusions are easy to form crack sources, seriously affecting the toughness and welding performance; therefore, the content of Si is designed to be ≤0.1%.

[0015] Mn: Mn is a good deoxidizer and desulfurizer, can produce solid solution strengthening effect in the steel, and is also beneficial to improving the hardenability and hot working performance; however, if the content of Mn is too high, the toughness and welding performance are deteriorated; therefore, the content of Mn is designed to be 0.6-0.8%.

[0016] Ni: Ni can improve the strength and plasticity of the material to a certain extent, and greatly improve the low-temperature impact toughness; Ni is dissolved in the matrix to form a solid solution, and when plastic deformation occurs, the screw dislocation is not easy to decompose, the cross-slip is promoted, and the plasticity is improved; the element Ni can reduce the low-temperature brittleness transition temperature of the material, and further improve the low-temperature toughness of the material; therefore, the content of Ni is designed to be 6.5-7.0%.

[0017] Cr: Cr can improve the hardenability of the material, and promote the uniform distribution of the martensite structure after quenching; appropriate Cr can improve the corrosion resistance of the material; therefore, the content of Cr is designed to be 0.8-1.0%.

[0018] V, Nb: V, Nb can both improve the strength of the material by precipitation strengthening, and Nb can also improve the strength and toughness of the material by fine-grain strengthening. Adding trace amounts of V and Nb can form carbides with C, promoting the formation of second-phase particles. In combination, the V content is designed to be 0.04-0.05%, and the Nb content is designed to be 0.01-0.02%.

[0019] Ti, Al: Taking advantage of the strong affinity of Ti and Al elements with O, Al-Ti composite wire is fed by stirring wire feeding method to generate dispersed in-situ nanophase in the ingot, thereby improving the strength of the material. However, large-sized Al2O3 particles are sticky and easy to accumulate and adhere to the water gap, causing the water gap to be blocked. In combination, the Al content is designed to be 0.03-0.05%, and the Ti content is designed to be 0.008-0.010%.

[0020] Co can also produce solid solution strengthening effect in steel. The addition of Co can change the ordered structure of the matrix, cause Fe to produce short-range order or long-range order, reduce its diffusion tendency, delay dislocation recovery during tempering, cause small-sized alloy carbides to be generated at dislocations, and improve the strength.

[0021] Mo element can improve the hardenability of the material and promote the uniform distribution of martensite structure after quenching. Mo element can reduce the lattice mismatch between precipitates and matrix, thereby facilitating the maintenance of coherent interface between precipitates and matrix. Mo element can partly form fine carbides with C, and the other part can be dissolved in the matrix of the steel to play a solid solution strengthening role, and the addition of Mo can effectively inhibit the coarsening of carbides.

[0022] Therefore, Mo element and Co element both have the effects of forming fine carbides and solid solution strengthening, and Mo element also has the effects of inhibiting the coarsening of carbides and improving the hardenability of the material. Excessive addition of Co will cause a large number of twinning to form, thereby damaging the plasticity and toughness of the material.

[0023] Therefore, the content of Mo is increased to reduce the content of Co.

[0024] In combination, the Mo content is designed to be 1.5-2.2%, and the Co content is designed to be 1.5-3.0%.

[0025] Alternatively, the steel plate of the low-cobalt high-low-temperature impact energy super-high-strength steel for ocean engineering has a thickness of 8-20 mm, an average grain size of 7-12 μm, and a phase structure of martensite with a lath width of 0.2-0.6 μm + nanophase with a size of 0.05-0.2 μm, and the shapes of the respective phase structures are lath-shaped and spherical-shaped, respectively.

[0026] Optionally, the low-C high low-temperature impact energy ultra-high strength steel plate for ocean engineering has a thickness of 8-20 mm, a yield strength of no less than 1200 MPa, a tensile strength of no less than 1300 MPa, a yield strength ratio of 0.91-0.94, an elongation of no less than 14%, a product of strength and plasticity of no less than 18.2 GPa%, and a V-notch low-temperature impact energy at -84 DEG C of no less than 100 J.

[0027] Optionally, the low-C high low-temperature impact energy ultra-high strength steel plate for ocean engineering has a maximum thickness of 20 mm, a maximum yield strength of 1232 MPa, a maximum tensile strength of 1328 MPa, a yield strength ratio of 0.91-0.94, a maximum elongation of 14.5%, a maximum product of strength and plasticity of 19.2 GPa%, and a maximum V-notch low-temperature impact energy at -84 DEG C of 138 J.

[0028] A preparation method of the low-C high low-temperature impact energy ultra-high strength steel plate for ocean engineering is provided.

[0029] S1, melting:

[0030] The raw materials are weighed according to the alloy chemical composition of the low-C high low-temperature impact energy ultra-high strength steel plate for ocean engineering, and then the raw materials are completely melted by vacuum melting heating of a vacuum melting furnace to obtain a molten steel;

[0031] S2, adjusting O, Al and Ti:

[0032] After the molten steel in the vacuum melting furnace of S1 is stable, Al-Ti composite wire is added, and argon is introduced into the bottom of the vacuum melting furnace of S1 to form a flow field of the molten steel, so as to adjust the contents of O, Al and Ti in the molten steel;

[0033] S3, preparing an electroslag ingot:

[0034] The molten steel of S2 is heated and superheated, and then cast to obtain an ingot, and the ingot is electroslag remelted to obtain an electroslag ingot;

[0035] S4, multi-pass hot rolling:

[0036] The electroslag ingot of S3 is multi-pass hot rolled, and then slowly cooled in the furnace to room temperature to obtain a hot-rolled steel plate;

[0037] S5, quenching + low-temperature tempering:

[0038] The hot-rolled steel plate of S4 is quenched and low-temperature tempered to obtain the low-C high low-temperature impact energy ultra-high strength steel plate for ocean engineering.

[0039] Optionally, in S2, the liquid level of the molten steel in the vacuum melting furnace is stabilized, and the content of the molten steel is measured to reach 5-30PPm; the diameter of the added Al-Ti composite wire is 3-5mm, and the component content is Al-(10-40)wt.%Ti.

[0040] Optionally, in S2, the flow field is a shear flow field.

[0041] Optionally, in S3, the superheating temperature is 30-45℃; the phase structure of the ingot is 1-5μm ferrite+2-5μm bainite, and the shapes of the respective phase structures are acicular and lath-shaped, respectively; and the phase structure of the electroslag ingot is 1-4.8μm ferrite+2-4.8μm bainite, and the shapes of the respective phase structures are acicular and lath-shaped, respectively.

[0042] Optionally, in S3, the cooling rate of the ingot casting process is 50-100℃ / h, and the flow line speed of the molten steel is 1.5-1.7m / s.

[0043] Optionally, in S4, the multi-pass hot rolling needs to be kept at 1230-1280℃ for 2h, the initial rolling temperature is 1130-1180℃, the total pass reduction is 80-95%, and the final rolling temperature is 800-850℃.

[0044] Optionally, in S5, the quenching treatment is to heat the hot-rolled steel plate to 810-850℃, keep it for 0.3-0.5h, and then take it out for water quenching treatment; and the low-temperature tempering treatment is to heat the steel plate after the water quenching treatment to 240-280℃, keep it for 1.5-3h, and then take it out for air cooling to room temperature.

[0045] Optionally, in S5, the heating rate of the quenching treatment is 75-85℃ / min, the cooling rate of the water quenching treatment is 75-100℃ / s; the heating rate of the low-temperature tempering treatment is 75-100℃ / min, and the cooling rate of the air cooling is 100-250℃ / h.

[0046] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0047] The above scheme provides a low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering and a preparation method thereof, overcomes the technical defects that the strength plasticity and the low-temperature impact performance cannot be improved simultaneously, can improve the low-temperature impact performance on the basis of retaining high strength plasticity, and further expands the processability and practicality, which is beneficial to industrial large-scale production and promotion.

[0048] The present application greatly reduces the content of Co element by increasing the content of Mo element and reducing the content of each alloying element, improves the low-temperature impact energy of the material and reduces the raw material cost on the basis of ensuring high yield strength.

[0049] The present application feeds Al-(10-40)wt.%Ti composite wires by the method of feeding and stirring, generates dispersed nano-phase Al2O3 and Ti3O5 in the matrix, and the nano-phase Al2O3 and Ti3O5 can be used as heterogeneous nucleation core, improve inclusions and refine grains.

[0050] The present application obtains the electroslag ingot by electroslag remelting the ingot, and the electroslag remelting technology improves the metal purity of the steel, reduces the content of non-metallic inclusions, and obtains the clean and dense steel ingot with uniform structure.

[0051] The present application provides the energy required for recrystallization of the matrix by multi-pass hot rolling of the electroslag ingot, refines the grains, and obtains the steel plate with fine matrix grains.

[0052] The present application obtains the low-Co high-low-temperature impact energy ultra-high strength steel for ocean engineering by quenching + low-temperature tempering, and the matrix structure is composed of lath martensite and dispersed nano precipitated phase, the maximum yield strength of the steel plate can reach 1232MPa, the maximum tensile strength can reach 1328MPa, the yield strength ratio is 0.91-0.94, the maximum elongation can reach 14.5%, the maximum strength-plasticity product can reach 19.2GPa%, and the V-notch low-temperature impact energy at-84℃ can reach 138J.

[0053] The steel plate of the low-Co high-low-temperature impact energy ultra-high strength steel for ocean engineering has a thickness of 8-20mm, an average grain size of 7-12μm, a phase structure of lath width 0.2-0.6μm martensite+0.05-0.2μm nano-phase, and the shapes of the phase structures are lath and spherical respectively.

[0054] The steel plate of the low-Co high-low-temperature impact energy ultra-high strength steel for ocean engineering has a thickness of 8-20mm, a yield strength not less than 1200MPa, a tensile strength not less than 1300MPa, a yield strength ratio of 0.91-0.94, an elongation not less than 14%, a strength-plasticity product not less than 18.2GPa%, and a V-notch low-temperature impact energy at-84℃ not less than 100J.

[0055] In summary, the method of the present application, compared with other conventional methods, efficiently and reasonably regulates the element content of the molten steel through the combined and coordinated use of alloying elements such as Mo, Ni, Co and wire feeding stirring, and then obtains the electroslag ingot suitable for multi-pass hot rolling through ingot remelting, and finally obtains the marine steel with improved comprehensive strength, plasticity and low-temperature impact property through quenching + low-temperature tempering; the process steps are simple, the operation is convenient, the processing cycle is short, the control is easy, and the obtained phase structure can well improve the comprehensive strength, plasticity and low-temperature impact property. BRIEF DESCRIPTION OF DRAWINGS

[0056] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0057] Figure 1 The microstructure morphology photo of the steel plate obtained by the preparation method of the low-cobalt high-low-temperature impact energy ultra-high strength steel for marine engineering in embodiment 1 under a scanning electron microscope;

[0058] Figure 2 The tensile curve diagram of the steel plate obtained by the preparation method of the low-cobalt high-low-temperature impact energy ultra-high strength steel for marine engineering in embodiment 1. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by those skilled in the art without creative effort belong to the protection scope of the present application.

[0060] A low-cobalt high-low-temperature impact energy ultra-high strength steel for marine engineering, the chemical composition of the low-cobalt high-low-temperature impact energy ultra-high strength steel for marine engineering is as follows in terms of mass percentage: C 0.05-0.07%, Mn 0.6-0.8%, Ni 6.5-7.0%, Cr 0.8-1.0%, V 0.04-0.05%, Nb 0.01-0.02%, Al 0.03-0.05%, Ti 0.008-0.010%, Mo 1.5-2.2%, Co 1.5-3.0%, Si≤0.1%, P≤0.01%, S≤0.002%, and the rest is Fe and inevitable impurities.

[0061] The design basis of the above chemical composition is as follows:

[0062] C: C can be dissolved in the Fe matrix to form a solid solution, producing solid solution strengthening, and can also generate carbides, playing the role of second phase strengthening. If the C content is too low, the strength of the test steel cannot be guaranteed, and if the content is too high, brittle structures are easily formed, leading to a decrease in low-temperature toughness and welding performance. Taking all factors into consideration, the C content is designed to be 0.05-0.07%.

[0063] Si: Si improves strength through solid solution strengthening, but if the content is too high, large-size inclusions are produced, which easily form crack sources during use, seriously affecting toughness and welding performance. Taking all factors into consideration, the Si content is designed to be ≤0.1%.

[0064] Mn: Mn is a good deoxidizer and desulfurizer, can produce solid solution strengthening effects in steel, and is also beneficial to improving hardenability and hot working performance. However, too high Mn will deteriorate toughness and welding performance. Taking all factors into consideration, the Mn content is designed to be 0.6-0.8%.

[0065] Ni: Ni can improve the strength and plasticity of the material to some extent, and greatly improve the low-temperature impact toughness. Ni dissolves in the matrix to form a solid solution, which makes it difficult for screw dislocations to decompose during plastic deformation, promotes cross-slip, and improves plasticity. Ni can reduce the low-temperature brittleness transition temperature of the material, thereby improving the low-temperature toughness of the material. Taking all factors into consideration, the Ni content is designed to be 6.5-7.0%.

[0066] Cr: Cr can improve the hardenability of the material and promote the uniform distribution of the martensitic structure after quenching. An appropriate amount of Cr can improve the corrosion resistance of the material. Taking all factors into consideration, the Cr content is designed to be 0.8-1.0%.

[0067] V, Nb: V and Nb can both improve the strength of the material through precipitation strengthening, and Nb can also improve the strength and toughness of the material through fine-grain strengthening. Adding a small amount of V and Nb can form carbides with C, promoting the formation of second-phase particles. Taking all factors into consideration, the V content is designed to be 0.04-0.05%, and the Nb content is designed to be 0.01-0.02%.

[0068] Ti, Al: Ti and Al elements have strong affinity with O, and Al-Ti composite wire is fed by stirring and feeding, generating dispersed in-situ nanophase in the ingot, thereby improving the strength of the material. However, large-size Al2O3 particles have strong viscosity and are easily accumulated and adhered in the water gap, causing the water gap to be blocked. Taking all factors into consideration, the Al content is designed to be 0.03-0.05%, and the Ti content is designed to be 0.008-0.010%.

[0069] Co can also produce solid solution strengthening effect in steel. The addition of Co can change the ordered structure of the matrix, make Fe produce short-range order or long-range order, reduce its diffusion tendency, delay dislocation recovery during tempering, generate small-sized alloy carbides at dislocations, and improve strength.

[0070] Mo element can improve the hardenability of the material and promote the uniform distribution of the martensite structure after quenching. Mo element can reduce the lattice mismatch between precipitates and the matrix, thereby facilitating the maintenance of coherent interface between precipitates and the matrix. Mo element can form fine carbides with C, and the other part is dissolved in the matrix of the steel to play a solid solution strengthening role. The addition of Mo can effectively inhibit the coarsening of carbides.

[0071] Therefore, Mo element and Co element both have the effects of forming fine carbides and solid solution strengthening, and Mo element also has the effects of inhibiting the coarsening of carbides and improving the hardenability of the material. Excessive addition of Co will lead to the formation of a large number of twins, thereby damaging the plasticity and toughness of the material.

[0072] Therefore, the content of Mo is increased to reduce the content of Co.

[0073] In summary, the content of Mo is designed to be 1.5-2.2%, and the content of Co is designed to be 1.5-3.0%.

[0074] In particular, the thickness of the steel plate of the low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering is 8-20mm, the average grain size is 7-12μm, the phase structure of the steel plate is martensite with a lath width of 0.2-0.6μm + nanophase with a size of 0.05-0.2μm, and the shapes of the respective phase structures are lath-shaped and spherical-shaped.

[0075] In particular, the thickness of the steel plate of the low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering is 8-20mm, the yield strength of the steel plate is not less than 1200MPa, the tensile strength is not less than 1300MPa, the yield strength ratio is 0.91-0.94, the elongation is not less than 14%, the strength-plasticity product is not less than 18.2GPa·%, and the V-notch low-temperature impact energy at-84℃ is not less than 100J.

[0076] In particular, the thickness of the steel plate of the low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering can reach 20mm at most, the yield strength of the steel plate can reach 1232MPa at most, the tensile strength can reach 1328MPa at most, the yield strength ratio is 0.91-0.94, the elongation can reach 14.5% at most, the strength-plasticity product can reach 19.2GPa·% at most, and the V-notch low-temperature impact energy at-84℃ can reach 138J at most.

[0077] A preparation method of the low-cobalt high-low temperature impact energy ultrahigh-strength steel for marine engineering based on the above.

[0078] S1, smelting:

[0079] According to the alloy chemical composition of the low-cobalt high-low temperature impact energy ultrahigh-strength steel for marine engineering, the raw materials are weighed, and then the raw materials are completely melted by the vacuum smelting heating mode of the vacuum smelting furnace to obtain a molten steel;

[0080] S2, adjusting O, Al and Ti:

[0081] After the molten steel liquid level in the vacuum smelting furnace of S1 is stable, Al-Ti composite wire is added, and argon is introduced into the bottom of the vacuum smelting furnace of S1 to form a flow field of the molten steel, so as to adjust the contents of O, Al and Ti in the molten steel;

[0082] S3, preparing an electroslag ingot:

[0083] The molten steel of S2 is heated and superheated, and then casted to obtain an ingot, and the ingot is electroslag remelted to obtain an electroslag ingot;

[0084] S4, multi-pass hot rolling:

[0085] The electroslag ingot of S3 is multi-pass hot rolled, and then slowly cooled to room temperature in the furnace to obtain a hot-rolled steel plate;

[0086] S5, quenching + low-temperature tempering:

[0087] The hot-rolled steel plate of S4 is quenched and low-temperature tempered to obtain a low-cobalt high-low temperature impact energy ultrahigh-strength steel for marine engineering.

[0088] In particular, in S2, the content of the molten steel in the vacuum smelting furnace is measured to be 5-30PPm; the diameter of the Al-Ti composite wire added is 3-5mm, and the component content is Al-(10-40)wt.%Ti.

[0089] In particular, in S2, the flow field is a shear flow field.

[0090] In particular, in S3, the superheating temperature is 30-45℃; the phase structure of the ingot is 1-5μm ferrite + 2-5μm bainite, and the shapes of the respective phase structures are acicular and lath-shaped, respectively; the phase structure of the electroslag ingot is 1-4.8μm ferrite + 2-4.8μm bainite, and the shapes of the respective phase structures are acicular and lath-shaped, respectively.

[0091] In particular, in S3, the cooling rate during the casting process of the ingot is 50-100℃ / h, and the flow line speed of the molten steel is 1.5-1.7m / s.

[0092] In particular, the multi-pass hot rolling in S4 needs to be kept at 1230-1280℃ for 2h, the initial rolling temperature is 1130-1180℃, the total pass reduction is 80-95%, and the final rolling temperature is 800-850℃.

[0093] In particular, the quenching treatment in S5 is to heat the hot-rolled steel plate to 810-850℃, keep for 0.3-0.5h, and take out for water quenching treatment; the low-temperature tempering treatment is to heat the steel plate after water quenching treatment to 240-280℃, keep for 1.5-3h, and take out for air cooling to room temperature.

[0094] In particular, the heating rate of the quenching treatment in S5 is 75-85℃ / min, the cooling rate of the water quenching treatment is 75-100℃ / s; the heating rate of the low-temperature tempering treatment is 75-100℃ / min, and the cooling rate of the air cooling is 100-250℃ / h.

[0095] Embodiment 1

[0096] The chemical composition of the low-cobalt high-low temperature impact energy ultrahigh-strength steel for ocean engineering in this embodiment is as follows in terms of mass percentage: C 0.051%, Mn 0.62%, Ni 6.55%, Cr 0.85%, V 0.04%, Nb 0.01%, Al 0.031%, Ti 0.009%, Mo 1.82%, Co 2.2%, Si 0.058%, P 0.0081%, S 0.0018%, and the rest is Fe and inevitable impurities.

[0097] A preparation method of the low-cobalt high-low temperature impact energy ultrahigh-strength steel for ocean engineering based on this embodiment, the preparation method of the low-cobalt high-low temperature impact energy ultrahigh-strength steel for ocean engineering is as follows:

[0098] S1, smelting:

[0099] The raw materials are weighed according to the alloy chemical composition of the low-cobalt high-low temperature impact energy ultrahigh-strength steel for ocean engineering, and then the raw materials are completely melted by the vacuum smelting heating mode of the vacuum smelting furnace to obtain a steel liquid;

[0100] S2, adjusting O, Al, Ti:

[0101] After the steel liquid level in the vacuum smelting furnace of S1 is stable, the content of the steel liquid is measured to reach 11PPm; Al-Ti composite wire is added, the diameter of the added Al-Ti composite wire is 3mm, and the component content is Al-20wt.%Ti; at the same time, argon is introduced into the bottom of the vacuum smelting furnace of S1 to form a flow field of the steel liquid, the flow field is a shear flow field, so as to adjust the contents of O, Al and Ti in the steel liquid.

[0102] S3, preparing an electroslag ingot:

[0103] The molten steel of S2 is cast after being heated and superheated by 30-45℃, the cooling rate of the casting process is 64℃ / h, the flow line speed of the molten steel is 1.6m / s, and the ingot is obtained after air cooling, the phase structure of the ingot is 1-5μm ferrite + 2-5μm bainite, and the shapes of each phase structure are acicular and lath-shaped respectively; the phase structure of the electroslag ingot is 1-4.8μm ferrite + 2-4.8μm bainite, and the shapes of each phase structure are acicular and lath-shaped respectively;

[0104] S4, multi-pass hot rolling:

[0105] The electroslag ingot of S3 is subjected to multi-pass hot rolling, which needs to be kept at 1280℃ for 2h, and needs to be rolled by 6 passes, the initial rolling temperature is 1150℃, the total pass reduction is 85%, the final rolling temperature is 850℃, and then the hot-rolled steel plate is obtained after furnace cooling to room temperature;

[0106] S5, quenching + low-temperature tempering:

[0107] The hot-rolled steel plate of S4 is subjected to quenching treatment and low-temperature tempering treatment, the quenching treatment is that the hot-rolled steel plate is heated to 840±5℃ at a heating rate of 80℃ / min, and kept for 0.5h, and then taken out for water quenching treatment at a cooling rate of 75-100℃ / s; the low-temperature tempering treatment is that the steel plate after water quenching treatment is heated to 240±5℃ at a heating rate of 85℃ / min, and kept for 2h, and then taken out for air cooling at a cooling rate of 130℃ / h until room temperature, to obtain the low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering.

[0108] The steel plate thickness of the low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering prepared in this embodiment is 18mm, as shown in Figure 1 , the average grain size is 9.1μm, and the phase structure of the steel plate is that the phase structure of the steel plate is 0.21-0.6μm lath width of martensite + 0.05-0.2μm nanophase, and the shapes of each phase structure are lath-shaped and spherical-shaped respectively.

[0109] The steel plate thickness of the low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering prepared in this embodiment is 18mm, as shown in Figure 2 , the yield strength of the steel plate is 1230MPa, the tensile strength is 1311MPa, the yield strength ratio is 0.93, the elongation is 14%, the strength-plasticity product is 18.354GPa%, and the V-notch low-temperature impact energy at-84℃ is 136J.

[0110] Example 2

[0111] The chemical composition of the low-cobalt high-impact-temperature-energy ultra-high-strength steel for ocean engineering of the embodiment, in terms of mass percentage, is: C 0.051%, Mn 0.62%, Ni 6.55%, Cr 0.85%, V 0.04%, Nb 0.01%, Al 0.031%, Ti 0.009%, Mo 1.82%, Co 2.2%, Si 0.058%, P 0.0081%, S 0.0018%, and the rest is Fe and inevitable impurities.

[0112] A preparation method of the low-cobalt high-impact-temperature-energy ultra-high-strength steel for ocean engineering based on the embodiment, the preparation method of the low-cobalt high-impact-temperature-energy ultra-high-strength steel for ocean engineering includes the following steps:

[0113] S1, smelting:

[0114] The raw materials are weighed according to the alloy chemical composition of the low-cobalt high-impact-temperature-energy ultra-high-strength steel for ocean engineering, and then the raw materials are completely melted by the vacuum smelting heating mode of a vacuum smelting furnace to obtain a molten steel;

[0115] S2, adjusting O, Al and Ti:

[0116] After the molten steel in the vacuum smelting furnace of S1 is stable, the content of the molten steel is measured to reach 11PPm; Al-Ti composite wire is added, the diameter of the added Al-Ti composite wire is 3mm, and the component content is Al-20wt.%Ti; at the same time, argon is introduced into the bottom of the vacuum smelting furnace of S1 to form a flow field of the molten steel, the flow field is a shear flow field, so as to adjust the contents of O, Al and Ti in the molten steel;

[0117] S3, preparing an electroslag ingot:

[0118] After the molten steel of S2 is heated and superheated by 30-45℃, casting is performed, the cooling rate of the casting process is 64℃ / h, the flow line speed of the molten steel is 1.6m / s, and a cast ingot is obtained after air cooling, the phase structure of the cast ingot is 1-5μm ferrite+2-5μm bainite, and the shapes of the phase structures are acicular and lath-shaped respectively; the phase structure of the electroslag ingot is 1-4.8μm ferrite+2-4.8μm bainite, and the shapes of the phase structures are acicular and lath-shaped respectively;

[0119] S4, multi-pass hot rolling:

[0120] The electroslag ingot of S3 is subjected to multi-pass hot rolling, the multi-pass hot rolling needs to be kept at 1280℃ for 2h, the initial rolling temperature is 1150℃, the total pass reduction is 85%, and the final rolling temperature is 850℃, and then the hot rolling steel plate is obtained after furnace cooling to room temperature;

[0121] S5, quenching+low-temperature tempering:

[0122] S4 hot-rolled steel plates were subjected to quenching and low-temperature tempering. The quenching process involved heating the hot-rolled steel plate to 840±5℃ at a heating rate of 80℃ / min, holding it at that temperature for 0.5h, and then removing it for water quenching at a cooling rate of 75-100℃ / s. The low-temperature tempering process involved heating the water-quenched steel plate to 260±5℃ at a heating rate of 75℃ / min, holding it at that temperature for 2h, and then removing it for air cooling at a cooling rate of 150℃ / h until it reached room temperature, thus obtaining low-cobalt high- and low-temperature impact-resistant ultra-high-strength steel for marine engineering.

[0123] The ultra-high strength steel plate with low cobalt high and low temperature impact energy for marine engineering prepared in this embodiment has a thickness of 18 mm and an average grain size of 9.2 μm. The phase structure of the steel plate is martensite with a lath width of 0.28-0.57 μm + nanophase with a width of 0.08-0.17 μm. The shapes of each phase structure are lath-shaped and spherical.

[0124] The ultra-high strength steel plate with low cobalt high and low temperature impact energy for marine engineering prepared in this embodiment has a thickness of 18 mm, a yield strength of 1221 MPa, a tensile strength of 1308 MPa, a yield ratio of 0.93, an elongation of 14.08%, a strength-ductility product of 18.41664 GPa%, and a V-shaped low temperature impact energy of -84℃ of 117.8 J.

[0125] Example 3

[0126] The chemical composition of the low-cobalt, high- and low-temperature impact-resistant ultra-high-strength steel for marine engineering in this embodiment, by mass percentage, is as follows: C 0.051%, Mn 0.62%, Ni 6.55%, Cr 0.85%, V 0.04%, Nb 0.01%, Al 0.031%, Ti 0.009%, Mo 1.82%, Co 2.2%, Si 0.058%, P 0.0081%, S 0.0018%, with the remainder being Fe and unavoidable impurities.

[0127] A method for preparing low-cobalt high- and low-temperature impact-resistant ultra-high-strength steel for marine engineering, based on this embodiment, comprises the following steps:

[0128] S1, Smelting:

[0129] The raw materials were weighed according to the alloy chemical composition of the low cobalt high and low temperature impact energy ultra-high strength steel for marine engineering. Then, the raw materials were completely melted by vacuum melting heating in a vacuum melting furnace to obtain molten steel.

[0130] S2, Adjusting O, Al, and Ti:

[0131] The liquid level in the vacuum melting furnace of S1 is stable, and the content in the molten steel is measured to reach 11PPm; Al-Ti composite wire is added, the diameter of the added Al-Ti composite wire is 3mm, and the component content is Al-20wt.%Ti; at the same time, argon is introduced into the bottom of the vacuum melting furnace of S1 to form a flow field of the molten steel, the flow field is a shear flow field, so as to adjust the contents of O, Al and Ti in the molten steel.

[0132] S3, preparing an electroslag ingot:

[0133] After the molten steel of S2 is heated and overheated by 30-45℃, casting is performed, the cooling rate of the casting process is 64℃ / h, the flow line speed of the molten steel is 1.6m / s, and a cast ingot is obtained after air cooling, the phase structure of the cast ingot is 1-5μm ferrite+2-5μm bainite, and the shapes of each phase structure are needle-shaped and lath-shaped respectively. The phase structure of the electroslag ingot is 1-4.8μm ferrite+2-4.8μm bainite, and the shapes of each phase structure are needle-shaped and lath-shaped respectively.

[0134] S4, multi-pass hot rolling:

[0135] The electroslag ingot of S3 is subjected to multi-pass hot rolling, the multi-pass hot rolling needs to be kept at 1280℃ for 2h, the initial rolling temperature is 1150℃, the total pass reduction is 85%, and the final rolling temperature is 850℃, and then the hot rolling steel plate is obtained by furnace cooling to room temperature.

[0136] S5, quenching+low temperature tempering:

[0137] The hot rolling steel plate of S4 is subjected to quenching treatment and low temperature tempering treatment, the quenching treatment is that the hot rolling steel plate is heated to 840±5℃ at a heating rate of 80℃ / min, kept for 0.5h, and then taken out for water quenching treatment at a cooling rate of 75-90℃ / s; the low temperature tempering treatment is that the steel plate after water quenching treatment is heated to 280±5℃ at a heating rate of 75℃ / min, kept for 2h, and then taken out for air cooling at a cooling rate of 145℃ / h until room temperature, to obtain the low-cobalt high-low-impact-energy ultrahigh-strength steel for ocean engineering.

[0138] The steel plate thickness of the low-cobalt high-low-impact-energy ultrahigh-strength steel for ocean engineering prepared in this embodiment is 18mm, the average grain size is 9.1μm, and the phase structure of the steel plate is that the phase structure of the steel plate is 0.24-0.59μm lath width of martensite+0.081-0.18μm nanophase, and the shapes of each phase structure are lath-shaped and spherical-shaped respectively.

[0139] The steel plate of the low-cobalt high low-temperature impact energy ultrahigh-strength steel for ocean engineering prepared in the embodiment has a thickness of 18 mm, a yield strength of 1224 MPa, a tensile strength of 1309 MPa, a yield strength / tensile strength ratio of 0.93, an elongation of 14.12%, a product of strength and plasticity of 18.48308 GPa%, and a V-notch low-temperature impact energy at -84 ℃ of 106 J.

[0140] Embodiment 4

[0141] The low-cobalt high low-temperature impact energy ultrahigh-strength steel for ocean engineering in the embodiment has a chemical composition by mass percent of C 0.06%, Mn 0.65%, Ni 6.67%, Cr 0.91%, V 0.0423%, Nb 0.013%, Al 0.03%, Ti 0.008%, Mo 1.89%, Co 2.41%, Si 0.085%, P 0.0045%, S 0.0018%, and the balance of Fe and inevitable impurities.

[0142] A preparation method of a low-cobalt high low-temperature impact energy ultrahigh-strength steel for ocean engineering based on the embodiment, the preparation method of the low-cobalt high low-temperature impact energy ultrahigh-strength steel for ocean engineering comprising the following steps:

[0143] S1, smelting:

[0144] The raw materials are weighed according to the alloy chemical composition of the low-cobalt high low-temperature impact energy ultrahigh-strength steel for ocean engineering, and then the raw materials are completely melted by a vacuum smelting furnace in a vacuum smelting heating mode to obtain a molten steel;

[0145] S2, adjusting O, Al and Ti:

[0146] After the molten steel in the vacuum smelting furnace in S1 is stable, the content of the molten steel is measured to reach 15 PPM; an Al-Ti composite wire is added, the diameter of the added Al-Ti composite wire is 5 mm, and the component content is Al-22wt.%Ti; at the same time, argon is introduced into the bottom of the vacuum smelting furnace in S1 to form a flow field of the molten steel, the flow field is a shear flow field, so as to adjust the contents of O, Al and Ti in the molten steel;

[0147] S3, preparing an electroslag ingot:

[0148] After the molten steel in S2 is heated and superheated by 30-45 ℃, casting is performed, the cooling rate of the casting process is 70 ℃ / h, the flow line speed of the molten steel is 1.7 m / s, and a cast ingot is obtained after air cooling, the phase structure of the cast ingot is 1-5 μm of ferrite + 2-5 μm of bainite, and the shapes of the respective phase structures are acicular and lath-shaped, respectively. The phase structure of the electroslag ingot is 1-4.8 μm of ferrite + 2-4.8 μm of bainite, and the shapes of the respective phase structures are acicular and lath-shaped, respectively.

[0149] S4, multi-pass hot rolling:

[0150] The electroslag ingot of S3 is subjected to multi-pass hot rolling, which requires holding at 1260℃ for 2h, initial rolling temperature is 1150℃, total pass reduction is 91%, and final rolling temperature is 840℃, and then slow cooling in the furnace to room temperature to obtain a hot-rolled steel plate;

[0151] S5, quenching + low-temperature tempering:

[0152] The hot-rolled steel plate of S4 is subjected to quenching treatment and low-temperature tempering treatment, the quenching treatment is that the hot-rolled steel plate is heated to 830±5℃ at a heating rate of 81℃ / min, and held for 0.35h, and then taken out for water quenching treatment at a cooling rate of 75-100℃ / s; the low-temperature tempering treatment is that the steel plate after water quenching treatment is heated to 240±5℃ at a heating rate of 90℃ / min, and held for 1.75h, and then taken out for air cooling at a cooling rate of 140℃ / h until room temperature, to obtain a low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering.

[0153] The low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering prepared in this embodiment has a steel plate thickness of 10mm, an average grain size of 7.9μm, and a phase structure of 0.22-0.55μm of martensite + 0.056-0.189μm of nanophase, and the shapes of the respective phase structures are lath-shaped and spherical-shaped, respectively.

[0154] The low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering prepared in this embodiment has a steel plate thickness of 10mm, a yield strength of 1220MPa, a tensile strength of 1313MPa, a yield strength ratio of 0.93, an elongation of 14.5%, a strength-plasticity product of 19.0385GPa·%, and a V-notch low-temperature impact energy at -84℃ of 138J.

[0155] Example 5

[0156] The chemical composition of the low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering of this embodiment, in terms of mass percentage, is: C 0.06%, Mn 0.65%, Ni 6.67%, Cr 0.91%, V 0.0423%, Nb 0.013%, Al 0.03%, Ti 0.008%, Mo 1.89%, Co 2.41%, Si 0.085%, P 0.0045%, S 0.0018%, and the rest is Fe and unavoidable impurities.

[0157] A preparation method of a low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering based on this embodiment, the preparation method of the low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering is as follows:

[0158] S1, smelting:

[0159] According to the alloy chemical composition of the low-cobalt high-low temperature impact energy ultrahigh strength steel for ocean engineering, the raw materials are weighed, and then the raw materials are completely melted by the vacuum smelting heating mode of the vacuum smelting furnace to obtain a molten steel;

[0160] S2, adjusting O, Al and Ti:

[0161] After the molten steel in the vacuum smelting furnace of S1 is stable, the content of the molten steel is measured to reach 15PPm; Al-Ti composite wire is added, the diameter of the added Al-Ti composite wire is 5mm, and the component content is Al-22wt.%Ti; at the same time, argon is introduced into the bottom of the vacuum smelting furnace of S1 to form a flow field of the molten steel, the flow field is a shear flow field, so as to adjust the contents of O, Al and Ti in the molten steel;

[0162] S3, preparing an electroslag ingot:

[0163] After the molten steel of S2 is heated and superheated by 30-45℃, casting is performed, the cooling rate of the casting process is 70℃ / h, the flow line speed of the molten steel is 1.7m / s, and a cast ingot is obtained after air cooling, the phase structure of the cast ingot is 1-5μm ferrite+2-5μm bainite, and the shapes of each phase structure are needle-shaped and lath-shaped respectively. The phase structure of the electroslag ingot is 1-4.8μm ferrite+2-4.8μm bainite, and the shapes of each phase structure are needle-shaped and lath-shaped respectively;

[0164] S4, multi-pass hot rolling:

[0165] The electroslag ingot of S3 is subjected to multi-pass hot rolling, the multi-pass hot rolling needs to be kept at 1260℃ for 2h, the initial rolling temperature is 1150℃, the total pass reduction is 91%, and the final rolling temperature is 840℃, and then the furnace is slowly cooled to room temperature to obtain a hot-rolled steel plate;

[0166] S5, quenching + low-temperature tempering:

[0167] The hot-rolled steel plate of S4 is subjected to quenching treatment and low-temperature tempering treatment, the quenching treatment is that the hot-rolled steel plate is heated to 830±5℃ at a heating rate of 85℃ / min, kept for 0.35h, and then taken out for water quenching treatment at a cooling rate of 75-100℃ / s; the low-temperature tempering treatment is that the steel plate after water quenching treatment is heated to 260±5℃ at a heating rate of 95℃ / min, kept for 1.75h, and then taken out for air cooling at a cooling rate of 120℃ / h until room temperature, to obtain a low-cobalt high-low temperature impact energy ultrahigh strength steel for ocean engineering.

[0168] The steel plate of the marine engineering low-cobalt high-low temperature impact energy ultrahigh-strength steel prepared in the embodiment has a thickness of 10 mm, an average grain size of 8.1 μm, and a phase structure of 0.2-0.59 μm of martensite + 0.059-0.195 μm of carbide, and the shapes of the respective phase structures are lath and spherical, respectively.

[0169] The steel plate of the marine engineering low-cobalt high-low temperature impact energy ultrahigh-strength steel prepared in the embodiment has a thickness of 10 mm, a yield strength of 1221 MPa, a tensile strength of 1328 MPa, a yield strength ratio of 0.92, an elongation of 14.3%, a product of strength and plasticity of 18.9904 GPa%, and a V-notch low-temperature impact energy at -84 ℃ of 109 J.

[0170] Embodiment 6

[0171] The marine engineering low-cobalt high-low temperature impact energy ultrahigh-strength steel of the embodiment has a chemical composition by mass percentage of C 0.06%, Mn 0.65%, Ni 6.67%, Cr 0.91%, V 0.0423%, Nb 0.013%, Al 0.03%, Ti 0.008%, Mo 1.89%, Co 2.41%, Si 0.085%, P 0.0045%, S 0.0018%, and the rest of Fe and inevitable impurities.

[0172] A preparation method of a marine engineering low-cobalt high-low temperature impact energy ultrahigh-strength steel based on the embodiment, the preparation method of the marine engineering low-cobalt high-low temperature impact energy ultrahigh-strength steel comprising the following steps:

[0173] S1, smelting:

[0174] The raw materials are weighed according to the alloy chemical components of the marine engineering low-cobalt high-low temperature impact energy ultrahigh-strength steel, and then the raw materials are completely melted by a vacuum smelting heating mode of a vacuum smelting furnace to obtain a molten steel;

[0175] S2, adjusting O, Al and Ti:

[0176] After the molten steel in the vacuum smelting furnace of S1 is stable, the content of the molten steel is measured to reach 15 PPM; an Al-Ti composite wire is added, the diameter of the added Al-Ti composite wire is 5 mm, and the component content is Al-22 wt.% Ti; at the same time, argon is introduced into the bottom of the vacuum smelting furnace of S1 to form a flow field of the molten steel, the flow field is a shear flow field, so as to adjust the contents of O, Al and Ti in the molten steel.

[0177] S3, preparing an electroslag ingot:

[0178] The molten steel of S2 is heated and superheated by 30-45 DEG C, and then cast, the cooling rate of the casting ingot process is 70 DEG C / h, the flow line speed of the molten steel is 1.7 m / s, and the ingot is obtained after air cooling, the phase structure of the ingot is 1-5 μm ferrite + 2-5 μm bainite, and the shapes of the phase structures are needle-shaped and lath-shaped respectively, the phase structure of the electroslag ingot is 1-4.8 μm ferrite + 2-4.8 μm bainite, and the shapes of the phase structures are needle-shaped and lath-shaped respectively;

[0179] S4, multi-pass hot rolling:

[0180] The electroslag ingot of S3 is subjected to multi-pass hot rolling, the multi-pass hot rolling needs to be kept at 1260 DEG C for 2 h, the initial rolling temperature is 1150 DEG C, the total pass reduction is 91%, the final rolling temperature is 840 DEG C, and then the ingot is slowly cooled in the furnace to room temperature to obtain a hot-rolled steel plate;

[0181] S5, quenching + low-temperature tempering:

[0182] The hot-rolled steel plate of S4 is subjected to quenching treatment and low-temperature tempering treatment, the quenching treatment is that the hot-rolled steel plate is heated to 830±5 DEG C at a heating rate of 85 DEG C / min, kept for 0.35 h, and then taken out for water quenching treatment at a cooling rate of 75-100 DEG C / s, and the low-temperature tempering treatment is that the steel plate after the water quenching treatment is heated to 280±5 DEG C at a heating rate of 95 DEG C / min, kept for 1.75 h, and then taken out for air cooling at a cooling rate of 140 DEG C / h until room temperature, to obtain the low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering.

[0183] The low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering prepared in the embodiment has a steel plate thickness of 10 mm, an average grain size of 7.8 μm, and a phase structure of 0.3-0.59 μm martensite + 0.059-0.195 μm carbide, and the shapes of the phase structures are lath-shaped and spherical-shaped respectively.

[0184] The low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering prepared in the embodiment has a steel plate thickness of 10 mm, a yield strength of 1210 MPa, a tensile strength of 1306 MPa, a yield strength ratio of 0.92, an elongation of 14.21%, a strength-plasticity product of 18.55826 GPa·%, and a V-notch low-temperature impact energy at-84 DEG C of 112 J.

[0185] The above scheme provides a low-cobalt high-low-temperature impact energy ultrahigh-strength steel for ocean engineering and a preparation method thereof, overcomes the technical defects that the strength-plasticity and low-temperature impact performance of the current ocean engineering cannot be improved simultaneously, can improve the low-temperature impact performance on the basis of retaining high strength-plasticity, and further expands the processability and practicability, and is beneficial to industrial large-scale production and promotion.

[0186] In the present application, by combined and coordinated use of alloying elements such as Mo, Ni and Co, especially by increasing the content of Mo element and reducing the content of Co element, and by reducing the content of each alloying element, the low temperature impact energy of the material is improved and the raw material cost is reduced on the basis of ensuring high yield strength.

[0187] The present application feeds Al-(10-40)wt.%Ti composite wires by the method of feeding wires and stirring, to generate dispersedly distributed nano-phase Al2O3 and Ti3O5 in the matrix; and the nano-phase Al2O3 and Ti3O5 can serve as heterogeneous nucleation core, improve inclusions and refine grains.

[0188] The present application obtains an electroslag ingot by electroslag remelting of the ingot, and the electroslag remelting technology improves the metal purity of the steel, reduces the content of non-metallic inclusions, homogenizes and refines the structure, and obtains a clean, dense and uniform steel ingot.

[0189] The present application obtains a steel plate with fine matrix grains by multi-pass hot rolling of the electroslag ingot, which provides the energy required for recrystallization of the matrix to refine the grains.

[0190] The present application obtains a low-Co high low-temperature impact energy ultra-high strength steel for ocean engineering by quenching + low-temperature tempering, with the matrix structure being lath martensite and dispersedly distributed nano precipitates, the maximum yield strength of the steel plate being 1232MPa, the maximum tensile strength being 1328MPa, the yield strength ratio being 0.91-0.94, the maximum elongation being 14.5%, the maximum strength-plasticity product being 19.2GPa%, and the V-notch low-temperature impact energy at-84℃ being 138J.

[0191] The steel plate of the low-Co high low-temperature impact energy ultra-high strength steel for ocean engineering has a thickness of 8-20mm, an average grain size of 7-12μm, a phase structure of lath width 0.2-0.6μm martensite + 0.05-0.2μm nano-phase, and the shapes of the respective phase structures being lath and spherical.

[0192] The steel plate of the low-Co high low-temperature impact energy ultra-high strength steel for ocean engineering has a thickness of 8-20mm, a yield strength not less than 1200MPa, a tensile strength not less than 1300MPa, a yield strength ratio of 0.91-0.94, an elongation not less than 14%, a strength-plasticity product not less than 18.2GPa%, and a V-notch low-temperature impact energy at-84℃ not less than 100J.

[0193] In summary, compared with other conventional methods, the method of the present application efficiently and reasonably regulates the element content of the molten steel through the combined and coordinated use of alloying elements such as Mo, Ni, Co, and wire feeding stirring, and then obtains an electroslag ingot suitable for multi-pass hot rolling through ingot remelting, and finally obtains a marine steel with improved comprehensive strength, plasticity and low-temperature impact resistance through quenching + low-temperature tempering; the process steps are simple, easy to operate, the processing cycle is short, easy to control, and the obtained phase structure can well synergistically improve the strength, plasticity and low-temperature impact resistance.

[0194] The above describes the preferred embodiments of the present application. It should be noted that, for those skilled in the art, without departing from the principles of the present application, several improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A low-Cobalt high high-temperature impact energy super-high strength steel for ocean engineering, characterized by, The chemical composition of the low-cobalt high-temperature impact energy ultrahigh-strength steel for ocean engineering, by mass percent, is: C 0.05-0.07%, Mn 0.6-0.8%, Ni 6.5-7.0%, Cr 0.8-1.0%, V 0.04-0.05%, Nb 0.01-0.02%, Al 0.03-0.05%, Ti 0.008-0.010%, Mo 1.5-2.2%, Co 1.5-3.0%, Si≤0.1%, P≤0.01%, S≤0.002%, and the balance being Fe and unavoidable impurities; The steel plate of the low-cobalt high-temperature impact energy ultrahigh-strength steel for ocean engineering has a thickness of 8-20 mm, an average grain size of 7-12 μm, and a phase structure of lath width 0.2-0.6 μm of martensite + 0.05-0.2 μm of nanophase, and the shapes of the respective phase structures are lath and spherical. The steel plate of the low-cobalt high-temperature impact energy ultrahigh-strength steel for ocean engineering has a thickness of 8-20 mm, a yield strength of not less than 1200 MPa, a tensile strength of not less than 1300 MPa, a yield strength ratio of 0.91-0.94, an elongation of not less than 14%, a strength-plasticity product of not less than 18.2 GPa·%, and a V-notch low-temperature impact energy at -84℃ of not less than 100 J.

2. A method for preparing the low-C high HSIY ultra-high strength steel for ocean engineering according to claim 1, characterized in that, The preparation method of the low-cobalt high-temperature impact energy ultrahigh-strength steel for ocean engineering comprises the following steps: S1, melting: The raw materials are weighed according to the alloy chemical composition of the low-cobalt high-temperature impact energy ultrahigh-strength steel for ocean engineering, and then the raw materials are completely melted by a vacuum melting furnace to obtain a molten steel; S2, adjusting O, Al and Ti: After the molten steel in the vacuum melting furnace of S1 is stable, an Al-Ti composite wire is added, and argon is introduced into the bottom of the vacuum melting furnace of S1 to form a flow field in the molten steel, so as to adjust the contents of O, Al and Ti in the molten steel; S3, preparing an electroslag ingot: The molten steel of S2 is heated and superheated, and then cast to obtain a cast ingot, and the cast ingot is electroslag remelted to obtain an electroslag ingot; S4, multi-pass hot rolling: The electroslag ingot of S3 is subjected to multi-pass hot rolling, and then slowly cooled to room temperature in the furnace to obtain a hot-rolled steel plate; S5, quenching + low-temperature tempering: The hot-rolled steel plate of S4 is subjected to quenching and low-temperature tempering to obtain the low-cobalt high-temperature impact energy ultrahigh-strength steel for ocean engineering.

3. The method of producing a low-C high HSIU superhigh strength steel for ocean engineering according to claim 2, characterized in that, In S2, the content of the molten steel in the vacuum melting furnace is measured to be 5-30 PPM; the diameter of the Al-Ti composite wire is 3-5 mm, and the component content is Al-(10-40) wt.% Ti.

4. The method of producing a low-C high HSIU superhigh strength steel for ocean engineering according to claim 2, characterized in that, In S2, the flow field is a shear flow field.

5. The method of producing a low-C high HSIU superhigh strength steel for ocean engineering according to claim 2, characterized in that, In S3, the superheating temperature is 30-45℃; the phase structure of the cast ingot is 1-5 μm of ferrite + 2-5 μm of bainite, and the shapes of the respective phase structures are acicular and lath-shaped; the phase structure of the electroslag ingot is 1-4.8 μm of ferrite + 2-4.8 μm of bainite, and the shapes of the respective phase structures are acicular and lath-shaped.

6. The method of producing a low-C high HSIU superhigh strength steel for ocean engineering according to claim 2, characterized in that, The multi-pass hot rolling in S4 needs to be kept at 1230-1280℃ for 2h, the initial rolling temperature is 1130-1180℃, the total pass reduction is 80-95%, and the final rolling temperature is 800-850℃.

7. The method of producing a low-C high HSIU superhigh strength steel for ocean engineering according to claim 2, characterized in that, The quenching treatment in S5 is to heat the hot-rolled steel plate to 810-850℃, keep for 0.3-0.5h, and then take out for water quenching treatment; the low-temperature tempering treatment is to heat the steel plate after water quenching treatment to 240-280℃, keep for 1.5-3h, and then take out for air cooling to room temperature.

8. The method of producing a low-C high HSIU superhigh strength steel for ocean engineering according to claim 7, characterized in that, The heating rate of the quenching treatment in S5 is 75-85℃ / min, the cooling rate of the water quenching treatment is 75-100℃ / s; the heating rate of the low-temperature tempering treatment is 75-100℃ / min, and the cooling rate of the air cooling is 100-250℃ / h.

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