High-performance corrosion-resistant marine steel and production method thereof

Abstract

The application discloses a high-performance corrosion-resistant marine steel and a production method thereof. The chemical composition of the steel is as follows: C: 0.02%-0.07%, Si: 0.10%-0.25%, Mn: 1.75%-2.50%, P: 0.022%-0.026%, S: ≤0.008%, Nb: 0.055%-0.060%, Als: 0.035%-0.045%, Cr: 0.90%-1.00%, Ni: 0.90%-1.00%, Co: 0.20%-0.25%, N: 0.0130%-0.0140%, V: 0.06%-0.065%, Ti: 0.035%-0.042%, Cu: 0.45%-0.52%, Sn: 0.03%-0.05% and RE: 0.03%-0.05%. After smelting, slab continuous casting, casting blank heating, rolling and cooling, the steel has the following properties: Rp0.2 is 550-582 MPa, A is greater than or equal to 20%, impact energy at-80 DEG C is greater than or equal to 200 J, corrosion resistance is less than 0.090 mm / a, fatigue life under peak stress 280 MPa load is greater than 2 million times, the maximum thickness can reach 150 mm, and Z-direction performance is greater than or equal to 40%. The application solves the problems of low strength, poor low-temperature impact toughness, insufficient corrosion resistance and insufficient fatigue resistance of the existing marine engineering steel plate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal material preparation, and particularly relates to a high-performance corrosion-resistant marine steel and a production method thereof. BACKGROUND

[0002] Marine equipment manufacturing steel is subjected to complex marine waves, temperature, humidity, salinity and other complex environments, and higher requirements are put forward for the performance of the steel, especially the corrosion and fatigue performance. For example, the steel should have high strength, large thickness, low-temperature impact toughness, good Z-direction performance, and also good corrosion resistance and fatigue resistance. The existing steel is difficult to meet the above performance requirements at the same time.

[0003] Patent No. 201510314696.X discloses a low yield ratio weather-resistant wind power tower steel and a production method. The steel plate has a yield strength of ≥420 MPa, a tensile strength of 640-850 MPa, an elongation A of ≥25%, a yield ratio of ≤0.64, a corrosion resistance performance index I of not less than 6.44, a KV2 of ≥200 J at -50℃, and a KV2 of ≥185 J at -60℃. However, it fails to provide data for producing thick steel plates, and has no evaluation of aging performance, corrosion resistance and fatigue resistance, which is not suitable for the needs of marine engineering equipment steel plates.

[0004] Patent No. 202010557893.5 discloses a 550 MPa grade weather-resistant steel plate with excellent weldability and a manufacturing method thereof. The TMCP process is optimized, the yield strength is ≥460 MPa, the tensile strength is ≥570 MPa, the Charpy impact energy at -40℃ (single value) is ≥120 J, the impact toughness KV2 at -40℃ is ≥100 J, and the weld heat affected zone (HAZ) has an Akv at -40℃ of ≥100 J. However, the strength is relatively low, the low-temperature toughness is only at -40℃, and the corrosion resistance and fatigue resistance are not solved.

[0005] Patent No. 201410036368.3 discloses a corrosion-resistant steel plate for resisting South China Sea marine environment and a production process thereof. The production process includes converter smelting process, LF refining process, vacuum degassing process, continuous casting process, controlled rolling and controlled cooling process, etc. The microstructure type of the steel plate is theoretically single-phase polygonal ferrite fine structure (average grain size 10.17 μm), and inevitably contains a small amount of pearlite structure in industrial actual production. Compared with conventional ship structure steel EH36, the corrosion resistance of the steel plate in marine environment (marine atmosphere, tidal range, full immersion, etc.) is improved by more than 50%, and the steel plate has good strength-toughness matching and welding performance. However, the strength is relatively low, the low-temperature toughness is insufficient, and the fatigue resistance is not evaluated.

[0006] The patent with the application number 201910712227.1 discloses a yield strength 345 MPa grade high fatigue structural steel and a manufacturing method thereof. The chemical composition of the steel is: C 0.13%~0.16%, Mn 1.30%~1.60%, Nb 0.020%~0.050%, Alt 0.020%~0.030%, Ti≤0.010%, Si≤0.12%, P≤0.010%, S≤0.005%, and the balance is iron and inevitable impurities. By adopting large reduction + controlled cooling process, the obtained steel plate has good comprehensive mechanical properties and better surface quality. However, the strength of the steel plate is low, and its corrosion resistance is not evaluated, only the impact toughness at-20℃ is evaluated, which cannot meet the use requirements in different marine environments.

[0007] The patent with the application number 202110068169.0 discloses an engineering anti-corrosion fatigue steel and a preparation method thereof. The steel is based on the main elements of E690 steel (C 0.04%~0.07%, Si 0.20%~0.26%, Mn 1.45%~1.60%, P≤0.01%, S≤0.015%, Cr 0.44%~0.50%), and the elements are controlled and characteristic elements are added, Cu 0.28%~0.66%, Ni 0.76%~1.55%, Sb 0.03%~0.12%, and the rest is Fe and inevitable impurities. The corrosion fatigue strength is improved by up to 52%, but the low temperature toughness of the steel is not evaluated. SUMMARY

[0008] In view of the deficiencies of the prior art, the purpose of the present application is to provide a high-performance corrosion-resistant marine steel and a production method thereof. The basic characteristics are low carbon and low alloying, and the steel plate is compounded with Cr, Ni, Co and other multi-alloy strengthening elements and V, N precipitation strengthening elements, and P, Al and Sn, RE are added as the basic characteristics to improve the strength, low temperature toughness and corrosion resistance and fatigue resistance of the steel plate. The problems of low strength, poor low temperature impact toughness, insufficient corrosion resistance and fatigue resistance of the existing marine engineering steel plate are solved.

[0009] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0010] The present application takes a steel plate with excellent low-temperature toughness, high strength and corrosion resistance as basic features. In the present application, the content of the chemical components of the steel plate is as follows: C: 0.02% to 0.07%, Si: 0.10% to 0.25%, Mn: 1.75% to 2.50%, P: 0.022% to 0.026%, S: ≤0.008%, Nb: 0.055% to 0.060%, Als: 0.035% to 0.045%, Cr: 0.90% to 1.00%, Ni: 0.90% to 1.00%, Co: 0.20% to 0.25%, N: 0.0130% to 0.0140%, V: 0.06% to 0.065%, Ti: 0.035% to 0.042%, Cu: 0.45% to 0.52%, Sn: 0.03% to 0.05%, RE: 0.03% to 0.05%, wherein 0.09 ≥ (Nb+V+Ti) / Mn ≥ 0.06, 7 ≥ Si / Al ≥ 2, (Cu+P+Co) / Cr ≥ 0.7, 5.0 ≥ Cr / Co ≥ 3.5, Ni / Cr ≥ 0.9, (Nb+V+Ti+Als) / N ≥ 14, Ni / Cu ≥ 1.7, 36Nb / Mn ≥ 0.80, (Nb+V+Ti) / RE ≥ 3.0, RE / P ≥ 1.2; and the rest is Fe and inevitable impurities.

[0011] The above alloying elements and their contents are selected because of their roles in the steel plate with excellent low-temperature toughness, high strength, corrosion resistance and good fatigue resistance.

[0012] C: C and Cr can form alloy cementite (Fe·Cr)3C, and can also form carbides such as Cr7C3, Cr 23 C6, etc. The melting point, hardness, wear resistance and stability of these carbides are higher than those of Fe3C, which can improve the strength of the steel. C and strong carbide forming elements such as V, Nb and Ti can form carbides such as VC, NbC and TiC, which have the highest stability and the highest melting point, hardness and wear resistance. Therefore, C is the most effective element for improving the strength of the steel plate, and when its content is lower than 0.02%, the strength of the steel plate will be greatly reduced. However, C has a great influence on the low-temperature toughness, elongation and weldability of the steel. From the perspective of improving the toughness, corrosion resistance, fatigue resistance and weldability of the steel, the content of C in the steel should be appropriately low. Therefore, the content of C in the present application is selected to be 0.02% to 0.07%.

[0013] Si: Si is necessary for steelmaking deoxidation, has a certain solid solution strengthening effect, although Si can improve the strength of the steel plate, but Si reduces the critical cooling rate of martensite transformation, seriously damages the low temperature toughness, elongation and weldability of ultra-high strength steel plate, Si not only promotes the formation of M-A island, but also the size of the formed M-A island is relatively large and unevenly distributed, which seriously damages the toughness of the welding heat affected zone (HAZ), therefore the Si content in the steel should be controlled as low as possible. A certain amount of Si can effectively improve the resistance of steel to marine corrosion, and the combined addition of Si and Al can improve the corrosion resistance and high temperature oxidation resistance. The content of Si in the application is controlled at 0.10% to 0.25%, and 7≥Si / Al≥2.

[0014] Mn: Mn is the main element to improve strength and toughness, can significantly improve the hardenability of steel, and is very low in cost, which is the main additive element in steel. When the C content is low, a higher Mn content can effectively improve the hardenability of the steel, and improve the strength of the steel plate through microstructure refinement and promoting bainite transformation, while having excellent low temperature toughness; Mn expands the austenite region, promotes grain growth, and needs to be combined with the composite addition of grain refining elements Nb, V and Ti to promote grain refinement and improve the fatigue performance of the steel; but Mn is easy to segregate during the solidification of molten steel, which aggravates the segregation and porosity in the center of the casting blank, resulting in low toughness of the ultra-high strength steel plate at low temperature and cracks in the welded joint, which needs to be improved by optimizing the continuous casting process and heating process. The content of Mn in the application is selected at 1.75% to 2.50%, and 0.09≥(Nb+V+Ti) / Mn≥0.06.

[0015] P: P has strong solid solution strengthening effect in steel, as an alloying element added to low alloy structural steel, it can improve the strength and corrosion resistance of the steel. When its content is greater than or equal to 0.02%, it can significantly improve the corrosion resistance. But when its content is too large, it will have an adverse effect on the low temperature toughness of the base material and the toughness of the welding heat affected zone, so its content should be controlled in a reasonable range as much as possible. The content of P in the application is controlled at 0.022% to 0.026%.

[0016] S: S is severely segregated in steel, which deteriorates the quality of the steel. S is an inclusion forming element, which forms FeS, MnS and other inclusions, thereby reducing the ductility of the steel, and the inclusions will become the source of corrosion, which is not conducive to the corrosion resistance of the steel plate. And FeS is easy to melt at the grain boundary due to its low melting point, which weakens the bonding force between the grains, resulting in the thermal brittleness of the steel, therefore a certain amount of Mn element should be added, which can form MnS with high melting point and deformation ability. Therefore, the content of S in the application is controlled at less than or equal to 0.008%.

[0017] Co: Co mainly plays a solid solution strengthening role in the steel, improves the oxidation resistance and the ability of corrosion resistance of the steel, Co can increase the interaction between Fe atoms, reduces the critical concentration of Cr atoms forming clusters, and further improves the stability of Cr atom clusters, when Co and Cr atoms act on the steel at the same time, the surface forms a smooth passivation film with high structural stability, which can well protect the matrix, thus has excellent corrosion resistance. Co promotes precipitation hardening by promoting more (Ti, Al) Ni3 nucleation sites, improves strength and toughness, the addition of Co has little effect on the precipitation ratio of Ni and Ti, but can reduce the size of the precipitated phase, Co increases the nucleation rate of Ni3Ti, and increases the number density of precipitated phase, that is, Co can make the distribution of precipitated phase more dispersed, improve the fatigue resistance of the steel, and enhance the precipitation strengthening effect of precipitated phase. Therefore, the content of the present application is controlled at 0.20% to 0.25%, and 5≥Cr / Co≥3.5.

[0018] Cr: Cr can improve the strength and hardness of the steel. Cr is a ferrite forming element, which helps to increase the ferrite content in the steel and thus improve the low temperature toughness of the steel. Cr is an element that improves the corrosion resistance of the steel, but adding Cr alone sometimes reduces the corrosion resistance, even worse than that of ordinary carbon steel, and needs to be used in combination with other corrosion-resistant alloy elements such as Cu, P, Co, etc. The corrosion resistance will be significantly improved. The content of the present application is controlled at 0.90% to 1.00%, and (Cu+P+Co) / Cr≥0.7.

[0019] Ni: Ni strengthens ferrite and refines pearlite in the steel, and the overall effect is to improve the strength, and has no significant effect on plasticity. Ni can improve the fatigue resistance of the steel and reduce the sensitivity of the steel to notches, so Ni can improve the fatigue performance of the steel. Ni does not form carbides, and plays a role in strengthening ferrite by forming a simple substitution solid solution, reduces the ductile-brittle transition temperature of the steel, and improves the low temperature toughness of the steel; a certain Ni content can ensure that the steel plate has sufficient hardenability, uniform performance in the thickness direction, and at the same time, ensure the matching of strength and toughness of the steel plate and low temperature toughness. Adding Ni to the steel can also reduce the copper brittleness of Cu-containing steel, reduce intergranular cracking during hot rolling, improve the atmospheric corrosion resistance of the steel plate, and Ni and Cr can significantly improve the corrosion resistance of the steel. The content of the present application is controlled at 0.90% to 1.00%, and Ni / Cr≥0.9, Ni / Cu≥1.7.

[0020] Cu: Cu is the most main and most commonly used alloying element in corrosion-resistant steel. Cu can activate the cathode, promote the passivation of steel anode to slow down corrosion; a layer of copper-rich phase will be formed on the surface of steel during corrosion process, and there is a dense and strongly adherent intermediate layer between the corrosion layer on the surface of steel and the copper-rich layer, which further relieves the corrosion of steel, especially when used with P, it can significantly improve the performance of resistance to marine atmospheric corrosion and seawater corrosion; Cu and Ni composite addition can not only reduce the copper brittleness of copper-containing steel and reduce the intergranular cracking during hot rolling, but more importantly, Cu and Ni are both austenite stabilizing elements, and Cu and Ni composite addition can greatly reduce Ar3 and improve the driving force of austenite to ferrite phase transition; at the same time, Cu can accelerate the strain-induced precipitation of carbonitride niobium at high temperature, and the recrystallization stop temperature is increased, which is beneficial to the non-recrystallization zone controlled rolling to refine the phase transition product and improve the fatigue resistance of the material. The content of Cu in the application is controlled at 0.45% to 0.52%.

[0021] Nb: Nb is an important element in controlled rolling and controlled cooling steel, Nb is a strong carbide forming element, and the NbC and NbN two-phase particles formed by C and N are important elements in controlled rolling and controlled cooling steel, which can effectively refine the grain, thereby improving the strength and low temperature impact toughness. The composite addition of Nb and Mn can effectively inhibit the recovery, recrystallization and other processes of austenite during rolling, on the one hand, it can increase the austenite recrystallization temperature, thereby increasing the rolling temperature and reducing the rolling unit load; on the other hand, it can effectively refine the phase transition structure of the steel plate, thereby improving the strength and low temperature impact toughness; it can prevent intergranular corrosion of the steel by oxidizing medium. Nb can increase the solid solution amount of rare earth in steel, thereby improving the corrosion resistance of the steel, and the content of Nb in the application is controlled at 0.055% to 0.060%, and 36Nb / Mn≥0.80.

[0022] V: V has great affinity with O and N, and is a strong carbide forming element; generally, the dispersion degree of VC is very high and very stable, so it can obtain a dense and fine-grained structure by deoxidizing and degassing, improve plasticity, toughness and strength, and its impact performance and fatigue strength are higher than those of steel without V, and it has high strength and good toughness at high temperature and low temperature (<0℃). Since the high dispersion of VC prevents the grain of the weld from growing too large, the weldability of the steel can be improved, but the steel will grow strongly when heated to the VC dissolution temperature. When dissolved in the solid solution at high temperature, the hardenability is increased; otherwise, if it exists in the form of carbide, the hardenability is reduced. V increases the tempering stability of quenched steel and produces a secondary hardening effect. V can increase the solid solution amount of rare earth in steel, thereby improving the corrosion resistance of the steel, and the content of V in the application is controlled at 0.06% to 0.065%.

[0023] Ti: Ti has very strong affinity with N, O and C, and stronger affinity with S than Fe. Therefore, it is a good deoxidizing and degassing agent and an effective element for fixing N and C. Ti is a strong carbonitride forming element, and a trace amount of Ti can combine with N in steel to form TiN, preventing the growth of austenite grains during soaking, and also preventing the growth of austenite grains in the heat-affected zone of welding, thereby improving weldability. TiC and TiN have strong binding force, are stable and not easy to decompose, and can only slowly dissolve into the solid solution in steel when heated to above 1000℃, thus significantly controlling the growth of grains in the heat-affected zone of welding and improving the weldability of the material. Since Ti fixes N and S to form TiN, the plasticity and impact toughness of the steel can be significantly improved. Ti can increase the solid solution amount of rare earth in steel, thereby improving the corrosion resistance of the steel. However, Ti has very strong affinity with N and O and is prone to form TiN and TiO2, resulting in a large number of non-metallic inclusions and subcutaneous porosity and other defects at a relatively low temperature. The content of Ti in the present application is controlled at 0.035% to 0.042%.

[0024] N: N and C can be dissolved in Fe to form interstitial solid solution, N expands the austenite phase region of steel, and is a very strong austenite forming and stabilizing element, which can replace a part of Ni within a certain limit, and N on the surface of steel can combine with elements such as Nb, Al, V and Ti to form extremely stable nitrides, becoming surface hardening and strengthening elements, and improving the corrosion resistance of the steel. However, too high residual nitrogen content in steel can lead to loose macrostructure or porosity, so a certain amount of Al needs to be added to form stable AlN to avoid nitrogen escaping to form porosity and other defects during solidification. Therefore, the content of N in the present application is controlled at less than or equal to 0.0130% to 0.0140%, and (Nb+V+Ti+Als) / N≥14.

[0025] Al: Al is mainly used for deoxidization and grain refinement. Al generates effective fine dispersions with N or O to inhibit the grain growth of steel during heating, promotes the decomposition of austenite during cooling of steel to improve the hardenability of steel, becomes a nucleation site for recrystallization to promote the nucleation of ferrite and refine the grains, and improves the fatigue resistance of steel. AlN itself has high stability during heating, thereby improving the thermal stability of steel, reducing the tendency of overheating of steel, and improving the oxidation resistance of steel; Al generates effective surface hardening layer through low-temperature diffusion of N (nitriding) to improve the oxidation resistance and corrosion resistance of steel; and a certain amount of Si is added when Al is used for deoxidization to significantly improve the deoxidization of Al; however, if the amount of Al is too large, abnormal structure of steel and tendency of graphitization of steel are promoted. Therefore, the content of Als in the present application is controlled at 0.035% to 0.045%.

[0026] Sn: At austenitic temperatures, Sn in steel precipitates at MnS inclusions and along the original austenite grain boundaries, thereby inhibiting the enrichment and precipitation of MnS inclusions at the grain boundaries. Sn helps improve the corrosion resistance of the material and can significantly enhance its corrosion resistance performance. Sn forms a corrosion-resistant SnO2 oxide film on the steel surface, which effectively prevents the interaction between the matrix and the corrosive medium, inhibiting the corrosion of the steel in the corrosive medium. Sn obtained after hydration... 2+ The precipitates formed in the anodic micro-regions fill corrosion cracks or cavities, enhancing the resistance to corrosion. - Sn's ability to penetrate; Sn can also be detected by Cl - Hydration under environmental media inhibits Fe 3+ Hydrolysis produces H + The process improves the pH value of the corrosion micro-zone and alleviates the anodic dissolution process. Sn, as a corrosion inhibitor, alters the anode and cathode reaction processes, significantly improving the steel's resistance to marine corrosion. In this invention, its content is controlled at 0.03%–0.05%.

[0027] Rare earth elements (REs) are highly reactive and have strong binding properties. Adding REs to steel can improve solidification structure, alter solid-state phase transformation structure, form harmless low-melting-point inclusions, strengthen interfaces through segregation, and passivate surface rust layers. REs can increase the self-corrosion potential and polarization resistance of weathering steel, thereby inhibiting anodic reactions, increasing the resistance to the entire electrochemical reaction, and significantly reducing the corrosion rate of the steel. REs are enriched at grain boundaries through diffusion mechanisms, inhibiting the segregation of inclusions at grain boundaries, and improving the low-temperature performance and corrosion resistance of steel. Adding REs to phosphorus-containing steel can reduce macroscopic segregation, reducing the segregation of phosphorus at grain boundaries and ferrite interfaces, making the distribution of phosphorus in the steel more reasonable, thereby significantly improving the toughness, corrosion resistance, and fatigue resistance of the steel. However, REs are a scarce resource, and their addition must be controlled. In this invention, the RE content is controlled at 0.03%–0.05%, (Nb+V+Ti) / RE ≥ 3.0, and RE / P ≥ 1.2.

[0028] The above describes the content range and function of various added elements. The manufacturing method of this invention for producing high-performance corrosion-resistant marine steel includes:

[0029] 1. The steel is smelted according to the above composition, and the process includes:

[0030] 1) During converter smelting, the content of elements such as Si, O, P, and S is adjusted to be within the range of this invention. During the smelting process, the molten iron is first desulfurized and pretreated. After desulfurization, the S content in the molten iron is ≤0.0025%. A combined top and bottom blowing process is adopted, and the converter tapping temperature is 1630~1650℃. Then, Si-Ca wire feeding treatment is carried out, and the Ca content is controlled at 0.0015%~0.0025%.

[0031] 2) The molten steel is refined, and the contents of Co, Cr, Ni and other alloying elements are adjusted to the range of the present application.

[0032] 3) 20% rare earth alloy 1.95-3.25 kg / t steel is added to the LF furnace 7-9 minutes before the end of vacuum treatment in the LF furnace, argon blowing is then performed for 5-10 minutes, and RH treatment is then performed, with the RH treatment time being 30-35 minutes, nitrogen being blown throughout the RH treatment, the content of [H] in the steel being controlled to be ≤1.0 ppm, the content of [O] being controlled to be ≤20 ppm, and the net circulation time before removal being 6-10 minutes.

[0033] 4) Sn element is added before the end of RH treatment, with the amount of Sn added being 1.2-1.3 times the target control amount, so as to ensure that the end content can be controlled within the target range.

[0034] 2. The molten steel obtained in step 1 is cast into a desired continuous casting billet. In order to control the content of equiaxed crystals in the continuous casting billet, the tundish superheat is 20-30°C. Lower superheat can reduce the solidification time of the molten steel, and can reduce the segregation of carbon, manganese and other elements in the center of the billet, and can reduce porosity, shrinkage and other defects in the billet, so as to ensure the Z-direction performance and fatigue resistance of the steel plate. Full protection pouring is adopted, and the casting speed of the continuous casting billet is controlled to be 1.2-1.4 m / min, and the specific water quantity of the secondary cooling water is 0.90-1.00 m 3 / t, so as to make the equiaxed crystal ratio of the continuous casting billet be >28.0%, and electromagnetic stirring is adopted at the solidification end, so as to uniformly stir the molten steel and then realize high-strength and high-density solidification as soon as possible. Heavy press-down is adopted during the continuous casting process, and the press-down amount is 15.0-20.0 mm.

[0035] 3. In order to control the grain size of the continuous casting billet to be not greater than 500 μm, the continuous casting billet is rapidly cooled, the open cooling temperature is 960-990°C, the cooling speed is 10.0-11.0°C / s, and after cooling to 650-680°C, the billet is placed into a slow cooling pit for slow cooling, and then cooled to below 150°C at a cooling speed of 5.0-15.0°C / h.

[0036] 4. The continuous casting billet obtained in step 3 is sent into a heating furnace for heating. Subsection heating process is adopted, the billet is put into the furnace when the furnace temperature is 550-600°C, and the billet is kept at temperature for 1.5-2.5 h to release the internal stress of the billet. Slow heating process is adopted below 950°C to further release the internal stress caused by the cooling and heavy press-down of the continuous casting billet, and to prevent temperature stress caused by too fast heating, the heating speed is controlled to be 5-7°C / min, the billet is kept at temperature for 30-50 min at 950°C. Fast heating and appropriately prolonged holding time process is adopted above 950°C to prevent austenite grain coarsening and to make the alloying elements in the billet sufficiently diffuse and dissolve, further reducing element segregation, the heating speed is controlled to be 15-20°C / min, the billet is kept at temperature for 3.0-4.0 h at 1200-1220°C.

[0037] 5. The cast blank is rolled into finished steel plate through three stages, in the first stage, in order to fully break the columnar crystal of the continuous casting blank, a high-temperature slow rolling and large reduction process is adopted, the cast blank is directly rolled after descaling, the rolling speed is 1.2-1.7 m / s, the reduction of the first three passes is >40 mm, the billet is cooled by rolling mill cooling water between each pass, the cooling time is 5-7 s, the finish rolling temperature is 1000-1030 DEG C, the thickness of the warm billet is 1.6-2.5 times the thickness of the finished product, in order to inhibit the growth of the intermediate billet grains, the warm billet is cooled by water spraying, the cooling speed is 6.0-8.0 DEG C / s, and the temperature is cooled to 10-25 DEG C above the second stage rolling starting temperature; the second stage rolling starting temperature is 900-920 DEG C, the rolling speed is 1.8-2.2 m / s, the finish rolling temperature is 840-860 DEG C, and the thickness of the warm billet is 1.1-1.4 times the thickness of the finished product; the third stage rolling starting temperature is 780-820 DEG C, and the finish rolling temperature is 740-760 DEG C.

[0038] 6. The rolled steel plate adopts a rapid cooling (ACC) process, the cooling speed is 8.0-12.0 DEG C / s, the steel plate red temperature is 560-600 DEG C, the fine grains after rolling can be maintained, and the grain growth is prevented.

[0039] Compared with the prior art, the present application has the following beneficial effects:

[0040] The present application adopts a low-carbon and high-manganese content design, controls the range of composite addition of alloying elements to be 0.09 >= (Nb+V+Ti) / Mn >= 0.06, 7 >= Si / Al >= 2, (Cu+P+Co) / Cr >= 0.7, 5.0 >= Cr / Co >= 3.5, Ni / Cr >= 0.9, (Nb+V+Ti+Als) / N >= 14, Ni / Cu >= 1.7, 36Nb / Mn >= 0.80, (Nb+V+Ti) / RE >= 3.0, and RE / P >= 1.2; the strength of the steel is improved while the steel plate has excellent low-temperature toughness, corrosion resistance and fatigue resistance. The influence of element segregation on the fatigue performance and low-temperature performance of the steel plate is controlled by optimizing the continuous casting process, slow and long-time segmented heating process is adopted for heating, three-stage process of high-temperature slow rolling and large reduction, medium-temperature rapid recrystallization zone rolling and low-temperature rolling is adopted for rolling, and the subsequent ACC controlled cooling process is adopted, the strength of the steel plate is guaranteed by fine-grain strengthening, dislocation strengthening, solid solution strengthening and second-phase strengthening; the low-temperature toughness of the steel plate is guaranteed by grain refinement; the steel plate has good corrosion resistance by relying on the oxides formed by Cr, Ni, Co and other elements; the fatigue resistance of the steel plate is improved by fine and dispersed two-phase particles control and element segregation control; the corrosion resistance of the steel plate is improved by composite addition of a small amount of Sn, RE and P elements, and the segregation of P elements is reduced.

[0041] 1. The application proposes to add Co, Ni and Cr elements in combination, so that the steel plate has good comprehensive mechanical properties, i.e. yield strength of 550-582 MPa, elongation of ≥20%, and impact energy at -80℃ of ≥200 J;

[0042] 2. The application proposes to add a small amount of Sn, RE and P elements in combination, so as to improve the corrosion resistance of the steel plate, and the corrosion resistance rate of the steel plate to marine atmosphere is less than 0.090 mm / a;

[0043] 3. The steel plate has good fatigue resistance, and the fatigue life of the steel plate under peak stress of 280 MPa is more than 2 million times;

[0044] 4. The steel plate can be produced in a large thickness range, and the maximum thickness can reach 150 mm, and the Z-direction performance is more than or equal to 40%. DETAILED DESCRIPTION

[0045] The application will be described in detail through the following examples.

[0046] According to the above chemical composition and production process, the actual smelting composition of the application is shown in Table 1, the actual process parameters of the application are shown in Tables 2-6, and the physical properties are shown in Table 7.

[0047] Table 1: Smelting composition, Wt%

[0048]

[0049] Table 2: Steelmaking process parameters

[0050] No. Argon blowing time RH treatment time Net circulation time 1 10 35 6 2 10 35 10 3 5 30 6 4 10 35 10 5 8 34 8 6 8 32 8 7 8 35 8 8 6 35 9 9 5 35 8 10 5 35 8

[0051] Table 3: Continuous casting process parameters

[0052]

[0053]

[0054] Table 4: Heating process parameters

[0055]

[0056] Table 5: One-stage rolling process parameters

[0057]

[0058] Table 6: Two-stage and three-stage rolling and cooling process parameters

[0059]

[0060]

[0061] Table 7: Physical properties

[0062]

[0063] As can be seen from Table 7, the yield strength of the steel of the embodiments of the present application is 560-582 MPa, all of which reaches the design strength of 550 MPa or more, the elongation is greater than 20%, the Z-direction performance is greater than 40%, and the impact energy at -80℃ is greater than 200 J, indicating that the strength and toughness of the steel of each embodiment not only meets the design requirements, but also has a certain margin. The fatigue performance test is carried out by using an Instron 8802 fatigue testing machine under a conventional environment, the loading mode is tension-compression fatigue, the stress ratio Rs = -1, the test frequency is 20 Hz, the fatigue life number under the peak stress 280 MPa load is greater than 2 million times, the inventive steel is subjected to 168-hour periodic immersion rapid corrosion evaluation test according to the test method stipulated in GBT 19746-2005, the corrosion resistance of the inventive steel is evaluated by using the weight loss method, and the average annual corrosion rate is converted, and the average annual corrosion rate is less than 0.09 mm / a.

[0064] It is indicated herein that the above embodiments are only for illustrating the technical concept and characteristics of the present application, and are not a limitation on the present application. Any equivalent replacement or modification or improvement without departing from the essence of the present application falls within the protection scope of the present application.

Claims

1. A high-performance corrosion-resistant marine steel, characterized by, The steel has the following chemical composition by weight percentage: C: 0.02%~0.07%, Si: 0.10%~0.25%, Mn: 1.75%~2.50%, P: 0.022%~0.026%, S: ≤0.008%, Nb: 0.055%~0.060%, Als: 0.035%~0.045%, Cr: 0.90%~1.00%, Ni: 0.90%~1.00%, Co: 0.20%~0.25%, N: 0.0130%~0.0140%, V: 0.06%~0.065%, Ti: 0.035%~0.042%, Cu: 0.45%~0.52%, Sn: 0.03%~0.05%, RE: 0.03%~0.05%, wherein 0.09≥(Nb+V+Ti) / Mn≥0.06, 7≥Si / Al≥2, (Cu+P+Co) / Cr≥0.7, 5.0≥Cr / Co≥3.5, Ni / Cr≥0.9, (Nb+V+Ti+Als) / N≥14, Ni / Cu≥1.7, 36Nb / Mn≥0.80, (Nb+V+Ti) / RE≥3.0, RE / P≥1.2, and the rest is Fe and inevitable impurities; the production method comprises smelting, slab continuous casting, casting blank heating, rolling and cooling, and the slab is rolled into finished steel plate through three-stage rolling, the slab is directly rolled after descaling after being discharged from the furnace, the rolling speed is 1.2~1.7m / s, the reduction of the first three passes is >40mm, the blank is cooled by rolling mill cooling water between each pass, the cooling time is 5~7s, the finish rolling temperature is 1000~1030℃, the thickness of the warm blank is 1.6~2.5 times the thickness of the finished product, the warm blank is cooled by water spraying, the cooling speed is 6.0~8.0℃ / s, and the temperature is cooled to 10~25℃ above the second-stage rolling temperature; the second-stage rolling temperature is 900~920℃, the rolling speed is 1.8~2.2m / s, the finish rolling temperature is 840~860℃, and the thickness of the warm blank is 1.1~1.4 times the thickness of the finished product; the third-stage rolling temperature is 780~820℃, and the finish rolling temperature is 740~760℃; the steel plate is rapidly cooled after rolling, the cooling speed is 8.0~12.0℃ / s, and the steel plate is red after cooling to 500~600℃.

2. The high-performance corrosion-resistant marine steel according to claim 1, characterized in that, The steel has a yield strength of 550~582MPa, an elongation of ≥20%, and an impact energy of ≥200J at -80℃.

3. The high-performance corrosion-resistant marine steel according to claim 1, characterized in that, The steel has a corrosion rate of <0.090mm / a in marine atmosphere.

4. The high-performance corrosion-resistant marine steel according to claim 1, characterized in that, The fatigue life of the steel is >200 million times under a peak stress of 280MPa.

5. The high-performance corrosion-resistant marine steel according to claim 1, characterized in that, The maximum thickness of the steel plate can reach 150mm, and the Z-direction performance is ≥40%.

6. A method of producing the high-performance corrosion-resistant marine steel according to any one of claims 1 to 5, comprising melting, slab continuous casting, casting slab heating, rolling, and cooling, characterized in that, The slab is rapidly cooled in the continuous casting process, the cooling temperature is 960-990℃, the cooling speed is 10.0-11.0℃ / s, and the slab is cooled to 650-680℃ and then enters the slow cooling pit for slow cooling, and then the cooling speed is 5.0-15.0℃ / h to cool to below 150℃; the slab is heated by the sectional heating process, and enters the furnace when the furnace temperature is 550-600℃, and the holding time is 1.5-2.5h; the heating speed is controlled at 5-7℃ / min below 950℃, and the holding time is 30-50min when heated to 950℃; the heating speed is controlled at 15-20℃ / min above 950℃, and the slab is uniformly heated to 1200-1220℃, and the holding time is 3.0-4.0h; the slab is rolled into finished steel plate by three-stage rolling, the slab is directly rolled after descaling, the rolling speed is 1.2-1.7m / s, the reduction per pass is >40mm, the slab is cooled by rolling mill cooling water between passes, the cooling time is 5-7s, the final rolling temperature is 1000-1030℃, the thickness of the slab is 1.6-2.5 times the thickness of the finished product, the slab is cooled by water spraying, the cooling speed is 6.0-8.0℃ / s, and the temperature of the second stage is cooled to 10-25℃ above the second stage rolling temperature; the second stage rolling temperature is 900-920℃, the rolling speed is 1.8-2.2m / s, the final rolling temperature is 840-860℃, and the thickness of the slab is 1.1-1.4 times the thickness of the finished product; the third stage rolling temperature is 780-820℃, and the final rolling temperature is 740-760℃; the steel plate is rapidly cooled after rolling, the cooling speed is 8.0-12.0℃ / s, and the red temperature of the steel plate is 500-600℃.

7. The method of producing a high-performance corrosion-resistant marine steel according to claim 6, characterized by, In the smelting process, the molten iron is pretreated by desulfurization, the S content in the molten iron after desulfurization is ≤0.0025%, a combined blowing process is used, the tapping temperature of the converter is 1630-1650℃, then Si-Ca wire feeding treatment is performed, and the Ca content is controlled at 0.0015%-0.0025%; 20% rare earth alloy is added to the LF furnace 7-9min before the vacuum treatment in the LF furnace is completed, argon blowing is performed for 5-10min, and then RH treatment is performed, the RH treatment time is 30-35min, nitrogen is blown during the whole RH treatment, and the net circulation time before removal is 6-10min.

8. The method of producing a high-performance corrosion-resistant marine steel according to claim 6, characterized by, In the continuous casting process, the tundish is heated to 20-30℃, the whole process is protected, the casting speed of the continuous casting slab is controlled at 1.2-1.4m / min, the specific water consumption of the secondary cooling water is 0.90-1.00m3 / t, and heavy reduction is used in the continuous casting process, and the reduction is 15.0-20.0mm.

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