460mpa grade offshore steel having excellent hydrogen-induced cracking resistance and method for manufacturing the same

Abstract

The application discloses a 460MPa-grade offshore steel with excellent hydrogen-induced cracking resistance and a manufacturing method thereof, and belongs to the technical field of steel material preparation. The offshore steel with good comprehensive mechanical properties is prepared through coupling design of alloy component design-smelting-controlled rolling-controlled cooling-quenching and tempering heat treatment process, and the problems that the strength, plasticity, low-temperature toughness (-40 DEG C) and hydrogen-induced cracking resistance of the 460MPa-grade steel plate are difficult to match and reconcile are solved. The yield strength of the produced steel plate is greater than or equal to 460MPa, the tensile strength is 540-720MPa, the elongation is greater than or equal to 19%, the Z-direction reduction of area is greater than or equal to 60%, the Charpy impact energy of the core of the steel plate at -40 DEG C is greater than or equal to 100J, and the hydrogen-induced cracking resistance is that the CSR is less than or equal to 2%, the CLR is less than or equal to 15%, and the CTR is less than or equal to 5%.

Description

Technical Field

[0001] This invention belongs to the field of steel material preparation technology, and specifically relates to a 460MPa grade marine steel with excellent resistance to hydrogen-induced cracking and its manufacturing method. Background Technology

[0002] Steel, as a key structural material for marine engineering equipment, is widely used in offshore wind power, production platforms, and subsea pipelines. Marine engineering equipment typically has a service life of 30 years, 50% longer than traditional ships. The operating environment of marine engineering equipment is extremely harsh, subject not only to its own weight but also to the effects of service conditions. This necessitates that marine engineering steel designs and material selections consider specific sea conditions. How to simultaneously achieve ultra-high strength, high toughness, and high resistance to hydrogen-induced cracking has become a core issue and technical challenge in the development of deep-sea engineering steel. To ensure the safe operation of marine engineering platforms in complex environments, there is an urgent need to develop ultra-high strength marine engineering steel with excellent resistance to hydrogen-induced cracking.

[0003] The invention patent CN105803327B, entitled "An Economical HIC-Resistant X90 Pipeline Steel Plate and Its Manufacturing Method", proposes an X90-grade pipeline steel plate with a maximum thickness of 20mm and an HIC-resistant steel manufacturing method. However, its thickness is relatively small and cannot meet the large thickness requirements of ultra-high strength marine engineering steel used in marine engineering platform equipment. The invention patent CN106521332A, entitled "A Steel Plate for Stress-Directed Hydrogen-Induced Cracking Resistance and Its Production Method", proposes a steel plate for stress-directed hydrogen-induced cracking resistance. It has the characteristics of high purity, excellent impact toughness at -20℃, excellent resistance to lamellar tearing, and excellent resistance to stress-directed hydrogen-induced cracking. However, it cannot guarantee low-temperature toughness at -40℃.

[0004] The patent comparison above shows that the marine steels currently available with excellent resistance to hydrogen-induced cracking still have the following shortcomings: 1. The product thickness is relatively small, the strength level is relatively low, and the application range is narrow; 2. The product has a low ultra-low temperature toughness level, which cannot meet the requirements of marine steel to take into account both ultra-high strength and high toughness. Summary of the Invention

[0005] To address the problems in the background art, the present invention aims to provide a 460MPa grade marine engineering steel with excellent resistance to hydrogen-induced cracking and its manufacturing method. The present invention employs a coupled design of alloy composition design, smelting, controlled rolling, controlled cooling, and tempering heat treatment processes, ultimately obtaining a 460MPa grade marine engineering steel with excellent resistance to hydrogen-induced cracking and a thickness of up to 80mm. The resulting steel plate exhibits ultra-high strength (yield strength ≥ 460MPa, tensile strength 540~720MPa, elongation after fracture ≥ 19%), excellent low-temperature toughness (core impact energy ≥ 100J at -40℃), excellent Z-direction properties (Z-direction reduction of area ≥ 60%), excellent resistance to hydrogen-induced cracking (CSR ≤ 2%, CLR ≤ 15%, CTR ≤ 5%), and uniform microstructure and properties.

[0006] The objective of this invention is achieved through the following means:

[0007] This invention provides a 460MPa grade marine engineering steel with excellent resistance to hydrogen-induced cracking. The chemical composition and mass percentage of the marine engineering steel are as follows: C: 0.05%~0.09%; Si: 0.10%~0.30%; Mn: 0.60%~0.95%; P: ≤0.012%; S≤0.002%; Cu: 0.10%~0.40%; Ni: 0.20%~0.50%; Cr: 0.20%~0.09% 0.50%; Nb: 0.015–0.03%; V: 0.015–0.03%; Mo: 0.10%–0.30%; Ti: 0.007%–0.02%; B: 0.0007%–0.002%; Als: 0.01%–0.025%; O ≤ 0.001%; ​​N ≤ 0.005%, balance being Fe and unavoidable impurities, Ceq ≤ 0.47%, Pcm ≤ 0.24%.

[0008] Where, Ceq=C+Mn / 6+(Cu+Ni) / 15+(Cr+Mo+V) / 5,

[0009] Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

[0010] The mechanisms of action of each alloy component in the marine engineering steel of this invention are as follows:

[0011] Carbon (C) is an essential element for ensuring strength and hardenability. It plays a significant role in improving the strength of steel through solid solution strengthening and precipitation strengthening. However, an increase in carbon content seriously affects the weldability and low-temperature toughness of steel. From the perspective of product performance, it is preferable to control the C content between 0.05% and 0.09%.

[0012] Si: As a solid solution strengthening element, although Si is beneficial to improving the strength of steel plates and their oxidation resistance at high temperatures, Si promotes packet size coarsening, which seriously impairs the low-temperature toughness, elongation and weldability of ultra-high strength steel plates. Considering the economics and operability of steelmaking, the preferred Si content is 0.10% to 0.30%.

[0013] Mn: As the most important alloying element, in addition to improving the strength of steel plates, it also has the functions of expanding the austenite phase region, lowering the Ar3 point temperature, refining ferrite grains, and improving the low-temperature toughness of steel plates. However, when the quality of Mn is too high, Mn segregation and strip-shaped MnS are easily formed, resulting in poor low-temperature toughness and resistance to hydrogen-induced cracking in the core of thick plates, and a decrease in the performance of the weld heat-affected zone. Therefore, the preferred Mn content range is 0.60% to 0.95%.

[0014] P: is an element that has an adverse effect on the impact value. It can impair low-temperature toughness by segregating in the center of the slab and agglomerating at grain boundaries. The material content of this invention is controlled to be no higher than 0.012%.

[0015] S: is an element that has an adverse effect on the impact value and can form sulfide inclusions, which can become crack initiation sites. The material in this invention is controlled to be no higher than 0.002%.

[0016] Cu: ε-Cu precipitation strengthening can significantly improve the strength of steel. Appropriate amounts of Cu can increase strength without compromising impact toughness. Cu is also an austenite-forming element, expanding the austenite phase region while promoting austenite formation and stability during tempering. Cu precipitates can increase the density of effective hydrogen traps, resulting in smaller hydrogen-induced cracks. When used with Ni, it can significantly reduce Ar3 and prevent hot brittleness; however, excessive Cu content can cause hot brittleness, which is detrimental to the toughness of the base material and the heat-affected zone. Therefore, the Cu content in this invention ranges from 0.10% to 0.40%.

[0017] Ni: Nickel dissolves in austenite, inhibiting austenite recrystallization, refining austenite grains, and improving the low-temperature toughness of steel plates. Ni can reduce the diffusion rate of various elements in steel, thus delaying the decomposition and transformation of austenite, thereby improving the hardenability of steel. The simultaneous addition of Ni and Mo can improve the toughness of steel while increasing its strength. However, excessive Ni content will increase Ceq and Pcm, affecting weldability. Therefore, the Ni content in this invention is controlled at 0.20% to 0.50%.

[0018] Cr: It can improve the hardenability and strength of steel plates. The presence of Cr can enhance the tempering stability of steel and ensure that the steel obtains tempered bainite structure during high-temperature tempering. Cr has a similar solid solution strengthening effect to Mn and is not prone to segregation. However, if the Cr content is too high, it will increase the tendency of temper brittleness and increase the difficulty of welding. If the content is too low, it will not be able to effectively exert its strengthening effect. In this invention, the Cr content is controlled at 0.20% to 0.50%.

[0019] The addition of niobium (Nb) is to promote grain refinement of the microstructure in steel rolling, which can simultaneously improve strength and toughness. Niobium can effectively refine the microstructure by inhibiting austenite recrystallization during controlled rolling and strengthen the matrix through precipitation. At the same time, the appearance of Nb precipitates increases the density of effective hydrogen traps, making hydrogen-induced cracks smaller. The combined addition of Nb and B effectively suppresses austenite recrystallization and grain refinement during rolling while also inhibiting C diffusion. This effectively suppresses the precipitation of M23(C,B)6 at austenite grain boundaries, ensuring effective segregation of B at ferrite nucleation sites, improving the hardenability of the steel, and giving it higher strength and better low-temperature toughness. The addition of Nb and the formation of Nb(C,N) in the steel suppress the appearance of coarse M23(C,B)6 structures. This reduces C diffusion, improves B utilization efficiency, and promotes the homogenization of the microstructure. However, when the Nb content exceeds a certain range, MA islands will form in the welded HAZ, which is detrimental to toughness. The Nb content in this invention is preferably controlled at 0.015-0.03%.

[0020] V: Adding V to steel can refine the grain structure, improve strength and toughness, and enhance the steel plate's resistance to tempering softening during tempering. The effect is not obvious when the addition amount is less than 0.01%. When the V content is too high, the toughness and weldability of the steel decrease. With an appropriate amount of N content, V can be fully precipitated, significantly reducing the particle size and spacing in the steel, which can produce precipitation strengthening and improve strength. Therefore, this invention controls the V content to be between 0.015% and 0.03%.

[0021] Mo (Mo) can shift the C-curve of steel, thereby significantly improving its hardenability. It promotes the formation of martensite or bainite with a large number of dislocations within the grains over a wider cooling range, resulting in phase transformation strengthening and dislocation strengthening effects, significantly improving the strength and microstructure uniformity of the steel. In this invention, the combined addition of Mo and Nb not only has the strengthening effect of adding molybdenum and niobium alone, but molybdenum can also segregate at the NbC matrix interface, preventing the coarsening of NbC particles. The combined addition of Mo and B increases the content of effective (solid-dissolved) B in the steel, inhibits the diffusion of C to the grain boundaries, inhibits the precipitation and growth of M23(C,B)6 at the grain boundaries, promotes the segregation of B at the grain boundaries, reduces the nucleation sites of ferrite, and improves the hardenability of the steel. The combined addition of Mo and Ni can improve the toughness of the steel while increasing its strength. However, with the increase of Mo, the number of Mo-containing carbides also increases. The carbides distributed at the grain boundaries disrupt the continuity of the matrix and deteriorate the toughness of the steel. Therefore, the Mo content in this invention is controlled at 0.10% to 0.30%.

[0022] Ti: Inhibits excessive austenite grain growth during slab heating, improving steel toughness. Ti also helps to solidify nitrogen (N), ensuring a certain amount of dissolved boron (B) in the steel and improving hardenability. However, excessive Ti content can lead to TiC precipitation as TiC on martensite / bainite laths and grain boundaries, severely degrading the low-temperature toughness of the steel. Therefore, the Ti content in this invention is controlled between 0.007% and 0.02%.

[0023] B: It can improve the hardenability and strength of steel plates, but if the B content is too high, it will form coarse BN particles that are detrimental to hardenability and toughness. At the same time, it will also affect the weldability and surface quality of steel plates. Therefore, the Mo content in this invention is controlled at 0.0007% to 0.002%.

[0024] Als: A deoxidizing and grain-refining element. At high temperatures, Al forms fine AlN precipitates, which inhibit austenite grain growth during the austenitization of slabs / steel plates, thereby refining the austenite grains and improving the toughness of steel at low temperatures. Excessive Al content leads to the formation of larger Al oxides, reducing the low-temperature impact performance of the steel plate. At the same time, the slab is prone to edge and corner cracks during continuous casting. The preferred Al content is controlled between 0.01% and 0.025%.

[0025] O: is an element that has an adverse effect on impact toughness. It combines with other elements in steel to form non-metallic inclusions, which become crack initiation sites. In this invention, the O content is controlled to be no higher than 0.001%.

[0026] N: N element will form BN with B element and form coarse ALN with AL, which precipitates along the original austenite grain boundary, affecting the hardenability and low temperature impact toughness of steel. In this invention, the N content is controlled to be no higher than 0.005%.

[0027] Based on the above technical solution, the marine steel further has a yield strength ≥460MPa, tensile strength 540-720MPa, elongation at section ≥19%, Z-direction reduction of area ≥60%, Charpy impact energy of steel plate core at -40℃ ≥100J, and resistance to hydrogen-induced cracking CSR≤2%, CLR≤15%, and CTR≤5%.

[0028] This invention also provides a method for manufacturing the above-mentioned 460MPa grade marine steel with excellent resistance to hydrogen-induced cracking, which mainly includes the following steps: smelting process → continuous casting and billet slow cooling process → rolling process → rapid cooling process → slow cooling process → quenching process → tempering process.

[0029] Based on the above technical solution, further, the molten iron is desulfurized before the smelting process, and the smelting process includes converter smelting, ladle refining and vacuum treatment.

[0030] Based on the above technical solution, further, in the continuous casting and billet slow cooling process, the superheat of the molten steel in the ladle is 25-30℃, the casting is protected throughout the process, the light reduction is 6-9mm, the thickness of the continuous casting billet is 250-300mm, the continuous casting billet is stacked and slow cooled after leaving the line, the stacking temperature is ≥650℃, and the stacking slow cooling rate is 5-6℃ / h.

[0031] Based on the above technical solution, furthermore, in the rolling process, the continuously cast billet adopts a 4-stage heating process, namely a preheating stage, heating stage 1, heating stage 2, and soaking stage. The heating temperature of the preheating stage is 750-820℃, the heating temperature of heating stage 1 is 900-1080℃, the heating temperature of heating stage 2 is 1150-1200℃, the heating temperature of the soaking stage is 1050-1150℃, the heating time of the preheating stage is 0.1-0.2 min / mm, the heating time of heating stage 1 is 0.2-0.4 min / mm, the heating time of heating stage 2 is 0.1-0.3 min / mm, and the heating time of the soaking stage is 0.3-0.5 min / mm.

[0032] The rolling process is carried out in two stages. The first stage rolling temperature is 950-1000℃, and the single-pass reduction rate is ≥15% except for the widening pass. The thickness of the intermediate billet is 2-3 times the thickness of the finished product. The intermediate billet is water-cooled with a cooling rate of ≥2℃ / s. The second stage rolling temperature is 760-790℃, the single-pass reduction rate is ≥11%, and the final rolling temperature is 720-780℃.

[0033] Based on the above technical solution, the billet is further subjected to high-pressure water descaling 1 to 5 times after being heated and tapped out of the furnace, which removes the iron oxide scale on the surface and reduces the temperature of the continuous casting billet.

[0034] Based on the above technical solution, the final rolled steel plate directly enters the rapid cooling process, with an average cooling rate of ≥3℃ / s and a reddening temperature of 400~500℃.

[0035] Based on the above technical solution, the rapid cooling process further adopts the DQ+ACC rapid cooling system.

[0036] Based on the above technical solution, further, in the slow cooling process, the temperature of the tank entering the tank is not lower than 350℃, and the slow cooling time is not less than 24 hours.

[0037] Based on the above technical solution, further, in the quenching process, a two-stage heating quenching heat treatment is adopted. The first stage is held at a temperature of 730-770℃, and after the steel plate thickness reaches 1 / 2 of the temperature, it is held for 5-10 minutes. The second stage is held at a temperature of 880-920℃, and after the steel plate thickness reaches 1 / 2 of the temperature, it is held for 10-30 minutes. After quenching, the plate is taken out of the furnace and quenched to room temperature.

[0038] Based on the above technical solution, further, in the tempering process, the tempering temperature is 580~620℃, the furnace time is 3~5min / mm, and after exiting the furnace, it is air-cooled to obtain the final product.

[0039] The advantages of this invention over the prior art are as follows:

[0040] (1) This invention uses a coupled design of alloy composition design, smelting, controlled rolling, controlled cooling and tempering heat treatment processes to prepare steel plates with good comprehensive mechanical properties. It solves the problem of difficulty in matching and harmonizing the strength, plasticity, low temperature toughness (-40℃) and resistance to hydrogen-induced cracking of 460MPa grade steel plates. The produced steel plates have a yield strength ≥460MPa, tensile strength 540-720MPa, elongation at section ≥19%, Z-direction reduction of area ≥60%, Charpy impact energy of the steel plate core at -40℃ ≥100J, and resistance to hydrogen-induced cracking CSR≤2%, CLR≤15%, and CTR≤5%.

[0041] (2) This invention fully leverages the technical equipment advantages of the heavy plate rolling mill and heat treatment unit, and combined with 250-360mm thick continuous casting slabs, the developed ultra-high strength and high toughness marine engineering steel thick plate has a maximum thickness of up to 80mm.

[0042] (3) The present invention adopts a reasonable rolling process and offline quenching and tempering process. Compared with online quenching of ultra-high strength steel of the same strength, offline quenching can accurately control the temperature at the start of quenching, and the temperature of the whole plate is uniform, resulting in more stable performance of the produced steel plate.

[0043] (4) The microstructure of the steel plate is tempered bainite. Attached Figure Description

[0044] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0045] Figure 1This is a schematic diagram of the two-stage heat preservation and quenching process in the embodiment;

[0046] Figure 2 Metallographic image (500x) of the marine steel prepared in Example 13. Detailed Implementation

[0047] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0048] Examples 1-14

[0049] This embodiment provides a method for preparing 460MPa grade marine engineering steel with excellent resistance to hydrogen-induced cracking. The chemical composition and weight percentage of the marine engineering steel in this embodiment are shown in Table 1, and the carbon equivalent and welding crack sensitivity coefficient of the marine engineering steel are shown in Table 2.

[0050] Table 1 shows the chemical composition and weight percentage (wt%) of the marine steel in the examples.

[0051] Example C Si Mn P S Cu Ni Cr Nb V Mo Ti B Alt O N 1 0.089 0.23 0.65 0.008 0.002 0.25 0.44 0.36 0.023 0.025 0.24 0.014 0.0008 0.014 0.0009 0.0031 2 0.061 0.26 0.69 0.008 0.002 0.39 0.39 0.44 0.018 0.019 0.19 0.012 0.0009 0.012 0.0008 0.0024 3 0.079 0.29 0.79 0.008 0.002 0.19 0.29 0.22 0.029 0.026 0.14 0.016 0.001 0.011 0.001 0.0033 4 0.069 0.19 0.71 0.008 0.002 0.22 0.31 0.29 0.015 0.016 0.21 0.009 0.0012 0.019 0.0007 0.0035 5 0.055 0.14 0.81 0.008 0.002 0.31 0.41 0.39 0.021 0.021 0.25 0.017 0.0014 0.02 0.0008 0.0042 6 0.051 0.11 0.88 0.008 0.002 0.18 0.22 0.38 0.019 0.024 0.22 0.014 0.0013 0.021 0.0009 0.0041 7 0.071 0.21 0.61 0.008 0.002 0.27 0.36 0.41 0.022 0.019 0.18 0.013 0.0016 0.024 0.0007 0.0034 8 0.081 0.24 0.69 0.008 0.002 0.16 0.26 0.31 0.028 0.018 0.17 0.011 0.0018 0.022 0.0009 0.0028 9 0.062 0.16 0.79 0.008 0.002 0.36 0.44 0.29 0.017 0.019 0.18 0.015 0.0011 0.014 0.0007 0.0035 10 0.059 0.14 0.88 0.008 0.002 0.24 0.34 0.32 0.022 0.022 0.24 0.013 0.0019 0.013 0.0007 0.0033 11 0.084 0.18 0.76 0.008 0.002 0.14 0.21 0.24 0.025 0.029 0.15 0.016 0.0012 0.023 0.0008 0.0032 12 0.075 0.13 0.79 0.008 0.002 0.29 0.37 0.21 0.019 0.018 0.16 0.014 0.001 0.018 0.0009 0.0041 13 0.071 0.19 0.91 0.008 0.002 0.19 0.42 0.41 0.019 0.024 0.24 0.009 0.0009 0.017 0.0007 0.0043 14 0.081 0.14 0.79 0.008 0.002 0.36 0.37 0.36 0.021 0.021 0.21 0.009 0.0011 0.019 0.0008 0.0035

[0052] Table 2 shows the carbon equivalent and welding crack sensitivity coefficient of the marine steel in the examples.

[0053]

[0054]

[0055] Includes the following steps:

[0056] 1) Smelting, continuous casting and slow cooling of billet: The production process adopts deep desulfurization of molten iron, converter smelting, ladle refining, vacuum treatment and continuous casting. The superheat of molten steel in the tundish is shown in Table 3. The casting process is protected throughout, and electromagnetic stirring is turned on and combined with a light reduction process. The amount of light reduction is shown in Table 3. After continuous casting, a continuous casting billet is obtained with a thickness of 250-300 mm. After the continuous casting billet is removed from the line, it is stacked and slow cooled. The stacking temperature and stacking slow cooling rate are shown in Table 3.

[0057] Table 3 shows the continuous casting and billet slow cooling stacking process parameters for marine engineering steel in the embodiments.

[0058]

[0059] 2) Rolling process: The continuously cast billet is heated in four stages: preheating stage, heating stage 1, heating stage 2, and soaking stage. The heating temperatures and times for the preheating stage, heating stage 1, heating stage 2, and soaking stage are shown in Table 4. After the billet exits the furnace, it undergoes 2-3 high-pressure water descaling passes to remove surface iron oxide scale and lower the billet temperature. A two-stage rolling process is adopted. The starting rolling temperature and minimum single-pass reduction rate (excluding the widening pass) for the first stage are shown in Table 5. This improves the as-cast microstructure of the slab, reduces the billet thickness before heating, and shortens the heating time of the steel plate. The thickness of the intermediate billet is 2.5 times the thickness of the finished product. The intermediate billet is water-cooled, and the cooling rate is shown in Table 5. The starting rolling temperature, minimum single-pass reduction rate, and final rolling temperature for the second stage are shown in Table 5. The two-stage rolling process controls the uniform and refined phase transformation microstructure, preparing the initial microstructure for tempering heat treatment.

[0060] 3) Cooling process: The steel plate is directly cooled after final rolling using the DQ+ACC rapid cooling system. The average cooling rate and reddening temperature are shown in Table 5.

[0061] Table 4 shows the slab heating process parameters for marine engineering steel plates in the embodiments.

[0062]

[0063] Table 5 shows the rolling and cooling process parameters for marine engineering steel plates in the embodiments.

[0064]

[0065] 4) Slow cooling process: After cooling is completed, immediately place the product into a slow cooling tank. The temperature of the product entering the tank should not be lower than 350℃, and the slow cooling time should not be less than 24 hours.

[0066] 5) Quenching process: The steel plate is subjected to two-stage heating and quenching heat treatment. The steel plate thickness, the first stage holding temperature and the holding time after the steel plate thickness reaches 1 / 2 of the temperature are shown in Table 6. Then, it enters the second stage. The second stage holding temperature and the holding time after the steel plate thickness reaches 1 / 2 of the temperature are shown in Table 6. After quenching, the plate is taken out of the furnace and quenched to room temperature.

[0067] 6) Tempering process: The steel plate is tempered. The tempering temperature and furnace time are shown in Table 6. After being taken out of the furnace, it is air-cooled to obtain the finished steel plate. The mechanical properties and hydrogen-induced cracking resistance of the finished steel plate are shown in Tables 7-8.

[0068] Table 6 shows the heat treatment process parameters for marine engineering steel plates in the embodiments.

[0069]

[0070] Table 7 Mechanical properties of marine steel plates in the examples

[0071]

[0072] Table 8 shows the hydrogen-induced cracking resistance of the marine steel plates in the examples.

[0073]

[0074]

[0075] Note: The solution used was NACEA, which, according to relevant standards, consisted of 5% NaCl + 0.5% CH3COOH + saturated H2S aqueous solution and was continuously soaked for 96 hours.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A 460MPa grade marine steel with excellent resistance to hydrogen-induced cracking, characterized in that, The chemical composition and mass percentage of the marine engineering steel are as follows: C: 0.051%–0.09%; Si: 0.10%–0.30%; Mn: 0.60%–0.88%; P: ≤0.012%; S ≤0.002%; Cu: 0.31%–0.40%; Ni: 0.31%–0.50%; Cr: 0.20%–0.50%; Nb: 0.015%–0.03%; V：0.015～0.03％； Mo: 0.21%–0.30%; Ti: 0.007%–0.02%; B: 0.0007%–0.002%; Als: 0.01%–0.025%; O ≤ 0.001%; ​​N ≤ 0.005%, balance being Fe and unavoidable impurities, Ceq ≤ 0.47%, Pcm ≤ 0.24%. Where, Ceq=C+Mn / 6+(Cu+Ni) / 15+(Cr+Mo+V) / 5, Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B; The manufacturing method of the 460MPa grade marine steel with excellent resistance to hydrogen-induced cracking mainly includes the following steps: smelting process → continuous casting and billet slow cooling process → rolling process → rapid cooling process → slow cooling process → quenching process → tempering process. In the rolling process, the continuously cast billet is heated in four stages: preheating stage, heating stage 1, heating stage 2, and soaking stage. The heating temperature of the preheating stage is 750-820℃, the heating temperature of heating stage 1 is 900-1080℃, the heating temperature of heating stage 2 is 1150-1200℃, and the heating temperature of the soaking stage is 1050-1150℃. The heating time of the preheating stage is 0.1-0.2 min / mm, the heating time of heating stage 1 is 0.2-0.4 min / mm, the heating time of heating stage 2 is 0.1-0.3 min / mm, and the heating time of the soaking stage is 0.3-0.5 min / mm. The rolling process is carried out in two stages. The first stage rolling temperature is 950-978℃, and the single-pass reduction rate is ≥15% except for the widening pass. The thickness of the intermediate billet is 2-3 times the thickness of the finished product. The intermediate billet is water-cooled with a cooling rate of ≥2℃ / s. The second stage rolling temperature is 760-786℃, the single-pass reduction rate is ≥11%, and the final rolling temperature is 720-770℃. In the continuous casting and billet slow cooling process, the superheat of molten steel in the tundish is 25-30℃, the casting is protected throughout the process, the light reduction is 6-9mm, the thickness of the continuous casting billet is 250-300mm, the continuous casting billet is stacked and slow cooled after it leaves the line, the stacking temperature is ≥650℃, and the stacking slow cooling rate is 5-6℃ / h. After final rolling, the steel plate directly enters the rapid cooling process, with an average cooling rate of ≥3℃ / s and a reddening temperature of 400~500℃; in the slow cooling process, the temperature of the steel plate entering the tank is not lower than 350℃ and the slow cooling time is not less than 24 hours. In the quenching process, a two-stage heating and quenching heat treatment is adopted. The first stage is held at a temperature of 730-770℃, and after the steel plate thickness reaches 1 / 2 of the temperature, it is held for 5-10 minutes. The second stage is held at a temperature of 880-920℃, and after the steel plate thickness reaches 1 / 2 of the temperature, it is held for 10-30 minutes. After quenching, the plate is taken out of the furnace and then quenched to room temperature. In the tempering process, the tempering temperature is 580-620℃, the furnace time is 3-5 min / mm, and after taking it out of the furnace, it is air-cooled to obtain the final product.

2. The 460MPa grade marine steel with excellent resistance to hydrogen-induced cracking as described in claim 1, characterized in that, The molten iron undergoes deep desulfurization before the smelting process, which includes converter smelting, ladle refining, and vacuum treatment.

3. The 460MPa grade marine steel with excellent resistance to hydrogen-induced cracking as described in claim 1, characterized in that, After being heated and removed from the furnace, the billet is descaled with high-pressure water for 1 to 5 times.

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