High-performance anti-fatigue steel for ocean engineering and production method thereof

Abstract

The invention discloses high-performance anti-fatigue steel for ocean engineering and a production method of the high-performance anti-fatigue steel. The steel comprises the following chemical components: 0.02%-0.07% of C, 0.10%-0.25% of Si, 1.75%-2.50% of Mn, 0.022%-0.026% of P, less than or equal to 0.008% of S, 0.065%-0.070% of Nb, 0.070%-0.075% of V, 0.035%-0.042% of Ti, 1.25%-1.45% of Cr, 1.25%-1.45% of Ni, 0.30%-0.35% of Co, 0.035%-0.045% of Als, 0.0150%-0.0260% of N, 0.45%-0.50% of Cu, 0.03%-0.05% of Sb and 0.03%-0.05% of RE. Through smelting, slab continuous casting, casting blank heating, rolling, cooling and heat treatment, the Rp0.2 of the steel is 690-750 MPa, A is larger than or equal to 20%, the impact energy at the temperature of-80 DEG C is larger than or equal to 200 J, the corrosion resistance rate is smaller than 0.090 mm / a, the fatigue life under the peak stress load of 350 MPa is longer than 2 million times, the maximum thickness can reach 150 mm, and the Z-direction performance is larger than or equal to 40%. The problems that an existing steel plate for ocean engineering is low in strength, poor in low-temperature impact toughness and insufficient in corrosion resistance and fatigue resistance are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material preparation, and particularly relates to a high-performance fatigue-resistant marine engineering steel and a production method thereof. Background Art

[0002] Steel used in marine equipment manufacturing faces complex environments such as complex ocean waves, temperature, humidity, and salinity, which places higher demands on the performance of steel, especially corrosion and fatigue performance, such as higher strength, greater thickness, low-temperature impact toughness, good Z-direction performance, as well as better corrosion resistance and fatigue resistance, etc. It is difficult for existing steel to meet the above performance requirements at the same time.

[0003] The patent with application number 202011611587.1 discloses a 690MPa grade steel plate for marine engineering and its manufacturing method. The steel plate has a yield strength Rp0.2 ≥ 690MPa (for example, 710-762MPa), a tensile strength Rm ≥ 750MPa (for example, 760-793MPa), an elongation after fracture A ≥ 16% (for example, above 19%, 19.0%-23.0%), a cross-sectional shrinkage rate Z ≥ 60% (for example, above 68%, 68.0%-79.0%), and an impact energy KV2 ≥ 150J at -40°C. However, the deep sea and polar regions require lower temperature impact toughness, and the corrosion resistance problem has not been solved.

[0004] The patent with application number 202110788240.2 discloses a FH690 grade marine engineering steel with excellent low temperature toughness and its manufacturing method. The steel plate has a yield strength of ≥690MPa, a tensile strength of 770-940MPa, an elongation after fracture of ≥14%, and a low temperature toughness of -60℃ impact energy of ≥100J. However, its maximum thickness is only 50mm, and the corrosion resistance problem has not been solved, which cannot meet the needs of marine engineering construction.

[0005] The patent with application number 202110729125.8 discloses a 690MPa grade high-strength steel and its manufacturing method. After slab heating, high-pressure descaling water cooling, double-frame reversible rolling, rapid cooling, and heat treatment, it can produce 690MPa grade high-strength steel with a yield strength of no more than 0.43%, a yield strength of more than 690MPa, and a tensile strength of more than 800MPa. The product has the characteristics of low carbon equivalent, high strength, high toughness, low cost, and low internal stress of the steel plate. However, its low-temperature impact toughness is only -20℃, which does not meet the needs of deep sea and extremely cold environments.

[0006] The patent with application number CN201410036368.3 discloses a corrosion-resistant steel plate for the South China Sea marine environment and its production process. The production process includes converter smelting process, LF refining process, vacuum degassing process, continuous casting process, controlled rolling and controlled cooling process, etc. The organizational type of the steel plate is theoretically a single-phase polygonal ferrite fine structure (average grain size 10.17μm). In actual industrial production, it inevitably contains a very small amount of pearlite structure. Compared with conventional hull structural steel EH36, its corrosion resistance in marine environment (marine atmosphere, tidal range, full immersion, etc.) is improved by more than 50%, and it has good strength and toughness matching and welding performance. However, its strength is low, low-temperature toughness is insufficient, and its fatigue resistance has not been evaluated.

[0007] The patent with application number 201910712227.1 discloses a high fatigue structural steel with a yield strength of 345MPa and its manufacturing method. The chemical composition of the steel is: C 0.13%~0.16%, Mn 1.30%~1.60%, Nb0.020%~0.050%, Alt 0.020%~0.030%, Ti≤0.010%, Si≤0.12%, P≤0.010%, S≤0.005%, and the remainder is iron and unavoidable impurities. By adopting a large reduction + controlled cooling process, the obtained steel plate has good comprehensive mechanical properties and good surface quality. However, the strength of the steel plate is low, and its corrosion performance is not evaluated. Only the impact toughness at -20℃ is evaluated, which is far from meeting the use requirements of different marine environments.

[0008] The patent with application number 202110068169.0 discloses an engineering corrosion-resistant 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 element regulation and characteristic element addition are performed, Cu0.28%~0.66%, Ni 0.76%~1.55%, Sb 0.03%~0.12%, and the rest are Fe and unavoidable impurities. The corrosion fatigue strength of the steel can be increased by up to 52%, but the low-temperature toughness of the steel is not evaluated. Summary of the invention

[0009] In view of the deficiencies in the prior art, the purpose of the present invention is to propose a high-performance fatigue-resistant marine engineering steel and a production method thereof, which has low carbon and low alloying as basic characteristics, composite addition of Cr, Ni, Co multi-element alloy strengthening elements and V, N precipitation strengthening elements, and addition of P, Al and Sb, RE as basic characteristics, thereby improving the strength and low-temperature toughness of the steel plate, and having good corrosion resistance and fatigue resistance; and solves the problems of low strength, poor low-temperature impact toughness, insufficient corrosion resistance and fatigue resistance of existing marine engineering steel plates.

[0010] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0011] The present invention is characterized by a steel plate having excellent low temperature toughness, ultra-high strength, corrosion resistance and fatigue resistance. In the present invention, the chemical composition of the steel plate comprises 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: 0.065% to 0.070%, V: 0.070% to 0.075%, Ti: 0.03% to 0.04%, Cr: 1.25% to 1.45%, Ni: 1.25% to 1.45%, Co: 0.30% to 0.35%, Als: 0.035% to 0.04 5%, N: 0.0150%~0.0160%, Cu: 0.45%~0.50%, Sb: 0.03%~0.05%, RE: 0.03%~0.05%, among which 0.12≥(Nb+V+Ti) / Mn≥0.07, 6.0≥Si / Al≥2.0, (Cu+P+Co) / Cr≥0.54, 5≥Cr / Co≥3, Ni / Cr≥0.8, 36Nb / Mn≥0.90, (Nb+V+Ti+Als) / N≥13, Ni / Cu≥2.2, (Nb+V+Ti) / RE≥3.5, RE / P≥1.3, and the rest are Fe and unavoidable impurities.

[0012] The present invention selects the above alloying element types and their contents because of the role of each element in improving the strength, toughness, corrosion resistance and fatigue resistance of the steel in marine engineering steel plates:

[0013] C: C and Cr can form alloy cementite (Fe·Cr)3C, and can also form carbides such as Cr 7 C 3 Cr 23 C 6 The melting point, hardness, wear resistance and stability of these carbides are higher than those of Fe 3High C content can improve the strength of steel. C and strong carbide-forming elements such as V, Nb, and Ti will preferentially form carbides such as VC, NbC, and TiC, which have the highest stability, melting point, hardness, and wear resistance. Therefore, C is the most effective element for improving the strength of steel plates. 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 steel. From the perspective of improving the toughness, corrosion resistance, fatigue resistance, and weldability of steel, the C content in steel should be controlled to be appropriately lower. Therefore, the C content of the present invention is selected to be 0.02% to 0.07%.

[0014] Si: Si is a necessary element for steelmaking deoxidation and has a certain solid solution strengthening effect. Although Si can improve the strength of steel plates, Si reduces the critical cooling rate of martensitic phase transformation, seriously damaging the low-temperature toughness, elongation and weldability of ultra-high strength steel plates. Si not only promotes the formation of MA islands, but also the size of the formed MA islands is relatively large and unevenly distributed, which seriously damages the toughness of the welding heat affected zone (HAZ). Therefore, the Si content in steel should be controlled as low as possible. A certain Si content can effectively improve the marine corrosion resistance of steel, and the composite addition of Si and Al can improve the corrosion resistance and high-temperature oxidation resistance. The Si content of the present invention is controlled at 0.10% to 0.25%, 6.0≥Si / Al≥2.0.

[0015] Mn: Mn is the main element for improving strength and toughness, and can significantly improve the hardenability of steel. It is very cheap and is the main additive element in steel. When the C content is low, a higher Mn content can effectively improve the hardenability of steel, and improve the strength of the steel plate by refining the structure and promoting bainite transformation, while having excellent low-temperature toughness; Mn expands the austenite region and promotes grain enlargement. It is necessary to cooperate with the composite addition of grain-refining elements Nb, V, and Ti to promote grain refinement and improve the fatigue performance of steel; but Mn is prone to segregation during the solidification of molten steel, aggravating the segregation and looseness of the center of the ingot, resulting in low low-temperature toughness of ultra-high strength steel plates and cracks in welded joints, which need to be improved by optimizing the continuous casting process and heating process. The Mn content of the present invention is selected to be 1.75% to 2.50%, and 0.12≥(Nb+V+Ti) / Mn≥0.07.

[0016] P: P has a strong solid solution strengthening effect in steel. When added to low alloy structural steel as an alloy element, it can improve its strength and atmospheric corrosion resistance. When its content is greater than or equal to 0.02%, it can significantly improve corrosion resistance. However, when its content is too high, it will have an adverse effect on the low temperature toughness of the parent material and the toughness of the welding heat affected zone, so its content should be controlled within a reasonable range as much as possible. In the present invention, its content is controlled within 0.022% to 0.026%.

[0017] S: S segregates severely in steel, deteriorating the quality of steel. S is an inclusion-forming element, forming inclusions such as FeS and MnS, thereby reducing the ductility of steel, and the area near the inclusions will become the source of corrosion, which is not conducive to the corrosion resistance of the steel plate. Moreover, FeS is easy to melt at the grain boundary due to its low melting point, weakening the bonding force between the grains and causing the hot brittleness of the steel. Therefore, a certain amount of Mn element should be added to form MnS with a higher melting point and deformation ability. Therefore, the content of S in the present invention is controlled to be less than or equal to 0.008%.

[0018] Co: Co plays a major role in solid solution strengthening in steel, improving the oxidation resistance and corrosion resistance of steel. Co can increase the interaction between Fe atoms, reduce the critical concentration of Cr atoms to form clusters, and thus improve the stability of Cr atom clusters. When Co and Cr atoms act on steel at the same time, a smooth passivation film is formed on its surface, which has high structural stability and can well protect the matrix, thus having excellent corrosion resistance. Co promotes more (Ti, Al)Ni 3 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 Ni 3 The nucleation rate of Ti and the number density of the precipitated phase are increased, that is, Co can make the distribution of the precipitated phase more dispersed, improve the fatigue resistance of the steel, and enhance the precipitation strengthening effect of the precipitated phase. Therefore, the content of the present invention is controlled at 0.30% to 0.35%, 5≥Cr / Co≥3.

[0019] Cr: Cr can improve the strength and hardness of steel. Cr is a ferrite-forming element, which helps to increase the ferrite content in steel and thus improve the low-temperature toughness of steel. Cr is an element that improves the corrosion resistance of steel, but adding Cr alone sometimes reduces the corrosion resistance, and even has a lower corrosion resistance than ordinary carbon steel. It needs to be used in combination with other corrosion-resistant alloying elements, such as Cu, P, Co, etc., to significantly improve its corrosion resistance. In the present invention, its content is controlled at 1.25% to 1.45%, (Cu+P+Co) / Cr≥0.54.

[0020] Ni: Ni strengthens ferrite and refines pearlite in steel. The overall effect is to improve strength, and the effect on plasticity is not significant. Ni can improve the fatigue resistance of steel and reduce the sensitivity of steel to notches, so Ni can improve the fatigue performance of steel. Ni does not form carbides, but plays a role in strengthening ferrite by forming a simple substitutional solid solution, reducing the toughness-brittleness transition temperature of steel, and improving the low-temperature toughness of steel; a certain Ni content can ensure that the steel plate has sufficient hardenability and uniform performance in the thickness direction, while ensuring the strength and toughness matching and low-temperature toughness of the steel plate. Adding Ni to steel can also reduce the copper brittleness of Cu-containing steel, reduce intergranular cracking during hot rolling, and improve the atmospheric corrosion resistance of the steel plate. The combination of Ni and Cr can significantly improve the corrosion resistance of steel. In the present invention, its content is controlled at 1.25% to 1.45%, Ni / Cr≥0.8, Ni / Cu≥2.2.

[0021] Cu: Cu is the most important and most commonly used alloying element in corrosion-resistant steel. Cu can activate the cathode, promote the passivation of the steel anode and slow down the corrosion. During the corrosion process, a copper-rich phase will form on the surface of the steel. There is a dense and highly adherent intermediate layer between the surface corrosion layer and the copper-rich layer of the steel, which further alleviates the corrosion of the steel. In particular, when used in combination with P, it can significantly improve the performance of resisting marine atmospheric corrosion and seawater corrosion. In addition to reducing the copper brittleness of copper-containing steel and reducing the intergranular cracking during the hot rolling process, the composite addition of Cu and Ni is more importantly austenite stabilizing elements. The composite addition of Cu and Ni can significantly reduce Ar3 and increase the driving force of the phase transformation from austenite to ferrite. At the same time, Cu can accelerate the high-temperature strain-induced precipitation of niobium carbonitride and increase the recrystallization stop temperature, which is conducive to controlled rolling in the non-recrystallization zone to refine the phase transformation products and improve the fatigue resistance of the material. The content of Cu in the present invention is controlled at 0.45% to 0.50%.

[0022] Nb: Nb is an important element in controlled rolling and controlled cooling steel. Nb is a strong carbide-forming element. The two-phase particles NbC and NbN formed with C and N are important elements in controlled rolling and controlled cooling steel. They can effectively refine the grains, thereby improving the strength and low-temperature impact toughness at the same time. The composite addition of Nb and Mn can effectively inhibit the recovery and recrystallization of austenite during the rolling process. On the one hand, it can increase the austenite recrystallization temperature, thereby increasing the rolling temperature and reducing the load of the rolling unit; on the other hand, it can effectively refine the phase transformation structure of the steel plate, thereby improving the strength and low-temperature impact toughness at the same time; it can prevent the intergranular corrosion of the steel by the oxidizing medium. Nb can increase the solid solution amount of rare earth in steel, thereby improving the corrosion resistance of steel. In the present invention, its content is controlled at 0.065% to 0.070%, and 36Nb / Mn≥0.90.

[0023] V: V has a great affinity with both O and N and is a strong carbide-forming element; generally, VC has a high degree of dispersion and is extremely stable, so it is beneficial for deoxidation and degassing to obtain a dense fine-grained structure, improve plasticity, toughness and strength, and its impact performance and fatigue strength are higher than those of vanadium-free steel. It has high strength and good toughness at both high and low temperatures (<0°C). Since the high dispersion of VC prevents the weld grains from being coarse, it can improve the weldability of the steel, but heating to the VC dissolution temperature will cause the steel crystals to grow strongly. When dissolved into a solid solution at a high temperature, the hardenability is increased; conversely, when it exists in the form of carbides, 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 steel. In the present invention, its content is controlled at 0.070% to 0.075%.

[0024] Ti: Ti has a strong affinity with N, O, and C, and its affinity with S is stronger than that of Fe. Therefore, it is a good deoxidizer and degasser and an effective element for fixing N and C. Ti is a strong carbonitride-forming element. A trace amount of Ti can combine with N in steel to form TiN, which prevents the growth of austenite grains during equalization and can also prevent the growth of austenite grains in the heat-affected zone of welding, thereby improving weldability. TiC and TiN have strong binding force, stability, and are not easy to decompose. They can only be slowly dissolved into the solid solution in steel when heated to above 1000°C. Therefore, they can significantly control the growth of grains in the heat-affected zone of welding and improve the welding performance of the material. Since Ti fixes N and S and forms TiN, the plasticity and impact toughness of steel can be significantly improved. Ti can increase the solid solution content of rare earths in steel, thereby improving the corrosion resistance of steel. However, Ti has a great affinity with N and O and is very easy to form TiN and TiO 2 At a lower temperature, more non-metallic inclusions and subcutaneous pores are formed. The content of the present invention is controlled at 0.035% to 0.042%.

[0025] N: Like C, N can be dissolved in Fe to form interstitial solid solutions. N expands the austenite phase of steel and is a very strong element for forming and stabilizing austenite. It can replace a portion of Ni within a certain limit. N that penetrates into the surface of steel can be combined with Nb, Al, V, Ti and other elements to form extremely stable nitrides, improving the corrosion resistance of steel. However, excessive residual nitrogen in steel can lead to loose macroscopic structure or pores, so a certain amount of Al needs to be added to nitrogen-containing steel to form stable AlN to avoid defects such as pores formed by N escaping during solidification. Therefore, the N content in the present invention is controlled at 0.015% to 0.016%, (Nb+V+Ti+Als) / N≥13.

[0026] Al: Al is mainly used for deoxidation and grain refinement. Al and N or O form effective fine dispersions to inhibit grain growth when steel is heated. When steel is cooled, it promotes the decomposition of austenite to improve the hardenability of steel. It also becomes a nucleation point for recrystallization, promotes ferrite nucleation and grain refinement, and improves the fatigue resistance of steel. AlN itself has high stability when heated, so it can improve the thermal stability of steel, help reduce the overheating tendency of steel, and improve the oxidation resistance of steel; Al forms an effective surface hardening layer through the low-temperature diffusion (nitridation) of N, improves the oxidation resistance and corrosion resistance of steel, and adding a certain amount of Si when deoxidizing with Al can significantly improve the deoxidation of Al; but if the amount of Al is too much, it will cause abnormal structure of steel and promote the graphitization tendency of steel. Therefore, the Als content of the present invention is controlled at 0.035% to 0.045%.

[0027] Sb: Antimony (Sb) in steel at austenite temperature precipitates at MnS inclusions and along the original austenite grain boundaries, thereby inhibiting the enrichment and precipitation of MnS inclusions on the grain boundaries. Sb can also refine the secondary recrystallization grain size, refine the steel structure and improve the toughness, thereby improving the fatigue resistance and corrosion resistance of the steel; Sb forms Sb on the steel surface 2 O 5 The corrosion-resistant oxide film effectively prevents the interaction between the substrate and the corrosive medium, inhibiting the corrosion of steel in the corrosive medium; Sb obtained by hydration 3+ The precipitates formed in the anode micro-area fill the corrosion cracks or cavities, improving the barrier to corrosion. - The ability to penetrate; Sb can also pass through Cl - Hydration in ambient media inhibits Fe 3+ Hydrolysis produces H + The process improves the pH value of the corrosion micro-area and alleviates the anodic dissolution process. Sb, as a corrosion inhibitor, changes the cathode and anode reaction process and can greatly improve the marine environment corrosion resistance of steel. The content of the present invention is controlled at 0.03% to 0.05%.

[0028] RE: Rare earth (RE) atoms are active and have strong binding force. Adding RE to steel can improve solidification structure, change solid phase change structure, form harmless low melting point inclusions, strengthen interface through segregation, passivate surface rust layer, etc.; RE can improve the self-corrosion potential and polarization resistance of weathering steel, thereby inhibiting the anodic reaction, increasing the resistance of the entire electrochemical reaction, and significantly reducing the corrosion rate of steel; RE is enriched at the grain boundary through the diffusion mechanism, inhibiting the segregation of inclusions at the grain boundary, and improving the low temperature performance and corrosion resistance of steel; RE added to P-containing steel can reduce macrosegregation, reduce the segregation of P at the grain boundary and ferrite interface, and make the distribution of P in steel more reasonable, thereby significantly improving the toughness, corrosion resistance, fatigue resistance, etc. of steel. However, RE is a scarce resource, and its addition amount must be controlled. The RE content of the present invention is controlled at 0.03% to 0.05%, (Nb+V+Ti) / RE≥3.5, RE / P≥1.3.

[0029] The above are the content ranges and effects of adding various elements. The manufacturing method of the present invention for producing high-performance fatigue-resistant marine engineering steel includes:

[0030] 1. The steel is smelted according to the above composition, and the process includes:

[0031] 1) During converter smelting, the contents of elements such as C, Si, Mn, P, and S are adjusted to be within the scope of the present invention. During the smelting process, the molten iron is first subjected to a desulfurization pretreatment, and the S content in the molten iron after desulfurization is ≤0.0025%. A top and bottom composite blowing process is adopted, and the converter tapping temperature is 1630-1650°C. After that, Si-Ca wire feeding treatment is performed, and the Ca content is controlled at 0.0015%-0.0025%.

[0032] 2) Refining the molten steel and adjusting the contents of other alloy elements such as Co, Cr, Ni, etc. to within the range of the present invention.

[0033] 3) 7 to 9 minutes before the end of the vacuum treatment in the LF furnace, add 20% rare earth alloy 1.95 to 3.25 kg / ton steel into the LF furnace, and then blow argon for 5 to 10 minutes; then carry out RH treatment for 30 to 35 minutes, blow nitrogen throughout the RH treatment, control the [H] in the steel to ≤1.0ppm, [O] ≤20ppm, and the net circulation time before moving out is 6 to 10 minutes.

[0034] 4) Add RE and Sb elements before the end of RH treatment, and ensure that the added amount is 1.2 to 1.3 times the target control amount to ensure that the endpoint content can be controlled within the target range.

[0035] 2. Cast the molten steel obtained in step 1 into the desired continuous casting billet. In order to control the content of equiaxed crystals in the continuous casting billet, the tundish is superheated at 20-30°C. A lower superheat can reduce the solidification time of the molten steel, reduce the segregation of carbon, manganese and other elements in the center of the billet, reduce defects such as looseness and shrinkage of the billet, and ensure the Z-direction performance and fatigue resistance of the steel plate; adopt full-process protection casting, the continuous casting billet drawing speed is controlled at 1.1-1.3m / min, and the secondary cooling water ratio is 0.90-1.00m 3 / t, so that the proportion of equiaxed crystals in the continuous casting billet is greater than 30.0%, and electromagnetic stirring is used at the end of solidification to make the molten steel evenly stirred and achieve high-strength and high-density solidification as soon as possible. Heavy pressure is used in the continuous casting process, and the pressure reduction is 15.0-20.0mm.

[0036] 3. In order to control the grain size of the continuous casting billet to no more than 500μm, the continuous casting billet is cooled rapidly, with the start cooling temperature of 980-1000℃ and the cooling rate of 9.0-11.0℃ / s. After cooling to 690-730℃, it enters the slow cooling pit for slow cooling, and then cools to below 150℃ at a cooling rate of 3.0-20.0℃ / h.

[0037] 4. Send the continuous casting billet obtained in step 3 into the heating furnace for heating. The heating adopts a segmented heating process, enters the furnace at a furnace temperature of 600-700°C, and is kept warm for 2.0-3.0 hours to release the internal stress of the billet; a slow heating process is adopted below 950°C to further release the internal stress caused by the continuous casting billet cooling and heavy pressure, and to prevent the temperature stress caused by too fast heating. The heating rate is controlled at 8-10°C / min, and heated to 950°C and kept warm for 25-40 minutes; above 950°C, a process of rapid heating and appropriately extending the holding time is adopted to prevent the coarsening of austenite grains while allowing the alloy elements in the billet to fully diffuse and dissolve, further reducing element segregation, and the heating rate is controlled at 10-15°C / min, heated to 1200-1220°C for uniform temperature, and the holding time is 2.5-3.5 hours.

[0038] 5. The ingot is rolled into finished steel plate in three stages. In the first stage, in order to fully break the columnar crystals of the continuous casting ingot, a high-temperature slow rolling and large reduction process is adopted. The ingot is rolled directly after descaling. The rolling speed is 0.80-1.10 m / s. The reduction of each of the first three passes is greater than 35 mm. The billet is cooled by mill cooling water between each pass during the rolling process. The cooling time is 5-7 s. The final rolling temperature is 1050-1080 ° C. The thickness of the warm billet is 2.0-2. 5 times the thickness of the finished product. In order to suppress the growth of the grains in the intermediate billet, the warm billet is cooled by water spraying at a cooling rate of 6.0-8.0℃ / s, and is cooled to 15-25℃ above the second stage rolling temperature; the second stage rolling temperature is 900-920℃, the rolling speed is 1.2-1.6m / s, the final rolling temperature is 810-840℃, and the warm thickness is 1.5-2.0 times the thickness of the finished product; the third stage rolling temperature is 750-800℃, and the final rolling temperature is 720-740℃.

[0039] 6. The steel plate after rolling adopts the rapid cooling (ACC) process, the cooling rate is 10.0~15.0℃ / s, and the steel plate red-return temperature is 500~550℃, which can maintain the fine grains after rolling and prevent the grains from growing.

[0040] 7. The steel plate is subjected to quenching + tempering heat treatment, with a quenching temperature of 900-920°C and a holding time of 1.0-1.3 min / mm; a tempering temperature of 580-600°C and a holding time of 2.0-2.5 min / mm.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention adopts a low carbon and relatively high manganese content design, controls the range of composite added alloy elements to be 0.12≥(Nb+V+Ti) / Mn≥0.07, 6.0≥Si / Al≥2.0, (Cu+P+Co) / Cr≥0.54, 5≥Cr / Co≥3, Ni / Cr≥0.8, 36Nb / Mn≥0.90, (Nb+V+Ti+Als) / N≥13, Ni / Cu≥2.2, (Nb+V+Ti) / RE≥3.5, RE / P≥1.3; improves the strength of the steel while ensuring that the steel plate has excellent low temperature toughness, corrosion resistance and fatigue resistance. The influence of element segregation on fatigue performance and low temperature performance of steel plate is controlled by optimizing continuous casting process. Slow and long segmented heating process is adopted for heating. Three-stage process of high temperature, slow and large reduction, medium temperature rapid recrystallization zone rolling and low temperature rolling is adopted for rolling. In combination with subsequent ACC controlled cooling process and quenching + tempering heat treatment, the strength of steel plate is ensured by fine grain strengthening, dislocation strengthening, solid solution strengthening and second phase strengthening. Good low temperature toughness of steel plate is ensured by grain refinement. Good corrosion resistance of steel plate is ensured by oxides formed by elements such as Cr, Ni and Co. Fatigue resistance of steel plate is improved by controlling fine dispersed two-phase particles and element segregation. The segregation of P element is reduced and the corrosion resistance of steel plate is improved by adding a small amount of Sb, RE and P elements.

[0043] 1. A composite addition of Co, Ni and Cr elements is proposed, and the steel plate has good comprehensive mechanical properties, yield strength of 690-750MPa, elongation ≥20%, and impact energy of 200J or more at -80℃;

[0044] 2. A composite addition of a small amount of Sb, RE and P elements is proposed to improve the corrosion resistance of the steel plate, and its marine atmospheric corrosion rate is less than 0.090 mm / a;

[0045] 3. The steel plate has good fatigue resistance, and the fatigue life is more than 2 million times under the peak stress of 350MPa;

[0046] 4. The thickness range that can be produced is wide, the maximum thickness can reach 150mm, and the Z-direction performance is greater than or equal to 40%. DETAILED DESCRIPTION

[0047] The present invention is described in more detail below through examples.

[0048] According to the above chemical composition and production process, the actual smelting composition of the present invention is shown in Table 1, the actual process parameters of the present invention are shown in Tables 2 to 7, and the actual properties are shown in Table 8.

[0049] Table 1 Melting composition, Wt%

[0050]

[0051] Table 2 Steelmaking process parameters

[0052]

[0053]

[0054] Table 3 Continuous casting process parameters

[0055]

[0056] Table 4 Heating process parameters

[0057]

[0058] Table 5 First stage rolling process parameters

[0059]

[0060]

[0061] Table 6 Process parameters of second and third stage rolling and post-rolling cooling

[0062]

[0063] Table 7 Heat treatment process

[0064]

[0065] Table 8 Physical performance

[0066]

[0067]

[0068] As can be seen from Table 8, the yield strength of the embodiment steel of the present invention is 694-748MPa, all reaching the design strength of 690MPa or above, the elongation is greater than 20%, the Z-direction performance is greater than 40%, and the -80℃ impact energy is greater than 200J, indicating that the strength and toughness of each embodiment steel not only meet the design requirements, but also have a certain margin. The fatigue performance test was carried out under a conventional environment using an Instron8802 fatigue testing machine, the loading mode was tension-compression fatigue, the stress ratio Rs=-1, the test frequency was 20Hz, and the fatigue life number under the peak stress of 350MPa load was greater than 2 million times. According to the test method specified in GBT 19746-2005, the invention steel was subjected to a 168-hour cycle immersion rapid corrosion evaluation test, and the weight loss method was used to evaluate the corrosion resistance of the invention steel, and the annual average corrosion rate converted was not less than 0.09mm / a.

[0069] It is to be noted that the above embodiments are only for illustrating the technical concept and features of the present invention, and are not intended to limit the present invention. Any equivalent replacement or modification that does not deviate from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A high-performance fatigue-resistant marine engineering steel, characterized in that: The chemical composition of steel is as follows by weight: C: 0.02% ~ 0.07%, Si: 0.10% ~ 0.25%, Mn: 1.75% ~ 2.50%, P: 0.022% ~ 0.026%, S: ≤ 0.008%, Nb: 0.065% ~ 0.070%, V: 0.070% ~ 0.075%, Ti: 0.035% ~ 0.042%, Cr: 1.25% ~ 1.45%, Ni: 1.25% ~ 1.45%, Co: 0.30% ~ 0.35%, Als: 0.035% ~ 0.045%, N: 0.0150% ~ 0.0160%, Cu: 0.45% ~ 0.50%, Sb: 0.03% ~ 0.05%, RE: 0.03%~0.05%, among which 0.11≥(Nb+V+Ti) / Mn≥0.07, 6.0≥Si / Al≥2.0, (Cu+P+Co) / Cr≥0.54, 5≥Cr / Co≥3, Ni / Cr≥0.8, 36Nb / Mn≥0.90, (Nb+V+Ti+Als) / N≥13, Ni / Cu≥2.2, (Nb+V+Ti) / RE≥3.5, RE / P≥1.3, and the rest are Fe and unavoidable impurities.

2. The high performance fatigue resistant marine engineering steel according to claim 1, characterized in that: The yield strength of the steel is 690-750MPa, the elongation is ≥20%, and the impact energy at -80℃ is ≥200J.

3. The high performance fatigue resistant marine engineering steel according to claim 1, characterized in that: The marine atmospheric corrosion resistance rate of steel is less than 0.090mm / a.

4. The high performance fatigue resistant marine engineering steel according to claim 1, characterized in that: The fatigue life is greater than 2 million times under the peak stress of 350MPa.

5. The high performance fatigue resistant marine engineering 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 for producing high-performance fatigue-resistant marine engineering steel according to any one of claims 1 to 5, comprising smelting, slab continuous casting, slab heating, rolling and cooling, characterized in that: During the slab continuous casting process, the continuous casting billet is cooled rapidly, with the cooling temperature at 980-1000℃ and the cooling rate at 9.0-11.0℃ / s. After cooling to 690-730℃, it enters the slow cooling pit for slow cooling, and then cools to below 150℃ at a cooling rate of 3.0-20.0℃ / h. The billet adopts a segmented heating process, enters the furnace at a furnace temperature of 600-700℃, and is kept warm for 2.0-3.0h. The heating rate below 950℃ is controlled at 8-10℃ / min. Heat to 950℃ and keep warm for 25-40min; control the heating speed above 950℃ at 10-15℃ / min, heat to 1200-1220℃ for even temperature, and keep warm for 2.5-3.5h; roll the ingot into finished steel plate in three stages, the ingot in the first stage is rolled directly after being descaled after being taken out of the furnace, the rolling speed is 0.80-1.10m / s, the reduction of each of the first three passes is more than 35mm, and the mill cooling water is used between each pass during the rolling process The billet is cooled for 5 to 7 seconds, the final rolling temperature is 1050 to 1080°C, the thickness of the warm billet is 2.0 to 2.5 times the thickness of the finished product, the warm billet is cooled by water spraying, the cooling rate is 6.0 to 8.0°C / s, and it is cooled to 15 to 25°C above the second stage rolling temperature; the second stage rolling temperature is 900 to 920°C, the rolling speed is 1.2 to 1.6 m / s, the final rolling temperature is 810 to 840°C, and the warm thickness is 1.5 to 2.0 times the finished product thickness; the third stage rolling temperature is 750-800℃, and the final rolling temperature is 720-740℃; the steel plate after rolling adopts a rapid cooling process, the cooling rate is 10.0-15.0℃ / s, and the steel plate red-returning temperature is 500-550℃; the steel plate is subjected to quenching + tempering heat treatment, the quenching temperature is 900-920℃, the holding time is 1.0-1.3min / mm; the tempering temperature is 580-600℃, and the holding time is 2.0-2.5min / mm.

7. The method for producing high-performance fatigue-resistant marine engineering steel according to claim 6, characterized in that: During the smelting process, the molten iron is first subjected to a desulfurization pretreatment. After desulfurization, the S in the molten iron is ≤0.0025%. A furnace top and bottom composite blowing process is adopted, and the converter tapping temperature is 1630-1650°C. After that, Si-Ca wire feeding treatment is carried out, and the Ca content is controlled at 0.0015%-0.0025%, and the free O content should be controlled below 5ppm; 20% rare earth alloy 1.95-3.25kg / ton steel is added to the LF furnace 7-9min before the end of the vacuum treatment in the LF furnace, and then argon is blown for 5-10min; then RH treatment is carried out, the RH treatment time is 30-35min, nitrogen is blown throughout the RH treatment, and the net circulation time before moving out is 6-10min.

8. The method for producing high-performance fatigue-resistant marine engineering steel according to claim 6, characterized in that: During the continuous casting of slabs, the tundish is superheated at 20-30°C, and full-process protection casting is adopted. The continuous casting billet drawing speed is controlled at 1.1-1.3m / min, the secondary cooling water ratio is 0.90-1.00m3 / t, and heavy pressure is adopted during the continuous casting process, with a reduction of 15.0-20.0mm.

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