Corrosion-resistant offshore steel plate and production method thereof

Abstract

The present application discloses a corrosion-resistant marine steel plate and a production method thereof, comprising: steelmaking, wherein the molten steel contains 0.05-0.10% C, 0.2-0.5% Si, 0.2-0.5% Mn, 0.05-0.10% P, ≤0.005% S, 0.2-0.5% Cr, 0.02-0.05% Ni, 0.2-0.5% Cu, 0.02-0.05% Al, and 0.02-0.05% Ti. 0.02~0.05%, N≤0.005%, 0.5%≤Cr+Cu+P+Al≤1.0%, 0.05%≤Ni+Ti≤0.08%, Pcm≤0.19%, Ceq≤0.31%; continuous casting; heating, furnace time ≥220min, and control the furnace temperature of each heating section in the furnace; two-stage rolling, the thickness of the intermediate billet T=4t~5t, t is the thickness of the steel plate; controlled cooling, cooling rate ≥25℃ / s.

Description

Technical Field

[0001] The present application belongs to the technical field of steel preparation, and specifically relates to a corrosion-resistant marine engineering steel plate and a production method thereof. Background Art

[0002] Steel plates are important building materials for marine engineering, mainly serving as frame supports or pillars. From the perspective of the service environment, steel plates are required to have excellent resistance to marine atmospheric corrosion; from the perspective of processing and forming, steel plates need to have good welding performance; from the perspective of safety and service life, steel plates also need to have high strength, high toughness and excellent impact resistance.

[0003] Alloying is an important means to improve the comprehensive performance of steel plates for marine engineering. In the related technology, high nickel-chromium alloy composition system is used to produce corrosion-resistant steel plates. Although the corrosion resistance is improved, the alloy cost is high and the welding performance is poor; when copper-nickel-chromium-phosphorus low alloy steel composition system is used to produce steel plates, although the strength and toughness are good, it can only meet the corrosion resistance in ordinary atmospheric environment, and cannot meet the strict requirements of corrosion resistance in marine environment. In addition, controlled rolling, controlled cooling and heat treatment processes are required during production, and the production process is complicated and the process cost is high. Summary of the invention

[0004] In order to solve at least one of the above technical problems, the purpose of the present application is to provide a production method of a corrosion-resistant offshore steel plate and a corrosion-resistant offshore steel plate prepared by the production method.

[0005] To achieve the above application purpose, an embodiment of the present application provides a method for producing a corrosion-resistant offshore steel plate, comprising the following steps performed in sequence:

[0006] (1) Molten steel smelting

[0007] The chemical composition of the molten steel obtained by smelting includes, by mass percentage, C 0.05-0.10%, Si 0.2-0.5%, Mn 0.2-0.5%, P 0.05-0.10%, S≤0.005%, Cr 0.2-0.5%, Ni 0.02-0.05%, Cu 0.2-0.5%, Al 0.02-0.05%, Ti 0.02-0.05%, N≤0.005%, the balance is Fe and unavoidable impurities; and meets the following requirements: 0.5%≤Cr+Cu+P+Al≤1.0%, 0.05%≤Ni+Ti≤0.08%, welding cold crack sensitivity index Pcm≤0.19%, carbon equivalent Ceq≤0.31%;

[0008] Wherein, Pcm=C+Si / 30+Mn / 20+Cu / 20+Cr / 20+Ni / 60+Mo / 15+V / 10+5B;

[0009] Ceq=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15;

[0010] (2) Continuous casting

[0011] Continuously casting the molten steel obtained from the molten steel smelting process into continuous casting billets;

[0012] (3) Heating

[0013] A regenerative walking beam heating furnace is used to heat the continuous casting billet. The furnace time is ≥220min. The heating furnace includes a heat recovery section, a preheating section, a first heating section, a second heating section, and a soaking section arranged in sequence. The furnace temperature of the heat recovery section is 700~950℃, and this section is not equipped with a burner. The furnace temperature of the preheating section is 1050~1100℃, the furnace temperature of the first heating section is 1100~1150℃, the furnace temperature of the second heating section is 1150~1220℃, and the furnace temperature of the soaking section is 1220~1250℃;

[0014] (4) Two-stage rolling

[0015] The continuous casting billet is first rolled in a recrystallization zone to obtain an intermediate billet, and then rolled in a non-recrystallization zone to obtain a steel plate with a thickness t of 14-40 mm, the reduction of at least two passes in the recrystallization zone rolling stage is ≥30 mm, and the thickness of the intermediate billet T=4t-5t; the starting rolling temperature of the recrystallization zone rolling is 1000-1100° C., the starting rolling temperature of the non-recrystallization zone rolling is 880-900° C., and the final rolling temperature is 860-890° C.;

[0016] (5) Controlled cooling

[0017] The steel plate is cooled by a post-rolling accelerated cooling control system. The initial cooling temperature of the steel plate is 800~850℃, the final cooling temperature is 450~550℃, the roller speed is 1.5~2.0m / s, and the cooling rate is ≥25℃ / s.

[0018] As a further improvement of one embodiment, in the heating process, the residence time of the continuous casting billet in the heat recovery section is ≥40 min, and the residence time in the soaking section is ≥40 min.

[0019] As a further improvement of one implementation mode, in the heating process, the combustion medium of the heating furnace is coal gas, the volume fraction of CO in the coal gas is 35-40%, and the calorific value of each cubic meter of coal gas is ≥1100 kcal.

[0020] As a further improvement of one embodiment, in the heating process, the coal gas is a mixture of blast furnace gas and converter gas.

[0021] As a further improvement of one embodiment, in the heating process, in the preheating section, the first heating section, the second heating section, and the soaking section, the volume ratio of air to gas required in each section is 0.6-0.8.

[0022] As a further improvement of one embodiment, in the heating process, high-pressure water is used to remove oxide scale on the surface of the continuous casting billet after the continuous casting billet leaves the heating furnace, and the pressure of the high-pressure water is ≥20 MPa.

[0023] As a further improvement of one embodiment, in the continuous casting process, the superheat of the tundish is 35-45° C., and the continuous casting speed is 1.0-1.2 m / min.

[0024] As a further improvement of one embodiment, in the cooling process, the surface roughness of the steel plate after cooling is less than 3 mm / m.

[0025] As a further improvement of one embodiment, the molten steel smelting process includes the steps of molten iron desulfurization, converter smelting and LF refining performed in sequence.

[0026] As a further improvement of one embodiment, in the molten iron desulfurization step, the molten iron temperature at the desulfurization end point is ≥1300°C, and the S content is ≤0.015%.

[0027] As a further improvement of one embodiment, in the converter smelting step, desulfurized molten iron, scrap steel, copper blocks and nickel plates are loaded into the converter for smelting, the total loading amount of the converter is 200~205t, the loading amount of desulfurized molten iron is ≥160t, the amount of copper blocks added is 1.6~4.0kg / t, and the amount of nickel plates added is 0.05~0.15kg / t; the converter tapping temperature is 1620~1660℃, the carbon content at the tapping end is controlled to be 0.03~0.07%, slag is prohibited during tapping, and 0.6~1.5kg / t of aluminum blocks, 3~7.5kg / t of silicon manganese, 2.5~5.5kg / t of ferrosilicon and 2~4kg / t of ferrophosphorus are added to the ladle in sequence during the tapping process for deoxidation and alloying, and argon is blown throughout the tapping process.

[0028] As a further improvement of one embodiment, in the LF refining step, after the ladle arrives at the station, bottom blowing of argon is turned on, and the argon pressure in the argon pipeline is 0.4~0.6MPa. 3.6~9.0kg / t of low-carbon ferrochrome and 0.9~2.5kg / t of ferrotitanium are added to the ladle in sequence for alloying, and according to the sampling and detection results, nickel plates, aluminum particles, ferrosilicon, and silicomanganese are added to the molten steel, and lime, fluorite, calcium carbide, and refined slag are added for slag adjustment. After that, power is turned on to increase the temperature. After the temperature and chemical composition of the molten steel reach the target range, a refining covering agent is added to the surface of the molten steel and power is quickly turned on to melt the refining covering agent, followed by soft stirring, and the soft stirring time is ≥10min.

[0029] In order to achieve the above application purpose, an embodiment of the present application further provides a corrosion-resistant offshore steel plate, which is prepared by the production method of the corrosion-resistant offshore steel plate as described above.

[0030] As a further improvement of one embodiment, the structure of the steel plate is a composite structure of ferrite and pearlite, and the volume proportion of ferrite is 60-80%;

[0031] The thickness of the steel plate is 14-40 mm, the yield strength is ≥415 MPa, the tensile strength is ≥525 MPa, the elongation after fracture is ≥30%, and the impact energy KV2 at 0°C is greater than 220 J;

[0032] In a NaCl salt spray corrosion environment with a temperature of 35°C, a humidity of 70%, and a mass fraction of 5%, the relative value of the weight loss corrosion rate of the steel plate compared to the Q355B steel plate is ≤30%.

[0033] Compared with the prior art, the corrosion-resistant offshore steel plate and its production method of the present application have the following beneficial effects: on the basis of the chemical composition design scheme, a lower carbon content is designed to improve the corrosion resistance of the finally prepared offshore steel plate; at the same time, a small amount of titanium is added to improve the strength of the steel plate; combined with the addition of elements such as Cr, Cu, P, Al and their content, the phase change behavior of the supercooled austenite structure in the steel plate during the cooling process is affected; further combined with the control of the heating process, it is ensured that the alloy elements are fully dissolved, and at the same time, the temperature difference between the surface and the core of the continuous casting billet is too large to cause heating defects, thereby improving the uniformity of the structure and mechanical properties of the continuous casting billet; and further combined with the two-stage rolling process, it is beneficial to refine the steel plate structure and significantly improve the strength and plasticity of the steel plate, especially non-re-rolling. During the rolling stage in the crystallization zone, a larger reduction rate is beneficial to the refinement of the steel plate structure; a lower starting rolling temperature can prevent the grains from recrystallizing during rolling in the non-recrystallization zone; the rolling process refines the grains, which is beneficial to fine grain strengthening; a higher final rolling temperature can obtain a larger proportion of ferrite structure, thereby improving the plasticity of the steel plate; combined with the control of the post-rolling cooling process, the phase transformation behavior of the supercooled austenite structure during the cooling process can be controlled, so that the structure of the final prepared marine engineering steel plate is a composite structure of ferrite and pearlite, and the volume of ferrite accounts for more than half, and the surface unevenness of the steel plate is improved; the strength, plasticity and low-temperature toughness of the steel plate are simultaneously improved, thereby obtaining a corrosion-resistant marine engineering steel plate with excellent comprehensive performance, which not only has high strength and high toughness, but is also easy to weld, corrosion-resistant, and has controlled production costs. DETAILED DESCRIPTION

[0034] The technical solution of the present application is further introduced below in conjunction with specific implementation methods, but the scope of protection required is not limited to the description.

[0035] An embodiment of the present application provides a method for producing a corrosion-resistant offshore steel plate and a corrosion-resistant offshore steel plate prepared by the production method.

[0036] The various steps of the production method are described in detail below.

[0037] (1) Molten steel smelting

[0038] The chemical composition of the molten steel obtained by smelting includes, by mass percentage, C 0.05-0.10%, Si 0.2-0.5%, Mn 0.2-0.5%, P 0.05-0.10%, S≤0.005%, Cr 0.2-0.5%, Ni 0.02-0.05%, Cu 0.2-0.5%, Al 0.02-0.05%, Ti 0.02-0.05%, N≤0.005%, the balance is Fe and unavoidable impurities; and meets the following requirements: 0.5%≤Cr+Cu+P+Al≤1.0%, 0.05%≤Ni+Ti≤0.08%, welding cold crack sensitivity index Pcm≤0.19%, carbon equivalent Ceq≤0.31%;

[0039] Wherein, Pcm=C+Si / 30+Mn / 20+Cu / 20+Cr / 20+Ni / 60+Mo / 15+V / 10+5B;

[0040] Ceq=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15;

[0041] The symbols of each element in the formula represent the mass percentage of the corresponding element. For example, if the mass percentage of C is 0.05%, then the value of C in the Pcm and Ceq formulas is 0.05%, and the same is true for other elements.

[0042] It can be understood that the chemical composition of the molten steel obtained in the molten steel smelting process, the chemical composition of the continuous casting billet obtained in the subsequent continuous casting process, and the chemical composition of the high fracture toughness steel plate finally produced by the production method are all consistent.

[0043] In the chemical composition of this application:

[0044] C is a strengthening element that can significantly improve the strength of steel. However, too high a C content can easily form carbides, which reduces the corrosion resistance of the steel. It is also detrimental to the plasticity, toughness and welding performance of the steel.

[0045] As a deoxidizer, Si can significantly reduce the oxygen content in steel and reduce the formation of oxide inclusions. Si is also a strengthening element and ferrite-forming element, which is beneficial for regulating the structure and optimizing the mechanical properties. However, too high Si content is not conducive to welding.

[0046] Mn is a solid solution strengthening element that can significantly improve the strength and toughness of steel. However, if the Mn content is too high, it will increase the hardenability and easily form MnS inclusions, reducing the plasticity and corrosion resistance of the steel.

[0047] P is a corrosion-resistant element and works best with Cu; however, too high a P content will affect welding performance and easily segregate at grain boundaries, reducing the low-temperature toughness of the steel.

[0048] S is an impurity element, which easily forms MnS inclusions with Mn, reducing corrosion resistance. Too high S content can easily lead to hot brittleness of steel. However, too low S content will significantly increase the difficulty and cost of smelting.

[0049] Cr is a corrosion-resistant element that can accumulate on the surface of steel to promote the formation of a dense protective rust layer, thereby significantly improving the corrosion resistance of the steel. However, Cr is a hardenability element, and too high a content will deteriorate impact toughness and welding performance.

[0050] Ni can significantly improve the low-temperature impact toughness of steel; when added in combination with Cu, Cr, etc., it can significantly improve corrosion resistance; but Ni is a precious metal element, and if its content is too high, the cost will increase significantly.

[0051] Cu is a corrosion-resistant element. It can easily form a protective oxide film in the atmosphere, seawater and neutral salt solutions, and combine with the oxide on the surface of steel to form a dense protective layer, blocking the corrosive medium from entering the steel surface, thereby improving the corrosion resistance of the steel. In addition, the combination of Cu and P can also significantly improve the atmospheric corrosion resistance. However, too high a Cu content can easily cause "copper embrittlement".

[0052] Al is a corrosion-resistant element and can easily form a dense oxide film in humid air to improve corrosion resistance; however, Al can easily form oxides during the smelting process, increasing the difficulty of continuous production.

[0053] Ti is a strengthening element that can coordinate the strength and plasticity of steel through precipitation strengthening and fine grain strengthening. Ti is also beneficial to improving the welding performance of steel, but it is easy to form oxides during the smelting process, affecting the corrosion resistance.

[0054] N is an impurity element. Too high a content is detrimental to plasticity; too low a content makes smelting difficult.

[0055] The chemical composition design scheme of the present application constructs a corrosion-resistant component system through the multi-element coupling of low carbon + low chromium, low copper, low aluminum + high phosphorus. Low carbon can reduce the formation of carbides, which is beneficial to improving the corrosion resistance and low-temperature toughness of steel; by controlling the total amount of chromium, copper, phosphorus and aluminum elements, the synergistic effect between them can be fully exerted, and the corrosion resistance of steel in marine environments can be further improved; by controlling the sum of the contents of nickel and titanium elements, combined with the solid solution strengthening effect of silicon and manganese elements and their influence on phase change behavior, the strength, toughness and welding performance of steel can be simultaneously improved.

[0056] (2) Continuous casting

[0057] The molten steel obtained from the molten steel smelting process is continuously cast into continuous casting billets.

[0058] (3) Heating

[0059] A regenerative walking beam heating furnace is used to heat the continuous casting billet. The furnace time is ≥220min. The heating furnace includes a heat recovery section, a preheating section, a heating section, a second heating section, and a soaking section arranged in sequence. The furnace temperature of the heat recovery section is 700~950℃, and this section is not equipped with a burner. The furnace temperature of the preheating section is 1050~1100℃, the furnace temperature of the heating section is 1100~1150℃, the furnace temperature of the heating section is 1150~1220℃, and the furnace temperature of the soaking section is 1220~1250℃.

[0060] (4) Two-stage rolling

[0061] The continuous casting billet is first rolled in a recrystallization zone to obtain an intermediate billet, and then rolled in a non-recrystallization zone to form a steel plate with a thickness t of 14-40 mm. The reduction amount of at least two passes in the recrystallization zone rolling stage is ≥30 mm, and the thickness of the intermediate billet T=4t-5t; the starting rolling temperature of the recrystallization zone rolling is 1000-1100°C, the starting rolling temperature of the non-recrystallization zone rolling is 880-900°C, and the final rolling temperature is 860-890°C.

[0062] (5) Controlled cooling

[0063] The steel plate is cooled by a post-rolling accelerated cooling control system. The initial cooling temperature of the steel plate is 800~850℃, the final cooling temperature is 450~550℃, the roller speed is 1.5~2.0m / s, and the cooling rate is ≥25℃ / s.

[0064] The accelerated cooling control system after rolling, referred to as ACC, can achieve a stable water supply during the cooling process.

[0065] On the basis of the aforementioned chemical composition design scheme, a lower carbon content is designed to improve the corrosion resistance of the finally prepared marine engineering steel plate, and a small amount of titanium is added to improve the strength of the steel plate. The addition of elements such as Cr, Cu, P, Al and their contents are controlled to affect the phase change behavior of the supercooled austenite structure in the steel plate during the cooling process; further combined with the control of the heating process, it is possible to avoid heating defects caused by excessive temperature difference between the surface and the core of the continuous casting billet, and improve the uniformity of the structure and mechanical properties of the continuous casting billet; and further combined with the two-stage rolling process, it is beneficial to refine the steel plate structure and improve the strength and plasticity of the steel plate, especially in the non-recrystallization zone rolling stage, a larger reduction rate is beneficial to refine the steel plate structure. The lower starting rolling temperature can prevent recrystallization of grains during rolling in the non-recrystallization zone, and the rolling process can refine the grains, which is beneficial to fine grain strengthening. The higher final rolling temperature can obtain a larger proportion of ferrite structure, thereby improving the plasticity of the steel plate; combined with the control of the post-rolling cooling process, the phase transformation behavior of the supercooled austenite structure during the cooling process can be controlled, so that the structure of the final prepared marine engineering steel plate is a composite structure of ferrite and pearlite, and the volume of ferrite accounts for more than half, and the surface roughness of the steel plate is improved; the strength, plasticity and low-temperature toughness of the steel plate are simultaneously improved, thereby obtaining a corrosion-resistant marine engineering steel plate with excellent comprehensive performance, which not only has high strength and high toughness, but is also easy to weld, corrosion-resistant, and has controlled production costs.

[0066] In one embodiment, the molten steel smelting process includes the steps of molten iron desulfurization, converter smelting and LF refining performed in sequence to achieve smelting of molten steel and improve the cleanliness of molten steel. The following describes each step in the molten steel smelting process.

[0067] a. Hot metal desulfurization step

[0068] The molten iron temperature at the end of desulfurization is ≥1300℃ and the S content is ≤0.015%.

[0069] b. Converter smelting steps

[0070] Desulfurized iron water, scrap steel, copper blocks and nickel plates are loaded into the converter for smelting. The total loading capacity of the converter is 200-205t, the loading capacity of desulfurized iron water is ≥160t, the adding amount of copper blocks is 1.6-4.0kg / t, and the adding amount of nickel plates is 0.05-0.15kg / t. The tapping temperature of the converter is 1620-1660℃, and the carbon content at the tapping end is controlled to be 0.03-0.07%. Slag is prohibited during tapping. During the tapping process, 0.6-1.5kg / t of aluminum blocks, 3-7.5kg / t of silicon manganese, 2.5-5.5kg / t of ferrosilicon and 2-4kg / t of ferrophosphorus are added to the ladle in sequence for deoxidation and alloying. Argon is blown throughout the tapping process.

[0071] Among them, the scrap steel is selected from high-quality scrap steel, and the so-called high-quality scrap steel is the trimmings or the ends of the steel plates, so that the cleanliness of the molten steel can be improved.

[0072] c. LF refining steps

[0073] After the ladle arrives at the station, bottom blowing of argon is started, and the argon pressure in the argon pipeline is 0.4~0.6MPa. 3.6~9.0kg / t of low-carbon ferrochrome and 0.9~2.5kg / t of ferrotitanium are added to the ladle in sequence for alloying. According to the sampling and test results, nickel plates, aluminum particles, ferrosilicon, and silicon manganese are added to the molten steel. Lime, fluorite, calcium carbide, and refined slag are added for slag adjustment. Then, power is turned on to increase the temperature. After the temperature and chemical composition of the molten steel reach the target range, a refining covering agent is added to the surface of the molten steel and power is quickly turned on to melt the refining covering agent, followed by soft stirring, and the soft stirring time is ≥10min.

[0074] Among them, the C content in low-carbon ferrochrome is 0.15% and the Cr content is 58%; the Ti content in ferrotitanium is 30%.

[0075] In this way, by controlling the type of alloy added and the process parameters, fine control of alloy content, control of harmful elements and low-cost steelmaking are achieved.

[0076] In a specific embodiment, in the continuous casting process, the molten steel is continuously cast into a continuous casting billet with a thickness of 220 mm and a width of 850-1600 mm, and the superheat of the tundish is controlled to be 35-45° C., and the continuous casting speed is 1.0-1.2 m / min.

[0077] The chemical composition of the continuous casting ingot is the same as that of the molten steel obtained by smelting, and will not be repeated here.

[0078] In a specific embodiment, during the heating process, the residence time of the continuous casting billet in the heat recovery section is ≥40 minutes to avoid excessive temperature difference between the core and surface of the continuous casting billet, which may cause heating defects such as slab cracking. The residence time in the equalizing section is ≥40 minutes to ensure uniform temperature of the core and surface of the continuous casting billet, as well as uniform temperature of the head and tail of the continuous casting billet. This is beneficial to the organizational control, uniformity of mechanical properties and surface shape of the steel plate finally prepared, and improves the flatness.

[0079] The combustion medium of the heating furnace is coal gas, in which the volume fraction of CO is 35-40%, and the calorific value of each cubic meter of coal gas is ≥1100kcal. By using coal gas as the combustion medium, heat is transferred to the continuous casting billet by means of heat radiation and heat conduction to increase the temperature of the continuous casting billet, and the volume fraction of CO and the calorific value of coal gas are controlled to achieve a preset heating temperature, so as to achieve uniform heating of the continuous casting billet.

[0080] The coal gas preferably uses a mixed gas of blast furnace gas and converter gas. The volume fraction of CO in blast furnace gas is about 20-25%. Even if it is fully burned, the heat provided is relatively low, about 800kcal, which cannot meet the requirements of various parameters in the heating process; while the CO content in converter gas is relatively high. Mixing a small amount of converter gas into blast furnace gas can, on the one hand, ensure the heat provided by the full combustion of the gas and meet the heat requirements of the heating process; on the other hand, the combustion temperature of converter gas is high, and if its content is large, the requirements for the burner are relatively high. The use of a mixed gas of blast furnace gas and converter gas can also reduce the requirements for heating furnace equipment, especially the burner.

[0081] After the continuous casting billet enters the regenerative walking beam heating furnace, it passes through the heat recovery section, preheating section, heating section one, heating section two, and soaking section in sequence, and is taken out of the furnace after reaching the preset temperature in each section and being kept warm for a certain period of time.

[0082] Among them, the volume ratio of air to gas required in each of the preheating section, heating section 1, heating section 2, and soaking section is 0.6-0.8. In this way, the air supply can be guaranteed to fully burn the gas and ensure that the heat generated by the combustion reaches the preset temperature. At the same time, it can avoid the emission of unburned gas to cause energy waste and air pollution, and it can also avoid the oxidation and burning of the continuous casting billet caused by excessive heat generated by the combustion.

[0083] In addition, during the heating process, high-pressure water is used to remove the oxide scale on the surface of the continuous casting billet after it leaves the heating furnace. The pressure of the high-pressure water is ≥20MPa to remove the high-temperature oxide scale generated on the surface of the continuous casting billet during heating, thereby preventing the oxide scale from being pressed into the surface of the steel plate during the rolling process and affecting the surface quality of the finished steel plate, thereby affecting the corrosion resistance of the steel plate.

[0084] In the cooling process, the surface unevenness of the steel plate after cooling is less than 3mm / m. In other words, by controlling the temperature and cooling rate in the cooling process, it is possible to avoid uneven stress in the length and width directions of the steel plate, thereby reducing the surface unevenness of the steel plate.

[0085] The present application also provides a corrosion-resistant offshore steel plate, which is prepared using the aforementioned production method of the corrosion-resistant offshore steel plate.

[0086] After testing, it was found that the steel plate prepared by the above-mentioned production method of corrosion-resistant marine steel plate has a composite structure of ferrite and pearlite, and the volume proportion of ferrite is 60~80%.

[0087] Sampling was performed according to standard GB / T2975, and tensile tests and impact tests were performed according to standards GB / T228 and GB / T229. The yield strength of the steel plate was measured to be ≥415MPa, the tensile strength was ≥525MPa, the elongation after fracture was ≥30%, and the impact energy KV2 at 0°C was >220J.

[0088] In a NaCl salt spray corrosion environment with a temperature of 35°C, a humidity of 70%, and a mass fraction of 5%, the steel plate and the Q355B steel plate were subjected to weight loss corrosion tests respectively. After corrosion, pickling was performed to remove corrosion products, and the corrosion rate of the steel plate was tested by the weight loss method, that is, the ratio of the mass difference of the steel plate before and after corrosion to time.

[0089] The relative value of the weight loss corrosion rate of the steel plate compared to the Q355B steel plate is ≤30%, that is, based on the weight loss corrosion rate of the Q355B steel plate, the weight loss corrosion rate of the steel plate is less than the weight loss corrosion rate of the Q355B steel plate, and the ratio of the weight loss corrosion rate of the steel plate to the weight loss corrosion rate of the Q355B steel plate is ≤30%.

[0090] In summary, the steel plate prepared by the above-mentioned production method of corrosion-resistant marine engineering steel plate not only has high strength, high fracture toughness, good surface quality, low-temperature toughness, excellent welding performance, good safety, and can withstand large deformation cold forming, but also has good application prospects in the field of marine engineering steel such as offshore platforms and offshore wind power.

[0091] In order to make the purpose, technical scheme and advantages of the present application clearer, the present embodiment will be further described below in combination with Examples 1 to 5 according to an embodiment of the present application and Comparative Examples 1 to 5. Obviously, the described Examples 1 to 5 are part of the embodiments of the present application, not all of the embodiments. Other embodiments based on the aforementioned embodiments do not deviate from the technical purpose of the present application.

[0092] Specifically, Examples 1 to 5 all provide a corrosion-resistant marine steel plate. The chemical compositions of the steel plates of Examples 1 to 5 and Comparative Examples 1 to 5 are shown in Table 1, and the remainder is Fe and unavoidable impurities.

[0093] Table 1

[0094]

[0095] The production methods of the steel plates of Examples 1 to 5 and Comparative Examples 1 to 5 are specifically as follows.

[0096] (1) Molten steel smelting

[0097] The chemical composition of the molten steel obtained by smelting is also shown in Table 1. The process specifically includes the following steps:

[0098] a. Hot metal desulfurization step

[0099] The molten iron temperature at the end of desulfurization is ≥1300℃ and the S content is ≤0.015%.

[0100] b. Converter smelting steps

[0101] Desulfurized molten iron, scrap steel, copper block and nickel plate are loaded into the converter for smelting. The total loading capacity of the converter is 200-205t, and the loading capacity of desulfurized molten iron is ≥160t. The added amounts of copper block and nickel plate are shown in Table 2. The converter tapping temperature and the carbon content at the tapping end point are shown in Table 2. Slag is prohibited during tapping. During the tapping process, aluminum block, silicon manganese, ferrosilicon and ferrophosphorus are added to the ladle in sequence for deoxidation and alloying. Argon is blown throughout the tapping process. The added amounts of aluminum block, silicon manganese, ferrosilicon and ferrophosphorus are shown in Table 2.

[0102] Among them, the scrap steel is selected from high-quality scrap steel, and the so-called high-quality scrap steel is the trimmings or the ends of the steel plates, so that the cleanliness of the molten steel can be improved.

[0103] Table 2

[0104]

[0105] c. LF refining steps

[0106] After the ladle arrives at the station, bottom blowing of argon is started, and the argon pressure in the argon pipeline is 0.4~0.6MPa. 3.6~9.0kg / t of low-carbon ferrochrome and 0.9~2.5kg / t of ferrotitanium are added to the ladle in sequence for alloying. According to the sampling and test results, nickel plates, aluminum particles, ferrosilicon, and silicon manganese are added to the molten steel. Lime, fluorite, calcium carbide, and refined slag are added for slag adjustment. Then, power is turned on to increase the temperature. After the temperature and chemical composition of the molten steel reach the target range, a refining covering agent is added to the surface of the molten steel and power is quickly turned on to melt the refining covering agent, followed by soft stirring, and the soft stirring time is ≥10min.

[0107] Among them, the C content in low-carbon ferrochrome is 0.15% and the Cr content is 58%; the Ti content in ferrotitanium is 30%.

[0108] (2) Continuous casting

[0109] The molten steel obtained from the molten steel smelting process is continuously cast into continuous casting billets with a thickness of 220 mm and a width of 850-1600 mm, and the superheat of the tundish is controlled to be 35-45°C, and the continuous casting speed is 1.0-1.2 m / min.

[0110] (3) Heating

[0111] The continuous casting billet is heated by a regenerative walking beam heating furnace. The furnace time is shown in Table 3. The heating furnace includes a heat recovery section, a preheating section, a heating section, a second heating section, and a soaking section arranged in sequence. The furnace temperature of the heat recovery section is 700-950°C, and the section is not equipped with a burner. The furnace temperature of the preheating section is 1050-1100°C, the furnace temperature of the heating section is 1100-1150°C, the furnace temperature of the heating section is 1150-1220°C, and the furnace temperature of the soaking section is shown in Table 3. The residence time of the continuous casting billet in the heat recovery section is ≥40min, and the residence time in the soaking section is ≥40min.

[0112] The combustion medium of the heating furnace is coal gas, specifically a mixed gas of blast furnace gas and converter gas. The volume fraction of CO in the coal gas is 35-40%, and the calorific value of each cubic meter of coal gas is ≥1100kcal. In the preheating section, the first heating section, the second heating section, and the soaking section, the volume ratio of air to coal gas required in each section is 0.6-0.8.

[0113] After the continuous casting billet leaves the heating furnace, high-pressure water is used to remove the oxide scale on the surface of the continuous casting billet. The pressure of the high-pressure water is ≥20MPa to remove the high-temperature oxide scale generated on the surface of the continuous casting billet during heating.

[0114] (4) Two-stage rolling

[0115] The continuous casting billet is first rolled in the recrystallization zone to obtain an intermediate billet, and then rolled in the non-recrystallization zone to obtain a steel plate, and the thickness t of the steel plate is shown in Table 3. The reduction amount of at least two passes in the recrystallization zone rolling stage is ≥30 mm, and the thickness T of the intermediate billet is shown in Table 3; the starting rolling temperature of the recrystallization zone rolling is shown in Table 3, the starting rolling temperature of the non-recrystallization zone rolling is 880~900℃, and the final rolling temperature is shown in Table 3.

[0116] (5) Controlled cooling

[0117] The steel plate is cooled by adopting the accelerated cooling control system after rolling. The start cooling temperature of the steel plate is 800-850℃. The final cooling temperature and roller speed are shown in Table 3. The cooling rate is ≥25℃ / s.

[0118] After cooling, the surface roughness of the steel plate is <3mm / m.

[0119] Table 3

[0120]

[0121] The steel plates of Examples 1 to 5 and Comparative Examples 1 to 5 were sampled and subjected to metallographic structure testing, mechanical property testing, and corrosion resistance testing according to the same testing method. The specific testing methods and test results are as follows:

[0122] (1) Metallographic structure

[0123] Samples of 15×15 cm were taken from the head of the steel plate, and metallographic samples were made along the rolling direction. After mechanical grinding and polishing and nitric acid alcohol etching, they were placed under a metallographic microscope for structural observation. The proportion of the steel plate structure and ferrite structure phase is shown in Table 4.

[0124] (2) Mechanical properties

[0125] Sampling was performed according to standard GB / T2975, and tensile test and impact test were performed according to standards GB / T228 and GB / T229, and the yield strength, tensile strength, elongation after fracture, and 0°C impact energy KV2 of the steel plate were measured as shown in Table 4;

[0126] (3) Corrosion resistance

[0127] In a NaCl salt spray corrosion environment with a temperature of 35°C, a humidity of 70%, and a mass fraction of 5%, the Q355B steel plate was used as a reference, and weight loss corrosion tests were performed on the steel plates of Examples 1 to 5 and Comparative Examples 1 to 5 and the Q355B steel plate, respectively. The relative values ​​of the weight loss corrosion rates of the steel plates compared to the Q355B steel plates are shown in Table 4.

[0128] Table 4

[0129]

[0130] It can be seen from the above table that the steel plate prepared by the production method of the corrosion-resistant marine steel plate of the present application has a composite structure of ferrite and pearlite, and the volume proportion of ferrite is 60-80%; the yield strength is ≥415MPa, the tensile strength is ≥525MPa, the elongation after fracture is ≥30%, and the impact energy KV2 at 0°C is greater than 220J;

[0131] In a NaCl salt spray corrosion environment with a temperature of 35°C, a humidity of 70%, and a mass fraction of 5%, the relative value of the weight loss corrosion rate of the steel plate compared to the Q355B steel plate is ≤30%, and has excellent resistance to marine environment corrosion.

[0132] It should be understood that although this specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation mode may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0133] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of the present application. They are not intended to limit the scope of protection of the present application. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present application should be included in the scope of protection of the present application.

Claims

1. A method for producing a corrosion-resistant offshore steel plate, characterized in that: The process includes the following steps in sequence: (1) Molten steel smelting The chemical composition of the molten steel obtained by smelting includes, by mass percentage, C 0.05-0.10%, Si 0.2-0.5%, Mn 0.2-0.5%, P 0.05-0.10%, S≤0.005%, Cr 0.2-0.5%, Ni 0.02-0.05%, Cu 0.2-0.5%, Al 0.02-0.05%, Ti 0.02-0.05%, N≤0.005%, the balance is Fe and unavoidable impurities; and meets the following requirements: 0.5%≤Cr+Cu+P+Al≤1.0%, 0.05%≤Ni+Ti≤0.08%, welding cold crack sensitivity index Pcm≤0.19%, carbon equivalent Ceq≤0.31%; Wherein, Pcm=C+Si / 30+Mn / 20+Cu / 20+Cr / 20+Ni / 60+Mo / 15+V / 10+5B; Ceq=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; (2) Continuous casting Continuously casting the molten steel obtained from the molten steel smelting process into continuous casting billets; (3) Heating A regenerative walking beam heating furnace is used to heat the continuous casting billet. The furnace time is ≥220min. The heating furnace includes a heat recovery section, a preheating section, a first heating section, a second heating section, and a soaking section arranged in sequence. The furnace temperature of the heat recovery section is 700~950℃, and this section is not equipped with a burner. The furnace temperature of the preheating section is 1050~1100℃, the furnace temperature of the first heating section is 1100~1150℃, the furnace temperature of the second heating section is 1150~1220℃, and the furnace temperature of the soaking section is 1220~1250℃; (4) Two-stage rolling The continuous casting billet is first rolled in a recrystallization zone to obtain an intermediate billet, and then rolled in a non-recrystallization zone to obtain a steel plate with a thickness t of 14-40 mm, the reduction of at least two passes in the recrystallization zone rolling stage is ≥30 mm, and the thickness of the intermediate billet T=4t-5t; the starting rolling temperature of the recrystallization zone rolling is 1000-1100° C., the starting rolling temperature of the non-recrystallization zone rolling is 880-900° C., and the final rolling temperature is 860-890° C.; (5) Controlled cooling The steel plate is cooled by the accelerated cooling control system after rolling. The initial cooling temperature of the steel plate is 800~850℃, the final cooling temperature is 450~550℃, the roller speed is 1.5~2.0m / s, and the cooling rate is ≥25℃ / s. The structure of the steel plate is a composite structure of ferrite and pearlite, and the volume proportion of ferrite is 60-80%; The thickness of the steel plate is 14-40 mm, the yield strength is ≥415 MPa, the tensile strength is ≥525 MPa, the elongation after fracture is ≥30%, and the impact energy KV2 at 0°C is greater than 220 J; In a NaCl salt spray corrosion environment with a temperature of 35°C, a humidity of 70%, and a mass fraction of 5%, the relative value of the weight loss corrosion rate of the steel plate compared to the Q355B steel plate is ≤30%.

2. The method for producing a corrosion-resistant offshore steel plate according to claim 1, characterized in that: In the heating process, the residence time of the continuous casting billet in the heat recovery section is ≥40 min, and the residence time in the soaking section is ≥40 min.

3. The method for producing a corrosion-resistant offshore steel plate according to claim 1, characterized in that: In the heating process, the combustion medium of the heating furnace is coal gas, the volume fraction of CO in the coal gas is 35-40%, and the calorific value of each cubic meter of coal gas is ≥1100kcal.

4. The method for producing a corrosion-resistant offshore steel plate according to claim 3, characterized in that: In the heating step, the coal gas is a mixed gas of blast furnace gas and converter gas.

5. The method for producing a corrosion-resistant offshore steel plate according to claim 3, characterized in that: In the heating process, the volume ratio of air to gas required in each of the preheating stage, the first heating stage, the second heating stage and the soaking stage is 0.6-0.

8.

6. The method for producing a corrosion-resistant offshore steel plate according to claim 1, characterized in that: In the heating process, high-pressure water is used to remove the oxide scale on the surface of the continuous casting billet after the continuous casting billet leaves the heating furnace, and the pressure of the high-pressure water is ≥20MPa.

7. The method for producing a corrosion-resistant offshore steel plate according to claim 1, characterized in that: In the continuous casting process, the tundish superheat is 35-45° C., and the continuous casting speed is 1.0-1.2 m / min.

8. The method for producing a corrosion-resistant offshore steel plate according to claim 1, characterized in that: In the cooling process, the surface roughness of the steel plate after cooling is less than 3 mm / m.

9. The method for producing a corrosion-resistant offshore steel plate according to claim 1, characterized in that: The molten steel smelting process includes the steps of molten iron desulfurization, converter smelting and LF refining performed in sequence; In the molten iron desulfurization step, the molten iron temperature at the end of desulfurization is ≥1300°C, and the S content is ≤0.015%; In the converter smelting step, desulfurized molten iron, scrap steel, copper blocks and nickel plates are loaded into the converter for smelting, the total loading amount of the converter is 200-205t, the loading amount of desulfurized molten iron is ≥160t, the addition amount of copper blocks is 1.6-4.0kg / t, and the addition amount of nickel plates is 0.05-0.15kg / t; the converter tapping temperature is 1620-1660°C, the carbon content at the tapping end is controlled to be 0.03-0.07%, slag is prohibited during tapping, and 0.6-1.5kg / t of aluminum blocks, 3-7.5kg / t of silicon manganese, 2.5-5.5kg / t of ferrosilicon and 2-4kg / t of ferrophosphorus are sequentially added to the ladle during tapping for deoxidation and alloying, and argon is blown throughout the tapping process; In the LF refining step, after the ladle arrives at the station, bottom blowing of argon is started, and the argon pressure in the argon pipeline is 0.4-0.6 MPa. 3.6-9.0 kg / t of low-carbon ferrochrome and 0.9-2.5 kg / t of ferrotitanium are added to the ladle in sequence for alloying. According to the sampling test results, nickel plates, aluminum particles, ferrosilicon, and silicon manganese are added to the molten steel, and lime, fluorite, calcium carbide, and refined slag are added for slag adjustment. Then, power is turned on to increase the temperature. After the temperature and chemical composition of the molten steel reach the target range, a refining covering agent is added to the surface of the molten steel and power is quickly turned on to melt the refining covering agent, and then soft stirring is performed, and the soft stirring time is ≥10 min.

10. A corrosion-resistant marine steel plate, characterized in that: The steel plate is prepared by the production method of the corrosion-resistant offshore steel plate as described in any one of claims 1 to 9.

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