Corrosion resistant, pitting resistant 890mpa grade offshore steel and method of manufacture

Abstract

The present application relates to the technical field of corrosion-resistant and Bauschinger effect-resistant high-strength marine steel, in particular to a corrosion-resistant and Bauschinger effect-resistant 890MPa-grade marine steel and a manufacturing method thereof. The steel comprises the following chemical components by weight percentage: C: 0.08%-0.14%, Mn: 1.3%-1.8%, Ni: 1.0%-2.5%, Cr: 0.3%-0.8%, Mo: 0.3%-0.8%, and Cu: 0.2%-0.5%. The component design of C, Mn, Ni, Cr, Mo and Cu in combination with micro-alloy elements and special production processes such as electroslag remelting and forging are combined to maintain the mechanical properties of the EH890-grade high-strength steel, reduce the seawater corrosion resistance and marine atmospheric corrosion resistance, and significantly improve the Bauschinger effect resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of corrosion-resistant and Bauschinger effect-resistant high-strength offshore steel, in particular to a corrosion-resistant and Bauschinger effect-resistant 890MPa-grade offshore steel and a manufacturing method thereof. BACKGROUND

[0002] In the field of marine engineering equipment and shipbuilding, EH890-grade high-strength steel is widely used in key load-bearing structures such as offshore platforms, ship hulls and submarine pipelines due to its high strength, good weldability and toughness. However, the marine environment has characteristics such as high salt mist, high humidity and periodic dry-wet alternation, and the synergistic effect of chloride ion penetration, microbial attachment and wave impact can significantly accelerate material corrosion. The traditional EH890 offshore steel shows obvious insufficient corrosion resistance during long-term service, with a seawater immersion corrosion rate usually exceeding 0.3mm / a, and is more prone to local pitting and stress corrosion cracking in the splash zone and marine atmospheric environment, which seriously affects the structural life. In addition, due to the alternating load (such as wave impact, ship berthing, etc.) often borne by marine engineering structures, the EH890 steel is prone to Bauschinger effect after plastic deformation, resulting in a significant decrease in yield strength (decrease of more than 15% at a residual strain of 2%) during reverse loading, which reduces the load stability of the structure and increases the safety hazard.

[0003] A kind of seawater corrosion-resistant and fatigue-resistant ultra-high strength steel plate is disclosed in Chinese patent CN108624809B, which adopts a composition system of low C, low Mn and high Ni, Cr, although the impact toughness and corrosion resistance of the steel plate are improved, but the production process is still the conventional smelting, rolling and heat treatment process, and the low temperature toughness and Bauschinger effect resistance of the steel plate cannot meet the long life and high reliability requirements in extreme marine environments. Chinese patent CN108707822B discloses a high-strength steel with a fatigue stress amplitude of ≥400MPa and a production method, which adopts a high-C, low-Ni and Cr alloy system, although the steel plate has excellent fatigue performance, but the composition and process can only produce thin-gauge fatigue-resistant steel plates, and there is no composition and process design for corrosion resistance and Bauschinger effect resistance. SUMMARY

[0004] To overcome the shortcomings of the prior art, the present application provides a corrosion-resistant and Bauschinger effect-resistant 890MPa-grade offshore steel, which reduces the seawater corrosion rate to less than 40% of that of conventional materials, the marine atmospheric corrosion rate to less than 50%, and significantly improves the Bauschinger effect resistance (yield strength reduction at 2% residual strain ≤10%), meeting the long life and high reliability requirements in extreme marine environments.

[0005] To achieve the above object, the present application adopts the following technical solutions:

[0006] A kind of corrosion-resistant anti-bauschinger effect very high strength offshore steel, consisting of the following weight percentage of chemical components:

[0007] C: 0.08%~0.14%, Si: 0.15%~0.35%, Mn: 1.3%~1.8%, P≤0.02%, S≤0.01%, Ni: 1.0%~2.5%, Cr: 0.3%~0.8%, Mo: 0.3%~0.8%, Cu: 0.2%~0.5%, Co: 0.05%~0.15%, Sn: 0.05%~0.2%, Nb: 0.04%~0.09%, V: 0.04%~0.09%, Ti: 0.01%~0.015%, B: 0.0005%~0.001%, the rest is Fe and inevitable impurities.

[0008] The role of selecting the above alloy element type and its content:

[0009] 1, C in steel is mainly to form solid solution organization, improve the strength of steel, and form carbide organization, which can improve the hardness and stiffness of steel, and the steel plate is not easy to plastic deformation under external force, which can reduce the bauschinger effect of the steel plate to a certain extent, but too much C element is added in the steel, the corrosion resistance of the steel plate is reduced, so the content of C element should be accurately controlled. Therefore, the content of C is accurately controlled to 0.08%~0.14% in the present application.

[0010] 2, Si can improve the strength of the steel plate, and Si as a deoxidizer can reduce the content of O, Si can form a dense and stable oxide film to improve the corrosion resistance, and the low temperature toughness of the steel plate is reduced when the content of Si is too high. Therefore, the content of Si is accurately controlled to 0.15%~0.35% in the present application.

[0011] 3, Mn element is similar to Fe atomic radius, which can be dissolved in Fe matrix in large amount to improve the strength of the steel plate. Mn can refine the grain structure of the steel plate, increase the number of grain boundaries and improve the low temperature impact toughness of the steel plate. When the content of Mn element is too high, the hardening effect of Mn element will reduce the low temperature toughness of the core of thick plate. In the present application, the alloy strength is high, which is easy to cause segregation in the core of the blank, and the problem of uneven composition and structure in the core of the blank can be solved by combining with electroslag remelting+forging process, and the content of Mn element can be appropriately increased. Therefore, the content of Mn is accurately controlled to 1.3%~1.8% in the present application.

[0012] 4, P and S elements have no benefit to the mechanical properties of the steel plate, especially the elongation, and P≤0.02% and S≤0.01% should be controlled.

[0013] 5. Ni plays a particularly significant role in steel plates. Ni can significantly improve the toughness and corrosion resistance of steel plates. Its addition not only lowers the ductile transition temperature but also works synergistically with microalloying elements such as V to further enhance the strength, toughness, and corrosion resistance of the steel plate. Ni itself possesses excellent corrosion resistance, performing exceptionally well in acidic marine environments. Furthermore, when Ni is used in combination with other elements (such as Cr and Mo), it can effectively improve the hot strength and corrosion resistance of steel. Therefore, this invention precisely controls the Ni content to 1.0%~2.5%.

[0014] 6. The corrosion resistance of Cr in steel is mainly manifested in its ability to form a dense passivation film, significantly improving the corrosion resistance of steel. Combined with elements such as Ni, Co, and Sn, excellent resistance to marine corrosion can be achieved even at low Cr contents. Cr can also effectively increase the strength of steel plates; however, excessively high Cr content will produce a large amount of Cr carbides, reducing the impact toughness of the steel plate and causing temper brittleness after quenching and tempering. Therefore, this invention precisely controls the Cr content to 0.3%~0.8%.

[0015] 7. Mo can enhance corrosion resistance in reducing media, especially resistance to chloride ion corrosion and pitting corrosion, effectively preventing pitting corrosion caused by chloride ions. Mo can combine with carbides, reducing Cr precipitation and thus improving the corrosion resistance of steel plates. Mo can also improve the hardenability of steel plates, and at the same time, Mo can form fine carbides in steel, which can effectively improve the strength of steel plates. Therefore, this invention precisely controls the Mo content at 0.3%~0.8%.

[0016] 8. Cu, along with Cr and P in steel, works synergistically to inhibit pitting and uniform corrosion in steel within saline and humid environments, extending its service life. Cu also helps resist biofouling. However, excessive Cu content can cause Cu brittleness in the billet at high temperatures. Therefore, this invention precisely controls the Cu content to 0.2%~0.5%.

[0017] 9. Co can improve the strength and stiffness of steel plates and enhance their resistance to the Boushinger effect; however, excessive Co addition will reduce the low-temperature toughness of the steel plate. Co also possesses certain antioxidant properties, and when combined with alloying elements such as Ni and Cr, it can further improve the corrosion resistance of the steel plate. Therefore, this invention precisely controls the Co content to 0.05%~0.15%.

[0018] 10. Sn can synergistically work with Ni and Cr in steel to effectively inhibit intergranular corrosion. Sn can form a dense oxide film, which can significantly hinder the transport of corrosive ions. In a chloride ion environment, Sn can accumulate in the rust layer, greatly improving the corrosion resistance of the steel plate. Therefore, this invention precisely controls the Sn content to 0.05%~0.2%.

[0019] 11. Nitrogen (Nb) is an important additive element that increases the strength and high-temperature thermal stability of steel plates. It effectively lowers the transformation temperature from austenite to bainite, reducing the risk of stress corrosion cracking. Simultaneously, it combines with nitrogen (CN) to lower the diffusion thresholds of carbon (C) and nitrogen (N), preventing C and N enrichment at grain boundaries, thereby improving the corrosion resistance of the steel. Furthermore, Nb can synergistically work with elements such as chromium (Cr) and molybdenum (Mo) to further enhance the corrosion resistance of the steel and its ability to resist corrosion in acidic marine environments. Therefore, this invention precisely controls the Nb content to be between 0.04% and 0.09%.

[0020] 12. V is an important alloying element in the steel plate of this invention. V can refine the grain structure and improve the strength and toughness of the steel plate. V, together with C and N, forms V(C,N) particles in the matrix, which can also refine the grains. Adding V to tempered steel plates can significantly improve the core strength and low-temperature toughness of the steel plate. The combination of V and C can prevent C from accumulating around the grain boundaries and improve the steel plate's resistance to intergranular corrosion. Therefore, the V content in this invention is precisely controlled at 0.04%~0.09%.

[0021] 13. Ti can form TiCN with C and N, exhibiting extremely high stability at high temperatures, effectively preventing steel grain growth and thus refining the grain size. Therefore, this invention precisely controls the Ti content to 0.01%~0.015%.

[0022] 14. When boron (B) dissolves in a solid solution, the crystal lattice becomes larger, increasing strength. B inhibits recrystallization diffusion at grain boundaries, increasing the hot strength of steel. B-containing steel exhibits excellent comprehensive mechanical properties after quenching and tempering, including tempering stability, fatigue limit, and hardness. Simultaneously, B can synergistically enhance the corrosion resistance and thermal stability of steel with other alloying elements. Therefore, this invention precisely controls the B content to 0.0005%~0.001%.

[0023] The above-mentioned corrosion-resistant and anti-Bauschinger effect 890MPa grade marine steel has a yield strength of ≥890MPa, a tensile strength of 950-1080MPa, a transverse elongation of ≥16%, and a Charpy impact energy of ≥150J at the core of the steel plate at -40℃. The steel plate has a seawater corrosion resistance rate of less than 40% of the conventional EH890 marine steel performance, and a marine atmospheric corrosion resistance rate of less than 50% of the conventional EH890 marine steel performance. The yield strength of the steel plate at 2% residual strain is reduced by ≤10%, the anti-Bauschinger effect is excellent, the uniform elongation is ≥6%, and the maximum thickness of the finished steel plate is 50mm.

[0024] The microstructure at 1 / 2 of the thickness of the steel plate is tempered martensite + residual austenite (3%-8%). The dislocation density is ≥10 10 / cm 2 The proportion of high-angle grain boundaries is ≥55%, the effective grain size is 2-7μm, and the mechanical properties are good.

[0025] The above-mentioned corrosion-resistant and anti-Bauschinger effect 890MPa grade marine steel is manufactured by a high-purity and alloying smelting + electroslag remelting + forging breakdown + high-efficiency rolling + quenching + tempering process, which specifically includes the following steps:

[0026] 1. Molten steel refining:

[0027] The molten steel is refined by a converter, an LF furnace, an RH or VD furnace, to further reduce the contents of P, S and non-metallic inclusions.

[0028] 2. Electroslag remelting:

[0029] The electroslag remelting adopts a ternary slag system, the slag melting time is 60-100min, argon gas is opened 30-45min in advance, the whole process is protected by an atmosphere, the argon gas flow is 30-60m 3 / h, the crystallizer cooling water flow is 10-35m 3 / h, the crystallizer cooling rate is 0.3-0.8℃ / min, the feeding time is 3-5h, and the electroslag ingot demolding slow cooling is ≥72h.

[0030] The electroslag remelting process uses protective slag, argon protection, control of crystallizer water volume and cooling rate, etc. to precisely adjust the alloy composition, effectively inhibit the invasion of harmful gases and reduce alloy oxidation, so as to realize the optimization of the uniformity of the alloy internal composition. The composition and form of the protective slag can reduce segregation during the melting process and improve the steel plate resistance to Bauschinger effect; argon protection helps to control the oxygen content and improve corrosion resistance; argon and crystallizer cooling rate control can further inhibit the oxidation of impurities and gases in the alloy, effectively reduce the alloy potential difference, and improve the corrosion resistance of the steel plate. These comprehensive measures not only significantly improve the alloy corrosion resistance and anti-Bauschinger effect, but also significantly improve the mechanical properties of the core of the steel plate.

[0031] 3. Forging:

[0032] Forging heating temperature is 1250~1300℃, heating time is 6~10h, forging billet is upset in three directions, minimum upset amount in each direction is ≥60mm, thickness direction deformation rate is 30%~50%, forging ingot grinding amount is ≥20mm, and forging ingot equiaxed crystal ratio is ≥70%.

[0033] Forging processes significantly improve the homogenization and core mechanical properties of steel plates by controlling temperature, optimizing upsetting direction and upsetting amount, and reducing problems such as segregation and shrinkage cavities. Optimizing the forging reduction amount homogenizes the equiaxed grain structure, improving strength and toughness; slow cooling treatment reduces internal stress and refines grains, further improving mechanical properties.

[0034] 4. Rolling:

[0035] The billet is loaded into the heating furnace at a temperature of 400-700℃, held at low temperature for 1-2 hours, and heated at a rate of 2-7℃ / min. The aim is to maintain a uniform temperature along the thickness of the billet during the low-temperature stage, preparing for a homogeneous microstructure in the high-temperature stage. The heating temperature is 1300-1350℃, and the holding time is 1-3 hours. The initial rolling temperature is 1200-1330℃, the average reduction per pass is 6%-12%, and the final rolling temperature is 900-1150℃. Under the high pressure at high temperature, the steel plate deforms more uniformly, reducing inhomogeneities in the microstructure and thus improving the density and consistency of the material. High-temperature, high-reduction rolling effectively improves the tensile strength and yield strength of the material; and through high-temperature rolling and post-rolling recrystallization, local stress concentration can be reduced, improving the steel plate's resistance to the Baosinger effect. With reasonable control of process parameters, high-temperature, high-reduction rolling can complete large-scale batch production in a shorter time, improving efficiency.

[0036] 5. Quenching and tempering:

[0037] The quenching temperature is 750~900℃, the quenching holding time is 1~1.6min / mm, the cooling rate of the quenched steel plate is 2~6℃ / s, the tempering temperature is 400~700℃, and the tempering holding time is 3~4.5min / mm.

[0038] The purpose of quenching is to refine the rolled microstructure, prepare the microstructure for tempering, further improve the grain size of the tempered microstructure, and enhance the low-temperature toughness of the steel plate core.

[0039] Increasing the tempering temperature and tempering holding time can refine and redistribute fine precipitates while ensuring the strength of the steel plate, thereby maximizing the low-temperature toughness and corrosion resistance of the steel plate. Increased strength and stiffness of the steel plate can effectively prevent plastic deformation. By utilizing fine-grain strengthening and optimized precipitation strengthening, dislocation back pile-up during plastic deformation can be reduced, thus improving the steel plate's resistance to the Bauschinger effect.

[0040] Compared with the prior art, the present application has the following advantages:

[0041] 1、The present application utilizes the effects of Co and Sn alloy in resisting the Bauschinger effect and corrosion resistance, adds Co element to improve the strength and stiffness of the steel plate, improves the steel plate resistance to the Bauschinger effect, cooperates with alloy elements such as Ni and Cr, and further improves the corrosion resistance of the steel plate. Sn element cooperates with Ni and Cr elements in the steel to effectively inhibit intergranular corrosion in the steel; Sn element can form a dense oxide film, which can significantly hinder the transmission of corrosive ions; Sn can be enriched in the rust layer in a chloride ion environment, greatly improving the corrosion resistance of the steel plate.

[0042] 2、The electroslag remelting process of the present application improves the alloy corrosion resistance, resistance to the Bauschinger effect, and improves the core mechanical properties of the steel plate through optimization of alloy composition control and gas environment control. By means of protective slag, argon protection, control of crystallizer water volume cooling rate, etc., the alloy composition is precisely adjusted, the invasion of harmful gas is effectively inhibited, and the alloy oxidation is reduced, so as to realize the optimization of the uniformity of the alloy internal composition. These comprehensive measures not only significantly improve the alloy corrosion resistance, resistance to the Bauschinger effect, but also significantly improve the mechanical properties of the core of the steel plate.

[0043] 3、The forging process of the present application significantly improves the uniformity and core mechanical properties of the steel plate by controlling the temperature, optimizing the upsetting direction and upsetting amount, etc. to reduce segregation and shrinkage, etc. By optimizing the forging reduction amount, the equiaxed grain structure is homogenized, the strength and toughness are improved; the stacking slow cooling treatment reduces the internal stress and refines the grains, further improving the mechanical properties.

[0044] 4、The steel plate of the present application deforms more uniformly under the action of large pressure in the high temperature stage of the rolling process, reducing the non-uniformity in the microstructure, thereby improving the density and consistency of the material. The high temperature large reduction rolling process can effectively improve the tensile strength and yield strength of the material; and through high temperature rolling and recrystallization process after rolling, local stress concentration can be reduced, and the steel plate resistance to the Bauschinger effect can be improved. Through reasonable process parameter control, the high temperature large reduction rolling process can complete large-scale batch production in a relatively short time, improving the efficiency.

[0045] 5、The purpose of quenching in the present application is to refine the as-rolled structure and prepare for tempering, further improve the grain size of the tempered structure, and improve the low temperature toughness of the core of the steel plate. The increase of tempering temperature and tempering time can not only ensure the strength of the steel plate, but also refine and redistribute the fine precipitates, thereby maximizing the low temperature toughness and corrosion resistance of the steel plate. The improvement of the strength and stiffness of the steel plate can effectively prevent plastic deformation of the steel plate, and the use of fine grain strengthening and optimized precipitation strengthening can reduce the reverse pile-up of dislocations during plastic deformation, thereby improving the resistance to the Bauschinger effect of the steel plate.

[0046] In summary, the present application combines the component design of C, Mn, Ni, Cr, Mo, Cu and micro-alloying elements such as Co, Sn, Nb, V and the like with special production processes such as electroslag remelting, forging and the like to produce a maximum thickness of 50 mm offshore steel. The yield strength of the steel plate is ≥ 890 MPa, the tensile strength is 950-1080 MPa, the elongation is ≥ 16%, and the Charpy impact energy at the core of the steel plate is ≥ 150 J at -40 ℃. The seawater corrosion resistance of the steel plate is 40% or less than that of the conventional EH890 offshore steel, and the marine atmospheric corrosion resistance is 50% or less than that of the conventional EH890 offshore steel. The yield strength of the steel plate is reduced by ≤ 10% at 2% residual strain, the anti-Bauschinger effect is excellent, and the uniform elongation is ≥ 6%. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is a metallographic structure diagram of Example 1 of the present application. DETAILED DESCRIPTION

[0048] The present application discloses a kind of 890MPa grade offshore steel of corrosion resistance and anti-Bauschinger effect and manufacturing method thereof. Those skilled in the art can improve process parameters appropriately to realize by referring to the content herein. It is particularly pointed out that all similar substitutions and changes are obvious to those skilled in the art, and they are all regarded as including in the present application. The method and application of the present application have been described by preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application described herein without departing from the content, spirit and scope of the present application, to realize and apply the present application technology.

[0049] The chemical composition of the steel of the embodiment of the present application is shown in Table 1, the electroslag remelting and forging process of the embodiment of the present application is shown in Table 2, the rolling process of the embodiment of the present application is shown in Table 3, the quenching and tempering process of the embodiment of the present application is shown in Table 4, the mechanical properties of the steel plate of the embodiment of the present application are shown in Table 5, and the marine environment corrosion resistance of the embodiment of the present application and the comparative example is shown in Table 6.

[0050] Table 1 Chemical composition of steel of the embodiment of the present application (wt%)

[0051]

[0052] Table 2 Electroslag remelting and forging process of the embodiment of the present application

[0053]

[0054] Table 3 Rolling process of the embodiment of the present application

[0055]

[0056] Table 4 Quenching and tempering process of the embodiment of the present application

[0057]

[0058] Table 5 Mechanical properties of steel plates in embodiments of the present invention

[0059]

[0060] Table 6. Resistance to marine corrosion in the embodiments and comparative examples of the present invention

[0061]

[0062] The full immersion test reference standard is JBT7901, and the salt spray test reference standard is GBT10125. The comparison steel composition is 0.014C~0.2Si~1.40Mn~1.0Ni~0.4Cr~0.4Mo~0.04Nb~0.04V~0.01Ti.

[0063] like Figure 1 As shown, the metallographic structure of Example 1, at half the thickness of the steel plate, consists of tempered martensite + retained austenite (3%~8%). Dislocation density ≥102 10 / cm 2 It has a high-angle grain boundary ratio of ≥55%, an effective grain size of 2~7μm, and good mechanical properties.

[0064] As shown in Table 5, the maximum thickness of the finished steel plate of this invention is 50mm, with a yield strength ≥890MPa, tensile strength 950~1080MPa, elongation ≥16%, and Charpy impact energy of the steel plate core at -40℃ ≥150J. At 2% residual strain, the yield strength decreases by ≤10%, exhibiting excellent resistance to the Bauschinger effect and a uniform elongation ≥6%. As shown in Table 6, the seawater corrosion resistance rate of the steel plate is less than 40% of that of conventional EH890 marine engineering steel, and the marine atmospheric corrosion resistance rate is less than 50% of that of conventional EH890 marine engineering steel. This invention, while maintaining the mechanical properties of EH890 grade high-strength steel, reduces the seawater corrosion resistance rate to less than 40% of conventional materials and the marine atmospheric corrosion resistance rate to less than 50%, and significantly improves the resistance to the Bauschinger effect (yield strength reduction ≤10% at 2% residual strain), meeting the requirements for long service life and high reliability in extreme marine environments.

[0065] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method of manufacturing a corrosion resistant, pitting resistant 890 MPa grade offshore steel, characterized in that, The corrosion-resistant and Bauschinger effect-resistant 890 MPa grade offshore steel is composed of the following chemical components by weight percentage C: 0.08%~0.14%, Si: 0.15%~0.35%, Mn: 1.3%~1.8%, P≤0.02%, S≤0.01%, Ni: 1.0%~2.5%, Cr: 0.3%~0.8%, Mo: 0.3%~0.8%, Cu: 0.2%~0.5%, Co: 0.05%~0.15%, Sn: 0.05%~0.2%, Nb: 0.04%~0.09%, V: 0.04%~0.09%, Ti: 0.01%~0.015%, B: 0.0005%~0.001%, and the rest is Fe and inevitable impurities; The manufacturing method specifically comprises the following steps: 1) steel refining; 2) electroslag remelting: 3) forging: Electroslag remelting adopts ternary slag system, slagging time is 60~100 min, whole process is protected by atmosphere, crystallizer cooling water volume is 10~35 m 3 / h, crystallizer cooling rate is 0.3~0.8℃ / min; The forging heating temperature is 1250~1300℃, and the heating time is 6~10h; The forging is open-die upset in three directions, and the minimum upsetting amount in each direction is ≥60mm, and the thickness direction deformation rate is controlled to be 30%~50%; 4) rolling: The open-rolling temperature is 1200~1330℃, the average pass reduction rate is 6%~12%, and the finish rolling temperature is 900~1150℃; 5) quenching and tempering: The quenching temperature is 750~900℃, the quenching holding time is 1~1.6min / mm, the tempering temperature is 400~700℃, the tempering holding time is 3~4.5min / mm, and the quenching steel plate cooling rate is 2~6℃ / s.

2. The manufacturing method of the corrosion-resistant and Bauschinger effect-resistant 890 MPa grade offshore steel according to claim 1, characterized in that The maximum thickness of the steel plate finished product is 50mm, the yield strength is ≥890MPa, the tensile strength is 950~1080MPa, the transverse elongation rate is ≥16%, the Charpy impact energy of the steel plate core at -40℃ is ≥150J, the yield strength reduction at 2% residual strain is ≤10%, and the uniform elongation rate is ≥6%.

3. The manufacturing method of the corrosion-resistant and Bauschinger effect-resistant 890 MPa grade offshore steel according to claim 1, characterized in that 4. The manufacturing method of the corrosion-resistant and Bauschinger effect-resistant 890 MPa grade offshore steel according to claim 1, characterized in that The structure at the thickness of 1 / 2 of the steel plate is tempered martensite + residual austenite, the residual austenite is 3% to 8%, and the dislocation density is greater than or equal to 10 10 / cm 2 The proportion of large-angle grain boundaries is greater than or equal to 55%, and the effective grain size is 2 to 7 microns. 1) the molten steel is refined by a converter, an LF furnace, an RH or a VD furnace.

5. The manufacturing method of the corrosion-resistant and Bauschinger effect-resistant 890 MPa grade offshore steel according to claim 1, characterized in that 6. The manufacturing method of the corrosion-resistant and Bauschinger effect-resistant 890 MPa grade offshore steel according to claim 1, characterized in that 2) In the middle, open argon 30~45min in advance, argon flow 30~60m 3 / h; feeding time 3~5h, ESR ingot demoulding slow cooling ≥72h. 3) the forging ingot grinding amount is ≥20mm, and the forging ingot equiaxed crystal ratio is ≥70%.

7. The manufacturing method of the corrosion-resistant and Bauschinger effect-resistant 890 MPa grade offshore steel according to claim 1, characterized in that 4) the cast blank is loaded into a heating furnace at a furnace temperature of 400~700℃ and is kept for 1~2h; ​ The heating temperature is 1300-1350℃, the heating rate is controlled at 2-7℃ / min, and the holding time is 1-3h.

Images